Direct Sequence Ultra Wideband Research Articles

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.

Wireless LXI Bus Clock Synchronization and Triggering Design

In this paper, a wireless local area network (WLAN) extension for instrumentation (LXI) [WLXI] bus combining the technology of WLAN and LXI bus is proposed. Several different kinds of methods are designed to implement clock synchronization and triggering. For clock synchronization, a method using the IEEE 1588 protocol based on extended Kalman filter (EKF) is introduced as emphasis. For this method, the wireless IEEE 1588 protocol is used as a communication protocol of clock synchronization, and EKF is used to resolve the clock's nonlinear shifting. The EKF improves the precision of clock synchronization, thus, high-precision clock synchronization for WLXI is realized. For triggering, a method based on the direct-sequence (DS) ultrawideband (UWB) is introduced and emphasized. For this method, DS spread-spectrum (DSSS) UWB is used as a modulation mode, combined with “lagging delay” wireless triggering to realize high-precision synchronization triggering for WLXI.

Distributed water-filling algorithm for direct-sequence ultra wideband cognitive radio network with limit on aggregate power emission

Despite their near-noise power emission, ultra wideband (UWB) radios, particularly direct-sequence ultra wideband (DS-UWB), are still possible to cause harmful interference to legacy radio systems. When they participate in a large dense cognitive radio network (CRN) and transmit simultaneously, their joint power emission would be disastrous if without control. We address this problem by imposing a limit on the aggregate power emission of DS-UWB CRN. The limit is negotiable. It takes effect by letting each transmitter adapt to a spectrum void defined as the area below the limit itself and above the interference temperature experienced instantly by the transmitter. We propose a water-filling algorithm that maximises the sum capacity while enabling each transmitter to fit its power spectral density into, and thus to make the most of, the spectrum void. The algorithm is performed locally at the transmitter with low complexity. Numerical analysis based on a realistic office network shows that the algorithm can bring the aggregate power emission even down below the Federal Communications Commission limit for individual UWB device, but still guarantees a given bit-error performance to nearly 40 active users.

A New Method of Interference Evaluation Between an Ultrawideband System and a Wireless LAN Using a Gigahertz Transverse Electromagnetic Cell

A new method of evaluating the interference to a wireless LAN with a built-in antenna using a gigahertz transverse electromagnetic (GTEM) cell is proposed. The GTEM cell can generate a wideband electromagnetic field from dc up to several gigahertz with a high spatial uniformity in the cell. This is advantageous for configuring a system for a victim receiver with a built-in antenna. Furthermore, the strength of the interfering electromagnetic field to be applied to the victim can be directly calculated from a given equivalent isotropically radiated power and propagation distance of the interfering signal in free space. It should also be noted that a GTEM has a conductive enclosed structure that is much smaller than typical anechoic rooms. As an example of use of the method, the evaluation of interference between an IEEE 802.11a wireless LAN and a direct-sequence spread-spectrum UWB was conducted. Investigations are further conducted on the effects of the UWB signal on the throughput of the victim wireless LAN system on the basis of bit error rate estimated with measurement results of the amplitude probability distribution of the UWB signal.

Energy Normalized Correlation for Signal Acquisition in Power-Control-Absent UWB Networks

This letter presents a novel detection method for signal acquisition in a power-control-absent ultra-wideband (UWB) system where concurrent transmissions are unavoidable. In such a scenario, the conventional single-user detection method which is based on correlating the received signal with a template pulse train suffers from the near-far effect, since the matched-filter sum can easily be overwhelmed by a strong interferer. Our proposal copes with this near-far issue by compensating the correlation result based on the energy in the sliding window. Therefore the energy normalized correlation is sensitive to the existence of a pulse but not to its strength. Our proposal is compared with the conventional method in terms of the probability of faulty acquisition. Simulation results show substantial improvement using our proposed method in an indoor environment with uncontrolled multi-user interference (MUI). We also point out that hybrid time hopping (TH)/direct sequence (DS) UWB systems result in less faulty acquisition than TH UWB systems.

Narrowband Interference Mitigation in DS-UWB Systems

Interference suppression is important for ultra-wideband (UWB) systems to operate over spectrum occupied by pre-existing narrowband systems. In this letter, we first extend the code-aided interference suppression technique to a direct sequence (DS) UWB system which has been proposed for narrowband interference (NBI) suppression in direct sequence spread spectrum (DSSS) systems. Then, we introduce a new type of spreading sequence, which significantly improves the NBI suppression capability of the code-aided technique. We also discuss a preamble-aided synchronization scheme for utilizing the new type of spreading sequence.

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.

Medical applications adapting ultra wideband: a system study

In order to find the best solution of physical layer for medical wireless body area network (WBAN), two single-band ultra wideband (UWB) systems are studied, i.e., direct sequence ultra wideband (DS-UWB) and ultra wideband frequency modulation (UWB-FM). UWB is considered to be one of the most feasible techniques among those that can be applied to medical WBAN since it provides low power consumption, simple transceiver structure and good coexistence characteristics due to a low power spectral density. The simulation results indicate that UWB-FM has better performance than non-coherent DS-UWB in overall. It was expected that coherent DS-UWB with multiple rake fingers gives the best results, and this was justified by the simulation results.

System Simulations of Ds-Trd and Th-Ppm for Ultra-Wide Band (UWB)Wireless Communications

Following FCC approval of ultra-wide band (UWB) radio rules for commercial applications in 2002, a UWB radio physical layer standard is currently under development. Although the UWB transmitting UWB band are spelled out by the FCC, neither UWB signal forms nor modulation schemes are defined by the regulations, stated in ref. [1]. This paper presents the models of two types of impulse radio UWB modulation systems and their simulation performance. They are direct sequence UWB (DS-UWB) and time hopping UWB (TH-UWB). Unique ways of modulating and positioning the impulses, as in transmitted-reference delay (TRD) modulation and pulse-position modulation (PPM) , can result in the simple UWB radio architectures. Systems of TRD for DS-UWB and PPM for TH-UWB are simulated under the same UWB working data rate and under the same AWGN (additive white Gaussian noise) channel conditions. The simulation shows that DS-TRD system presents superior performance over PPM-TH system, which is shown in the comparison chart of the paper. The simulation was verified with ideal calculated performance for DS-TRD modulation. The UWB applications are also discussed in the paper. The original manuscript of the findings in the paper is published in the conference ref. [2].

Genetic Algorithm Based Equalizer for Ultra-Wideband Wireless Communication Systems

In this paper, we propose a genetic algorithm (GA) based equalization approach for direct sequence ultra-wideband (DS-UWB) wireless communication systems, where the GA is combined with a RAKE receiver to combat the inter-symbol interference (ISI) due to the frequency selective nature of UWB channels for high data rate transmission. The proposed GA based equalizer outperforms significantly the RAKE and the RAKE-minimum mean square error (MMSE) receivers according to results obtained from intensive simulation work. The RAKE-GA receiver also provides bit-error-rate (BER) performance very close to that of the optimal RAKE-maximum likelihood detection (MLD) approach, while offering a much lower computational complexity.

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.

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.

Robust Matched-Filter Acquisition for Direct-Sequence Ultrawideband Systems

In this paper, we propose and analyze a rapid acquisition loop for a direct-sequence ultrawideband (DS-UWB) system called robust matched-filter acquisition, which is mainly aimed at eliminating the cases of false alarm in signal acquisition. Moreover, we present a study on the acquisition performances of the serial search, conventional matched filter, and robust matched filter in UWB dense multipath environments. The mean acquisition time, the acquisition probability, and the mean number of false alarms are evaluated for CM1-CM4 channel models. We find that the robust matched-filter acquisition provides a significant improvement in performances over the conventional matched-filter algorithm for the specific UWB channel model.

Performance of BICM-OFDM systems in UWB interference

In this paper, we develop an analytical framework for performance analysis of generic bit-interleaved coded modulation orthogonal frequency-division multiplexing (BICMOFDM) systems impaired by ultra-wideband (UWB) interference. For practical relevance we consider multi-band OFDM (MB-OFDM), direct-sequence UWB (DS-UWB), and impulseradio UWB (IR-UWB) interference formats following recent IEEE/ECMA standards or standard proposals. Besides the exact analysis we calculate the bit error rate (BER) for the case when the UWB interference is modeled as additional Gaussian noise. Our results show that in general the BER of the BICM-OFDM system strongly depends on the UWB format and the OFDM sub-carrier spacing. While the Gaussian approximation is very accurate for DS-UWB, it may severely overor underestimate the true BER for MB-OFDM and IR-UWB interference. Our analysis is applicable to e.g. IEEE 802.11 wireless local area networks (WLANs), IEEE 802.16 wireless access systems (WiMAX), and 4th generation mobile communication systems. Furthermore, since the ECMA MB-OFDM standard is also based on the BICM-OFDM concept, our analysis can also be used to evaluate the impact of other UWB signals on ECMA MB-OFDM UWB systems.

Comparisons of various pulse shapes for DS-UWB signals over the UWB channel

In this paper, we first investigate the power spectral densities (PSD) of bipolar modulated Direct Sequence Ultra Wide Band (DS-UWB) signals using various pulse shapes under the FCC UWB emission mask. Considered pulse shapes are the first five derivatives of the Gauss pulse (p1, p2, p3, p4 and p5), the first four orthogonal modified Hermite waveforms, and Daubechies wavelets (db-q). It is observed in the PSD results that p4 and p5 Gauss pulses, the Daubechies (db-q) for q>4 comply with the FCC UWB rule by selecting proper values for the pulse duration. Then, we derive the pulse shape dependent probability of error expression for bipolar DS-UWB signals over the standard UWB channel. The five pulse shapes (p4, p5, db-5, db-6 and db-7) complying with the FCC emission mask are numerically compared by using the derived probability of error expression over the CM1 model of the Standard UWB channel. Results reveal that the Daubechies have better performance than those of the two Gauss pulses.

Adaptive blind equalization for ultra wideband system

A new adaptive blind equalization technology was proposed for Direct Sequence-Ultra WideBand(DS-UWB) and Time-Hopping-Ultra WideBand(TH-UWB) wireless communication systems.This method can effectively track the variation of Ultra WideBand(UWB) channels by using the variable forgetting factor to the adaptive algorithm and thus can compensate the interference due to the properties of channels.When receiving the signals,it can adjust the coefficients of equalizers without using the training sequence and then obtain the estimation of the sent signals.Furthermore,this method has relatively rapid convergence rate and good stability.Simulation results show that the proposed method has better performance in tracking UWB fading channels and it also help obtain lower Bit Error Rate(BER).

High-Chip-Count UWB Biphase Coding for Multiuser UWB-Over-Fiber System

In this paper, we propose and demonstrate a novel technique to optically generate high-chip-count, phase-coded direct-sequence (DS) ultrawideband (UWB) signals for multiple-access UWB communications. In the proposed system, a lightwave from a laser source is phase-modulated by a Gaussian pulse train. The phase-modulated lightwave is then sent to a polarization modulator, to modulate the polarization state of the lightwave by a code pattern. The polarization-coded optical signal is then converted into a biphase-coded DS-UWB signal by a polarization-dependent frequency discriminator. The key device in the proposed system is the frequency discriminator, which is implemented using a length of polarization maintaining fiber (PMF) and a polarizer. A 127-chip, biphase-coding DS-UWB that has a data rate of 26.46 Mb/s and a chip rate of 3.36 Gb/s is experimentally generated. A multiuser UWB-over-fiber system is then proposed and a two-user system is demonstrated, in which the encoding is performed experimentally and the decoding is performed by numerically calculating the correlation between the coded UWB signal and the signature sequence. The signal of each user is well recognized. An effective two-user UWB-over-fiber system based on the DS-UWB technology is thus demonstrated.

DS-UWB 시스템에서 송신 필터에 따른 초기 동기 획득 성능 비교

본 논문에서는 DS-UWB 시스템에 사용되는 송신 필터에 따른 초기 동기 획득 성능을 모의 실험을 통해 비교하고, 칩 레이트가 1.32 Gchip/s인 DS-UWB 디지털 송신기에서 interpolation factor가 4인 제곱근 코사인 필터를 적용한 경우와 구형 필터를 적용한 경우 DS-UWB 수신기의 초기 동기 획득 성능은 AWGN 채널 환경뿐만 아니라 CM1/CM3 채널 환경하에서도 비슷한 성능을 냄을 실험을 통해 살펴 본다. 또한, 55 MHz의 시스템 클럭으로 동작하는 24 병렬 처리 상관 연산기 및 동기 획득기 구조에 대해 설명하고 초기 동기 획득 방법을 기술한다. 본 논문에서는 DS-UWB 시스템 설계시 구형 송신 필터를 사용하여 1.32 Gsample/s D/A 변환기 및 A/D 변환기를 적용할 수 있게 함으로써 DS-UWB 칩셋 개발시 현실적으로 고려할 수 있는 솔루션을 제시한다. In this paper, we compare the performance of initial timing acquisition in direct sequence ultra-wideband(DS-UWB) systems with different transmit pulse shaping filters through extensive computer simulations. Simulation results show that the timing acquisition performance of the DS-UWB system, whose chip rate is 1.32 Gchip/s, employing a rectangular transmit filter is similar to that employing a square root raised cosine(SRRC) filter with an interpolation factor of 4 in the realistic UWB channels(CM1 and CM3) as well as the additive white Gaussian noise(AWGN) channel. Additionally, we present both a 24-parallel digital correlator structure and a 24-parallel processing searcher operating at a 55 MHz system clock, and then briefly discuss the initial timing acquisition procedure. Because we can adopt an 1.32 Gsample/s digital-to-analog(D/A) converter and an 1.32 Gsample/s analog-to-digital(AID) converter in the DS-UWB system by employing the rectangular transmit filter, we have a realistic solution for the DS-UWB chipset development.

Pre-equalization for MISO DS-UWB systems with pre-Rake combining

In this paper, we propose two novel pre-equalization schemes for multiple-input single-output (MISO) direct-sequence ultra-wideband (DS-UWB) systems with pre-Rake combining and symbol-by-symbol detection. The first scheme employs one pre-equalization filter (PEF) per transmit antenna, whereas in the second scheme, the simplified PEF (S-PEF) scheme, all transmit antennas share the same PEF. For both schemes the optimum finite impulse response (FIR) and infinite impulse response (IIR) PEFs are calculated based on the minimum mean squared error (MMSE) criterion. Our approach is sufficiently general to include also reduced-complexity versions of pre-Rake combining that employ a limited number of Rake fingers. We show that under certain conditions the S-PEF scheme achieves the same performance as the more complex PEF scheme. We also demonstrate that a single-input multiple-output (SIMO) DS-UWB system with post-Rake combining and MMSE post-equalization is the dual system to the considered MISO DS-UWB system with pre-Rake combining and MMSE pre-equalization. This uplink-downlink duality can be exploited for efficient calculation of the PEFs and for complexity reduction. Our simulation results show that the proposed PEF schemes achieve significant performance gains over pre-Rake combining without equalization, even if only short PEFs are employed.