The Mac Protocol Based On Dynamic Access Probability And The Application On LEO Satellites

LEO mobile satellites system is a complex communication network consisted of many satellites 700-1500km above the earth and a set of comprehensive network on earth, proposed by some scientists in 1980th. This system can provide real time voice and data service in the global range.Multiple access schemes are used to allow many mobile users to share simultaneously a finite amount of radio spectrum. The sharing of spectrum is required to achieve high capacity by simultaneously allocating the available bandwidth to multiple users. Therefore, multiple access techniques are being used in various wireless communication systems.This paper investigates the possibility of using the multiple access based on dynamic access probability in wireless packet networks. Dynamic access probability protocol can be depicted as a conjunction of DAP(Dynamic access probability) and slotted-ALOHA. First, the information of shared channel should be gathered by the central site of the system; second, an optimum access probability could be computed through an effective algorithm. This probability will be send to all users through down link. And each user will access the shared with this probability.The basic idea of DAP lies on: the up link channel information is estimated by the satellite to control the down link channel. A backoff time is needed when each user wishes to access the shared channel. Obviously, the purpose of this scheme is to adapt the access probability to the variation of channel load. One of the specific method is to divide the time interval into two type: estimation interval and announced interval. And the satellite must get the load information of the channel to determine the next channel access probability. A great problem has been existing in this scheme, that is the estimation of channel load. Without channel feedback, the estimation in satellite link can not be very accurate. Unfortunately, ZOHAR NAOR and HANOCH LEVY didn't analyze the effect between the performance of MAC protocol and the estimation error. So, before using this scheme, a deep analysis must be carried out first.The key point of this paper is focusing on these tow facts:1. Proposing a new method to analyze the impact of estimation error on theslotted-ALOHA system based on DAP.2. Proposing a creative iterative algorithm and designing an effective MACaccess protocol based on DAP to adapt the variation of load on channel. The chapter 1 of this paper introduces satellite telecommunication, satellite mobile telecommunication and its multi-access methods, studies the general MAC protocol classification.Chapter 2 studies the principle of MAC protocol of the LEO satellite CDMA transmission system.. Introduces ALOHA access protocol, ARQ technology, contention resolution, Quasi-realtime telecommunication based on single LEO satellite and MAC frame structure.Chapter 3 presents the implementation of the MAC protocol based on dynamic access probability and analyzes its performance in multi-users environment.Chapter 4 and chapter 5 discuss the impact of load estimation error on DAP protocol and the load estimation algorithm.Chapter 6 puts up computer simulation results based on DAP, and compare with S-ALOHA, fixed probability.