Pre-processed space-time trellis codes with one-bit feedback

This paper proposes new upper hounds on the performance of space-time trellis codes (STTC) over quasi-static fading channels (QSFC). The proposed bounding approach combines a new low signal-to-noise ratio upper bound together with the traditional union bound. The derived upper bounds show much improved ability to predict the performance of STTC over QSFC, as can be seen from applying them to a published example of STTC.

We consider the challenges of finding good puncturing patterns for rate-compatible low-density parity-check code (LDPC) codes over additive white Gaussian noise (AWGN) channels. Puncturing is a scheme to obtain a series of higher rate codes from a lower rate mother code. It is widely used in channel coding but it causes performance is lost compared to non-punctured LDPC codes at the same rate. Previous work, considered the role of survived check nodes in puncturing patterns. Limitations, such as single survived check node assumption and simulation-based verification, were examined. This paper analyzes the performance according to the role of multiple survived check nodes and multiple dead check nodes. Based on these analyses, we propose new algorithm to find a good puncturing pattern for LDPC codes over AWGN channels.

This paper presents asymptotic multiuser efficiency (AME) performance analysis of the decorrelator based successive interference cancellation (DBSIC) DS-CDMA multiuser receiver DBSIC is similar to the conventional SIC receiver except that a decorrelator is used at each detection stage prior to cancellation. AMEs of DBSIC are compared with those of single-user matched filter, optimum, decorrelating and conventional SIC receivers over both additive white Gaussian noise (AWGN) and Rayleigh fading channels. It is shown that over AWGN channels, DBSIC AME is lower than the optimum receiver AME when the interfering user is weaker than the user of interest but approaches the unity optimum receiver AME as the interferer becomes stronger than the user of interest. For all spreading codes cross-correlation considered, DBSIC has a similar AME curve shape as the conventional SIC receiver but has a higher AME which remains positive for all user energy ratios, illustrating its near-far resistance over AWGN channels. The AME of DBSIC is better than that of the decorrelating detector when the interferer is much weaker or slightly stronger than the user of interest and has worse performance when the interferer is not much weaker. It is shown that DBSIC is completely near-far resistant over Rayleigh fading channels with the same AME as the decorrelating scheme for user 1 and as the optimum scheme for user 2, both AMEs being independent of the user energy ratio. This shows that DBSIC is preferable compared to the decorrelating detector, while still being less complex than the optimum scheme over Rayleigh fading channels

This correspondence analyzes the performance of concatenated coding systems and modulation schemes operating over the additive white Gaussian noise (AWGN) channel by examining the loss of capacity resulting from each of the processing steps. The techniques described in this correspondence allow the separate evaluation of codes and decoders and thus the identification of where loss of capacity occurs. Knowledge of this capacity loss is very useful for the overall design of a communications system, e.g., for evaluating the benefits of inner decoders that produce information beyond the maximum-likelihood (ML) estimate. The first two sections of this correspondence provide a general technique for calculating the composite capacity of an orthogonal or a bi-orthogonal code and the AWGN channel in isolation. The later sections examine the composite capacities of an orthogonal or a bi-orthogonal code, the AWGN channel, and various inner decoders including the decoder estimating the bit-by-bit probability of a one, as is used in turbo codes. The calculations in these examples show that the ML decoder introduces a large loss in capacity. Much of this capacity loss can be regained by using only slightly more complex inner decoders, e.g., a detector for M-ary frequency-shift keying (MFSK) that puts out the two most likely frequencies and the probability the ML estimate is correct produces significantly less degradation than one that puts out only the most likely frequency.

Modulo lattice additive noise (MLAN) channels appear in the analysis of structured lattice codes with lattice decoding for Costa's dirty-paper channel and the additive white Gaussian noise (AWGN) channel. Building on the recent result on the optimal density of an infinite constellation over an AWGN channel, in this paper, it is shown that with a proper choice of the shaping lattice and the scaling parameter, the dispersion of the MLAN channel is asymptotically the same as that of the (zero-interference) AWGN channel at the same signal-to-noise ratio.

In this paper constellations for 16-quadrature amplitude modulation (16-QAM) in Rayleigh and Nakagami-m fading channels is studied. These constellation diagrams are useful for visualizing the effect of fading to the transmitted signal symbols. We simulated 16-QAM technique at different SNR and draw the constellation diagrams for Rayleigh and Nakagami-m fading channels for different values of m. At lower SNR the constellations are more dispersed. It shows that the effect of fading is more dominated at lower SNR. When the SNR is increased the effect of fading is reduced and it can be seen as constellations are less dispersed. We compare the BER versus SNR plot for AWGN and Rayleigh channel and also for AWGN and Nakagami-m fading channels for different values of m. It shows that the when we increase the value of m (nakagami factor) then the effect of fading increases and we need more SNR for reducing this effect of fading. Index Terms: 16-QAM, additive white Gaussian noise (AWGN), fading channels, constellation, BER, SNR

Diverse methodologies of Diversity combining schemes are used for performance improvements of Filter Bank Multicarrier (FBMC) by using Additive White Gaussian Noise and Rayleigh channels. These diversity combining schemes are Maximum Ratio combining and Selection Combining. The proposed schemes are implemented by using different channels of MIMO methodology, which results in high order diversity. This system simulation includes varying number of receiving antennas to analyzes the performance over AWGN and Rayleigh channel. The aim of the proposed schemes is to improve bit error rate (BER) performance with using two different diversity combining schemes. It observed through MATLAB simulations that the proposed schemes provides evident performance improvements.

Coherent detection of asynchronous Code-Division MultipleAccess (CDMA) data transmissions over a Rician fading channel is considered in the context of a multipoint-to-point communication system, where a centralized receiver that is assumed to have knowledge of the signature signals of the system uaers, including the arrival times of the former, observes a superposition of the specular and faded signal components of each of the users in additive noise, The channel itself is assumed to be non-dispersive, and with no fading memory, i.e., the random attenuations and phase shifts experienced by the users’ transmissions over different bit intervals are assumed to be independent of each other, rendering them inestimable. It turns out that this channel is equivalent to a fictitious CDMA-AWGN (Additive White Gaussian Noise) channel from the point of view of optimal detection [I]; it may be shown that the optimum decision rules over the two channels as well as the statistical characterization of the sufficient statistics in each case parallel each other. Unlike the optimum AWGN multiuser detector however, the optimum faded detector is unimplementable using a Viterbi algorithm. This motivates the derivation of the polynomial- complexity faded decorrelator for this channel. Detector performance in a multiuser faded environment may be adversely affected by both the interferer specular (or known) and faded (or unestimatable) signal components. The performance limiting effect of the former on conventional detection as well as the ability of fading channel strategies to withstand such interference has been studied earlier [I]. The issue of the limitations on detector performance, if any, due to interfering fading is addressed here. To this end, we introduce the fading susceptance and fading resistance measures; the former as a measure of whether degradations in detector performance due to interfering fading are so great so as to prevent them from being compete tive with optimum detection strategies over single-user channels, and the latter as a measure that captures the ability of detectors to withstand such interference These asymptotic measures characterize detector performance in regions where the fading of the interfering users as opposed to their specular energies, is the dominant impediment to detection. An analysis of the conventional detector’s performance in the multiuser faded environment reveals that fading interference is capable of limiting detector performance in a manner similar to specular component interference bringing out the hitherto unrecognized performance limiting effect of fading interference in Rician fading CDMA channels. The AWGN niultiuser detectors (optimal and decorrelating), which are designed for the CDMAAWGN channel, while sub-optimally resistant to specular interference, pay a penalty for ignoring the presence of fading in that they are also found to be susceptible to fading interference. Thus we demonstrate that, even in environments where specular interference is marginal, both of the above detectors are incapable of competing with detectors of isolated transmissions, if the fading of an intefering user dominates the background noise. The faded detectors, both optimal and decorrelating, are however found to withstand such interference. In light of their previously demon46 strated resistance to specular interference, and the additional computational considerations, our results make the case for the use of the faded decorrelators for multiuser detection over asynchronous Rician faded CDMA channels. The plots of Figure 1 are an illustiation of the irnplications of our results for detector Bit-Error Rates (BERs) in realistic as opposed to asymptotic environments. We observe that, over a two-user channel, even with a weak interferer specular signal, the first user of the faded decorrelator alone exhibits an exponential decay in BER with increasing Signal-to-Noise Ratio (SNR) with both the conventional detector and the AWGN decorrelator forced by the non-zero, fixed interferer fading, to approach error floors

In broadcast scenarios or in the absence of accurate channel probability distribution information, code design for consistent channel-by-channel performance, rather than average performance over a channel distribution, may be desirable. Root and Varaiya's compound channel theorem for linear Gaussian channels promises the existence of universal codes that operate reliably whenever the channel mutual information (MI) is above the transmitted rate. This paper presents two-dimensional trellis codes that provide such universal performance over the compound linear vector Gaussian channel when demultiplexed over two, three, and four transmit antennas. The presented trellis codes, found by exhaustive search, guarantee consistent performance on every matrix channel that supports the information transmission rate with an MI gap that is similar to the capacity gap of a well-designed additive white Gaussian noise (AWGN)-specific code on the AWGN channel. As a result of their channel-by-channel consistency, the universal trellis codes presented here also deliver comparable, or, in some cases, superior, frame-error rate and bit-error rate performance under quasi-static Rayleigh fading, as compared with trellis codes of similar complexity that are designed specifically for the quasi-static Rayleigh-fading scenario

This paper presents a new study in an attempt to apply Fast Euclidean Direction Search (FEDS) algorithm on adaptive smart antennas. The novelty in this work is the use of FEDS algorithm in a smart antenna system for mobile communications because up to our knowledge this algorithm is not applied on smart antenna so far. In order to properly evaluate the performance of smart antenna for mobile communication systems, an Additive White Gaussian Noise (AWGN) channel model is required that each received signal at each element in the array includes only an additive, zero mean, Gaussian noise . The ability of the FEDS algorithm to operate in a fast changing signal environment is examined by subjecting the input signal to Rayleigh fading with a Jakes power spectral density which is a popular choice for land mobile communications systems. Through simulation results of smart antennas for AWGN channel, the RLS and FEDS start to converge from the initial iteration and 10 respectively, whereas, the LMS and NLMS start to converge after 50 and 10 iterations respectively. In the presence of the Rayleigh fading channel, the LMS, and NLMS algorithms converge after 60 and 25 iterations respectively, while the RLS convergence from the initial iteration and FEDS converge from the iteration number 25. On the other hands, the FEDS algorithm shows better tracking and estimation of the desired input signal compared with both LMS and NLMS algorithms and comparable with RLS algorithm. The comparison of linear plot of array factor using FEDS and RLS , both algorithms generates the same deeper null for undesired signals of about í30 dB towards the interferer using an AWGN channel, while it generates deeper null of about -23 dB and -30 dB respectively using the Rayleigh fading channel.

The theory of group codes simplifies the construction of good rotationally invariant trellis codes for the additive white Gaussian noise channel. New geometrically uniform trellis codes, with spectral efficiency 3 bits/2D, based on multidimensional L/spl times/16-PSK constellations in 4, 6, and 8 dimensions, obtained by group trellis codes over nonbinary groups of the kind Z/sub 16//sup L/, are presented. Most of the codes improve, in terms of asymptotic gain and rotational invariance, the best codes known so far in the literature.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In this paper we propose a hybrid method to determine the positions and velocities of mobile stations (MSs) in a GSM (Global System for Mobile communication) network. The proposed method can be implemented within the existing GSM standard without any additional hardware changes. The hybrid method operates at two levels. At a lower level, time delay method (TDM) is used to obtain coarse values for distances between a MS and three or more Base Transceivers (BTSs). At a higher level, field strength method (FSM) uses the coarse distances estimates obtained using TDM as initial values to obtain refined values for distances. The accurate position of a MS then can be determined by the refined distance values. Subsequently, the velocity of the MS be can obtained using the FSM estimates of the sequential positions of the MS. Least mean square (LMS) method is used to determine the refined distances in the FSM algorithm and to estimate the actual position of the MS from the refined distance estimates. The proposed method was tested for several cases, including complex MS trajectories and varying speeds along the trajectory. The heights of the BTSs were allowed to vary between 20 m and 60 m. The convergence characteristics were found to be satisfactory. For a SNR of 20 dB, position measurements accuracy in a roughly 4 km2 cell is 30 m in a Gaussian channel, 60 m in a Rayleigh channel and 80 m in a Rician channel. The velocity accuracy for a MS traveling at 200 km/h is 15 km/h in a Gaussian channel, 30 km/h in a Rayleigh channel and 50 km/h in a Rician Channel.

It is well known that binary error-correcting codes with iterative decoders can achieve near Shannon-limit performance on the additive white Gaussian noise (AWGN) channel, but their performance on more realistic wireless channels can become degraded due to the presence of burst errors or impulsive noise due to interference. A better performing coding scheme is the class of non-binary codes, which are known to be more effective in correcting burst errors, but interestingly there is no research reported in the literature investigating non-binary codes on impulsive noise channels. In this paper, we investigate the performance of non-binary turbo codes defined in a finite field GF(4) on symmetric alpha-stable impulsive noise channels and compare with comparable binary turbo codes. A Cauchy receiver is also employed to mitigate the effects of the channel to assist the turbo decoding. Our simulation results show that although the non-binary turbo code performs similarly to the binary turbo code on the AWGN channel, it achieves a significant coding gain over the binary turbo code as impulsiveness increases.

Automatic identification of digitally modulated signal has to be able to identify the digitally modulated signal correctly and accurately. Importance of automatic identification of digitally modulated signals are rising increasingly. In this paper an advanced technique is presented, that automatically identifies the multi-user chirp modulated signals in Additive White Gaussian Noise (AWGN) channel. The proposed technique is implementing high order moments (fourth, sixth, and eighth) of detail coefficients of discrete wavelet transform (DWT) as a feature extraction set. Adaptive Neural-Fuzzy Inference System (ANFIS) is proposed as a classifier. The proposed identification procedure is capable of identifying multi-user chirp modulated signals with high accuracy at 0dB, 5dB, and 10dB Signal to Noise Ratio (SNR), over AWGN channel.

A definition of least cyclostationary order (LCO) is proposed based on the inner cyclic period of single carrier and orthogonal frequency division multiplexing (OFDM) signals. The LCOs of single carrier and OFDM signals are derived. Since the LCO has a relationship with the carrier frequency offset (CFO), a blind CFO estimation scheme for single carrier and OFDM signals can be proposed. The novel scheme is entirely blind without any priori information and is proved to be the same as cumulants estimation when the LCO is known. However, the new scheme is superior to the estimation based on cumulant when the LCO is unknown. The mean-square error of M-phase shift keying signals approaches the Cramer–Rao bound in additive white Gaussian noise (AWGN) channel. Simulation results are given to verify the effectiveness of the proposed blind estimation scheme in Rician fading channel and in AWGN channel.