Layer 2 (LL/MAC) performance analysis and improvement of wireless heterogeneous networks

by Jing Zhu

Institution: University of Washington
Degree: PhD
Year: 2004
Keywords: Electrical engineering
Record ID: 1745711
Full text PDF: http://hdl.handle.net/1773/5950


The contribution of this thesis can be divided into two components: the first is motivated by the expansion of the Internet into space, i.e., inclusive of a broadband satellite; the second centers around the evolution of WLANs into a 4G network that provides broadband wireless access with QoS support.The extension of Internet protocols to include broadband satellite networking infrastructure will define the next generation of IP-based broaband satellite networks. TCP, the predominant transport layer (Layer 4) protocol in today's terrestrial Internet will face greater challenges in satellite environments characterized by both unreliable wireless link and high bandwidth-delay product. Thus, the need for link layer (Layer 2) solutions for improving the E2E performance of TCP over satellite are gaining increasing attention from the literature and industry due to its advantages of easy implementation, backwards compatibility, localized system upgrade, etc., compared to layer 4 (E2E) solutions. In this dissertation, our research focuses on the interactions between TCP and layer 2 protocols, such as Selective-Repeat ARQ, are presented, including (i) Modelling TCP Enhancements in Satellite-Terrestrial Hybrid Networks (Chapter 2) and (ii) Enhancing Layer 2 Protocols for Land Mobile Satellite Channels with Shadowing (Chapter 3).On the other hand, in a local area network (LAN), the rapidly growing WLAN (IEEE 802.11) technology now allows user access to the Internet at rates up to 54 Mbps wirelessly. However, current WLAN networks are effectively limited to single hop scenario with infrastructure mode (wherein a central node also called access point is usually provided). Moreover, data is still the mainstream service in WLAN. The impetus to extend Wi-Fi technology into ad-hoc mode, multi-hop scenario and multi-media service is being driven by emerging applications in many different fields such as In-Home Networking and Battle-Field Communications. In WLAN environments, the main reason for network performance degradation is collision loss due to multiple access interference instead of wireless link loss, since the T-R (T: Transmitter; R: Receiver) separation distance in most cases is short (tens of meters in a dense network), but the number of active stations competing for the shared wireless bandwidth are large, e.g. Public WLAN HotSpot. Therefore, optimization of MAC (Medium Access Control) layer protocol will play a crucial role in the evolution of WLAN technology. We present two key research results (i) A Two-Radio Multi-Channel 802.11-based AP Mesh Network Optimized for Aggregate Throughput via Clustering and Physical Carrier Sensing (PCS) to Enhance Spatial Reuse (Chapter 4); (ii) A Markov Chain Method for 802.11e EDCF Throughput, Delay and Diff-Serv (Chapter 5).