Orthogonal Frequency Division Multiplexing Interleave Division Multiple Access Research Articles

OFDM-IDMA Sistemi İçin Genetik Algoritmaya Dayalı Biyo-İlhamlı Pilot Dizayn Yaklaşımı

It is well known that the efficiency of a channel estimator employing the strategy of comb-type pilot placement can be controlled by adjusting the positions of pilot tones. In this paper, by considering this situation, in order to maximize the estimation precision of the least squares (LS) algorithm utilized as a channel estimator in orthogonal frequency division multiplexing – interleave division multiple access (OFDM-IDMA) scheme, the genetic algorithm (GA) possessing a wide range of uses due to its powerful problem solving capability was utilized in the optimization of pilot positions. Besides, the computational load of mean square error (MSE) which is used as the objective function of GA was avoided by employing its upper bound during the optimization process. The upper bound of MSE was achieved by utilizing the Gershgorin disc theorem. In the simulations, the suggested pilot arrangement strategy based on the GA was compared to the conventional techniques like equispaced and random pilot placements in point of two criteria known as bit error rate (BER) and MSE. Simulation results put forth that GA-based pilot design strategy establishes a very clear superiority over the other considered methods by providing significant MSE and BER performances.

Advanced pilot design procedure based on HS algorithm for OFDM‐IDMA system

The direct effect of the pilot positions to the channel estimation performance gives an opportunity for minimising the estimation errors in multicarrier transmission technologies. To this end, harmony search (HS) algorithm is proposed for optimising the pilot distribution pattern in order to increase the performance of least squares estimator employed in orthogonal frequency division multiplexing-interleave division multiple access (OFDM-IDMA) system. Besides, the upper bound of mean square error (MSE) utilised as the fitness function of HS algorithm is obtained by using Gershgorin disc theorem to get rid of matrix inversion process required in MSE calculation. In the simulations, the authors' proposed HS-based pilot optimisation technique proves to be an effective way of pilot design for OFDM-IDMA system by providing a clear performance superiority over the other considered pilot placement strategies.

An efficient technique based on firefly algorithm for pilot design process in OFDM-IDMA systems

Accurate placement of pilot tones has been a crucial task in multicarrier transmission technologies since there is a strong relation between pilot positions and channel estimation performance. Therefore, the firefly algorithm (FA) is proposed for achieving the optimal pilot distribution by optimizing the pilot positions in order to minimize the estimation errors of the least squares algorithm employed in orthogonal frequency division multiplexing-interleave division multiple access (OFDM-IDMA) systems. According to the simulation results, our proposed FA-based pilot optimizer provides a great performance increase in OFDM-IDMA systems by obtaining the most appropriate pilot distribution pattern among the considered pilot placement strategies. The upper bound of mean square error (MSE) is used as the fitness function in the optimization process for avoiding the matrix inversion operation that is needed when calculating MSE itself.

TDCS-IDMA System for Cognitive Radio Networks With Cloud

Cognitive radio (CR) is a novel technology for improving the utilization of radio electromagnetic spectrum. Recently, a new model called cognitive radio networks with cloud (CRNC) has been proposed to eliminate the constraints (pertinent to traditional CR) on power, memory space, and computational capacity. To enable multiple access of CRNC system, orthogonal frequency division multiplexing-interleave division multiple access (OFDM-IDMA) has been investigated. Traditional OFDM-IDMA may not be applied to CRNC in a straightforward manner. This is because the spectral nulling in CR and the subsequent spectral sensing mismatch (between CR transmitter and receiver) could lead to unacceptable data error performance. This paper presents a new multiple access communication system, called transform domain communication system IDMA communication system, to deal with spectral nulling problems. Two improved schemes based on BPSK and cyclic code shift keying modulations are proposed. The proposed system structure integrates the advantages of both OFDM-IDMA and CRNC, which can make full use of other users’ information while satisfying CR constraints. Simulation results demonstrate that the two proposed system architectures can achieve significant improvement on BER performance, multiple access capability, and anti-interference ability with spectral nulling.

Joint Transmit Power Allocation and Splitting for SWIPT Aided OFDM-IDMA in Wireless Sensor Networks

In this paper, we propose to combine Orthogonal Frequency Division Multiplexing-Interleave Division Multiple Access (OFDM-IDMA) with Simultaneous Wireless Information and Power Transfer (SWIPT), resulting in SWIPT aided OFDM-IDMA scheme for power-limited sensor networks. In the proposed system, the Receive Node (RN) applies Power Splitting (PS) to coordinate the Energy Harvesting (EH) and Information Decoding (ID) process, where the harvested energy is utilized to guarantee the iterative Multi-User Detection (MUD) of IDMA to work under sufficient number of iterations. Our objective is to minimize the total transmit power of Source Node (SN), while satisfying the requirements of both minimum harvested energy and Bit Error Rate (BER) performance from individual receive nodes. We formulate such a problem as a joint power allocation and splitting one, where the iteration number of MUD is also taken into consideration as the key parameter to affect both EH and ID constraints. To solve it, a sub-optimal algorithm is proposed to determine the power profile, PS ratio and iteration number of MUD in an iterative manner. Simulation results verify that the proposed algorithm can provide significant performance improvement.

Regularized Recursive Least Square-Based Time Domain Iterative Channel Estimation Scheme for OFDM-IDMA Systems

In the recent time, there have been investigation efforts into time domain channel estimation techniques, exploiting underlying sparseness in OFDM channel, for multiuser-based orthogonal frequency division multiplexing-interleave division multiple access (OFDM-IDMA) systems. This paper developed and proposed a new channel estimation algorithm for the OFDM-IDMA systems. This is called regularized correlated time-averaged-based variable forgetting factor recursive least square (RCTVFF-RLS)-based channel impulse response (CIR) estimator. The performances of the proposed estimator are compared with the performances of some previous estimators in literature with the aid of computer simulation. It is found that the proposed RCTVFF-RLS-based CIR estimator outperforms all the other estimators considered in this paper, and these performances are documented for the system operating under fast and slow fading channel scenarios. However, the proposed estimator exhibits higher computational complexity than the poorest performing estimator considered in this paper. Its computational complexity is in the same neighborhood with some closely performing estimators considered.

Design and Analysis of Numerical Interleaver for IDMA Schemes with Iterative Multi-user Detection

Objective: This work provides a comprehensive study of a novel orthogonal interleaver set based on particular numerical equation for generation of user specific interleavers. Methods/Analysis: Performance analysis is done based upon the computer simulations in various scenarios with IDMA system and SC-FDMA-IDMA system, under different channel conditions including Additive White Gaussian Noise (AWGN) and Under Water Acoustic (UWA) channel to compare proposed interleaver with other interleavers in literature. The performance of different interleavers is compared on the basis of bit error rate (BER) results and also by hardware and bandwidth requirements. Findings: Compared to other interleavers discussed in literature, the proposed interleaver set is easy to generate, more-over this work has presented a method which doesn’t require common master random interleaving pattern to develop other interleaving patterns. The analysis confirms that the proposed method of interleaver generation outperforms various other interleavers in terms of BER performance and bandwidth requirement, while providing considerably lower complexity. Applications: Applications of orthogonal interleavers include all non-orthogonal multiple access schemes based on Multi-User Detection (MUD) strategy including Interleave Division Multiple Access (IDMA), Orthogonal Frequency Division Multiplexing-Interleave Division Multiple Access (OFDM-IDMA) and Single Carrier Frequency Division Multiple Access-Interleave Division Multiple Access (SC-FDMA-IDMA) scheme, employing user specific interleavers for user separation.

Channel estimation using an adaptive neuro fuzzy inference system in the OFDM-IDMA system

In this paper, a channel estimator based on an adaptive neuro fuzzy inference system (ANFIS) is proposed for the purpose of estimating channel frequency responses in orthogonal frequency division multiplexing-interleave division multiple access (OFDM-IDMA) systems. To see the performance of our proposed channel estimation method, five different techniques including well-known pilot-based estimation algorithms such as least squares (LS) and minimum mean square error (MMSE) with other heuristic methods like multilayered perceptron (MLP) trained by a backpropagation (BP) algorithm (MLP-BP), MLP trained by the Levenberg--Marquardt (LM) algorithm (MLP-LM), and radial basis function neural network (RBFNN) are compared with our proposed method by computer simulations. The comparisons are made with the aid of bit error rate and mean square error graphs. According to the simulation results, our proposed channel estimator based on ANFIS shows better performance than both the LS algorithm and the other considered heuristic methods like MLP-BP, MLP-LM, and RBFNN, whereas the MMSE algorithm still shows the best performance as expected because of exploiting channel statistics and noise information, which makes it very complex to be used in any system. As well as being less complex compared to the MMSE algorithm, the estimator based on ANFIS does not need pilot tones for channel estimation. These properties bring our proposed method to an advantageous position among the other estimation techniques.

GRP‐based interleaver for IDMA systems over frequency selective channel

An interleave-division multiple-access (IDMA) system supports the presence of multiple users in a cell by resorting to a different interleaver per user. Therefore the choice of the interleaver critically impinges on system performance. A new interleaver structure is proposed for the so-called STBC–OFDM–IDMA [space-time block coding (STBC), orthogonal frequency division multiplexing (OFDM) and IDMA] architecture, combining the viable features of the STBC, the OFDM and the IDMA techniques. This interleaver is based on the new idea of adopting permutation control keys generated using two cryptography elliptic curves in which the degree of randomness of the interleaved sequence is scalable by using several rounds and a different subkey in each round. In addition to offering a certain degree of data security, it is shows through simulation results that the resulting architecture incorporating the proposed interleaver yields a viable bit error rate performance.

Iterative receiver with soft‐input‐based‐channel estimation for orthogonal frequency division multiplexing‐interleave division multiple access systems

This article presents two sets of channel estimation methods that employ soft input from the decoder to enhance channel estimation process for orthogonal frequency division multiplexing -interleave division multiple access (OFDM-IDMA) system. The first channel estimation scheme exploits both time and frequency domains for channel estimation and prediction. The estimator exploits turbo principle while using iterative based sequential linear minimum mean square error (ISLMMSE) for channel transfer function (CTF) estimation, and regularised variable step size normalised least mean square (l1-VSSNLMS) algorithm for channel impulse response (CIR) prediction. The channel estimation scheme exchanges information with the Multi-User Detector (MUD), and also employs soft information feedback from the decoder for the enhancement of channel estimation. The second iterative channel estimation scheme, in time domain, is based on regularised noise power estimate-based variable forgetting factor recursive least square (l1-NPEVFF-RLS)-based CIR estimator. The performances of the proposed estimators are documented through computer simulation. Their comparative performances with other schemes in the literature are presented in this article. From the simulation results, the two proposed channel estimators exhibit better performance in comparison with other schemes in the literature, but with higher computational complexities. However, of the two proposed methods, the l1-NPEVFF-RLS-based CIR estimator that exhibits almost the same performance as the combined ISLMMSE-based CTF estimator and l1-VSSNLMS-based predictor exhibits lower computational complexity.

Adaptive Correction Algorithm for OFDM-IDMA Systems With Carrier Frequency OFFSET in A Fast Fading Multipath Channel

The Orthogonal Frequency Division Multiplexing-Interleave Division Multiple Access (OFDM-IDMA) scheme, which offers significant improvement on the performance of the conventional IDMA technique, has been in the forefront of recent mobile communication researches as it is expected to deliver a high quality, flexible and efficient high data-rate mobile transmission. Most papers on OFDM-IDMA scheme assume a system free of carrier frequency offset. However, the scheme is susceptible to synchronization errors and performance degradation because of the presence of OFDM, which is highly sensitive to carrier frequency offset (CFO) especially at the uplink. The effect of CFO on the performance of the scheme, in a slow fading multipath channel scenario, is therefore investigated, and analyzed. Also, the effect of CFO on the performance of the OFDM-IDMA scheme, in a fast fading multipath channel, which has not been hitherto reported in literature, is investigated and analyzed. An LMS-based adaptive synchronization algorithm is therefore employed to mitigate the degrading impact of carrier frequency offset errors on the OFDM-IDMA scheme. Simulation results clearly show that the presence of CFO degrades the performance of the system and that performance degradation due to CFO, increases in a fast fading multipath channel in comparison with slow fading channel scenario. Furthermore, results show substantial improvement in the overall output of the system upon the application of the adaptive synchronization algorithm, which is implemented in both slow, and fast fading Rayleigh multipath channel scenarios.

OFDM-IDMA with User Grouping

A generalized version of orthogonal frequency division multiplexing interleave division multiple access (OFDM-IDMA) referred to as grouped OFDM-IDMA (G-OFDM-IDMA) is introduced in this paper. By dividing users into groups and transmitting each group's data only on some (as opposed to all) subcarriers, G-OFDM-IDMA can have much lower decoding complexity compared with conventional OFDM-IDMA while preserving the bit error probability (BEP) performance and the bandwidth efficiency. The user grouping problem is formulated into an integer linear programming problem whose suboptimal solution is proposed and compared with the lower bound. The optimization complexity issue is also addressed. Simulations are carried out to test the performance of G-OFDM-IDMA under various system configurations. It is observed that up to 80% complexity could be saved when the conventional OFDM-IDMA is substituted by G-OFDM-IDMA configured according to the suboptimal grouping solution.

Signal Detection for OFDM-IDMA Uplink over Doubly Selective Channels

Orthogonal frequency division multiplexing-interleave division multiple access (OFDM-IDMA) systems may suffer from serious inter-carrier interference (ICI) in time-and frequency-selective (doubly selective) channels. In such case, the conventional OFDM-IDMA detection algorithm for quasi-static channels will result in significantly performance degradation. In this paper, signal detection is investigated for OFDM-IDMA uplink over doubly selective channels. Firstly, the impact of time-varying channels for OFDM-IDMA uplink is analyzed, which leads to the failure of the conventional algorithm. Secondly, a novel iterative detection algorithm is developed based on an integrated interference canceller, which can iteratively estimate and mitigate the ICI as well as multiple access interference (MAI) simultaneously. In addition, an improved detection algorithm is derived for reducing the complexity using an approximation to the mean and variance of the interference. Simulation results indicate that the proposed algorithm can significantly enhance the system performance to the conventional case, and the improved algorithm can strike a balance between performance and complexity.

Channel Estimation Algorithms for OFDM-IDMA: Complexity and Performance

In this paper, a number of channel estimation algorithms for iterative receivers are compared for the case of an up-link orthogonal frequency division multiplexing interleave division multiple access (OFDM-IDMA) system. Both pilot based algorithms, used to obtain an initial estimate, as well as semi-blind decision-directed algorithms working as a component of the iterative receiver are considered. Algorithms performing either joint minimum mean square error (MMSE) channel estimation, or iterative estimation using space-alternating expectation maximization (SAGE), are evaluated. The considered algorithms differ in terms of complexity, as well as performance. The main contribution of this paper is to give an overview of different channel estimation approaches for OFDM-IDMA, where the complexity versus performance tradeoff is at the focal point. There is no single channel estimator providing the best tradeoff and our analysis shows how the system load (number of users) and the SNR influence the estimator choice.

Improved Detection of Uplink OFDM-IDMA Signals with Carrier Frequency Offsets

This letter proposes an improved detection scheme to mitigate the influence of carrier frequency offsets (CFOs) in uplink orthogonal frequency division multiplexing-interleave division multiple access (OFDM-IDMA) systems. The basic principle is to iteratively estimate and cancel the combined interference from multiple users and CFOs at the receiver so that the additional interference due to the residual CFOs from other users can be suppressed. Simulation results show that the proposed scheme can effectively eliminate the interference and significantly improve the system performance in the presence of CFOs.

Improved SNR Evolution for OFDM-IDMA Systems

The bit error rate performance of interleave division multiple access (IDMA) based systems can be predicted by signal-to-noise ratio (SNR) evolution which tracks the average symbol SNR at each iteration and provides a faster solution than brute-force simulations. As the desired SNR in the evolution procedure is hard to obtain, approximate SNR updating formula has been widely adopted in the literature. In this paper a revised SNR updating formula is proposed for orthogonal frequency division multiplexing interleave division multiple access (OFDM-IDMA) systems in Rayleigh fading channels. Theoretical analysis shows that the new updating formula provides a tighter lower bound of the expected SNR in the evolution procedure compared with the existing one. We then verified this by simulations.

Variable Interleaver Allocation for Downlink OFDM-IDMA

In this letter, a variable interleaver allocation scheme is proposed to alleviate the high peak-to-average power ratio (PAPR) of downlink OFDM-IDMA (orthogonal frequency division multiplexing-interleave division multiple access). The basic idea is to allocate multiple interleaving patterns for each user, so as to decide the best pattern with the lowest peak value. Furthermore, a variable interleaver design scheme is combined to generate multiple patterns from an original one. It is shown that the proposed scheme can achieve the theoretical bound of PAPR reduction performance, while making a good tradeoff among PAPR reduction, system performance and computational complexity.

Analysis and design of OFDM‐IDMA systems

AbstractThis paper deals with the analysis and design of orthogonal frequency‐division multiplexing interleave‐division multiple‐access (OFDM‐IDMA). We begin with the analysis of the information‐theoretical advantages of non‐orthogonal transmission schemes in fading multiple‐access channels. We then turn attention to practical design issues. A signal‐to‐noise ratio (SNR) evolution technique is developed to predict the bit‐error‐rate (BER) performance of OFDM‐IDMA. This technique is applied to system design and optimisation. Through proper power allocation, OFDM‐IDMA can achieve the multi‐user gain (MUG) predicted by information‐theoretical analysis. It is also an attractive option in compensating for the clipping effect caused by peak‐power limitation. Numerical examples show that OFDM‐IDMA can (i) alleviate the PAPR problem commonly suffered by OFDM‐based schemes; (ii) deliver significant MUG compared with other orthogonal alternatives; (iii) provide robust communications in frequency‐selective channels; and (iv) support high single‐user throughput. Copyright © 2008 John Wiley & Sons, Ltd.