University of Khartoum

Computer Simulation Of The Physical And MAC Layers Of The IEEE 802.16a (Wimax)

Computer Simulation Of The Physical And MAC Layers Of The IEEE 802.16a (Wimax)

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Title: Computer Simulation Of The Physical And MAC Layers Of The IEEE 802.16a (Wimax)
Author: Ali, Nahla Mustafa Mohamed
Abstract: The IEEE 802.16 standard specifies the air interface of the fixed broadband wireless access (BWA) including the Media Access Control (MAC) layer supporting primarily Point to Multi Point PMP and optional MESH mode . The MAC is structured to support multiple physical specifications , each suits a different operational band. For 10-66 a direct line of sight is required between the BS and the Costumer Premises Equipment CPE with a single carrier . For the band lower than the 11 GHz, near line of sight or non line of sight is enough using three physical layer specifications: single carrier ,OFDM, OFDMA. The MAC layer consists of three sublayers : the Convergence Sublayer which is responsible for mapping the different services to the specific MAC service data units (SDUs). The Common Part Sublayer is core of the MAC layer. It is responsible for packet scheduling according to the QoS requirements . The lowest sublayer is the Security Sublayer which is responsible for the key exchange and encryption. The standard revises are the IEEE 802.16, IEEE 802.16a ,IEEE 802.16c and IEEE 802.16d. This project simulates and evaluate IEEE 802.16a concentrating on the physical layer and the three MAC sublayers using the point to multipoint access , the OFDM mode which is suitable for the license exempt bands . The Encryption algorithm used is the double keys triple Data Encryption Standard (DES) with, EBC mode ,FIPS 81 . Assuming packet by packet processing, a 128 bytes packet needs 16 rounds of encryption using the same keys. MATLAB version 7 simulation was built for the sake of the performance analysis. All mandatory blocks in the IEEE802.16a specification are included : Scheduler , Encryption , randomizer , Forward Error Correction (FEC) which includes Reed Solomon encoder , Convolutional Encoder , Interleaver and the Mapper , OFDM was simulated using 256 FFT . The channel was assumed to be Rican channel ,the channel estimator . To enhance the BER , diversity technique with maximal ration combining is also simulated. The rate ID was chosen according to the SNR ,and the number of packets that can be sent in one time slot are 6,4,3,2,2,2 packets as the rate ID increases. The so called the Unsolicited Grant Services are assigned a constant number of time slots .The scheduler chooses the connection having the highest priority function which is determined by the type of the connection and the ii state of the channel. If the satisfaction delay in the case of the real time services and the rate satisfaction in the case of the non real time services is not satisfied , the priority function is set to the maximum value . A desirable property of any encryption algorithm is that a small change in either the plain text or the key produces significant change in the cipher text. In particular , a change in one bit of the plain text or one bit in the key should produce a change in many bits of the cipher text . Avalanche effect test shows a change in a single bit produces difference in about half the ciphered block . The diversity results shows that the BER is enhanced dramatically by using the diversity technique. The BER is also increased as the Rate ID increases .However, when the Adaptive Modulation and Coding (AMC) is used ,the BER is set to the prescribed value 10-1 . The results shows that CP also enhances the BER performance.
Description: 170 Pages
URI: http://khartoumspace.uofk.edu/handle/123456789/10314
Date: 2015-05-05


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