Coded Continuous Phase Modulation Research Articles

Improving Spectral Efficiency of Non-Orthogonal Space Time Block Coded-Continuous Phase Modulation

Improving Spectral Efficiency of Non-Orthogonal Space Time Block Coded-Continuous Phase Modulation

Lower bounds on the symbol error probability for ring convolutional coded continuous phase modulation

Lower bounds on the symbol error probability for coded continuous phase modulation (CPM) with maximum likelihood sequence detection are investigated. The ring convolutional coded CPM schemes are considered when the channel encoder and the inherent encoder of CPM are over the same ring. The lower bounds are obtained by using a detector with uniform side information when the entire set of transmitted data sequences for every state are considered. The procedure for obtaining the bounds are given, and some numerical and simulation results are shown. From numerical comparisons, this method ensures the lower bounds to be appropriate when comparing to the method only considering one state. And the lower bounds are improved than only considering transmitted data sequences with the worst error event.

Non-orthogonal Amplify and Forward Relay Selection Systems with Distributed Space–Time Trellis Coded Continuous Phase Modulation

Most of the works on cooperative systems with or without relay selection have focused on linear modulations such as phase shift keying and quadrature amplitude modulation. Whereas, continuous phase modulation (CPM) is a good alternative to these modulations due to its constant envelope property which enables us to use inexpensive and energy-efficient non-linear power amplifiers. In the literature, a few works are based on relaying systems with CPM. To the best of our knowledge, none exists with relay selection. In this paper, we propose single and multiple relay selection CPM schemes based on a new generalized relay selection criterion for non-orthogonal amplify and forward (AF) systems operating with various time sharing protocols. In particular, using the proposed criterion, the best relay or the best two relays over a set of four available relays is/are selected. Error performances of the non-orthogonal AF relay selection systems and their counterparts are compared over frequency non-selective quasi-static Rayleigh fading channels using Viterbi algorithm at the destination terminal. Our numerical results present superiority of the proposed non-orthogonal relay selection systems.

Iterative data detection and channel estimation for space‐time block coded continuous phase modulation over flat fading channels

The problem of iterative data detection and channel estimation for space-time block coded continuous phase modulation (CPM) signals over quasi-static flat fading channels is studied in this study. Firstly, the combination of space-time block code with CPM is not as straightforward as with linear modulation schemes, because of the requirement of phase continuity and the associated inherent memory of CPM. Therefore a novel block construction method is proposed to insert a tail sequence into each block for ensuring the phase continuity. Secondly, at the receiver the expectation–maximisation algorithm is applied to channel estimation and the estimated channel information is used to evaluate a posteriori probability for data detection. The channel estimation and data detection work iteratively. Simulation results show that the spectral efficiency of transmission is improved by the proposed block construction method and that the proposed iterative receiver outperforms its non-iterative counterpart significantly.

Variable-Rate Ring Convolutional Coded Continuous Phase Modulation Using Puncturing

AbstractIn this paper, puncturing technique is used to establish variable-rate ring convolutional coded continuous phase modulation (CPM) systems. Maximum likelihood sequence detectors over both AWGN channels and Rayleigh flat-fading channels are considered. The suggested system provides us with different rates and performance when simple adjustment is taken to the puncturing matrix. Since the performance of the first error event of this system is represented by normalized minimum squared Euclidean distance (NMSED), some typical codes with maximum NMSED are searched and given. The performance of symbol error rate for the suggested system is simulated using computer software, and the results show that this system provides good performance of symbol error rate with variable-rate capabilities in time varying channels. Furthermore, simulation results also prove that the transmission efficiency increases when code rate is decreasing.

The Study of Coded CPM Schemes

Continuous Phase Modulation (CPM) schemes belong to a class of constant-envelope digital modulation schemes, the constant-envelope nature of the CPM signals makes them robust for the nonlinear and fading channels, and very useful for the satellite and/or the mobile radio channels. Comparing to PSK modulation, CPM modulation can not only provide spectral economy, but also exhibit a “coding gain”. CPM can be decomposed into a Continuous Phase Encoder (CPE) followed by a Memoryless Modulator (MM), this allows many new coded modulation schemes of combination of convolutional encoder and CPM modulator to be possible, such as serially-concatenated CPM (SC-CPM), SC-CPM with Convolutional Codes over Rings, pragmatic CPM (P-CPM), Concatenation of convolutional endocder and extended CE（CCEC）, etc. Some simulations show that these new CPM schemes can offer superior performance.

Rate-Compatible Punctured Ring Convolutional Coded Continuous Phase Modulation

In this paper, continuous phase modulation (CPM) with rate-compatible punctured ring convolutional codes is investigated. Some typical schemes with maximum normalized minimum squared euclidean distance (NMSED) are searched and given. The performance of bit error rate for rate-compatible punctured ring convolutional coded CPM on AWGN channel is simulated, and simulation results show that this system can provide good performance of bit error rate and variable-rate capabilities. Furthermore, simulation results also prove that the transmission efficiency increases when code rate is decreasing.

Receiver algorithm for coded multiuser CPM systems

The performance of multiuser systems employing coded continuous- phase modulation (CPM) in frequency-division multiplexed (FDM) uplink satellite communications is investigated. The spectral efficiency is improved reducing the inter-carrier frequency spacing. Since severe inter-channel interference (ICI) occurs in such cases, a simple iterative ICI cancellation algorithm is applied in conjunction with a bank of single-user (SU) receivers to perform demodulation and decoding. When modulation and coding parameters are suitably chosen, such a receiver achieves a performance close to the non-interfering multiuser case. ICI causes further degradation since the SU receivers are not perfectly matched to the received signal model. Moreover, the SU receivers require a perfect knowledge of the channel state information (CSI) in order to perform optimal demodulation in additive white Gaussian noise. To reduce the degradation caused by ICI, a new heuristic method for estimating the optimal CSI values to provide to the SU receiver is proposed. The proposed method is based on an approximation of the CSI vector provided to each SU receiver. Such a method proves useful since it leads to significant performance improvements of the considered schemes and exhibits a negligible complexity.

Analytical upper bounds for convolutional coded CPM over rings

Analytical upper bounds on symbol error probability for ring convolutional coded Continuous Phase Modulation (CPM) with maximum likelihood sequence detection (MLSD) are presented. The constructed bounds for the investigated systems are shown to be asymptotically tight for increasing channel signal-to-noise ratio (SNR) values. This work provides an analysis tool for the investigated systems. The analysis method is very general. It may be applied to any trellis based coding schemes.

Double Turbo Equalization of Continuous Phase Modulation with Frequency Domain Processing

In this paper, a doubly-iterative linear receiver, equipped with a soft-information aided frequency domain minimum mean-squared error (MMSE) equalizer, is proposed for the combined equalization and decoding of coded continuous phase modulation (CPM) signals over long multipath fading channels. In the proposed receiver architecture, the front-end frequency domain equalizer (FDE) is followed by the soft-input, softoutput (SISO) CPM demodulator and channel decoder modules. The receiver employs double turbo processing by performing back-end demodulation/decoding iterations per each equalization iteration to improve the a priori information for the front-end FDE. As presented by the computational complexity analysis and simulations, this process provides not only a significant reduction in the overall computational complexity, but also a performance improvement over the previously proposed iterative and noniterative MMSE receivers.

Capacity-Achieving CPM Schemes

The pragmatic approach to coded continuous-phase modulation (CPM) is proposed as a capacity-achieving low-complexity alternative to the serially-concatenated CPM (SC-CPM) coding scheme. In this paper, we first perform a selection of the best spectrally-efficient CPM modulations to be embedded into SC-CPM schemes. Then, we consider the pragmatic capacity (a.k.a. BICM capacity) of CPM modulations and optimize it through a careful design of the mapping between input bits and CPM waveforms. The so obtained schemes are cascaded with an outer serially-concatenated convolutional code to form a pragmatic coded-modulation system. The resulting schemes exhibit performance very close to the CPM capacity without requiring iterations between the outer decoder and the CPM demodulator. As a result, the receiver exhibits reduced complexity and increased flexibility due to the separation of the demodulation and decoding functions.

Joint Source and Channel Coding using Punctured Ring Convolutional Coded CPM

In this paper, a novel trellis source encoding scheme based on punctured ring convolutional codes is presented. Joint source and channel coding (JSCC) using trellis coded continuous phase modulation (CPM) with punctured convolutional codes over rings is investigated. The channels considered are the additive white gaussian noise (AWGN) channel and the Rayleigh fading channel. Optimal soft decoding for the proposed JSCC scheme is studied. The soft decoder is based on the a posteriori probability (APP) algorithm for trellis coded CPM with punctured ring convolutional codes. It is shown that these systems with soft decoding outperform the same systems with hard decoding especially when the systems operate at low to medium signal-to-noise ratio (SNR). Furthermore, adaptive JSCC approaches based on the proposed source coding scheme are investigated. Compared with JSCC schemes with fixed source coding rates, the proposed adaptive approaches can achieve much better performance in the high SNR region. The novelties of this work are the development of a trellis source encoding method based on punctured ring convolutional codes, the use of a soft decoder, the APP algorithm for the combined systems and the adaptive approaches to the JSCC problem.

Capacity-Based Parameter Optimization of Bit-Interleaved Coded CPM With Differential Detection

The design of bit-interleaved coded continuous phase modulation (CPM) is characterized by the code rate, alphabet size, modulation index, and pulse shape. This paper outlines a methodology for determining the optimal values of these parameters under bandwidth and receiver complexity constraints. The cost function that is used to drive the optimization is the information theoretic minimum epsiv <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> , which is found by evaluating the constrained channel capacity. The capacity can be estimated using Monte Carlo integration. A search for optimal parameters is conducted over a range of coded CPM parameters, bandwidth efficiencies, and channels. To limit complexity and allow any modulation index to be considered, the receiver is constrained to use a soft-output differential phase detector. Bit error rate curves using a binary turbo code confirm that the constrained capacity is a very good indicator of the performance of the complete system.

On Joint Source and Channel Coding Using Trellis Coded CPM: Analytical Bounds on the Channel Distortion

Joint source and channel coding (JSCC) using trellis coded quantization (TCQ) in conjunction with trellis coded continuous phase modulation (CPM) is studied. The channel is assumed to be the additive white gaussian noise (AWGN) channel. Analytical bounds on the channel distortion for the investigated systems with maximum-likelihood sequence detection (MLSD) are developed. The bounds are based on the transfer function technique, which was modified and generalized to include continuous-amplitude discrete-time signals. For a memoryless uniform source, the constructed bounds for the investigated systems are shown to be asymptotically tight for increasing channel signal-to-noise ratio (SNR) values. For a memoryless nonuniform source, the constructed bounds are not as tight as the one for the uniform source, however, it still can be used as an indication to how the system performs. It is concluded that the minimum Euclidean distance of the system alone is not enough to evaluate the performance of the considered systems. The number of error events having minimum Euclidean distance and the total distortion caused by those error events also affect the asymptotic performance. This work provides an analysis tool for the investigated systems. The analysis method is very general. It may be applied to any trellis based JSCC schemes.

An improved algorithm for evaluating trellis phase codes (Corresp.)

A method is described for evaluating the minimum distance parameters of trellis-phase codes, including continuous phase frequency shift keying (CPFSK), partial-response FM, and, more importantly, coded continuous-phase modulation (CPM) schemes. The algorithm provides dramatically faster execution times and smaller memory requirements than previous algorithms. Results of sample calculations and timing comparisons are included.