System design and performance analysis of spread-spectrum multiple-access networks
Abstract
In this thesis, the system architecture, protocol design and performance evaluation of CDMA networks are studied under the lower three layers of the Open System Interconnection (OSI) reference model. The network performance, especially the throughput is analyzed from both the communication and network points of view using Markovian models. In the data link layer, error control schemes in CDMA systems, are much more important than those in traditional radio networks due to the fact that CDMA systems generally have higher error rates. Both block codes and convolutional codes for pure forward error correction (FEC) are evaluated in terms of the throughput performance and reliability of the received data. To satisfy the need of a CDMA system with frequently changing channel activities, this thesis also explores an advanced hybrid-ARQ protocol using convolutional code with a modified Viterbi decoder to improve CDMA system performance. Markovian models are developed and a simple computational method based on the underlying Markov chains is developed to compute both the probability of receiving correct packets and the probability of channel errors. Under these models, one can incorporate both the communication system parameters such as signal powers, chip sequence rate, and coding schemes, and network parameters such as packet length, channel traffic rate, and system activities. A slightly lower chip sequences rate (shorter length per data symbol) or a smaller transmitting power can be used under this scheme while still obtaining the desired reliability. Degradation of throughput is expected but can be reasonably controlled by adjusting a threshold set by each individual station. This hybrid-ARQ scheme in comparison to pure FEC offers a more flexible set of parameters from which individual users can select. Considering the network layer, a Receiver-Based Hand-Shake (RBHS) protocol is proposed to improve the spreading code protocols for CDMA networks. The RBHS protocol uses a receiver sensing and a handshake procedure to pair up the receiver, thus avoiding unwanted collisions. The numerical results based on a Markov model show that this protocol enjoys the advantages of channel load sensing effect without suffering from the accuracy problem in estimating the channel load. An unslotted, simplified version of RBHS protocol is also analyzed and the results show that its performance is comparable to the hybrid-ARQ control protocols, in both throughput and reliability. We also study the possible application of CDMA systems with RBHS protocol in multihop networks, cellular CDMA systems, and mobile communication systems. We also discuss the possible internetworking of CDMA systems with optical fiber communication systems.
Degree
Ph.D.
Advisors
Hsiao, Purdue University.
Subject Area
Electrical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.