Uncoded Bits Research Articles

DeepRx: Fully Convolutional Deep Learning Receiver

Deep learning has solved many problems that are out of reach of heuristic algorithms. It has also been successfully applied in wireless communications, even though the current radio systems are well-understood and optimal algorithms exist for many tasks. While some gains have been obtained by learning individual parts of a receiver, a better approach is to jointly learn the whole receiver. This, however, often results in a challenging nonlinear problem, for which the optimal solution is infeasible to implement. To this end, we propose a deep fully convolutional neural network, DeepRx, which executes the whole receiver pipeline from frequency domain signal stream to uncoded bits in a 5G-compliant fashion. We facilitate accurate channel estimation by constructing the input of the convolutional neural network in a very specific manner using both the data and pilot symbols. Also, DeepRx outputs soft bits that are compatible with the channel coding used in 5G systems. Using 3GPP-defined channel models, we demonstrate that DeepRx outperforms traditional methods. We also show that the high performance can likely be attributed to DeepRx learning to utilize the known constellation points of the unknown data symbols, together with the local symbol distribution, for improved detection accuracy.

LDPC-Coded Modulation Performance Analysis and System Design

In this work, the low-density parity-check (LDPC)-coded modulation scheme which has been selected for inclusion in the next generation of International Telecommunication Union (ITU) broadband standard is investigated. The multi-level mapping of this scheme offers excellent performance along with a straightforward modulation which is separable into simple one-dimensional schemes. A subset of modulated bit positions are protected by the LDPC code, while the remaining positions benefit from improved Euclidean distance through assignment to distinct constellation regions. To date, there has been a lack of analytical treatment of the scheme. This is problematic given the number of tunable scheme and code parameters, necessitating time-consuming Monte Carlo simulation. This motivates the novel analytical work of this article, which derives overall error-rate and threshold performances through considering separately the effects of the channel on the coded and uncoded bits. First, new closed-form expressions are derived for the hard-decision performance of the bit mapping of the multi-level modulation scheme, for both coded and uncoded bits. Extrinsic information transfer (EXIT) analysis is then applied to the coded bits in the scheme. The derived theoretical performance of the uncoded bit positions is used in combination with the derived EXIT threshold to provide for the first time for this modulation scheme a method to evaluate analytically whether a designed system will offer capacity-approaching performance. Following this, an approximation to the capacity curve for the coded modulation scheme is produced, again based on the derived analytical performance. Finally, through the relationship between mutual information and error rate performance for error control codes, the derived analytical expressions are used to produce a semi-analytical finite-length performance predictor, whereby error rate results for a given code on the binary input additive white Gaussian noise (AWGN) channel can be mapped to the coded modulation scheme under consideration for any coded system parameters.

Blind Index Coding

We introduce the blind index coding (BIC) problem, in which a single sender communicates distinct messages to multiple users over a shared channel. Each user has partial knowledge of each message as side information. However, unlike classical index coding, in BIC, the sender is uncertain of what side information is available to each user. In particular, the sender only knows the amount of bits in each user’s side information but not its content. This problem can arise naturally in caching and wireless networks. In order to blindly exploit side information in the BIC problem, we develop a hybrid coding scheme that XORs uncoded bits of a subset of messages with random combinations of bits from other messages. This scheme allows us to strike the right balance between maximizing the transmission rate to each user and minimizing the interference leakage to others. We also develop a general outer bound, which relies on a strong data processing inequality to effectively capture the senders uncertainty about the users’ side information. Additionally, we consider the case where communication takes place over a shared wireless medium, modeled by an erasure broadcast channel, and show that surprisingly, combining repetition coding with hybrid coding improves the achievable rate region and outperforms alternative strategies of coping with channel erasure and while blindly exploiting side information.

Application of 16-State TCM-UGM and TCM for Improving the Quality of Compressed Color Image Transmission

Abstract —The aim of this paper is to investigate the quality of transmitted color images using 16-state TCM-UGM or TCM channel code over Rayleigh fading channel. Considering SPIHT-based compression algorithm and image quality metrics (IQMs), the simulation results for throughput of 2 bit/s/Hz, showed that the communication system using TCM-UGM allows better performance compared to TCM and better protects the compressed color image during transmission. For transmission tests compressed colors images, the TCM-UGM system outperforms the performance of the TCM by 3 dB at BER = -10 5 and 4.59 dB at FER = 3.10 -3 . For example, for Lena color image, the 16-state TCM-UGM system gives best performance that the 16-state TCM system. The gain is the 5.02 dB and 17.90 % for the PSNR and MMSIM respectively. Index Terms —TCM-UGM, TCM, compressed color image, SPIHT. I. I NTRODUCTION The trellis-coded modulation (TCM) was introduced by Ungerboeck in 1982 [1]. This coding technique improves error performance of synchronous data links without sacrificing data rate or requiring more bandwidth. This is achieved by channel coding with expanded sets of multilevel/phase signals in a manner which increases free Euclidean distance. The TCM codes can be interpreted as binary convolutional codes with a mapping of coded bits into channel signals using mapping by set partitioning. A new variant of the TCM modulation based on Ungerboeck mapping combined with Gray coding, called ‗Trellis-Coded Modulation with Ungerboeck-Gray Mapping‘ (TCM-UGM) has been proposed by Bassou [2]. Bassou and Djebbari have proposed this new schema for a spectral efficiency greater than or equal to 3 bits/s/Hz. The difference between these two structures resides in the positioning of the uncoded bits out in the encoder. Indeed, for TCM-UGM the uncoded bits are placed before the parity bit. The latter cannot in any way represent the MSB or the LSB of the transmitted symbol. In the absence of uncoded bits, the TCM-UGM is equivalent to the proposed Ungerboeck TCM. A variant of the TCM-UGM for spectral efficiency of 2 bits/s/Hz, 8PSK modulation and rate equal to 2/3 is proposed by Benaissa

Combining-after-Decoding Turbo Hybrid ARQ by Utilizing Doped-Accumulator

This letter proposes a doped-accumulator assisted packet-combining-after-decoding (ACC-CAD) technique with different doping rates per transmission phases for hybrid automatic repeat request (ARQ). Horizontal iteration (HI) performed for decoding the serially concatenated codes (SCC) is followed by Vertical iteration (VI) to exchange extrinsic log-likelihood ratio (LLR) of the uncoded (systematic) bits, and the HI/VI chain is repeated. The doped-accumulator enables the two extrinsic information transfer (EXIT) curves of the SCC to match very well and the convergence tunnel to open until a point very close to the (1.0,1.0) mutual information point. Excellent performance of our technique is verified through EXIT analysis as well as frame-error-rate (FER) and throughput simulations.

Inspection-Resistant Memory Architectures

The ability to safely keep a secret in memory is central to the vast majority of security schemes, but storing and erasing these secrets is a difficult problem in the face of an attacker who can obtain unrestricted physical access to the underlying hardware. Depending on the memory technology, the very act of storing a 1 instead of a 0 can have physical side effects measurable even after the power has been cut. These effects can't be hidden easily, and if the secret stored on chip is of sufficient value, an attacker might go to extraordinary means to learn even a few bits of that information. The architecture has an interesting role to play here. Just as one uses architectural techniques to detect and correct errors, so too can one create efficient methods to hide critical bits from physical inspection. The authors present a first step toward this goal by focusing on a backbone of any hardware system: on-chip memory. They examine the relationship between security, area, and efficiency in these architectures and quantitatively examine the resulting systems through cryptographic analysis and microarchitectural impact. In the end, they find an efficient scheme in which, even if an adversary is able to inspect the value of a stored bit with a probabilistic error of only 5 percent, the system will be able to prevent that adversary from learning any information about the original uncoded bits with 99.9999999999 percent probability.

RS-Enhanced TCM for Multilevel Flash Memories

Multilevel flash memories store more than one bit per storage cell and are further characterized by large word (page) sizes and very low target error rates. In this paper, a high-rate error control scheme is presented that uses inner trellis-coded modulation (TCM) for storing two bits per cell with five possible charge levels. The coded subset-label bits and the uncoded signal-label bits of TCM are independently protected by separate outer Reed-Solomon (RS) codes. The resulting scheme permits multistage decoding. Errors made by the TCM decoder in the subset-label bits occur in bursts and are corrected by the associated first RS decoder prior to determining signal-label bits and correcting errors in those bits by the associated second RS decoder. The multi-stage decoding avoids the significant spread of errors from subset-label bits into the generally larger number of signal-label bits which is typical for conventional serial RS-TCM concatenation when the inner TCM system operates at relatively low SNR. The error performance of the proposed scheme is evaluated at low error rates by a mixed simulation-analytic method. It is shown that the proposed scheme exhibits highly favorable performance vs. complexity tradeoffs compared to the other schemes.

Inspection resistant memory

The ability to safely keep a secret in memory is central to the vast majority of security schemes, but storing and erasing these secrets is a difficult problem in the face of an attacker who can obtain unrestricted physical access to the underlying hardware. Depending on the memory technology, the very act of storing a 1 instead of a 0 can have physical side effects measurable even after the power has been cut. These effects cannot be hidden easily, and if the secret stored on chip is of sufficient value, an attacker may go to extraordinary means to learn even a few bits of that information. Solving this problem requires a new class of architectures that measurably increase the difficulty of physical analysis. In this paper we take a first step towards this goal by focusing on one of the backbones of any hardware system: on-chip memory. We examine the relationship between security, area, and efficiency in these architectures, and quantitatively examine the resulting systems through cryptographic analysis and microarchitectural impact. In the end, we are able to find an efficient scheme in which, even if an adversary is able to inspect the value of a stored bit with a probabilistic error of only 5%, our system will be able to prevent that adversary from learning any information about the original un-coded bits with 99.9999999999% probability.

Throughput of Type II HARQ‐OFDM/TDM Using MMSE‐FDE in a Multipath Channel

In type II hybrid ARQ (HARQ) schemes, the uncoded information bits are transmitted first, while the error correction parity bits are sent upon request. Consequently, frequency diversity cannot be exploited during the first transmission. In this paper, we present the use of OFDM/TDM with MMSE‐FDE and type II HARQ to increase throughput of OFDM due to frequency diversity gain.

A Simplified Decoding Algorithm Using Symbol Transformation for Turbo Pragmatic Trellis-Coded Modulation

This paper presents the application of a turbo coding technique combined with a bandwidth efficient method known as trellis-coded modulation. A transformation applied to the incoming I-channel and Q-channel symbols allows the use of an off-the-shelf binary/quadrature phase shift keying (B/QPSK) turbo decoder without any modifications. A conventional turbo decoder then operates on transformed symbols to estimate the coded bits. The uncoded bits are decoded based on the estimated coded bits and locations of the received symbols.

High code rate error correction code design for partial response systems

In recent years, code designers have been interested in finding high code rate solutions for coded partial response systems. The focus of the attention has been given to increasing the code rate of modulation codes. In this paper we turn our attention to increasing the code rate of error correction codes designed fur partial response systems. An analysis of low distance preceded input error events illustrates how an error correction code should exploit the structure of these error events in order to achieve an increase in rode rate. We describe a method of using a combination of interleaved Reed-Solomon codes interspersed with uncoded bits to achieve a higher code rate than the classical ECC solution. Simulation results suggest good performance of this scheme.

Adaptive bit-interleaved coded modulation

Adaptive coded modulation is a powerful method for achieving a high spectral efficiency over fading channels. Previously proposed adaptive schemes have employed set-partitioned trellis-coded modulation (TCM) and have adapted the number of uncoded bits on a given symbol based on the corresponding channel estimate. However, these adaptive TCM schemes do not perform well in systems where channel estimates are unreliable, since uncoded bits are not protected from unexpected finding. In this paper, adaptive bit-interleaved coded modulation (BICM) is introduced. Adaptive BICM schemes remove the need for parallel branches in the trellis-even when adapting the constellation size, thus making these schemes robust to errors made in the estimation of the current channel fading value. This motivates the design of adaptive BICM schemes, which will lead to adaptive systems that can support users with higher mobility than those considered in previous work. In such systems, numerical results demonstrate that the proposed schemes achieve a moderate bandwidth efficiency gain over previously proposed adaptive schemes and conventional (nonadaptive) schemes of similar complexity.

A two-stage decoder for pragmatic trellis-coded M-PSK modulation using a symbol transformation

A two-stage decoding procedure for pragmatic trellis-coded modulation (TCM) is introduced. It applies a transformation from the received I-channel and Q-channel samples onto points in a two-dimensional (2-D) signal space that contains a coset constellation. For pragmatic TCM over M-PSK signal sets with /spl nu/ coded bits per symbol, /spl nu/=1, 2, the signal points in the coset constellations represent cosets of a B/QPSK signal subset-associated with the coded bits-in the original M-PSK signal constellation. A conventional Viterbi decoder operates on the transformed symbols to estimate the coded bits. After reencoding these bits, the uncoded bits are estimated in a second stage, on a symbol-by-symbol basis, with decisions based on the location of the received symbols. In addition to requiring no changes in the Viterbi decoder core, it is shown that the proposed method results in savings of up to 40% in the memory required to store (or in the size of the logic required to compute) metrics and transformed symbols.

Efficient performance computations for trellis-coded modulation

The algorithm given by Rouanne and Costello (1989) for the computation of the distance spectrum is improved for trellis-coded modulation schemes having uncoded bits, i.e., for trellis diagrams having parallel paths. It is shown that, when through a trellis corresponding to such kind of codes, all parallel transitions (labeled by signal selectors) between states are considered as a single branch labeled by a subset, then defining subset selector distance polynomials makes the computational complexity of the distance spectrum dependent on the number of states as compared to the complexity of Rouanne and Costello algorithm which depends on the number of paths to be extended.

Bandwidth-efficient turbo trellis-coded modulation using punctured component codes

We present a bandwidth-efficient channel coding scheme that has an overall structure similar to binary turbo codes, but employs trellis-coded modulation (TCM) codes (including multidimensional codes) as component codes. The combination of turbo codes with powerful bandwidth-efficient component codes leads to a straightforward encoder structure, and allows iterative decoding in analogy to the binary turbo decoder. However, certain special conditions may need to be met at the encoder, and the iterative decoder needs to be adapted to the decoding of the component TCM codes. The scheme has been investigated for 8-PSK, 16-QAM, and 64-QAM modulation schemes with varying overall bandwidth efficiencies. A simple code choice based on the minimal distance of the punctured component code has also been performed. The interset distances of the partitioning tree can be used to fix the number of coded and uncoded bits. We derive the symbol-by-symbol MAP component decoder operating in the log domain, and apply methods of reducing decoder complexity. Simulation results are presented and compare the scheme with traditional TCM as well as turbo codes with Gray mapping. The results show that the novel scheme is very powerful, yet of modest complexity since simple component codes are used.