Design of low-density parity-check codes in relay channels

Recent breakthroughs in forward error correction, in the form of low-density parity-check (LDPC) and turbo codes, have seen near Shannon limit performances especially for pointto- point channels. The construction of capacity-achieving codes in relay channels, for LDPC codes in particular, is currently the subject of intense interest in the research and development community. This thesis adds to this field, developing methods and supporting theory in designing capacity-achieving LDPC codes for decode-and-forward (DF) schemes in relay channels. In the first part of the thesis, new theoretical results toward optimizing the achievable rate of DF scheme in half-duplex relay channels under simplified and pragmatic conditions (equal power or equal time allocation) are developed. We derive the closed-form solutions for the optimum parameters (time or power) that maximize the achievable rates of the DF scheme in the half-duplex relay channel. We also derive the closed-form expression for the DF achievable rates under these simplified and pragmatic conditions. The second part of the thesis is dedicated to study the problem of designing several classes of capacity-achieving LDPC codes in relay channels. First, a new ensemble of LDPC codes, termed multi-edge-type bilayer-expurgated LDPC (MET-BE-LDPC) codes, is introduced to closely approach the theoretical limit of the DF scheme in the relay channel. We propose two design strategies for optimizing MET-BE-LDPC codes; the bilayer approach and the bilayer approach with intermediate rates. Second, we address the issue of constructing capacity-achieving distributed LDPC codes in the multiple-access and two-way relay channels, with broadcast transmissions and time-division multiple accesses. We propose a new methodology to asymptotically optimize the code’s degree distribution when different segments within the distributed codeword have been transmitted through separate channels and experienced distinct signal-to-noise ratio in the relay system. Third, we investigate the use of LDPC codes under the soft-decode-and forward (SDF) scheme in the half-duplex relay channel. We introduce the concept of a K-layer doping matrix that enables one to design the rate-compatible (RC) LDPC code with a lower triangular parity-check matrix, subsequently allowing the additional parity bits to be linearly and systematically encoded at the relay. We then present the soft-decoding and soft-re-encoding algorithms for the designed RC-LDPC code so that the relay can forward soft messages to the destination when the relay fails to decode the source’s messages. Special attention is given to the detection problem of the SDF scheme. We propose a novel method, which we refer to as soft fading, to compute the log-likelihood ratio of the received signal at the destination for the SDF scheme

Full-duplex user-centric communication using non-orthogonal multiple access

This paper proposes an improved user-centric Non-Orthogonal Multiple Access (NOMA) communication in two-base station networks with in-band full duplex (IBFD) user. We derive the achievable rates of the proposed user-centric NOMA systems. For benchmarking purposes, we also derive the achievable rate for the user-centric system deploying conventional NOMA schemes, Orthogonal Multiple Access (OMA) schemes and point-point communication systems. We then analyze and simulate the performance of the proposed and all the benchmarked systems. We found that our proposed user-centric NOMA approach has a 64% improvement in the total achievable rate when compared to the benchmarked approach under similar power constraint

Performance Analysis of IIR and FIR Filters for 5G Wireless Networks

This paper analyses the performances of the Infinite Impulse Response (IIR) and Finite Impulse Response (FIR) filters. By studying the relationship between filter responses with filter orders and delay, the goal is to choose feasible filters that can accommodate more carriers in a bandwidth thus, the spectral efficiency can be increased. For IIR filtering, we employ filters namely Butterworth, Chebyshev, and Elliptic, while the Equiripple, Bohman, and Hamming are studied for FIR filtering. We evaluate these filters in terms of magnitude response, phase response and group delay, and identify the minimum filter order that characterized nearly to an ideal filter response. The results show that the IIR filter has a steep transition region when compared to the FIR filters under the similar order.  Our performance analysis showed that the IIR filters, with similar filter order of FIR filters, have also the fastest roll-off, small transition region, and low implementation cost. On the other hand, the FIR filters have linear phase response that related to group delay.  Finally, our analysis concluded that Elliptic able to suppress the sidelobes with a minimum order of 10th   and Equiripple have the fastest roll-off and narrowest transition region compare to other tested FIR filter. Thus, make these two types of filter feasible candidates to be implemented in 5G wireless networks

Spectrum gap analysis with practical solutions for future mobile data traffic growth in Malaysia

In this paper, an efficient spectrum forecasting model is developed to estimate the required spectrum and calculate the spectrum gap in future. This developed model is essentially based on five main metrics and one constant. The five main metrics are the currently available spectrum, sites number growth, data traffic growth, average network utilization, and spectrum efficiency growth. The constant metric is considered to give a space for our model to be used in another country or when a new technology is coming. This developed model is then used to forecast the required spectrum and spectrum gap for Malaysia in 2020. The estimation is performed based on the input market data of four main mobile telecommunication operators in Malaysia: Maxis, Celcom, Digi, and U-Mobile. The input data for this model are collected from various sources, such as the Malaysian Communications and Multimedia Commission, OpenSignal, Analysys Mason, GSMA, and HUAWEI. The results indicate that by 2020, Malaysia will require around 307 MHz of additional spectrum to fulfill the enormous increase of mobile data demands. Addressing this increment can be achieved by launching additional spectrum bands, enhancing spectrum efficiency, off-loading mobile data to unlicensed bands or deploying more site numbers

Key challenges, drivers and solutions for mobility management in 5G networks: a survey

Ensuring a seamless connection during the mobility of various User Equipments (UEs) will be one of the major challenges facing the practical implementation of the Fifth Generation (5G) networks and beyond. Several key determinants will significantly contribute to numerous mobility challenges. One of the most important determinants is the use of millimeter waves (mm-waves) as it is characterized by high path loss. The inclusion of various types of small coverage Base Stations (BSs), such as Picocell, Femtocell and drone-based BSs is another challenge. Other issues include the use of Dual Connectivity (DC), Carrier Aggregation (CA), the massive growth of mobiles connections, network diversity, the emergence of connected drones (as BS or UE), ultra-dense network, inefficient optimization processes, central optimization operations, partial optimization, complex relation in optimization operations, and the use of inefficient handover decision algorithms. The relationship between these processes and diverse wireless technologies can cause growing concerns in relation to handover associated with mobility. The risk becomes critical with high mobility speed scenarios. Therefore, mobility issues and their determinants must be efficiently addressed. This paper aims to provide an overview of mobility management in 5G networks. The work examines key factors that will significantly contribute to the increase of mobility issues. Furthermore, the innovative, advanced, efficient, and smart handover techniques that have been introduced in 5G networks are discussed. The study also highlights the main challenges facing UEs' mobility as well as future research directions on mobility management in 5G networks and beyond

Network coded LDPC code design for a multi-source relaying system

We investigate LDPC code design for a multi-source single-relay system, with uniform phase-fading Gaussian channels. We specifically consider the asymmetric channels for multiple sources, where the channel condition for each source in the system is different. We focus on LDPC code design when network coding (NC) at the relay is utilized. For the asymmetric sources, we firstly introduce a binary field rate splitting theorem which is used to discover an appropriate NC scheme at the relay. This NC scheme is then used to determine the achievable rates of each source and the whole system. These steps assist us in the development of the main contribution of our work, namely, network coded multi-edge type LDPC (NCMET-LDPC) code design. Extrinsic mutual information transfer (EXIT) chart analysis is utilized to optimize the code profiles. Our results demonstrate two key points. (1) From the whole system point of view, our NCMET-LDPC codes achieve better error performance than that of LDPC codes designed for the system without NC. (2) As a consequence of the binary field rate-splitting theorem, our NCMET-LDPC codes also guarantee better error performance of each asymmetric source. The improvement in error performance is typically about 0.3 dB relative to a system without NC

Multichannel cooperative spectrum sensing that integrates channel decoding with fusion-based decision

This paper considers coded multichannel cooperative spectrum sensing (MC-CSS) employing local Neyman-Pearson testing at each sensor and channel decoding integrated with fusion-based decision. A joint multichannel decoding and decision fusion (JMCDDF) algorithm for performing a likelihood ratio test at the fusion center is derived based on the belief propagation technique. For benchmark comparison, we also derive the analytical performance of MC-CSS with error-free reporting channels that do not require channel coding, employing equal decision thresholds at each sensor. Using the JMCDDF algorithm, we compare the performance between uncoded and coded MC-CSS schemes when applying low-density parity-check (LDPC) codes in the presence of reporting channel errors. Monte- Carlo simulation results show considerable performance gains when using the proposed coded MC-CSS schemes. A 3-dB saving in link budget can be achieved by such coded MC-CSS schemes with a short (3, 6) regular LDPC code of codeword length n c = 200, over uncoded MC-CSS. Finally, it is shown that in some cases, protecting the primary user (PU) channels by using variable nodes of higher degrees improves the performance. To equalize the performance for all sensed PU channels, we introduce a simple permutation technique, where, in each transmission, different variable nodes are used to protect local decisions

Coded collaborative spectrum sensing with joint channel decoding and decision fusion

This paper considers the integration of channel decoding with fusion based decision, for coded collaborative spectrum sensing (CSS) employing local Neyman-Pearson (NP) testing at each sensor. We derive a belief-propagation (BP) algorithm for joint channel decoding and decision fusion (JCDDF), based on a factor graph model for coded CSS schemes. Using the Lloyd-Max method, we also propose a new methodology for the local sensor to quantize its observation. The design of the quantizer embeds the binary NP test outcome in the quantization bits. Using the JCDDF algorithm, we show that coded CSS paired even with a short (8,4) extended Hamming code outperforms not only uncoded CSS, but also schemes where channel decoding and decision fusion are executed separately. Then, we consider the design of good channel codes for such CSS schemes. We demonstrate that the JCDDF algorithm employing unequal error protection (UEP) coding improves performance and outperforms equal error protection coding. Furthermore, we present a simple code search algorithm for identifying short UEP codes. Using such UEP codes, we finally show that a performance improvement over uncoded CSS can be attained also without bandwidth expansion using higher order modulations