Frame control encoder/decoder for robust OFDM frame transmissions

Abstract

An encoder/decoder scheme for robust transmission of PHY layer frame control information (to support medium access) in OFDM frames (or packets). The PHY layer frame control information to be modulated onto carriers in OFDM symbols is encoded using a product coding to form a product code block or matrix. The product coding is based on a shortened hamming code codeword set having properties of symmetry. Elements of the product code matrix are interleaved so that the elements are modulated onto the carriers of the symbols in diagonal groupings (across time and frequency) and with some degree of redundancy. The modulated elements are demodulated to produce soft decision values, which are de-interleaved to combine copies of the soft values for elements and re-order the soft values in the order of the elements prior to interleaving. The soft values for each row and each column are provided to a turbo product decoder, which performs a number of iterations of row/column decoding, each iteration applying a weighting to the results to enhance the reliability of the results of each next successive iteration. Upon completion of the final iteration, the decoder applies a hard decision to the soft values to produce a set of hard values for each of the soft values that corresponds to the frame control information. Given the symmetry of the code set, the row/column decoding generates a complete set of correlation values from only a subset of the complete set of correlation values and uses a reduced number of MAP decoding operations to select the best correlation values for each of the soft values.

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