Sparsity-Driven Multiple Access Ultra-Wideband Signal Detection

A novel method to generate ultra-wideband (UWB) signals based on two differential group delay modules and one Mach-Zehnder Modulator is proposed. Both simulation and experiments verified that the method could generate two kinds of UWB monocycles using low bit-rate non-return-to-zero data source (1Gbps). The monocycles have a fractional bandwidth of 127% at centre frequency 5.5GHz. Keywords: Ultra wideband (UWB), radio-over-fiber (RoF), differential group delay (DGD) 1. INTRODUCTION Ultra-wideband (UWB) is a fast emerging technology for short-range broadband wireless communication such as wireless personal area network and sensor network, etc. The UWB signal occupies wide bandwidth and has low power density, and it has immunity to multi-path fading [1]. As a carrier-free modulation scheme, direct-sequence impulse radio is more cost-effective and simpler compared with multi-band orthogonal frequency scheme. Since UWB is a room-scaled short range wireless communication technique, the wireless networks can operate mainly in indoor environment in standa lone mode. Considering the integration of UWB access networks and fixed wired networks, the combination of UWB-over-fiber technology and fiber-to-the-home (FTTH) technology is a competitive candidate for future wideband access networks [2]. So many all-optical schemes that fit for UWB-over-fiber technology to generate and distribute UWB impulses have been reported recently. Zeng et al. proposed two approaches to generate UWB impulses using one phase modulator (PM), and 25-km single mode fiber (SMF) or FBG to convert phase-modulated light to UWB pulses [3, 4]. Wang and Dong proposed UWB signal generation using cross-gain modulation or cross-phase modulation in semiconductor optical amplifier [5, 6], which requires two laser sources and may increase the system complexity. Chen proposed a scheme based on optical polarization time delay [7]. It is a simple method, but the elect rical signal source needs at least twice bit-rate compared to the carried data. Most of the schemes n eed an electrical Gaussian pulse source, which is comm only composed of a high-speed pulse pattern generator (PPG). This is an expensive construction, for which the PPG should work at least 10 Gbps. Furthermore, if data are carried on the UWB pulses, another modulator should be added to the systems, which increase the system cost and complexity. In this paper, we proposed and experimentally demonstrated a simple method to generate data-carried UWB monocycle pulses based on two differential group delay (DGD) modules and one Mach-Zehnder modulator (MZM). Instead of the data pattern “1000 0000 ”, which has one “1” followed by several “0”s to form the UWB signal, we use electrical non-return-to-zero (NRZ) data. The NRZ data modulate the optical signal in MZM to get an optical binary phase shift keying (BPSK) signal, which is then fed into two cascade DGD module s while the polarization of the light is carefully adjusted

1.1 Impulse Radio (IR) Ultra Wideband (UWB) Communications Ultra wideband (UWB) communication is a fast emerging technology that offers new opportunities such as high data rates, low equipment cost, low power, precise positioning capability and extremely low interference Ghawami (2005). A wide range of possible UWB communication system applications includes radars due to UWB ultra high precision ranging at the centimeter level, wireless personal area networks (WPAN), sensor networks, imaging systems, UWB positioning systems, etc. Yang (2004), Kshetrimayum (2009). From a commercial point of view, the high data rates are the most attractive feature of UWB systems for which speeds of over 100Mb/s have been demonstrated Ghawami (2005). There exist three main types of UWB technologies: impulse radio (IR UWB), direct sequence (DS UWB), and multi-band orthogonal frequency division multiplexing (MB OFDM) Ran (2009). IR UWB communication technique is essentially different from all other communication techniques because it is carrier free and uses for communication between transmitters and receivers very narrow radio frequency (RF) pulses generated from the UWB pulse generator, while traditional transmission systems transmit information by varying the power, frequency, and/or phase of a sinusoidal wave in a modulation process Kshetrimayum (2009), Yao (2007). Consequently, complicated frequency mixers and local oscillators for carrier frequency up and down conversion are not necessary Yao (2007). IR UWB modulation techniques are especially important because the UWB spectrum has been made available by the Federal Communication Commission (FCC) and it can be used with IRs developed to date Lin (2005). Waveforms for IR UWB are designed to obtain a flat frequency response over the bandwidth of the pulse and to avoid a DC component. The large spectrum of a UWB signal may interfere with existing users. In order to keep this interference to the minimum, FCC specifies spectral masks for different applications, i.e. the allowed power output for specific frequencies Ghawami (2005). A contiguous bandwidth of 7.5GHz is available in the frequency interval of (3.1− 10.6)GHz at a maximum power output of −41.3dBm/MHz which is considered as extremely low Ghawami (2005). The power spectral density (PSD) of UWB systems defined as a ratio of the transmitted power P in watts and a signal bandwidth B in hertz is extremely low as compared to other communication systems due to the very wide bandwidth B of short pulses that are typically of nanosecond or picosecond order Ghawami (2005). The selection of the impulse signal type for IR UWB communication system is essential since it determines

Wireless ultra-wideband (UWB) receivers usually employ a deterministic clean pulse or a pulse derived from a Gaussian waveform as a template for correlation. A deterministic template is not expected to have the capability of correlating highly with random UWB signals all the time. The resulting mismatch, however, can significantly degrade the system error performance. We therefore optimize a deterministic template to achieve the maximum energy capture capability in the sense of ensemble average. The UWB correlator using the optimal deterministic template can be employed along with combining to enhance signal detection. The resulting receivers outperform their counterparts using a clean pulse, as evidenced by theoretical analysis and numerical results based on real UWB data.

This paper presents results of coexistence measurement studies between multiple ultra wideband (UWB) transmitters and a global positioning system (GPS). In addition, mathematical models for UWB aggregate noise rise in the GPS, universal mobile telecommunications system (UMTS) and wireless local area network (WLAN) 802.11a/g bands are illustrated. In GPS coexistence measurements, a realistic satellite constellation and outward circumstances were created using a commercial GPS simulator and receiver. Each measurement was carried out using Federal Communications Commission (FCC) compatible prototype singleband UWB transmitters. The measurements took place in an anechoic chamber to minimize any radio interference. The results clearly show that GPS can survive even under a large number of interfering UWB devices which are operating using realistic transmission parameters. Still, if a large number of interfering UWB devices or high UWB activity factor and pulse repetition frequency is used UWB can be regarded as a threat to GPS usage.

Sampling designs for the detection of sure signals in Gaussian noise are considered. Both deterministic and random sampling schemes, using optimal and nonoptimal detectors, are presented and their performance is studied. The analytical results are supplemented by comparison of performance for small and large Sample size for some representative processes including the Gauss-Markov and Wiener processes.

The problem of distributed detection of a deterministic signal with unknown strength using a neural network approach is considered. Since the signal level Is not known there does not exist a uniformly powerful detection scheme for the problem. The neural network architecture used Is a two layer feedforward perceptron model with N Inputs M nodes In the hidden layer and two output nodes that correspond to the signal and noise hypotheses. The back propagation algorithm Is used to train the system with a known noise distribution. For fixed false alarm probabilities the performance of the trained network with regard to a set of test signals is estimated and compared to the performance of some known detection procedures such as Fisher''s method Tlppett''s method and the optimum test. Simulation results are presented for a network with two input nodes and three or four nodes In the hidden layer. When Laplace noise Is assumed the network performs better than the Tlppett method. For the detection of weak and moderate signals in Gaussian noise the network performs reasonably close to the optimum detection scheme. The decision regions for the neural network detection scheme is comparable to those of the Fisher''s and Tlppett''s methods. However unlike the Tippett''s method which has a fixed decision region regardless of the noise distribution the neural network''s decision region changes with the noise distribution. 1. SIGNAL DETECTION

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

Received ultra wideband (UWB) signals in most indoor environments are stochastic in nature, typically composed of abundant multi-path components with random attenuation and arrival time. A commonly adopted detection strategy is to use a chosen deterministic template to correlate the received signal segment by segment, and only those segments having significant cross-correlation with the template are selected, temporally synchronized and co-phased in their projections for coherent combining. Correlating a deterministic template with a random signal usually results in only partial energy captured by the receiver since a random signal is of multidimensions. In this paper, we construct a receiver with multiple orthogonal branches to fully capture the signal energy, in much the same way as a quadrature receiver does in conventional digital communications. The local reference signals are derived from the orthogonal expansion of UWB signals. The random projections of a UWB signal onto different orthogonal basis functions are non-coherently combined, leading to the concept of dimension diversity. Dimension diversity can be either used alone, or alongside a Rake receiver to further exploit path diversity. The error performance of proposed receivers is analyzed, and their superiority over the conventional ones is examined by numerical results based on real UWB data.

The performance of ultra wideband (UWB) signals transmission using radio-over-fiber (ROF) technology is analyzed. UWB signals are directly modulated onto the optical carrier of wavelength 1550 nm for single mode fiber (SMF) system and 850 nm for multimode fiber (MMF) system. Bit error rates (BER) as a function of SMF and MMF lengths are presented. The ranges of SMF length are 0 to 5.5 km and 25.2 km to 31 km and 0 to 700 m for MMF. By varying the attenuation between the UWB transmitter and ROF modulator and between the photo-detector and UWB receiver, BER of less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> is achieved for SMF system. Reliable transmission of UWB signals using ROF technology is thus demonstrated. MMF system achieves a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> for lengths less than 450 m

This work presents an M-ary multiple access code-selected direct sequence (DS) ultra wideband (UWB) communication system. A high data rate multiple access UWB system can be obtained by a code selection mechanism. In the proposed system, each user is assigned a DS code set with M/2 DS code sequence and a particular DS code sequence can be selected by the log2 (M/2) bits from the DS code set. More importantly for this M-ary UWB communication system, with the increase of the modulation level M, it allows to reduce the required transmitter power maintaining the number of users, the data transmission rate and the multiple access performance. In this paper, we also introduce the detailed algorithm to compute the bit error rate (BER) over the AWGN channel and correlation receivers.

This paper considers compressed sensing (CS) techniques for signal reconstruction and channel estimation in OFDM-based high-rate ultra wideband (UWB) communication systems. We employ a parallel CS structure that exploits frequency domain sparsity. We also consider multipath UWB channels in both the line-of-sight and non line-of-sight environments. UWB signal detection and channel estimation from sub-Nyquist analog projections is carried out using an optimized orthogonal matching pursuit algorithm and the smoothed l 0 algorithm. Simulation results demonstrate significant gains in the form of reliable signal recovery and channel estimation as well as dramatically sub-Nyquist sampling rates for the analog-to-digital converters while maintaining high data rates.

Partial Discharge (PD) measurement is an effective method to detect degradation processes in medium and high voltage equipment. As an example, after-laying PD test have become mandatory in many countries as a commissioning test for high voltage cable systems. This type of test can assess the presence of defects just after installation, but thermal cycling, electrical and thermal stress as well as contamination can lead to the onset of defects at a later time. To cope with defects arising during operation, the key is PD monitoring (offline tests are often too costly in terms of equipment, personnel and loss of revenues). This paper presents the application a of permanent PD monitoring system based on a Ultra-Wide band (UWB) detector to high voltage transition joints linking old fluid-filled cables with new XLPE cable lines. These cable accessories are highly critical because of the complexity of their insulation system and the fact they are realized on field (uncontrolled environment). The innovative monitoring scheme fully exploits the benefits coming from using a UWB detector, i.e., selective tracking of PD based on PD pulse characteristics. This approach enables to trend various PD sources separately, highlighting those that are associated with degradation phenomena within the insulation system. This approach will be unraveled and demonstrated by monitoring data coming from two cable lines.

For precise synchronization of ultra wide band (UWB) signals in wireless channels, narrow band interference (NBI) suppression is a challenging issue. This is more relevant for real time channels which are non-linear in nature and are coexisted by narrow band wireless systems. An interference suppression scheme coupled to an energy detection based synchronization approach designed using second-order complex adaptive notch filter (ANF) is reported in this paper. This ANF uses a gradient descent algorithm for tracking the filter coefficients. The use of the same exploits the correlation difference property of signals received and suppresses NBIs in UWB signals. Consequently, it significantly reduces the computational complexity compared to the existing adaptive filters and requires lower power for an efficient hardware implementation. The data rate of UWB is usually high, so a combined pipelined-parallelism (CPP) approach is proposed which effectively simplifies the hardware design unlike direct and cascade forms. Detailed analysis suggest that the proposed scheme provides better performance in terms of power, speed, convergence and stability. Moreover, this scheme when used in conjunction with energy detection receivers significantly improves the interference tolerance margin, thereby raising the performance levels of synchronization with energy detection approach in non-coherent energy detection receivers.

Ultra-Wide Band (UWB) signals have become attractive for their particular advantage of having narrow pulse width which makes them suitable for remote sensing of vital signals. In this work, a MATLAB framework is presented which simulates an environment whereby the UWB signals can be observed and evaluated at different locations of the simulated channel for wireless measurement of heart rate. Main parts of the simulated system include UWB signal generator, transmitter and receiver, channel model which contains human body. The proposed system enables us to evaluate the effect of different parameters, such as thickness of channel layers and heart motion parameters on the accuracy of heart rate measurement. One of the main features of this work is employing a five layers channel model with arbitrary attenuation parameters defined by user for simulation of human body. In our experiments attenuation of transmitted Gaussian monocycle pulse centered at 4 GHz frequency in each layer with different thickness for all existing multipath are calculated. Moreover, the effects of receiver sensitivity and three types of irregularities in the accuracy of measured heart rates are investigated.

The interference of ultra wideband (UWB) signals on conventional radio systems, called victims, is still an open issue. In this paper we show that not only the interference power but also the amplitude statistics have significant influence on the bit error rate (BER) of the victim. The amplitude probability distribution (APD) of UWB signals at the channel and inside the victim's receiver is studied analytically and verified by simulation. It is shown under which boundary conditions the UWB signal looses its pulsed behavior inside the victim's receiver. From this an interference model for the additional BER caused by UWB is proposed. The theoretical model is evaluated by simulations with a WLAN and a UMTS victim