Cooperative coding using serial concatenated convolutional codes

We compare the asymptotic performance of parallel concatenated codes (PCCs) and serial concatenated codes (SCCs) over GF(4). We construct such codes using optimal nonbinary convolutional codes where optimality is in the sense of achieving the largest minimum distance for a fixed number of encoder states. Code rates of the form K/sub 0//(K/sub 0/ + 1) for K/sub 0/ = 1, 8, and 64 are considered. For all of these code rates, we find the minimum distance and its multiplicity for both concatenated code systems. This is accomplished by feeding the encoder with all possible weight-two and weight-three input information patterns and monitoring, at the output of the encoder, the weight of the corresponding codewords and their multiplicity. Our analytical results indicate that the SCC codes outperform their counterpart PCC codes with much lower complexity.

In this paper, we focus on the design of optimized binary convolutional codes (CCs) and serially concatenated convolutional codes (SCCCs) in the presence of a-priori information (API) at the receiver. For large signal-to-noise ratios (SNRs), we first propose a CC design criterion based on the minimization of a union bound on the bit error probability (BEP). In this case, relevant performance gains, with respect to previously proposed CCs, are obtained. These gains persist even in the presence of estimation errors on the API. Then, we apply the same union bound-based design criterion to SCCCs. Since the BEP of SCCCs is characterized by a typical waterfall shape, the proposed union bound-based design criterion is accurate only at large SNR, to estimate the BEP floor. In order to complement this analysis, we propose a density evolution-based approach to optimize the SCCC design in terms of minimization of the SNR of the knee of the BEP curve. The obtained simulation results show substantial gains with respect to previously proposed parallel concatenated convolutional coding (PCCCing) schemes optimized under the assumption of no API at the decoder. Moreover, in the presence of strong API the proposed SCCCs allow to approach the Shannon limit (SL) more than any previously proposed turbo coding scheme.

When channel state information (CSI) is not available, unitary space-time symbol-based parallel concatenated convolutional code (UST-SB-PCCC) can give a good performance and remain an acceptable calculation complexity, however it also meet with the error floor phenomenon. We propose a scheme utilizing UST-SB serial concatenated convolutional code (SCCC) for multiple-antenna wireless communication systems over rapid fading channels which can avoid the error floor. We also give the corresponding multi-ary MAP decoding algorithm for both the systematic and the parity symbols. With iterative decoding and/or multi-antennas, it can further improve the system performance, which helps to give an acceptable bit error rate (BER).

We give an overview of iterative techniques for bit‐interleaved coded modulation. We start with simple methods where a convolutional code is concatenated with a standard QAM modulation scheme. The mapping is carefully chosen different from Gray mapping such that significant gains can be obtained by an iterative (turbo) receiver. The idea can also be applied to transmit antenna diversity as well as spatial multiplexing (MIMO). We then consider various powerful iterative coding schemes which are under discussion in standardisation for wireless systems beyond 3G such as serial or parallel concatenated convolutional codes, repeat accumulate codes and LDPC codes. We give a comparison in terms of complexity and performance.The main intention is to provide an illustrative overview over relevant applications of the turbo principle in demodulation and decoding. It is a summary of results which have been obtained in collaboration between the Institute of Communications Engineering, TUM and DoCoMo Euro‐Labs. Copyright © 2007 John Wiley & Sons, Ltd.

Concatenation is a method of building long codes out of shorter ones, it attempts to meet the problem of decoding complexity by breaking the required computation into manageable segments. Concatenated Continuous Phase Frequency Shift Keying (CPFSK) facilitates powerful error correction. CPFSK also has the advantage of being bandwidth efficient and compatible with non-linear amplifiers. Bandwidth efficient concatenated coded modulation schemes were designed for communication over Additive White Gaussian noise (AWGN), and Rayleigh fading channels. An analytical bounds on the performance of serial concatenated convolutional codes (SCCC), and parallel concatenated convolutionalcodes (PCCC), were derived as a base of comparison with the third category known as hybrid concatenated trellis codes scheme (HCTC). An upper bound to the average maximum-likelihood bit error probability of the three schemes were obtained. Design rules for the parallel, outer, and inner codes that maximize the interleaver's gain were discussed. Finally, a low complexity iterative decoding algorithm that yields a better performance is proposed.

The paper proposes an analytical method to solve the rate allocation problem in serial concatenated convolutional codes (SCCCs). The goal is to find the best rate allocation between the inner and the outer constituent convolutional codes of an SCCC for constant overall code rate, interleaver size and complexity. Simulation results are shown in the paper to demonstrate the optimum and superior design criteria. In addition, the ‘density evolution’ model is shown to verify the proposed rate allocation method, while indicating that a high rate inner code should not be used for SCCCs. Finally, it is also shown that the upper bounds on BER of ML decoded SCCCs do not provide good design criteria for allocating the rate in iteratively decoded SCCCs.

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This paper addresses the design of semi-random, prunable interleavers for parallel concatenated convolutional codes (PCCC). The proposed technique is iterative and is based on the growth of a smaller interleaver up to the desired length N. The optimization is achieved via a minimization using a cost-function strictly related to both the correlation properties of the extrinsic information and the concept of spread of an interleaver. Performance of the designed interleavers are given in terms of bit error rate (BER) and frame error rate (FER). Comparisons are given with respect to other prunable and ad-hoc interleaver design techniques already proposed in literature. The designed interleavers are prunable and have a behavior very similar to the interleavers designed with techniques which maximize the spread of the permutation

The energy efficient design of coded automatic-repeat-request (ARQ) systems is studied in this paper. The optimization aims to minimize the energy required for the successfully delivery of one information bit from a transmitter to a receiver. The design is performed by incorporating a wide range of practical system parameters and metrics, such as hardware power consumption, modulation, channel coding, and frame error rate (FER) in the physical layer, and frame length and protocol overhead in the media access control layer. A new log-domain threshold approximation method is proposed to analytically quantify the impacts of the various system parameters on the FER, and the results are used to facilitate the system design. The optimum transmission energy and frame length that minimize the energy per information bit are identified in closed-form expressions as functions of the various practical system parameters. The analytical and simulation results demonstrate that the total energy consumption in a coded ARQ system can be reduced by increasing the transmission energy during one transmission attempt, and significant energy saving as high as 9.5 dB is achieved with the optimum system.

In this letter, we propose and compare some new rate-compatible serially concatenated convolutional code (SCCC) families. To obtain them, inner coded bits only are punctured. However, and this is the novelty proposed in the letter, the puncturing is not limited to inner parity bits, but extended also to inner systematic bits, thus obtaining high rate SCCCs (i.e., beyond the outer code rate). The two main applications of this technique are its use in hybrid Automatic-Repeat-reQuest/Forward-Error Correction (ARQ/FEC) schemes and to achieve unequal error protection (UEP) of an information sequence.

Wireless systems based on WLAN (802.11), ZigBee (802.15.4) and Bluetooth (802.15.1) are continuously deployed in new applications covering consumer, industry or medical fields. Especially, Bluetooth is recommended by the Health-Care-Organization for medical applications as frequency hopping is considered as a robust scheme. However dealing with frequency-dynamic sources of interference in the 2.4GHz ISM band is important due to the increase of wireless devices. Adaptive frequency hopping (AFH) suggested by the Bluetooth standard and implemented in many of todays products identifies and avoids using bad channels. It is a good and established coexistence mechanism in the presence of frequency-static sources of interference such as WLANs when the 2.4GHz band is not crowded. However, AFH is facing problems in a crowded 2.4GHz band, especially when the interference is dynamic. We developed a cross-layer algorithm SAFH (Smooth Adaptive Frequency Hopping) that is inspired by entropy maximization and the conventional Bluetooth AFH. SAFH assigns usage probabilities to all channels based on an exponential smoothing filter for frame error rates to estimate and predict the channel conditions. The application layer can adapt SAFH by parameter settings in a cross-layer approach. SAFH achieves low average frame error rate and responds fast to changing channel conditions if required from the application. Simulative Evaluation in the presence of different types of interference (802.11b, 802.15.4 and 802.15.1) shows that our algorithm outperforms conventional frequency hopping and AFH. Additionally, SAFH works smoothly and stable exploiting frequency diversity compared to previous approaches like entropy-maximization based adaptive frequency hopping and Utility Based Adaptive Frequency Hopping (UBAFH).

In wireless sensor networks, fault-tolerant and energy efficiency are two important topics. Some link failures may happen during data transmission. In this paper, we propose a fault-tolerant and energy efficient multipath-routing (FEEM) scheme aided with channel coding and interleaver, which is a cross-layer design approach. For multipath selection, we propose an energy and mobility-aware geographical multipath routing (EM-GMR) scheme, which is based on fuzzy logic system considering the remaining battery capacity, mobility, and distance to the destination node. Simulation results show that our EM-GMR scheme can extend the network lifetime longer than the original geographical routing scheme which only considers distance to the destination location, and this scheme can reduce the frame loss rate and link failure rate since mobility is considered. We demonstrate that even if certain paths have failures, our FEEM scheme is still able to recover the transmitted message from failure with very low bit error rate and frame error rate

Recently, low-density parity-check (LDPC) codes have attracted much attention especially in mobile communication system as a good simple error correcting codes achieving the data throughput near Shannon limit with lower complexity. In this paper, we design some regular LDPC codes with very low bit error rate (BER) and frame error rate (FER) according to the downlink parameters in TD-SCDMA system. We construct the downlink physical layer emulation model with matlab according to TD-SCDMA system's baseband signal disposing flow chart, and execute the link simulation with the performance analysis for some available channel codes and the designed regular LDPC codes based on the proposed emulation model. Passing the simulation, we obtain some conclusions that the regular LDPC codes are better than the convolutional codes or turbo codes in error rate performance.

We propose an incremental redundancy (IR) cooperative coding scheme employing punctured turbo codes for quasi-static wireless networks. Our scheme enhances the network performance by embedding IR cooperative coding into an existing noncooperative route. More precisely, for each of the noncooperative hops, we consider the following cooperation strategy: we form collaborating cluster of M nodes consisting cf the (hop) sender and its M-1 neighbors. A decode-and-forward algorithm within the cluster enables the IR turbo coding scheme. The approach improves the reliability of multihop routing by employing a powerful coding scheme to enable cooperative diversity. We study its frame-error rate (FER) performance for quasi-static Rayleigh-fading channels based on the threshold behavior of turbo codes. A FER upper bound on the maximum-likelihood decoding and its asymptotic version are derived as a function of channel SNRs and the mother code noise threshold. Simulation results show that our bounds are very good predictors of the proposed scheme performance.

The paper considers the application of forward error correction (FEC) and automatic repeat request (ARQ) schemes over correlated wireless channels. In particular, the depth of the interleaver and its influence on the frame-error-rate and transmission delay in the presence of correlated fading and delay constraints is investigated. It is found that an increased interleaver depth in a correlated channel, although improving the bit-error-rate, does not always improve the frame-error-rate (FER). Further, it is shown that, in the case of bursty channels, a large interleaver depth is required to improve the FER, thus negatively influencing the delay. In this case, the use of a retransmission scheme can improve delay performance.