Study Of Radio Link And Transport Layer Protocols And Network Performance Evaluation

With the rapid development of wireless communication services, the conflict between spectrum resources and customer's demand grows more and more acutely. Tremendous information requirement drives the development of Code-Division Multiple-Access (CDMA) wireless communication technology rapidly, and all kinds of service demand result in packet-switched oriented cellular wireless network data. In this paper, HARQ, RLP, TCP and TCP/RLP will be investigated in great details.First of all, average diversity combining oriented CDMA system is analyzed, and signal-to-noise ratio of average diversity combining is discussed. Aiming at interference-limited characteristics of CDMA, effective throughput is introduced as the normalizd throughput to measure throughput gain of cell corresponding to unit of power allocation percentegy, and the effective throughput performance is investigated in details. The results show that the throughput can reach saturation with the increase of power allocation, and the power allocation can be optimized to achieve maximum effective throughput. The selection of BER before error-correcting coding of variable spreading gain system is analyzed, and the result shows that maintaining an optimized value of BER before error-correcting coding will do good for the throughput performance of single link and the power utilization of whole cell.Thereafter, in analysing radio link protocol (RLP), an extended capacity definition for packet-switched CDMA system is introduced based on the interference-limited characteristics of CDMA. According to the extended definition, the capacity of packet-switched CDMA system for different ARQ and different channel models is investigated. It is shown that, compared with the traditional definition, the adoption of extended definition can discribe more accurately the utilization of wirelss channel resource and spectrum effiency. For i.i.d channel model, the capacity characteristics of SR is super to that of GBN, but for correlated channel model, the fading of wireless channel may improve the capacity characteristics of GBN. With the slower fading, the capacity characteristics of GBN will approach that of SR.Effective system throughput is also introduced as a new metric taking into account the wireless channel occupation of error correcting coding redundant bit. By evaluating the performance of SR and GBN on i.i.d and correlated channel model, it is indicated that the proper selection of the number of redundant bits can maximize system effective throughput for given coding and decoding scheme, frame size and retransmission mode of RLP.Next, performance of TCP and UDP over i.i.d is investigated for different round trip time (RTT) and maximum congestion control window(Wmax). According to the interference-limited characteristics of CDMA, effective factor is introduced as a new metrics for transport layer protocol over correlated wireless channel model. Then TCP and UDP over correlated channel are investigated for different RTT and Wmax. Our results show that, with the decrease of Wmax and slower of fading, the effective factor performance of TCP will be improved, in usual voice and data communication, the increase of RTT may do good for the effective factor of TCP. Concerning effective factor metric, for Reno and Tahoe version of TCP, their performance are almost the same. In fact, the impact of Wmax on the throughput and effective factor performance of TCP is contradicted, the increase of Wmax will improve the throughput performance but will decrease the effective factor performance. Therefore the selection of Wmax can be compromised between throughput of single link and cell capacity.Then, aiming at TCP Reno under wireless fading channel, an analytical model of steady-state throughput of TCP is generalized from i.i.d channel to two-state Markov channels. Steady-state throughput of TCP as a function of fading margin, average packet error rate and RTT is obtained under the condition that a large amount of data is sent with long RTT. Our analytical model captures not onl...