CROSS LAYER TECHNIQUE

Computer Engineering electronics Engineering Civil Engineering

Wireless research has experienced an avalanche of cross layer design techniques. Due to the special characteristics of wireless communication, the traditional layered architecture is coming under closes scrutiny. Cross layer is something that researcher are relying on to solve these problems. There is several different interpretation of cross layer design. It is because researchers have developed cross layer techniques independently. In a broad sense cross layer design refers to protocols that actively use the dependence and communication between different layers to obtain performance gain. But it is also observed that synergy between the performance and implementation complexity is weak. Most of the proposals emphasis on the performance gain keeping implementation concerns unattended. In this report first of all cross layer techniques will be classified into certain categories few protocols of each category will be studied and compared. In the later part of the report current problems and future scope of cross layer technology will be discussed. 1. Congestion in Wireless Network Wireless networks [1] are inherently limited by battery power and bandwidth constraints. They are characterized by mobility, random changes in connectivity, fluctuations in channel and interference due to neighboring nodes etc. Due to these factors, packet loss of a wireless network is much more than that of a wired network, in which packet loss occurs mainly due to congestion in the network. Congestion in a network is characterized by delay and packet loss in the network Transport Control protocol (TCP) is used as a reliable transport layer protocol in the traditional best effort (wired) network and deals with congestion effectively The congestion control mechanism of various versions of TCP provides better throughput in an wired network, where the packet loss is mainly due to congestion at various nodes and routers. However, this mechanism may not be suitable in a wireless network, where packet loss due to time-varying nature of channel and interference of other nodes are considerably high Hence, instead of usual congestion control technique; we propose a cross layer technique involving TCP and MAC (Medium Access Control) layer. TCP layer performs the windowing flow control and MAC layer varies transmission power of wireless nodes depending on the channel condition and interference. Our approach consists of (1) Formulation of TCP congestion control mechanism in terms of control system equations (2) Use of transmission power of wireless nodes as a function of cost in an optimization equation (3) Use of optimization techniques to determine the maximum aggregate utility of all the sources, subject to capacity constraints and maximum transmission power [2] of wireless nodes. loading..