Author Topic: Performance Evaluation of Adaptive Modulation Techniques and Offered Load in OFD  (Read 2554 times)

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Author : Pratyush Sharma, Abhishek Sharma, Kailash C.Bandhu
International Journal of Scientific & Engineering Research Volume 2, Issue 11, November-2011
ISSN 2229-5518
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Abstractó WiMax uses orthogonal frequency division multiple access technique in wireless communication. Orthogonal frequency division multiple access (OFDM) is what puts the max in WiMAX, OFDM delivers a wireless signal much farther with less interference.
This technique uses Adaptive modulation coding (AMC) on physical layer of WiMAX. Adaptive modulation technique uses the concept of cyclic prefix that adds additional bits at the transmitter end. The receiver removes these additional bits.
Cyclic Prefix is used to combat intersymbol inter-ference (ISI) and intercarrier interference (ICI) introduced by the multipath fading channel.
This paper investigates the performance of WiMAX network by varying physical layer parameter such as modulation and coding scheme and cyclic prefix. It also investigates the performance of WiMAX network by increasing traffic (number of downloading nodes) in network with different cyclic prefix.The performance of WiMAX network is measured in terms of throughput and goodput

Index Termsó Downlink (DL), Adaptive Modulation techniques, IEEE-802.16, OFDMA, Cyclic Prefix, Throughput, Goodput

1   INTRODUCTION                                                                     
WiMAX is abbreviation `Worldwide Interoperability for Micro-wave Access', is a new wireless OFDM-based technology that provides high throughput broadband connection over long distances based on IEEE.802.16 wireless
WiMAX network increasingly more intelligent and agile communication systems, capable of providing spectrally efficient and flexible data rate access.
The WiMAX standard supports adaptive modulation, effectively balancing different data rates and link quality.

The modulation method may be adjusted almost instanta-neously for optimum data transfer. WiMAX is able to dynamically shift modulations from 64-QAM to QPSK via 16-QAM, displaying its ability to overcome QoS issues with dynamic bandwidth allocation over the distance between the BS and the SS.
 As the range increases, modulation step down to lowermodulations (in other words, BPSK), but as you are closer you can utilize higher order modulations like QAM for increased throughput.

   Thus the modulation coding schemes ensure a quality-signal is delivered over distance by decreasing througput.
An example of utilization of the cited adaptive modultion and coding scheme is illustrated in Fig. 1. It shows that as the range increases, the system steps down to a lower modulation, but as closer to the base station, higher order modulations can be used for increased throughput.
The rest of the paper is structured as follows. The system model for the investigation is introduced in Section 2.

In our system we investigated the behavior of adaptive modulation technique of WiMAX network. The adaptive modulation used Binary Phase Shift Keying (BPSK), Quadra-ture Phase Shift Keying (QPSK),16-Quadrature Amplitude Modulation(16-QAM),64-Quadrature Amplitude Modula-tion(64-QAM) for modulating and demodulating the signal. Based on these modulation techniques the  throughput and goodput were investigated   

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