Interleave Division Multiple Access Receiver Research Articles

A Memory-Efficient IDMA Architecture Based on On-the-Fly Despreading

This paper presents a memory-efficient receiver architecture for interleave division multiple access (IDMA). For the iterative multiuser detection, existing IDMA architectures first store all log-likelihood ratios (LLRs) into a memory in an iteration, and then despread them in the following iteration. To store new LLRs in the following iteration without overwriting the previous ones to be despread, the memory needs to be duplicated. The proposed architecture, on the other hand, despreads the LLRs on-the-fly while storing them by immediately processing one LLR per cycle. As a result, the architecture finishes despreading within one iteration and is free of the duplicate memory. Since the hardware complexity and the power consumption of an IDMA receiver are dominated by the memory usage, the proposed architecture is particularly effective in alleviating such measures. Moreover, the proposed architecture mitigates the overall latency slightly, as it is exempted from the additional cycles required to despread in the last iteration. Implementation results demonstrate that the IDMA receivers based on the proposed architecture require 57% bits in memories, occupy only 39% silicon area, and consume only 30% power on average, compared to the latest low-latency architecture.

Low Latency IDMA With Interleaved Domain Architecture for 5G Communications

Non-orthogonal multiple access (NOMA) is a promising candidate for the future fifth generation systems because of its ability to provide greater spectral efficiency. Interleave division multiple access (IDMA) is one of the NOMA techniques that can support multiple access for a large number of users in the same bandwidth. One of the problems in the hardware implementation of IDMA is its high latency due to iterative processing. In this paper, we propose a novel architecture for the IDMA receiver with low latency while maintaining low complexity. In the conventional architecture, the IDMA receiver sequentially handles deinterleaving, despreading, spreading, and interleaving for multi-user detection. The proposed architecture which we call interleaved domain multi-user detection can perform multi-user detection directly without deinterleaving the received frame in the interference canceller iteration resulting in the decrease of latency by almost half. We also describe the memory design which is able to implement the proposed architecture. The results show that due to the reduction of the latency by half, the throughput can be increased by twice compared with the conventional architecture. VLSI implementation results show that the proposed architecture has reduced circuit area and power consumption by 53% and 58%, respectively, compared with the conventional architecture with the same throughput condition.

An interleave division multiple access receiver for multi-user underwater acoustic communication

A downlink interleave division multiple access (IDMA) receiver, employing sparse channel estimation and interference canceller (IC), is proposed for multi-user underwater communications. To eliminate inter-symbol interference (ISI) and multiple access interference (MAI), an equalizer, a decoder, and an interference canceller are implemented in the receiver. The equalizer is used to eliminate ISI. The channel parameters used in the equalizer are estimated by a modified OMP sparse channel estimation algorithm. The performance of channel estimation is further improve ed using the decoder soft output information during the receiver iteration. MAI, reconstructed by the decoder output and channel parameters, can be eliminated in IC section of other users. The receiver’s performance is verified in shallow water acoustic channels during a sea-trail in the South China Sea. Three different ranges between the transmitter and the receiver, i.e., 4.5 km,6 km, and 7 km, were investigated with a maximum of four users at the data rate of 500 bps per user. The results demonstrated that the proposed IDMA receiver provides good performance with low bit error rate (BER). Furthermore, the receiver has been applied in a real-time underwater communication network.

IDMA Based Anti-collision in RFID Networks

Even though object identification is its main objective, it is generally accepted that there are some technological challenges that should be addressed in order to exploit the full potential of RFID (Radio frequency identification). The anti-collision problem is one of them. Despite the different proposed methods, it still needs further study on how to improve identification ability. This paper presents a novel algorithm with IDMA (Interleave division multiple access) scheme to resolve the anti-collision problem for RFID. IDMA, which is one of the most promising technologies for high data rate wireless systems, can be regarded as a special case of CDMA (Code division multiple access). In contrast to CDMA, which separates tags by signatures or spreading codes, distinct interleavers are the only means to separate tags for IDMA. In this paper, a RFID based IDMA receiver is proposed and compared to classical systems. Simulation results demonstrate that this system provides an improvement in performance in terms of bit error rate in dense scenarios (large number of tags) and it offers an efficient alternative to systems with classical spreading sequence.

Optimal Spreading Mechanism with Different Modulation Techniques Using Random Interleaver in IDMA System

The Interleave-Division Multiple-Access (IDMA) scheme is known for property of orthogonality amongst its user-specific interleavers. The interleavers are, therefore, referred has the core heart of IDMA Transceivers. Now-adays, the IDMA scheme is being thought as a strongest candidate for radio access in cellular mobile communication systems. It is attractive for wireless access due to its numerous advantages over TDMA, FDMA and CDMA and other multiple access schemes. In this paper, IDMA system is being simulated using random interleaver foe each user. On comparing various spreading techniques including repition, Gold code and Walsh code spreading, it is observed from simulation results, that the performance is almost similar for all the spreading mechanisms. However, from implementation point of view, repition spreading is concluded as optimum mechanism because it requires less memory, less computational complexity, easy implementation and also defines larger number of users as compared to Gold code and Walsh code for same spreading length. In this paper, the performance analysis of iterative IDMA receivers have been evaluated with BPSK & QPSK modulation techniques employing random interleavers in uncoded and rate ½ convolutional coded conditions with Additive White Gaussian Noise (AWGN) channel. During the simulation, it has been observed that IDMA system with QPSK modulation techniques employing QPSK outperforms its counterpart BPSK optimally.

Iterative Multiuser Detection for Underwater Acoustic Channels

Two different synchronous downlink multiple-access schemes, interleave-division multiple access (IDMA) and code-division multiple access (CDMA), are considered for pragmatic underwater communications channels exhibiting extended multipath spread and time variability. Two single-element DFE-IDMA and DFE-CDMA receivers are proposed that utilize chip-level adaptive decision feedback equalization (DFE) and carrier phase tracking along with iterative interference cancellation (IC) and channel coding. The receiver equations describing the detection algorithms are derived and their performance is investigated and compared. To track and compensate for the channel effects, the DFE and carrier phase tracking units are jointly optimized based on the mean square error (MSE) criterion and adapted iteratively by exchanging soft information in terms of log-likelihood ratio (LLR) estimates with the turbo processing stage. The detection is implemented by using soft chip cancellation to remove multiple-access interference (MAI) effects between users. The performance of the proposed receiver structures is investigated and compared in short-range shallow-water acoustic channels using offline processing of signals acquired during sea trials in the North Sea. Results for synchronous multiuser scenarios, with two and four users at an effective rate of 439.5 b/s per user, demonstrate that the proposed DFE-based IDMA and CDMA receivers can provide bit error rate (BER) performances of approximately 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> at an average signal-to-interference-and-noise ratio (SINR) of 11 dB . The experimental results also demonstrate that these direct adaptive receivers have better performance and significantly mitigate the bit errors associated with the channel estimation (CE)-based IDMA and CDMA receivers with Rake reception while maintaining lower complexity. Furthermore, in some cases, the receivers with partial knowledge of the interleavers' patterns or codes can still achieve performance comparable to those with full knowledge.

An efficient uplink transmission technique for IDMA based on time-reversal

In this paper, we propose an efficient uplink transmission technique for interleave-division multiple access (IDMA) systems based on time-reversal (TR) technique (named as TDR-IDMA). In TDR-IDMA systems, the time-reversed version of the channel impulse responses (TR-CIR) obtained from the uplink is used to process the received signal preceding the elementary signal estimator (ESE) at the receiver. By exploiting the weak correlations of multi-paths for different users, the signal to interference and noise ratio (SINR) at the beginning of turbo-like detection of TDR-IDMA becomes significantly higher than that of the traditional IDMA. As a result, substantially less number of iterations is needed for the convergence in the proposed TDR-IDMA as compared with traditional IDMA. Our proposed technique effectively breaks the bottleneck of multi-user detection (MUD) in IDMA receiver, and the receiver's complexity is approximately independent of the number of the multi-path channels.

Performance analysis of a generic system model for uncoded IDMA using serial and parallel interference cancellation

AbstractThis paper shows how to accurately describe a fully synchronised interleave division multiple access (IDMA) scheme without channel coding by a matrix model. This model allows the derivation of the optimal detector and provides additional insights into the IDMA principle, and we show that the matrices are structured and sparse. We use BER and EXIT charts to study the performance of parallel and serial interference cancellation schemes and demonstrate that the latter converges faster and is independent of the scrambling code. Any bit interleaved DS‐CDMA system can be viewed as a special case of IDMA, and an IDMA receiver can therefore be used to detect DS‐CDMA signals. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Interleave division multiple-access

This paper provides a comprehensive study of interleave-division multiple-access (IDMA) systems. The IDMA receiver principles for different modulation and channel conditions are outlined. A semi-analytical technique is developed based on the density evolution technique to estimate the bit-error-rate (BER) of the system. It provides a fast and relatively accurate method to predict the performance of the IDMA scheme. With simple convolutional/repetition codes, overall throughputs of 3 bits/chip with one receive antenna and 6 bits/chip with two receive antennas are observed for IDMA systems involving as many as about 100 users.