DIVERSITY WITH DISTRIBUTED DECISIONS COMBINING FOR DIRECT-SEQUENCE CDMA IN A SHADOWED RICIAN-FADING LAND-MOBILE SATELLITE CHANNEL

The performance of two diversity schemes with distributed decisions co mbining is analyzed and compared with that of the selection and maxima l ratio-combining schemes for binary-phase shift keying (BPSK) direct- sequence code-division multiple access (DS-CDMA) in a shadowed Rician- fading land-mobile satellite channel. In the first scheme of distribut ed decisions combining, the combiner collects only the binary branch d ecisions to make the data decision. In the second scheme, the combiner makes the data decision using the branch decisions and the channel st ates. Both symmetrical and asymmetrical diversity branches are conside red. Based on optimal likelihood ratio testing, a new data decision ru le is devised for the detection of the spread-spectrum signals in the DS-CDMA system. Upper bounds are employed for the performance evaluati on of the diversity combining schemes when the bit error probability i s difficult to compute. Numerical results are presented for the satell ite channel under light, average, and heavy shadowing.