Browsing by Subject "Convolutional codes"

Now showing 1 - 10 of 10

Open Access
Massive random access with trellis-based codes and random signatures
(IEEE, 2021-01-05) Tanc, A. K.; Duman, Tolga M.
We investigate unsourced and grant-free massive random access in which all the users employ the same codebook, and the basestation is only interested in decoding the distinct messages sent. To resolve the colliding user packets, a novel approach relying on user transmissions with random-like amplitudes selected from a large number of possible signatures is proposed. The scheme is combined with convolutional coding for error correction. The receiver operates by first identifying the signatures used by the transmitting nodes employing a sparsity-based detection algorithm, and then utilizing a trellis-based decoding algorithm. Despite its simplicity, the proposed solution offers excellent performance.
Open Access
A new wireless asynchronous data communications module for industrial applications
(2013) Ege, Y.; Şensoy, M.G.; Kalender O.; Nazlibilek, S.; Çitak H.
All the sensors such as temperature, humidity, and pressure used in industry provide analog outputs as inputs for their control units. Wireless transmission of the data has advantages on wired transmission such as USB port, parallel port and serial port and therefore has great importance for industrial applications. In this work, a new wireless asynchronous data communications module has been developed to send the earth magnetic field data around a ferromagnetic material detected by a KMZ51 AMR sensor. The transmitter module transmits the analog data obtained from a source to a computer environment where they are stored and then presented in a graphical form. In this design, an amplitude shift keying (ASK) transceiver working at the frequency of 433.92 MHz which is a frequency inside the so called Industrial Scientific Medical band (ISM band) used for wireless communications. The analog data first fed into a 10-bit ADC controlled by a PIC microcontroller and then the digital data is sent to the transmitter. A preamble bit string is added in front of the data bits and another bit string for achieving synchronization and determination the start of the data is used. The data arriving at the receiver is taken by the microcontroller and sent to a LCD display as well as the serial port of a computer where it is written in a text file. A Visual Basic based graphics interface is designed to receive, store and present the data in the form of graphical shapes. In the paper, all the work has been explained in detail. © 2013 Published by Elsevier Ltd. All rights reserved.
Open Access
An overview of physical layer security with finite-alphabet signaling
(Institute of Electrical and Electronics Engineers Inc., 2019) Aghdam, Sina Rezaei; Nooraiepour, A.; Duman, Tolga M.
Providing secure communications over the physical layer with the objective of achieving secrecy without requiring a secret key has been receiving growing attention within the past decade. The vast majority of the existing studies in the area of physical layer security focus exclusively on the scenarios where the channel inputs are Gaussian distributed. However, in practice, the signals employed for transmission are drawn from discrete signal constellations such as phase shift keying and quadrature amplitude modulation. Hence, understanding the impact of the finite-alphabet input constraints and designing secure transmission schemes under this assumption is a mandatory step toward a practical implementation of physical layer security. With this motivation, this paper reviews recent developments on physical layer security with finite-alphabet inputs. We explore transmit signal design algorithms for single-antenna as well as multi-antenna wiretap channels under different assumptions on the channel state information at the transmitter. Moreover, we present a review of the recent results on secure transmission with discrete signaling for various scenarios including multi-carrier transmission systems, broadcast channels with confidential messages, cognitive multiple access and relay networks. Throughout the article, we stress the important behavioral differences of discrete versus Gaussian inputs in the context of the physical layer security. We also present an overview of practical code construction over Gaussian and fading wiretap channels, and discuss some open problems and directions for future research.
Open Access
Performance and computational analysis of polarization-adjusted convolutional (PAC) codes
(2022-06) Moradi, Mohsen
We study the performance of sequential decoding of polarization-adjusted con- volutional (PAC) codes. We present a metric function that employs bit-channel mutual information and cutoff rate values as the bias values and significantly re- duces the computational complexity while retaining the excellent error-correction performance of PAC codes. With the proposed metric function, the computa- tional complexity of sequential decoding of PAC codes is equivalent to that of conventional convolutional codes. Our results indicate that the upper bound on the sequential decoding compu- tational complexity of PAC codes follows a Pareto distribution. We also employ guessing technique to derive a lower bound on the computational complexity of sequential decoding of PAC codes. To reduce the PAC sequential decoder’s worst-case latency, we restrict the number of searches executed by the sequential decoder. We introduce an improvement to the successive-cancellation list (SCL) decod- ing for polarized channels that reduces the number of sorting operations without degrading the code’s error-correction performance. In an SCL decoding with an optimum metric function, we show that, on average, the correct branch’s bit- metric value must be equal to the bit-channel capacity. On the other hand, the average bit-metric value of a wrong branch can be at most 0. This implies that a wrong path’s partial path metric value deviates from the bit-channel capacity’s partial summation. This enables the decoder to identify incorrect branches and exclude them from the list of metrics to be sorted. We employ a similar technique to the stack algorithm, resulting in a considerable reduction in the stack size. Additionally, we propose a technique for constructing a rate profile for PAC codes of arbitrary length and rate which is capable of balancing the error- correction performance and decoding complexity of PAC codes. For signal-to- noise ratio (SNR) values larger than a target SNR value, the proposed approach can significantly enhance the error-correction performance of PAC codes while retaining a low mean sequential decoding complexity. Finally, we examine the weight distribution of PAC codes with the goal of providing a new demonstration that PAC codes surpass polar codes in terms of weight distribution.
Open Access
Polar code construction for non-binary source alphabets
(IEEE, 2012) Çaycı, Semih; Arıkan, Orhan; Arıkan, Erdal
In this paper, approximation methods for binary polar code construction proposed by Tal and Vardy are extended to non-binary source alphabets. Additionally, a new approximation method that enables accurate polar code construction with less usage of computational resources is proposed. Efficiency and accuracy of proposed methods are supported analytically and numerically. © 2012 IEEE.
Open Access
Randomized convolutional and concatenated codes for the wiretap channel
(2016-10) Nooraiepour, Alireza
Wireless networks are vulnerable to various kinds of attacks such as eavesdropping because of their open nature. As a result, security is one of the most important challenges that needs to be addressed for such networks. To address this issue, we utilize information theoretic secrecy approach and develop randomized channel coding techniques akin to the approach proposed by Wyner as a general method for confusing the eavesdropper while making sure that the legitimate receiver is able to recover the transmitted message. We first study the application of convolutional codes to the randomized encoding scheme. We argue how dual of a code plays a major role in this construction and obtain dual of a convolutional code in a systematic manner. We propose optimal and sub-optimal decoders for additive white Gaussian noise (AWGN) and binary symmetric channels and obtain bounds on the decoder performance extending the existing lower and upper bounds on the error rates of coded systems with maximum likelihood (ML) decoding. Furthermore, we apply list decoding to improve the performance of the sub-optimal decoders. We demonstrate via several examples that security gaps achieved by the randomized convolutional codes compete favorably with some of the existing coding methods. In order to improve the security gap hence the system performance further, we develop concatenated coding approaches applied to the randomized encoding scheme as well. These include serial and parallel concatenated convolutional codes and serial concatenation of a low density generator matrix code with a convolutional code. For all of these solutions low-complexity iterative decoders are proposed and their performance in the wiretap channel is evaluated in terms of the security gap. Numerical examples show that for certain levels of confusion at the eavesdropper, randomized serially concatenated convolutional codes oer the best performance.
Open Access
Randomized convolutional codes for the wiretap channel
(Institute of Electrical and Electronics Engineers Inc., 2017) Nooraiepour, A.; Duman, T. M.
We study application of convolutional codes to the randomized encoding scheme introduced by Wyner as a way of confusing the eavesdropper over a wiretap channel. We describe optimal and practical sub-optimal decoders for the main and the eavesdropper's channels, and estimate the security gap, which is used as the main metric. The sub-optimal decoder works based on the trellis of the code generated by a convolutional code and its dual, where one encodes the data bits and the other encodes the random bits. By developing a code design metric, we describe how these two generators should be selected for optimal performance over a Gaussian wiretap channel. We also propose application of serially concatenated convolutional codes to this setup so as to reduce the resulting security gaps. Furthermore, we provide an analytical characterization of the system performance by extending existing lower and upper bounds for coded systems to the current randomized convolutional coding scenario. We illustrate our findings via extensive simulations and numerical examples, which show that the newly proposed coding scheme can outperform the other existing methods in the literature in terms of security gap.
Open Access
Randomized turbo codes for the wiretap channel
(IEEE, 2017-12) Nooraiepour, Alireza; Duman, Tolga M.
We study application of parallel and serially concatenated convolutional codes known as turbo codes to the randomized encoding scheme introduced by Wyner for physical layer security. For this purpose, we first study how randomized convolutional codes can be constructed. Then, we use them as building blocks for developing randomized turbo codes. We also develop iterative low-complexity decoders corresponding to the randomized schemes introduced and evaluate the code performance. We demonstrate via several examples that the newly designed schemes can outperform other existing coding methods in the literature (e.g., punctured low density parity check (LDPC) and scrambled BCH codes) in terms of the resulting security gap.
Open Access
Short block length code design for interference channels
(IEEE, 2016) Sharifi, S.; Dabirnia, Mehdi; Tanç, A. K.; Duman, Tolga M.
We focus on short block length code design for Gaussian interference channels (GICs) using trellis-based codes. We employ two different decoding techniques at the receiver side, namely, joint maximum likelihood (JML) decoding and single user (SU) minimum distance decoding. For different interference levels (strong and weak) and decoding strategies, we derive error-rate bounds to evaluate the code performance. We utilize the derived bounds in code design and provide several numerical examples for both strong and weak interference cases. We show that under the JML decoding, the newly designed codes offer significant improvements over the alternatives of optimal point-to-point (P2P) trellis-based codes and off-the-shelf low density parity check (LDPC) codes with the same block lengths.
Open Access
Short length trellis-based codes for gaussian multiple-access channels
(Institute of Electrical and Electronics Engineers Inc., 2014) Ozcelikkale, A.; Duman, T. M.
We focus on trellis-based joint code design for two-user Gaussian multiple-access channel (MAC) in the short block length regime. We propose a design methodology, provide specific code designs and report numerical performance results. We compare the performance of the jointly designed codes with the performance of the codes designed for point-to-point (P2P) channels including optimum (in terms of minimum distance) convolutional codes. Our results show that the proposed codes achieve superior performance compared to these alternatives especially in the high signal-to-noise (SNR) regime in equal power scenarios.