We examine techniques for increasing spectral efficiency of cellular systems by using slow frequency hopping (FH) with dynamic frequency-hop (DFH) pattern adaptation. We first present analytical results illustrating the improvements in frequency outage probabilities obtained by DFH in comparison with random frequency hopping (RFH). Next, we show simulation results comparing the performance of various DFH and RFH techniques. System performance is expressed by cumulative distribution functions of codeword error rates. Systems that we study incorporate channel coding, interleaving, antenna diversity, and power control. Analysis and simulations consider the effects of path loss, shadowing, Rayleigh fading, cochannel interference, coherence bandwidth, voice activity, and occupancy. The results indicate that systems using DFH can support substantially more users than systems using RFH. Index Terms-Cellular, code-division multiple access (CDMA), dynamic channel allocation (DCA), dynamic channel assignment, EDGE, frequency hopping, orthogonal frequency-division multi-plexing (OFDM), spectral efficiency, wireless.
The presence of multipath leads to a loss of orthogonality between the signals transmitted simultaneously on a wideband code-division multiple access (WCDMA) downlink. We derive general analytical expressions for the orthogonality factor (OF), which quantifies this loss of orthogonality, as a function of the instantaneous multipath fade realization of the channel. We show that the OF exhibits a significant temporal variation for the three channel profiles suggested in the WCDMA standard, namely, typical urban, rural area, and hilly terrain, which span a wide range of realistic cases. Moreover, its temporal variations and statistics vary significantly from one channel profile to another. Also, while the pulse shape and the number of Rake fingers has only a marginal impact on the OFs statistics, the granularity in setting the finger positions has a considerable impact. The results of the work can be directly used for evaluation of the system performance of WCDMA cellular systems.Index Terms-Code-division multiple access (CDMA), intracell interference, multipath channels, orthogonality factor, Rake receiver.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.