Design of interleavers for turbo codes: iterative interleavergrowth algorithms of polynomial complexity

This paper addresses the problem of designing interleavers for parallel concatenated convolutional codes (PCCCs) tailored to specific constituent codes. We start by establishing the role of the interleaver in the PCCC and the various parameters that influence the performance of the PCCC with a given interleaver. Subsequently, we define a canonical form of the interleaving engine denoted as the finite-state permuter (FSP) and demonstrate the minimal delay property of this canonical form. For any given permutation, we present a procedure for deriving the canonical FSP engine. We address the issue of implementation of the FSP and propose a very simple structure for the FSP. Next, using the structural property of the FSP engine, we develop a systematic iterative technique for construction of interleavers with a complexity that is polynomial in the interleaver size. Subsequently, we develop a cost function that, coupled with the iterative interleaver growth procedure, can be used to design optimized interleavers for PCCCs. We provide examples of application of the interleaver design technique, and compare the designed interleavers with some of the interleavers of comparable size found in the literature     

Optimized prunable single-cycle interleavers for turbo codes

This paper is aimed at the problem of designing optimized interleavers for parallel concatenated convolutional codes (PCCC) that satisfy several requirements simultaneously: 1) designing interleavers tailored to the constituent codes of the PCCC; 2) improving the distance spectra of the resulting turbo codes which dominate their asymptotic performance; 3) constructing optimized interleavers recursively so that they are implicitly prunable; and 4) completely avoiding short permutation cycles in order to reduce the risk of having strong correlations between the extrinsic information during iterative decoding. To this end, we present two theorems that lead to a modification of a previously developed iterative interleaver growth algorithm (IGA) that can be used to design optimized variable-length interleavers, whereby at every length the optimized permutation implemented by the interleaver is a single-cycle permutation. Two more modifications of the IGA are presented to improve the performance of the optimized interleavers at a reduced complexity. The optimization is achieved via constrained minimization of a cost function closely related to the asymptotic bit-error rate or frame-error rate of the code.     

Stream-oriented turbo codes

This work considers the design and performance of a stream-oriented approach to turbo codes which avoids the need for data framing. The stream paradigm applies to both serial and parallel turbo codes using continuous, free-running constituent encoders along with continuous, periodic interleavers. A stream-oriented turbo code based on parallel concatenated convolutional codes (PCCC) is considered and interleaver design criteria are developed for both block and nonblock periodic interleavers. Specifically, several nonblock interleavers, including convolutional interleavers, are considered. Interleaver design rules are verified using simulations where it is shown that nonblock interleavers with small-to-moderate delay and small synchronization ambiguity can outperform block interleavers of comparable delay. For large-delay designs, nonblock interleavers are found which perform within 0.8 dB of the capacity limit with a synchronization ambiguity of N=11     

Turbo-coded optical PPM communication systems

A number of parallel concatenated convolutionally coded (PCCC) photon communication systems is introduced and investigated. It is assumed that the optical channel is an intensity modulated (IM) channel and that the received optical signal is detected using a direct-detection (DD) scheme. Two modes of operation are considered. In one scenario, it is assumed that the receiver is limited by shot noise (i.e., negligible receiver thermal noise, or Poisson channel). In the other case, we consider a nonnegligible receiver thermal noise where an avalanche photodetector (APD) is employed to detect the received optical signal. It is also considered that the modulation scheme is the binary pulse-position modulation (PPM). With the aid of the best available upper bounds, the performance of the rate 1/n PCCC encoded optical PPM systems is assessed in terms of the upper bound on the system bit error rate (BER) for the shot-noise-limited IM/DD systems with nonnegligible background noise and for the thermal-noise-limited systems with APD detectors when a uniform interleaver is used. Numerical results for the rate 1/3 PCCC encoded PPM channels are presented. The numerical results demonstrate the enormous potential of this novel coding scheme in enhancing the performance of the aforementioned optical channels by a sizeable margin across the board     

Convolutionally interleaved PSK and DPSK trellis codes forshadowed, fast fading mobile satellite communication channels

Using a model from the literature, the performance of convolutionally interleaved phase-shift-keying (PSK) and differential phase-shift-keying (DPSK) trellis codes for digital speech transmission over shadowed mobile satellite communication channels is determined by computer simulation. First the characteristics of fading channels are examined and analyzed in terms of the probability distributions of amplitude, phase, and burst errors. A statistical method, using a histogram approach, is utilized along with the simulations of fading channels to generate these probability distributions. A test for channel burst error behavior is presented. A periodic convolutional interleaver/deinterleaver to be used with trellis coding to combat slow fading in digital, shadowed mobile satellite channels is designed. This interleaver ha less than half the time delay for the same bit error performance than a block interleaver. The results show that the periodic convolutional interleaver provides considerable improvement in the error and time delay performance of mobile satellite communication channels for up to average shadowing conditions as compared to other techniques     

A cost-function based technique for design of good prunable interleavers for turbo codes

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.     

Collision free row column S-random interleaver

Parallel decodable turbo codes (PDTCs) are suitable for concurrent decoding and hence have low latency. Memory collision issue is an important problem met during parallel processing. In this article, we propose a collision free interleaver for parallel processing operations. The performance of PDTCs is analyzed with the proposed random interleaver preventing the memory collision problem. Distance spectra of PDTCs with the proposed interleaver are computed and compared to those with S-random interleaver.     

Design of flexible-length S-random interleaver for turbo codes

We introduce a method for generating a sequence of semi-random interleavers, intended to be optimally stored and employed in a turbo coding system that requires flexibility of the input block (i.e., interleaver) size N. A distinctive feature of this method is seen in the very simple rules for obtaining shorter/longer interleavers by pruning/adding positions to the interleaver currently used in the system. For each N, the obtained bit error rate (BER) is not higher than the BER for ordinary S-random interleaver of the same N. The method always converges and is suitable for obtaining interleavers of large lengths.     

Turbo coded multiple-antenna systems for near-capacity performance

For a turbo coded BLAST (Bell LAbs Space-Time architecture) system with N_t transmit antennas and N_r receive antennas, there is a significant gap between its detection threshold and the capacity in case N_t > N_r. In this paper, we show that by introducing a convolutional interleaver with block delay between the BLAST mapper and the turbo encoder, the threshold can be improved. Near-capacity thresholds can be achieved for some cases. To take advantage of the low detector complexity in Alamouti STBC (space-time block code), we also investigate a STBC system, which is the concatenation of the Alamouti STBC with a turbo trellis coded modulation. By using a proper labelling and adding a convolutional interleaver with block delay to such a STBC system, we achieve both lower error floors and lower thresholds.     

高速并行Turbo译码中的交织器技术研究

为了适应高速率通信系统的发展要求,Turbo码可采用并行译码的结构方式来降低时延.然而在并行Turbo码译码中,交织器的随机特性可能会导致多个数据同时写入同一个存储器,这就造成了存储器的访问冲突.如何设计出无冲突交织器是并行Turbo译码器的设计难点.文中对当前国内外的并行Turbo译码无冲突交织器设计方案进行了综述,对几种新的交织器分析研究.     

Turbo-coded optical direct-detection CDMA system with PPMmodulation

The performance of an optical code division multiple access (CDMA) system with turbo coding is analyzed and simulated. Turbo codes are parallel concatenated convolutional codes (PCCCs) in which the information bits are first encoded by a recursive systematic convolutional code, and then, after passing through an interleaver, are encoded by a second systematic convolutional encoder. Turbo coding is superimposed on an intensity-modulated optical channel with pulse-position modulation (PPM) and direct detection of the received optical signal, and the performance is evaluated in terms of an upper bound on bit error probability. From the simulation results, it is seen that turbo coding offers considerable coding gain over other methods, with reasonable encoding/decoding complexity. Also, it is demonstrated that, for a fixed code rate, the performance of the optical CDMA system can be substantially improved by increasing the interleaver length and the number of iterations. Serially concatenated convolutional codes (SCCCs) are also considered, and are shown to perform comparably to PCCC in general and better than PCCCs for the case of large signal photocounts. The results in this paper can be applied, for example, to indoor optical wireless LANs     

Multilevel turbo coding with short interleavers

The impact of the interleaver, embedded in the encoder for a parallel concatenated code, called the turbo code, is studied. The known turbo codes consist of long random interleavers, whose purpose is to reduce the value of the error coefficients. It is shown that an increased minimum Hamming distance can be obtained by using a structured interleaver. For low bit-error rates (BERs), we show that the performance of turbo codes with a structured interleaver is better than that obtained with a random interleaver. Another important advantage of the structured interleaver is the short length required, which yields a short decoding delay and reduced decoding complexity (in terms of memory). We also consider the use of turbo codes as component codes in multilevel codes. Powerful coding structures that consist of two component codes are suggested. Computer simulations are performed in order to evaluate the reduction in coding gain due to suboptimal iterative decoding. From the results of these simulations we deduce that the degradation in the performance (due to suboptimal decoding) is very small     

Interleaver properties and their applications to the trelliscomplexity analysis of turbo codes

In this paper, the basic theory of interleavers is revisited in a semi-tutorial manner, and extended to encompass noncausal interleavers. The parameters that characterize the interleaver behavior (like delay, latency, and period) are clearly defined. The input-output interleaver code is introduced and its complexity studied. Connections among various interleaver parameters are explored. The classes of convolutional and block interleavers are considered, and their practical implementation discussed. The trellis complexity of turbo codes is tied to the complexity of the constituent interleaver. A procedure of complexity reduction by coordinate permutation is also presented, together with some examples of its application     

Simultaneous Interleaver Assignment Requests Handling in Inverse Tree Interleaver Deployment Scenario for Multi-user 5G Communications

Interleaver centric systems have a significant role to play in fifth generation (5G) real-time communication. Flip Left–Right approach based Inverse Tree Interleavers (FLRITIs) are among one of the recently developed interleavers for these interleaver centric systems. During the real-time communication, interleaver assignment requests from multiple users often arrive at next generation NodeB (gNB) simultaneously. Therefore, a mechanism is essentially needed to handle these simultaneous interleaver assignment requests at the gNB. In this paper, an efficient mechanism to handle the simultaneous interleaver i.e. FLRITI assignment requests originated from different wireless transmit receive units is proposed. This mechanism helps the network in taking a correct logical decision based on pre-configured policy/policies while assigning correct sequence number and hence, the correct FLRITI to each 5G user from the inverse tree structure. The method is equally effective in all types of time-critical and non-time critical 5G communication scenarios e.g. Ultra reliable low latency communication 5G new radio, enhanced mobile broadband etc.

     

基于TURBO码和分块传输的新型HARQ系统

本文采用TURBO码为纠错码,在分析传统的反馈重传方式的基础上,将分块传输系统和码合并技术相结合,提出了一种新型HARQ系统,并为其设计了新型交织器。新型HARQ系统将每帧数据多次重传合并,转化为在一帧的多个分块之间合并,不需要重传。该系统大幅度降低了重传次数、交织的时延和平均迭代次数,实现了数据的实时通信;译码器接收的数据在解扩之前充分合并,更加有效地利用了软信息;该系统还省去了常用Ⅰ型HARQ系统中必须使用的收发端复杂的反馈重传控制和庞大的存储器;新型HARQ系统巾TURBO码的最小距离增加为原来的许多倍。通过理论分析和仿真比较了新型HARQ系统和Ⅰ型HARQ系统的性能,结果证明了新型HARQ系统性能的优越性。新型HARQ系统为第三代无线通信技术提供了一种较好地选择。     

Performance Improvement of IS-95 CDMA Uplink Using Decision Feedback and Sub-Optimal Viterbi Decoding

This paper presents a methodology designed to improve the effectiveness of a non-iterative decision feedback (DF) receiver/decoder for IS-95 Code Division Multiple Access (CDMA) uplink in additive white Gaussian noise (AWGN) and Rayleigh fading. The effectiveness of the DF receiver/decoder is linked to the interleaver specification and the decoding delay of the convolutional decoder. Using sub-optimal convolutional decoding the average decoding delay is reduced resulting in more effective decision feedback decoding (DFD). Simulation results of average decoding delay, bit error rate (BER) and frame error rate (FER) are presented for coherent and noncoherent detection of unfaded single-path and Rayleigh fading multipath signals. Instead of the usual performance degradation these results show that the DF receiver/decoder benefits from some forms of sub-optimal Viterbi decoding. The additional performance gain can further improve the quality of service and/or capacity of a cellular IS-95 system.     

PCCC for the performance improvement of the wireless optical communication system

Opticalwireless,alsoknownasfree spaceoptics,isa cost effectiveandwidebandwidthaccesstechniqueandreceivesgrowingattentionwithrecentcommercialization success.Buttheperformanceofwirelessopticalcommu nicationwouldbeimpairedintheatmosphericchannelbyattenuation…     

Optimal Distributed Location Management in Mobile Networks

An important issue in the design of future Personal Communication Services (PCS) networks is the efficient management of location information. In this paper, we consider a distributed database architecture for location management in which update and query loads of the individual databases are balanced. We obtain lower bounds to the worst-case delay in locating a mobile user, to the average delay, and to the call blocking probability. We then propose a dynamic location management algorithm that meets these lower bounds. The optimality of this algorithm with respect to these three performance measures, as well as simplicity, make it an appealing candidate for distributed location management in PCS networks.     

Turbo码的一种并行译码方案及相应的并行结构交织器研究

Turbo码基于MAP算法译码的递推计算所引入高的译码延迟限制了Turbo码在高速率数据传输中的应用。为了解决这个问题,该文提供了一种降低译码延迟的并行译码方法。并行处理方案的实现必须通过适当的交织以避免两个译码器对外信息读写的数据冲突。该文在分析了任意无冲突交织方式可能性的存在之后,给出了设计任意地适用于并行处理方案的S随机交织器的方法。仿真验证了并行译码方案的误比特性能。