| In Personal Communications, people can exchange any forms of information with others whenever and wherever. To reach this goal, the available wireless communication systems should be modified and integrated step by step. This leads to the rapid development of Public Wireless Local Area Network (PWLAN). PWLAN can support high-data-rate in hot spot by means of Wireless Local Area Network (WLAN) and cover a large area by means of mobile communications network, such as GPRS (General Packet Radio Service) network, so it can meet the requirements on both mobility and wideband communications. Before PWLAN is used widely as a public communication system, the key technologies on the integration of WLAN and mobile network should be solved.The research work in this dissertation carries a deep research on key techniques in PWLAN. The major achievements are outlined as follows.In chapter two, a mobility management protocol is proposed, which is based on Operation WLAN (OWLAN), one of PWLAN system architecture. There are two mobile modes, walk between WLAN cells and roam between WLAN and GPRS, so it includes two protocols, walk and roam management protocols.Based on the analysis of Inter Access Point Protocol (IAPP) in WLAN, an IAPP in OWLAN, AC-IAPP, is proposed for walk management. Based on the assignment of location database in Access Point (AP) and Access Control (AC), and the frame type of Local Area Network (LAN) linking APs, four location management strategies are presented in this chapter. Based on the controller of handover, two handover methods are proposed in this chapter. The analysis results show that AC-IAPP, adopting two-layer location database based on AC and AP and AC-based handover method, is the best in database size, query time and cost of handover.Based on the analysis of Mobile Internet Protocol (MIP) in Internet, OWMIP is proposed to support MIP in OWLAN for roam management. After consideration of OWLAN system structure, OWMIP includes smooth handover, route optimization, buffer storage management, and secure authentication. AC is in full charge of handover between WLAN cells, so it may lighten the load of core network. Authentication Server (AS) and Serving GPRS Supporting Node (SGSN) are in charge of handover management, and AC and Gateway GPRS Supporting Node (GGSN) are in charge of packets storage and transmission. Analysis results show that OWMIP has advantages incost of handover, packet drop probability and security.In chapter three, load balance methods in PWLAN are proposed.First, the load balance method in WLAN, AP-based central load balance (AP-CLB), is discussed and its disadvantages are pointed out.Second, two modified load balance methods are proposed for PWLAN, AC-based central load balance (AC-CLB) and distributed load balance (DLB). The analysis results show that DLB is the best in cost of network, security and delay.Finally, to realize load balance methods, two arithmetic methods, ADCF and VDCF, are proposed to estimate and pre-estimate the number of terminals in a WLAN cell, which are based on the performance analysis of IEEE 802.11 distributed coordination function (DCF). Simulation results show that ADCF and VDCF can estimate and pre-estimate the number of terminals in a cell quickly and accurately, and VDCF performs better and is more suitable for DLB than ADCF.In chapter four, two modified protocols on QoS in PWLAN are proposed, which are based on DCF and point coordination function (PCF) of WLAN, respectively.Based on the analysis of Enhanced DCF (EDCF) in WLAN, a modified DCF in PWLAN, QG-DCF, is proposed. In QG-DCF, QoS grades include both delay grade and packet drop probability grade. QG-DCF supports the two grades by means of adjusting the minimum contention window and the maximum re-transmission limit. The analysis and simulation results show that QG-DCF is better than DCF and EDCF in ensuring QoS, and the analytical model is valid.Based on the analysis of hybrid coordination function (HCF) in WLAN, a modified PCF in PWLAN, MPCF, is propose...
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