Imran A. Tasadduq

Detection of OFDM-CPM signals over multipath channels

A class of orthogonal frequency division multiplexing-continuous phase modulation (OFDM-CPM) signals is introduced in which binary data sequence is mapped to complex symbols using the concept of correlated phase states of a CPM signal. Canonical optimum and suboptimum multiple-symbol-observation OFDM-CPM receivers are derived. Multipath channel with AWGN is assumed. The receivers are analyzed for bit-error-rate (BER) performance in terms of highand low-SNR bounds. These bounds are illustrated as a function of parameter h, time delay and attenuation level. It is shown through numerical computation that the OFDM-CPM system outperforms a similar OFDM-PSK system in a two-ray multipath model. Moreover, an OFDM-CPM system gives the best error performance when the parameter h is 0.5 with an observation interval of 2.

OFDM-CPM signals for wireless communications

A class of orthogonal frequency division multiplexingcontinuous phase modulation (OFDM-CPM) signals is introduced in which the binary data sequence is mapped to complex symbols using the concept of correlated phase states of a CPM signal. A multiple-symbol-observation receiver is used to decode the received sequence, and an investigation of bit error rate over typical wireless multipath channels with additive white Gaussian noise is presented. The performance of a variety of OFDM-CPM signals is presented and analyzed. Performance is a function of parameter and the observation interval, both of which are at the disposal of the system designer. It is shown that OFDM-CPM is a promising signalling scheme in multipath fading channels. Results for multi- and asymmetric OFDM-CPM signals are also presented. The peak-to-average power ratio (PAPR) performance of these signals is also presented, and an algorithm to reduce PAPR is proposed that is based on a multi-amplitude CPM constellation. It is shown through numerical simulations that the proposed algorithmreduces the PAPR of a 128-carrier OFDM-CPM signal by more than 4 dB.

Novel SLM Based Techniques for PAPR Reduction of OFDM

Three new algorithms based on minimization of autocorrelation of transmitted symbols and the SLM approach which are computationally less demanding have been proposed. In the first algorithm, autocorrelation of complex data sequence is minimized to a value of 1 that results in reduction of PAPR. Second algorithm generates multiple random sequences from the sequence generated in the first algorithm with same value of autocorrelation i.e. 1. Out of these, the sequence with minimum PAPR is transmitted. Third algorithm is an extension of the second algorithm and requires minimum side information to be transmitted. Multiple sequences are generated by modifying a fixed number of complex numbers in an OFDM data sequence using only one factor. The multiple sequences represent the same data sequence and the one giving minimum PAPR is transmitted. Simulation results for a 256 subcarrier OFDM system show that significant reduction in PAPR is achieved using the proposed algorithms

Performance of optimum and suboptimum OFDM-CPM receivers over multipath fading channels

Summary A class of orthogonal frequency division multiplexing-continuous phase modulation (OFDM-CPM) signals is introduced in which binary data sequence is mapped to complex symbols using the concept of correlated phase states of a CPM signal. Canonical optimum and suboptimum multiple-symbol-observation OFDM-CPM receivers are derived. Multipath channel with AWGN is assumed. The receivers are analyzed for bit error rate (BER) performance in terms of high- and low-SNR bounds. These bounds are illustrated as a function of parameter h, time delay and attenuation level. It is shown that OFDM-CPM systems, with h ¼ 0:5; 0:25 and an observation interval length of two symbols, can outperform conventional OFDM-PSK system for a two-ray multipath model. Copyright # 2005 John Wiley & Sons, Ltd.

PAPR reduction of OFDM signals using autocorrelation based SLM without side information

Aperiodic autocorrelation and power variance are two parameters that play an important role in PAPR reduction in OFDM symbols. In this paper, we have tackled the aperiodic autocorrelation factor and based on it, two algorithms have been proposed. In the first algorithm, called selective autocorrelation (SA), the value of first aperiodic autocorrelation coefficient is minimized to 1 for reducing the PAPR. In the second algorithm, called selected sequences with variable autocorrelation SLM (SSVA), multiple sequences are generated by modifying a fixed number of complex numbers. The one giving minimum PAPR is transmitted. Simulation results show significant reduction in PAPR. Further a novel technique based on data insertion is used to handle the side information generated by the two algorithms without degrading the PAPR performance.

Hand Off Issues in 3G UMTS Networks

Universal Mobile Telecommunication System (UMTS) is a third generation mobile communication technology based on wideband CDMA (WCDMA) and can facilitate the users in much better way as compared to the second generation of mobile communication. UMTS is superior to second generation in terms of bandwidth efficiency, quality of service, speech quality, speed and capacity. At present, more than 60 countries using WCDMA technology are operating commercially in 25 countries. In this paper, we focus on soft and hard handover issues in UMTS networks. In order to simulate a typical UMTS scenario we use OPNET modeler where a number of users are generating traffic and are free to move in various cells.

Error performance of 8-QAM trellis-coded MC-CDMA with controlled equalization over wireless channels

This paper presents a novel combination of 8-QAM trellis codes with multi-carrier code division multiple access (MCCDMA) and controlled equalization for multiuser downlink Rayleigh fading channel. In literature, minimum mean square error (MMSE) is known to be the optimal single user detection (SUD) technique. We show that the proposed system, with 16-state encoder and full system load, outperforms an equivalent system that uses MMSE as the equalization technique. Moreover, as the number of active users increase from single user load to a fully loaded system, error performance of the proposed system surpasses an equivalent system using MMSE. This suggests that the proposed system is more robust to multiple access interference (MAI) as compared to that with MMSE.

Efficient Power Variance Algorithms for PAPR Reduction in OFDM Signals

In this paper, the expression of the power variance (PV) of an OFDM symbol has been explored for peak to average power ratio (PAPR) reduction. It is seen through simulation results and complementary cumulative distribution function (CCDF) curves that PV expression used in PAPR comparison can be simplified to a point where it becomes practical to use such a computationally complex PV expression for PAPR comparison.

Performance of optimum and suboptimum OFDM-CPM receivers over multipath fading channels: Research Articles

A class of orthogonal frequency division multiplexing-continuous phase modulation (OFDM-CPM) signals is introduced in which binary data sequence is mapped to complex symbols using the concept of correlated phase states of a CPM signal. Canonical optimum and suboptimum multiple-symbol-observation OFDM-CPM receivers are derived. Multipath channel with AWGN is assumed. The receivers are analyzed for bit error rate (BER) performance in terms of high- and low-SNR bounds. These bounds are illustrated as a function of parameter h, time delay and attenuation level. It is shown that OFDM-CPM systems, with h=0.5,0.25 and an observation interval length of two symbols, can outperform conventional OFDM-PSK system for a two-ray multipath model. Copyright