Intercarrier Interference In Orthogonal Frequency Division Multiplexing Systems Research Articles

Hybrid Micro Genetic Algorithm Assisted Optimum Detector for Multi-Carrier Systems

<p>A low-complexity detection scheme, which consists of a Hybrid Micro Genetic Algorithm (Hybrid- µGA), is proposed for Orthogonal Frequency Division Multiplexing (OFDM) systems. In the absence of orthogonality, intercarrier-interference (ICI) occurs because a signal from one subcarrier causes interference to others. In several environment, the OFDM signal reflections from a far obstacle generate inter-block-interference (IBI) due to long time delays. To avoid these unpleasant effects of IBI and ICI in OFDM system, a Hybrid-µGA detection algorithm is proposed. The proposed detector combines the conventional one-Tap equalizer and the Micro Genetic Algorithm (µGA) search engine. The output of one-Tap equalizer is considered as the input to µGA search engine. Therefore, the µGA starts with some knowledge rather than blindly to speed up the search. Theoretical analysis and simulation results show that the proposed detection Hybrid- µGA scheme substantially improves the performance of OFDM systems. Moreover, its complexity is 10 times lower than the conventional GA.</p>

Design and EXIT Chart Analysis of a Doubly Iterative Receiver for Mitigating Impulsive Interference in OFDM Systems

In this paper, a doubly iterative receiver for orthogonal frequency-division multiplexing (OFDM) systems is designed to mitigate impulsive interference based on pulse blanking. Although being a very efficient countermeasure, pulse blanking introduces intercarrier interference in OFDM systems leading to system performance degradation. The doubly iterative receiver is designed to overcome this drawback. The inner loop combines iterative demodulation and decoding to cancel intercarrier interference. To make soft information available to the outer loop, the equivalent noise power is derived to employ soft demodulation. The outer loop improves the performance of pulse blanking by performing a hypothesis test, which is used to decide if peaks in the received signal are due to impulsive interference or the large peak-to-average-power ratio common to OFDM signals. This allows to optimize the blanking threshold through maximizing the signal-to-interference-and-noise ratio. To evaluate performance and complexity of the proposed receiver, extrinsic information transfer (EXIT) chart analysis is carried out, where EXIT functions for pulse blanker, demodulator, and decoder are derived. An EXIT chart-based trellis search approach is introduced to calculate the loop schedule achieving target bit-error-rate performance with minimized complexity. Numerical results show a considerable bit-error-rate performance improvement as well as a remarkable complexity reduction.

Architectures for MIMO-OFDM Systems in Frequency-Selective Mobile Fading Channels

Orthogonal frequency-division multiplexing (OFDM) is used in third and fourth generation and is being planned for fifth-generation (5G) systems. OFDM requires that the received subcarriers be orthogonal. However, various factors, such as residual carrier frequency offset due to Doppler shift in mobile fading channels, can lead to a loss in orthogonality between subcarriers, which results in intersymbol interference (ISI), intercarrier interference (ICI), and bit error rate (BER) degradation. In developing the conjugate cancelation (CC) scheme for mitigating these ISI and ICI of OFDM systems, we integrate the CC scheme together with a space–time (ST) system and form an STCC multiple-input–multiple-output (MIMO) scheme. This STCC system improves the BER without expending power or bandwidth or complexity. Additionally, a Walsh–Hadamard (WH) transform is employed as a precoder for this STCC system and forms a novel WHSTCC scheme. It provides a low peak-to-average power ratio (PAPR) at the transmitter and a significant diversity gain at the receiver. Simulations indicate that both STCC and WHSTCC schemes outperform the regular CC and ST systems in mobile fading channels. Both schemes are simple and are backward compatible, and they can serve as the baseband building block for reconfigurable 5G multiuser MIMO systems.

A new windowing function to reduce ICI in OFDM systems

A new transmitter side windowing function to reduce inter-carrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) systems with carrier frequency offset is proposed in this paper. The results show that the proposed method outperforms all the recently proposed windowing functions in the literature in terms of average signal power to average ICI power ratio (SIR), bit error rate (BER) and peak to average power ratio (PAPR).

Particle filter with ant colony optimization for frequency offset estimation in OFDM systems with unknown noise distribution

Orthogonal frequency division multiplexing (OFDM) is sensitive to carrier frequency offset (CFO) that causes inter-carrier interference (ICI). In this paper, a particle filter (PF) method augmented with ant colony optimization (ACO) is developed to estimate the CFO. The ACO for continuous domains is incorporated into PF to optimize the sampling process. Unlike the standard PF, resampling is not required in the method. Moreover, it does not require the noise distribution. Simulation results show that the proposed method is effective when estimating the CFO and can effectively combat the effect of ICI in OFDM systems.

Linear suppression of intercarrier interference in time-varying OFDM systems: From the viewpoint of multiuser detection

Intercarrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) systems, which causes substantial performance degradation in time-varying fading channels, is analyzed. An equivalent spreading code formulation is derived based on the analogy of OFDM and code division multiple access (CDMA) systems. Techniques as linear multiuser detection in CDMA systems are applied to suppress the ICI in OFDM systems. The performance of linear detection, measured using multiuser efficiency and asymptotic multiuser efficiency, is analyzed given the assumption of perfect channel state information (CSI), which serves as an upper bound for the performance of practical systems. For systems without CSI, time domain and frequency domain channel estimation based linear detectors are proposed. The performance gains and robustness of a linear minimum mean square error (LMMSE) filter over a traditional filter (TF) and matched filter (MF) in the high signal-to-noise ratio (SNR) regime are demonstrated with numerical simulation results.

A bandwidth-efficient method for cancellation of ICI in OFDM systems

Orthogonal frequency division multiplexing (OFDM) is a very important modulation technique in wideband wireless communication and multimedia communication systems. While, it can effectively deal with multipath delay spread produced by frequency fading channels, its main drawback is the effect of frequency offset (FO) produced by the receiver local oscillator or by motion-induced Doppler. The FO breaks the orthogonality among the subcarriers and hence causes intercarrier interference (ICI). In this paper, ICI caused by frequency drift is eliminated by equalizing the complex weighting coefficients of interference. In most of the commonly used ICI cancellation schemes, bandwidth efficiency suffers because of the requirement of redundancy in the transmission. In the proposed scheme, repetition of data symbols or transmission of training sequence is not required. Thus, the bandwidth efficiency of normal OFDM system is maintained. The improved performance of the present scheme is confirmed through extensive simulations.

A Bayesian State–Space Approach to Combat Inter-Carrier Interference in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) is an emerging multi-carrier modulation scheme, which has been adopted for several wireless standards such as IEEE 802.11a and HiperLAN2. A well-known problem of OFDM is its sensitivity to frequency offset between the transmitted and received carrier frequencies. This frequency offset introduces inter-carrier interference (ICI) in the OFDM symbol. In this letter, we investigate two methods for combating the effects of ICI: the extended Kalman filter (EKF) method and a form of the sequential Monte Carlo (SMC) method called sequential importance sampling (SIS). Through simulations, we explore the efficiency of these two methods for various frequency offsets and different signal-to-noise ratios (SNRs). Our estimates of the frequency offset are very satisfactory, especially in the latter case, resulting in performance improvement of the OFDM modulation scheme.

Partial transmit sequence arid selected mapping schemes to reduce ICI in OFDM systems

Orthogonal frequency division multiplexing (OFDM) is sensitive to the carrier frequency offset (CFO). We introduce the peak interference-to-carrier ratio (PICR) to measure the resulting intercarrier interference (ICI). This paper shows that PICR can be reduced by selected mapping (SLM) and partial transmit sequence (PTS) approaches. These schemes are analyzed theoretically and their performances are evaluated by simulation.