On the statistics of multipath fading using a direct sequence CDMA signal at 2 GHz,in microcellular and indoor environment

This paper describes the results of field tests consisting of received signal variations and multipath returns seen by a mobile receiver using direct-sequence (DS) code-division multiple-access (CDMA) waveforms. The experimental data for outdoor (microcellular environment) reveals that the instantaneous received power lost due to fading (sometimes called the fade margin) increases dramatically as the signaling bandwidth decreases below 11 MHz. It also shows that for most outdoor locations the significant multipath was confined primarily to 1s of excess delay with average delay of less than 200 ns. A broader-band CDMA system, having a bandwidth exceeding 10 MHz, could resolve the multipath components and could use a RAKE receiver to further reduce the transmitted power. However, a narrower-band CDMA system could not resolve these multipath components and thereby would suffer signal fading which would have to be compensated by 15 dB or more signal amplification. As a result, a narrower-band CDMA system would interfere with its other users and reduce its user capacity if no other forms of diversity are used. Our results also reveal that at some locations, returns with delays of more than 1s can be seen by the receiver with enough energy that could be collected using a RAKE receiver. However, these locations were found to be confined to a very low probability of existence within a prescribed cell (3-mile radius).