Orthogonal frequency division multiplexing (OFDM) has been adopted for several wireless network standards due to its robustness against multipath fading. Main drawback of OFDM is its high peak-to-average power ratio (PAPR) that causes a signal degradation in a peak-limiting (e.g., clipping) channel leading to a higher bit error rate (BER). At the receiver end, the effect of peak limitation can be removed to some extent to improve the system performance. In this paper, a joint iterative channel estimation/equalization and clipping noise reduction technique based on minimum mean square error (MMSE) criterion is presented. The equalization weight that minimizes the mean square error (MSE) between the signal after channel equalization and feedback signal after clipping noise reduction is derived assuming imperfect channel state information (CSI). The MSE performance of the proposed technique is theoretically evaluated. It is shown that the BER performance of OFDM with proposed technique can be significantly improved in a peak-limited and doubly-selective (i.e., time- and frequency-selective) fading channel. Copyright © 2011 John Wiley & Sons, Ltd.

Orthogonal frequency division multiplexing (OFDM) signals have a problem with a high peak-to-average power ratio (PAPR). A distortionless selected mapping (SLM) has been proposed to reduce the PAPR, but a high computational complexity prohibits its application to an OFDM system with a large number of subcarriers. Recently, we proposed OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency-domain equalization (MMSE-FDE) to improve the bit error rate (BER) performance of conventional OFDM with a lower PAPR. The PAPR problem, however, cannot be completely eliminated. In this paper, we present an SLM combined with symbol re-mapping for OFDM/TDM using MMSE-FDE. Unlike the conventional OFDM, where SLM is applied over subcarriers in the frequency domain, we exploit both time and frequency dimensions of OFDM/TDM signal to improve the performance with respect to PAPR and BER. A mathematical model for PAPR distribution of OFDM/TDM with SLM is presented to complement the computer simulation results. It is shown that proposed SLM can further reduce the PAPR without sacrificing the BER performance with the same or reduced computational complexity. Copyright © 2010 John Wiley & Sons, Ltd.

Broadcast nature of the wireless channel enables wireless communications to make use of network coding at the physical layer (PNC) to improve the network capacity. Recently, narrowband and later broadband analog network coding (ANC) were introduced as a simpler implementation of PNC. The ANC schemes require two time slots while in PNC three time slots are required for bi-directional communication between two nodes and hence ANC is more spectrum efficient. The coherent detection and self-information removal in ANC require accurate channel state information (CSI). {In this paper, we theoretically analyze the bit error rate (BER) performance with imperfect knowledge of CSI for broadband ANC using orthogonal frequency division multiplexing (OFDM), where the channel estimation error is modeled as a zero-mean complex Gaussian random variable. We investigate the BER performance for three cases: (i) the effect of imperfect self-information removal due to channel estimation (CE) error with fading tracking errors, (ii) the effect of imperfect self-information removal due to CE error without fading tracking errors}, and (iii) the ideal CE case. We discuss how, and by how much, our results obtained by theoretical analysis can be used for design of broadband ANC system with the imperfect knowledge of CSI. Our results show that imperfect channel estimation due to the noise effect has less impact on self-information removal than the imperfect channel estimation due to fading tracking errors. The tracking against fading is an important problem for accurate self-information removal as well as coherent detection and thus, the effect of channel time-selectivity is also theoretically studied. The achievable BER performance gains due to the polynomial time-domain channel interpolation are investigated using the derived close-form BER expressions and it was shown that the broadband ANC schemes with practical CE in a time- and frequency-selective channel should include a more sophisticated channel interpolation techniques since the impact of Doppler shift has prevalent effect on the achievable BER performance.

In this work the effects of impulsive noise from number of home electrical appliances in power line medium is investigated. This is an extension to a paper already published in ISPLC 2011 [1]. The analysis in this work focuses on the properties of impulse noise in frequency range of 100MHz – 200MHz and compares the effect of noise with the lower frequency bands.

Vehicular networks are a promising field in wireless networks enabling connection vehicles among themselves or between a vehicle and an infrastructure. These networks aim to offer several potential applications ranging from road safety applications and driver assistance to infotainment. However, these networks have limited coverage and capacity. Among the options that may help overcome these limitations, we can quote cooperative communications and analog network coding (ANC). The idea of this paper is to combine these two concepts in order to improve the vehicular network connectivity and capacity. The proposed solution is divided into three stages. The first stage aims at identifying the coding and relaying opportunities. The second stage uses a distributed scheme to select the Best Vehicular Relay among potential candidates when relaying is required, while the last stage performs our joint relaying and coding strategy on the received signals. In order to validate our approach, numerical analysis is performed to evaluate the performances in terms of raw Bit Error Rate (BER) and throughput. This confirmed our expectation showing that cooperative relaying achieves better performance than the direct transmission in terms of raw BER but decreases the throughput. However, by deploying analog network coding on the Best Vehicular Relay, the throughput is improved considerably at the price of a slight deterioration of the raw BER.

Cooperative transmission, where spatially distributed users form a multi-antenna system and assist in forwarding the information from source to destination node, achieves the diversity gain of a multiple-input multiple-output (MIMO) system. Cooperative network based on OFDM has been proposed to cope with the channel frequency-selectivity but due to high peak-to-average power ratio (PAPR) of OFDM, expensive power amplifier are required. In this paper, we present cooperative network based on OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency-domain equalization (MMSE-FDE) in a frequency-selective fading channel. We theoretically analyze the network performance with respect to the bit error rate (BER). The conditional signal-to-interference plus noise ratio (SINR) expressions are derived based on Gaussian approximation of the residual inter-slot interference (ISI) after MMSE-FDE for the given set of channel gains. The average BER performance for OFDM/TDM is evaluated by Monte-Carlo numerical computation method using the derived theoretical expressions and confirmed by computer simulation. The results show that the lower BER is achieved with cooperative OFDM/TDM in comparison with OFDM based cooperative network because OFDM/TDM exploits both cooperative and frequency diversity gains.