Direct-sequence Ultra-wideband Systems Research Articles

A FPGA implementation of GMM MUD algorithm for space formation aircraft communication system

Space formation aircraft communication system needs to meet strong anti-interference ability, low power consumption and high transmission rate performance. Ultra-wideband (UWB) has high data transfer rate, low device complexity, high interference resistance and confidentiality. Therefore, UWB technology is used in space formation aircraft communication system, which is direct sequence ultra-wideband (DS-UWB) space formation aircraft communication system. This paper, we put forward a multi-user detection (MUD) algorithm based on Gaussian Mixture Model (GMM) in DS-UWB communication system and its field-programmable gate array (FPGA) implementation. We adopt a way which based on MATLAB and FPGA platform, and results show that MUD algorithm based on GMM has better bit error rate (BER) performance compared to classical multi-user detection algorithm.

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.

Asynchronous direct‐sequence ultra‐wideband communication using spatiotemporal chaotic sequences

In this work, the authors address the effect of spreading sequences and pulse waveforms on the performance of asynchronous direct-sequence ultra-wideband systems. Regarding spreading sequences, they consider the two cases of short and long sequences. The expression of the multi-user interference (MUI) variance is derived using long sequences at the output of a rake receiver, when propagating through multipath channels. The authors also propose the use of sequences generated with a family of spatiotemporal chaotic systems, namely piecewise coupled map lattices (PCML), as spreading sequences. Such sequences are shown to reduce the MUI variance with regard to independent identically distributed and Gold sets for both short and long sequences. Simulation results show that the use of long PCML codes in additive white Gaussian noise and multipath fading channels results in an improvement of the system average bit error rate, hence an increase of the system capacity in terms of number of active users.

A Multiuser Detector Based on Artificial Bee Colony Algorithm for DS-UWB Systems

Artificial Bee Colony (ABC) algorithm is an optimization algorithm based on the intelligent behavior of honey bee swarm. The ABC algorithm was developed to solve optimizing numerical problems and revealed premising results in processing time and solution quality. In ABC, a colony of artificial bees search for rich artificial food sources; the optimizing numerical problems are converted to the problem of finding the best parameter which minimizes an objective function. Then, the artificial bees randomly discover a population of initial solutions and then iteratively improve them by employing the behavior: moving towards better solutions by means of a neighbor search mechanism while abandoning poor solutions. In this paper, an efficient multiuser detector based on a suboptimal code mapping multiuser detector and artificial bee colony algorithm (SCM-ABC-MUD) is proposed and implemented in direct-sequence ultra-wideband (DS-UWB) systems under the additive white Gaussian noise (AWGN) channel. The simulation results demonstrate that the BER and the near-far effect resistance performances of this proposed algorithm are quite close to those of the optimum multiuser detector (OMD) while its computational complexity is much lower than that of OMD. Furthermore, the BER performance of SCM-ABC-MUD is not sensitive to the number of active users and can obtain a large system capacity.

A complexity-performance-balanced multiuser detector based on artificial fish swarm algorithm for DS-UWB systems in the AWGN and multipath environments

In this article, an efficient multiuser detector based on the artificial fish swarm algorithm (AFSA-MUD) is proposed and investigated for direct-sequence ultrawideband systems under different channels: the additive white Gaussian noise channel and the IEEE 802.15.3a multipath channel. From the literature review, the issues that the computational complexity of classical optimum multiuser detection (OMD) rises exponentially with the number of users and the bit error rate (BER) performance of other sub-optimal multiuser detectors is not satisfactory, still need to be solved. This proposed method can make a good tradeoff between complexity and performance through the various behaviors of artificial fishes in the simplified Euclidean solution space, which is constructed by the solutions of some sub-optimal multiuser detectors. Here, these sub-optimal detectors are minimum mean square error detector, decorrelating detector, and successive interference cancellation detector. As a result of this novel scheme, the convergence speed of AFSA-MUD is greatly accelerated and the number of iterations is also significantly reduced. The experimental results demonstrate that the BER performance and the near–far effect resistance of this proposed algorithm are quite close to those of OMD, while its computational complexity is much lower than the traditional OMD. Moreover, as the number of active users increases, the BER performance of AFSA-MUD is almost the same as that of OMD.

A new optimal MUD algorithm based on searching in the local space of sub-optimal MMSE solutions for DS-UWB communication systems

In this paper, we have studied the multiuser detection (MUD) technology applied in multiaccess (MA) direct sequence ultrawideband (DS-UWB) systems. Some typical MUD algorithms were analyzed and a new approximate optimal MUD algorithm based on searching in the local space of suboptimal minimum mean-squared error (MMSE) solution was proposed. In this new algorithm, the suboptimal solution of MMSE is considered as the initial value for the local search, and then a local solution space of this suboptimal solution is constructed by Euclidean distance. Within this space, some likely solutions for the classical optimal MUD algorithm (OMUD) are searched and the optimal one of them is chosen as the solution of this new optimal MUD algorithm. Theoretical analysis and simulation results indicate that, the BER performance and the Near-far Effect resistant ability of this proposed algorithm are much better than those of MMSE and adaptive MMSE detections, which are very close to those of OMUD. Furthermore, its time complexity is much lower than OMUD's. Compared to adaptive MMSE, this algorithm has no difficulty in choosing the suitable parameters for adaptive MMSE. Besides these, we examine the application of this new algorithm to the problem of suppressing the digital narrowband interference (NBI). It is clearly seen that this approximate optimal algorithm has perfect performance under strong NBI circumstance and coincides with the classical OMUD algorithm bound in the same condition.

A hybrid ant colony optimization algorithm for optimal multiuser detection in DS-UWB system

A hybrid ant colony optimization algorithm is proposed by introducing extremal optimization local-search algorithm to the ant colony optimization (ACO) algorithm, and is applied to multiuser detection in direct sequence ultra wideband (DS-UWB) communication system in this paper. ACO algorithms have already successfully been applied to combinatorial optimization; however, as the pheromone accumulates, we may not get a global optimum because it can get stuck in a local minimum resulting in a bad steady state. Extremal optimization (EO) is a recently developed local-search heuristic method and has been successfully applied to a wide variety of optimization problems. Hence in this paper, a hybrid ACO algorithm, named ACO–EO algorithm, is proposed by introducing EO to ACO to improve the local-search ability of the algorithm. The ACO–EO algorithm is applied to multiuser detection in DS-UWB communication system, and via computer simulations it is shown that the proposed hybrid ACO algorithm has much better performance than other ACO algorithms and even equal to the optimal multiuser detector.

Interference cancellation for HNNPSO multiuser detection of UWB systems over multipath fading channel

The problem of multiple access interference (MAI) and inter-symbol interference (ISI) suppression in direct-sequence ultra-wideband (DS-UWB) systems is considered. This paper is dedicated to the application of intelligence computational techniques based on bionics to solve the difficult issue of multiuser detection (MUD) design capable of canceling the so-called MAI to reach low bit error rate (BER) with acceptable computation complexity. We apply the stochastic algorithm that employs a Hopfield neural network (HNN) and particle swarm optimization (PSO) for the MUD problem in DS-UWB system. The use of the HNN embedded PSO (HNNPSO) technique for multiuser detection is a novel ideal, and it leads to efficient techniques that can find a satisfactory solution by maximizing likelihood (ML) function in a small number of iterations. The computer experiments showed that the proposed HNNPSO technique not only can find optimal or close-to-optimal solutions but also obtain both better and more robust results than the existing algorithm reported recently in this literature.

Blind Reduced-Rank Adaptive Receivers for DS-UWB Systems Based on Joint Iterative Optimization and the Constrained Constant Modulus Criterion

A novel linear blind adaptive receiver based on joint iterative optimization (JIO) and the constrained-constant-modulus design criterion is proposed for interference suppression in direct-sequence ultrawideband systems. The proposed blind receiver consists of the following two parts: 1) a transformation matrix that performs dimensionality reduction and 2) a reduced-rank filter that produces the output. In the proposed receiver, the transformation matrix and the reduced-rank filter are jointly and iteratively updated to minimize the constant-modulus cost function subject to a constraint. Adaptive implementations for the JIO receiver are developed using the normalized stochastic gradient (NSG) and recursive least squares (RLS) algorithms. To obtain a low-complexity scheme, the columns of the transformation matrix with the RLS algorithm are individually updated. Blind channel estimation algorithms for both versions (i.e., NSG and RLS) are implemented. Assuming perfect timing, the JIO receiver only requires the spreading code of the desired user and the received data. Simulation results show that both versions of the proposed JIO receivers have excellent performance in terms of suppressing the intersymbol interference (ISI) and multiple-access interference (MAI) with low complexity.

FPGA-based architecture and implementation techniques of a low-complexity hybrid RAKE receiver for a DS-UWB communication system

In this paper, the architecture of a low-complexity Direct Sequence Ultra-Wideband (DS-UWB) receiver subsystem which incorporates a Channel Estimator (CE) and a novel hybrid Partial/Selective (HPS) maximal ratio combining (MRC) RAKE receiver is presented. Three different design techniques followed by FPGA implementation are investigated and compared and system performance results are provided. The proposed architectures combine the benefits of both partial and selective RAKE receiver algorithms and the obtained results demonstrate the trade-off between energy capture, performance and receiver complexity. All design approaches focus on a highly parallel, modular and optimized for high performance system which is necessary for demanding and low-cost applications of UWB communications.

Pre-Equalization for Pre-Rake DS-UWB Systems with Spectral Mask Constraints

In this paper, we propose a novel optimization-based pre-equalization filter (PEF) design framework for direct-sequence ultra-wideband (DS-UWB) systems with pre-Rake combining. The key feature in our design is that we explicitly take into account the spectral mask constraints that are usually imposed in practice by the telecommunications regulation and standardization bodies. This avoids the need for an inefficient power back-off, which is necessary for the existing pre-Rake-based transmitter structures designed solely based on average transmit power constraints. We consider two PEF design structures. In the first structure, the PEF is placed before the up-sampling unit at the transmitter. In the second structure, the PEF is placed after the up-sampling unit. We show that these two structures are significantly different in terms of their capabilities in reducing the residual inter-symbol interference at the receiver and also in following the spectral mask at the transmitter. This introduces a trade-off such that one design structure outperforms the other one, depending on the system parameters. In this regard, we show that if the spreading factor is large enough, the second design structure has a superior performance. Simulation results confirm that both of the proposed PEF structures lead to significant performance gains over PEF designs without explicit spectral mask considerations. In addition, our PEF designs have the capability of adhering to spectral masks with arbitrary shapes.

Reduced-Rank Linear Interference Suppression for DS-UWB Systems Based on Switched Approximations of Adaptive Basis Functions

In this paper, we propose a novel low-complexity reduced-rank scheme and consider its application to linear interference suppression in direct-sequence ultrawideband systems (DS-UWB). First, we investigate a generic reduced-rank scheme that jointly optimizes a projection vector and a reduced-rank filter by using the minimum mean square error (MMSE) criterion. Then, a low-complexity scheme, which are denoted the switched approximation of adaptive basis functions (SAABFs), is proposed. The SAABF scheme is an extension of the generic scheme, in which the complexity reduction is achieved by using a multibranch framework to simplify the structure of the projection vector. Adaptive implementations for the SAABF scheme are developed by using least mean squares (LMS) and recursive least squares (RLS) algorithms. We also develop algorithms for selecting the branch number and the model order of the SAABF scheme. Simulations show that, in the scenarios with severe intersymbol interference (ISI) and multiple-access interference (MAI), the proposed SAABF scheme has fast convergence and remarkable interference suppression performance with low complexity.

BER analysis of DS-UWB system employing a laplace distribution model

This letter takes a new approach to extract a closed-form expression for the bit error rate (BER) of direct-sequence ultra wideband (DS-UWB) system. In the analysis, the main signal is impaired by multi-user interference (MUI) and an external source of interference originated by simultanously transmitting multiband orthogonal frequency division multiplexing (MB-OFDM) systems which are located in the vicinity of the DS-UWB receiver. All the transmission channels are affected by Nakagami-m fading. A Laplacian distribution is considered for MUI to comply more with real statistical behaviors of this kind of interference.

Design of a Dual-band Bandpass Filter for GSM and Direct Sequence Ultra-wideband Communication Systems

In this paper, the design of a dual-band bandpass filter (BPF) with narrow- and wide-band performances simultaneously is presented. The proposed filter only uses two stepped-impedance resonators (SIRs) to achieve the narrow- and wide-band performances. Moreover, transmission zeros are created near the passband edges to improve the band selectivity and can be controlled easily by arranging the coupling structures. A filter example is designed and implemented for global system for mobile communications (GSM) at 1.8 GHz and lower passband of the direct sequence ultra-wideband systems (DS-UWB) at 3–5 GHz. The measured results of the fabricated filter confirm the concepts of the proposed design and match the simulated results.

Performance analysis of rake-MBER-equalizer for DS-UWB communication systems

A joint rake and minimum bit-error rate (MBER) equalizer receiver for direct-sequence ultra-wideband (DS-UWB) communication systems is proposed, where the receiver combats against inter-symbol interference (ISI) by utilizing the rake and equalization techniques. Theoretical analysis and simulation results of the proposed receiver performance are given. Monte Carlo simulations show that the performance of this receiver outperforms rake-MMSE-equalizer receiver and it will degrade with the increase of data speed and the decrease of rake fingers.

Impact of Chip Duty Factor on DS, TH and DS-TH UWB Systems in Realistic Environment

In this paper, the impact of chip duty factor (DF) on direct sequence (DS), time hopping (TH) and hybrid DS-TH ultra wideband (UWB) systems is investigated in realistic environments. Rake receivers are designed to perform energy capture (EC) on received UWB signals over multipath and multi-user environment in the presence of narrowband interference. It is found that by applying lower DF in the signal design, multipath resolvability can be increased and system performance can be improved. However, in contrary to the common belief, lower DF does not always contribute to performance improvement. On the other hand, it is observed that at extremely low DF, EC capability may be compromised, causing performance degradation. The optimum DF values for respective systems are determined and discussed in this paper. Additionally, the strength and tradeoff for DS, TH and DS-TH UWB systems employing varying DF are investigated and compared over multipath and multi-user environment. In a multipath environment, a selective Rake receiver with less than 10 fingers is found to be sufficient for energy capture. In a single user environment, DS-UWB system has the most superior performance, followed by DS-TH-UWB and TH-UWB systems. And in a multi-user environment, DS-TH-UWB is found to outperform the rest, followed by DS-UWB and TH-UWB systems.

Performance Comparison of RAKE Receivers in SC-UWB Systems and DS-UWB Systems

RAKE receivers are generally employed to collect multipath energy in single-carrier ultra-wideband (SC-UWB) systems and direct-sequence ultra-wideband (DS-UWB) systems. Performance of RAKE receivers in these two kinds of systems is studied and compared with each other in this letter. Both theoretical analysis and simulation results over IEEE 802.15.3a UWB channels are presented. Our results show that, with the same signal to noise ratio (SNR) per bit, the same occupied bandwidth and the same number of RAKE fingers, RAKE receivers with maximum ratio combination (MRC) in SC-UWB systems can achieve exactly the same performance as that in DS-UWB systems.

Frequency-domain adaptive detectors for single-carrier frequency-domain equalisation in multiuser direct-sequence ultra-wideband systems based on structured channel estimation and direct adaptation

Here, the authors propose two adaptive detection schemes based on single-carrier frequency-domain equalisation (SC‐FDE) for multiuser direct-sequence ultra-wideband systems, which are termed structured channel estimation (SCE) and direct adaptation (DA). Both schemes use the minimum mean square error (MMSE) linear detection strategy and employ a cyclic prefix. In the SCE scheme, adaptive channel estimation is performed in the frequency domain and the despreading is implemented in the time domain after the FDE. In this scheme, the MMSE detection requires the knowledge of the number of users and the noise variance. For this purpose, simple algorithms are proposed for estimating these parameters. In the DA scheme, the interference suppression task is fulfilled with only one adaptive filter in the frequency domain and a new signal expression is adopted to simplify the design of such a filter. Least mean squares, recursive least squares and conjugate gradient adaptive algorithms are then developed for both schemes. A complexity analysis compares the computational complexity of the proposed algorithms and schemes, and simulation results for the downlink illustrate their performance.

Effects of MB-OFDM System Interference on the Performance of DS-UWB

So far, two ultrawideband (UWB) standards have been proposed as high-speed physical technologies for next-generation wireless personal area networks (WPANs). These standards are based on multiband orthogonal frequency-division-multiplexing (MB-OFDM) UWB or direct-sequence UWB (DS-UWB). However, because of the withdrawal of the plan for a unique standardization process by the IEEE 802.15.3a task group (TG3a), these two technologies will coexist in the future. In this context, this correspondence provides a performance analysis of DS-UWB communication in the presence of MB-OFDM interfering transmissions, where the channel is modeled through the IEEE 802.15.3a standard model, and the network topology for the MB-OFDM interferers is based on a clustered structure as per the IEEE 802.15.3 descriptions for medium access control (MAC) and physical layer specifications for high-rate WPANs. The DS-UWB system performance is assessed in terms of bit error rate (BER). Specifically, an analytical expression for the average BER is derived, conditioned on the channel impulse response using a pulse collision model. Numerical and simulation results are provided and compared for different coexistence scenarios.

Novel modulation scheme and six-port based RAKE receiver for DS-UWB

This paper describes a novel modulation scheme for direct sequence ultra-wideband systems (DS-UWB), which have been considered a type of physical layer (PHY) suitable for high-speed wireless personal area networks (WPANs) in IEEE 802.15.3a. In DS-UWB systems, rake reception is essential to capture dispersive energy and to compensate interference generated by multipath fading. Simulation results show that the proposed modulation, named QBOK (quadrature binary orthogonal keying), outperforms the existing 4-ary biorthogonal keying (4-BOK) scheme under multipath environments in terms of bit error rate (BER) whilst allowing more simultaneous users. Additionally, a new correlator and I-Q demodulator structure based on the well-known six-port architecture is described from a theoretical perspective. Additionally, its application as RF frontend in RAKE receivers with analog emphasis is also investigated in this paper, resulting in reduction of the amount of digital signal processing, easing hardware requirements.