Convolutional Turbo Codes Research Articles

Blind parameter estimation of turbo convolutional codes: Noisy and non-synchronized scenario

Blind estimation of forward error correction code parameters at the receiver plays a significant role in non-cooperative communication, adaptive modulation and coding systems, and reconfigurable receiver systems. Turbo convolutional codes, a parallel concatenation of multiple convolutional codes, are used in digital communication and storage systems to achieve low bit error rate. The present paper proposes innovative algorithms for the blind estimation of code parameters and reconstruction of turbo convolutional encoder over noisy scenario. The turbo convolutional code is designed using two component codes along with an interleaver. Recursive systematic convolutional codes are used as component codes. Any imperfection in synchronization of received data for the proposed code parameter estimation algorithm is compensated through a bit position adjustment parameter. The performance of the proposed algorithms in terms of parameter estimation accuracy is investigated for different modulation order, code rate, and constraint length values. It is observed that the performance improves with decrease in modulation order and constraint length values.

Analyzing Impacts of Spatial Correlation for Multi-user Environment with Robust Concatenation of Advanced FEC Schemes

In recent days, the enhancement of MIMO in the area of wireless communications with spatial correlation characteristics by means of the forward-error-correction (FEC) techniques has been introduced as a vital technology. To overcome the limitations of the FEC in MIMO–OFDM systems, this paper introduces the effect of spatial correlation in FEC for multi-user MIMO–OFDM system. Here, the error correction codes (ECC) namely low-density parity check (LDPC-CC), turbo code CC, convolutional code (CC) and Reed–Solomon code (RSC-CC), and polar code CC (PC-CC) are authenticated for three channel representations known as Rayleigh, Rician and additive white Gaussian noise for multi-user (MU) with 8 users and single user MIMO–OFDM system. The investigation is carried out by means of four modulation techniques like, binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), quadrature amplitude modulation (QAM)-16 and QAM-64. It is done under three antenna configurations like 2 × 2, 2 × 4, and 4 × 4. In addition, the peak signal to noise ratio is deployed to recognize the image transmission and the bit error rate, is employed to recognize the data transmission. Furthermore, from the experimental results, the PC-CC in MU system is found to offer better performance than the other configurations.

A Novel Architecture of Modified Turbo Codes with an area efficient high speed interleaver

SummaryModified Turbo Codes (MTC) is preferred over conventional Turbo Convolutional Codes (TCC) as they provide nearly the same performance but with the additional benefit of reduced decoding complexity. The Improved Low Complexity Hybrid Turbo Codes (ILCHTC) is a type of MTC, which achieves a Bit Error Rate (BER) performance near to Shannon's limit. This paper presents a high speed novel encoder structure called Enhanced ILCHTC and a high speed low power novel interleaver for the MTC and analyzes its BER performance. From the simulation results, it is observed that BER performance of Enhanced ILCHTC and ILCHTC with proposed interleaver is better and has high degree of error convergence and requires less than 50% of computations than TCC. From the synthesized results, it is observed that the computation time required to shuffle the bits by the proposed interleaver is 7.4% less than the time required by the existing interleaver. In addition, it is observed that the number of logic elements utilized by the proposed interleaver is 95, which is 8% less than the number of logic elements, utilized by the existing interleaver but the tradeoff is power, which is 1.63% more when compared to the existing interleaver. Thus, a high speed area efficient interleaver is proposed along with a novel encoder structure.

Modification of extrinsic information for parallel concatenated Gallager/Convolutional code to improve performance/complexity trade-offs

To benefit the properties of both Low-Density Parity-Check (LDPC) and Turbo Convolutional Codes (TCC), we propose a practical concatenated Gallager/Convolutional code in a turbo coding way. The modified code creates a balance between the advantages and the disadvantages of LDPC and TCC in terms of the overall complexity and latency. This will be done through two different component SISO decoders; LDPC and convolutional code of the same rate 1/2 without interleaver. Since the two SISO decoders are different in nature, they exchange extrinsic information that will be easily adapted to each other. The study of computation complexity and decoding performance over an AWGN channel indicates that such approach leads to excellent performance because of several factors. The proposed approach achieves a trade-off between waterfall and error floor regions. It reduces complexity decoding compared to TCC and 3D - TCC. It provides a better coding gain over LDPC and PCGC (Parallel Concatenated Gallager Codes). These features will ensure optimal outcomes and cost-performance ratio, and thus, this trend can be the best choice for today's communication systems.

FPGA Implementation of Decoder Architectures for High Throughput Irregular LDPC Codes

Objective: VLSI implementation of Decoder Architecture for high throughput using LDPC codes. Methods/Analysis: In this paper, the VLSI architecture of layered partial parallel soft decoding algorithm based decoder for different code size is presented. Findings: LDPC codes provide remarkable error detection performance. Proposed decoder is well matched for VLSI implementation and it is implemented on Xilinx FPGA family. LDPC codes are well-known linear block codes. The computational complexity of LDPC codes is very high as compared to other existing codes like Convolutional codes and Turbo codes. The major benefit is that they offer an enhanced performance, which is very close to the Shannon’s capacity for many different channels and complex algorithms for decoding Novelty/Improvement: By using layered partial parallel soft decoding algorithm, we proposed a pipelined structure that is helpful to achieve higher throughput. The proposed architecture is implemented and tested on FPGA Virtex-5 family with device as 5XC5VLX85. The decoder can attain a throughput of 1.5 Gbps with reduced hardware resources.

Bahl–Cocke–Jelinek–Raviv decoding algorithm applied to the three‐user binary adder channel

The Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm is a well-known maximum a posteriori probability decoding algorithm which has been proposed earlier for point to point communication applications, employing block codes or convolutional codes and turbo codes. This study describes an application of the BCJR algorithm for decoding the output of a multiple-access channel called the noisy three-user binary adder channel, in the presence of additive white Gaussian noise. The computer simulation results are presented for the overall coding performance in terms of bit error rate against signal-to-noise ratio.

Low-Complexity Error Correction for ISO/IEC/IEEE 21451-5 Sensor and Actuator Networks

ISO/IEC/IEEE 21451-5 standard provide a wireless communication model to facilitate access of smart sensors and actuators to a network. However, the 21451-5 standard integrates different wireless communication protocols in a sensor network system, and the overall complexity is higher than traditional sensor networks. Moreover, 21451-5 sensor networks that used in industrial control systems require better bit-error rate performance, and error correction is one of the key issues for the sensor networks. To address these obstacles, the double binary convolutional turbo code is applied to the 21451-5 sensor and actuator networks, and a low-complexity decoding solution is proposed for the iterative decoding, in which the focus is concentrated on simplification of the multivariable max <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sup> operator. In the implementation of a multivariable max <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sup> operator, this research shows recursion of the Jacobian logarithm is not necessary, and the computational error is small. Furthermore, we propose to approximate the Jacobian logarithm with simple compare, shifting, and addition operations. Since errors introduced by recursion of the Jacobian logarithm are removed, decoding performance of the proposed solution is superior to that of the near optimal decoding algorithm, and only slightly reduced as compared with the Log-MAP algorithm. By hardware implementation analysis, decoding complexity related to the multivariable max <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sup> operator is substantially reduced.

Research and Simulation on the Performance of HARQ Technologies in Advanced Orbiting Systems

To improve the transmission reliability of important satellite data, an improved transmission method of Advanced Orbiting Systems (AOS) is proposed, in which Hybrid Automatic Repeat reQuest (HARQ) technologies are introduced. The performances of commonly used ARQ schemes are compared, and the selective repeat ARQ scheme is chosen for the combination with channel coding to form HARQ. An AOS simulation model in which HARQ technology is introduced is also established, and the performance of AOS using difierent HARQ schemes including HARQ-I, HARQ-II, chase HARO-III and IR HARQIII are studied from four aspects: the bit error rate, frame error rate, average transmission times and throughput. The research results show that the proposed AOS transmission method with any HARQ scheme of the four kinds mentioned above performs better than the common AOS transmission method without HARQ technology in all of the four aspects, which proves the practicability of our proposed method. Further research shows that using whether convolutional code or Turbo code in HARQ, the performance of AOS using IR HARQ-III scheme is the better than that of AOS using any of the other three HARQ schemes. It is also shown that when using IR HARQ-III scheme, the performance of AOS using Turbo code is much better than that of AOS using convolutional code.

Reduced memory decoding schemes for turbo decoding based on storing the index of the state metric

In the implementation of turbo-like decoder, the size of state metrics cache (SMC) has a predominant impact on the core area and the overall power dissipation. Different from previous reported decoding schemes, in the proposed decoding schemes, a compressing module and a regeneration module are added to the decoder. The compressing module sorts the forward state metrics from the minimum to the maximum, by which an index sequence and the corresponding increase metrics are calculated, and subsequently are stored in the SMC. In the regeneration module, the forward state metrics are estimated with the index sequence and the increase metrics that accessed from the SMC. With the cost of dummy calculation that is performed by the compressing and the regeneration modules, two decoding schemes are proposed. For an eight-state turbo codes, the linear and the nonlinear estimation based decoding schemes reduce the SMC size by 62.5% and 57.5%, respectively. The bit error rate (BER) simulation is performed for both binary turbo code and duo binary convolutional turbo code, and shows BER of the linear estimation-based scheme is superior to that of the enhanced max-log-MAP (the maximum a posteriori probability) algorithm, whereas BER of the non-linear estimation-based decoding scheme is very close to that of the near optimal decoding scheme.

Convolutional codes from group rings

Convolutional codes have been widely used and studied. Many of the best current convolutional codes have been found through computer search. However, constructing these codes by algebraic means will allow bigger codes to be found while maintaining high speed and low memory. Units in the group ring have been used to construct convolutional codes. These have been used to construct several known codes and several new codes. These known constructions are extended to a new construction. This new construction allows for calculations of lower bounds of the free distances produced by some types of generators. It is shown that all (2, 1) systematic convolutional codes may be constructed using group rings with the new construction. The new construction is hoped be used to find new convolutional codes that would allow for less storage requirements for larger codes. This may be extended to consider LDPC convolutional codes and turbo codes.

A low-memory intensive decoding architecture for double-binary convolutional turbo code

Memory accesses take a large part of the power consumption in the iterative decoding of double-binary convolutional turbo code (DB-CTC). To deal with this, a low-memory intensive decoding architecture is proposed for DB-CTC in this paper. The new scheme is based on an improved maximum a posteriori probability algorithm, where instead of storing all of the state metrics, only a part of these state metrics is stored in the state metrics cache (SMC), and the memory size of the SMC is thus reduced by 25%. Owing to a compare-select--recalculate processing (CSRP) module in the proposed decoding architecture, the unstored state metrics are recalculated by simple operations, while maintaining near optimal decoding performance.

A State Metrics Cache Reduced Decoding Architecture for Double Binary Convolutional Turbo Code

A State Metrics Cache Reduced Decoding Architecture for Double Binary Convolutional Turbo Code

A novel decoding scheme based on recalculation for double binary convolutional turbo code

AbstractTo decrease the storage complexity of a double binary convolutional turbo code (DB‐CTC) decoder, a novel decoding scheme is proposed in this paper. Different from the conventional decoding scheme, only a part of the state metrics is stored in the last‐in first‐out (LIFO) state metrics cache (SMC). Based on an improved maximum a posteriori probability (MAP) algorithm, we present a method to recalculate the unstored state metrics at the corresponding decoding time slot, and discuss in detail the procedures of the recalculation are discussed. Because of the compare–select–recalculate processing operations, compared to the classical decoding scheme, the proposed decoding scheme reduces the storage complexity of SMC and the amount of memory accesses by approximately 40% while limiting involved computational cost. Moreover, simulation results show that the proposed scheme achieves good decoding performance, which is close to that of the well‐known Log‐MAP algorithm. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Improving the performance of BICM-ID and MLC systems with different FEC codes

Abstract. In bandwidth limited communication systems, the high data rate transmission with performance close to capacity limits is achieved by applying multilevel modulation schemes in association with powerful forward error correction (FEC) coding, i.e. coded modulation systems. The most important practical approaches to coded modulation systems are multilevel coding with multistage decoding (MLC/MSD) and bit interleaved coded modulation with iterative demapping and decoding (BICM-ID). Multilevel modulation formats such as M-QAM, which can be used as a part of coded modulation systems, have the capability of multilevel protection. Based on this fact, we investigate the methods to improve the performance of BICM-ID using multiple interleavers with different binary channel coding schemes such as convolutional codes, turbo codes and low-density parity-check (LDPC) codes. Moreover, an MLC system with parallel decoding on levels (PDL) at the receiver is considered. In our contribution, we propose to design the individual coding schemes using the extrinsic information transfer (EXIT) charts for individual bit levels in the constellation. Our simulation results show that the BICM-ID systems, taking into account different bit-level protections, can provide an improvement of 0.65 dB, 1.2 dB and 1.5 dB for 256-QAM with turbo, LDPC and convolutional codes, respectively. On the other hand, MLC systems with PDL designed using EXIT charts for individual bit levels can slightly improve the performance and eliminate the error floor compared to the systems with MSD.

Performance of Turbo Product Code in Wimax

IEEE 802.16 is a standard for Broadband Wireless Access (BWA) air interface. 802.16e supports mobile broadband wireless access, which is an additional feature over its predecessors, which support fixed wireless access. Binary Convolutional Turbo Coding (CTC) is used as mandatory Forward Error Correction method in 802.16e. In this paper the performance of a simple and efficient optional coding scheme namely Turbo Product Code (TPC) is proposed for 802.16e system and is compared with CTC.

SPECIFIC FEATURES OF APPLICATION OF INTERFERENCE-RESISTANT CODING IN MOBILE WIMAX SIGNALS

The article discusses the features of reception of mobile WiMAX signals. The applied types of interference-resistant coding are discussed; the dependence of the decoding error probability on the signal/noise ratio for a diagram with a convolutional turbo coding is obtained.

Efficient Window-Based Stopping Technique for Double-Binary Turbo Decoding

In order to reduce the number of computations for convergent values, a window-based stopping criterion is proposed for double-binary convolutional turbo decoding. The proposed technique can detect and tag convergent windows by detecting the a posteriori values of each window with a threshold. Thus, the number of computations for convergent windows can be reduced in further iterations. Additionally, the proposed algorithm employs the hard bits to provide approximate values for extrinsic value exchanging. From simulation results obtained using the WiMAX convolutional turbo code, we found that the proposed stopping technique can reduce around 47% of the convergent windows at Eb/N0 of 1.4 dB with a small coding gain loss.

A Memory Access Decreased Decoding Scheme for Double Binary Convolutional Turbo Code

A Memory Access Decreased Decoding Scheme for Double Binary Convolutional Turbo Code

Design space exploration of high throughput finite field multipliers for channel coding on Xilinx FPGAs

Abstract. Channel coding is a standard technique in all wireless communication systems. In addition to the typically employed methods like convolutional coding, turbo coding or low density parity check (LDPC) coding, algebraic codes are used in many cases. For example, outer BCH coding is applied in the DVB-S2 standard for satellite TV broadcasting. A key operation for BCH and the related Reed-Solomon codes are multiplications in finite fields (Galois Fields), where extension fields of prime fields are used. A lot of architectures for multiplications in finite fields have been published over the last decades. This paper examines four different multiplier architectures in detail that offer the potential for very high throughputs. We investigate the implementation performance of these multipliers on FPGA technology in the context of channel coding. We study the efficiency of the multipliers with respect to area, frequency and throughput, as well as configurability and scalability. The implementation data of the fully verified circuits are provided for a Xilinx Virtex-4 device after place and route.

Video streaming exploiting multiple-antenna techniques of wirelessMAN-advanced systems

In this paper, a novel video streaming technique is proposed for the recently standardized IEEE802.16m system also known as the Wireless MAN-Advanced or WIMAX2 system. The antenna mode considered is single user spatially multiplexed (SUSM) transmission suitable for video streaming. In previous works, the linear signal detection method was used in order to achieve unequal error protection (UEP). In this paper, it is shown that a joint signal detection method can also be used to achieve UEP. Computer simulations demonstrate improved performance using the proposed method. In the simulations, H.264/AVC compressed video is used, and the PHY layer procedures such as resource unit allocation, convolutional turbo code (CTC), pilot tone insertion, and pre-coding are implemented in strict accordance with the IEEE 802.16m standard.