CDMA cellular systems performance with fading, shadowing, and imperfect power control

Abstract

This paper addresses capacity estimation for cellular code-division multiple-access (CDMA) systems, assuming the IS-95 standard as a reference, Extending the analytical method from [6], we obtain a sequence of bounds on capacity, and then we introduce an accurate approximation to reduce computation complexity. The analysis accounts for interference internal and external to the reference cell, fading, shadowing, and imperfect power control. Outage probability is expressed in terms of the characteristic functions (cf's) of the interference and imperfect power control random variables (rv's), The interference contributions are computed on the basis of a Poisson distribution for the number of users in a lognormally shadowed channel. Results are provided for different channel conditions and are validated against Monte Carlo simulations, A comparison against previously published CDMA capacity estimates is carried out, aimed at clarifying some controversial issues. It is also confirmed that large system capacity is achievable under tight power control

Effect of Power Control Imperfections on the Reverse Link of Cellular CDMA Networks Under Multipath Fading

“…If inequality (13) does not hold, the mobile will switch to BS0 and will generate intracell interference. Note that condition (13) is equivalent to (14) with (15) Therefore, the moment of order of the intercell interference generated by an active mobile located in region will be given by (16) The second, third, and fourth factors in (16) are the same as those calculated in (9)- (11), and the first factor can be shown to be given by [15], [19] (17)…”

“…Usually, imperfections in power control after despreading are modeled as a log-normal random variable [12]- [15]. Recently, in [11] it has been analytically verified that this assumption is a reasonable good one.…”

“…Considering statistically independent random variables, it can be found that the moment of order of the interference generated by an active mobile in region will be given by (5) with (6) Dependence on point (x,y) has been omitted for the sake of clarity. The first factor in (5) can be found to be given by [15], [19] (7) with (8) The second and third factors in (5) can be found by simply solving the following integrals (9) (10) And finally, the fourth factor can be calculated as (11) Note that (10) is the moment of order of the power transmitted by a mobile to compensate the multipath fading at the base station to which it is connected. For and , it is clear from (10) that the mean and variance, respectively, of the interference at BS0 will be infinite.…”

“…Thus, the main aim in these systems is to maintain power level variations at a low enough level to avoid drastic reductions in system capacity and, therefore, the effect on system performance of imperfections in power control must be considered. The issue of the effect of power control errors on CDMA systems has received a great deal of attention over the last few years [10]- [15]. Many of the previous papers analyzing the effects of power control imperfections on cellular CDMA networks do not explicitly address the effect of multipath fading, and its effect is included in the ratio of required energy per bit to interference density or in power control errors.…”

“…An analysis explicitly considering the interference due to other-cell users can be found in [14] for a system in which shadowing is not considered and users connect to the nearest base station. In [15], a detailed analysis is performed for a system in which users connect to a given base station on a minimum attenuation basis and shadowing is considered for the calculation of intercell interference, but its effect is omitted for the derivation of the intracell interference statistics. Moreover, a theoretical approach to analyze the effect of multipath fading on interference statistics and its interaction with imperfect fast power control is not addressed in any of the mentioned papers.…”