EXIT Chart Aided Design of DS-CDMA UltraWideBand Systems Using Iterative Decoding

This paper presents a novel ultrawideband (UWB), direct sequence code division multiple access (DS-CDMA) aided system designed for the IEEE 802.15.3a UWB channel specifications. Substantial performance improvements can be attained by serially concatenated channel encoding combined with a unity rate code (URC). We compare the performance of the iterative aided decoding correlation (Corr) and minimum mean square error (MMSE) detectors exchanging extrinsic information between the URC´s decoder as well as the outer recursive systematic convolutional (RSC) code´s decoder. Moreover, the iterative decoding convergence analysis of the proposed system is carried out with the aid of extrinsic information transfer (EXIT) charts. As expected, the iteratively decoded fully-loaded system employing MMSE detection outperforms its counterpart employing the equivalent Corr detection. Explicitly, UWB DS-CDMA using the MMSE detector attains a BER of 10^-5 at E_b/N_o=2 dB when supporting U=32 users employing i=12 decoding iterations, while the same system using the Corr detector operates at BER-10^-1.