Adaptive intemally turbo-coded ultra wideband-impulse radio (AITC-UWB-IR) system

Abstract

As a new spread spectrum system, an ultra wideband-impulse radio (UWB-IR) has attracted much attention in high speed indoor multiple access radio communications. Since the UWB-IR system repeats and transmits pulses for each bit, the UWB-IR system is considered as a coded scheme with a simple repetition block code. As an error correcting code, turbo-codes proposed by C. Berrou et al. in 1993 have attracted much attention beyond the field of coding theory, because the performance is very close to the Shannon limit with practical decoding complexity. In this paper, we propose an adaptive internally turbo-coded UWB-IR (AITC-UWB-IR) system. The proposed system employs a turbo code in addition to a repetition block code and shares the transmission bandwidth adaptively between them. We evaluate the performance of the AITC-UWB-IR by theoretical analysis and computer simulation. From our numerical and simulation results, we show that the BER of the AITC-UWB-IR is superior to that of the SOC-UWB-IR on an AWGN channel when the bit rate is high. We also showed that the AITC-UWB-IR system using low rate turbo codes improves the BER on an AWGN channel and a real Gaussian fading channel. Consequently, we confirm that for the same bit rate, we had better make the code rate of turbo codes lower and make the number of repetitions of the repetition codes smaller to achieve the better BER.