Dispensing with Channel Estimation…

In this article, we investigate the feasibility of noncoherent detection schemes in wireless communication systems as a low-complexity alternative to the family of coherent schemes. The noncoherent schemes require no channel knowledge at the receiver for the detection of the received signal, while the coherent schemes require channel inherently complex estimation, which implies that pilot symbols have to be transmitted resulting in a wastage of the available bandwidth as well as the transmission power

Error Rate Analysis of Amplitude-Coherent Detection over Rician Fading Channels with Receiver Diversity

Amplitude-coherent (AC) detection is an efficient detection technique that can simplify the receiver design while providing reliable symbol error rate (SER). Therefore, this work considers AC detector design and SER analysis using M-ary amplitude shift keying (MASK) modulation over Rician fading channels. More specifically, we derive the optimum, near-optimum and a suboptimum AC detectors and compare their SER to the coherent, noncoherent and the heuristic AC detectors. Moreover, the analytical SER of the heuristic detector is derived using two different approaches for single and multiple receiving antennas. One of the derived expressions is expressed in terms of a single integral that can be evaluated numerically, while the second approach gives a closed-form analytical expression for the SER, which is also used to derive a simple formula for the asymptotic SER at high signal-to-noise ratios (SNRs). The obtained analytical and simulation results show that the SER of the AC and coherent MASK detectors are comparable, particularly for high values of the Rician K-factor, and small number of receiving antennas. Moreover, the obtained results show that the SER of the optimal AC detector is equivalent to that of the coherent detector. However, the optimal AC detector complexity is prohibitively high, particularly at high SNRs. In most of the scenarios, the heuristic AC detector significantly outperforms the optimum noncoherent detector, except for the binary ASK case at low SNRs. Moreover, the obtained results show that the heuristic AC detector is immune to phase noise, and thus, it outperforms the coherent detector in scenarios where system is subject to considerable phase noise

Coded DS-CDMA Systems with Iterative Channel Estimation and no Pilot Symbols

In this paper, we describe direct-sequence code-division multiple-access (DS-CDMA) systems with quadriphase-shift keying in which channel estimation, coherent demodulation, and decoding are iteratively performed without the use of any training or pilot symbols. An expectation-maximization channel-estimation algorithm for the fading amplitude, phase, and the interference power spectral density (PSD) due to the combined interference and thermal noise is proposed for DS-CDMA systems with irregular repeat-accumulate codes. After initial estimates of the fading amplitude, phase, and interference PSD are obtained from the received symbols, subsequent values of these parameters are iteratively updated by using the soft feedback from the channel decoder. The updated estimates are combined with the received symbols and iteratively passed to the decoder. The elimination of pilot symbols simplifies the system design and allows either an enhanced information throughput, an improved bit error rate, or greater spectral efficiency. The interference-PSD estimation enables DS-CDMA systems to significantly suppress interference.Comment: To appear, IEEE Transactions on Wireless Communication

Asymptotic performance of M-ary signals on Rician fading diversity channels / by Hongwei Zhang.

In this thesis, we will study the average symbol error rate of M-ary signals on wireless Rician fading channels at high average signal-to-noise ratio (SNR) in both single-carrier and multicarrier orthogonal frequency division multiplexing (OFDM) systems. In the system discussed, diversity reception with maximal ratio combining (MRC) and equal gain combining (EGC) is adopted. A general theorem relates the asymptotic error rate to the multidimensional integral of the conditional error probability is presented. Two other theorems are presented for the special cases where the conditional error probability is function of the sum of received SNR's and the sum of received amplitudes corresponding to the cases using MRC diversity and EGC diversity respectively. Then theorems are provided to analyze the asymptotic error rate performance of M-ary signals including M-ary phase-shift keying (MPSK), M-ary pulse amplitude modulation (MPAM), and M-ary quadrature amplitude modulation (MQAM) signals in both single-carrier and multicarrier OFDM systems

Broadband wireless communication systems: Channel modeling and system performance analysis

Wideband channel modeling, which can accurately describe the most important characteristics of wideband mobile fading channels, is essential for the design, evaluation, and optimization of broadband wireless communication systems. In the field of wideband channel modeling, the tradeoff between the prediction accuracy and simulation efficiency has to be taken into account. On one hand, channel models should be as accurate as possible. On the other hand, channel models are supposed to be simple and easy to put into use. There are several commonly used approaches to channel modeling, e.g., measurement-based channel modeling and deterministic channel modeling. Both methods are efficient in capturing the fading behavior of real-world wireless channels. However, the resulting channel models are only valid for the specific environments as those where the measurements were carried out or the ray-tracing scenario was considered. Moreover, these methods are quite time consuming with high computational cost. Alternatively, the geometry-based stochastic channel modeling approach can be employed to model wideband mobile fading channels. The most attractive feature of this method is that the derived channel models are able to predict fading behavior for various propagation environments, and meanwhile they can be easily implemented. Thus, the dissertation will complete the wideband channel modeling task by adopt the geometry-based stochastic approach. In the dissertation, several geometry-based channel models are proposed for both outdoor and indoor propagation scenarios. The significance of the work lies in the fact that it develops channel models under more realistic propagation conditions which have seldom been considered, such as for non-isotropic scattering environxi ments and mobile-to-mobile (M2M) fading channels. In addition, the proposed channel models remove the scarcity that proper geometry-based channel models are missing for indoor environments. The most important statistical properties of the developed channel models including their temporal autocorrelation function (ACF), the two-dimensional (2D) space cross-correlation function (CCF), and the frequency correlation function (FCF) are analyzed. Furthermore, efficient channel simulators with low realization expenditure are obtained. Finally, the validity of the proposed channel models is demonstrated by comparing their analytical channel statistics with the empirical ones measured from real world channels. Besides the work in the field of wideband channel modeling, another part of the dissertation is dedicated to investigate the performance of SISO1 orthogonal frequency division multiplexing (OFDM) broadband communication systems and space-time (ST) coded MIMO2 OFDM broadband communication systems. This work provides a deep insight into the performance of a broadband mobile radio communication system over realistic wideband fading channels. Analytical expressions are derived for bit error probability (BEP) or symbol error rate (SER) of systems. In order to confirm the correctness of the theoretical results as well as to show the usefulness of the wideband channel models in the testing and analysis of a broadband communication system, SISO OFDM systems and space-time coded MIMO OFDM systems are simulated in the dissertation. In order to improve the reliability of digital transmission over broadband wireless radio channels, a differential super-orthogonal space-time trellis code (SOSTTC) is designed for noncoherent communications, where neither the transmitter nor the receiver needs the channel state information (CSI) for decoding. In addition, a new decoding algorithm is proposed. The new algorithm has exactly the same decoding performance as the traditional one. However, it is superior from the standpoint of overall computing complexity

Residue number system coded differential space-time-frequency coding.

Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2007.The rapidly growing need for fast and reliable transmission over a wireless channel motivates the development of communication systems that can support high data rates at low complexity. Achieving reliable communication over a wireless channel is a challenging task largely due to the possibility of multipaths which may lead to intersymbol interference (ISI). Diversity techniques such as time, frequency and space are commonly used to combat multipath fading. Classical diversity techniques use repetition codes such that the information is replicated and transmitted over several channels that are sufficiently spaced. In fading channels, the performance across some diversity branches may be excessively attenuated, making throughput unacceptably small. In principle, more powerful coding techniques can be used to maximize the diversity order. This leads to bandwidth expansion or increased transmission power to accommodate the redundant bits. Hence there is need for coding and modulation schemes that provide low error rate performance in a bandwidth efficient manner. If diversity schemes are combined, more independent dimensions become available for information transfer. The first part of the thesis addresses achieving temporal diversity through employing error correcting coding schemes combined with interleaving. Noncoherent differential modulation does not require explicit knowledge or estimate of the channel, instead the information is encoded in the transitions. This lends itself to the possibility of turbo-like serial concatenation of a standard outer channel encoder with an inner modulation code amenable to noncoherent detection through an interleaver. An iterative approach to joint decoding and demodulation can be realized by exchanging soft information between the decoder and the demodulator. This has been shown to be effective and hold hope for approaching capacity over fast fading channels. However most of these schemes employ low rate convolutional codes as their channel encoders. In this thesis we propose the use of redundant residue number system codes. It is shown that these codes can achieve comparable performance at minimal complexity and high data rates. The second part deals with the possibility of combining several diversity dimensions into a reliable bandwidth efficient communication scheme. Orthogonal frequency division multiplexing (OFDM) has been used to combat multipaths. Combining OFDM with multiple-input multiple-output (MIMO) systems to form MIMO-OFDM not only reduces the complexity by eliminating the need for equalization but also provides large channel capacity and a high diversity potential. Space-time coded OFDM was proposed and shown to be an effective transmission technique for MIMO systems. Spacefrequency coding and space-time-frequency coding were developed out of the need to exploit the frequency diversity due to multipaths. Most of the proposed schemes in the literature maximize frequency diversity predominantly from the frequency-selective nature of the fading channel. In this thesis we propose the use of residue number system as the frequency encoder. It is shown that the proposed space-time-frequency coding scheme can maximize the diversity gains over space, time and frequency domains. The gain of MIMO-OFDM comes at the expense of increased receiver complexity. Furthermore, most of the proposed space-time-frequency coding schemes assume frequency selective block fading channels which is not an ideal assumption for broadband wireless communications. Relatively high mobility in broadband wireless communications systems may result in high Doppler frequency, hence time-selective (rapid) fading. Rapidly changing channel characteristics impedes the channel estimation process and may result in incorrect estimates of the channel coefficients. The last part of the thesis deals with the performance of differential space-time-frequency coding in fast fading channels