basics of FCH or DLFP in wimax

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.