On partial transmit sequences for PAR reduction in OFDM systems

Partial transmit sequences (PTS) is a popular technique to reduce the peak-to-average power ratio (PAR) in orthogonal frequency division multiplexing (OFDM) systems. PTS is highly successful in PAR reduction and efficient redundancy utilization, but the considerable computational complexity for the required search through a high-dimensional vector space and the necessary transmission of side information (SI) to the receiver are potential problems for a practical implementation. In this paper, we revisit PTS for PAR reduction and tackle these two problems. To address the complexity issue, we formulate the search problem of PTS as a combinatorial optimization (CO) problem. This enables us to (i) unify various search strategies proposed earlier in the PTS literature and (ii) adapt efficient search algorithms known from the CO literature to PTS. We also propose a modified PTS objective function, which reduces the number of multiplications required for PTS. Numerical results show that, perhaps surprisingly, simple random search yields the best performance-complexity tradeoff for moderate PAR reduction, whereas two novel CO-based methods excel if close-to-optimum PAR reduction is desired. The SI transmission problem is solved by a simple preprocessing of the data stream before PAR reduction. This preprocessing introduces the minimal possible redundancy and allows SI embedding without affecting the PAR reduction capability of PTS or causing peak regrowth.