Combined power control and turbo code

Abstract

In this thesis, we focus on the combined power control and turbo code. The main contributions of the thesis are as follows. First, we propose reallocating the power resource among the code symbols in such a way to minimize the decoding error probability of turbo code. We consider several power reallocation schemes and investigate their performance in slowly-varying Rayleigh flat fading channel. We show that the proposed scheme can reduce the decoding error probability by two orders of magnitude and provide a power gain of 0.86 dB at BER of $10^{-6}$ over the traditional equal power allocation among all code symbols. We also propose applying different power levels and cut-off thresholds on systematic and parity check bits depending on the channel gain, and investigate the effect of channel gain estimation error. Second, we consider reallocating the power resource among the code symbols in a turbo code sequence to allow an effective use of limited power in lognormal shadowing and Rayleigh fading channel. The motivation is that when the error-control coding is employed, the received SNR need not be equally maintained at a fixed level for all code symbols because a certain number of symbol errors that are within the correction capability can be corrected regardless of the received SNR for those erroneous symbols. Therefore, for an effective use of limited power, power reallocation among code symbols in a code sequence is necessary. We show that the proposed power reallocation can provide a power gain of 0.85 dB over the constant power transmission scheme which allocates equal power among all code symbols. We also propose applying different power levels and cut-off thresholds on systematic and parity check bits, and investigate the effect of channel estimation error. Third, we consider allocating different powers on systematic and parity bits at turbo encoder outputs with total transmission power fixed. We investigate how the transmission power should be allocated...