Queueing Analysis of CDMA Unslotted ALOHA Systems with Finite Buffers

Hiraku OKADA  Takaya YAMAZATO  Masaaki KATAYAMA  Akira OGAWA  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E81-A    No.10    pp.2083-2091
Publication Date: 1998/10/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Information Theory and Its Applications)
Category: Spread Spectrum System
CDMA unslotted ALOHA,  finite buffer capacity,  packet queueing,  Markov chain,  

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CDMA unslotted ALOHA system with finite size of queueing buffers is discussed in this paper. We introduce an analytical model in which the system is divided into two Markov chains; one is in the user part, and the other is in the channel part. In the user part, we can model the queueing behavior of the user station as an M/G/1/B queue. In the channel part, we can consider the number of simultaneously transmitted packets as an M1 + M2/D///K queue. We analyze the queueing system by using this analytical model, and evaluate the effect of buffer capacity in terms of the throughput, the rejection probability and the average delay. As a result, increase in the buffer size brings about an improvement in the grade of service in terms of higher throughput and lower rejection probability.