A new iterative soft-output Viterbi algorithm and its application to the “dicode” channel

We present an iterative soft-output decoding algorithm for serially concatenated coding systems. It has better performance than the conventional noniterative decoding algorithm. When applied together with an outer convolutional code to the dicode channel with partial response (1 — D), we obtain an additional coding gain of about 1 dB at a bit-error rate of 10^-4 after two iterations. This new algorithm can also be applied advantageously to satellite communication and fading channels.     

A CDMA overlay system using frequency-diversity spread spectrum

The frequency bands currently used by existing narrow-band users might be shared with a code-division multiple-access (CDMA) spread-spectrum (SS) overlay system. Thus, the spectral efficiency is improved, providing more capacity for future personal communications services. Since both narrow- and wide-band signals interfere with each other, an SS modulation scheme with a good resistance to narrow-hand interference results in an increased number of acceptable overlay users. We study a frequency-diversity SS modulation scheme for which optimal detection in the presence of narrow-band interference is easy to implement. The acceptable number of overlay users is evaluated and compared to that of conventional direct-sequence SS (DS-SS) modulation schemes with and without interference rejection filters. The proposed system also presents the following advantage: by suppressing transmission of replicas where narrow-band signals (NBSs) are present, the mutual interference can be avoided completely