A thesis submitted in partial fulfillment of the requirement for the degree of Master of Engineering.School of Advanced Technologies

Thesis (M.Eng.) - Asian Institute of Technology, 1999

Parallel Concatenated Convolutional Codes (PCCCs), popularly termed as turbo codes have been found to be a potential candidate for their use in future generation wideband mobile radio communication systems. High data rate transmission required for the next generation mobile radio systems causes the wideband signals to suffer from correlated multipath fading. The performance. of turbo codes has been found to degrade significantly with the increase in correlation. Their performance evaluation for moderate interleaving delay with perfect channel estimation has proved its applicability for next generation higher bit rate applications. In this thesis, performance evaluation of turbo codes is carried out with a realistic channel. Two channel estimation techniques, correlative estimation and recursive least square (RLS) estimation, for downlink synchronous CDMA systems with BPSK modulation have been incorporated in the Rake receiver. Performance of both estimation techniques has been investigated and compared in a correlated fading environment. Simulation results at low mobile speed show that performance of turbo codes with the correlative channel estimation is comparable to the RLS estimation method where the channel estimates are updated once every symbol interval. In such case, the performance loss compared to the perfect case was found to be within 2 dB for the UMTS requirements of BER of 10·6 . It was also found that the RLS channel estimation with channel estimates updated every chip interval perf01med quite near to the perfectly estimated case with a difference of within 1 dB from the perfect case at lower mobile speed. Thus, turbo codes are still found to be attractive even in the correlative channel with the above estimation techniques where 2 dB performance loss can be accepted.