CDMA for cellular mobile radio systems

Lee, Chin-Chun (1994) CDMA for cellular mobile radio systems. University of Southampton, Doctoral Thesis.

Abstract

An evaluation of the capacity of the types of code division multiple access (CDMA) systems used in second generation mobile radio networks is made and compared to the corresponding time division multiple access (TDMA) systems. Both hexagonal cellular and microcellular structures are addressed. After a brief review of cellular radio we analysed macrocellular systems operating with a hexagonal structure. For TDMA systems, we employed power control, frequency hopping and discontinuous transmission in order to increase the signal-to-noise ratio (SIR) of the base station (BS)-mobile station (MS) links. The minimal omnicell cluster size was found to be three for a voice activity factor (VAF) of 3/8, yielding a capacity of 15 channels/cell/MHz. VAF signifies the fraction of time that users were transmitting. The effect of sectorisation on teletraffic was also evaluated. For CDMA systems, the up-link supported 29, 28 and 26 users, when the power control errors in the received bit energy-to-interference power spectral density (PSD) ratios (E_b/I₀) had standard deviations of 1.5, 2.0 and 2.5 dB, respectively, the VAF being 3/8.

The performances of both CDMA and TDMA systems in a rectilinear city street environment were investigated. Two types of microcells were considered. The rectangular microcell was a street on one side of a city block. The cross-shape microcell was formed by a BS at a road junction and extended half a block in the four perpendicular street directions. The capacity of TDMA systems was found to be 22 and 11 channels/microcell/MHz for cross-shape microcells and rectangular-shape microcells, respectively. (DX184247)

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