PAPR minimisation in OFDM by allocating the same information to two groups of sub-carriers and transposing the information in one of the groups

摘要

This invention relates to a method of minimising Peak-to-Average-Power Ratio (PAPR) in OFDM transmission. The sub-carriers are divided into a first group (e.g. X2 to X63 of Fig. 5 on the fight hand side of the DC baseband carrier) and a second group (e.g. X67 to X128 on the left hand side of the DC baseband carrier). Symbols for transmission are mapped to the first group of caters, and the same symbols are copied and then transposed before being mapped to the second group of carriers. Transposition is by means of a transposition algorithm such as equations 8 and 9. In one embodiment the transposition associated with each one of the even numbered carriers of the second group is based on symbol information from both an even subcarrier and an odd sub-carrier of the first group, and may incorporate a mutual polarity function. Preferably transposition involves rendering a symbol into its negative form (i.e. reversing the sign of real and imaginary components). The invention is particularly suited to multiband-OFDM, especially in the case of conjugate symmetric mapping or dual cater modulation.