A comparison of CDMA and frequency hopping in a cellular environment

Citation

Mandell, Michael I. (1993) A comparison of CDMA and frequency hopping in a cellular environment. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/xsbz-qt92. https://resolver.caltech.edu/CaltechETD:etd-08302007-154436

Abstract

This paper compares the performances of Direct Sequence Code Division Multiple Access (CDMA) and Frequency Hopping (FH) schemes in a cellular multiuser environment. Our multiuser channel model incorporates the effects of propagation, frequency selective fading, and interference among users in the presence of a constrained system bandwidth. This channel model is applicable for cellular mobile communications, as well as other forms of personal communications. The CDMA and FH systems are compared using BPSK modulation. The main point of contrast between these systems is that the orthogonal hopping patterns in a FH system result in a decreased additive interference power, however, the frequency spreading nature of CDMA results in both the ability to combat fading, and the ability to effectively use low rate codes. An information-theoretic analysis is presented, and shows that the system capacity is larger for CDMA than for FH. Hence, with sufficient coding the CDMA system can achieve a higher level of performance than the FH system. However, it is unclear what level of complexity would be required to achieve such performance, and what effect such complexity would have on the practicality of the system. Finally, through the use of simulation, the performances of several simple coding schemes are measured and compared to the theoretical limits. These simple coding schemes perform far below the theoretical limits and also display a tradeoff in performance where the FH system performs better at high levels of traffic, and the CDMA system performs better at low levels of traffic.

Thesis Files