Simulation Based Analysis of Random Access CDMA Networks

Ali Taha Koç, Özgür Özdemir, Murat Torlak

Department of Electrical Engineering,
The University of Texas at Dallas, Richardson, TX 75083 USA
e-mail:{atk016000, ozdemir, torlak}@utdallas.edu

Abstract

As large mobile networks have become commonplace, the allocation of resources has become critical. The most important and restricted resource is the system bandwidth for this kind of networks. In order to use the system bandwidth efficiently, multiple access systems are used. For multiple access systems, MAC (medium access control) protocols have primary effect in the throughput and delay performance of the system. Among MAC protocols, the ALOHA scheme has enjoyed the advantage of simplicity, however, the throughput of ALOHA decreases under heavy traffic conditions. Alternative random access systems have been proposed based on code division multiple access (CDMA) systems to improve the throughput [1,2]. Random access CDMA systems have been shown to efficiently allocate scarce radio communication channels (bandwidth) in such a way that users with bursty traffic can share the same frequency without significant degradation to the overall throughput. However, large system simulation of random access CDMA networks with unslotted implementation has been difficult. Therefore, in this paper, we develop a simulation model in OPNET to analyze random access CDMA system for different channel models. Such simulation can provide means to observe and report the system specifications and performance of the large CDMA networks under different circumstances.

Keywords: CDMA, fading channels, MAC protocols, OPNET, random access networks