Trellis Coded Modulation Schemes Using A New Expanded 16-Dimensional Constant Envelope Quadrature-Quadrature Phase Shift Keying Constellation

In this thesis, the author presents and analyzes two 4-dimensional Constant Envelope Quadrature-Quadrature Phase Shift Keying constellations. Optimal demodulators for the two constellations are presented, and one of them was designed and implemented by the author. In addition, a novel expanded 16-dimensional CEQ2PSK constellation that doubles the number of points without decreasing the distance between points or increasing the peak energy is generated by concatenating the aforementioned constellations with a particular method and restrictions. This original 16-dimensional set of symbols is set-partitioned and used in a multidimensional Trellis-Coded Modulation scheme along with a convolutional encoder of rate 2/3. Effective gain of 2.67 dB over uncoded CEQ2PSK constellation with low complexity is achieved theoretically. A coding gain of 2.4 dB with 8 dB SNR is obtained by using Monte Carlo simulations. The TCM systems and demodulators were tested under an Additive White Gaussian Noise channel by using Matlab\u27s Simulink block diagrams

Trellis Coded Modulation Schemes Using A New Expanded 16-Dimensional Constant Envelope Quadrature-Quadrature Phase Shift Keying Constellation

In this thesis, the author presents and analyzes two 4-dimensional Constant Envelope Quadrature-Quadrature Phase Shift Keying constellations. Optimal demodulators for the two constellations are presented, and one of them was designed and implemented by the author. In addition, a novel expanded 16-dimensional CEQ2PSK constellation that doubles the number of points without decreasing the distance between points or increasing the peak energy is generated by concatenating the aforementioned constellations with a particular method and restrictions. This original 16-dimensional set of symbols is set-partitioned and used in a multidimensional Trellis-Coded Modulation scheme along with a convolutional encoder of rate 2/3. Effective gain of 2.67 dB over uncoded CEQ2PSK constellation with low complexity is achieved theoretically. A coding gain of 2.4 dB with 8 dB SNR is obtained by using Monte Carlo simulations. The TCM systems and demodulators were tested under an Additive White Gaussian Noise channel by using Matlab\u27s Simulink block diagrams

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

A Novel Expanded 16-Dimensional Constant Envelope Q2PSK Constellation

We introduce a 16-dimensional constant-amplitude constellation that is generated by concatenating either four constant envelope quadrature-quadrature phase shift keying (CEQ2PSK) symbols from Saha and Birdsall or four CEQ2PSK symbols recently discovered by Cartwright and also introduced here. Our new constellation doubles the number of points available for data transmission without decreasing the distance between points or increasing energy, and may therefore be used in a trellis coded modulation (TCM) system without constellation expansion penalty. Because the new constellation has constant envelope, the modulation scheme becomes very attractive for nonlinear channels such as the magnetic recording channel or the satellite channel with traveling wave tube amplifiers

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

Visualization of 4D Q2PSK and CE Q2PSK in Ideal Bandlimited Channels

This paper presents new visualization techniques for 4D Quadrature-Quadrature Phase Shift Keying (Q2PSK), Saha’s Constant Envelope (CE) Q2PSK, and Cartwright’s CEQ2PSK in ideal bandlimited channels. The signal diagrams analyzed are: time-signal eye patterns for 4D passband signals, 2D complex trajectory diagrams of baseband signals, and time-signal eye patterns for the 1D outputs of the baseband matched filter. These methods may be applied to other multidimensional modulation systems to obtain insight into the effects of noise, interference, and channel filtering

A time spread diversity technique with integrated coding and interference cancellation

Conventional signal diversity techniques increase system complexity and/or result in an increase in the required signal bandwidth. A novel Time Spread (TS) diversity technique has been proposed in [1] aimed at improving the performance of digital communication systems in flat-fading channels without increasing their complexity or bandwidth usage. With TS, time diversity is obtained by transmitting a modulated spreading sequence, spanning over a temporal period longer than the channel coherence time Tc, for each information symbol. Unfortunately, this TS technique exhibits a Bit Error Rate (BER) performance floor at higher SNR values that renders the original technique less attractive. This dissertation is primarily concerned with the nullification of this BER performance floor. Sec¬ondly, the ability of the TS technique to transform a flat-fading channel into an Additive White Gaus¬sian Noise (AWGN) channel is investigated and exploited to enhance the performance of coding techniques designed for AWGN channels, when used in flat-fading channels. A new method is described by which TS sequences can be temporally expanded, thereby increas¬ing their obtainable time diversity gains. This method also reduces the computational complexity of a TS system, while retaining the signal diversity properties of a longer non-expanded sequence. The BER floor in TS systems is caused by the distortion of the Aperiodic Auto-Correlation (AAC) properties of overlapping spreading sequences in fading channels, resulting in Inter Code(Sequence) Interference (ICI) between spreading sequences. A Pilot Symbol Aided Modulation (PSAM) tech¬nique is adapted for the TS system to provide accurate channel estimates required by the Inter Code(Sequence) Interference Cancellation (lCIC) module. A hybrid ICIC technique, which corrects the fading TS symbol amplitudes during periods of above average instantaneous SNR levels, is shown to be the most effective. This ICIC technique enables the TS technique to provide gains similar to that of conventional third order diversity techniques at average Eb/ No ratios above 10 dB. Finally, the transparency and ability of the TS technique to transform fading channels into Gaus¬sian channels are exploited to allow the integration of conventional convolutional codes with the TS system. The coded TS system achieves substantial gains when operating in a Rayleigh flat-fading channel when a soft decision Viterbi decoder is used in the TS receiver. A strategy by which Turbo Code (TC) techniques can be integrated with the TS technique is discussed as a concluding notion to illustrate the flexibility of the TS technique. Future research areas are identified based on the findings of this dissertation. These include the investigation of more effective adaptive ICIC schemes and the possibility of using Code Division Multiple Access (CDMA) communication techniques over a narrow band channel by employing TS- and Multi-User (MU)-detection methods, combined with existing ICIC techniques. The cryptographic value of the TS technique also provides ground for future research.Dissertation (MEng (Electronic Engineering))--University of Pretoria, 2006.Electrical, Electronic and Computer Engineeringunrestricte