An Energy Efficient QAM Modulation with Multidimensional Signal Constellation

Packing constellations points in higher dimensions, the concept of multidimensional modulation exploits the idea drawn from geometry for searching dense sphere packings in a given dimension, utilising it to minimise the average energy of the underlying constellations. The following work analyses the impactof spherical shaping of the constellations bound instead of the traditional, hyper-cubical bound. Balanced constellation schemes are obtained with the N -dimensional simplex merging algorithm. The performance of constellations of dimensions 2, 4 and 6 is compared to the performance of QAM modulations of equivalent throughputs in the sense of bits transmitted per complex (two- dimensional) symbols. The considered constellations give an approximately 0.7 dB to 1 dB gain in terms of BER over a standard QAM modulation

Performance and Spectral Analysis of Q2PSK and CE Q2PSK Systems in Ideal Bandlimited Channels

The authors present theoretical performance analysis and simulation results for Quadrature-Quadrature Phase Shift Keying (Q2PSK), Constant Envelope (CE) Q2PSK, and trelliscoded 16D CEQ2PSK in ideal bandlimited channels of various bandwidths. The performance of receivers with and without channel estimation is reported. Spectral analysis is presented for each system, in addition to MSK and expanded uncoded 16D CEQ2PSK. We show that the effects of bandlimiting are most severe for Q2PSK. Knowledge of the channel information aids 4D CEQ2PSK the least. Only 6.8 dB of SNR is needed for the TCM system for a bit error rate of 10−5 for the narrowest channel bandwidth studied here, if the receiver has knowledge of the channel

Design and Software Validation of Coded Communication Schemes using Multidimensional Signal Sets without Constellation Expansion Penalty in Band-Limited Gaussian and Fading Channels

It has been well reported that the use of multidimensional constellation signals can help to reduce the bit error rate in Additive Gaussian channels by using the hyperspace geometry more efficiently. Similarly, in fading channels, dimensionality provides an inherent signal space diversity (distinct components between two constellations points), so the amplitude degradation of the signal are combated significantly better. Moreover, the set of n-dimensional signals also provides great compatibility with various Trellis Coded modulation schemes: N-dimensional signaling joined with a convolutional encoder uses fewer redundant bits for each 2D signaling interval, and increases intra-subset minimum squared Euclidean distance (MSED) to approach the ultimate capacity limit predicted by Shannon\u27s theory. The multidimensional signals perform better for the same complexity than two-dimensional schemes. The inherent constellation expansion penalty factor paid for using classical mapping structures can be decreased by enlarging the constellation\u27s dimension. In this thesis, a multidimensional signal set construction paradigm that completely avoids the constellation expansion penalty is used in Band-limited channels and in fading channels. As such, theoretical work on performance analysis and computer simulations for Quadrature-Quadrature Phase Shift Keying (Q2PSK), Constant Envelope (CE) Q2PSK, and trellis-coded 16D CEQ2PSK in ideal band-limited channels of various bandwidths is presented along with a novel discussion on visualization techniques for 4D Quadrature-Quadrature Phase Shift Keying (Q2PSK), Saha\u27s Constant Envelope (CE) Q2PSK, and Cartwright\u27s CEQ2PSK in ideal band-limited channels. Furthermore, a metric designed to be used in fading channels, with Hamming Distance (HD) as a primary concern and Euclidean distance (ED) as secondary is also introduced. Simulation results show that the 16D TCM CEQ2PSK system performs well in channels with AWGN and fading, even with the simplest convolutional encoder tested; achievable coding gains using 16-D CEQ2PSK Expanded TCM schemes under various conditions are finally reported

Wavelet based design of digital multichannel communications systems

The huge penetration of the personal communications systems in the market is constantly presenting new challenges to the research, aimed at satisfying people's needs and requirements for effective communication systems. At present, the cellular telephone network is perhaps the most evident example of communication system that has had a great impact on the lives of ordinary people and, at the same time, is the subject of interest of many researchers both at academic and industrial level. For the future, one of the main challenges in telecommunications will be the provision of ubiquitous broadband tetherless integrated services to mobile users. Such a pretentious goal cannot be achieved without a continuous research facing such problems as service quality, complete mobility support, and affordable complexity that are still open problems. However, present telecommunication problems are not only a matter of implementation or development of new services, exploiting a totally assessed doctrine. In order to respond to the mobility of the users personal communication systems have to deal with the wireless communication channel whereby mobility and non-stationarity of the propagation conditions require a stochastic description of the channel parameters. While this fact can be viewed as strong limitation to the development of a solid theory whose validity can be assesed in practice, on the other hand allows for an investigation and study of novel communication schemes, sometimes encompassing basic aspects of digital communications. This thesis, is the result of a research work that has investigated one of the basic building block of every communication systems, the modulation scheme, and the design of the pulse shape carrying the digital information. We have studied the design of multichannel communication scheme exploiting the mathematical theory of wavelets. Such a theory, developed recently, has had a great impact in many fields of engineering and of other scientific disciplines. In particular, wavelet theory has become very popular in the signal processing area; in fact it is a flexible toolbox for signal analysis allowing effective representation of signals for features extraction purposes. The main features that make wavelet waveforms suitable to be used as shaping pulses for modulation are their substantial compact support both in the time and frequency domains, and the fact that they are ISI-free pulses over frequency flat channels. The study presented in this thesis is focused on application of wavelet theory to design high-efficiency multichannel communication schemes and to the performance evaluation over linear and non-linear channels. We present a general method to design wavelet based multichannel communication schemes that we denoted Wavelet Orthogonal Frequency Division Multiplexing (WOFDM). We show that such schemes, having a largerspectral efficiency for a small number of channels, are a valid alternative to the classical OFDM. Potential advantage of wavelet modulation are shown presenting other applications examined in this thesis: a joint use of WOFDM and Trellis Coded Modulation to shape the power spectrum in order to match a frequency selective channel and minimize distortion, and application to spread spectrum modulation. Particular attention has been devoted to the timing recovery problem in multichannel communication schemes, exploiting the timing information of the different subchannels to improve the error variance in estimation of the sampling instant leading to a reduction of the adjacent channels interferenc