Performance enhancement of wireless mobile adhoc networks through improved error correction and ICI cancellation

Zeeshan Sabir,M Inayatullah Babar,Syed Waqar Shah

doi:10.1186/1687-6180-2012-216

Abstract

Mobile adhoc network (MANET) refers to an arrangement of wireless mobile nodes that have the tendency of dynamically and freely self-organizing into temporary and arbitrary network topologies. Orthogonal frequency division multiplexing (OFDM) is the foremost choice for MANET system designers at the Physical Layer due to its inherent property of high data rate transmission that corresponds to its lofty spectrum efficiency. The downside of OFDM includes its sensitivity to synchronization errors (frequency offsets and symbol time). Most of the present day techniques employing OFDM for data transmission support mobility as one of the primary features. This mobility causes small frequency offsets due to the production of Doppler frequencies. It results in intercarrier interference (ICI) which degrades the signal quality due to a crosstalk between the subcarriers of OFDM symbol. An efficient frequency-domain block-type pilot-assisted ICI mitigation scheme is proposed in this article which nullifies the effect of channel frequency offsets from the received OFDM symbols. Second problem addressed in this article is the noise effect induced by different sources into the received symbol increasing its bit error rate and making it unsuitable for many applications. Forward-error-correcting turbo codes have been employed into the proposed model which adds redundant bits into the system which are later used for error detection and correction purpose. At the receiver end, maximum a posteriori (MAP) decoding algorithm is implemented using two component MAP decoders. These decoders tend to exchange interleaved extrinsic soft information among each other in the form of log likelihood ratio improving the previous estimate regarding the decoded bit in each iteration.

Highlights

Mobile adhoc network (MANET) represents a set of wireless mobile nodes that have the capability of communicating with each other without the help of a preexisting infrastructure [1]
We propose a novel channel equalization technique based on frequency-domain block-type pilotassisted channel estimation (PACE) strategy that uses turbo detection-based approach at the receiver side
In this article, we have proposed a novel error correction and intercarrier interference (ICI) cancellation scheme for orthogonal frequency division multiplexing (OFDM) system

Summary

Introduction

Mobile adhoc network (MANET) represents a set of wireless mobile nodes that have the capability of communicating with each other without the help of a preexisting infrastructure [1]. This step is known as “OFDM modulation” During this process, the pilot symbols are inserted in parallel and at the receiving end they are used for calculating H matrix which consists of channel estimates for different subcarrier positions and is later used for data equalization. The data symbols after being demodulated from the orthogonal subcarriers are fed to the channel equalization/estimation block which uses pilot tones to remove the effects of impulse response offered by the channel from the received signal. Algorithm for channel estimation and equalization The channel estimation and equalization technique implemented in the proposed system uses PACE approach In this method, pilot symbols send prior to every data block nullify the impulse response effects offered by the channel from the received data symbols. For a rate 1/n component codeword, first MAP decoder produces the LLR given by [14]

CCCCAβt

Conclusions