QAM Constellations Research Articles

Asymptotically optimal cooperative wireless networks with reduced signaling complexity

This paper considers an orthogonal amplify-and-forward (OAF) protocol for cooperative relay communication over Rayleigh-fading channels in which the intermediate relays are permitted to linearly transform the received signal and where the source and relays transmit for equal time durations. The diversity-multiplexing gain (D-MG) tradeoff of the equivalent space-time channel associated to this protocol is determined and a cyclic-division-algebra-based D-MG optimal code constructed. The transmission or signaling alphabet of this code is the union of the QAM constellation and a rotated version of QAM. The size of this signaling alphabet is small in comparison with prior D-MG optimal constructions in the literature and is independent of the number of participating nodes in the network.

Optimising quasi-orthogonal STBC through group-constrained linear transformation

The generic algebraic structure of a quasi-orthogonal space-time block code (QO-STBC) has been derived, and group-constrained linear transformation (GCLT) as a mean to optimise the diversity and coding gains of a QO-STBC with square or rectangular QAM constellations has been proposed. Compared with QO-STBC with constellation rotation (CR), QO-STBC with GCLT requires only half the number of symbols for joint detection, hence lower maximum-likelihood decoding complexity. The optimum GCLT parameters for QO-STBC with square QAM constellation have been derived analytically. The optimised QO-STBCs with GCLT are able to achieve full-transmit diversity and have negligible performance loss compared with QO-STBCs with CR at the same code rate.

A Tight BER Upper Bound for Bit-Interleaved Coded Modulation with Square QAM and Gray Labeling

Bit-interleaved coded modulation (BICM) is a bandwidth-efficient coded system with diversity order higher than that of Ungerboeck's trellis-coded modulation on fading channels. In this paper, we investigate the BER (bit error rate) performance of BICM in the additive white Gaussian and Rayleigh fading channels. A new upper bound is given for the square QAM constellation with gray labeling, which constitutes a large portion of practical applications of BICM systems. The new upper bound is tighter than the well-known BICM union bound proposed in G. Caire et al. (1998)

Effective Radio Resource Management for MBMS in UMTS Networks

Broadcast and multicast offer a significant improvement of spectrum utilization, and becomes particularly important where information channels are shared among several users. Mobile cellular environments are expected to evolve with the technological approaches necessary to facilitate the deployment of multimedia services, such as streaming, file download and carousel services. The perspective that video streaming in wireless networks services is an attractive service to end-users has spurred the research in this area. To provide for a video delivery platform in UMTS, the Third Generation Partnership Project (3GPP) addressed this problem with the introduction of the Multimedia Broadcast and Multicast Services (MBMS) in 3GPP Release 6. In this document we analyse several effective radio resource management techniques to provide MBMS, namely, use of non-uniform QAM constellations, multi-code and macro-diversity to guarantee the optimal distribution of QoS depending on the location of mobiles.

A Semidefinite Relaxation Approach to MIMO Detection for High-Order QAM Constellations

A new and conceptually simple semidefinite relaxation approach is proposed for MIMO detection in communication systems employing high-order QAM constellations. The new approach affords improved detection performance compared to existing solutions of comparable worst-case complexity order, which is nearly cubic in the dimension of the transmitted symbol vector and independent of the constellation order for uniform QAM, or affine in the constellation order for nonuniform QAM

Effective Radio Resource Management for Multimedia Broadcast/Multicast Services in UMTS Networks

Broadcast and multicast offer a significant improvement of spectrum utilization, and become particularly important where information channels are shared among several users. Mobile cellular environments are expected to evolve with the technological approaches necessary to facilitate the deployment of multimedia services, such as streaming, file download, and carousel services. The perspective that video streaming in wireless networks services is an attractive service to end-users has spurred the research in this area. To provide for a video delivery platform in UMTS, the third generation partnership project (3GPP) addressed this problem with the introduction of the multimedia broadcast and multicast services (MBMS) in 3GPP Release 6. In this document we analyse several effective radio resource management techniques to provide MBMS, namely, use of nonuniform QAM constellations, multicode, and macrodiversity to guarantee the optimal distribution of QoS depending on the location of mobiles.

Complete Complementary Orthogonal (CCO) Code-Based CDMA Using Natural Mapping QAM Constellations

In this short paper we propose a CCO code-based CDMA system that uses a natural mapping QAM scheme, in order to conserve both bandwidth and average transmitted power. We also suggest a design approach to obtain an optimal QAM mapping to further improve system performance. This is in contrast to the original CCO code-based system which used PAM transmission over twice as many channels. Here we present preliminary results for the 2-user case and the downlink.

QAM constellation classification based on statistical sampling for linear distortive channels

The classification method for phase-amplitude-modulated signals transmitted through linear, frequency-selective fading channels is presented. Utilizing a Monte Carlo (MC) sampling technique, QAM constellation classification is based on Gibbs sampling. Constellation classification is achieved along with joint estimation of unknown system parameters, including channel taps and data symbols. When all channel parameters are known, direct steps are proposed for classification and data estimation without altering the general approach. Moreover, a multistage classification algorithm is also presented to improve computational efficiency. The proposed QAM classification methods are shown to perform well on various constellations with different cardinalities, as well as constellations with symbols.

High-Speed Turbo-TCM-Coded Orthogonal Frequency-Division Multiplexing Ultra-Wideband Systems

One of the UWB proposals in the IEEE P802.15 WPAN project is to use a multiband orthogonal frequency-division multiplexing (OFDM) system and punctured convolutional codes for UWB channels supporting a data rate up to 480 Mbps. In this paper, we improve the proposed system using turbo TCM with QAM constellation for higher data rate transmission. We construct a punctured parity-concatenated trellis codes, in which a TCM code is used as the inner code and a simple parity-check code is employed as the outer code. The result shows that the system can offer a much higher spectral efficiency, for example, 1.2 Gbps, which is 2.5 times higher than the proposed system. We identify several essential requirements to achieve the high rate transmission, for example, frequency and time diversity and multilevel error protection. Results are confirmed by density evolution.

Comments on "Exact error-rate analysis of diversity 16-QAM with channel-estimation Error"

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.

Two Proposed Blind Equalizers Using Different Constellation Matched Error Functions for QAM Signals

Although Constant Modulus Algorithm (CMA) is effective to equalize non-minimum phase channels blindly, it suffers from residual intersymbol interference (ISI) and large Mean Square Error (MSE) when applied to higher order constellations (QAM). Methods based on cost function matched to the signal constellation namely alphabet matched algorithm (AMA) were previously reported and proves its superiority on CMA concerning the MSE. Thus dual mode algorithms between CMA and AMA were introduced. A hybrid technique combining CMA and AMA using a cosine square function as a constellation matched error (CME) was lately reported. In this paper two different CME functions are introduced. The MSE of the proposed algorithms are calculated using Matlab simulation under multipath slow fading channels for different signal to noise ratios (SNR) and different levels of QAM constellations. A comparison is established among them. Depicted results show the effectiveness of the two proposed CME functions.

Coded modulation schemes based on partial Gray mapping and unpunctured high rate turbo codes

The paper deals with coding for the band-limited AWGN channel. Coded modulation schemes based on high rate unpunctured turbo codes are proposed. It is shown that, owing to efficient decoding based on the trellis of the dual code and to the optimised code design, coded modulations based on this class of turbo codes allow excellent performance with moderate complexity for practical values of block size and redundancy. A mapping rule already envisaged in previously published papers, based on the partition /spl Zopf//2/sup l//spl Zopf/ with Gray mapping of l bits is exploited. Schemes based on the partition chain /spl Zopf//2/spl Zopf//4/spl Zopf/ are also presented in a comparative way. From this comparison it is concluded that, when constraints are imposed on the number of dimensions and on the redundancy of the coded modulation, partial Gray mapping based on /spl Zopf//4/spl Zopf/ should be preferred to pure mapping by set partitioning and, with QAM constellations with more than 16 points, it should also be preferred to pure Gray mapping.

Optimal Constellation Labeling for Iteratively Decoded Bit-Interleaved Space–Time Coded Modulation

We consider the design of iteratively decoded bit-interleaved space-time coded modulation (BI-STCM) over fast Rayleigh-fading channels with N/sub t/ transmit and N/sub r/ receive antennas. We propose the design criterion to achieve the largest asymptotic coding gain inherited in the constellation labeling. In particular, for orthogonal space-time block codes, the labeling design criterion reduces to maximizing the (-N/sub t/N/sub r/)th power mean of the complete set of squared Euclidean distances associated with all error-free feedback events in the constellation. Based on this power mean criterion, we show that the labeling optimization problem falls into the category of quadratic assignment problems for constellations of any shape and with an arbitrary number of transmit and receive antennas. For a set of practical values of N/sub t/ and N/sub r/, we present optimal labeling maps for 8-PSK, 16-QAM, and 64-QAM constellations.

A Closed-Form Expression for the Exact BER of Generalized PAM and QAM Constellations

We derive an explicit closed-form expression for the exact bit-error rate (BER) computation of generalized hierarchical M-ary pulse amplitude modulations over additive white Gaussian noise (AWGN) and fading channels. This expression can also be used to obtain the exact BER of generalized hierarchical quadrature amplitude modulations (square and rectangular). For the AWGN case, these expressions are in the form of a weighted sum of complementary error functions, and are solely dependent on the constellation size M, the carrier-to-noise ratio, and a constellation parameter which controls the relative message importance.

Search for space – time trellis codes: novel codes for Rayleigh fading channels

The authors address the problematic issues in generating space–time trellis codes, and propose novel methods for reducing the exponentially growing full code search. It is proved that by exploiting the symmetry in QAM and PSK constellations, together with the modulo operation in the encoder, the number of possible combinations in the generator matrix can be halved when performing a full search to obtain optimal codes. It is also shown that for a fixed set of columns in the generator matrix, interchanging columns yields identical results, hence reducing the full code search by the factorial of the number of transmit antennas. Furthermore, the existing sub-optimal (but fast) method for obtaining codes is investigated and results from this method are compared with those obtained from the two proposed methods. Using the suggested methods, novel space–time codes for both slow and fast fading environments are generated and their performance is evaluated through frame error probabilities obtained by simulation.

Constellation shaping for pragmatic turbo coded modulation

A new turbo encoding scheme for high spectral efficiency is proposed. The scheme combines non-uniform signalling on a Gaussian channel, and pragmatic turbo coded modulation. A table is used to map equiprobable input symbols into non-equiprobable points in the QAM constellation. It is shown that the new scheme provides shaping gains of 0.6 and 0.93 dB, at rates 2 and 3 bits/dim, respectively, and reach about 1 dB from the Gaussian channel capacity.

Blind phase recovery in cross QAM communication systems with eighth-order statistics

A new method for blind phase estimation that uses eight-order statistics is described. For cross QAM constellations, it provides about the same root mean square error (RMSE) as the fourth power method with about one-sixth to one-fourth the number of samples. Monte Carlo simulations are provided to demonstrate the usefulness of the method.

Design, analysis, and performance evaluation for BICM-ID with square QAM constellations in Rayleigh fading channels

We consider bit-interleaved coded modulation with iterative decoding (BICM-ID) for bandwidth-efficient transmission over Rayleigh fading channels. We propose the design criteria that utilize a large Hamming distance inherited in a low-rate code and a new labeling technique designed specifically for fading channels. This results in a large coding gain over noniterative coded modulation and performance close to that of turbo coded modulation with less complexity. We also show that BICM-ID designed for fading channels usually has a very good performance over the additive white Gaussian noise (AWGN) channel while the converse is difficult to achieve. When combined with signal space diversity, diversity order can be improved to twice the diversity order of conventional BICM-ID; therefore, the code complexity can further be reduced while maintaining the same level of performance. Specifically, with the bandwidth efficiency of 2 bits/s/Hz over Rayleigh fading channels, a bit error rate (BER) of 10/sup -6/ can be achieved with 16-QAM, a four-state rate 1/2 code at E/sub b//N/sub 0/ of about seven dB. We also derive performance bounds for BICM-ID with and without signal space diversity over Rayleigh fading channels, which can be easily extended for other types of fading channels.

Low-SNR limit of the Cramer-Rao bound for estimating the carrier phase and frequency of a PAM, PSK, or QAM waveform

We consider the Cramer-Rao bound (CRB) for the estimation of the carrier phase and frequency of a noisy linearly modulated signal with random data symbols. The observation vector consists of the matched filter output samples taken at the symbol rate, assuming known symbol timing. Because of the presence of the random data, the evaluation of this CRB is quite tedious. Instead, here we derive a simple closed-form expression for the limit of the CRB at low-signal-to-noise ratio (SNR), which holds for arbitrary PAM, PSK, and QAM constellations.

Performance of a baseband adaptive predistorter in presence of orthogonal multicarrier modulation

AbstractThe performance of a baseband adaptive predistortion system to linearize memoryless high power amplifier (HPA) are analyzed in the presence of an Orthogonal Frequency Division Multiplexing (OFDM) signal. The predistortion scheme adopted is based on a digital signal processing microprocessor and a memory look—up table to predistort the baseband drive signal. Stability of the adaptation algorithm, rate of convergence and effect of quantization are assessed through simulation. The curves of Total Degradation versus the Output Back—off have been calculated for QPSK, 16QAM and 64QAM constellations. Starting from these results, the improvement brought by the use of the predistorter and the degradation caused by the quantization has been assessed.