Non-ideal Channel Estimation Research Articles

UWB RSS-Based Localization for Capsule Endoscopy Using a Multilayer Phantom and In Vivo Measurements

In recent years, the localization for capsule endoscopy applications using ultrawideband (UWB) technology has become an attractive field of investigation due to its potential benefits for patients. The literature concerning performance analysis of radio frequency-based localization techniques for in-body applications at UWB frequencies is very limited. Available studies mainly rely on finite-difference time-domain simulations, using digital human models and on experimental measurements by means of homogeneous phantoms. Nevertheless, no realistic analysis based on multilayer phantom measurements or through in vivo experiment has been reported yet. This paper investigates the performance of the received signal strength-based approach for 2-D and 3-D localizations in the UWB frequency band. For 2-D localization, experimental laboratory measurements using a two-layer phantom-based setup have been conducted. For 3-D localization, data from a recently conducted in vivo experiment have been used. Localization accuracy using path loss models, under ideal and non-ideal channel estimation assumptions, is compared. Results show that, under nonideal channel assumption, the relative localization error slightly increases for the 2-D case but not for the in vivo 3-D case. Impact of receivers selection on the localization accuracy has also been investigated for both 2-D and 3-D cases.

Performance Investigation of Spatial Modulation Systems Under Non-Stationary Wideband High-Speed Train Channel Models

In this paper, the bit error rate (BER) performance of a new multiple-input-multiple-output technique, named spatial modulation (SM), is studied under a novel non-stationary wideband high-speed train (HST) channel model in different scenarios. Time-varying parameters obtained from measurement results are used to configure the channel model to make all results more realistic. A novel statistic property called the stationary interval in terms of the space-time correlation function is proposed to describe the channel model’s time-varying behavior. The accurate theoretical BER expression of SM systems is derived under the time-varying wideband HST channel model with the non-ideal channel estimation assumption. The simulation results demonstrate that the BER performance of SM systems shows a time-varying behavior due to the non-stationary property of the employed HST channel model. The system performance can maintain a relative stationary status within the specified stationary interval. It can also be observed that the BER performance of SM systems under the HST channel model is mainly affected by the correlation between sub-channels, inter-symbol-interference, Doppler shift, and channel estimation errors.

An Efficient Practical MIMO–OFDM Scheme with Coded Modulation Diversity for Future Wireless Communications

An efficient coded modulation diversity scheme is proposed to improve the performance of multiple-input-multiple-output orthogonal-frequency-division-multiplexing (MIMO---OFDM) systems in frequency-selective time-varying fading channels. By introducing the rotated modulation and space-time-frequency component interleavers, the proposed scheme globally optimizes powerful forward error correction codes, rotated quadrature amplitude modulation, linear precoding MIMO, and OFDM, thus can achieve modulation diversity and space-time-frequency diversities as much as possible. A simple efficient optimal precoder selection criterion is put forward for this scheme. Based on the analysis of average mutual information, optimal rotation angles are given for different modulation and coding schemes, and the superiority of the proposed scheme is proved. Both software simulation and hardware prototype test results also verify that this new scheme can significantly outperform the conventional bit-interleaved coded modulation scheme under the non-ideal channel estimation, which is up to 4.5 dB signal-to-noise-ratio gain. In a word, the proposed scheme is a simple, efficient and robust transmission technique for the future MIMO---OFDM wireless systems.

Physical‐layer transceiving techniques on data‐aided orthogonal frequency‐division multiplexing towards seamless service on vehicular communications

Frequency error, non-ideal channel estimation (CE) and inefficient seamless road side unit (RSU) service are critical issues occurring in conventional systems that are completely specified by current IEEE 802.11p standards. This study investigates novel techniques for achieving accurate frequency offset compensation and effective CE and RSU selection for handover in signal-overlapping areas. Recently, communications using data-aided orthogonal frequency-division multiplexing (DA-OFDM), such as pseudo-random-postfix OFDM and time-domain-synchronous OFDM (TDS-OFDM), have been actively studied because of their higher effectiveness, efficiency and better transmission quality. This study consists of three parts: (i) derivation of the maximum likelihood estimation for DA-OFDM, (ii) design of an accurate RSU selection scheme and (iii) implementation of a superior TD CE technique. Performance comparisons between the conventional and the proposed techniques are conducted through comprehensive computer simulations.

Cooperative mobile-to-mobile communications over double Nakagami-m fading channels

Double Nakagami-m fading model can be used to provide a realistic description of the mobile-to-mobile (M2M) channel. The moment generating function (MGF)-based approach is used to derive the symbol error probability (SEP) expressions for the multiple-mobile-relay-based M2M system. Under the consideration of better performance and lower complexity, both decode-and-forward (DF) and amplify-and-forward (AF) protocols are addressed in this study. For adaptive DF (ADF) relaying, the asymptotic SEP at high signal-to-noise ratio regime in addition to the exact SEP formulations are derived. Furthermore, the impacts of channel estimation error for the insight of non-ideal channel estimation are analysed. For fixed-gain AF (FAF) relaying, the authors present approximate SEP and asymptotic SEP to indicate the cooperative gain. For L mobile relays and under the assumption of independent and identically distributed (i.i.d) source- relay channels and i.i.d relay-destination channels, it is shown in this paper that asymptotic diversity orders of L × min(mRD,1, mRD,2) + min(mSD,1, mSD,2) and L × min(mSR,1, mSR,2, mRD,1, mRD,2) + min(mSD,1, mSD,2) can be achieved for ADF-M2M and FAF-M2M schemes, respectively. Simulations are performed to verify the analytical results.

On the SNR Penalties of Ideal and Non-ideal Subset Diversity Systems

Subset diversity (SSD) techniques, which select and combine the signals from a subset of the available diversity branches, are important for practical wireless systems. This paper characterizes the performance loss, or signal-to-noise ratio (SNR) penalty, of one SSD system with respect to another. Both ideal and non-ideal channel estimation are considered, and the analysis is valid for the important case of arbitrary two-dimensional signal constellations. Expressions are given for the asymptotic SNR penalty, for both small and large SNR, for all the comparisons considered. Additionally, we develop bounds and approximations to quantify the performance of one system in terms of another for all SNRs of interest. Furthermore, for some signal constellations, we derive the exact SNR penalty of a non-ideal system with respect to an ideal system, as well as the exact penalty associated with two non-ideal systems with varying degrees of estimation energy. The SNR penalty enables the assessment of system sensitivity to channel estimation energy, combining architecture, and signal constellation.

Does Fast Adaptive Modulation Always Outperform Slow Adaptive Modulation?

Link adaptation techniques are important modern and future wireless communication systems to cope with quality of service fluctuations in fading channels. These techniques require the knowledge of the channel state obtained with a portion of resources devoted to channel estimation instead of data and updated every coherence time of the process to be tracked. In this paper, we analyze fast and slow adaptive modulation systems with diversity and non-ideal channel estimation under energy constraints. The framework enables to address the following questions: (i) What is the impact of non-ideal channel estimation on fast and slow adaptive modulation systems? (ii) How to define a proper figure of merit which considers both resources dedicated to data and those to channel estimation? (iii) Does fast adaptive always outperform slow adaptive techniques? Our analysis shows that, despite the lower complexity and feedback rate, slow adaptive modulation (SAM) can achieve higher spectral efficiency than fast adaptive modulation (FAM) in the presence of energy constraint, diversity, and non-ideal channel estimation. In addition, SAM satisfies bit error outage requirements also in FAM-denied region.

Optimized simple bounds for diversity systems

Diversity techniques play a key role in modern wireless systems, whose design benefits from a clear understanding of how these techniques affect system performance. To this aim we propose a simple class of bounds, whose parameters are optimized, on the symbol error probability (SEP) for detection of arbitrary two-dimensional signaling constellations with diversity in the presence of non-ideal channel estimation. Unlike known bounds, the optimized simple bounds are tight for all signal-to-noise ratios (SNRs) of interest. In addition, these bounds are easily invertible, which enables us to obtain bounds on the symbol error outage (SEO) and SNR penalty. As example applications for digital mobile radio, we consider the SEO in log-normal shadowing and the SNR penalty for both maximal ratio diversity, in the case of unequal branch power profile, and subset diversity, in the case of equal branch power profile, with non-ideal channel estimation. The reported lower and upper bounds are extremely tight, that is, within a fraction of a dB from each other.

Antenna subset diversity with non-ideal channel estimation

In modern wireless systems employing diversity techniques, combining all the available diversity branches may not be feasible due to complexity and resource constraints. To alleviate these issues, subset diversity (SSD) systems have been proposed. Here, we develop a framework for evaluating the symbol error probability for antenna SSD, where the signals from a subset of antenna elements are selected and combined in the presence of channel estimation error. We consider independent identically distributed Rayleigh fading channels and use an estimator structure based on the maximum likelihood (ML) estimate which arises naturally as the sample mean of Np pilot symbols. The analysis is valid for arbitrary two-dimensional signaling constellations. The expressions give insight into the performance losses of non-ideal SSD when compared to ideal SSD. Due to estimation error, these losses occur in branch combining as well as in branch selection. However, our analytical results show that the practical ML channel estimator still preserves the diversity order of an ideal SSD system with Nd branches. Finally, we investigate the asymptotic signal-to-noise ratio penalty due to estimation error.

Bit error ratio performance of a receiver diversity scheme with channel estimation

The performance of diversity combining techniques with channel estimation for the case of unequal power branches is discussed. The performance of binary phase shift keying (BPSK), pulse amplitude modulation (PAM) and quadrature amplitude modulation (QAM) formats is investigated and their performance with nonideal channel estimation is explored. The case of combining multiple branches with unequal power levels is considered and optimal weighting factors for a log likelihood ratio test (LLRT) detector for the BPSK case are presented. These weights are shown to operate in a similar manner to those obtained by the linear minimum mean squared error (LMMSE) criterion and are compared with the well known maximal ratio combining (MRC) technique. The probability of error of this receiver is derived and simplifications for high signal-to-noise ratios are presented. Finally, numerical results are presented to compare the performance of the LLRT, LMMSE and MRC based receivers.