MAC constraints in hybrid optical-wireless 802.11 broadband access networks

• Main Author: Kalantari-Sabet, Bahman
• Published: University College London (University of London) 2008
• Subjects: 621.3827
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505293

This thesis deals with the characteristics and performance analysis of hybrid optical-wireless 802.11 broadband access networks. The main focus of this work is on the behaviour and performance of the IEEE 802.11 MAC layer when Radio over Fibre technology is used to distribute Radio Frequency signals from a Central Site to Remote Antenna Units. Data throughput impairments due to constraints imposed by the IEEE 802.11 MAC are considered in Single Mode Fibre systems. The results presented in this thesis are based on the current DCF access scheme specifications using both the Basic Access and RTS/CTS Access mechanisms (at the MAC layer), as well as TCP and UDP protocols (within the transport layer). It is shown that the length of the fibre is constricted to a maximum limit in a standard hybrid system. However, with minimal changes to the parameters of IEEE 802.11 standard this limit can be expanded. It is also realised that data throughput decreases with different rates (depending on parameters chosen) as fibre length increases. It has been observed that the network fails long before physical layer limitations set in due to the timeout values defined within the MAC protocol. In this thesis experimental enquiries are first used to provide a set of validation points before extending these results by simulations using the NS-2 platform. Mathematical approximations are then presented to these results that would allow designers of Radio over Fibre systems to quickly and accurately predict the data throughput and performance behaviour given the specific parameters of their network. Finally, two different strategies are investigated within an 802.11 Fibre Friendly MAC that significantly enhance the data throughput. Due to the common functionality of the MAC layer the basis of this work can be applied to a number of IEEE 802.11 systems, including 802.11a/b/g networks. To the knowledge of the author this is the first analysis of this kind for a long reach fibre system.