UBC Theses and Dissertations
Analysis and performance evaluation of an efficient protocol for the CDPD forward channel Zhang, Xu (Jake)
The purpose of this thesis is to analyze and evaluate the performance of the Cellular Digital Packet Data (CDPD) forward channel at the Medium Access Control (MAC) layer, and propose an efficient protocol to improve the MAC layer throughput. First we study the MAC layer by several performance measures, such as the Block Error Rate (BLER), Packet Error Rate (PER), and the throughput. According to our studies on the forward channel MAC layer structure, we analyze the relationship among the three performance measures, and between them and the channel Bit Error Rate (BER), in the presence of the Additive White Gaussian Noise (AWGN) channel. For comparison purposes, computer simulations have also been conducted with the AWGN channel, and land-mobile Rayleigh fading channel, with the employment of both a coherent and a 1-bit differential GMSK receiver. As a result of this study, a source of performance inefficiency, namely, the Correct but Unusable Data (CUD), is identified. We argue that the MAC layer throughput is affected not only by the error performance of the physical layer, but also by the MAC layer block segmentation, which is the main cause of the CUD. The percentage of CUD peaks to about 45% regardless the channel conditions. In order to eliminate this inefficiency we propose a MAC - ARQ protocol which performs ARQ operation at the MAC layer. Verified by computer simulations, this protocol effectively improves the throughput at certain channel conditions, while slightly degrades the performance at other conditions. Finally, in order to maintain maximum throughput over all channel conditions, we propose an adaptive scheme which automatically switches back and forth between the conventional ARQ protocol and the MAC - ARQ protocol according to the channel conditions.
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