Call Admission Control for Soft Handoff Coverage in CDMA Cellular System

Abstract

In code division multiple access mobile cellular networks, the transmission quality can be improved by using the soft handoff techniques. The present investigation is concerned with the admission control policies by exploiting the soft handoff coverage area of the cellular radio network. We suggest finite Markov models for the admission control based on reserve channel and sub-rating policies. In reserve channel policy, a fixed number of channels are reserved exclusively to serve the handoff calls whereas according to sub-rating policy, the occupied channels can be split into two half rate channels to accommodate more handoff voice calls. It is also considered that the new call generation rate per unit area is uniformly distributed over the service area. Various performance indices are derived in terms of steady state probabilities. For some special situations, we validate and compare the models developed with previous existing models by setting the system descriptors. To examine the effect of various parameters on the performance measures, the sensitivity analysis is carried out by taking illustrations.

Appendix 1

1.1 Product type solution

Using the appropriate transition rate and with the help of the state transition diagram i.e. Fig. 3, the following set of equations is constructed.

$$- (\lambda_{n} + \lambda_{h} )P_{0} + \mu \,P_{1} = 0$$

(30)

$$(\lambda_{n} + \lambda_{h} )P_{j - 1} - (\lambda_{n} + \lambda_{h} + j\mu )P_{j} \, + \mu (j + 1)\,P_{j + 1} = 0, \quad1 \le j \le C - r - 1$$

(31)

$$(\lambda_{n} + \lambda_{h} )P_{C - r - 1} - (\lambda_{n} + \lambda_{h} + (C - r)\mu )P_{C - r} \, + \mu (C - r + 1)\,P_{C - r + 1} = 0$$

(32)

$$\lambda_{h} \,P_{j - 1} - (\lambda_{h} + j\mu )P_{j} \, + \mu (j + 1)\,P_{j + 1} = 0,\,C - r + 1 \le j \le C - 1$$

(33)

$$\lambda_{h} \,P_{C - 1} - \,C\,\mu \,P_{C} \, = 0$$

(34)

Equation (30) can be written as

$$P_{1} = \frac{{(\lambda_{n} + \lambda_{h} )}}{\mu }P_{0}$$

(35)

Solving Eqs. (31) and (32) recursively, we obtain product type result given in Eq. (15) for the interval $1 \le j \le C - r$.

Similarly, on solving Eqs. (33) and (34) recursively, we get the product type result as given in Eq. (15) for the range $C - r + 1 \le j \le C$.

Now, on applying the normalizing condition i.e. $\sum\nolimits_{j = 0}^{C} {P_{j} = 1}$, we obtain Eq. (16).