QAM Schemes Research Articles

Amplify-forward and decode-forward cooperation relying on systematic Luby transform coded Hybrid Automatic-Repeat-reQuest

Systematic Luby transform (SLT) codes constitute rateless codes, which are capable of adaptively adjusting their code rate depending on the channel quality without any explicit channel state information (CSI) at the transmitters. SLTs are also suitable for space time collaboration-aided relay networks. In this study, an iterative decoding-aided SLT scheme is combined with 16 quadrature amplitude modulation (QAM) transmission in a wireless relay-aided network. The bit error ratio (BER) results and extrinsic information transfer (EXIT) charts are provided to evaluate the performance of the proposed scheme. The simulation results show that the proposed scheme using amplify-and-forward (AF) relaying achieves a 2.5 dB gain at a BER of 1025, while the attainable improvement is nearly 6 dB for decode-and-forward (DF) relaying, compared to the non-iterative detection scheme operating without the relay’s assistance. Moreover, the AF relaying-aided SLT coded 16-QAM scheme is more beneficial, when the relay station is close to the source. By contrast, the DF relaying performs best near the mid-point between the source and the destination. Additionally, a modified Hybrid Automatic-Repeat-reQuest (HARQ) protocol using incremental redundancy is applied along with the SLT-coded 16-QAM scheme in order to enhance the achievable throughput and energy efficiency of cooperative networks. This arrangement reduces the total transmit power by about 5%, compared to the classic HARQ scheme.

On (.+-.1) Error Correctable Integer Codes

Integer codes correct errors of a given type, which means that for a given communication channel and modulator we can choose the type of the errors (which are the most common) then construct integer code capable of correcting those errors. A new general construction of single (±1) error correctable integer codes will be presented. Comparison between single and multiple (±1) error correctable integer codes over AWGN channel using QAM scheme will be presented.

Analysis of Single-Symbol Detectable Space-Time Block Codes With COD and GCIOD

In this paper, we present a simplified maximum likelihood detection metric for the newly emerging space-time block codes (STBCs) with generalized coordinate interleaved orthogonal design (GCIOD). We also derive the symbol pairwise error probability (PEP) and the union bound on symbol error rate (SER) for a space-time block coded (STBCed) system with single-symbol detection and rotated QAM scheme over flat Rayleigh fading channels. In particular, linear STBCs with complex orthogonal design (COD) and GCIOD are considered. Based on the theoretical analysis, the symbol PEP of the GCIOD codes is related to the transmit power, signal-to-noise ratio, and the rotated angle of the rotated QAM scheme. However, the symbol PEP of the COD code is irrelevant to the rotated angle. It is shown that simulation results match well with our analysis. Thus, the union bounds on SER can be applied to predict the performance of a STBCed system with adaptive code selection between the full-rate COD and GCIOD codes.

Intelligent Decision Making System for Digital Modulation Scheme Classification in Software Radio Using Wavelet Transform and Higher Order Statistical Moments

This paper proposes a neural network (NN) based intelligent decision making system for digital modulation classification using wavelet transform, histogram peak and higher order statistical moments. The decision making system is developed to classify the modulation schemes buried in additive white Gaussian noise and channel interference utilizing NN classifier. The performance is verified and validated for M-ary PSK, M-ary FSK, M-ary QAM and GMSK modulation schemes by examining the receiver operating characteristics, confusion matrix and probability of correct identification for various signal-to-noise ratios (SNR) and also for various decision parameters. The performance of the proposed system also has been compared with existing methods and found that this method can be considered as reliable classification method for Digital Modulation Scheme with lower SNR upto ? 5 dB.

A Family of Distributed Space-Time Trellis Codes With Asynchronous Cooperative Diversity

In current cooperative communication schemes, to achieve cooperative diversity, synchronization between terminals is usually assumed, which may not be practical since each terminal has its own local oscillator. In this paper, based on the stack construction proposed by Hammons and El Gamal, we first construct a family of space-time trellis codes for BPSK modulation scheme that is characterized to possess the full cooperative diversity order without the synchronization assumption. We then generalize this family of the space-time trellis codes from BPSK to higher order QAM and PSK modulation schemes based on the unified construction proposed by Lu and Kumar. Some diversity product properties of space-time trellis codes are studied and simplified decoding methods are discussed. Simulation results are given to illustrate the performance of the newly proposed codes

Direct Conversion EHM Transceivers Design for Millimeter-Wave Wireless Applications

A direct conversion modulator-demodulator with even harmonic mixers for fixed wireless applications is presented. The circuits consist of even harmonic mixers (EHMs) realized with antiparallel diode pairs (APDPs). A communication link is set up to examine the overall performance of proposed modulator-demodulator. The transmission of 16-QAM signal with 110 Mbps data rate over fixed wireless link has been examined. We also evaluate the different levels of I/Q imbalances and DC offsets and use signal space concepts to analyze the bit error rate (BER) of the proposed transceiver using M-ary QAM schemes. The results show that this structure can be efficiently used for fixed wireless applications in Ka band.

Configuration and error ratio performance of M‐QAM whose number of signal points is not a power of 2

AbstractThis study examines the practicality of M‐quadrature amplitude modulation (M‐QAM) where the number of signal points M is not a power of two. A practical problem is the complexity of the configuration because one symbol in an M‐QAM signal does not correspond to an integer number of bits, and the symbol error does not simply convert to the bit error. Therefore, from the perspective of simplifying the configuration and minimizing bit error rate (BER) properties, multidimensional encoding (binary/M‐ary conversion) for converting a binary sequence to correlated symbols is proposed and the theoretical formulas of the symbol error rate (SER) and the bit error rate (BER) are clarified. SER properties of 40QAM, 44QAM, 48QAM, 56QAM, and 60QAM fall between 32QAM and 64QAM. The configuration of a QAM scheme where the number of signal points becomes 3 × 2p−1 where p is an integer greater than or equal to 3 is shown, as are theoretical values for the SER properties of 12QAM and 24QAM in particular. Also shown are the theoretical values of the BER properties with and without differential encoding; these are verified with a computer simulation. A discussion based on these results concerns the effectiveness of M‐QAM in the sense of expanding decision branches for adaptive modulation. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(2): 46–57, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20269

Performance of decorrelating receivers in multipath Rician fading channels

This letter focuses on the performance analysis of the decorrelating receiver in multipath Rician faded CDMA channels. M-ary QAM scheme is employed to improve the spectral efficiency. Approximate expressions are first derived for the two performance indexes: the average symbol error rate (SER) and the average bit error rate (BER) when the decorrelating-first receiver perfectly knows the channel information of the user of interest. To achieve desirable closed-form expressions of the SER and the BER, we exploit results in large system analysis and make assumptions of a high signal-to-interference ratio (SIR) and/or a small Rician K-factor. To measure the receiver performance in the practical scenario, we further derive expressions to approximate the average SER and BER of the decorrelating-first scheme with channel uncertainty. Simulation results demonstrate that the analytical results can also be employed to evaluate the performance of the combining-first receiver.

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.

POWER AND BANDWIDTH-EFFICIENT CIRCULAR M-ARY APSK SCHEMES WITH LOW PAPR

This paper presents a class of circular M-ary Amplitude-Phase Shift Keying (APSK) signaling techniques with high bandwidth efficiency and low peak-to-average power ratio (PAPR) suitable for systems using nonlinear power amplifiers to achieve high power efficiency. For nonlinear amplification, good performance requires not only high squared minimum distance to average power ratio (DPR) but also low PAPR. A search algorithm for M-ary APSK schemes using circular constellations suitable for nonlinear amplification with minimum PAPR and maximum DPR is developed. Results for 8-, 16-, 32-, 64- and 128-APSK signalling schemes are presented. The effects of bandlimiting filter sharpness on the PAPR are examined and considered in the development. The analytical and simulation results show that this class of circular M-ary APSK signals outperforms the square and cross M-ary QAM schemes.

Nonlinear analysis of the phase noise in the OFDM communication system

For the detailed analysis of OFDM system, we present a novel approach of the nonlinear approximation including the second order term of phase noise. Phase noise of PLL (phase locked-loop) frequency synthesizer is analyzed when the commercial components of the PLL are considered for the practical analysis. It is shown that BER results by analytical approach closely match with simulation results of the OFDM communication system using QPSK and 16QAM modulation. DF (degradation factor) that is the ratio of SNR without phase noise ((S/N)/sub without{/spl Phi/}/) to SNR with phase noise ((S/N)/sub with{/spl Phi/}/) is used for the performance measure. When the phase noise variances controlled by the PLL closed- loop bandwidth are 0.005, 0.008, and 0.012 respectively, it can be shown that there are about 0.6 dB, 1.0 dB and 1.7 dB power penalties in QPSK scheme and about 1.9 dB, 3.2 dB, and 6.7 dB in 16QAM scheme to meet BER=10/sup -4/ in AWGN channel than OFDM communication system without phase noise. Furthermore, BER performance of QPSK-OFDM communication system is considerably degraded when phase noise variance is bigger than 0.03. Difference between the results of this work and the previous work is shown more obvious if the phase noise variance exceeds 0.02.

Error rate performance of multiple‐symbol differential detection over transmission channels with nonlinear amplification

AbstractWhen efficient power amplification is considered in digital wireless communications, even the nonlinear region of an amplifier is used. In such cases, the symbol error rate deteriorates due to AM‐AM and AM‐PM distortion. This paper studies the spectral expansion, intersymbol interference, and symbol error rate when a nonlinear amplifier is used for transmission in a multivalued amplitude and phase modulation scheme. Multiple‐symbol differential detection using the RLS (Recursive Least Squares) algorithm is compared with coherent detection in order to eliminate the effect of nonlinear amplification and fading. The transmission characteristics when these detection methods are applied to transmission of the star QAM scheme in a white Gaussian noise channel and a Rayleigh fading channel are studied. It is confirmed that multiple‐symbol differential detection provides better symbol error rates than coherent detection. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(3): 1–10, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10183

Adaptive modulation based MC-CDMA systems for 4G wireless consumer applications

Adaptive modulation based MC-CDMA systems can play a vital role in future generation consumer communication electronics. Adaptive modulation, combined with MC-CDMA based transmission technology, is a promising way to increase the data rate that can be reliably transmitted over the wireless radio channels. For 4G wireless networks, which demand very high data rate up to 100 Mbits/s with the constraints limiting higher data rate being severe ISI due to multipath and limited spectrum, such kind of adaptive modulation based multi-carrier systems applied to a wide-area environment, can achieve very large average user throughputs. In this paper, adaptive modulation based M-ary PSK, M-ary QAM, M-ary CPM, M-ary MHPM and GMSK systems applied to a turbo coded MC-CDMA system in a Rayleigh fast fading channel environment have been investigated and the BER performance of all these digital modulation techniques have been compared. Results of the comparative study indicate that the continuous phase modulation schemes like CPM, MHPM, and GMSK gives better performance as compared to PSK and QAM schemes. At most of the time, the MHPM systems outperforms both GMSK and CPM. The PSK and QAM based systems perform well till the number of users are around 10. As a whole, the adaptive MHPM system is found to give the optimum performance among the considered digital modulation schemes for the MC-CDMA system in a 4G environment.

CM-based channel estimators for space-time block-coded M-PSK and M-QAM systems

A constant modulus (CM)-based channel estimation scheme for space-time block-coded M-PSK and M-QAM transmission systems is derived. Exploiting the orthogonal structure of the space-time block coded transmission model, the analytical solutions to minimize the CM cost function are given for 2/sup k/ PSK (k>2) and 2/sup 2k/-QAM schemes, and used to derive the expressions for the CM-based channel estimators. Illustrative results on the performance are presented.

Optimum discrete-power adaptive QAM scheme for Rayleigh fading channels

In this letter, the utilization of a finite number of power levels per constellation in adaptive QAM schemes for flat fading channels is analyzed. Assuming a maximum target BER, the optimum switching thresholds in order to maximize the spectral efficiency are found for Rayleigh fading. Both analysis and simulation results show that a small number of power levels per constellation allows to obtain a good compromise between high spectral efficiency and low feedback information rate.

A noncoherent coded modulation for 16QAM

We present a noncoherent coded 16QAM (NC-16QAM) scheme by modifying the trellis-coded 16QAM (TC-16QAM) scheme. Our simulation results show that the performance of the NC-16QAM with noncoherent detection is close to the one of the original TC-16QAM with coherent detection. The NC-16QAM is an extension of the NC-8PSK previously obtained by Wei and Lin (see IEEE Commun. Lett., vol.2. p.260-62, 1998). A noncoherent initial phase estimation algorithm is also proposed.

Performance analysis and design of pilot-symbol aided TCM for a Rayleigh fading channel

A Chernoff bound is derived on the pairwise error event probability of pilot-symbol aided TCM schemes with L-fold space diversity in a Rayleigh fading channel. In the scheme, pilot-symbols are inserted periodically to estimate the channel characteristics. The fading processes experienced by the pilot-symbols are used to estimate those suffered by the data symbols using interpolation. The estimated fading characteristics are used to compute the symbol metrics of the Viterbi decoder. With the Chernoff bound derived, the cutoff rate of 16QAM and the bit error probability (BEP) of the trellis coded 16QAM scheme are calculated as a function of the signal-to-noise ratio (SNR) and the Doppler shift. New trellis codes are constructed according to the proposed design rule and are shown to result in a performance improvement over the conventional trellis code.

Suboptimum Viterbi algorithm for trellis-coded QAM scheme in multipath Rayleigh fading channels

A new suboptimum Viterbi algorithm for trellis-coded quadrature amplitude modulation based on the channel state information of the multipath Rayleigh fading channel is proposed. Simulation results show that the proposed algorithm has merits for applications that require low bit energy-to-noise ratio.

Multilevel coded 16-QAM schemes for Rayleigh fading channels

Multilevel codes show better performance compared with trellis codes on Rayleigh fading channels at comparable decoder complexity and bandwidth. However, they suffer from performance degradation due to error propagation in the multistage decoder. The authors, with a view to minimising the error propagation, compare three multilevel coded 16-QAM schemes which are four-level codes, I/Q separated two-level codes and I/Q separated two-level codes with a new set partitioning.

A coded 16 QAM scheme for fast fading mobile radio channels

An adaptive Viterbi algorithm, derived from a dynamic estimate of the fading channel is used for the decoding of a convolutional coded 16 QAM system in a mobile environment. The estimates are obtained by a sequence of known pilot symbols embedded in the data stream, and perform compensation for Rayleigh fading. The likelihood criterion in the Viterbi decoder is also modified by these channel estimates through a metric weighting function. We demonstrate through computer simulations, that our new technique achieves a BER improvement of 7-10 dB at P/sub e/=10/sup -3/ in a fast flat Rayleigh fading environment compared to an uncoded system. The BER performance of our new technique in a co-channel interference (CCI) controlled environment is also studied, and the results show that it may achieve a 40% to 85% improvement in capacity over the standard modem scheme for the new US digital cellular system, /spl pi//4-QPSK. >