Presence Of Multiuser Interference Research Articles

Iterative signal detection to mitigate ISI and MUI for diffusion-based molecular communications

Molecular communication via diffusion (MCvD) where bio-molecules carry information is a most promising and viable solution for communication between nanoscale devices. However, slow moving molecules cause inter-symbol-interference (ISI) which is one of the major impediments in MCvD systems. In this work, a novel iterative block-wise non-coherent signal detection method is proposed to mitigate the ISI at the receiver. Since the proposed method does not require the channel state information at the receiver, this reduces the molecular communication system’s complexity. The bit error rate (BER) performance of the proposed iterative detection method is evaluated in the presence of both ISI and counting noise. Substantial improvement in MC system’s BER performance is observed by using the proposed detection method as compared to conventional approach. Furthermore, effectiveness of the proposed scheme is also analyzed in the presence of multiuser interference.

UWB Receiver via Deep Learning in MUI and ISI Scenarios

In this paper, we consider a multiuser impulse radio ultra-wideband (UWB) system and focus on a single target user 's signal reception in the presence of multiuser interference (MUI) and/or inter-symbol interference (ISI). We propose a deep learning (DL) based receiver, which is trained off-line by simulated data to learn the joint effect of UWB pulsing, channel effect, and signal detection. Then we apply it online to recover the real-time transmitted data symbols. Numerical results demonstrate that the deep-learning based receiver can efficiently learn such joint effect in the presence of MUI and ISI, leading to much better bit error rate (BER) performance than conventional correlation receiver and other existing receivers.

Equal Gain Combining-Based Maximum Likelihood Detector for FFH/MFSK Systems

In this letter, a new multi-user detector based on equal gain combining (EGC) and maximum likelihood (ML) principle is proposed, which is referred to as an EGC-aided ML (EGC-ML) detector. The detection performance of fast frequency-hopping $M$ -ary frequency-shift keying (FFH/MFSK) systems with a novel EGC-ML receiver is investigated in the presence of multi-user interference and additive white Gaussian noise over Rayleigh fading channels. After envelop detection and frequency de-hopping operations, the proposed algorithm picks up several most possible estimations based on the EGC principle and then make final decision via an ML detector within the possible searching range. Our simulation results show that this novel EGC-ML detector may noticeably reduce the complexity of the ML detector with an acceptable bit error rate performance decrement, when a reasonable searching range is chosen by the EGC principle.

TH-PPM with non-coherent detection for multiple access in electromagnetic wireless nanocommunications

Terahertz band (0.1–10 THz)-based electromagnetic nanocommunications could advance several nanotechnology applications in the biomedical, environmental, and military fields. One of the fundamental challenges with nanocommunications is the need for an appropriate modulation and channel access mechanism. In multi-user nanocommunications, detrimental effects of path loss and interference could pose a significant problem for multiple nano-devices trying to access the channel concurrently. This would result in retransmissions, which is barely affordable at the nano-level due to the minute size and energy constraints of nano-devices. In this paper, time-hopping (TH) combined with M-ary pulse position modulation (PPM) is proposed as a modulation and multiple access scheme for multi-user nanocommunications systems. PPM, being the most energy-efficient modulation scheme, with TH would allow nano-devices to communicate simultaneously with greater efficiency. Decoding at the receiver is done after non-coherent detection. The symbol-error rate (SER) in the presence of multi-user interference is evaluated in terms of signal-energy-to-noise ratio and the number of interfering users. Moreover, capacity of the system is also evaluated in terms of bits per symbol for different design parameters. Numerical results show that the SER and capacity of the system can be improved by choosing appropriate TH-PPM parameters for a given network condition. The comparisons of simulation results for TH-PPM with another existing scheme witnesses an improved energy efficiency and reduced computational complexity.

HSBCS framework based performance detection for DS-UWB Systems

Multi-users interference in direct sequence ultra wideband (DS-UWB) communication is the hotspot research for wireless communication. In this paper, using the wavelet coefficient transform signal in DS-UWB communication, we establish the tree-based hierarchy shrinkage Bayesian compressive sensing (HSBCS) framework for multi-users interference models and noise model generalization. The Markov chain Monte Carlo (MCMC) multi-user interference algorithm by use of HSBCS framework is proposed to suppress noise in the presence of multi-user interference in the DS-UWB communications. The target of this paper is to detect the noise suppression performance of multi-user interference in the DS-UWB communications including normal mean square error (NMSE) performance and peak signal-to-noise-ratio (PSNR) performance using HSBCS framework. Simulation results show that NMSE and PSNR performance of tree-based HSBCS algorithm is better than that of the other algorithms with no tree structure. Otherwise, with more users increasing, the error probability performance of MCMC multiuser interference algorithm in the presence of multiuser interference by use of HSBCS framework is lowest and gradually approach zero.

Multi-User Visible Light Communication Broadcast Channels With Zero-Forcing Precoding

This paper studies zero-forcing (ZF) precoding designs for multi-user multiple-input single-output visible light communication (VLC) broadcast channels. In such broadcast systems, the main challenging issue arises from the presence of multi-user interference (MUI) among non-coordinated users. In order to completely suppress the MUI, ZF precoding, which is originally designed for radio frequency (RF) communications, is adopted. Different from RF counterpart, VLC signal is inherently non-negative and has a limited linear range, which leads to an amplitude constraint on the input data signal. Unlike the average power constraint, obtaining the exact capacity for an amplitude-constrained channel is more cumbersome. In this paper, we first investigate lower and upper bounds on the capacity of an amplitude-constrained Gaussian channel, which are especially tight in the high signal-to-noise regime. Based on the derived bounds, optimal beamformer designs for the max-min fairness sum-rate and the maximum sum-rate problems are formulated as convex optimization problems, which then can be efficiently solved by using standard optimization packages.

Performance Evaluation of Non-prefiltering vs. Time Reversal Prefiltering in Distributed and Uncoordinated IR-UWB Ad-Hoc Networks

Time Reversal (TR) is a prefiltering scheme mostly analyzed in the context of centralized and synchronous IR-UWB networks, in order to leverage the trade-off between communication performance and device complexity, in particular in presence of multiuser interference. Several strong assumptions have been typically adopted in the analysis of TR, such as the absence of Inter-Symbol / Inter-Frame Interference (ISI/IFI) and multipath dispersion due to complex signal propagation. This work has the main goal of comparing the performance of TR-based systems with traditional non-prefiltered schemes, in the novel context of a distributed and uncoordinated IR-UWB network, under more realistic assumptions including the presence of ISI/IFI and multipath dispersion. Results show that, lack of power control and imperfect channel knowledge affect the performance of both non-prefiltered and TR systems; in these conditions, TR prefiltering still guarantees a performance improvement in sparse/low-loaded and overloaded network scenarios, while the opposite is true for less extreme scenarios, calling for the developement of an adaptive scheme that enables/disables TR prefiltering depending on network conditions.

Analytical Characterisation of the Terahertz In-Vivo Nano-Network in the Presence of Interference Based on TS-OOK Communication Scheme

The envisioned dense nano-network inside the human body at terahertz (THz) frequency suffers a communication performance degradation among nano-devices. The reason for this performance limitation is not only the path loss and molecular absorption noise, but also the presence of multi-user interference and the interference caused by utilising any communication scheme, such as time spread ON—OFF keying (TS-OOK). In this paper, an interference model utilising TS-OOK as a communication scheme of the THz communication channel inside the human body has been developed and the probability distribution of signal-to-interference-plus-noise ratio (SINR) for THz communication within different human tissues, such as blood, skin, and fat, has been analyzed and presented. In addition, this paper evaluates the performance degradation by investigating the mean values of SINR under different node densities in the area and the probabilities of transmitting pulses. It results in the conclusion that the interference restrains the achievable communication distance to approximate 1 mm, and more specific range depends on the particular transmission circumstance. Results presented in this paper also show that by controlling the pulse transmission probability and node density, the system performance can be ameliorated. In particular, SINR of in vivo THz communication between the deterministic targeted transmitter and the receiver with random interfering nodes in the medium improves about 10 dB, when the node density decreases one order. The SINR increases approximate 5 and 2 dB, when the pulse transmitting probability drops from 0.5 to 0.1 and 0.9 to 0.5.

Training Sequence Design for NBI Mitigation in Compressive Sensing UWB Systems

Ultra wideband (UWB) is a promising technology in delivering high data rate for short range wireless communication systems. Because of their large bandwidth, UWB signals may encounter some problems especially with high sampling rate requirements. Moreover, coherence existence with other narrowband systems is a major concern which needs to be addressed through proper mechanisms. The problem becomes so complex if multiple users exist. Since narrowband interference (NBI) signals have sparse representation in the discrete cosine transform (DCT) domain, they can be estimated and suppressed using Compressive Sensing (CS). CS also has the ability to reduce the high sampling rate requirements. For training based NBI mitigation with CS, three groups of pilot symbols are used to estimate the NBI signal subspace, the UWB signal subspace, and to provide information about the channel. In this paper, the distribution of pilot symbols among the three groups is investigated in the presence of strong NBI. The investigation is based on the bit error rate performance and throughput. The influence of each pilot symbols group is studied. The performance is also evaluated in the presence of multiuser interference in addition to the NBI. Simulation results show that the size of the third group of pilot symbols which is used to estimate the channel is the most dominant one.

Generalized Diversity Reception in the Presence of Multiple Distinct Interferers: An Outage Performance Analysis

The analytical performance evaluation of various coherent diversity combining reception techniques in the presence of multiuser interference is presented into this paper. Particularly, the outage probability of the generalized selection combining (GSC) and its two extreme cases, namely the maximum ratio combining (MRC) and the selection combining (SC), are evaluated. The multiple interferers undergo independent and non-identically distributed Nakagami-m fading channels, with distinct average received powers and arbitrary fading scales. New analytical outage expressions are presented including several channel fading conditions regarding the desired user's signal. Although the proposed approach is formed as an infinite series representation, it includes only simple elementary and Gamma functions, while it delivers a rapidly converging formula achieving a sufficiently high precision level. Moreover, the derived computational complexity of this function is thoroughly discussed, while a corresponding comparison with another popular technique indicates the usefulness of the proposed approach. Finally, the accuracy of the approach is verified with the aid of selected numerical results accompanied with equivalent simulation ones.

Carrier frequency offset estimation for OFDMA uplink using null sub-carriers

Carrier synchronization in OFDMA uplink systems comprises estimation and compensation of carrier frequency offsets (CFOs) corresponding to different users. We propose a null sub-carrier-based CFO estimation algorithm for OFDMA uplink systems, employing generalized or sub-band sub-carrier allocation scheme. We analyze the effect of location and number of null sub-carriers on the performance of the algorithm, in the presence of multi-user interference (MUI) and channel frequency selectivity. We calculate the acquisition range of the proposed estimation algorithm and prove that the identifiability of CFO estimation is guaranteed in the presence of MUI and channel nulls. We also evaluate the computational complexity and the performance of the proposed estimation algorithm and, compare it with some of the existing approaches in the literature.

Performance Analysis of Multiuser Selection Scheme in Dynamic Home Area Networks for Smart Grid Communications

In this paper, multiuser selection scheme is employed in dynamic home area networks (HANs) for smart grid communications, to reduce the effects of fading at the receiver part of smart meter. The performance of multiuser selection scheme is evaluated in two cases: in the absence of interference and in the presence of multiuser interference (MUI). In the former case, the closed-form capacity outage probability as well as the numerical values of the bit error rate (BER) are obtained via the probability density function (PDF) of signal to noise ratio (SNR) that is derived from the amplitude distribution property of the classic indoor Saleh-Valenzuela (S-V) channel. In the latter case, the multiuser interference cancellation coefficient as a random variable is added for the calculation of signal to interference noise ratio (SINR). In addition, due to free space path loss and log-normal shadowing, the sum of MUI is treated as another log-normal-distributed random variable by exploiting central limit theorem. Numerical results show that the performance of multiuser selection scheme in HANs of smart grid is due to several factors, i.e., total number of devices in HANs, traffic intensity, modulation scheme, and multiuser interference cancellation coefficient, etc.

A frequency domain multiple-antenna and channel estimation approach for facilitation of UWB technologies coexistence in heterogeneous WPANs

Ultra wideband (UWB) communications is a promising technology which provides high data rates for short-range communications. There are currently two proposals as UWB standards, namely, multiband orthogonal frequency division multiplexing (MB-OFDM) UWB and direct-sequence (DS) UWB. These two standards can cause interference on each other and also to other wireless technologies when they are located in their vicinity. In this paper, we focus on the mutual interference of these two UWB standards. In the first part of the paper, we address the channel estimation issue for DS-UWB receiver, in the presence of multi-user interference (MUI) and MB-OFDM interference within the framework of wireless personal area networks (WPANs). In fact, we use the minimum mean square error estimation (MMSE) to estimate the channel based on a pilot transmission scheme. In the second part, we propose a simple but effective design for the receiver structure of the DS-UWB which utilizes a frequency domain multiple-antenna approach in order to mitigate MUI as well as the MB-OFDM external interference. Channel estimation performed in part one will be used in the detection process in part two. Numerical results are provided to evaluate the effectiveness of the proposed techniques for interference mitigation in DS-UWB.

Synchronization for Impulse-Radio UWB With Energy-Detection and Multi-User Interference: Algorithms and Application to IEEE 802.15.4a

Energy-detection (ED) receivers can take advantage of the ranging and multipath resistance capabilities of impulse-radio ultra-wideband (IR-UWB) physical layers at a much lower complexity than coherent receivers. However, ED receivers are extremely vulnerable to multi-user interference (MUI). Therefore, the design of IR-UWB ED architectures must take MUI into account. In this paper, we present the design and evaluation of two complementary algorithms for reliable and robust synchronization of IR-UWB ED receivers in the presence of MUI: 1) power-independent detection and preamble code interference cancellation (PICNIC) and 2) detection of start-frame-delimiter through sequential ratio tests (DESSERT). PICNIC addresses packet detection and timing acquisition while DESSERT focuses on start-frame-delimiter (SFD) detection. Both algorithms are evaluated with the IEEE 802.15.4a IR-UWB physical layer, standardized for low data-rate networks. The performance evaluation with extensive simulations show that our algorithms outperform nonrobust synchronization algorithms by up to two orders of magnitude in the presence of MUI.

Training-Based Synchronization and Demodulation With Low Complexity for UWB Signals

In this paper, we propose a low-complexity data-aided (DA) synchronization and efficient demodulation technique for an ultrawideband (UWB) impulse radio system. Depending on the autocorrelation property of a judiciously chosen training sequence, a redundance-included demodulation template (RDT) can be extracted from the received signal by separating, shifting, and realigning two connected portions in the observation window. After constructing the RDT, two receiver designs are available. One approach is to demodulate transmitted symbols by correlating the RDT in a straightforward manner, which does not require the explicit timing acquisition and, thus, considerably reduces the complexity of the receiver. An alternative approach is accomplished with the assistance of a non-RDT (NRDT). The NRDT-based receiver is able to remove the redundant noisy component of the RDT by acquiring timing offset via a simple synchronization scheme, therefore achieving a better bit error rate (BER) performance. Both the schemes can counteract the effects of interframe interference (IFI) and unknown multipath channels. Furthermore, analytical performance evaluations of the RDT- and NRDT-based receivers are provided. Simulations verify the realistic performance of the proposed receivers in the presence of multiuser interference (MUI) and timing errors.

Precise BER Computation for Binary Data Detection in Bandlimited White Laplace Noise

Investigation into the characteristics and behaviours of Laplace noise is of crucial importance for evaluating the performance of communication systems operating in impulsive noise, as well as for ultra-wideband wireless systems operating in the presence of multi-user interference. The bit error rate performances of a binary data communication system operating in the presence of additive bandlimited white Laplace noise is analyzed theoretically. A theoretical expression for the average bit error rate is derived using the Beaulieu series for the optimal soft-limiting detector and the matched-filter detector when arbitrary pulse shapes are used. The bit error rate performance of a reduced complexity version of the optimal detector, the hard-limiting detector, and a reduced complexity version of the matched-filter detector, the sum-of-samples detector, are also analyzed. The analytical expressions for the bit error rate are validated by numerical examples.

Novel approach of UWB multi-band system based on orthogonal function for transports applications

Ultra Wide Band (UWB) is based on the transmission of very short pulses with relatively low energy. This technology may see increased use in the wireless communications and sensing application. Having the available bandwidth of 7.5 GHz and the minimum signal bandwidth of 500 MHz, UWB systems can be divided into two groups: impulse communication system and multi-band system. In multi-band, the spectrum is divided into several subbands. In this paper, we propose this technique for subway transport systems; especially for communication between trains or train-infrastructure. So, the main purpose of this paper is to make use of the original mathematical tools called orthogonal functions to allow a multi-user communication system for multi-band UWB transmission. The BER values will be calculated and analyzed using computer simulations in the presence of multi-user interference, in order to evaluate the performances of the proposed system. These BER values will be given for two cases: the users in the same subband and a single user per subband. We will show that the proposed orthogonal waveforms give good performances in terms of BER and are able to reduce multi-user interference. The proposed method has many potentials advantages in terms of complexity and implementation.

UWB WPAN receiver optimization in the presence of multiuser interference

We propose two new receiver architectures for a ultra wide band (UWB) system based on the IEEE 802.15.4a standard. The design objective is robustness against strong multiple access interference (MAI). The first proposed structure models MAI as an additive white Gaussian noise (AWGN) whose power is estimated at each frame, rather than on average, in such a way to take account of the impulsive nature of interference. The second approach aims at jointly optimizing demodulation and decoding, and, in this case, MAI is modeled as a generalized Gaussian mixture process. In both cases, the maximum likelihood receiver is derived. Numerical results in a IEEE 802.15.4a scenario show that the AWGN receiver with local power estimate provides a performance comparable to the best existing techniques, while requiring a much lower computational complexity. The joint optimization of demodulation and decoding provides a further gain, especially at low packet error rates, at the cost of an additional signal processing effort. Still, low complexity solutions holding the performance gap are identified in this latter class.

Design and analysis of robust detectors for TH IR-UWB systems with multiuser interference

In this letter, we design and analyze the performance of single-user-type non-linear detectors that are able to cope with the impulsive nature of multiuser interference (MUI) in timehopping impulse-radio ultra-wideband (TH IR-UWB) systems. We collectively refer to these detectors as detectors. We first propose two novel detectors and then derive semi-analytical expressions for the bit-error rate (BER) of TH IR-UWB with general robust detection. The evaluation of these expressions greatly facilitates the optimization of detector parameters and provides insight into the effects of MUI. A performance comparison shows that (1) robust detection significantly improves performance over conventional detection in the presence of MUI, (2) the parameters for various parametric robust detectors can be chosen to be constant over many transmission scenarios with only little performance degradation compared to using the optimal parameter value, and (3) the proposed two-term detector, which requires a modest amount of parameter estimation, achieves consistently the best performance.

Rate adaptation using acknowledgement feedback in finite-state markov channels with collisions

We investigate packet-by-packet rate adaptation so as to maximize the throughput. We consider a finite-state Markov channel (FSMC) with collisions, which models channel fading as well as collisions due to multi-user interference. To limit the amount of feedback data, we only use past packet acknowledgements (ACKs) and past rates as channel state information. The maximum achievable throughput is computationally prohibitive to determine, thus we employ a two-pronged approach. Firstly, we derive new upper bounds on the maximum achievable throughput, which are tighter than previously known ones. Secondly, we propose the particle-filter-based rate adaptation (PRA), which employs a particle filter to estimate the a posteriori channel distribution. The PRA can easily be implemented even when the number of available rates is large. Numerical studies show that the PRA performs within one dB of SNR to the proposed upper bounds for a slowly time-varying channel, even in the presence of multi-user interference.