Design and Performance Evaluation of Error Control Protocols in Mobile Wireless Communications

• Main Authors: Hung-Yi Chen, 陳宏義
• Other Authors: Jin-Fu Chang
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/37904548026556675503

博士 === 國立臺灣大學 === 電機工程學研究所 === 91 === In earlier, even today’s mobile communication networks, voice services dominate. Due to that the Internet has become inseparable from our daily life, its seamless con-nection to the wireless networks to consolidate service mobility and availability is de-sired. It is recognized that multimedia services, blending voice, video, and data, must be supported in future mobile communication systems. For multimedia services, qual-ity guarantee is a key design goal. Unfortunately, a wireless channel is notorious in its varying and high error rate nature which is fatal to the guarantee of high quality. In order to heal, techniques are efficient weaponries. Along the road paved in the above, the topics studied in this dissertation are as fol-lows. We first propose a quality-of-service based link control scheme to counteract corre-lated channel errors for wireless multimedia communications. Both the medium ac-cess control (MAC) and data link control (DLC) layers are treated. The performance of the proposed scheme is evaluated via both analysis and simulation. The delay and jitter behaviors are examined for both the constant bit rate (CBR) traffic and variable bit rate (VBR) traffic. The throughput performance is also obtained for the available bit rate (ABR) traffic. Through numerical experiments, we found that the proposed scheme is not only robust against channel impairments but also capable of providing the desired QoS for wireless multimedia communications. Two different multi-layer error control mechanisms implemented for wireless data communications are proposed as the second and third research topics. The interaction between two error recovery mechanisms operated independently to act against wire-less channel errors is examined. Error control designs are implemented at two differ-ent layers in the protocol stack. Retransmissions at the lower layer are performed as primary error removal by virtue of finite retransmissions. Packet-level coding tech-nique at the upper layer is implemented as secondary error elimination. Performance of the proposed scheme is analyzed and verified by simulations. We demonstrated how system performance is influenced by layer-parameters, and discovered that error correcting capability is necessary to function at the upper layer to guarantee good system performance. In the third topic, an adaptive hierarchy error recovery protocol is proposed. Com-pare to the error control mechanism in the second topic, the error control scheme here demands that the retransmissions at the lower layer be constrained by a timeout value set at the upper layer. Additionally, the size of the upper layer protocol data unit (UPDU) is adjusted by channel condition. We not only demonstrated how the selec-tion of parameters influences system performance but discovered that variable-size UPDU more effectively accommodates channel conditions than fixed-size UPDU. Finally, an error control method employing adaptive transmission window to coun-teract feedback channel errors is proposed. The window size (in the forward direction) is adjusted according to the number of erroneous packets, the number of lost feedback messages, and the remaining buffer space at the receiver. Through numerical experi-ments, it is discovered that as the channel is clean enough, expanding the window size tends to alleviate burden on the feedback channel; but while the channel becomes noisy, shrinking the window size at the expense of increasing load on the feedback channel effectively reduces unnecessary retransmissions due to buffer overflow.