Data Subcarrier Modulation Format (802.16 OFDM)

Data Subcarrier Modulation specify the Data Subcarrier Modulation Format. The modulation format is shown in the SubFrame Info error summary trace data. This parameter does not affect the demodulation of the pilot subcarriers, which are always BPSK Binary phase shift keying - A type of phase modulation using 2 distinct carrier phases to signal ones and zeros. modulation.

OFDM IEEE 802.16a/d FCH Symbol - RATE_ID Field

The 802.16 OFDM Orthogonal Frequency Division Multiplexing: OFDM employs multiple overlapping radio frequency carriers, each operating at a carefully chosen frequency that is Orthogonal to the others, to produce a transmission scheme that supports higher bit rates due to parallel channel operation. OFDM is an alternative tranmission scheme to DSSS and FHSS. downlink subframe contains Preamble symbols followed by the FCH symbol and Data symbols. The FCH symbol is always transmitted using BPSK modulation. The FCH symbol contains information about the first four data bursts in the downlink subframe. However, the data modulation formats of the 2nd through 4th burst are described by referring to a DIUC, which is not available to the VSA. Because of this, the VSA uses FCH only for the first data burst in the subframe.

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The FCH symbol's Rate_ID and Length fields describe the first data burst. The Rate_ID field transmits the modulation and coding to be used in the first downlink burst immediately following the FCH. The Rate_ID encoding is shown in the following table. The Rate_ID encoding is static and cannot be changed during system operation. The Length field contains the number of OFDM symbols in the burst. This information is shown in the Subframe Info when a FCH is present.

OFDM Rate ID encodings

Rate_ID	Modulation RS-CC rate
0	BPSK 1/2
1	QPSK Quadrature phase shift keying 1/2
2	QPSK 3/4
3	16-QAM Quadrature Amplitude Modulation 1/2
4	16-QAM 3/4
5	64-QAM 2/3
6	64-QAM 3/4
7-15	reserved

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