Serially Concatenated Continuous Phase Modulation Research Articles

Design and Simulation of Bit-interleaved SCCPM with Physical-layer Network Coding

Serially concatenated continuous phase modulation (SCCPM) is bandwidth and power efficient in point-to-point communication systems. The physical-layer network coding (PNC) protocol propsed in 2006 can boost the throughput of a two-way relay channel (TWRC). In this paper, we integrate SCCPM with bit interleavers into PNC, i.e., SCCPM-PNC, which inherits the advantages of the both, in wireless TWRC. The decoding structure of the relay for the superimposed SCCPM signals is designed. Furthermore, the influences of various parameters such as the constraint length of convolutional code (CC), the interleaver size and the number of iterations, on the performance of SCCPM-PNC are simulated and discussed.

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.

Simulation and Performance Analysis of Symbol Interleaved Serially Concatenated Continuous Phase Modulation

Serially concatenated continuous phase modulation (SCCPM) is a kind of constant envelope concatenated coding and modulation scheme with high power and bandwidth efficiency. SCCPM with symbol interleaver is studied in this paper. Compared with traditional bit-wise interleaving scheme, SCCPM with symbol interleaver can get better performance in convergence threshold but higher error floor. The influence of system parameters, such as outer code, interleaver size, and baseband shaping pulse on the performance of SCCPM is studied through simulation and theoretical analysis. The difference between SCCPM with symbol interleaver and bit interleaver is discussed. Finally we present some design principles for SCCPM with symbol-wise interleaving.

Design of serially concatenated continuous phase modulation with symbol-wise interleaving

In this letter we consider serially concatenated continuous phase modulation (SCCPM) schemes with symbolwise interleaving and an additional intra-symbol interleaving. We use extrinsic information transfer (EXIT) chart to optimize the outer code and intra-symbol interleaver. We show that, for various continuous phase modulation (CPM) parameters, the outer code with memory 2 may not always be the best choice. For CPM with modulation index h = 1/2, considerable improvements can be achieved by moderately increasing the outer code memory.

Serially concatenated continuous phase modulation for satellite communications

In this paper, serially concatenated continuous phase modulation (SCCPM) is considered for the uplink of satellite communications. A three-step design procedure is proposed to optimize the association of the outer code and the CPM for a wide range of spectral efficiencies, ranging from 0.75 to 2.25 bit/s/Hz. Firstly, EXIT chart analysis is applied to derive general guidelines for choosing SCCPM parameters. A significant result is that a high-rate outer code is required to achieve good convergence threshold, given a spectral efficiency. At a second stage, union bounds to the error probability are considered to choose the outer code under the constraints arising from the EXIT charts analysis. From this analysis, extended BCH codes and extended Hamming codes are proposed as outer code for broadband and narrowband transmission, respectively. For the latter, double-binary convolutional codes and symbol interleaving is also proposed as a valid alternative. Finally, combining both EXIT charts and union bounds we optimize the association of code and CPM to achieve both low error rates and good convergence. The proposed concatenated structure offers very low error floors and good performance in the waterfall region for all considered spectral efficiencies. A significant improvement with respect to previous concatenated CPM schemes is shown.

A reduced state SISO iterative decoding algorithm for serially concatenated continuous phase modulation

In this paper, serially concatenated continuous phase modulation (SCCPM) system is analyzed and a reduced state soft input soft output (SISO) a posteriori probability algorithm is proposed. Based on the reduced state sequence detection (RSSD), it has the more general form compared with other reduced state SISO algorithms. The proposed algorithm can greatly reduce the state number, thus leads to the computation complexity reduction. It also minimizes the degradation in Euclidean distance with decision feedback in the reduced state trellis. Analysis and simulation results show that the performance degradation is little with proper reduction scheme.

Serially concatenated continuous phase modulation with reduced iterative demodulation and detection

A reduced state Soft Input Soft Output (SISO) a posteriori probability algorithm for Serially Concatenated Continuous Phase Modulation (SCCPM) is proposed in this paper. Based on the Reduced State Sequence Detection (RSSD), it has more general form compared with other reduced state SISO algorithms. The proposed algorithm can greatly reduce the state number, thus leads to the computation complexity reduction. It also minimizes the degradation in Euclidean distance with decision feedback in the reduced state trellis. Analysis and simulation results show that the performance degradation is little with proper reduction scheme.

Serially concatenated continuous phase modulation with convolutional codes over rings

In this paper, we investigate serially concatenated continuous phase modulation (SCCPM) with convolutional codes (CC) over rings. The transmitted signals are disturbed by additive white Gaussian noise. The properties for systems with both infinite and finite block lengths are investigated. For an infinite-length system, we check the convergence threshold using the extrinsic information transfer chart. For a finite-length system, we use union-bound techniques to estimate the error floors. In the union-bound analysis, we consider both the order and the position of nonzero permuted symbols. A simple method for determining a CPM error event through the sum of the input symbol sequence is shown. Thus, we can determine if the output symbol sequence of an error event in the ring CC can form an error event in CPM. Two properties concerning the interleaver gain (IG) are investigated. A recursive search algorithm for the maximal IG is shown. Compared with previous SCCPM with a binary CC, the proposed system shows an improvement concerning the convergence threshold or error floors

Innovations-based MAP estimation with application to phase synchronization for serially concatenated CPM

A novel adaptive soft-input soft-output (A-SISO) module is developed for maximum a posteriori (MAP) symbol detection with parameter uncertainty. In contrast to the existing A-SISO algorithms that use linear prediction, the parameter estimation in the proposed structure is operated in a more general least-squares sense. Based on this scheme, a family of fixed-interval A-SISO (FI-A-SISO) algorithms is utilized to implement blind iterative phase synchronization for serially concatenated continuous phase modulation (SCCPM). For SCCPM systems, the forward-only FI-A-SISO algorithms are shown to be much more robust than the forward-backward FI-A-SISO algorithms in acquiring and tracking a time-varying carrier phase. The reason has to do with rotational invariance of CPM signals. This result can be extended to any rotationally invariant convolutional coded system with an unknown carrier phase.

Irregular repeat continuous phase modulation

We propose combining irregular repeat accumulate (IRA) codes with continuous phase modulation (CPM) and call this irregular repeat CPM (IRCPM). In this scheme, CPM is used as the accumulator of IRA codes to explore its built-in phase accumulate property. A property of the degree-1 check node (doping node) ratio is investigated. We use the EXIT chart/function method to optimize the degree profile. We also provide the EXIT function for CPM when the SNR (Signal-to-noise ratio) is fixed. Numerical results show that this scheme converges up to 0.49 dB earlier (lower SNR) than the best found serially concatenated CPM (SCCPM).

Multiuser SCCPM with iterative decoding

The recent technique of serially concatenated continuous phase modulation (SCCPM) is extended to a multiuser system with a carrier frequency offset between the users. Simulation results for up to five users with an iterative decoder show that the performance loss is small considering the substantial spectral overlap. Consequently, power/bandwidth efficiencies which are better than for SCCPM are achievable.