The Research On Key Technologies Of MAC And Routing Protocols For Wireless Public Bus Networks

Wireless public bus networks are the key supported technologies and important car-rieroftheintelligentpublictransportsystem(IPTS)andthedevelopmentisbeingfocusedon by most countries. Public bus network is composed by public buses and hence it is atype of wireless vehicular network which employs wireless communication technologies.ProvidingvariousInternetserviceinpublicbusesallowsbuspassengerstoentertainthem-selves during their travel time, thus significantly improving their quality of life and theefficiency of the IPTS.Communication protocols and mechanisms of traditional vehicular networks havenot considered the unique characteristics of buses (group moving effect, predicted mobil-ity and high dynamics). Hence they may be unsuitable for the communication of buses,especially for the Internet access service. In order to satisfy passengers'various servicerequirements better, efficient communication protocols need to be proposed and there-fore several communication problems need to be investigated deeply for bus networks.Among them, several important remained problems are generated at the MAC layer androuting layer, which bring big challenges for the better use of the unique characteristicsof buses.This dissertation mainly focuses on the key technologies of the MAC layer and rout-ing layer for bus networks. In this dissertation, the lack of existing MAC protocols, hand-off mechanisms and routing protocols and the design requirements of them for bus net-works are discussed. Then, the important problems at MAC layer and routing layer lie in:channel access with high throughput guarantee, efficient handoff triggering, adaptive AP(Access Point) association selection, good routing pattern determination and stable andefficient routing metric selection. Combing mobility and communication characteristicsofbuses, thisdissertationproposesthesolutionforeachproblemwhichdescribedindepthin the following.The proposed MAC protocol-BusMAC is designed to support the channel access ofInternet service for bus users (passengers). The proposed protocol aims to decrease colli-sions caused by multiple access due to the group moving effect. A super-frame structureis proposed to decrease the communication bottleneck in the bus network based on thedynamical contention and piggyback mechanisms. Also, through effective data schedul- ing scheme, BusMAC can satisfy various different services. Based on request contentionmodel and data scheduling model, the performance analysis of BusMAC is carried out.Extensive simulations are also conducted to evaluate the BusMAC protocol. The resultsshow that BusMAC can achieve better performance than the traditional ones.Handoff is quite important in bus networks due to high mobility of buses. To provideseamless connectivity, this dissertation proposes an adaptive handoff triggering mecha-nism to minimize communication time for a bus with an AP switch (i.e., whether andwhen to trigger a handoff process).Combined with a data transmission rate based trig-ger, handoff triggering decision is made based on three different communication methods(i.e., C-Dire, C-Relay and C-ALLRelay) to minimize the transmission delay, consider-ing a bus moves from an AP to another. Transmission time is derived with respect tobus mobility and transmission rate diversity. By this method, buses can adaptively selectthe optimal triggering pattern when crossing APs. The simulation results show that theproposed method is effective.WithmultipleAPsusuallydeployedaroundabusstop,APassociationcontrolisusedfor buses to select a suitable AP to communicate with. The proposed dynamic associa-tion control mechanism mainly focuses on the high cost and instability of the traditionalmethods under dynamic scenario. Combined with the predicted mobility, this dissertationproposes a dynamic AP-Bus graph to describe the dynamics (dynamic bus transmissionrate, dynamic bus arrival and dynamic user arrival/departure). Then the association prob-lem is described as an integer-linear programming optimization problem based on theAP-Bus graph and two approximation solutions are proposed further. By the simulationexperiments, the dynamic solutions outperform traditional methods.The link lifetime based single-path routing protocol, R-BUS, is proposed due to theinaccuracy and low performance of the existing routing metrics for bus communication.R-BUS selects a route based on the link's lifetime and its communication signal quality.Theprotocoltakesintoaccountthebusmobilityandtheradiopropagationcharacteristics.It can guarantee the communication quality and the route reliability. Compared to theexisting routing protocols, R-BUS can achieve higher performance.Because of the frequent bus mobility, single-path routing protocols in bus networksstill may bring low efficiency and instable performance. Hence, this dissertation furtherstudiestheopportunisticroutingprotocolsinbusnetworkstoimprovethesystemthrough- put and reduce the access delay. In this dissertation, an end-to-end transmission Timebased Opportunistic Routing (OR) framework is proposed. The main focus is the calcu-lation of the routing metric. This dissertation derives three OR protocols, i.e., EETOR,EETMcORandEETCcOR.EETORandEETMcORbuildtheroutemetricmodelthroughconsidering the transmission behavior of buses at network layer and MAC layer, respec-tively. EETCcOR can further improve the network performance for congestion controlconsideration. Simulations also demonstrate the effectiveness of all three protocols.Insummary,thisdissertationinvestigatesfiveproblemsforthebusnetworksatMAClayer and routing layer. All proposed protocols and mechanisms are proved to be effec-tiveness. These works are helpful for construction of the whole IPTS in the future.