A New IDMA System Based on CSK Modulation for Multiuser Underwater Acoustic Communications

A novel code division multiple access (CDMA) using cyclic shift keying (CSK) signaling, namely CSK-CDMA, has been proposed for multiuser underwater acoustic communication. The proposed method uses the cyclic correlation characteristic of spread spectrum signals and time reversal processing to increase the data rate each user and to reduce the complexity of the receiver. In CSK-CDMA system, multiple bits information is represented by the cyclically shifted version of the basic spread spectrum waveform at the transmitter. Therefore, the CSK scheme provides a higher data rate than conventional direct sequence spread spectrum. At the receiver, the peak position of the cyclic correlator output is estimated to recovery information. Multiuser communications are demonstrated with lake experimental recorded data. The data rate is 40 bits/s/user for 4 users with zeros error bits and 20 bits/s/user for 8 users with BER around 10−2 at low signal-to-noise ratio (−3 dB), given 4kHz bandwidth, respectively.

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).

Direct sequence spread spectrum (DSSS) signal uses phase coherent signals where the information symbols are multiplied with a code sequence, commonly known as chips. The signals are processed at the receiver using the code sequence as a matched filter to extract the information symbols. Taking advantage of the spread processing gain derived from the matched filter, communications can be carried out at low signal levels, which is the preferred method for high quality underwater acoustic (UWA) communication and remote UWA communication. However, in practical applications, DSSS UWA communication will face lots of interferences including multipath interference, Doppler compression interference and phase fluctuation interference, which will seriously affect the performance of DSSS. This paper first analyzes the interferences that DSSS faces in practical applications based on multiple actual received data collected in different water areas. By calculating the gain of the matched filter loss, one can find that influence of phase fluctuation interference has the most serious impact on DSSS. Secondly, the corresponding receiver processing algorithms are given for these interferences, including the differential energy detector and Doppler estimation method. The performance of differential energy detector under the above interferences is analyzed, which shows that the differential energy detector is insensitive to slow phase fluctuation interference and multipath interference and the differential energy detector combined with Doppler compensation can work well based on moving at-sea data. Finally, the parameter design of DSSS system in practical application is discussed and parameter design of DSSS UWA communication system should comprehensively consider the Doppler compression interference and phase fluctuation interference.

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.

In an interleave-division multiple access (IDMA) system, interleavers have a crucial role for the system performance. This paper presents a new approach to random interleavers for traditional IDMA systems. The proposed interleaver uses a random variable which is defined by Rayleigh distribution for mapping. Simulation results demonstrate that the proposed interleaver approach improves the bit-error rate (BER) performance of the IDMA systems.

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.

This letter presents a conversion‐less algebraic interleaver architecture for low‐latency interleave division multiple access (IDMA) systems. The existing architectures adopt the two‐step approach that first generates a set of sequential indices, and then converts it into a set of interleaved indices, elongating the latency. In contrast, the proposed structure directly produces the interleaved indices by employing a logic that keeps returning the next index corresponding to the current one. As a result, it can greatly alleviate the latency compared with the existing schemes in the literature.

In this paper we investigate the detection algorithms for interleave division multiple access (IDMA) systems in the presence of carrier frequency offsets (CFOs). The existing IDMA detection algorithm is designed under the zero CFO assumption and its performance will be degraded when the CFOs are present. We first extend the existing algorithm to the nonzero CFO case by utilizing effective channel coefficients which take the CFO effects into account. Then we turn to a more practical scenario with imperfect CFO estimates. We propose an algorithm that can cope with the residual CFO effects by integrating the CFO updating into the iterative receiver. Signal-to-interference-plus-noise ratio analysis and simulations show the feasibility and superiority of our proposed algorithms.

In this paper, we propose a parallel interleaver design for interleave-division multiple-access (IDMA) systems. The advantages of our approach are the low complexity induced from an algebraic solution and the parallel processing with negligible performance degradations against random interleavers. It is specially suitable for parallel implementation of multiple user detections and decoding of IDMA signals, resulting in efficient improvements of system throughput. Simulation results show that the parallel interleavers perform as well as the random interleavers in an IDMA system.

A channel estimation scheme for interleave-division multiple access (IDMA) systems is presented. Training and data are superimposed, i.e., no bandwidth expansion compared to a system without any training is necessary. A semi-blind linear minimum mean squared error (MMSE) channel estimator is derived. Monte Carlo simulation results are presented showing that the derived channel estimator in combination with the proposed training scheme is able to track fast-fading frequency-selective channels. As opposed to conventional channel estimation techniques, the BER performance even improves with increasing Doppler spread. An error performance close to the case of perfect channel knowledge can be achieved with high power efficiency

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.

To address the inability to quantitatively analyze the performance of the direct sequence spread spectrum (DSSS) communication system in the presence of short-period pseudo-noise (PN) sequences, this study derives the interference components resulting from correlation processing of single-frequency interference. Given the short period of the spread spectrum sequence used in underwater acoustic systems, a theoretical expression is proposed for analyzing the anti-single-frequency interference performance of DSSS communication systems in underwater acoustics. This expression combines the interference power output by the system to enable quantitative analysis. Simulations are conducted to validate the accuracy of the theoretical expression. The results reveal that the interference sequence generated by correlation processing assumes either a direct current (DC) or sinusoidal distribution. The bit error rate (BER) of the system is influenced by signal-to-interference ratio (SIR), interference frequency offset, phase deviation, and the structure of the spreading code itself. The BER exhibits regular variation with changes in the interference phase. In all working conditions where the interference frequency offset is an integer multiple of the bit bandwidth, single-frequency interference with a frequency offset equivalent to the bit bandwidth has the greatest impact on the system. The concise theoretical expression presented in this study has significant practical value as it allows for quick prediction of variation in the anti-single-frequency interference performance of underwater acoustic DSSS communication systems using short-period PN sequences.

In this paper, we develop a new one-dimensional chaotic map, completely based on the logistic map: ”New Logistic Map (NLM)”; this new map expand the definition domain of logistic map and their utilization. The simulation results and theoretical analysis of chaotic dynamical behaviours show that the NLM is a chaotic system and has an ideal distribution. It is also characterized by its wide range of definition, and depends on the number of the desired real values.We have applied the NLM to generate the interleaver matrix for Interleave Division Multiple Access (IDMA): NLMInterleaver. Our design easy to generate, and requires a low memory bandwidth consumption (low amount of data can travel over a communications channel), and low computational complexity compared to the literature algorithms.

A signal transmitted in an Underwater Acoustic Communication (UAC) system operating in a shallow-water channel suffers from strong time dispersion due to multipath propagation. This causes the Inter-Symbol Interference (ISI) observed in the received signal, which significantly limits the communication system’s reliability and transmission rate. In such propagation conditions, the Direct-Sequence Spread Spectrum (DSSS) method is one of the solutions that make reliable data transmission possible. In systems with one-to-one communication, it ensures communication with a satisfactory Bit Error Rate (BER). Additionally, it makes it possible to implement the Code-Division Multiple Access (CDMA) protocol in underwater acoustic networks. This paper presents the results of simulation and experimental communication tests on a DSSS-based UAC system using three types of spreading sequence, namely m-sequences, Kasami codes and Gold codes, and occupying different bandwidths from 1 kHz to 8 kHz around a carrier frequency equal to 30 kHz. The UAC channel was simulated by impulse responses calculated by the virtual sources method and the UAC chanel models available in the Watermark simulator. The experimental tests were conducted in a model pool. Based on the obtained results, a transmission rate was estimated, which is possible to achieve in strong multipath propagation conditions, assuming reliability expressed as BER less than 0.001.

The interference by time-varying and intense underwater acoustic multi-path is one of the most obstructive phenomena in underwater acoustic communication. Time-Reversal (TR) communication techniques utilize the reciprocity of acoustic channels to converge the spread signals to the original one, and are considered one of the most effective methods to overcome multi-path interference as shown in many past studies. It is recognized empirically that the large number of multi-path arrival could generally raise the demodulation result of TR. However, its relationship is rarely evaluated quantitatively. In this paper, we investigate the efficiency of the TR acoustic communication techniques for the multi-path interference cancelation by applying our passive TR method to the synthetic datasets of horizontal acoustic communication in shallow water environment. Mainly, we focused on the relation between the Signal to Interference Noise Ratio (SINR) and the output SNR of demodulation result. The result shows: 1) SINR and output SNR has a nearly linear relation up to a limitation, and 2) above the limitation, output SNR reaches its ceiling or slightly decreases.