IDMA for the Multiuser MIMO-OFDM Uplink: A Factor Graph Framework for Joint Data Detection and Channel Estimation

The data rates of wireless communication systems operating in a frequency selective background can be improved by using Multiple-Input Multiple-Output (MIMO) in association with Orthogonal Frequency Division Multiplexing (OFDM). The shortcomings of Code Division Multiple Access (CDMA) can be overcome by using Interleave Division Multiple Access (IDMA) which is easily integrated into MIMO systems. IDMA combined with OFDM can be used to implement frequency-selective channels. In this paper we outline the basic principles of an OFDM-IDMA transmitter and receiver followed by simulation results to compare the efficiency of implementing OFDM-IDMA. The performance of our receiver is defined by the simulation results of the energy per bit to noise power spectral density ratio (Eb/N0) and Bit Error Rate (BER). A dramatic decrease in BER is achieved by using the channel decoding and channel estimation techniques proposed. It is found that the OFDM-IDMA system is more effective than just using IDMA or OFDM-CDMA. Thus the whole research is to try and implement a technique that proves to be extremely effective over the already existing techniques.

A novel Multiuser Detection (MUD) scheme is proposed for DS-CDMA systems employing the so-called Harmony Search (HS) algorithm, which is a novel meta-heuristic optimisation method. We specifically design the HS aided MUD for the communications problem considered and apply it in an iterative joint Channel Estimation (CE), MUD and channel decoding framework. The simulation results demonstrate that a near-single-user performance can be achieved by the proposed algorithm while avoiding the excessive-complexity full-search-based optimum detection even in overloaded DS-CDMA systems. Moreover, the HS algorithm can be efficiently applied in the Expectation Maximisation (EM) based CE framework.

This paper carries comprehensive comparison of Interleave Division Multiple Access (IDMA) and Code Division Multiple Access (CDMA) systems in terms of performance (BER) and behavior to different number of users. Performance analysis of two systems whose transmitter and receiver structures are almost same are studied under Additive White Gaussian Noise (AWGN) and performance differences are illustrated by simulation results. Although Multiple Access Interference (MAI) and Intersymbol Interference (ISI) can affect the performance of the CDMA system, simulation results illustrates that IDMA system model achieves this type of problem using their interleavers. Results also show that large number of users can easily be adapted by the IDMA scheme much easier than CDMA scheme.

Interleave-division multiple access (IDMA) has recently been proposed as an alternative to CDMA. IDMA employs user-specific interleavers combined with low-rate channel coding for user separation. It can outperform coded CDMA when iterative receivers are used, and it allows the design of multiuser detectors with moderate complexity. In this paper, we extend IDMA to MIMO multiuser systems employing spatial multiplexing. We also develop an iterative receiver for MIMO-IDMA that incorporates an efficient soft multiuser detector whose complexity is linear in the number of users. Both flat-fading and frequency-selective MIMO channels are considered. The performance of the proposed MIMO-IDMA system is assessed through simulation results.

In this paper, turbo multiuser detectors in Interleave Division Multiple Access (IDMA) based systems are considered for short range underwater acoustic channels (UACs). In such long reverberant channels that demand high computational complexity, turbo detectors based on minimum mean square error (MMSE) criterion are an attractive solution to achieve a good balance between performance and complexity. Two different synchronous IDMA structures are studied and applied to signals acquired during sea trials in the North Sea; firstly, a channel estimation (CE) based IDMA with Rake reception, and secondly, an adaptive interference canceller (IC-IDMA). Both schemes include phase tracking, channel coding and are based on a chip-rate equalization and detection, which are fed in by a composite multiuser signal of the users' feedback soft information. Experimental results of three different channel ranges demonstrate that the direct adaptive receiver has better performance and additionally mitigates the errors associated with the CE based IDMA receiver while maintaining lower complexity.

This paper is concerned with the power allocation problem for practically coded interleave-division multiple-access (IDMA) systems with iterative multi-user detection (MUD) over multiple access channels (MACs). Both Additive White Gaussian Noise (AWGN) and fading channels are considered. For AWGN channels, two power allocation methods based on linear programming are discussed and compared with an interior-point method (IPM). These techniques are extended to power allocation over fading channels. Numerical results show that, with power optimization, IDMA can achieve significant performance improvements over TDMA in fading environments.

This paper investigates the gains harvested through base station cooperation in the up-link for a multi-user (MU) Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system, operating in a real indoor environment. The base stations perform joint detection using an iterative receiver that carries out multi-user detection and channel estimation via soft information from the single-user decoders. Performance evaluation is carried out using real channels from an indoor dynamic dual MIMO link measurement campaign. The measured scenario represent a real life situation where two users communicate with two base stations, each with two antennas, in an environment resembling a shopping mall or an airport terminal. System performance is evaluated in terms of both Bit-Error Rate (BER) vs. Signal-to-Interference Ratio (SIR) and Cumulative Distribution Functions (CDF) for the instantaneous BER. Also, the impact of using soft information in the channel estimation is analyzed.

We propose a layered space time (LST) transceiver in a multiuser code division multiple access (CDMA) mobile communication system. In particular, we examine a multiuser iterative receiver with joint detection, channel estimation and decoding in a frequency selective fading channel. The iterative parallel interference canceller (PIC) with statistics combining is used as the multiuser detection scheme and a least mean square (LMS) adaptive algorithm is applied to estimate the multiple input and multiple output (MIMO) frequency selective fading channel. Simulation results are presented to demonstrate the performance of this receiver. It is shown that the performance of the receiver with iterative channel estimation is close to that of the receiver with perfect channel state information (CSI).

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.

In this new information age, high data rate and strong reliability features our wireless communication systems and is becoming the dominant factor for a successful deployment of commercial networks. MIMO-OFDM (multiple input multiple output-orthogonal frequency division multiplexing), a new wireless broadband technology, has gained great popularity for its capability of high rate transmission and its robustness against multi-path fading and other channel impairments. A major challenge to MIMO-OFDM systems is how to obtain the channel state information accurately and promptly for coherent detection of information symbols and channel synchronization. In the first part, this dissertation formulates the channel estimation problem for MIMO-OFDM systems and proposes a pilot-tone based estimation algorithm. A complex equivalent base-band MIMO-OFDM signal model is presented by matrix representation. By choosing equally-spaced and equally-powered pilot tones from sub-carriers in one OFDM symbol, a down-sampled version of the original signal model is obtained. Furthermore, this signal model is transformed into a linear form solvable for the LS (least-square) estimation algorithm. Based on the resultant model, a simple pilot-tone design is proposed in the form of a unitary matrix, whose rows stand for different pilot-tone sets in the frequency domain and whose columns represent distinct transmit antennas in the spatial domain. From the analysis and synthesis of the pilot-tone design in this dissertation, our estimation algorithm can reduce the computational complexity inherited in MIMO systems by the fact that the pilot-tone matrix is essentially a unitary matrix, and is proven an optimal channel estimator in the sense of achieving the minimum MSE (mean squared error) of channel estimation for a fixed power of pilot tones. In the second part, this dissertation addresses the wireless location problem in WiMax (worldwide interoperability for microwave access) networks, which is mainly based on the MIMO-OFDM technology. From the measurement data of TDOA (time difference of arrival), AOA (angle of arrival) or a combination of those two, a quasi-linear form is formulated for an LS-type solution. It is assumed that the observation data is corrupted by a zero-mean AWGN (additive white Gaussian noise) with a very small variance. Under this assumption, the noise term in the quasi-liner form is proved to hold a normal distribution approximately. Hence the ML (maximum-likelihood) estimation and the LS-type solution are equivalent. But the ML estimation technique is not feasible here due to its computational complexity and the possible nonexistence of the optimal solution. Our proposed method is capable

The channel estimation techniques based on comb-type pilot arrangement, which is used in multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) system, is investigated in this paper. In view of the contradiction of the time-domain least squares (LS) channel estimation bit error rate (BER) performance and the practical realization complexity, a novel optimal pilots design method for multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) is proposed. By using this approach no large matrix pseudo-inverse is required, which greatly reduces the complexity of algorithms. Simulation results show that the proposed method provides better BER performance and lower complexity. And it is easy to implement in practical systems.

Problem statement: This study presents the performance analysis of turbo assisted Interleave Division Multiple-Access (IDMA) system with Multi Input Multi Output (MIMO) support for multi user scenario over correlated frequency selective and uncorrelated frequency selective channel. Approach: The key principle of IDMA is that interleaver unique which distinguishes the users in contrast to spreading sequence in Code Division Multiple Access System (CDMA). Results: In this work, we assume that Interleavers are generated independently and randomly. At the receiver, we employed Ordered SIC (OSIC) technique using ZF and MMSE criterion to combat Inter Antenna Interference (IAI) and Multi User Interference (MUI) problem along with iterative decoding to improve the performance in terms of BER. The performance of system has been discussed for different channel conditions with realistic channel model using extensive simulation runs based on Monte Carlo simulation trials. We have exhibited the flexibility and robustness provided by MIMO-IDMA. Conclusion/Recommendations: It has been proved from the results that IDMA principle can be applied to realize many potential performance gains highlighted by information theory, including coding gain multiplexing gain and multiuser gain. Simulation results presented to demonstrate the benefits of IDMA with MUD and iterative decoding. It is discerned that IDMA performs better than CDMA in frequency selective channel for high load conditions which is assessed through computer simulation results.

In this paper, we propose a joint channel estimation and symbol detection (JCESD) algorithm relying on message-passing algorithms (MPA) for orthogonal frequency division multiple access (OFDMA) systems. The channel estimation and symbol detection leverage the framework of expectation propagation (EP) and belief propagation (BP) with the aid of Gaussian approximation, respectively. Furthermore, to reduce the computation complexity involved in channel estimation, the matrix inversion is transformed into a series of diagonal matrix inversions through the Sherman-Morrison formula. Simulation experiments show that the proposed algorithm can reduce the pilot overhead by about 50%, compared with the traditional linear minimum mean square error (LMMSE) algorithm, and can approach to the bit error rate (BER) performance bound of perfectly known channel state information within 0.1 dB.

Interleave division multiple access (IDMA) is a potential candidate for the future fifth generation (5G) systems. In this paper, we propose a novel architecture for IDMA system with low latency while maintaining low complexity. In the conventional architecture, the IDMA receiver sequentially processes deinterleaving, despreading, spreading and interleaving for multiuser detection. The proposed architecture, which is called the interleaved domain, can perform multi-user detection directly without deinterleaving the received frame. Because of this, the interleaving is no longer needed in the interference cancellation loop resulting in the decrease of latency by half and the increase of throughput by twice. In VLSI implementation results, the proposed architecture has reduced circuit area and power consumption by 53% and 58% compared to the conventional architecture on the same throughput condition.

In this contribution, we consider the performance of multi-user transmitter pre-processing (MUTP) assisted interleaved division multiple access (IDMA) scheme for downlink (DL) communications. We realize MUTP using Zero Forcing (ZF)algorithm. In this paper, we consider turbo coded system to achieve high coding gain. We construct the turbo code using parallel concatenated convolutional encoder and certain bits are punctured periodically to achieve code rate ½. We construct the pre-processing matrix using channel state information of all the users. We evaluate the performance of such coded ZF-MUTP assisted IDMA system for realistic channel model based on SUI channel model specifications. From our simulations, we observe that the ZF-MUTP assisted multi-user IDMA system provides better performance in terms of bit error rate (BER) with low signal to noise ratio (SNR).