WiMAX Frame Structure
This page covers fixed wimax frame structure as per OFDM technique and mobile wimax frame structure as per OFDMA technique. The figures here are only for illustrative purpose only and it may vary in the actual wimax system/standard.
Fixed WiMAX Frame Structure:
As mentioned in the figure below fixed wimax frame structure composed of two main parts downlink subframe and uplink subframe. It is made of symbols on X axis or time axis. Here resources are allocated to subscribers time wise only.
Downlink subframe:
It is composed of preamble,header,broadcast burst and normal downlink bursts.
Preamble composed of 2 OFDM symbols all made of QPSK carriers.
The first symbol consists of 50 carriers and the second symbol consists of 100 carriers.
One OFDM symbol contains total 256 carriers.
Header is one symbol length and contains 88 bits, which uses BPSK 1/2 modulation-CC rate. Header is also called as DLFP i.e. Downlink Frame Prefix.
Broadcast burst consists of DLMAP,ULMAP,UCD(Uplink channel descriptor) and DCD(Downlink channel descriptor). DLMAP defines location of downlink bursts and ULMAP defines location of uplink bursts. DCD/DIUC(Downlink Interval Usage Code) defines modulation-code rate for downlink bursts. UCD/UIUC(Uplink Interval Usage Code) defines modulation-code rate for uplink bursts.
DLMAP made up of DL MAP IEs and other constant fields.ULMAP made up of ULMAP IEs and other constant fields. IEs stand for Information elements.
For each downlink or uplink burst one IE is required.
Normal burst carries data meant for subscriber stations(SS). One burst can take multiple MAC PDUs for one or more than one SSs.
Downlink Frame Prefix = [BS ID(4 bit),Frame No.(4 bit),CCC(4 bits),Reserved(4 bits),Rate ID(4 bits),Preamble(1 bit),Length Burst No.1 (11 bits),DIUC(4 bits),Preamble(1 bit),Length Burst No.2 (11 bits),DIUC(4 bits),Preamble(1 bit),Length Burst No.3 (11 bits),DIUC(4 bits),Preamble(1 bit),Length Burst No.4 (11 bits),HCS(8 bits)]
DLMAP IE = [CID(16 bits),DIUC(4bits),Preamble (1 bit),Start time(11 bits)]
ULMAP IE = [CID(16 bits),Start time(11 bits),Sub channel Index(5 bits),UIUC(4 bits),Duration(10 bits)]
UCD = [Burst Profiles for Uplink-6 bytes in TLV format which mentions modulation-code rate profiles for uplink bursts,other constant system fields for CCC,backoff, rf center frequency etc.]
DCD = [Burst Profiles for Downlink-6 bytes in TLV format which mentions modulation-code rate profiles for downlink bursts,other constant fields BSID,frame number,frame duration etc.]
Uplink subframe:
It is composed of contention slot for ranging,contention slot for bandwidth request and normal uplink bursts.
As mentioned there are slots reserved for SSs to send ranging request to obtain network entry and to send bandwidth request messages asking BS for resource allocation capacity.
Normal burst is prefixed with preamble which is similar to second symbol of downlink subframe preamble. Also called short preamble as it occupies only one symbol. Downlink subframe preamble is called as long preamble.
TTG and RTG Gap
TTG gap is provided between downlink and uplink subframe and RTG gap is provided between uplink and downlink subframe.
These gaps are provided to allow RF handware circuitry to switch from Tx(Transmit) to Rx(Receive) and from Rx to Tx.
Refer TTG gap and RTG gap in WiMAX and LTE frame structures.
Mobile WiMAX Frame Structure:
As mentioned in the figure below mobile wimax frame structure composed of two main parts downlink subframe and uplink subframe.
It is made of symbols on X axis and subchannels on Y axis. This frame structure is only for PUSC zone both in downlink and uplink.
Here resources are allocated to mobile subscribers both time and frequency wise in units of slots.
Further unlink fixed wimax, frame structure in mobile wimax consists of various mandatory and optional zones. It include mandatory zones PUSC,FUSC & AMC for downlink subframe while PUSC & AMC for uplink subframe.
subchannel and symbol definition varies based on FFT size used hence frame structure vary accordingly.
There are four FFT sizes supported in the 16e standard viz. 2048,1024,512 and 128. Out of these 1024 and 512 are commecialized in the wimax products such as base station and mobile subscriber station.
For downlink PUSC slot is 1 subchannel X 2 symbols and for uplink PUSC slot is 1 subchannel X 3 symbols. For FUSC it is 1 X 1. For AMC it is 2 X 3.
Downlink subframe:
It is composed of preamble,header,DLMAP,ULMAP and normal downlink bursts. There are 114 preambles defined in the standard out of which one will be active in one sector at a time.
Uplink subframe:
It is composed of region for ranging,bandwidth request,periodic ranging,handover request,CQICH and normal uplink bursts. There is no preamble defined for uplink subframe or uplink bursts.
TTG and RTG Gap
TTG gap is provided between downlink and uplink subframe and RTG gap is provided between uplink and downlink subframe.
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
Frame structure of wireless standards, technologies
Frame structure of various wireless standards/technologies are mentioned below.
It include WiMAX, WLAN, Zigbee, GSM, GPRS, UMTS, LTE, TD-SCDMA, GPS, SDH, 11ac WLAN, AMPS, Ethernet, VLAN etc.
WiMAX physical layer Frame Structure as per 802.16d and 802.16e standards
WiMAX MAC layer Frame Structure as per OFDM 802.16d standard
Zigbee RF4CE Frame Structure
Zigbee physical layer Frame Structure
Zigbee MAC layer Frame Structure
GPRS Frame Structure
GPS Frame Structure
LTE Frame Structure
TD-SCDMA Frame Structure
UMTS Frame Structure
SONET Frame Structure
SDH Frame Structure
802.11ac PHY Frame Structure
802.11ac MAC layer Frame Structure
WLAN Frame Structure as per 802.11a,11b,11n,11ac standards
AMPS Frame Structure
Ethernet Frame Structure
VLAN Frame Structure
GSM Frame Structure