Iterative IDMA Receivers with Random and Tree Based Interleavers

In recent days, on the horizon of wireless world, newly proposed multiple access scheme known as Interleave-Division Multiple-Access (IDMA) has made its remarkable impact. Researchers all over world, are making hard marks to establish the scheme to establish its claim as potential candidate for 4th generation wireless communication systems. This paper is concerned with the performance enhancement of iterative IDMA systems under coded & uncoded environment. The performance of an interleave division multiple access (IDMA) system can be improved by the optimized power allocation techniques. Based on the optimized power allocation technique we compare the performance of coded & uncoded IDMA system with random interleaver & tree based interleaver. During the simulation, it has been observed that tree based interleaver demonstrate the similar bit error rate (BER) performance to that of random interleaver however on other fronts including bandwidth and memory requirement at transmitter and receiver ends, it outperforms the random interleavers. Keywords: Tree Based Interleaver, Random Interleaver, IDMA, linear programming, power allocation, BER

Performance Evaluation of Maximal Ratio Receiver Combining Diversity with Prime Interleaver for Iterative IDMA Receiver

The antenna diversity mechanism is established as the well known mechanism for reduction of probability of occurrence of communication failures (outages) caused by fades. In receiver diversity, multiple antennas are employed at the receiver side in case of transmitter diversity, multiple antennas are the integral part of transmitter section.. In this paper, Maximal Ratio Receiver Combining (MRRC) diversity technique is evaluated to mitigate the effect of fading in IDMA scheme employing random interleaver and prime interleaver with single transmit two receiving antennas in low rate coded environment. For the performance evaluation, channel is assumed to be Rayleigh multipath channel with BPSK modulation. Simulation results demonstrate the significant improvement in BER performance of IDMA with maximal ratio receiver combining (MRRC) diversity along with prime interleaver and random interleaver and it has also been observed that BER performance of prime interleaver is similar to that of random interleaver with reduced bandwidth and memory requirement at transmitter and receiver side. Keywords: Multipath Fading, MRRC diversity, Multi user detection, Interleave-Division Multiple Access (IDMA) Scheme, Random Interleaver, Prime Interleave

Performance analysis of a novel OWDM-IDMA approach for wireless communication system

Efficiency and adaptivity play a major role in the design of fourth-generation wireless systems (4G). These systems should be efficient in terms of bandwidth and power allocation and will satisfy the users requirement on low power consumption, little interferences with other systems, and high rate transmission. Moreover, low complexity transceivers are expected. This paper will propose a novel multiple access technique called OWDM-IDMA (Orthogonal Wavelength-Division Multiplexing-Interleave Division Multiple Access) as the combination of the OWDM (Orthogonal Wavelength-Division Multiplexing) and IDMA (Interleave Division Multiple Access) schemes. The IDMA and OWDM principles are also outlined. The comparison between the conventional OFDM-IDMA and the proposed OWDM-IDMA is performed in term of Power to Average Power Ratio PAPR, as well as evaluating the performance of our presented technique over Additive White Gaussian Noise AWGN multipath channels by estimating the BER (Binary Error Rate)

Capacity Approaching Coding Strategies for Machine-to-Machine Communication in IoT Networks

Radio access technologies for mobile communications are characterized by multiple access (MA) strategies. Orthogonal MA techniques were a reasonable choice for achieving good performance with single user detection. With the tremendous growth in the number of mobile users and the new internet of things (IoT) shifting paradigm, it is expected that the monthly mobile data traffic worldwide will exceed 24.3 exabytes by 2019, over 100 billion IoT connections by 2025, and the financial impact of IoT on the global economy varies in the range of 3.9 to 11.1 trillion dollars by 2025. In light of the envisaged exponential growth and new trends, one promising solution to further enhance data rates without increasing the bandwidth is by increasing the spectral efficiency of the channel. Non-orthogonal MA techniques are potential candidates for future wireless communications. The two corner points on the boundary region of the MA channel are known to be achievable by single user decoding followed by successive decoding (SD). Other points can also be achieved using time sharing or rate splitting. On the other hand, machine-to-machine (M2M) communication which is an enabling technology for the IoT, enables massive multipurpose networked devices to exchange information among themselves with minor or no human intervention. This thesis consists of three main parts. In the first part, we propose new practical encoding and joint belief propagation (BP) decoding techniques for 2-user MA erasure channel (MAEC) that achieve any rate pair close to the boundary of the capacity region without using time sharing nor rate splitting. While at the encoders, the corresponding parity check matrices are randomly built from a half-rate LDPC matrix, the joint BP decoder employs the associated Tanner graphs of the parity check matrices to iteratively recover the erasures in the received combined codewords. Specifically, the joint decoder performs two steps in each decoding iteration: 1) simultaneously and independently runs the BP decoding process at each constituent sub-graph to recover some of the common erasures, 2) update the other sub-graph with newly recovered erasures and vice versa. When the number of erasures in the received combined codewords is less than or equal to the number of parity check constraints, the decoder may successfully decode both codewords, otherwise the decoder declares decoding failure. Furthermore, we calculate the probability of decoding failure and the outage capacity. Additionally, we show how the erasure probability evolves with the number of decoding iterations and the maximum tolerable loss. Simulations show that any rate pair close to the capacity boundary is achievable without using time sharing. In the second part, we propose a new cooperative joint network and rateless coding strategy for machine-type communication (MTC) devices in the multicast settings where three or more MTC devices dynamically form a cluster to disseminate messages between themselves. Specifically, in the basic cluster, three MTC devices transmit their respective messages simultaneously to the relay in the first phase. The relay broadcasts back the combined messages to all MTC devices within the basic cluster in the second phase. Given the fact that each MTC device can remove its own message, the received signal in the second phase is reduced to the combined messages coming from the other two MTC devices. Hence, this results in exploiting the interference caused by one message on the other and therefore improving the bandwidth efficiency. Furthermore, each group of three MTC devices in vicinity can form a basic cluster for exchanging messages, and the basic scheme extends to N MTC devices. Furthermore, we propose an efficient algorithm to disseminate messages among a large number of MTC devices. Moreover, we implement the proposed scheme employing practical Raptor codes with the use of two relaying schemes, namely amplify and forward (AF) and de-noise and forward (DNF). We show that with very little processing at the relay using DNF relaying scheme, performance can be further enhanced. We also show that the proposed scheme achieves a near optimal sum rate performance. In the third part, we present a comparative study of joint channel estimation and decoding of factor graph-based codes over flat fading channels and propose a simple channel approximation scheme that performs close to the optimal technique. Specifically, when channel state information (CSI) is not available at the receiver, a simpler approach is to estimate the channel state of a group of received symbols, then use the approximated value of the channel with the received signal to compute the log likelihood ratio. Simulation results show that the proposed scheme exhibits about 0.4 dB loss compared to the optimal solution when perfect CSI is available at the receiver

Coherent receiver design and analysis for interleaved division multiple access (IDMA)

This thesis discusses a new multiuser detection technique for cellular wireless communications. Multiuser communications is critical in cellular systems as multiple terminals (users) transmit to base stations (or wireless infrastructure). Efficient receiver methods are needed to maximise the performance of these links and maximise overall throughput and coverage while minimising inter-cell interference. Recently a new technique, Interleave-Division Multiple Access (IDMA), was developed as a variant of direct-sequence code division multiple access (DS-CDMA). In this new scheme users are separated by user specific interleavers, and each user is allocated a low rate code. As a result, the bandwidth expansion is devoted to the low rate code and not weaker spreading codes. IDMA has shown to have significant performance gains over traditional DS-CDMA with a modest increase in complexity. The literature on IDMA primarily focuses on the design of low rate forward error correcting (FEC) codes, as well as channel estimation. However, the practical aspects of an IDMA receiver such as timing acquisition, tracking, block asynchronous detection, and cellular analysis are rarely studied. The objective of this thesis is to design and analyse practical synchronisation, detection and power optimisation techniques for IDMA systems. It also, for the first time, provides a novel analysis and design of a multi-cell system employing a general multiuser receiver. These tools can be used to optimise and evaluate the performance of an IDMA communication system. The techniques presented in this work can be easily employed for DS-CDMA or other multiuser receiver designs with slight modification. Acquisition and synchronisation are essential processes that a base-station is required to perform before user's data can be detected and decoded. For high capacity IDMA systems, which can be heavily loaded and operate close to the channel capacity, the performance of acquisition and tracking can be severely affected by multiple access interference as well as severe drift. This thesis develops acquisition and synchronisation algorithms which can cope with heavy multiple access interference as well as high levels of drift. Once the timing points have been estimated for an IDMA receiver the detection and decoding process can proceed. An important issue with uplink systems is the alignment of frame boundaries for efficient detection. This thesis demonstrates how a fully asynchronous system can be modelled for detection. This thesis presents a model for the frame asynchronous IDMA system, and then develops a maximum likelihood receiver for the proposed system. This thesis develops tools to analyse and optimise IDMA receivers. The tools developed are general enough to be applied to other multiuser receiver techniques. The conventional EXIT chart analysis of unequal power allocated multiuser systems use an averaged EXIT chart analysis for all users to reduce the complexity of the task. This thesis presents a multidimensional analysis for power allocated IDMA, and shows how it can be utilised in power optimisation. Finally, this work develops a novel power zoning technique for multicell multiuser receivers using the optimised power levels, and illustrates a particular example where there is a 50% capacity improvement using the proposed scheme. -- provided by Candidate

Analysis and optimization of CDMA systems with chip-level interleavers

In this paper, we present an unequal power allocation technique to increase the throughput of code-division multiple-access (CDMA) systems with chip-level interleavers. Performance is optimized, respectively, based on received and transmitted power allocation. Linear programming and power matching techniques are developed to provide solutions to systems with a very large number of users. Various numerical results are provided to demonstrate the efficiency of the proposed techniques and to examine the impact of system parameters, such as iteration number and interleaver length. We also show that with some very simple forward error correction codes, such as repetition codes or convolutional codes, the proposed scheme can achieve throughput reasonably close to that predicted by theoretical limit in multiple access channels