Memory efficient data symbol interleaver which adaptively applies odd only, or odd and even interleaving processes, depending on OFDM mode

摘要

In this abstract "cell" is used in place of "data symbol" to avoid confusion with "OFDM symbol". A cell interleaver for OFDM is capable of operating a first (e.g. "odd") interleaving process and a second (e.g. "even") interleaving process. When the interleaver is used in a first OFDM mode (e.g. the 32K mode) with a first number of sub-carriers the first interleaving process is applied to input cells destined for odd numbered OFDM symbols and the second interleaving process is applied to input cells destined for even numbered OFDM symbols, but when the interleaver is used in a second OFDM mode (e.g. the 16K mode), with a number of sub-carriers which is less than or equal to half the number of sub-carries of the first OFDM mode, the first interleaving process is applied to cells for both odd and even numbered OFDM symbols. The first interleaving process involves writing cells into interleaver memory in sequential order and reading cells from memory in an order defined by a permuted code, whilst the second interleaving process involves writing cells into the same interleaver memory in the order defined by the same permuted code and reading cells out from the memory in sequential order. Thus, a single memory location can be used to simultaneously process an odd symbol and an even symbol. This invention combines this memory efficiency for the 32K mode with improved interleaver performance for lower modes. The invention finds particular application in DVB-T.