Performance Of Ultra-wideband Systems Research Articles

Performance analysis and optimisation of a cooperative frequency-modulated differential chaos shift keying ultra-wideband system under indoor environments

A cooperative frequency-modulated differential chaos shift keying (FM-DCSK) ultra-wideband (UWB) systems, named cooperative FM-DCSK UWB system, is investigated under indoor environments of IEEE 802.15.4a in this article. The performance of the cooperative FM-DCSK UWB system is evaluated in such channel models (CMs), that is, CM1–CM4, by means of the moment generating function. Monte Carlo simulation results show that the bit-error-rate performance of the proposed system is much better than the conventional multi-access FM-DCSK UWB system, which is showed to be highly consistent with the theoretical results. The integration interval of the proposed cooperative UWB system is optimised to further improve the system performance through the binary search algorithm. Meanwhile, aiming to provide a good compromise between the system performance and implementation complexity, the number of received antenna at the destination (single-input multiple-output architecture) is also investigated and discussed. For the aforementioned advantages, the proposed system can be seen as a viable alternative to other multi-access FM-DCSK UWB schemes for the low-rate and low-power wireless personal area network and wireless sensor network applications.

Adaptive Rake Receiver Joined with Chip Equalization for DS-CDMA UWB Systems over ISI Channels

Since there is much larger channel delay spread, there is serious inter-symbol interference (ISI) when ultrawideband (UWB) wireless communication systems work at high data speed. The serious ISI affects the performance of UWB systems seriously. In this paper, a scheme to suppress ISI is developed for direct sequence spread-code division multiple access (DS-CDMA) UWB systems with a high data speed and an adaptive joint chip equalization Rake (AJCE-Rake) receiver is proposed. The proposed AJCE-Rake receiver spreads the number of traditional Rake receiver taps to collect multi-path component and equalize the inter-chip interference simultaneously. Then the soft output of AJCE-Rake receiver is despreaded with the user's spreading code. Finally, the decision is made to recover the transmitted symbol. The simulation results verify that ISI is suppressed effectively and the system performance is improved evidently.

Performance of UWB Systems with Direct-Sequence Bipolar Pulse Amplitude Modulation and RAKE Reception over IEEE 802.15.3a Channel

Direct-Sequence Pulse Amplitude Modulation (DS-PAM) has been widely proposed for Ultra-Wideband (UWB) communication systems because it provides better performance with low computational complexity. UWB signals suffer from severe multi-path interference when employed in indoor fading environments. But using RAKE reception can make use of the rich multi-path of UWB systems to improve system performance. In this paper we present the performance of a RAKE receiver employing maximal ratio combining (MRC) in a DS UWB system with BPAM modulation. Performance in a practical multi-path fading Channel (IEEE 802.15.3a Channel) is considered to analyze the performance of DS-PAM UWB systems with different RAKE receivers. The bit error rate (BER) of ARake, PRake, and SRake over DS-BPAM UWB systems is simulated. The results indicate that ARake has the best performance, SRake is better than PRake when the number of fingers is the same.

Design and Analysis of Timing Synchronization in Block Transmission UWB Systems

In this paper, timing synchronization in high-rate ultra-wideband (UWB) block transmission systems is investigated. A new joint timing and channel estimation scheme is proposed for orthogonal frequency division multiplexing (OFDM) and single carrier block transmission with frequency domain equalization (SC-FDE) UWB systems. The scheme is based on a newly designed preamble for both coarse timing and the subsequent channel estimation. Despite of the presence of coarse timing error, the estimated channel impulse response (CIR) is simply the cyclic shifted version of the real CIR, thanks to the unique structure of the preamble. The coarse timing error (CTE) is then determined from the CIR estimation and used to fine tune the timing position and the frequency domain equalization coefficients. The proposed scheme saves preamble overhead by performing joint synchronization and channel estimation, and outperforms existing timing acquisition methods in the literature in dense multipath UWB channels. In addition, the impact of timing error on channel estimation and the performance of SC-FDE UWB systems are analyzed, and the bit-error-rate (BER) degradation with respect to a certain timing error is derived.

Joint Detection of Primary Systems Using UWB Impulse Radios

Regulation in Europe and Japan requires the implementation of detect-and-avoid (DAA) techniques in some bands for the coexistence of licensed primary systems and secondary ultra wideband (UWB) systems. In a typical coexistence scenario, a primary system may have potentially interdependent uplink-downlink communication channels (e.g., simultaneous uplink-downlink communications in a frequency division duplex system) overlapping with the frequency band of a UWB system. If such interdependencies of primary systems' activities are known, the UWB system's ability to detect primary systems can be improved. In this study, we are interested in determining the possible gains in the detection performance when taking interdependencies into account for practically implementable detection methods. Contrary to selecting the detection thresholds individually for each band as in a conventional detection approach, the bands are jointly processed. To this end, maximum a posteriori (MAP) decision variables are generated at the receiver, and bias terms are introduced to achieve a desired trade-off between the probabilities of detection and false alarm. In addition to finding the optimal detection results based on the Neyman-Pearson (NP) test, a suboptimal but practically implementable approach is also considered, and the gain compared to conventional independent detection is quantified for various practical scenarios. The results obtained from this study can be used for improving the primary system detection performance of UWB systems, as well as for cognitive radios that perform spectrum sensing in multiple bands.

EFFECTS OF ANTENNAS AND PROPAGATION CHANNELS ON SYNCHRONIZATION PERFORMANCE OF A PULSE-BASED ULTRA-WIDEBAND RADIO SYSTEM

Synchronization performance of a pulse-based ultra- wideband (UWB) system is investigated by taking into account of distortions caused by transmitter and receiver antennas and wireless propagation channels in difierent environments. The synchronization scheme under consideration can be achieved in two steps: a slide correlator and a phase-locked loop (PLL)-like flne tuning loop. Efiects of the non-idealities are evaluated by analyzing the distortion of the received UWB pulse and subsequently the synchronization performance of the pulse-based UWB system. It is found that generally a smaller step is required for the sliding correlator due to distortions introduced by the antennas and channels. However, the flne tuning loop can always be stabilized by adjusting the loop parameters. Therefore, synchronization can always be achieved.

Reliability of Generalized Normal Laplacian Distribution Model in TH-BPSK UWB Systems

In this letter, the reliabilty of the generalized normal-Laplace (GNL) distribution used for modeling the multiple access interference (MAI) plus noise in time-hopping (TH) binary phase-shift keying (BPSK) ultra-wideband (UWB) systems is evaluated in terms of the probability density function and the BER. The multiple access performance of TH-BPSK UWB systems based on GNL model is analyzed. The average BER performance obtained by using GNL approximation well matches with the exact BER results of TH-BPSK UWB systems. The parameter estimates of GNL distribution based on the moments estimation method is also presented.

Performance of Receive Diversity UWB Systems with Pulse Amplitude and Position Modulation

In this paper, we extend ultra-wideband (UWB) single input single output (SISO) systems with a hybrid pulse amplitude and position modulation (PAPM) to single input multiple output (SIMO) systems using receive antenna diversity. The performance of a rake receive diversity combining scheme for UWB SIMO systems with a PAPM is examined in a log-normal multipath fading channel and also compared with that of a time-switched transmit diversity (TSTD) multiple input single output (MISO) system. It is seen that as the number of receive antennas increases, the receive diversity combining system improves the error performance. It is shown that the TSTD UWB MISO systems offer the performance equivalent to the receive diversity combining scheme for SIMO systems.

Improved performance of UWB system for wireless body area networks

In this paper, we propose and analyze ultra wide band (UWB) systems employing binary ZCD (zero correlation duration) code for wireless body area network (WBAN). When there are several wireless communication devices on a human body, multiple access interference (MAI) can occur. Hence, in order to reject MAI and enhance overall system performance, binary ZCD code is utilized as spreading code for UWB system. The performance is evaluated in terms of bit error rate (BER). From simulation results, it is confirmed that the UWB system with the ZCD code achieves better performance compared with that of pseudonoise (PN) code. The results of the paper can be applied to design and implementation of UWB systems for WBAN applications.

Ultra wideband technologies coexistence in Nakagami- m fading channels

The wide spectrum of ultra wideband (UWB) communications makes it inevitable to consider strategies for avoiding and mitigating interference from narrowband wireless systems such as GPS, UMTS, and WLAN, or other UWB wireless technologies. In this paper, we provide a performance analysis of multiband orthogonal frequency division multiplexing (MB-OFDM) UWB in the presence of binary phase-shift keying time-hopping (BPSK-TH) UWB or BPSK-DS UWB interfering transmissions under Nakagami-m fading. In the bit-error rate (BER) analysis, several UWB interferers are considered to affect the MB-OFDM signal. A Gaussian approximation is considered for the UWB interferers and used in the analysis of the BER performance of the MB-OFDM UWB system. The Nakagami-m distribution is applied to characterise the amplitude of the fading channels for both the reference signal and the interference signals. Furthermore, a waveforming technique is considered for mitigating the effect of interference and its efficiency is illustrated in terms of BER improvement. Numerical and simulation results are provided and compared for different coexistence scenarios.

Error Analysis of Hybrid DS-Multiband-UWB Multiple Access System in the Presence of Narrowband Interference

This paper proposes a hybrid multiband (MB) ultra wideband (UWB) system with direct sequence (DS) spreading. The theoretical error analysis for the DS-MB-UWB multiple access system with Rake receiver in the presence of multipath and narrowband interference is developed. The developed theoretical framework models the multiple access interference (MAI), multipath interference (MI) and narrowband interference for the designed UWB system. It is shown that the system error performance corresponding to the combining effects of these interference can be accurately modeled and calculated. Monte Carlo simulation results are provided to validate the accuracy of the model. Additionally, it is found that narrowband interference can be mitigated effectively in the multiband UWB system by suppressing the particular UWB sub-band co-existing with the interfering narrowband signal. A typical improvement of 5dB can be achieved with 75% sub-band power suppression. On the other hand, suppression of UWB sub-band is also found to decrease frequency diversity, thus facilitating the increase of MAI. In this paper, the developed model is utilized to determine the parameters that optimize the UWB system performance by minimizing the effective interference.

A fast acquisition system for ultra-wideband wireless multiple-access communications

The fast and accurate timing acquisition of short ultra-wideband (UWB) pulse shapes and, implicitly, the required high sampling rates play a significant role in UWB receiver-structure design and create challenges for signal acquisition under non-ideal conditions. Furthermore, the pulse shape is seen as one of the key factors influencing the performance of UWB systems. While fulfilling the power-spectral-density emission requirements, the pulse shape must offer the highest detection capabilities with suitable levels of accuracy. In this paper, a fast acquisition system for UWB wireless multiple-access communications is presented. The proposed acquisition system has explicit design characteristics that offer greatly improved acquisition time, accuracy, and implementation cost, while also yielding very satisfactory performance at high noise and multi-user interference levels. In addition, the impact of pulse shapes on the performance of this fast acquisition system is evaluated to determine the most suitable pulse shape for its implementation.

Analytical performance of M-ary time-hopping orthogonal PPM UWB systems under multiple access interference

In this paper, we extend the characteristic-function approach to derive an exact symbol error rate expression for the M-ary time-hopping orthogonal pulse position modulation (THPPM) ultra-wideband (UWB) system under the interference from multiple users. Monte Carlo simulations are then used to validate the analytical solutions. The results are found to be valid even when that the chip width is greater than the pulse duration. Moreover, the analytical results are compared to those found by Gaussian approximation and the Gaussian quadrature rule method. We further show that compared to a binary system, M-ary systems can produce better error rate performance.

An Effective Selective Detection Scheme Based on Pulse Repetition for Noncoherent UWB Systems

We propose a selective detection scheme based on pulse repetition considering the bit-error rate (BER) performance and complexity of noncoherent ultra-wide-band (UWB) systems. To take system complexity into account, the proposed scheme transmits the UWB signals by simple pulse repetition at the transmitter, like conventional pulse repetition coding (PRC). However, to effectively improve the BER performance, the proposed scheme performs selective detection by estimating the signal-to-noise ratio of the received pulse-repeated signals at the UWB receiver. Hence, the proposed scheme effectively improves the BER performance of the noncoherent UWB systems without much increasing system complexity, as compared to the conventional PRC.

Statistical Analysis of UWB Channel Correlation Functions

Various performance metrics of impulse-radio (IR) ultrawideband (UWB) receivers are closely connected to the correlation functions of the multipath channel responses to UWB pulses. Interpulse interference is related to the autocorrelation function (ACF) of the received pulse (RP), the RP energy and its fading correspond to the ACF at zero lag, and multiple access interference is connected to the cross-correlation function (CCF) between two channel pulse responses. Each realization of the multipath channel shows different correlation functions due to the ldquorandomnessrdquo of the UWB propagation environment. This paper derives the first- and second-order statistics of the ACF and CCF, capturing this randomness. Such results are useful for incorporating the multipath channel into the performance and design optimization studies of UWB systems. The analysis is based on a model of the received UWB pulse. The model describes the random channel response by two continuous functions of the excess delay time-one expresses the power, the other expresses power variations-and by a prototype pulse shape representing all linear system components including the band limitation of the RP and antenna effects. The analytical results are validated through the analysis of simulated and measured channel responses.

Accurate Bit-Error Rate Evaluation for TH-PPM Systems in Nakagami Fading Channels Using Moment Generating Functions

Analytical expressions based on the Gauss-Chebyshev quadrature (GCQ) rule technique are derived to evaluate the bit-error rate (BER) for the time-hopping pulse position modulation (TH-PPM) ultra-wide band (UWB) systems under a Nakagami-m fading channel. The analyses are validated by the simulation results and adopted to assess the accuracy of the commonly used Gaussian approximation (GA) method. The influence of the fading severity on the BER performance of TH-PPM UWB system is investigated.

Characterization of wall dispersive and attenuative effects on UWB radar signals

Abstract This paper addresses the potentials of ultra-wideband (UWB) through-wall imaging radars compared with conventional narrowband systems. The challenges that limit the utilization of high precision UWB systems are examined with the aim of mitigating them. These challenges include multi-path, pulse dispersion, and antenna effects on the pulse shape due to angles of transmission and arrival. The propagation of UWB signals through walls is a crucial factor in determining the success of UWB radar technology. UWB signals, when propagating through walls, not only suffer attenuation but also distortion due to dispersive properties of the walls. This paper examines time- and frequency-domain techniques for measuring the electromagnetic properties of construction materials in the UWB frequency range. The measured parameters provide valuable insights in appreciating the capabilities and limitations of the UWB technology. Special attention is paid to time gating as a mean to extract the direct-path signal from the multi-path components. Both single-pass and multi-pass models are discussed. Multi-pass models account for the multiple reflections within the wall while the single-pass model assumes the possibility of gating out a single transmission. The partition-dependent narrowband propagation model is modified to account for the ultra-wide bandwidth of the signal. The paper illustrates the application of the modified model in indoor environments. The modified model is helpful in estimating the link power budget. It is also useful in studying the performance of UWB systems for indoor communication and positioning applications.

O [formula omitted]-based linear decorrelating detector for asynchronous UWB systems over multipath fading channels

In this paper, a convenient signaling scheme, termed orthogonal on–off Ultra wideband (UWB) (O 3 UWB), along with a simple one-shot linear decorrelating detector (LDD) and a Rake bank, is proposed. This scheme is useful for conducing multi-user detection because temporally adjacent bits in receiver signals from different users are decoupled using on–off signaling. This mechanism also leads to one-shot detection that overcomes the main disadvantage, long detection delay, of the conventional LDD. In addition, the data rate is maintained, with no increases in the transmission rate, by adopting an orthogonal structure. In this paper, we study the system performance over a flat fading channel. Four types of channel models, including Rayleigh fading, Nakagami- m fading, Rician fading, and Lognormal fading, are considered. Since multipath fading still significantly degrades UWB system performance, the Rake bank is included to recover multipath diversity gain. Numerical analysis and simulation results show that the O 3 UWB LDD receiver still offers a good near-far resistant property over fading channels compared to the conventional UWB receiver.

Signal-to-Interference-Plus-Noise Ratio Analysis for Direct-Sequence Ultra-Wideband Systems in Generalized Saleh–Valenzuela Channels

In this paper, exact signal-to-interference-plus-noise ratio (SINR) analysis of direct-sequence ultra-wideband (UWB) systems with Rake receiving in the presence of inter-symbol interference and multiple-access interference over a generalized Saleh-Valenzuela (GSV) channel with a generic pulse shaping function is provided. The SINR expression, for synchronized multiple-access, is first obtained without assuming random spreading. The GSV channel structure under consideration is a generalization of the Saleh-Valenzuela channel structure with generalized path-gain and path-arrival models, examples of which can include all the IEEE 802.15.3a UWB channel models and some of the IEEE 802.15.4a models. Then, by the novel treatment of renewal processes, the exact average SINR over the GSV channel statistics is obtained. Our analytical results well match computer simulations and can readily be applied to evaluate and improve the performance of UWB systems over realistic channel and interference models.

Performance Analysis of Multiband OFDM UWB Systems With Imperfect Synchronization and Intersymbol Interference

This paper provides performance analysis of MB-OFDM UWB systems that not only captures the characteristics of realistic ultra-wideband (UWB) channels, but also takes into consideration of the imperfection of the frequency and timing synchronizations and the effect of intersymbol interference. The systems are considered in multipath fading channels, the IEEE 802.15.3a channel standard, with four channel models: CM1, CM2, CM3, and CM4. These channel models are characterized by cluster arrival rate, ray arrival rate within clusters, and cluster and ray decay factors. First, an average signal-to-noise ratio with imperfect synchronizations and intersymbol interference is derived. Then a closed-form bit error rate performance formulation that provides insightful understanding of the system performance in various synchronization conditions is obtained under Rayleigh fading assumption. This analytical performance formulation serves as an upper bound on the bit error rate performance of UWB systems. Finally, simulation results under various channel and synchronization conditions are provided to validate the theoretical analysis.