Robust Impulse Response Shortening for Discrete Multitone Transceivers

In this paper, we investigate the optimum detection of MIMO signals in the presence of channel estimation errors. A maximum likelihood (ML)-based detection algorithm is proposed for optimal MIMO signal detection based on the modified ML criterion which takes into account channel estimation errors. Moreover, we evaluate for both the uncoded and coded case, the bit-error-rate (BER) performance of the hard decoded MIMO systems. The new algorithm, taking into account channel estimation errors, achieves improvement in terms of BER gain over the conventional MIMO detector algorithm ignoring channel estimation errors. Moreover, the optimal designed constellations taking channel estimation errors into account, show an increase in the capacity over conventional schemes.

Pair-wise error probability (PEP) is analyzed in the presence of channel estimation error (CEE) for orthogonal frequency division multiplexing (OFDM) in a quasi-static Rayleigh fading channel. Subcarriers in OFDM are grouped in an equi-spaced manner with the number of subcarriers in a group equal to the number of channel taps. One group is dedicated for training and the rest are for data transmission. A linear minimum mean square error (LMMSE) based channel estimation for coherent detection is considered in this paper. This enables the signal dependent CEE to be uncorrelated to the data. Since ML decoding employed with perfect CSI becomes suboptimal in the presence of CEE, an optimal ML decoding is derived. It is observed from our training-based PEP expression that the CEE does not reduce the diversity order but contributes to a loss of coding gain. Moreover, a code design criterion is established. To reduce the loss of coding gain, an optimal training scheme is developed, based on the PEP expression. Loss of performance due to an imperfect channel estimate is quantified in terms of bounds on bit error probability (BEP) for high SNR. Our analytical findings are corroborated by simulation examples.

This paper presents the performance analysis of decode-and-forward (DF) relaying system in presence of both channel estimation error (CEE) and radio frequency impairments (RFI). First, the end-to-end signal-to-noise-plus-distortion-and-error ratio (SNDER) expression is derived, followed by an exact closed-form outage probability (OP) expression for Nakagami-m fading channel. As a special case, the OP analysis for Rayleigh fading channel is also provided. From the derived expressions, the relation amongst CEE and RFI is analyzed. For a complete study, the high SNR analysis of the derived equations is also carried out. The analytical results have been verified using the Monte Carlo simulations. Finally, intriguing results are presented with the help of plots shown in the numerical analysis.

In this paper, we consider the transmission coordination among multiple cell sites, namely the Coordinated MultiPoint (CoMP) transmission scheme, where several Base Stations (BSs) cooperate to serve a set of Mobile Stations (MSs) and both BSs and MSs are equipped with multiple antennas. We model this multicell cooperative system under the presence of channel estimation errors that can significantly influence the obtained results. We derive the exact sum rate expression of the multicell cooperative system in the presence of channel estimation errors and we evaluate the performance of the Block-Diagonalization (BD) and Zero-forcing (ZF) beamforming approaches. Furthermore, we investigate a power allocation policy that maximizes the system sum rate in the presence of channel estimation errors. We show that in the multicell cooperative system, the performance of the BD or ZF beamforming approaches in terms of the maximization of the system sum rate, depends essentially on the system configuration parameters (i.e., number of antennas per BS and per MS). Simulation results are given to support our claims.

Recently, Cao and Beaulieu presented an insightful analysis on the bit-error performance of 16-quadrature amplitude modulation (QAM) scheme on Rayleigh fading channels with maximal ratio combining diversity and channel estimation errors. Unfortunately, although exact, the results presented in that paper are based on a complicated parabolic cylinder function, and a two-dimensional numerical integration has to be performed to evaluate the average probability of bit error. In this letter, we present a surprisingly simple expression for the average probability of error in a well-known closed form. We point out that the error rates for any N-ary square/rectangular QAM constellation with Gray mapping can also be expressed in this form. Furthermore, we show that the presented results can also be modified, in a simple fashion, for a generalized selection combining scheme in the presence of channel estimation errors.

The paper presents expressions for the received signals for rate 1, 1/2 and 3/4 space-time block codes in the presence of channel estimation errors and over mutually correlated flat frequency Rayleigh fading channels. It is shown analytically and through simulations how these codes suffer performance degradation as a consequence of the loss of orthogonality of the code produced by channel estimation errors. Quantitative results are provided which allow the space-time block codes performance to be evaluated and compared as a function of the channel estimation error power.

We consider Multiple-input multiple-output (MIMO) wiretap channel with one transmitter, one receiver, one cooperative jammer, and one eavesdropper, where each node equips with multiple antennas. Eigenbeam-space division multiplexing (E-SDM) and cooperative jamming are known as the techniques improving secrecy rate. E-SDM enables the transmitter and the legitimate receiver to communicate with each other in parallel using channel state information (CSI) known to them to maximize the legitimate receiver's mutual information. On the other hand, cooperative jamming is to jam only the eavesdropper to degrade eavesdropper's mutual information. However, co-channel interference and residual interference from the cooperative jammer are caused by channel estimation error, which degrades legitimate receiver's mutual information. How these interference influence on the secrecy rate has not been clarified. In this paper, we derive lower and upper bounds on secrecy rate using legitimate receiver's mutual information in the presence of channel estimation error and eavesdropper's mutual information who uses minimum mean square error (MMSE) receiver. We analyze the effect of co-channel interference and residual interference from the cooperative jammer on the secrecy rate.

Lower bounds are computed on the throughput of packet-switched space-time coded systems with delay constraints. The delay constraints are accounted for by defining a delay-limited throughput as the instantaneous throughput of each packet that can be maintained with a certain probability. The analysis assumes quasi-static and independent fading across packets, packet retransmissions until success, and negligible overhead for acknowledgment packets and guard times. Upper bounds on the outage probabilities of orthogonal space-time block codes (OSTBC) and spatial multiplexing with horizontal encoding (SM-HE) are computed in the presence of channel estimation errors to obtain lower bounds on the delay-limited throughput. The target physical-layer data rate is selected at each signal-to-noise ratio (SNR) to maximize the lower bounds on the throughput. The results indicate that higher throughput is achieved using OSTBC at low SNR and SM-HE at high SNR. Furthermore, the loss of throughput due to channel estimation errors is quantified.

The main objective of this paper is to provide an extensive and complete examination on the effect of practical impairments such as channel estimation errors (CEEs) and feedback delay (FD) on the performance of diversity schemes over Nakagami‐mfading channels. Under erroneous channel estimation and outdated feedback cases, statistical expressions and several performance metrics related to the post‐processing signal‐to‐noise ratio (SNR) are derived for four different diversity schemes: transmit antenna selection (TAS)/orthogonal space–time block coding, TAS/maximal‐ratio transmission (MRT), MRT/receive antenna selection (RAS), and joint transmit and RAS. Exact analytical expressions for outage probability and average error rates ofM‐ary modulations are derived in order to provide insightful perspectives on the capacity and error performance of diversity schemes that experience both CEE and FD. The asymptotic diversity order of the investigated diversity schemes are derived via a high‐SNR approximation approach. In order to assess the real‐world performance of the investigated diversity schemes and to observe their robustness or sensitivities in practical imperfections, various configurations are considered together with several performance comparisons. Also, Monte Carlo simulations are performed in order to validate the theoretical results. Copyright © 2014 John Wiley & Sons, Ltd.

In this paper, we propose the analytical approach for amplify-and-forward (AF) relay cooperative transmission in the presence of channel estimation error (CEE) generated by pilot symbol assisted-channel estimation (PSA-CE) schemes over quasi-static Rayleigh fading channels. Average symbol error rate (SER) is expressed as the well-known closed-form by using moment generating function (MGF) of the received signal-to-noise ratio (SNR), which quantifies the SNR penalty arising from CEE. Moreover, the effect of CEE on SER performance is verified based on the number of pilot symbols and the accuracy of the derived average SER expression of M-ary phase shift keying (MPSK) is confirmed by comparison with simulation results.

In a multicarrier modulation system, a time domain equalizer (TEQ) traditionally shortens the transmission channel impulse response (CIR) to mitigate intersymbol interference (ISI). In this paper, we propose a data-rate optimal TEQ filter bank whose data rates at the equalizer output of this filter bank are significantly better than those of the Maximum Bit Rate and Minimum ISI methods and similar to those of the least-squares per-tone equalizer method for ADSL CIRs, transmit filters, and receive filters. The contributions of this study are: (1) a new model for multicarrier demodulator output SNR that includes ISI, near-end crosstalk, white Gaussian noise, and the digital noise floor, (2) data rate optimal time domain per-tone TEQ filter bank, and (3) a new achievable upper bound on achievable bit rate.

The requirement for an automated test system has immensely increased due to the realization that manual testing is associated with additional resources and staffing constraints. In order to achieve a competitive edge, reduced development cost, timely product delivery, and product quality are mandatory in today's organization. Manual testing requires skilled operators that increase cost, time, and product delivery. The low cost computer based automated system helps to get an edge by fulfilling these organizational demands. In this paper, an automated testing system has been developed to support functional testing of Nortel Network's modem system (1-Meg SUT). The modem is an inherently complex asymmetric digital subscriber line (ADSL) product and its testing is far more complex than just verification of process faults. The complexity of ADSL system renders automated test system an important and imperative part of ADSL testing. The subject paper demonstrates the indispensable need of automated test system for ADSL testing and its advantages in providing a competitive edge for the organization.

This paper compares the performance of a MIMO system applying a Mismatched Maximum Likelihood Detector (MMLD) with that applying a Generalized Likelihood Ratio Detector (GLRD) in the presence of channel estimation errors. Two sources of error are considered: errors due to noise and errors due to time variations induced by Doppler effects. The MMLD relies on the available channel estimate whereas the GLRD combines the channel estimate with a block of received data and uses a joint channel-symbol estimation approach to solve for the transmitted symbols. The GLRD is shown to outperform the MMLD whenever errors in channel estimation are incurred and the performance gap depends on the amount of error. Furthermore, the GLRD provides a unified receiver structure which can also be applied to differentially encoded MIMO systems and to situation where no channel estimate is available as in blind MIMO. The improved performance of the GLRD comes with increased computational complexity. This problem is addressed through search efficient algorithms based on the branch-estimate-bound optimization framework. We analyze the performance of the GLRD and provide a tight upper bound on the BER of the system at high SNR. Simulation results are shown for a 2 × 2 MIMO system.

In this paper, we consider the random access of nodes adapting their transmissions based on the local channel state information (CSI) in a decentralized manner, which we call channel-aware random access (CARA). The CSI at each node is not perfect but has some errors. Thus, the performance of CARA depends on the accuracy of CSI, which is the focus of this paper. Specifically, an exact stability analysis is carried out for the scenario in which two sources that have bursty packet arrivals compete to access a common receiver. The analysis needs to resolve the complex coupling between the queues at the sources having interdependent services. The analysis also takes into account the compound effects of the multipacket reception capability at the receiver. In summary, our contributions in this paper are twofold: first, we obtain an exact stability region of CARA in the presence of channel estimation errors; such an assessment is necessary as errors in channel estimation are inevitable in practical situations. Second, we compare the performance of CARA to that achieved by the class of stationary scheduling policies making decisions in a centralized manner based on the CSI feedback.

In this paper the general ADSL (asymmetric digital subscriber line) noise environment is reviewed in the context of the telephone loop plant. Special attention is given to the unique unidirectional transmission nature of ADSL. A set of noise environments is presented for related computer simulation studies and hardware tests. A set of mid-CSA test loops is also proposed for performance evaluation under conditions of T1 NEXT interference. To simplify calibration procedures, noise and loop models are revealed in FIR (finite impulse response) filter form and can be measured in dB loss or dBm/Hz power density terms. A subchannel signal to noise ratio (SNR) based computer simulation method is then used to estimate potential ADSL performance under different noise environments for different serving areas. >