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basics of FCH or DLFP in wimax

As we know wimax frame consists of downlink subsubframe and uplink subframe. Downlink Subframe consists of preamble(2 OFDM symbols), header, downlink bursts(1, 2, 3 or 4). After downlink subframe, uplink subframe starts with some gap used for TTG and contention slots. The transmissions from BS to SSs is referred as downlink and transmissions from SSs to BS is referred as uplink subframe. Header mentioned above is known ad FCH (Frame Control Header) or DLFP (Downlink Frame Prefix). On this page we will see header used in fixed wimax as per OFDM specifications for 256 point FFT.


WiMAX frame

Figure shows DLFP after L.P.(Long Preamble) in downlink subframe. The modulation-code rate of wimax FCH or DLFP is fixed to BPSK-1/2. It has total size of about 88 bits as mentioned below.

WiMAX FCH/DLFP: { BS ID(4 bits), Frame No.(4 bits), CCC(4 bits), Reserved(4 bits),
Rate ID(4 bits), Preamble(1bit), Length(11 bits), DIUC(4bits), Preamble(1bit), Length(11 bits),
DIUC(4bits), Preamble(1bit), Length(11 bits), DIUC(4bits), Preamble(1bit), Length(11 bits),
HCS(8 bits)

These fields are described below in the table with example values.

WiMAX FCH/DLFP header format


WiMAX DLFP
BS ID(4 bits) 0x5
Frame No.(4 bits) 0x0
CCC(4 bits) 0xF
Reserved(4 bits) 0x0
Rate ID(4 bits) 0x0 (i.e. BPSK1/2)
Preamble(1bit) 0
Length of DL Burst#1(11 bits) 0x13 (decimal=19) (Check Note-1)
DIUC(4bits) 0x0
Preamble(1bit) 0
Length of DL Burst#2(11 bits) 0x0
DIUC(4bits) 0x0
Preamble(1bit) 0
Length of DL Burst#3(11 bits) 0x0
DIUC(4bits) 0x0
Preamble(1bit) 0
Length of DL Burst#4(11 bits) 0x0
HCS(8 bits) Header Check Sequence,
Calculated based on
g(D)= D8+ D2 + D + 1 polynomial.
Table-1

NOTE-1: Length of burst#1 is calculated in units of number of OFDM symbols. This is done using following equation.

No. of symbols in a burst = ceil {Length of burst in bytes*8*R/ (bm*192)}

No. of symbols = 226 bytes in broadcast burst *8*2/ (1*192) = 19 OFDM symbols

Here only one downlink bursts exist and hence length field for downlink burst 2, burst 3 and burst 4 is set to zero. Rate-ID details are mentioned in the table-2 below.

Rate-ID for Burst#1 Modulation/RS-CC rate bm R
0 BPSK-1/2 1 2
1 QPSK-1/2 2 2
2 QPSK-3/4 2 4/3
3 16QAM-1/2 4 2
4 16QAM3/4 4 4/3
5 64QAM2/3 6 3/2
6 64QAM-3/4 6 4/3
Table-2

DIUC in tandem with DCD represents modulation-code rate for burst 2 to 4. Refer wimax UCD UIUC DCD DIUC page for more details.


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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