Mitigation of ICI Through Optimized SSR ICI Self Cancellation Scheme in OFDM

Abstract

Abstract:Orthogonal frequency division multiplexing (OFDM) is extensively used in wireless communication systems because it offers high data rates and provides a better solution to inter symbol interference (ISI) caused by a multipath channel. A well known problem of OFDM system is sensitive to carrier frequency offset (δ) between the transmitted and received signals. The Frequency offset in wireless communication systems ruins the Orthogonality between subcarriers resulting in Inter Carrier Interference (ICI).Which is a severe problem in OFDM system and eventually decrease the performance of the system. There are numerous techniques are in existence to mitigate the effect of ICI caused by CFO (carrier frequency offset). This paper investigates an innovative ICI cancellation method termed as optimized SSR (symmetric symbol repeat) ICI self cancellation scheme. The proposed method utilizes an optimum data allocation (1,-λ) and combining (1,-µ) scheme to improve CIR performance for an estimated normalized frequency offset δ. However, this requires continuous CFO estimation and feedback circuitry. To avoid the requirement of CFO, sub optimal values (λso, µso) are considered for combating the effect of ICI. This paper mainly focus on comparison of proposed method with the previous reduction methods and standard OFDM system in terms of CIR (carrier to interference) & BER (bit error rate) performance. Keywords: OFDM, ICI, ISI, CFO, CIR, BER, QAM I.INTRODUCTIONIn Today's world OFDM plays vital role in wireless communication systems, which is a promising modulating technique for high data rate transmission in wireless communication [1] systems. OFDM is a form of multi-carrier modulation technique [2], which effectively utilizes the spectrum by spacing the channels much closer together. This spectral efficiency can be achieved by making orthogonality between the sub carriers and preventing interference between the subcarriers. In OFDM, a high-rate data stream is divided into many lowerrate streams which are mapped (by using QAM or QPSK) onto mutually overlapping subcarriers and transmitted simultaneously i.e., high rate bit stream is split into N parallel lower rate bit streams and each of these streams are modulated using one of N orthogonal sub-carriers. However, OFDM is being widely used in many applications such as IEEE 802.11a, the multimedia mobile access communication (MMAC), HIPER-LAN/2, Digital Video Broadcasting (DVB) and so on.. In a basic communication system, the input data is modulated using only one carrier frequency. Therefore the available channel bandwidth is totally occupied by each symbol. This type of mechanism can lead to inter symbol-interference (ISI) in frequency selective channels.By inserting Guard interval with the cyclic extension of the OFDM symbol, the inter symbol interference (ISI) can be easily avoided. A well known problem with OFDM is its vulnerability to slight differences in frequency at the transmitter and receiver, normally referred as frequency offset, caused by Doppler shift due ...