The OFDM Baseband Processor is a custom baseband processor, which implements the physical layer of an OFDM, time division duplexing (TDD) system. The baseband processor includes both transmission and reception bit-level and symbol-level processing chains including a sophisticated synchronization unit. The host interface is based on SPI protocol as well as with handshaking/interrupt ports. This custom system implements a subset of 802.16d standard functional options/features and is highly configurable via the integrated register file. An RF interface module is also included, compatible with Analog Devices AD9361 RF transceiver.
The Bit-level processing block (BLPB) transmission chain implements the following functional units : randomization, FEC encoding, interleaving and symbol mapping. In BLPB reception chain the following operations are implemented: soft symbol demapping, deinterleaving, FEC decoding and derandomization. The FEC module is based on the implementation of the Reed Solomon algorithm.
The Symbol-level processing block (SLPB) transmission chain implements the following functional units: OFDM symbol transmitter, IFFT , CP insertion. In reception chain the SLPB module is preceded by the synchronization unit, which is searching for known preamble values in order to locate the start an incoming wimax sub-frame. Once the sub-frame is located, frequency offset compensation is applied and received information is propagated down to SLPB reception chain. In SLPB reception chain the following operations take place: CP removal, FFT, OFDM symbol receiver, channel estimation, phase offset compensation and channel equalization.