This paper proposes applying fast transmit power control (TPC) to the forward link of a direct sequence-code division multi-access (DS-CDMA) cellular system. Orthogonal spreading is assumed at a base station transmitter and coherent RAKE combining is assumed at a mobile station receiver. In DS-CDMA cellular mobile radio, the multiple access interference (MAI) from other cells and background noise limit the forward link capacity. Therefore, to increase the link capacity, fast transmit power control (TPC) can be introduced, which is similar to that developed for the reverse link, i. e. , the transmit powers of forward link channels are independently raised or lowered according to the instantaneous signal-to-background noise plus interference ratios (SIR's) measured at mobile stations. Fast TPC is fast enough to track the multipath fading as well as slow variations in the distance-dependence path loss and shadowing. On the average, the transmit power is increased to a user closer to the cell edge so that the effects of both other-cell MAI and background noise can be reduced while it is decreased to a user closer to the cell center. The effect of the TPC parameters (TPC interval, TPC target value, TPC step size, etc) on the forward link capacity in single- and multi-cell environments is evaluated by computer simulation. It is shown that fast TPC can almost double the forward link capacity in a multi-cell environment.

This paper presents a generation method of orthogonal spreading codes with different spreading factors (SFs), which are called orthogonal multi-SF spreading codes in this paper, for DS-CDMA mobile radio. The generated orthogonal multi-SF spreading codes have a tree structure and the codes are applied to the forward link such that all users, who transmit data at different rates, are orthogonalized. A group spreading modulator that simplifies the base station transmitter structure is also described. The transmission performance of the orthogonal multi-SF forward link under multi-user and frequency selective Rayleigh fading environments is evaluated by computer simulation to show that its performance is identical to that achieved by using multiple orthogonal spreading codes in parallel (orthogonal multicode forward link). Unlike the orthogonal multicode forward link, only a single Rake combiner is required at a mobile receiver which significantly simplifies the mobile receiver structure.

This paper presents a method to examine the effect of introducing data application services on existing wireless CDMA networks where conventional voice communications service is being provided. Since the total number of channels used in a cell is limited in the interfering cellular environments, some voice-traffic channels should be sacrificed when an additional channel is introduced for data services. We investigate this trade-off by analyzing the interference the forward link channels generate. It is also an objective of this paper to examine the forward link capacity in terms of the numbers of paging and voice-/data-traffic channels so as to determine the impact of introducing data services via paging and traffic channels. Different capacity regions are plotted for various cellular environments.