Информатика, кибернетика и программирование

Within the market, the main competition WiMAX comes from existing, widely deployed wireless systems such as UMTS and CDMA2000, as well as a number of Internet-oriented systems, such as HiperMAN and long range mobile Wi-Fi Mesh and networks. The major cellular standards currently developed so-called 4G, high bandwidth and low latency...



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Within the market, the main competition WiMAX comes from existing, widely deployed wireless systems such as UMTS and CDMA2000, as well as a number of Internet-oriented systems, such as HiperMAN and long range mobile Wi-Fi Mesh and networks.

The major cellular standards currently developed so-called 4G, high bandwidth and low latency, all-IP networks with voice services built on top. All over the world to upgrade to 4G for GSM/UMTS and AMPS/TIA (including CDMA2000) is the 3GPP Long Term Evolution efforts. It is planned to replace CDMA2000-called Ultra Mobile Broadband has been discontinued. For 4G systems, available interfaces of air released in favor of OFDMA on the downlink and various techniques for OFDM Uplink similar to WiMAX.

In some parts of the world, the wide availability of UMTS and a General desire for standardization mean spectrum has not been allocated for WiMAX: in July 2005, the EU-wide distribution of frequencies for WiMAX was blocked.

One of the significant advantages of advanced wireless systems such as WiMAX is spectral efficiency. For example, 802.16-2004 (fixed) has a spectral efficiency of 3.7 (bit / s) / Hertz, and other 3.5-4G wireless systems offer spectral efficiency, which is similar to the tenth of a cent. A notable advantage of WiMAX comes from combining SOFDMA with smart antenna technology. This increases the effective spectral efficiency through reuse and smart deployment topologies of the network. Direct use of the frequency domain organization facilitates projects using MIMO-AAS compared to CDMA / WCDMA methods, resulting in more efficient systems.

Table 1. A comparison of the main suppliers of the Internet resource.



Basic use

Radio Technology

Down (Mbps)

Uplink (Mbps)




General 4G




LTE-Advanced update to offer several Gbps speed.



Mobile Internet




WiMAX m pack we offer up to 1 Gbit / s fixed speeds.



Mobile Internet

mobility up to 200mph (350km / h)








The mobile range of 18miles (30 km)

extended range 34 miles (55 km)



Mobile Internet







Mobile Internet (indoors)



(Supports 600MBps @ width 40MHz channel)

Antenna, RF front accessories end and a small timer settings (310 km & 382km).



Mobile Internet




Cell Radius: 3-12 кмSpeed: 250kmph

Spectral efficiency: 13 bits / s / Hz / Cell

EDGE Evolution


Mobile Internet




3GPP Release 7





General 3G









HSDPA is widely deployed. Typical descending speed today 2 Mbit / s, ~ 200 kbit / s line connection "descending HSPA + up to 42 Mbps.



Mobile Internet




Marked speed according to IPWireless using 16QAM modulation similar to HSDPA + HSUPA



Mobile phone




Successor EV-DO

EV-DO 1x Rev. 0

EV-DO 1x Rev.A



Mobile phone








Rev B note: N is the number of pieces of 1.25 MHz spectrum is used. Not yet deployed

1.1 Comparison of key technologies WiMAX and HSPA

System with HSPA (3GPP release 6) commercially available since 2007. The technology provides a frequency dupliciranje (FDD) with the width of each duplex channel 5 MHz. In the downward channel is used modulation QPSK or 16-QAM, streaming speeds of 14 Mbps. In the ascending channel, BPSK modulation, the peak speed of 5.8 Mbps.

At the same time on the market were the WiMAX system (release 1.0) with a temporary dupliciranjem (TDD). Under similar bandwidth 10 MHz they provide the speed in the downward channel is 2-3 times higher than HSPA (as WiMAX TDD when the total bandwidth is dynamically shared between downward and upward channels).

Table 2. Comparison of HSPA systems (releases 7 and 8) and WiMAX (release 1.5)





Релиз 7

Релиз 8

Релиз 1.5

The GHz Range







The channel bandwidth MHz




Antenna BS




Antenna AC



Modulation and encoding rate

In a descending channel

64 QAM 5/6

16 QAM 3/4

64 QAM 5/6

64 QAM 5/6

In an upside channel

16 QAM 3/4

64 QAM 5/6

Peak rate, Mbps

In a descending channel






In an upside channel






The development of technology has created HSPA+ (HSPA release 7 and some of the amendments release 8). In a descending channel they are distinguished by modulation 64-QAM c SIMO (1x2) or 64-QAM SIMO c (2x2). The ascending channel added modulation 64-QAM and enhanced features for VoIP. Amended in accordance with release 8, you can use in a descending channel mode MMO (2x2) with modulation 64-QAM, the possibility of using Mobilisa orders of magnitude in a descending channel and MMO (2x2) - the ascending channel.

When comparing mobile WiMAX and HSPA+, you can make the following conclusions:

-mobile WiMAX release 1.5) is comparable to HSPA+ (release 8) peak speed in a descending channel with the same modulation, coding rate and channel width. While mobile WiMAX in the ascending channel peak rate 2-3 times higher.

-System HSPA+ is limited by the channel width of 2x5 MHz in the traditional spectral conditions of 3G networks. Mobile WiMAX supports bandwidth up to 20 MHz as frequency and temporal dupliciranje. Its frequency profiles are planned in the range of 700, 1700, 2300, 2500 and 3500 MHz. Mobile WiMAX provides a "smooth IP network" (from end to end).

1.2 comparison of the key technologies for WiMAX and LTE

The next step of evolution of 3GPP systems are system Long Term Evolution (LTE). They are distinguished by the OFDMA technology in a descending channel and SC-FDMA in uplink. Modulation - 64-QAM, channel width to 20 MHz, dupliciranje TDD and FDD. Applied adaptive antenna systems, flexible network access. Network architecture fully IP network. In the LTE system is applied technologies and methods already used in mobile WiMAX, so we should expect similar performance of LTE systems (table 1-2 and 1-3).

Table 3. The comparison of the parameters of real systems LTE WiMAX and molar (release 1.5) in the same frequency conditions at FDD with stripes h MHz



WiMAX Релиз 1.5




Down channel

Antenna BS






Modulation and encoding rate

64 QAM 5/6

64 QAM 5/6

64 QAM 5/6

64 QAM 5/6

Speed Mbps






Ascending channel

Нет данных

Antenna AC




Modulation and encoding rate

64 QAM 5/6

64 QAM 5/6

64 QAM 5/6

Speed Mbps




The LTE system is a revolutionary improvement in 3G. LTE represents the transition from CDMA to OFDMA systems, as well as the transition to a fully IP system to the communication packets. Therefore, the introduction of this technology on existing cellular networks means you need a new radio resources to obtain benefits from broad channel. For backward compatibility required dual mode subscriber device. Therefore, a smooth transition from 3G to LTE is very complicated.

Table 4. Comparison of key parameters of LTE and WiMAX



WiMAX Релиз 1.5







The frequency range for analysis

2000 МГц


Channel width

До 20 МГц

До 20 МГц

From the base






Spectral efficiency, bits/Hz/s

A downward channel, MIMO (2x2)



Ascending channel, SIMO (1x2)



The maximum speed of the mobile station km/h



Frame duration, MS



Antenna systems

Down channel

2х2, 2х4, 4х2, 4х4

2х2, 2х4, 4х2, 4х4

Down channel

1х2, 1х4, 2х2, 2х4

1х2, 1х4, 2х2, 2х4

Figure 1 - Comparison of the average spectral efficiency.

Note that the advantage in spectral efficiency means winning in the cost of network deployment (including unit costs relative to network bandwidth). In addition, increasing the channel capacity, allowing operators to introduce additional services. Mobile WiMAX is smooth IP network, the LTE network is more complex (figure 2).

Figure 2 - Comparison of system architectures WiMAX and LTE

If the WiMAX network is based entirely on IP protocols IEEE, the LTE network is more complex, involves more protocols, including proprietary protocols 3G. It is important that intellectual property in the field of WiMAX technology, the relevant patents are distributed among many companies, created open patent Alliance, which reduces the prices of subscriber devices.

Conclusions comparison of WiMAX and LTE:

- WiMAX, and LTE meet the objectives of IMT-Advanced;

specifications of IMT-Advancedеще not fully defined;

- IEEE802.16m will fully reflect the specifications and requirements of IMT-Advanced;

-mobile WiMAX release 1.5 and LTE share similar characteristics. In both on-line database is used OFDMAс multilevel modulation and coding. Peak speed is almost the same with the same multiplicities modulation speeds and correcting code. In both used and FDD, and TDD duplexsonography channel width to 20 MHz. In both uses MIMO large multiplicities and reduction of delays;

-mobile WiMAX has a two-year time to market and smooth e2e IP network architecture;

- throughput and spectral efficiency of mobile WiMAX release 2.0 has better options than LTE;

mobile WiMAX release 2.0 is compatible with releases 1.0 and 1.5;

- investments for network transformation from 2G/3Gв LTEи in mobile WiMAXпримерно same;

-and for LTE networks and WiMAX networks requires a new range;

-both networks need a multi-mode subscriber devices;

1.3 Comparison of key technologies WiMAX and Wi-Fi.

Comparisons and confusion between WiMAX and Wi-Fi are frequent because both are related to wireless connectivity and Internet access.

WiMAX uses spectrum to deliver a point-to-point connection to the Internet. Various 802,16 standards require different types of mobile switches (similar to a cordless telephone) for fixed (alternative to wired access where wireless connection point end users recorded in the region.)

Wi-Fi uses unlicensed spectrum to provide access to the network. Wi-Fi is more popular in end user devices.

WiMAX and Wi-Fi have quite different quality of service (QoS) mechanisms. WiMAX uses a mechanism based on communication between a base station and a user device. Each connection is based on specific scheduling algorithms. Wi-Fi has QoS mechanism similar fixed Ethernet, where the packets can get different priorities based on their tags.

Wi-Fi runs on the Media Access Control's CSMA / CA Protocol, which is connectionless and statements are based, while WiMAX works connection-oriented MAC.

Standard 802,16 spreading across a wide bandwidth in the RF spectrum and WiMAX can operate on any frequencies below 66 GHz (higher frequencies would lead to a decrease in the operating range of the base station to several hundred meters in an urban environment).

WiMAX profiles define channel size, TDD / FDD and other necessary attributes in order to have Inter-operating products. The current fixed profiles are determined both for FDD and TDD profiles. Currently, all mobile profile TDD only. The profiles have a fixed size channel 3.5 MHz, 5 MHz, 7 MHz and 10 MHz. Mobile profiles 5 MHz, The 8.75 MHz and 10 MHz. (Note: 802,16 standard allows a much wider range of channels, but only the above subsets are supported WiMAX profiles.)

It is expected that WiMAX will be able to provide high-speed Internet access easier and cheaper than existing cellular technologies. This technology also has the capability of zooming through which you can arrange affordable broadband access across India. WiMAX wireless infrastructure can be extended to provide support for handheld and mobile devices that will emerge in the future. This provides additional benefits for countries with developing economies like India that do not yet have a well-developed broadband infrastructure.

Due to the fact that WiMAX technology is based on standards, it allows for economies of scale that can reduce the cost of broadband access, to ensure interoperability and to simplify the implementation. In the absence of standards, manufacturers of specialized equipment offer a full range of hardware and software components, and because of the restrictive licensing expenditures increase. Service providers more profitable to work with standard products, because the compatibility of various devices and large production volumes allow to reduce the cost of equipment.


2.1 Standard 802.16: a Protocol stack.

The set of protocols used by the 802.16 standard, is shown in figure 3. The overall structure is similar to other 802 series standards, but more Sublevels. The lower sublayer is involved in the physical transfer of data. Using conventional narrowband radio system with the ordinary schemes of modulation of the signal. Above the physical layer is a sublayer of the data (with the accent on the second syllable), hiding from the level of data transmission technology differences.

The data consists of three sublevels. The lower one refers to the protection of information in which Data transfer is carried out in the ether, not physically protected from eavesdropping. This sublevel is citrate, decoding the data, and also control keys.

Figure 3 - Standard 802.16: a Protocol stack.

Then, the General part of the MAC sublayer. It is at this level of the hierarchy are the main protocols - in particular, the protocols of the control channel. Here the station in control of the entire system. She very effectively distributes the order of transmission of the incoming traffic to subscribers, plays a significant role in the management of outbound traffic (from the subscriber to the base station). From all other 802 standards.x MAC sub-layer the 802.16 standard is different in that he is fully focused on the connection. Thus, it is possible to guarantee a certain quality of service in the provision of telephone services and the transfer media.

2.2 Standard 802.16: physical layer

Broadband wireless networks, a broad frequency spectrum, which can only be found in the range from 10 to 66 GHz. Millimeter waves have one interesting property that no longer microwaves: they are distributed in all directions (as a sound), and straight lines (as light). Consequently, the base station must be installed multiple antennas covering different sectors of the surrounding area, as shown in figure 4. Each sector will have its own users. The sectors do not depend on each other, which is not true of mobile radio communication, in which signals propagate in all directions.

Figure 4 - operating environment data 802.16 networks.

Since the power signal is transmitted millimeter waves is greatly reduced with increasing distance from the transmitter (base station), and the ratio signal/noise is also reduced. For this reason 802.16 uses three different modulation schemes depending on removal of subscriber stations. If the subscriber is located close to the BS, applied ZAHM 64 with six bits per sample. On average, the deletion is used CDM-16 and 4 bits/baud. If the subscriber is away then the circuit operates CRC with Two bits per sample. For example, in a typical spectrum band 25 MHz CDM-64 gives a speed of 150 Mbps, SEAM-16 - 100 Mbps, and SFC 50 Mbit/s. Thus the farther the subscriber from the base station, the lower the data rate. Phase diagrams of all three methods were shown on risk 5.

Figure 5 - Phase diagrams of methods used.

The 802.16 standard provides flexible allocation of bandwidth. Apply two modulation schemes: FDD (duplex communication frequency division) and ТDD (full-duplex communication with time division). The latter method is shown in figure 6. The base station periodically transmits the frames are separated by time intervals Ia. The first part of the time intervals allocated for incoming traffic. Then, the guard interval (separator), allowing the stations to switch between transmission and reception, followed by intervals of outgoing traffic. The number of allocated cycles can change dynamically, allowing you to adjust the bandwidth under traffic each direction.

Figure 6 Duplex communication with time division: frames and time slots

Incoming traffic is split into time slots to the base station. She completely controls the direction of transmission. Outbound traffic from subscribers is controlled by more complex and depends on the required quality of service. We will return to the distribution of time intervals, when we discuss the MAC sublayer.

Another interesting property of the physical layer is its ability to pack multiple adjacent frames MAC in one physical transmission. This gives you the opportunity to increase the efficiency of spectrum allocation by reducing the number of different preambles and headers, so loved by the physical layer.

For immediate correction of errors at the physical layer uses a Hamming code. All network technologies simply rely on checksums and encounter bugs with their help, requesting retransmission of the corrupted fragments. But with broadband wireless connectivity at greater distances there are many mistakes that their treatment have to deal with the physical level, although at higher levels and method of checksums. The main task of error correction at the physical level is to make the channel look better than he actually is (exactly the same CDs seem so reliable carriers only due to the fact that more than half of the total number of bits allocated for error correction at the physical level).

2.3 Standard 802.16 Protocol MAC sublayer

The level data is divided into three sublevels, as shown in figure 7.

Footage WT always occupy an integer number of time intervals in the physical layer. Each frame is divided into parts, the first two of which contain a map of the distribution of intervals between incoming and outgoing data traffic. There is information that is transmitted in each clock cycle, and on what beats free. Map of the distribution of the incoming stream also contains a wide range of system parameters that are important for stations that have just joined the airwaves.

The incoming traffic channel consists of a base station, which determines what to put in each part of the frame. Outgoing channel has a competing station wishing to access it. Its distribution is closely linked to the issue of quality of service. Defined four classes of services:

1. Service with a constant bit rate;

2. Service real-time variable bit rate;

3. The service not running in real-time, variable bit rate;

4. Service with a commitment apps best-effort services.

All provided by the 802.16 standard services focused on the connection, and each connection has access to one of the earlier classes of service.

Service with a constant bit rate is designed to transmit uncompressed speech, what is channel T1. Here you want to send a predefined amount of data in predefined time intervals. This is implemented by assigning each connection of this type is their intervals. Once the channel is allocated, the access time intervals is performed automatically, and there is no need to request each of them separately.

Service real-time variable bit rate used in the transmission of compressed multimedia data and other software applications real-time. Necessary in a time throughput may vary. Or that the bandwidth allocated by the base station, which polls at certain intervals of time subscriber to identify necessary at the moment the channel width.

The service not running in real-time, variable bit rate is suitable for heavy traffic - for example, to transfer large files. Here, the base station polls also subscribers quite often, but not in a strictly defined time points. The subscriber is operating with a constant bit rate, can be set in unit of one of the special bits of his frame, thereby offering a base station to interview him (that means the subscriber has data that you want to transfer with the new bit rate).

Service with a commitment to maximum effort is used for all other types of transmission. No polls here, and the station wishing to seize the channel, must compete with other stations that require the same class of service. The bandwidth request is performed at time intervals that are marked in the map of the distribution of outgoing flow as available for competition. If the request was successful, it will be noted in the following map of the distribution of the incoming stream. Otherwise, subscribers-losers must continue to fight. To minimize the number of collisions is used is taken from Еsегпеt; algorithm binary exponential rollback.

The standard defines two forms of capacity allocation: for the station and for the connection. In the first case, the subscriber station collects together all the requirements of its subscribers (for example, computers that belong to residents of the building) and provides collective inquiry. Upon receiving the bandwidth, it distributes it between users at their discretion. In the latter case, the base station works with each connection separately.

2.4 Standard 802.16: frame structure

All frames sublayer management media access control (MAC) begin with the same header. It is followed (or not) the data field, and the ends of the frame also optional checksum field. It is shown in Fig. 4.31. The data field is not in service frames that are designed, for example, for the query time intervals. The checksum is optional due to the fact that error correction is performed on a physical level and never attempts to resend frames of information transmitted in real time.

Consider a header field (figure 7, a). Bit the EU suggests that the data field is encrypted. The Type field specifies the type of the frame (in particular, reports about whether the frame is Packed and whether fragmentation). Field C1 indicates the presence or absence of the field the final checksum. Field EC indicates which of the encryption keys is used (if it is used). In the Length field contains information about the overall length of the frame, including the header. The connection identifier is reported, which compounds the current frame belongs to. At the end of a header Checksum field of the header whose value is calculated using the polynomial x8 + x2 + x + 1.

Figure 7 - Normal frame (a); the request frame channel (b).

Figure 7 b shows another type of frame. This is a request frame channel. It begins with the individual and not the zero bits and generally resembles a conventional header of the Frame, with the exception of the second and third bytes that make up the 16-bit number, indicating the required bandwidth for transmission of the corresponding number of bytes. In the request frame is not transmitted data field, and no checksum of the entire frame.

The 802.16 network can cover whole areas of cities and the distances thus calculated kilometers. Therefore, a received signal stations may be of different capacities depending on their distance from the transmitter. These deviations affect the ratio signal/noise, which, in turn, leads to the use of multiple modulation schemes.

In each cell broadband regional network can be much more users than in the conventional 802.11 cell, and wherein each user has a much higher bandwidth than the user of the wireless LAN. Unlicensed (15M) bandwidth is insufficient for the load, so the network 802.16 working in the high frequency range 10-66 GHz.

802.11 support the transmission of information in real time (PCP), but actually they are not intended for telephony and great multimedia traffic. The 802.16 standard, by contrast, is focused on supporting such applications because it is designed both for citizens and for business people.


At the physical layer the IEEE 802.16 standard provides for three fundamentally different methods of data transfer: a method of modulation of a single carrier (SC, in the range below 11 GHz) modulation method by orthogonal carrier OFDM (orthogonal frequency division multiplexing method and multiplexing (multiple access) through orthogonal carrier OFDMA (orthogonal frequency division multiple access).

3.1 Features of the application of OFDM modems.

Mode OFDM is a modulation of the flow of data in a single frequency channel (width 1-2 MHz or more) with a center frequency fc. The division of the channels, as in the case of SC - frequency. Recall that when the modulation data through orthogonal carriers in the frequency channel allocated to N subcarriers:

fk= fc + k∆ f,          (1)

where: k-is an integer in the range of [6 N/2, N/2] (in this case k ≠ 0). The distance between the orthogonal carriers.

where: k is an integer in the range of [6 N/2, N/2] (in this case k ≠ 0). The distance between the orthogonal carriers.

where Tb-is the duration of a data symbol.

In addition to the data OFDM6символ includes a guard interval duration Tg, so that the total duration of the OFDM symbol

Ts= Tb+ Tg, (3)

Guard interval is a copy of the final fragment of the symbol. The duration Tg can be 1/4, 1/8, 1/16 and 1/32 from Tb.

Each subcarrier is modulated independently by quadrature amplitude modulation.

Figure 8 - OFDM-symbol.

The total signal is calculated by the method of inverse fast Fourier transform (OBPF) as a complex representation is convenient, since the generation of radio signals takes place with the help of the quadrature modulator in accordance with the expression



where: - a comprehensive view of the square symbol modulation (QAM symbol)

For FFT algorithms/OBPF it is desirable that the number of points in match 2 . Therefore, the number of carriers is chosen equal to the minimum number NFFT = 2 greater than N. In the OFDM mode of IEEE 802.16 N = 200, respectively NFFT = 256. 55 ( k = 6128...6101 and 101...127) form a guard interval at the boundaries of the frequency range of the channel. The Central frequency of the channel ( k= 0) and frequency protection intervals are not used (i.e. the amplitudes of the corresponding signals is equal to zero). Of the remaining 200 bearing eight frequencies - pilot (with indexes±88, ±63, ±38, ±13), the rest are divided into 16 subchannels bearing 12 each, and in one subchannel frequencies are not consecutive. For example, subchannel 1 are bearing index -100, -99, -98, -37, -36, -35, 1, 2, 3, 64, 65, 66. The division into sub-channels is necessary because in the real WirelessMAN-OFDM is provided (optionally) an opportunity to operate in all 16, and one, two, four and eight sub-channels - a type of multiple access scheme OFDMA. To do this, each subchannel and each group of sub-channels have an index (0 to 31).

The duration of the useful part Tb OFDM6символа depends on the bandwidth of the channel BW and system clock frequency (sampling rate) Fs;

        Fs = NFFT/ Tb.          (5)

  The ratio Fs/ BW = n is normalized, and depending on the bandwidth of the channel takes values 86/75 (BW multiple of 1.5 MHz), 144/125 (BW multiples of 1.25 MHz), 316/275 (BW is a multiple of 2.75 MHz), 57/50 (multiple of BW 2 MHz ) and 8/7 (BW multiples of 1.75 MHz, and in all other cases). Guard interval in OFDM-modulation is a powerful tool to combat intersymbol interference (intersymbol interference, ISI) arising from inevitable in an urban environment reflections and multipath propagation of the signal. ISI causes the receiver right on the propagating signal is superimposed multipath signals containing the previous character. When OFDM modulation multipath signal falls within the guard interval and does not cause harm. However, this mechanism does not prevent vnutrishkolnoe interference - the superposition of signals with the same symbol that came with the phase delay. As a result, information can be distorted or completely (e.g., with a phase shift of 180°) just disappear. To prevent information loss in case of failure of individual characters or parts of the IEEE 802.16 standard provides an effective means of channel coding.

  The data encoding at the physical layer is divided into three stages - the randomization, noise-immune coding and interleaving. Randomization is the multiplication of the data block in a pseudo-random sequence (SRP), which forms the PRS generator sets with polynomial 1 + x14 + X15. In the downward flow of the PRS generator is initialized with the beginning of the frame by means of code words A. Starting with the second batch frame of the PRS generator is initialized on the basis of the identification number of the base station BSID, ID profile package DIUC (downlink interval usage code) and frame number (figure 9). In an upward flow of everything is similar, with the only difference that the initialization of the generator of the SRP in the circuit shown in Fig.2, with the first package (DIUC is used at UIUC - uplink interval usage code).



Figure 9 - the Formation of the initialization vector generator of the SRP for randomization downstream OFDM.

  Coding data involves a cascade code with the two stages of the encoder reed-Solomon from Galois field GF (256) and a convolutional encoder. In basic form, a reed-Solomon code operates on blocks of raw data 239 bytes, forming of them encoded block size of 255 bytes (adding 16 bytes test). This code is able to recover up to 8 damaged bytes. As actually used smaller blocks of data of length K, they are added (239 - K zero bytes. After encoding these bytes are removed. If you want to reduce the number of test words, to reduce the number of bytes restoring T, used only 2 of the first test of bytes. Mandatory to support in IEEE 802.16 options cascade code is given in table 5.

Table 5. The main modes in the IEEE 802.16 standard.


The data block encoding byte

The Encoder Reed-Solomon

Encoding rate of the convolutional encoder

Total encoding rate

Block of data after encoding byte











































  After Reed-Solomon encoder receives data at a convolutional encoder (Figure 3) with generators sequences (code generators) G1 = 171 (exit X) and G2 = 133 (for Y) - the so-called standard code NASA. Its basic coding rate - 1/2, ie, each of the input bits it generates a pair of coded bits of X and Y. The sequence of pairs Missing elements Xi or Yi, we can obtain various coding rates.

After encoding interleaving procedure should - mixing bits within the encoded data block corresponding to the OFDM-symbol. This operation is carried out in two stages. The purpose of the first - to make sure that adjacent bits were separated by non-contiguous carriers. In a second step adjacent bits are separated into different halves sequence. All this is done to ensure that when the group errors in the symbol damaged noncontiguous bits that are easy to recover when decoding. Interleaving is implemented in accordance with the formulas

mk = ( Ncbps / 12) – ( kmod 12) + floor ( k / 12);

jk = s – floor ( mk / s) + ( mk + Ncbps – floor (12 mk / Ncbps)) mod s, (6)

k = 0… Ncbps – 1,

where mk and jk is the number of the original bits after the first and second stage of interleaving, respectively;

Ncbps is the number of coded bits per OFDM symbol (for a given number of sub-channels),

s - 1/2 the number of bits on the carrier (1 / 2 / 4 / 6 bits for BPSK / QPSK / 166QAM / 646 QAM, respectively, for BPSK s= 1).

Function floor ( x) is the greatest integer not exceeding x; function ( x mod r) is the remainder of x/ r.

Figure 10 - Generation of the modulating sequence for a pilot bearing.

Each group is defined in accordance with the values of Q and I from vector diagrams warming (figure 10), which are then used in direct modulation of the carrier.

Pilot carriers modulated by BPSK.

After determining modulation symbols by OBPF the radio signal is calculated and transmitted to the transmitter. When taking all procedures performed in the opposite order. Mode OFDM physical layer for networks with architecture "Toccata" human transmission structure is fundamentally little different from the SC mode. As in the high-frequency region, information exchange takes place through a sequence of frames (frames). Each frame (Fig.6) is divided into two subframe - descending (DL from the BS to MSS) and ascending (UL - from the MSS to the BS). The separation of the ascending and descending channels - as a temporary (TDD) or frequency (FDD). In the latter case DL and UL are broadcast simultaneously in different frequency bands.

The downward subframe includes a preamble, a control frame header (FCH frame control header) and the sequence of data packets. Preamble in a descending channel - making of two OFDM6symbols (long preamble), intended for synchronization. First OFDM6 symbol uses carriers with indices that are multiples of 4, the second only even carriers (modulation - QPSK).

For the preamble should the control header of the frame - one OFDM6символ with BPSK and a standard encoding scheme (encoding rate 1/2). It contains the so-called prefix frame of the descending channel (DLFP - Downlink Frame Prefix), which describes the profile and length of the first (or initial) package in DL6субкадре.

In the first packet includes a broadcast message intended for all AU) - map of the location of the packet DL-MAP, UL-MAP, the descriptors of the descending/ascending channel DCD/UCD, other service information. Each package has its own profile (coding scheme, modulation, etc.) and is transmitted by means of an integer OFDM6символов. The point of beginning, and profiles of all packages, other than the first, contained in the DL-MAP.

Figure 11 - structure of the OFDM frame in the temporary depletirovannoi.

The downward subframe contains the interval of competitive access, including the periods for initializing the AU (join the network) and bandwidth request transmission. Followed by the time slots assigned to a certain base station subscriber stations for transmission. The distribution of these intervals (start point) is contained in the message UL-MAP. ACE in the time interval starts a broadcast transmission of a short preamble (one OFDM6символ, uses only even carriers). It is followed by the actual information packet generated on Masarova.

The duration of the OFDM frame can be 2,5; 4; 5; 8; 10; 12,5; and 20 MS. A given base station, the period of building frames cannot be altered, as in this case you'll need to resync all the speakers.

The request to establish the connection does not differ from those generally accepted in the IEEE 802.16 standard, except for the additional mode "concentrated" query (Region-Focused). It is intended only for stations that are able to work with individual sub-channels. In this mode, in the intervals of competitive access (defined in UL-MAP) of the AU can send short Arany code on one of the 48 sub-channels, each of which includes four load-bearing. There are a total of eight codes. Table of codes and sub-channels are given in the text of the standard IEEE 802.16. Code and channel number AC selects randomly.

After receiving a coded message, the BS provides the AC interval for the transmission of "normal" request to grant access (request header Masarova) - if possible. However, unlike other mechanisms, BS in UL6MAP does not indicate the identifier of the requesting station, and quotes the code number of request subchannels and the sequence number of the access interval during which was handed over to the inquiry. These speaker parameters and determines that the interval for the query band transmission is suitable for her. The timing of the transfer arastradero code access request is random, the above-described algorithm appeals to the competitive access channel.

Note that in mode OFDM channel resource may be provided not only in the time domain, but in a separate subchannels (subchannel groups), if the BS and subscriber stations support this. One of the most important applications of such option - Mesh-network.

3.2 MESH network

Formally, a Mesh network is a type of network topology in IEEE 802.16 OFDM mode, and its physical layer is OFDM. Therefore, the differences Mesh6сети with considered modes are manifested not only and not so much on a physical level. The main difference Mesh6сети from considered still architecture "Toccata" - that if in the latter case, the speaker can only communicate with the BS, Mesh6сети interaction can take place directly between the speakers. Because network IEEE 802.16 standard is designed to work with a wide frequency channels, Mesh6сети entered standard not to create peer-to-peer local area networks - for this is the standards group IEEE 802.11. The reason given is a necessary tool for building a broadband network in which traffic can be transmitted via a chain of several stations, thereby eliminating the problem of transmission in the absence of direct visibility. Respectively, and of all the mechanisms of governance, in principle allowing you to build a decentralized distributed network, all focused on a tree-like architecture, with a dedicated base station (root node) and the dominant streams of BS-AC. In Mesh6сети all stations (nodes) are formally equivalent. However, almost always traffic throughout the Mesh network with the external environment occurs through one particular node (Fig.7). Such a node called the base station Mesh network, it is necessary to control Mesh network functions. While access control can take place either on the basis of the mechanism of distributed control or centralized way, under control of the BS. Different combinations of these methods.

A basic concept in the Mesh network are neighbors. Under the neighbors understand a particular node, all nodes that can establish a direct connection. They all form a neighborhood environment. Nodes associated with the specified node via the neighbor nodes, called neighbors of second order. Can be neighbors of the third order, etc.

In the Mesh network has no concept of ascending/descending channels. All communication is through frames. Stations transmit messages either within their allotted time intervals (in accordance with the previous channel assignment), or access channels with arbitrary (random) manner. Each node has a unique 486 bit MAC address. In addition, to identify within the Mesh network stations assigned 166 bit network identifier.

Figure 12 - example of a Mesh network

The allocation of channel resources in the Mesh network can be centralized and decentralized (distributed). In turn, the decentralized allocation is coordinated with the BS and not coordinated. The decentralized allocation of resources implies that the distribution occurs within one group of neighbors (i.e., between stations can directly communicate with each other). At coordinated decentralized distribution nodes communicate among themselves by special message control the distribution (distributed scheduling - DSCH).

Coordination is that the period of issuance of such messages each station are determined and known to her neighbors. Coordinated DSCH messages are transmitted in subcateg precedence constraints of access specified in the network descriptor intervals. Uncoordinated DSCH messages are transmitted in the subframe of data. DSCH messages are requests to receive channel resource and response messages with the provision (confirmation) of available resource (time slot per subframe data).

  Resource is provided to the neighbor for a specific connection. Centralized allocation of resources implies a tree-like network topology with the BS at the top. It is implemented through two types of messages - centralized configuration CSCF and Central planning CSCH. These control messages are placed at the beginning of the subframe chart management access. Using message Central planning CSCH, each node determines the need for traffic to its child nodes (i.e., traffic from (to) BC passes through the node), and reports their needs to the parent node until the BS. After analyzing the need, the BS sends a message CSCH, informing each node on its allocated bandwidth (in bps) in the ascending and descending directions. Based on these data, each node asks himself (or assigns) the location of the packet in the subframe of data from (to) of its neighboring nodes through messages decentralized planning DSCH.

Message to centrally configure CSCF BS are formed and transmitted over the network to inform all nodes about the current state. CSCF includes information such as the number of available logical channels and their list, the list of nodes in the network indicating the number of child nodes for each of them, as well as profiles of the ascending/descending packages for each child node.

3.3 application Features multiple access OFDMA

Mode WirelessMAN-OFDMA (hereinafter - OFDMA) as its name implies, is a method of multiple access by dividing the orthogonal carriers. Unlike discussed in a previous publication [2] method, WirelessMAN-OFDM, it is not only about the mechanism of modulation, but also about the way of channel separation. This mechanism is already well known, in particular, it has found wide application in systems of digital television DVB (terrestrial, cable and satellite). One logical OFDMA channel is formed by a fixed set of carriers, generally distributed over the available frequency band of the physical channel. In simplified form this optional mechanism is used in the OFDM mode - recall the decomposition of the channel into 16 subchannels.

From the point of view of forming a modulation OFDMA symbols similar OFDM: OFDMA symbol includes the actual zone data and the preceding guard interval (repetition of the initial fragment of a symbol) that is designed to prevent seismology interference). The symbol is a combination of the modulated orthogonal carriers. In the OFDMA mode of carrying significantly more than in OFDM - 2048 instead of 256, respectively, and the number of subchannels becomes sufficient for the organization of the network in different modes from 32 to 70, 24, or 48 information carriers in each. Are not all 2048 carrying about 200 and bottom 200 of the upper frequencies make a guard interval channel and not modulated. Also, do not use a Central frequency of the channel (frequency index 1024). In addition, part of bearing - pilot intended for service purposes and not for data transfer. The exact number of pilot carriers and frequencies in the protective intervals varies slightly depending on the OFDMA modes, described below.

The system clock frequency is always 8/7 bandwidth physical channel BW. The width of the physical channel is not standard (the standard says "not less than 1 MHz), but in real applications are unlikely to be effective channels for less than 5 MHz.

The method of formation, the structure of OFDM symbols and the mechanism of channel coding in OFDMA is similar to that described for OFDM [2]. Channel coding includes the randomization, error-correction coding, interleaving and modulation. Method of randomization is almost identical OFDM, only different ways of generating the initialization vector of the pseudorandom sequence generator (PRSG).

Error-correction coding in OFDMA as binding provides only the convolutional encoder is the same as in OFDM, and with the same set of velocity encoding. Encoder reed-Solomon no. Optional provision for the use of block and convolutional turbo codes. The method of alternation is also almost identical.

In a descending channel, the first symbol is a preamble. Bearing in characters of preambles modulated by BPSK special pseudo-random code depending on the segment (in PUSC mode) and variable IDcell is defined at the MAC layer [3]. The preamble is modulated every third carrier of the entire channel (except for bearing protection intervals and Central), with the initial shift [0..2] is set to advanced. Recognizing the type of the preamble, the AU defines the value of the variable IDcell and mode of operation of BS.

For the preamble is followed by two symbols, the transmission frame header FCH and map the field distribution for the descending channel DL-MAP. The header is transmitted by QPSK with rate 1/2 coding. It contains the prefix of the descending channel (DL Frame prefix) that identifies segments used and the settings of the descending channel DL-MAP (length, encoding method used and the number of repetitions), broadcast immediately after the frame header. Also in the header flag is used, the installation of which means a change in the location of the field of competitive access in the ascending sub frame to the previous frame.

Next broadcast map upside channel UL-MAP and the downstream data packets for different AC.

The FUSC mode means that uses all physical channels (all possible carriers). This 1702 carrying frequency information and a guard interval (173 and 172 of the bearing in the top and bottom of the range, respectively). Center frequency at index 1024 is not used.

Figure 13 - the Combination of different “zones reshuffle” in the OFDMA frame.

In FUSC mode is primarily assigned to the pilot frequency. They are divided into fixed and variable. Lists and those others mentioned in the standard. The term "variables pilot frequency" means that in each even-numbered OFDMA-symbol indexes are presented in document IEEE 802.16, in each odd - climb 6 (numbered OFDMA symbol starts with 0). There are a total of 166 of the pilot frequencies, 24 of which are fixed. Both fixed and variable pilot frequencies are divided into two sets of equal volume. This break is only important when working with adaptive antenna systems in the regime of space-time coding (STC).

After determining the pilot frequencies of the remaining 1536 carriers are intended for data transmission. They are divided into Nsubchannels = 32 subchannels on Nsubcarriers = 48 bearing in each. The goal of the information-carrying sub-channels is in accordance with the formula:

where subcarrier(k,s) - carrier index k in subchannel s, s = [0...Nsubchannels - 1],

k = [0...Nsubcarriers - 1],

nk = (k + 13s) mod Nsubcarriers. IDCell

- the ID of the segment BC, which is defined at the MAC layer (specified by the base station a variable in the range 0-31). P(x) means the x-th element of the sequence of permutations {P}, given in the standard (P= {3, 18, 2, 8, 16, 10, 11, 15, 26, 22, 6, 9, 27, 20, 25, 1, 29, 7, 21, 5, 28, 31, 23, 17, 4, 24, 0, 13, 12, 19, 14, 30}). The operation x mod k is the remainder of x/k.

Obviously, before applying the formulas of information carriers shall be renumbered so that their indices within the range 0-1535 (the last value corresponds to the physical index 1702), i.e. numbered in a row, excluding the pilot frequencies. Because the even and odd symbols, the location of the pilot frequencies are different, the distribution of information carriers for them also need to be calculated independently.

In the PUSC mode entire available range is divided into 60 sub-channels. By definition, the work is only a part of them, but not less than 12. The subchannels are grouped into six segments, three basic (segments 0, 1 and 2), each includes 12 subchannels (0-11, 20-31 and 40-51 sub-channels, respectively). Obviously, based on the requirement of a minimum of 12 subchannels, the base segments can be used only in conjunction with basic. The division into segments is introduced to BS it easier to communicate, in any moment), but it works (just report the numbers of segments).

Figure 14 - structure of the cluster

The symbols in the PUSC mode is formed by the following principle. There are a total of 2048 frequencies, of which the Central (index 1024) and protective (184 lower and 183 upper) not used. The remaining 1680 bearing successively divided into 120 clusters, each contains a bearing 14. After that, consecutive physical clusters are renumbered in a "logical" in accordance with the formula LogicalCluster = RenumberingSequence [(PhysicalCluster+13 IDcell) mod 120], where RenumberingSequence (x) is the corresponding element described in the IEEE 802.16 a sequence of permutations, IDcell is defined at the MAC level identifier of the individual segment BS (base station asked a variable in the range 0-31). This operation actually means interleaving - distribution of consecutive groups of carriers across the band of the physical channel. Next logical clusters are divided into six groups(0-23, 24-39, 40-63, 64-79, 80-103, 104-119), on 24 and 16 clusters. Large groups correspond to large segments (default, group 0 corresponds to the segment 0 group 2 - segment 1, group 4 segment 2). In each cluster are determined pilot bearing - for even symbols this is the 5th and 9th are load-bearing, for odd - 1-I and 13-I (figure 14).

Thus, the set of subchannels within a segment or multiple segments is assigned to a set of carriers (12 subchannels - bearing 336, 24 of the pilot information and 288). Information carriers in the segment are numbered in a row, not including the pilot frequency, and then in accordance with formula (1) to each subchannel are assigned by bearing 24. In this case, in equation (1) uses the values Nsubchannels = 12 or 8, Nsubcarriers = 24, and also a special permutation of the sequence of P12 and P8 for the segments 12 and 8 channels, respectively (given in the standard [3]).

In addition to reviewing the methods of distribution of bearing, the standard and optional mechanisms - in particular, the so-called optional FUSC, not fundamentally different from that considered.

Ascending channel

Rising subframe immediately follows the top-down through the TTG interval. It contains the packets from the subscriber stations and the interval for the access-request/initialize. The minimum size of a single message in an upward subframe (slot) - 3 OFDMA symbol within the subchannel. This has led to the appearance in document IEEE 802.16 term "fragment" (mosaic element, tile).

Figure 15 - structure of the “fragment” of a rising channel.

A fragment is a set of three symbols and four load-bearing, in which the position of the pilot frequencies are rigidly defined (figure 15). The entire frequency range of the channel (1680 carriers) 420 is divided into sequential fragments, 4 carriers in each. Provided 70 subchannels. Each of them consists of 6 pieces - i.e. 24 bearing on the character in one subchannel. The distribution of fragments on the sub-channels is as follows. All 420 of the fragments are broken into 6 groups of 70 fragments. In each subchannel is enabled by one segment from each group in accordance with the equation:

Tile (n, s) = 70n + {P[(n + s) mod 70] + UL_IDcell} mod 70, (8)

where Tile(n, s) - a fragment of the n subchannels s, n = [0...5], s = [0...69].

P(x) is a permutation sequence,

UL_IDcell - variable in the range of 0-69, asked BS to the MAC layer.

As a result, each subchannel in each symbol has its own set of carriers.

After the distribution of the sub-channels occurs numbering information carriers in each slot making a total of three characters 48. Information frequency subchannels are numbered starting with the lowest carrier of the fragment with the smallest index first in the first character, then second and third. Then the information carriers in each slot are renumbered in accordance with the formula:

subcarrier (n, s) = (n + 13s) mod 48, (9)

where s is the number of subchannels, n = [0...47] (i.e., there is a cyclic shift of numbering information bearing on 13s in each subchannel s).

Note that in the text of the document IEEE 802.16 is substitution of terms: a subchannel in an upward subframe songwriters of IEEE 802.16 is called slot information structure the size of the bearing 24 on 3 characters. And when the document is English and white - it is written that in the subchannel 48 information carrier, it should be remembered that from the point of view of correct terminology it is not about the subchannel, but about slot. Real carriers (i.e. natural frequencies) in the subchannel only 24. Multiplying them by 3 (the number of OFDMA symbols in the slot) and subtracting 24 pilot bearing, just obtain 48 information carriers.

Optional in the ascending channel has a mode in which in a fragment of one pilot frequency (figure 16), 6 fragments on subchannel, 96 subchannels (1728 used frequencies).

The mechanisms of the first initialization request in the network and the primary request bandwidth in OFDMA mode is similar and fundamentally different from other modes. For these requests in OFDMA uses a dedicated channel. He is assigned to the BS and consists of six consecutive subchannels, the indices of which are given in the UL-MAP. The query is a 144-bit CDMA code transmitted by BPSK, i.e. 1 bit per carrier in one symbol. As a result of the transfer of such code is 6 subchannels (24 information carriers in each). The code itself is generated in the generator of the SRP - 15-bit shift register with defining polynomial 1 + X1 + X4 + X7 + X15. Senior 6 bits of the initialization vector generator of the SRP is $ variable UL_IDcell, the other 9 is a constant. The code number is determined by the initial point (i.e., the number of cycles of the generator of the SRP after initialization) - there is a total of 256 codes. Moreover, the BS uses only a subset of all possible codes - first N codes first initialization, followed by M code the periodic determination of the parameters AC, then L codes of the query band. For each BS set the start point of the sequence (N + M + L).

Figure 16 - structure of a “fragment” of a rising channel in optional mode

Initialization occurs as follows: AC, taking the handle of the rising channel and the UL-MAP defines a set of CDMA codes and sends in the designated interval randomly chosen code from the group is possible. The same code is transmitted in two consecutive OFDMA-symbols. If the interval of competitive access is more than one slot, the MSS can send CDMA code for the four consecutive symbols, and codes must be adjacent (i.e., sequential fragments SRP).

Successfully adopting and recognizing the CDMA code (and this may not happen, because in the interval of competitive access possible conflict with simultaneous operation of several transmitters AC), base station does not know from which the speaker came the request. Therefore, in response to UL-MAP of the next frame, it indicates the received CDMA code, subchannel and character in which the code was sent. So the MSS determines that the request is accepted, and understands that following this broadcast message indicating the range of the query (number symbol, subchannel, and duration) is intended for her. In this message, the BS transmits the necessary parameters for the initialization process in the network (including the connection identifier CID assigned to the MAC address, a set of physical parameters, etc.). Further specified in UL-MAP interval, the MSS proceeds to the standard procedure of registration in the network.

  The primary request of bandwidth in OFDMA method can occur in two ways: through the request headers of the strip, as in the other modes, and by sending a CDMA code of the bandwidth request in the interval of competitive access. The sending of a code request page (as well as the code of the periodic measurement of parameters) occurs in one OFDMA symbol. Possible and sending three consecutive codes in three characters (which you must use is specified in UL-MAP). Adopting the CDMA code, the BS in the UL-MAP repeats his room and options, and also reports the interval for sending the request header strip is already in the normal way.

3.4 Support for adaptive antenna system

  The most important feature of the IEEE 802.16 standard, which principally differ from, say, standards IEEE 802.11 a/b/g, is the presence of built - in support tools for adaptive antenna systems (AAS). Of course, the use of AAS is not a requirement of the standard. AAS is a system with sectored directional antennas (method of forming the antenna patterns in the standard does not specify), i.e. antenna system with multiple antenna elements. The use of AAS significantly increases the potential capacity of the network IEEE 802.16, since different sectors of BS can work in the same channel (frequency and OFDMA). In addition, directional antennas can significantly reduce the total radiated power. The result is reduced and interchannel interference. No less important is the use of multiple antenna systems to improve the passage of signals in fading channels, the so - called methods of space-time coding (explode) STC.

  Support for ASS in IEEE 802.16 means a modification of the protocols at the physical and MAC levels, the presence of special control and Supervisory messages to work with adaptive antennas.

Figure 17 - Structure of the frame with the area ААS.

  The standard permits within one frame to broadcast both undirected and directed (by AAS) traffic (Fig.6). For the delineation of zones of non-AAS and AAS-traffic uses a special message. The principle use of AAS in modes OFDM and OFDMA (and SCa) are quite similar. More fully described in the standard for the case of OFDMA [3], so focus on it.

  The Mechanism Of Diversity-Map Scan. In the OFDMA mode provides two ways of working with AAS - distributed carriers in subchannel (FUSC, PUSC) and consistent with bearing (AMC). Each of the methods at the beginning of the AAS zone provides for the transfer of OFDMA symbol of the preamble AAS zone and header prefix AAS zone. For the transmission of these messages in the AAS zone downward subframe allocated to the special sub-channels (for two senior FUSC/PUSC and the fourth and the last-in AMC subchannels). Messages within these sub-channels may be repeated several times - that if you are not using broadcast broadcast and transmission shifting rays, messages prefixed with reach all the speakers. In the prefix code indicates the beam of the antenna, the type and size of the preamble ASS-zone (uplink and downlink), the area for initial initialization / query strip, and the area in the frame for each AAS connection. The prefix, as in the normal mode, is transmitted through QPSK with rate 1/2 coding and double repeat (within one character). The main purpose of the prefix is to inform the AC about how will be transferred to cards DL/UL channels for the split in the directions of the rays of user groups (obviously, the allocation of channel resources may occur independently in each beam).

For operation in mode AMS-AAS footage can join in supercar lasting not less than 20 ordinary frames. In supercat includes at least one broadcast frame containing the descriptors and maps DL/UL channels. The meaning of this Association is to provide at least a control message for the group shots.

  These methods work with AAS use so-called mechanism of Diversity-Map scan (subscriber stations) posted maps of the distribution of channel resources. In the OFDMA mode provides another way of working with AAS - direct method alarm (Direct Signaling Method).

  Method Direct Signaling uses a mechanism of sequential distribution of bearing the AMC. It is unique in each frame in AAS zone is allocated from one to four channels of access /allocation of resources (BWAA - bandwidth allocation/access). Each BWAA-channel consists of two sub-channels located in the upper and lower parts of the range symmetrically about the center frequency (if BWAA-channel one, it includes the upper and the lower sub-channels). This channel is used to transmit the prefix downward subframe (for Direct mode Signaling Method), map UL-MAP and DL-MAP for each of the spatially separated speakers or groups of speakers. Due to the precise spatial configuration AAS this method allows a single frame to transmit messages to multiple users.

  In the method of direct signaling there are four special coded messages - learning connections back RLT (reverse link training), access to the reverse connection RLA (reverse link access), training FLT direct connection (forward link training) and initiate a direct connection FLI (forward link initiation). The first two messages uses AC, the latter two BS. For initializing or bandwidth request of the MSS sends a message to the RLA in the channel of the BWAA. It precedes the request message strip or initial access of the BS and is used for fine tuning of your antenna system on this speaker. In response, the BS transmits the message FLI is a unique code for each speaker (LH itself may initiate communication by sending FLI). FLI is transmitted in a subchannel allocated to this AC. Each subscriber station scans all the sub-channels and finding the code sequence addressed to her the first initialization message, sends a reply in the same channel in a time interval) sequence RLT designed to fine tune the antenna BS to the MSS in this subchannel. As a result, after completing all of the necessary corrections, the BS and the MSS establish a connection over which data is transferred. Moreover, the data packets are preceded by a training sequence FLT (BS) and RLT (from AC).


4.1 Services networks Mobile WiMAX technology.

WiMAX networks are designed to provide services to both fixed and mobile users. WiMAX supports the following types of mobility:

1) fixed. In this case, the operator has accepted the user's position in which he receives the service, e.g., concrete honeycomb. Good for that user terminals with a fixed antenna outside the building aimed at the base station.

2) vagus (nomadic), i.e. with a variable location. The user has the ability to connect to the operator's network from any location where the operator provides coverage. During one session, the user must be stationary.

3) mobile (portable). The user has the ability to move at speeds up to 5 km/h without losing the established session, including optional network) to move from one cell to another (handover). During the handover permitted breaks in data transmission (up to the value for maximum service current TCP/IP session), up to 2 s. Allowed data loss during handover, the contracted quality of service, QoS, is restored only after the completion of handover.

4) limited mobility (simple mobility). The user can move, including the move from honeycomb to honeycomb, with speeds up to 60 km/h without compromising the quality of service, and up to 120 km/h are permissible with the gradual deterioration of service quality. For applications unreal (non-real time) time (work with e-mail, the web, watching videos buffered data, transferring files using FTP, IPsec/VPN) quality of service is guaranteed. The handover time should not exceed 1 when switching between IP subnets and 150 MS in the same subnet, the interruption time of data transmission does not exceed 150 MS. Mandatory support standby (idle), sleeping (sleeping) modes of operation of user terminals, and user call (paging), see the relevant sections.

5) full mobility full mobility). The user can move, including the move from honeycomb to honeycomb, with speed up to 120 km/h without compromising quality of service. Guaranteed quality of service for real-time applications (VoIP, video telephony, video without buffering) and unreal (see the limited mobility). The handover time is not greater than 50 MS, the interruption time of data transmission does not exceed 5 MS (or no more than the duration of one frame).

4.2 Principles of WiMAX networks

The following are the principles of WiMAX (Release 1 version 4):

1) WiMAX is based on 802.16 standard

2) WIMAX network architecture includes 2 global parts: ASN - subnet access, CSN - subnet that provides connectivity to IP networks, see below. Support 802.16 standard is fully implemented in ASN. Usually subnet CSN is owned by the ISP, IP services, NSP - Network Server Provider, subnet ASN - radio access provider, NAP - Network Access Provider. NSP and NAP can be a provider.

3) one subnet access, ASN, can be used multiple service providers (NSP), i.e. to a single ASN can be connected to multiple CSN, and one provider of IP services, the NSP may use several different subnets access, i.e. to one CSN can be connected several ASN.

4) the architecture provides standard interfaces (reference points, Reference Points), see below, in particular between an MS, ASN, CSN to ensure efficiency in the use of equipment from different manufacturers.

5) the network needs to support mobile telephony based on VoIP, multimedia services, as well as the mandatory features defined by the regulator, such as emergency, legal, listening, etc.

6) the network must provide the services in accordance with the agreed service level agreement (SLA) to support, if required, multiple voice sessions for a single user, simultaneous voice and data, prioritization of emergency calls.

7) the network must be able to interact with the gateways, providing the existing services based on IP: SMS over IP, MMS, WAP, and others;

8) the system must support broadcast and multi-user (multicast) services;

9) the system must support mutual authentication of MS and the network, as defined in the 802.16 standard;

10) the system must support user authentication using a login/password, SIM, USIM, RUIM;

11) the system must support confidentiality (confidentiality) and integrity of transmitted data by using the functions implemented in the ASN;

12) the system must support the establishment/removal of a VPN (Virtual Private Network), MS initiated

13) the network should not prevent you from switching (handover) multi-standard MS network other technology - Wi-Fi, 3GPP, 3GPP2, DSL;

14) the system must support IPv4 mobility or IPv6;

(15) the network should not prevent roaming between service providers (NSP). The network must allow the access provider (NAP) to serve the MS, using different domain names (served by different service providers) ;

16) the system must support seamless handover at speeds of traffic;

17) the system must support different levels of QoS;

18) the system must support interoperability with other wireless (3GPP, 3GPP2) or wired (DSL) networks. The interface used for such interaction should be based on the protocols of the IETF and IEEE;

19) the system must support roaming with other operators WiMAX

20) the system must support change settings and update subscriber devices over the air Over-the-Air (OTA) ;

21), the network architecture must ensure interoperability of devices from different manufacturers;

within ASN (BS and transport network), between different ASN, as well as different elements of the ASN and CSN;

22), the network architecture must support the following types of CS (from the list of CS defined in 802.16).

Enlargement WiMAX network consists of the following logical objects:

1) SS (Subscriber Station) ;

2) ASN (Access Service Network) ;

3) CSN (Connectivity Service Network) .

  Each object can be implemented in a single physical module (e.g., SS) or multiple (ASN, CSN).

  Several CSN can be connected to the same ASN, and Vice versa; several ASN can be connected to a single CSN. ASN and CSN can belong to the same operator or different:

  A network architecture according to WiMAX, shown in figure 17:

Figure 17 - Architecture the WiMAX network.

Figure 18 - Components of the WiMAX network architecture.

The operator may own WiMAX network fully or partially. The operator providing radio access is called NAP - Network Access Provider. He may belong to one or more ASN. The operator providing network services (Internet, voice, access to certain content) is referred to as NSP - Network Service Provider, he may belong to one or more CSN.

In more detail the network architecture shown in figure 19:

Figure 19 - the Elements of the WiMAX network.

  User terminal or Mobile Station, MS, or Subscriber Station SS - a device providing a connection between the user equipment (e.g., a computer) and the network. MS may be a CPE, Customer Premises Equipment that connects to a network of multiple computers.

  Base Station BS, the base station is a logical network element that handles the physical and MAC levels according to the standard 802.16. BS represents one sector with one frequency. BS can connect to multiple ASN GW to provide redundancy and/or load balancing. One natural product may include multiple BS (logical objects).

ASN-GW, the gateway radiopacity is a logical network element that performs the aggregation (consolidation) of the signal functions, and, if necessary, routing data streams of users. ASN-GW may be associated with other ASN-GW to provide redundancy and load balancing.

  AAA server, Authentication, Authorisation, Accounting, - device (server) that performs the procedure:

- user authentication, i.e., authenticate and access the network

- authorization - dedicated network resources in accordance with the services to which he signed

- account - counting of resources utilized by the user (amount of time or amount of data transferred) to bill for the use of the network.

  MIP HA - Mobile IP Home Agent. It is used to support mobility, bankernas in CSN, see Chapter "mobility". He is typically an edge router - a router-gateway, located on the border of the WiMAX network and external networks.

IMS, Content services, Billing Support System (BSS), Operator Support System (OSS) is a standard system that is not specific to WiMAX, provide support functions to the operator.

Roaming is the ability to provide subscriber services while in a foreign network (visited network). The subscriber can use the services defined in the agreement between home network and foreign network. The main advantage of roaming is a large area of provision of services with a single invoice.

Key features SI3000 Light ASN:

Infrastructure with the lowest cost based on commercial routers

- Available mobile services

- Available fixed communications services

- Compatibility with future regenumvaluea guarantee investment protection

- Interaction SI3000 ASN-GW

4.3 WiMAX Solutions with advanced features and performance.

Figure 20 - architecture of the WiMAX network with advanced features

Effective WiMAX solution with advanced features and performance

To achieve higher energy potential of the communication line (link budget), reduce the signal attenuation and the best coating of micro-spots (micro-spot), can be used various technologies explode.

Note: Iskratel supports both technologies: STC/MRC currently and MIMO with its platforms 16e. Profitable business model of WiMAX with higher coverage of users, user satisfaction and improve the power potentials of the communication lines (link budget) WiMAX can be achieved with the use of advanced antenna technologies (MIMO and AAS): MIMO A/B & STC: the Effect of MIMO A/B lies in its ability to switch between A MIMO and MIMO B.

Variant MIMO with A single receiving antenna also known as the mode STC (Space Time Coding with space-time coding) and are particularly suitable in NLOS conditions.

ААS - adaptive antenna systems: AAS uses multiple antennas to dynamically generate a directional beam. This beam is controlled by a base station (BS) for sending to a subscriber station (SS), and (BS) communicates. The AAS system is particularly suitable for use in scripts

with limited interference and can provide a significant benefit in an environment with direct visibility (LOS). System Iskratel default support for MIMO A/B & STC, AAS system will be added where it will be technically and commercially profitable.

Figure 21 - General view of the deployment of WiMAX technology in Egoryevsk area.

Solution SI3000 Light ASN provides simple network design and the use of "commodity" items (i.e., homogeneous elements, elements of mass production with the same properties) to establish a mobile connection to the network service provider. The result is a mechanism of handover and to continue the IP session, providing a handover in real-time for a fixed WiMAX network and handover carrier-class mobile WiMAX network. The SI3000 solution Light ASN also supports standard network elements outside of the ASN. In addition, the possible migration type SI3000 ASN - GW Mobile WiMAX. When the market and technology intersect, you'll be ready to offer full support for roaming and interoperability with a wide range of applications CSN.

Figure 22 - Physical connection to the WiMAX network.

Light from ASN Iskratel can offer:

- mobile services with much less infrastructure costs.

- SI3000 Light ASN - new network architecture

- In decision SI3000 Light ASN uses a new network architecture (New Network Architecture), which is a unique structure that allows you to use inexpensive and homogeneous (commoditized) network elements to create a managed, mobile, rich multimedia services networks.

New network architecture SI3000 Light ASN, based on a simple hierarchy configured with homogeneous (commodity) network elements, provides structure between the base network CSN and WiMAX radio network.

Figure 23 is a Logical connection to the WiMAX network.

The advantages of the new network architecture:

- Unique and innovative architecture;

- Deployment of homogeneous (commodity) elements (switch, router) with little cost;

- Sufficient WiMAX SS/SSM; no MobileIP stack for SSM;

- "Subversive" influence (disruptive impact);

- Ensures the mechanism of handover and to continue the IP session;

- Provides the ability to control QoS for Triple Play service delivery.

5. Development of a WiMAX NETWORK FOR the realization of BROADBAND ACCESS TO the INTERNET

5.1 Choice of the characteristics of the radio interface

Base station WiMAX is a modular solution which may, if necessary, be supplemented by the various units, for example, modules for connections to backbone network provider. In the minimal configuration is installed, the radio interface module and the connection module with a wired network.

When choosing WiMAX equipment in addition to its technical characteristics and the prices are important and often decisive importance is such a factor as to Russia's specific difficulties completing frequency permits. The fact is that in Russia there are practically no "unlicensed" bands. For different types of equipment provided different procedures for obtaining a frequency permits. To work in all ranges of the operators should get quite complex and multi-level resolution as frequency of services and services oversight communication [5].

It is obvious that in our country the chief factor affecting the speed of deployment of WiMAX systems, are the issues of regulation of the spectrum, since the development of WiMAX services market is directly dependent on the allocation of operators required frequency resource. Today the most perspective from the point of view of the future development of WiMAX technology are the ranges in the area of 2.4 and 3.5 and 5.6 GHz.

Note that the propagation of radio waves in different frequency bands has its own characteristics that largely determine the range of the equipment, as well as resistance to multipath.

Equipment must be performed by a specialized company with experience in the development and production of wireless equipment that is some guarantee of quality.

Technical characteristics of the equipment provided by the manufacturer, should be complete enough for you to make a conclusion about its capabilities. The representation of such characteristics speaks about the professionalism of the staff and to some extent ensures that we are talking about the original product and not about the resale of an unknown brand under the brand name of the seller.

It is desirable that the base station is able to centrirovannyi and gradual increase performance, for which she should be able to connect an external antenna. Then the first step one base station with omnidirectional antenna, the next two, the antennas with the width of the diagram 180°, and so on.

The equipment must be certified.

Must be able to obtain permission for the use of frequencies in the ranges used in the equipment.

The system must have acceptable cost, especially important minimum cost of subscriber equipment.

The principle of operation of Mobile WiMAX identical cellular networks: multiple adjacent base stations Mobile WiMAX form a honeycomb, honeycomb unites each other to ensure the continuous coverage of the whole city. Equipment Mobile WiMAX provides high speed data transmission, compared with cellular networks, and comparable to the speed of wired access networks. Key features WiMAX devices:

Technical characteristics of WiMax:

• Range: up to 50 km;

• Maximum data transfer rate: up to 70 Mbps per sector of one base station;

• Operating frequency: 2-11 GHz;

• Spectral efficiency: up to 5 bits/sec/Hz;

• Coverage: extended operation beyond line of sight greatly improve the quality of coverage of service area;

• Speed access to the Internet within a sector of the base station on the client devices - up to 10 Mbps;

• The coverage area of a single sector base stations in dense areas - from 800 to 1500 meters;

• Mobility: instantaneous switching client Mobile WiMAX equipment between the base stations at speed up to 120 km/h.

5.2 Calculation of frequency channels

The total number of frequency channels allocated to sweep the cellular network connection in a given location, determined by the formula


where int(x) is the integer part of the number x;

Fk - the frequency band occupied by a single frequency channel system (frequency separation between the channels).

5.3 determining the dimensionality of the cluster

To determine the required dimension of the cluster With given values of p0 and pt are used, the ratio


where p(C) - the percentage of time during which the ratio of signal power/ interference power at the receiver input of MS will be below the protective relationship .

The integral represents the tabulated Q-function:

.                                                                   (12)

The lower side of the interval has the form:

,                                                                                  (13)

where and expressed in dB;

 - is determined by the ratio

.                                                            (14)

In turn, the values and are defined by the formulas

,                                                                                        (15)

 ,                                         (17)

- the parameter that determines the range of random fluctuations of the signal level at the receiving end:

.                                                                                          (18)

  The coefficient in (17) is the median attenuation of radio waves in the i-th direction you increase the noise. These factors are inversely proportional to the quarters of the degrees of the distance to the source of interference. The value M represents the number of base stations that are "disturbing", located in the neighbouring clusters.

  First consider the case for Omni-directional antennas, where

, , и , , ;

where is the number of sectors.

We choose the value C=3.

, (19)


Calculating the square root of the resulting value obtained

It follows

  Now we calculate the lower boundary of the Q-function:

  This value  in the table corresponds to the value , this value is approximately equal to one. Considering the equation (3.2), we obtain

  The resulting value is clearly more which job is 10. Hence, this type of antenna and the selected value of the cluster is not suitable for the specified standard.

  Now consider the case for a directional antenna, in which the angle of directivity pattern , , М=2 и , .

  We choose the value C=4.



Calculating the square root of the resulting value obtained

It follows:

Now we calculate the lower boundary of the Q-function:

This value in the table corresponds to a value equal 0,0838. Considering the equation (3.2), we obtain

The resulting value is slightly smaller hence , this type of antenna is the best.

5.4 calculation of the frequency channels that are used for customer service BS

The number of frequency channels that are used for customer service in one sector is determined by the formula:


где - the number of sectors.

5.5 Calculation of the allowable load of BS

The value of the permissible load in one sector is determined by the ratio:


provided that

,                                   (22)

where ;

- the number of subscribers that can simultaneously use the same frequency channel. In this case, the value of =1 because you are using the analog standard.

Radical expression greater than the magnitude of ,  because .

5.6 Calculation of the number of subscribers served by one BS

For a given activity per subscriber per hour maximum load you can calculate the number of subscribers served by one BS to the formula


5.7 calculation of the number of BS

The required number of base stations in a given service area is determined by the ratio:

,                                          (24)

where is a specific number of subscribers, which serves the cellular network connection.

5.8 calculation of the radius of the service area of BS

The radius can be determined using the expression





6.1 the Calculation of the size of the clearance distance

The magnitude of the clearance distance between the BTS with the same frequency channels is determined by the ratio


6.2 Calculation of the signal level at the receiver input

The required power at the receiver input when and determine, using the so-called first equation of transfer.


where - gain base station antennas, dB;

f - the average frequency of the selected frequency range;

 - the BTS transmitter power, dBW;

 - losses in the feeder BTS, dB;

 - long feeder, which may be equal to or greater than the height of the BTS antenna;

 - linear attenuation of the feeder, dB/m.

6.3 Calculation of error probability

To determine the probability of error when the MS is located on the border of the service area of the BTS, you must use the ratio



6.4 Calculation of efficiency of use of radio spectrum

An important parameter of the cellular network connection is efficient use of radio spectrum , due to the number of active subscribers at 1 MHz frequency band for transmission (or reception) BTS, that is


where the frequency band for transmission (or reception)  the number of active subscribers 


where is the radius of the territory that is served by,





Functionally, the WiMAX equipment is divided into base and subscriber. The first generation of chips for base stations has a lower level of integration than for subscriber stations. To implement the MAC Protocol of the base station need to increase performance of these solutions. For this purpose, external processors that perform the top-level MAC Protocol. Thus, the WiMAX chipsets implement the functions of the physical layer and lower MAC layer Protocol.

7.1 Selection of equipment subscriber stations

For developers WiMAX subscriber equipment, the most promising are "systems on a chip" from four manufacturers: Fujitsu, Intel, Sequans, and Wavesat.

Intel first offered to the developers of "system on chip" PRO/Wireless 5116 for WiMAX mobile stations, which were integrated functions, both physical and MAC levels. Chip MB87M3400 Fujitsu is designed for a wider range of applications and allows you to develop both basic and subscriber equipment. The company Sequans has developed separate chips SQN1010 and SQN2010 - for base and subscriber equipment, respectively.

"The SOC from Fujitsu, Intel and Sequans fully implement the functions of the MAC Protocol for WiMAX mobile stations. Another approach to the development said the company Wavesat, releasing two chips: OFDM modem DM256 (implements the functions of the physical layer) and MC336 (is a computational kernel that implements the lower level of the MAC Protocol). To develop a subscriber modem on the basis of the SOC from Fujitsu, Intel and Sequans not require an additional external processor.

Characteristics of these chips, depending on the type of duplex, channel width and other parameters are very different. For the organization full-duplex operation based on Fujitsu MB87M3400 requires two chips. Sequans chip SQN1010 is the first "system on a chip", which supports full-duplex mode. The company's decision Wavesat DM256/MC336 also allows for full duplex mode based on the single chip OFDM modem DM256.

Chip companies Fujitsu and Sequans allow you to organize the channel width to 20 and 28 MHz respectively, while the maximum width of the channel for Intel chips and Wavesat is 10 MHz with intermediate values of 3.5 and 7 MHz.

The air is considered "systems on chip" contains blocks ADC/DAC for direct analog connection to an external transceiver. In table. 2 presents the main parameters of solutions for WiMAX subscriber equipment [6].

Table 6. The main parameters of solutions for WiMAX subscriber equipment.


Fujitsu MB87

Intel PRO/Wireless 5116

Sequans SQN1010

Wavesat DM256/MC336






Maximum channel width

20 MHz

10 MHz

28 MHz

10 MHz


H-FDD, TDD, FDD (2 chip)




System interface

Mill, 32-bit generic




7.2 the choice of the equipment of base stations

  Consider options for the development of WiMAX base stations on the basis of known chips. Fujitsu has developed a chip MB87M3400 for both base and subscriber stations. However, unlike Intel, Fujitsu chip has an interface to the external processor. To implement full-duplex mode you want to use two chips, one of which functions as a physical layer and lower MAC layer Protocol, and the second is an external processor (third party company) for implementation of the top level of the MAC Protocol. To develop base stations Fujitsu provides a debug kit that implements a full-duplex mode of operation, processor Freescale MPC8560, but does not supply software that provides the functions of the upper MAC layer Protocol.

  The company PicoChip offers a solution PC102/PC8520, built on two of its parallel processors PC102. The company provides software that implements the physical layer and lower MAC layer Protocol chips on the PC102. And Fujitsu, the company uses PicoChip Freescale MPC8565 to implement top-level MAC Protocol in your debug kit. However, unlike the Fujitsu, PicoChip has licensed its software to the top of the MAC layer Protocol. Since the decision PC102/PC8520 not embedded encryption-decryption, for their implementation should be used by the external processor.

Chip for the development of base stations SQN2010 company Sequans is the first "system on a chip" having a full-duplex mode. SQN2010 implements all the functions of the physical and MAC levels required for full-duplex operation of the base station. Chip SQN2010 different from SQN1010 presence of a second CPU that implements the top level of the MAC Protocol. On the chip SQN1010 provides a PCI interface to allow the connection of external processor.

The decision DM256/MC336 of Wavesat company can be used to develop base stations. This solution supports full duplex mode, but it should be noted that the implementation of encryption-decryption it requires an external processor. Like Fujitsu, Wavesat provides no software support for the upper MAC layer Protocol required to develop base stations.

Of the four solutions described only chips PicoChip PC102 not integrate in themselves the functions of the ADC/DAC. Therefore, for developments that use analog radio interface, you also require a device ADC/DAC. The main parameters of the considered solutions for the development of base stations is presented in table. 3 [6].

Table 7. The main parameters of the considered solutions for the development of WiMAX base stations.


Fujitsu MB87

PicoChip PC102/PC8520

Sequans SQN2010

Wavesat DM256/MC336






Maximum channel width

20 MHz

10 MHz

28 MHz

10 MHz

The number of chips

1 chip

1 chip

2 chip

2 chip

1 chip

1 chip

1 chip

1 chip


Mill, 32-bit generic





Analog and digital


Analog and digital

Analog and digital

The choice of the manufacturer of chips for the development of WiMAX systems is an important strategic decision. For fast and effective system development requires the most complete hardware and software support and tools for development and debugging. The presence of the debug kits can significantly increase the speed and reduce the cost of development of WiMAX equipment, which is one of the main criteria when choosing a product.

Deploying WiMAX systems:

Building a network of fixed wireless access involves the use of three types of equipment - base stations, subscriber stations and equipment for communication between base stations.

To two or more radio signals do not interfere with each other's work, it is necessary that they coincide (overlap) in the frequency (frequency spectrum), time and space. Thus, each system for its proper functioning must be frequency-territorial spacing (CHTR) with interfering signal (interference). In addition, since we are dealing with digital systems, the radio signals which have a pulse shape, the condition of the timing means the coincidence or overlap in time of the pulses of the signals coming into the system. Thus, the time spacing of the pulses of the signals can be provided time synchronization of system operation with sources of interference.

Network standard IEEE 802.16 WiMAX are by far the most high-tech system BWA in the field of wireless telecommunications and place high demands on the parameters and quality of your antenna-feeder tract. Antenna and microwave circuitry in General is the most capricious part of any wireless access systems, in the case of WiMAX, the incorrect integration of active equipment and microwave can nullify all advantages of this technology. In base stations of WiMAX networks can be used Omni-directional and sector antenna with a sector angle of 60, 90 and 120 degrees.

When installing base stations uses the existing infrastructure.

Figure 24 - Typical operating circuit WiMAX BS placed on the existing sites using BWA NGN transport channels

The location of the WiMAX sites should be selected in such a way as to ensure maximum performance. From the standpoint of operating efficiency, special attention should be paid to operational support, deployment platforms, as well as their standardization. This saves time and money spent on the design of each individual site. Standardization involves the creation of a small set of configurations, which are taken as finished projects and adjusted with minimal changes to the specifics of a particular site. On the market there are inventory solutions that support the automation of this process. Special attention in such decisions should be given to the updating of inventory data, because in the future they will be required to expand the WiMAX sites as demand growth and to guarantee a high level of service.





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