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WiMAX Ranging Procedure

This page describes fixed wimax ranging procedure and mention various ranging types as per IEEE 802.16 OFDM MAC layer specifications. It covers RNG REQ and RNG RSP MAC messages used for ranging by wimax SS.

As soon as wimax subscriber is switched on it establishes RF communication link by scanning available RF channels. After this, it synchronizes itself with Base Station using received long preamble(2 symbols) and performing time, frequency and channel estimation and equalization. After synchronization it decodes header(coded with BPSK1/2) information which helps to know modulation-code rate information of downlink burst#1 carring broadcast message. This broadcast message transmits DLMAP,DCD,ULMAP and UCD. Based on ULMAP and UCD, SS knows about when it has to transmit ranging messages in the uplink subframe.

The process by which the SS and BS maintain of RF communication link between them is referred as ranging. As mentioned RNG REQ and RNG-RSP MAC management message described below or special CDMA code modulated message is transmitted by the wimax SS for this purpose. There are various wimax ranging procedures as mentioned below.

1. Initial Ranging:
• Acquire correct transmission parameters (Power adjustment, timing offset estimation, and synchronization) to communicate with the BS

2. Periodic Ranging:
• To maintain uplink communication with the BS
• Adjust transmission parameters

3. Contention Ranging:
• Required by the SS to access the system for the first time
• No dedicated connection resources assigned to the SS

4. Non-Contention Ranging:
• Regulated by the BS to allow the SS to finish system access earlier when dedicated channel is provided
• Polled initial ranging

WiMAX RNG REQ


RNG REQ field Example Value
GEN HEADER(6 bytes) 0x00, 0x40, 0x1a, 0x00, 0x00, 0xbe
Ranging req.type( 1 byte) 0x04
DL Channel ID (1 byte) 0x00
Requested DL Burst Profile (TLV) 0x01, 0x01,0x11
SS MAC Address(TLV) 0x02,0x06,0x00,0x0a,0x1e,0x0a,0x1e,0x01
MAC Version(TLV format) 0x94,0x01,0x04
CRC(4 bytes) 0x5d,0x00,0x9c,0xfb
padding bytes if any 0x00,0x00

WiMAX RNG RSP


RNG RSP field Example Value
Genetic MAC Header(6 bytes) 0x00, 0x40, 0x32, 0x00, 0x00, 0x00
initial ranging msg type 0x05
Uplink channel id 0x00
SS mac address 0x08, 0x06, 0x00, 0x0a, 0x1e, 0x0a, 0x1e, 0x01
basic cid 0x09, 0x02, 0x00, 0x08
primary cid 0x0a, 0x02, 0x10, 0x08
ranging status 0x04, 0x01, 0x01
timing adjust 0x01, 0x04, 0xff, 0xff, 0xff, 0x9e
power level adjust 0x02, 0x01, 0xec
offset frequency adjust 0x03, 0x04, 0xff, 0xff, 0xfd, 0xdb
downlink operational burst profile 0x07, 0x02, 0x01, 0x01
CRC 0x00, 0x00, 0x00, 0x00
Padding if required 0x00, 0x00

RNG REQ is transmitted by SS to BS. After performing Synchronization (Time, Freq, Channel) RNG REQ Frame is decoded to bits at BS. Type field just after GMH will describe message type which is '0x04' for RNG REQ, which tells BS what need to be done after receiving the message.


RNG RSP decoded by SS will analyze following:

1. 'Timing Adjust' field (signed 32 bit) and will drive PHY to advance frame Transmission accordingly.

2. 'Power level Adjust' field (signed 8-bit, 0.25dB) and will drive RF attenuators at RF layer accordingly.

3. 'Offset Frequency Adjust' field (signed 32 bit, Hz units) and will drive RF synthesizer/Ref. OCXO accordingly.

4. Ranging Status (if status is 're range') will indicate whether SS need to do retransmit RNG REQ or (if status is 'Success') start BW REQ transmission for determining slot for SBC REQ.


What is Difference between

difference between FDM and OFDM
Difference between SC-FDMA and OFDM
Difference between SISO and MIMO
Difference between TDD and FDD
Difference between 802.11 standards viz.11-a,11-b,11-g and 11-n
Bluetooth vs zigbee
Bluetooth vs zigbee
wibro vs mobile wimax
Microcontroller vs microprocessor
FDMA vs TDMA vs CDMA
FDM vs TDM
CDMA vs GSM
OFDM vs OFDMA
wimax vs lte

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

               

RF and Wireless Terminologies


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