This paper analyzes the performance of a protocol proposed to improve the performance of Joint CDMA/PRMA protocol under heavy data traffic load condition. The proposed protocol features a demand-based assignment scheme for data transmission. Its performance is evaluated using two analysis methods: a Traditional Markov Analysis and a Transient Fluid Analysis. Simulation results are also given to validate the assumptions made in the mathematical models developed. Our work shows that demand-based assignment scheme is suitable for random data traffic transmission, especially when there are a large number of active data terminals with short random messages.
Today's mobile communication systems are designed primarily to provide cost efficient wide area coverage for a large number of users with moderate bandwidth demands (voice+low rate data). The consumer of telecommunication services of tomorrow will expect to receive the same services in a wireless fashion as he receives from a fixed network. To meet this demand, third generation wireless systems are currently under development around the globe and are likely to be deployed with limited capabilities by the end of this year with major deployment at least a couple of years later. However, from the air interface point of view, the goal of providing higher bit rates is still valid. In addition to applications calling for higher bit rates, users will also want to use multiple services simultaneously. Emerging requirements for higher data rate services and better spectrum efficiency are the main drivers identified for the future mobile radio systems. In a wireless system consisting of a number of mobile terminals that transmit traffic of any type on a shared medium to a centralized base station (BS), a procedure must be invoked to distribute packet transmission among all users, which is known as a Medium Access Control (MAC) protocol.
Many MAC protocols have been developed to support speech and data traffic and can be found in Refs. [1], [2], [3], [4], [5], [6] and [7]. Other MAC protocols that have considered multimedia traffic can be found in Refs. [8], [9], [10], [11] and [12]. Among these protocols, a transmission protocol for packet voice terminals in a cellular system proposed by Goodman and Wei called PRMA [2], deserves mentioning. It is a frequency division duplex based multiple access protocol that allows a group of spatially dispersed terminals to transmit packet voice and low bit rate data over a common channel. The key feature of this protocol is the utilization of user transmission to gain access to the radio resources. Once the radio resource has been acquired, it is up to the transmitter to release the reservation. Following PRMA, many other modified PRMA protocol were published, which extend this mechanism to many other areas. Dynamic Packet Reservation Multiple Access (DPRMA) is a MAC protocol developed for wireless ATM networks [13]. The Centralized PRMA (CPRMA) MAC protocol was designed for a micro cellular environment [14]. In Ref. [8], as an extension of classical PRMA protocol proposed by Goodman and Wei [2] to CDMA, Joint CDMA/PRMA was proposed by Brand and Aghvami. Access to the radio channel is controlled such that interference variance is reduced and throughput is increased compared to the random access CDMA.
In Ref. [15], a modified protocol of Joint CDMA/PRMA was proposed, which is for the integrated voice/data services scenario, employing slotted packet CDMA and PRMA. A mechanism for combining the random access scheme and the demand-based assignment scheme was introduced. A modified scheme of Ref. [15] is introduced in this paper, which increases the number of simultaneous calls admitted to the system while still maintain almost the same performance. The detailed modifications will be described in Section 2. Moreover, to evaluate the performance of the modified protocol, two analytical methods are introduced: a Traditional Markov Analysis (TMA) and a Transient Fluid Analysis (TFA). TMA is employed to evaluate the voice call blocking probability while TFA is used to evaluate the average data packet delay.
In this paper, two analytical models are developed to evaluate a proposed protocol featuring a demand-based assignment scheme for data transmission with code division multiple access/packet reservation multiple access (CDMA/PRMA). A TMA is employed to assess the voice call blocking probability. However due to TMA's complexity to evaluate data traffic performance, TFA is introduced to assess the average data packet delay. Simulation results are also given to validate the assumptions made in the mathematical models developed. Our performance evaluation shows that demand-based assignment scheme is suitable for random data traffic transmission, especially when there are a large number of active data terminals with short random messages. In future, efficient admission control and congest control mechanisms can be employed to make the proposed protocol more competent.
