Turbo codes for M-ary pulse position modulated pulses over ultra wide band channels

In this paper we propose the use of Turbo Codes for M-ary pulse position modulated pulses over UWB communication channels with multipath. The transmitted power of the UWB pulses is required to be very small as they are used in the existing spectrum designated to other uses. This constraint requires that UWB signals have good performance at low SNR's. Turbo codes have been shown to perform well at low SNRs. We present the simulation results of using rate 1/2 and 1/3 turbo codes. Also, the effects of varying the symbols set size, the SNR of the channel and the interleaver size are presented. It has been shown in this paper that for a fixed SNR (4 dB), the rate 1/3 code shows an improvement of 2 orders of magnitude when M = 2 and 3 orders of magnitude when M = 4 or M = 8. For the same SNR, the rate 1/2 code shows an improvement of 1 to 2 orders of magnitude. To achieve a BER of 10^-5, the rate 1/3 turbo code requires SNR = 6 dB when M = 4 and SNR = 3 dB when M = 8. Increase in the size of the interleaver from 2⁹ to 2¹⁴ results in a decrease in BER from 10^-2 to 10^-3 for SNR = 4 and M = 2.