24-01-2010, 08:27 AM
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Distributed Medium Access Control for Next Generation CDMA Wireless Networks
Generic Distributed Network Model
we focus on a generic network model where a number of wireless mobile nodes are organized in a flat fashion, communicating with each other via one-hop or multiple-hop connections without any central control. Connections to outside correspondence nodes are supported through a gateway (e.g., in the wireless backbone) or an access point (e.g.,in ad hoc networks or WPAN).
In the past decade, code-division multiple access (CDMA) technology has been developed and deployed popularly with great success in the second-generation (2G) cellular systems (e.g., IS-95). It also been selected as the major multiple access technology for the third-generation (3G) systems. CDMA has many promising merits such as universal frequency reuse, soft handoff, and high spectrum efficiency.
Desired Features of Distributed MAC:
AMAC scheme is to coordinate the mobile nodes access to the shared medium such that efficiency
can be achieved. Although MAC schemes in traditional cellular networks and WLAN have been extensively studied in the literature, more efforts are still needed for distributed MAC supporting multimedia traffic in the network without a central controller. In a centralized network such as the cellular network, the central controller makes decisions on when and how the mobile nodes should access the medium. However, in a network without a central controller, MAC is carried out in a collectively coordinated manner, where a mobile node determines its access behavior according to its local observation.
Features Of Distributed MAC:
Quality of service (QOS) support
Service differentiation
Low overhead
Bandwidth Efficiency
Distributed Code Assignment
Generally, before a transmission, the transmitter and receiver need to know the code (sequence) to be used. In cellular networks, the BS collects information from all the nodes, and informs them what codes are used in upcoming transmissions. However, as our network model dose not have central authority, distributed code assignment is desired.
CONCLUSION
We have discussed the limitations of existing distributed CDMA-based MAC schemes when applied to our generic network model with distributed control. By letting active receivers estimate potential increase in the interference level, our proposed MAC scheme can achieve bit-level QoS, low overhead, accurate channel and interference estimation, and high bandwidth efficiency.
OUTLINE:
ABSTRACT
INTRODUCTION
GENERIC DISTRIBUTED NETWORK MODEL
DESIRED FEATURES OF DISTRIBUTED MAC
DISTRIBUTED CODE ASSIGNMENT
DISTRIBUTED INTERFERENCE CONTROL
THE PROPOSED DISTRIBUTED MAC
CONCLUSIONS
