WiMAX Tutorial
This wimax tutorial covers what is wimax,wimax standards,wimax terminology,WiMAX Frame Structure,WiMAX Network Architecture, wimax Protocol Stack,wimax physical layer,wimax MAC layer,802.16m,fixed wimax versus mobile wimax,wiBro versus mobile wimax, Wimax Base station and subscriber station suppliers.
Introduction
WiMAX is used for providing broadband internet using wireless medium mainly at 2.5GHz,3.5GHz and 5.8GHz radio frequencies. It is also known as 4G technology. It delivers about 4 times fast internet compare to its 3G counterpart. OFDM is behind this increase in speed as it carry multiple carriers, each carrying more than one data bits based on modulation techniques(QPSK,16QAM). This carriers are concisely packed together to save bandwidth.Intel is behind the developement and proliferation of wimax throughout the world. This wimax tutorial covers what is wimax,wimax standards,wimax terminology,wimax physical layer,wimax MAC layer,802.16m,fixed wimax versus mobile wimax,wiBro versus mobile wimax,Wimax Base station and subscriber station suppliers.
WiMAX is referred as one of the metropolitan area network. It replaces DSL technologies for providing wireless internet at about 70Mbps upto the distance of 35 Km. There are two main versions of wimax viz. fixed wimax and mobile wimax. In Fixed wimax terminal or subscriber is fixed to a location and in mobile wimax they can move at various speeds. Fixed wimax is referred as 802.16d or 16d and mobile wimax is referred as 802.16e or 16e.
There are many physical layers as per IEEE 802.16 standard. The mainly used among them are Single carrier,OFDM and OFDMA. Single carrier is used for 10-66 GHz of frequency range while OFDM/OFDMA is used for 2-11GHz frequency band. OFDM is employed in fixed wimax and OFDMA is employed in mobile wimax.
Refer WiMAX Network Architecture➤ and WiMAX Network Entry Procedure➤.
• WirelessMAN-SC PHY:
-Single carrier modulation
-Targeted for 10-66 GHz frequency band
• WirelessMAN-SCa PHY:
-Single carrier modulation
-Frequency bands below 11GHz for NLOS
• WirelessMAN-OFDM PHY:
-OFDM modulation with a FFT size of 256
-Frequency bands below 11GHz for NLOS
-AAS and MIMO (also for OFDM-PHY)
• WirelessMAN-OFDMA PHY:
-OFDM modulation with scalable FFT sizes
-Frequency bands below 11GHz for NLOS
-Hybrid ARQ
-Fast-feedback mechanisms
-Handover support
Fixed WiMAX System Features
Following are the features of Fixed WiMAX System.
| Feature | Fixed wimax support |
|---|---|
| IEEE Standard | 802.16-2004 OFDM PHY/MAC, 16d |
| Symbol Parameters | Cyclic Prefix (1/4,1/8,1/16,1/32),FFT size(256), Channel Bandwidth(1.75/2.5/3/3.5/5/5.5/7/10MHz) Long Preamble for Downlink sub frame and Short Preamble for Uplink Bursts |
| Frame duration | 2.5, 4, 5,8, 10, 12.5, 20 ms |
| Modulation | DL BPSK,DL QPSK, DL 16 QAM, DL 64 QAM,UL BPSK, UL QPSK,UL 16 QAM, UL 64 QAM |
| Channel Models | SUI channel models |
| Channel coding | Randomization, Concatenated RS-CC, Interleaving |
Useful Calculations
Sampling Frequency Fs= (n* BW/8000)*8000
if n=144/125 has been chosen,
For BW of 20MHz
Fs=23.04MHz
Sub carrier Spacing Delf=Fs/Nfft
Delf =23.04/256= 90KHz, Sub carrier spacing
Symbol Time without CP , Tb=1/Delf
Tb=11.11µs
Guard Period, Tg ( Tb/4=2.77µs;Tb/8=1.39µs;Tb/16=0.69µs;Tb/32=0.35µs;)
Total Symbol Time , Ts=Tb + Tg;
Ts=11.8 µs , symbol time with CP of Tb/16
Sampling Time , Tb/ Nfft =0.04375µs
Physical Slot(PS) duration =4/Fs , Unit of BW allocation
Hence PS= 4/23.04MHz=0.174µs
Mobile WiMAX System Specifications
| Feature | Mobile wimax support |
|---|---|
| IEEE Standard | 802.16-2005 OFDMA PHY/MAC,16e |
| FFT Size | 2048/1024/512/128 |
| Sampling Factor | If channel bandwidth is a multiple of 1.75MHz then n=8/7 else if channel bandwidth is a multiple of any of 1.25, 1.5,2 or 2.75 MHz then n=28/25 else if not otherwise specified then n=8/7. |
| Cyclic Prefix | 1/8 |
| Frame Size | 5 ms |
| DL Subcarrier allocation | PUSC,FUSC,AMC2x3 |
| UL Subcarrier allocation | PUSC,AMC2x3 |
| DL Modulation | QPSK,16QAM,64QAM |
| UL Modulation | QPSK,16QAM |
| Convolutional Coding | Tail biting/CTC |
| MAP Type | Normal/Compressed |
| DL MIMO | 2-antenna, matrix A, 2-antenna, matrix B vertical encoding |
| UL MIMO | Collaborative SM for two MS with single transmit antenna |
Useful Calculations
For FFT size( Nfft ) of1024 and System BW of 10MHz
Sampling Frequency, Fs=n*BW
Fs=28/25*10MHz
Fs=11.2MHz
Subcarrier frequency spacing, Delf=Fs/Nfft,
Delf =11.2/1024=10.9375KHz
Useful symbol time, Tb=1/?f, this is without CP
Tb=91.4285µs
Guard time, Tg=Tb/8 =11.4285 µs.
OFDMA symbol time=Ts=Tb+Tg=102.8571 µs;
STEP By STEP GUIDE on WiMAX OFDM PHY and MAC layer
Refer following links which describes WiMAX Physical layer transmitter step by step.
WiMAX OFDM PHY layer protocol➤
Fixed wimax MAC layer protocol➤
Links to WiMAX MAC Layer resources
REG REQ and REG RSP SBC REQ and SBC RSP DSA REQ and DSA RSP UCD,UIUC,DCD,DIUC DLMAP and ULMAP WiMAX Ranging Procedure WiMAX Bandwidth Request procedure WiMAX Network Entry Procedure WiMAX CID vs SFID WiMAX FCH header format WiMAX TLV Format basics WiMAX Timers WiMAX Network Interface types WiMAX QoS Classes
More WiMAX RELATED LINKS
WiMAX-OFDMA PHY wimax network architecture WiMAX protocol stack Fixed wimax versus mobile wimax what is wimax wibro versus mobile wimax WiMAX Frame Structure WiMAX Terminology wimax versus lte wimax tutorial WiMAX Hardware vendors WiMAX Base station WiMAX System on Chip WiMAX subscriber station RF circulator for WiMAX RF isolator for WiMAX WiMAX MAC IP Core WiMAX PHY IP Core wireless channel emulator
