Multiuser Ultra-wideband Research Articles

WUB-IP: A High-Precision UWB Positioning Scheme for Indoor Multiuser Applications

High-precision positioning scheme, an important part of indoor navigation, can be implemented using an ultra-wideband (UWB) based ranging system. Recently, solutions for precise positioning in dense multipath and non-line-of-sight (NLOS) conditions have attracted a lot of attentions. On the other hand, it is expected that waveform division multiple access (WDMA) technology for multiuser UWB positioning applications will be indispensable in the near future. In this regard, a WDMA-UWB-based positioning scheme is investigated in this paper, to enhance the positioning accuracy in multiuser applications. In accordance with practical requirements of indoor positioning, we propose a new indoor positioning scheme, termed as WDMA-UWB-based indoor positioning (WUB-IP). This scheme adopts WDMA for multiple access, and utilizes an entropy-based approach for the time of arrival estimation. Moreover, a transfer learning approach is used to mitigate the ranging error in NLOS conditions, in order to improve the positioning accuracy in NLOS conditions. System-level simulations demonstrate that the proposed scheme enhances the performance of indoor positioning for multiuser applications.

Performance of Polar Codes for OFDM-Based UWB Channel

A multiuser Ultra Wide Band (UWB) channel suffers seriously from realistic impairments. Among this, multipath fading and interferences, such as Multiple Access Interference (MAI) and Inter Symbol Interference (ISI), that significantly degrade the system performance. In this paper, a polar coding technique, originally developed by Arikan, is suggested to enhance the BER performance of indoor UWB based Orthogonal Frequency Division Multiplexing (OFDM) communications. Moreover, Interleave Division Multiple Access (IDMA) scheme has been considered for multiuser detection depending on the turbo type Chip-By-Chip (CBC) iterative detection strategy. Three different models as Symmetric Alpha Stable (SαS), Laplace model and Gaussian Mixture Model (GMM), have been introduced for approximating the interferences which are more realistic for UWB system. The performance of the proposed Polar-coded IDMA OFDM-based UWB system is investigated under UWB channel models proposed by IEEE 802.15.3a working group and compared with Low Density Parity Check (LDPC)-coded IDMA OFDM-based UWB system in terms of BER performance and complexity under the studied noise models. Simulation results show that the complexity of the proposed polar-coded system is much lower than LDPC-coded system with minor performance degradation. Furthermore, the proposed polar-coded system is robust against noise and interferences in UWB indoor environment and gains a significant performance improvement by about 5 dB compared with un-coded IDMA-OFDM-UWB system under the studied noise models.

Multi-user Communication Based OFDM-UWB System under Gaussian and Non-Gaussian Noisy Channel

For a multiuser Ultra Wide Band (UWB) system, the performance is mainly limited by inherent noise and interferences such as Multiple Access Interference (MAI) and Inter Symbol Interference (ISI) which are poorly approximated by a Gaussian distribution because of their impulsive nature. A combination between Orthogonal Frequency Division Multiplexing (OFDM) and Interleave Division Multiple Access (IDMA) has been considered as an efficient technique due to its bandwidth efficiency, and robustness against MAI and ISI. Moreover, OFDM-IDMA technique has the ability to allow frequency diversity and performance improvement with the help of efficient FEC coding technique such as Low Density Parity Check (LDPC) code. Therefore, this paper addresses the performance of LDPC-coded-IDMA-based OFDM-UWB communication system under Gaussian and non-Gaussian noisy channels. Three different models as Symmetric Alpha Stable (SS), Laplacian model and Gaussian Mixture Model (GMM), have been introduced for approximating the non-Gaussian noise which are more realistic for UWB system. Simulation results show that LDPC-coded OFDM-IDMA system is robust against noise and interferences in UWB indoor environment, and achieves good performance under Cauchy (SS) model rather than other non-Gaussian models with simple Chip-By-Chip (CBC) iterative receiver. Furthermore, the proposed system gains a significant performance improvement compared with the un-coded OFDM-IDMA-UWB system under the studied noise models.

A New Multi-user Ultra Wide Band System Based on Modified Gegenbauer Functions and M-OAM Modulation for Communication of Intelligent Transportation Systems

Ultra-wideband technology is based on the transmission of very short pulses with relatively low energy, which make it a promising option for short range wireless communication system. In this paper, we propose to use this technology to establish a new multi-user technique dedicated to intelligent transport systems, especially vehicle-to-vehicle and vehicle-to-infrastructure communications. Indeed, the design of such system must provide good quality of service for a large number of users simultaneously and with high data rate. The proposed system is based on the use of a new modulation schemes named orthogonal amplitude modulation to reach high data rate; and an original multiple access technique that allows a maximum number of users simultaneously with good performances.

Novel multiuser ultra‐wideband receiver based on adaptive modelling of generalised normal‐Laplace distribution

This study takes a new receiving approach to detect an ultra-wideband (UWB) signal in the presence of multiple access interference (MAI). A generalised normal-Laplace (GNL) distribution is exploited for designing a novel multiuser UWB receiver. To more accurately comply with real statistical behaviours of the MAI-plus-noise in time-hopping multiple access UWB systems, a modified parameter estimator, which is an adaptive method of moments estimation (aMME), is proposed. In the existing studies, the analysis about GNL model shows appropriate results for UWB simulations, while it requires heavy complexity to obtain the precise distribution because of no existence of a closed-form probability density function (PDF) expression. To practically evaluate the GNL PDF, the fast Fourier transform, which can significantly reduce the computational complexity is considered. The GNL using the aMME outperforms the conventional matched filter UWB receiver, the soft-limiting receiver, the Gaussian–Laplace mixture receiver, the p-order metric receiver and the previous GNL receivers, especially in high SNR ranges. Furthermore, the presented GNL receiving method is applied to each finger of the conventional Rake receiver for signal detection in IEEE UWB multipath channels. The proposed Rake receiver based on the GNL distribution performs better than the conventional Rake receiver in multipath fading channels.

Robust Design of Widely Linear Pre-Equalization Filters for Pre-Rake UWB Systems

Pre-rake ultra-wideband (UWB) systems are appealing for UWB communications applications which include devices with different processing capabilities so that signal processing complexity need to be shifted from the receiver of one or more devices to the transmitter of another. Recently, basic pre-rake schemes have been extended to include full pre-equalization, multiple-antenna, and multi-user interference processing. All these design approaches for pre-rake UWB systems have relied on the availability of accurate channel state information (CSI) at the transmitter. However, uncertainties in the acquisition of CSI can drastically affect the overall system performance. Therefore, in this paper, we present robust design methods for pre-equalization filters (PEFs) for pre-rake UWB systems that take CSI uncertainties into account. We treat the general case of a broadcast (i.e., multiuser) pre-rake UWB system, which includes single-user communication often considered in literature as a special case. For this general setting, we derive new PEF designs that improve system performance with imperfect CSI. Similar to the literature on robust filter designs for multiple-input multiple output (MIMO) systems, we consider two uncertainty models, namely stochastic and bounded uncertainty, which correspond to different performance optimization paradigms, and we adjust these according to channel estimation of UWB channels. As most of previous work on (pre-rake) UWB, we focus on binary transmission. We argue that widely linear filter design should be applied in this case and thus extend the robust filter design methodology accordingly. Our numerical results for typically UWB test channels demonstrate the efficacy of the proposed design procedures to achieve reliable communication in multiuser pre-rake UWB systems.

All-optical binary phase-coded UWB signal generation for multi-user UWB communications

An all-optical incoherent scheme for generation of binary phase-coded ultra-wideband (UWB) signals is proposed and experimentally demonstrated. The binary phase coding is performed based on all-optical phase modulation in a semiconductor optical amplifier (SOA) and phase modulation to intensity modulation (PM-IM) conversion in a fiber delay interferometer (DI) that serves as a multichannel frequency discriminator. By locating the phase-modulated light waves at the positive and negative slopes of the DI transmission spectra, binary phase encoded UWB codes (0 and π) are generated. We also experimentally demonstrate a bipolar UWB coding system with a code length of 4, operating at 1.25 Gb/s. And the decoding is analyzed as well. Our proposed system has potential application in future high-speed UWB impulse radio over optical fiber access networks.

Low complexity RAKE receiver for TH-based multiuser UWB system with realistic UWB indoor channel

We have considered multiuser communication scenario with ultra wideband (UWB) communication. UWB device is transmitting the data by time hopping (TH)-based system, TH-PPM, TH-PAM and DS-UWB. The UWB device is transmitting data over multipath rich channel model recommended by IEEE 802.15.3a working group. This channel model is based on Saleh-Valenzuela model. For better performance at receiver side, adaptive equaliser is required; this increases the complexity of receiver. Here we have considered the RAKE receiver for TH-based UWB system. This RAKE receiver structure is not a conventional RAKE, but it is pre-RAKE structure. In this case, we have evaluated performance of system by considering the RAKE receiver at the transmitter side. Here we have assumed the condition that channel sounding is available before transmission for quasi static UWB channel. Based on this knowledge RAKE fingers are selected for pre-RAKE. UWB channel is multipath rich channel so full RAKE adds more complexity in receiver and hence put limitation on effective data rate. Here we have considered low branch RAKE receiver. Performance of the system model is evaluated with realistic UWB channel model.

Joint Downlink Beamforming and Time-Reversed Matched Filtering for Multiuser UWB Signals

This paper proposes a simple delay-line (DL) downlink beamformer for pulsed ultra-wideband (UWB) systems to compensate for propagation delay, which is detrimental to UWB signals. Moreover, we propose a prefiltering-based transmission scheme at the fixed access point (i.e., base station) by shifting the signal processing needs from the receiver at the mobile unit to the transmitter where power and computational resources are plentiful. The DL transmitter array can steer signals to the direction of the desired mobile user such that the desired signals stemming from each antenna are coherently combined and the multiuser interference (MUI) is averaged out. Furthermore, the prefiltering scheme is composed of a set of time-reversed matched filters (TR MFs) subject to multiple-input single-output (MISO) finite impulse response (FIR) channels. A simple correlation receiver is proposed at the mobile unit to extract the information of the time-hopping (TH) UWB signal. The performances under different scenarios are extensively evaluated.

Near-optimal and suboptimal receivers for multiuser UWB impulse radio systems in multipath

In this paper, near-optimal and suboptimal receivers are proposed for multiuser ultra-wideband (UWB) impulse radio (IR) systems in dense multipath channels, where <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">non-Gaussian</i> multiuser interference (MUI) seen at each finger of a RAKE receiver is taken into account. The receivers exploit two dimensional diversity that is offered by UWB signaling, namely multipath diversity and repetition diversity (i.e., repetition coding). Non-Gaussian modeling of the MUI results in employing a nonlinear process at each finger, jointly considering the desired users, path gain being estimated and the order associated with MUI statistics. For this, the MUI statistics are characterized in terms of their second and fourth order moments, especially considering the channel <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sparseness</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cluster overlapping</i> observed in realistic UWB channels, which leads to modeling the MUI by a <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">generalized</i> Gaussian distribution. It is shown that the MUI statistics exhibit non-Gaussian nature even for relatively large number of users, and the diversity gain against MUI can be significant when relatively small number of users coexist.

Time Domain Equalizer Design Using Bit Error Rate Minimization for UWB Systems

Ultra-wideband (UWB) communication systems occupy huge bandwidths with very low power spectral densities. This feature makes the UWB channels highly rich in resolvable multipaths. To exploit the temporal diversity, the receiver is commonly implemented through a Rake. The aim to capture enough signal energy to maintain an acceptable output signal-to-noise ratio (SNR) dictates a very complicated Rake structure with a large number of fingers. Channel shortening or time domain equalizer (TEQ) can simplify the Rake receiver design by reducing the number of significant taps in the effective channel. In this paper, we first derive the bit error rate (BER) of a multiuser and multipath UWB system in the presence of a TEQ at the receiver front end. This BER is then written in a form suitable for traditional optimization. We then present a TEQ design which minimizes the BER of the system to perform efficient channel shortening. The performance of the proposed algorithm is compared with some generic TEQ designs and other Rake structures in UWB channels. It is shown that the proposed algorithm maintains a lower BER along with efficiently shortening the channel.

Power controlled channel allocation for multiuser multiband UWB systems

Emerging ultra-wideband (UWB) technology offers a great potential for the design of high-speed short-range communications. However, in order for a UWB device to coexist with other devices, the transmitted power level of UWB is strictly limited by the FCC spectral mask. Such limitation poses a significant design challenge to any UWB system. An efficient management of the limited power is thus a key feature to fully exploit the advantages of UWB. In this paper, a cross layer multiuser multiband UWB scheme is proposed to obtain the optimal subband and power allocation strategy. Optimization criteria involve minimization of power consumption under the constraints on the packet error rate, the data rate, and the FCC limit. To ensure the system feasibility in variable channel conditions, an algorithm to jointly manage the rate assignment of UWB devices, subband allocation, and power control is proposed. A computationally inexpensive suboptimal approach is also developed to reduce the complexity of the problem, which is found to be NP hard. Simulation results under UWB channel model specified in the IEEE 802.15.3a standard show that the proposed algorithm achieves comparable performances to those of the complex optimal full search approach, and it can save up to 61% of transmit power compared to the current multiband scheme in the standard proposal. Moreover, the proposed algorithm can obtain the feasible solutions adaptively when the initial system is not feasible for the rate requirements of the users.

A less complicated adaptive equalization for UWB channels

In this paper, a new adaptive equalization scheme aiming at the intersymbol and interuser interferences in the multiuser ultra-wide band (UWB) channels is presented specially for direct-sequence UWB/time-hopping UWB (DS-UWB/TH-UWB) receivers. Its computational complexity and convergence rate are compared with the conventional algorithms. The simulation results show that the computational complexity of this scheme is less than employing the RLS method alone and the convergence rate of this scheme is farther off employing LMS method alone.

Multi-User Ultra-Wide Band Communication System Based on Modified Gegenbauer and Hermite Functions

In this paper a multi-user communication system based on ultra-wide band (UWB) technology is studied. UWB uses very short pulses, so that the spectrum of the emitted signals may spread over several GHz. In order to implement multi-user communication, the emitted signal must be modulated. One modulation scheme for UWB communications is to use analog waveforms to modulate the data. In this study, orthogonal waveforms called modified Gegenbauer functions are introduced as basis functions for the pulse shape and compared to the previously proposed modified Hermite functions. It is shown that Gegenbauer functions offer better performance for multi-user UWB communications.

Performance of M-ary PPM UWB radio in fading channels

This paper investigates the performance of M-ary pulse position modulation (PPM) multiuser ultra-wideband (UWB) communication systems in terms of symbol error rate (SER) over fading and additive white Gaussian noise (AWGN) channel. Based on Gaussian approximation for the multiple access interference, an expression for the signal-to-noise ratio (SNR) is derived for the UWB system. This expression is used to derive exact SER expressions for coherent UWB receivers. The effect of pulse selection on the SER of multiuser UWB system is studied. In addition to rectangular pulse, the 2nd derivative Gaussian waveform and Rayleigh pulses were considered. We show that the system capacity and/or SER performance can be significantly increased by using the monocycle pulse in fading channels.