Impulse Radio Ultra-wideband Systems Research Articles

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A joint timing synchronization, channel estimation, and SFD detection for IR-UWB systems

This paper proposes a joint timing synchronization, channel estimation, and data detection for the impulse radio ultrawideband systems. The proposed timing synchronizer consists of coarse and fine timing estimation. The synchronizer discovers synchronization points in two stages and performs adaptive threshold based on the maximum pulse averaging and maximum (MAX-PA) method for more precise synchronization. Then, iterative channel estimation is performed based on the discovered synchronization points, and data are detected using the selective rake (S-RAKE) detector employing maximal ratio combining. The proposed synchronizer produces two signals-the start signal for channel estimation and the start signal for start frame delimiter (SFD) detection that detects the packet synchronization signal. With the proposed synchronization, channel estimation, and SFD detection, an S-RAKE receiver with binary pulse position modulation binary phase-shift keying modulation was constructed. In addition, an IEEE 802.15.4a channel model was used for performance comparison. The comparison results show that the constructed receiver yields high performance close to perfect synchronization.

高速脉冲超宽带系统和芯片设计

Impulse radio (IR) ultra-wideband (UWB) wireless communication system has the advantages of low power consumption and low complexity. However, its transmission rate is usually limited. This paper proposes a high-speed IR-UWB system scheme. By using high sampling rate, low resolution quantization, and digital processing, the proposed scheme achieves more than 100 Mbps wireless transmission rate with reasonable power consumption and complexity. The system scheme, core algorithms, key implementations in the chip design, and simulation results are given in the paper. As a core algorithm, a joint synchronization and channel estimation (JSCE) algorithm is proposed. The JSCE algorithm conducts synchronization and channel estimation at the same time. It has the advantage of low complexity and is feasible to real-time implementation. The implementation issues in the chip design, including the digital baseband chip structure, the state transform of the receiver, and the implementation of the JSCE algorithm are introduced. Based on the proposed system scheme, a digital baseband chip is designed and fabricated. The core power consumption of the chip is less than 100 mW. An experimental system is also implemented which uses the baseband chip as a core processor. The system is capable of real-time high de nition video transmission. Experimental results on the experimental system validate the proposed system scheme.

Routing of Power Efficient IR-UWB Wireless and Wired Services for In-Building Network Applications

We present a wireless link budget analysis for impulse-radio ultrawideband (IR-UWB) systems with different pulse-shaping techniques using a realistic path loss model. Simulation results confirm that a proper pulse design technique is crucial for satisfying Federal Communications Commission mask requirements and performance enhancement of IR-UWB systems. We present a novel pulse design technique, based on a linear combination of modified doublets pulses and compare it with conventional pulses such as monocycle, doublet and fifth-order derivative of Gaussian pulses. The proposed pulse outperforms the conventional pulses in terms of spectral power efficiency and achievable reach using an M-ary pulse-amplitude modulation format and a fixed data rate. Furthermore, we propose and experimentally demonstrate routing over a hybrid wired-wireless network of IR-UWB services using the proposed pulse shape. The routing functionality is realized using a single semiconductor optical amplifier based on the cross-gain modulation technique. Error-free transmission of both 1.25 Gb/s baseband wired services and 2 Gb/s wireless IR-UWB services has been achieved over 1 km fiber link. The proposed technique can efficiently distribute and multicast both wireless IR-UWB and wired services in future in-building networks.

IFI and ISI Premitigation for Block-Code-Modulated Noncoherent UWB Impulse Radio: A Code Optimization Approach

Codeword matching and signal aggregation (CMSA) is a recently proposed low-complexity noncoherent receiver for block-code-modulated ultrawideband impulse radio (UWB-IR) systems. As the frame/symbol duration is shortened to boost data rate, interframe interference (IFI) or intersymbol interference (ISI) occurs and degrades the detection performance of CMSA. In this paper, an effective IFI/ISI premitigation scheme is proposed for CMSA through a code optimization approach. By employing a tailored interference model that highlights the codeword properties, the system performance in the presence of moderate IFI/ISI is evaluated, and the average collected channel gain is introduced as the metric for code optimization. With the primary focus on binary modulation, the following two IFI/ISI-robust code properties are generalized: 1) shifted orthogonality and 2) shifted repetition. Based on these properties, the optimal code is constructed. It is observed that, when the optimal code occurs, the leaked signal energy or the interference can partially be used to enhance the detection performance of CMSA in the presence of IFI/ISI. Unlike most of the existing IFI/ISI mitigation schemes for noncoherent UWB-IR, which mainly focus on signal processing after the nonlinear detector, the optimized code is exploited to aggregate the leaked signal energy, along with the linear predetection operation already involved in the CMSA receiver. Both analysis and simulation show that a distinct performance improvement is achieved.

Joint IR-UWB Power Spectral Lines and Interference Suppression Based on Coded Auxiliary Independent Signaling in Presence of Pulse Attenuation and Timing Jitter

This paper deals with spectral shaping problem in impulse radio ultra-wideband systems based on coded auxiliary independent signaling (AIS), as a modified version of transmitted-reference approach. In this manuscript, the main contribution includes a unified theoretical framework for spectral analysis which is, not only able to address all effective parameters in the emergence of spectral lines and coexistence issues, but also provides a convex optimization based method. This can produce AIS-aided signals using random process characteristics as optimization variables. In particular, the specific novelty insights of this paper are as follows: (i) to propose a new signal model, where each transmitted symbol is represented by a preamble AIS pulse followed by a set of transmitted data pulses that are synthesized in accordance with a codeword design and within this context, the preamble signal is designed to eliminate spectral lines via an adaptive monitoring of data-stream statistics as the optimal policy; (ii) to exploit the proposed spectral optimization strategies to maximize spectral flexibility.

On the performance of a rapid synchronization algorithm for IR‐UWB receivers

ABSTRACTBecause of the very low signal duty cycles, synchronization is the most critical issue in ultra wideband (UWB) impulse radio (IR) systems. Some effective synchronization schemes like a symbol‐differential (SD) IR‐UWB receiver have been proposed to synchronize received signals rapidly. Yet, SD IR‐UWB receiver is unsuitable for operation in multi‐user environment because of multiple access interference (MAI). By taking advantage of frame‐differential IR‐UWB receivers, we propose a parallel frame‐differential (PFD) IR‐UWB receiver to do so. Our proposed PFD IR‐UWB receiver manifests better immunity against message passing interface and MAI than the SD IR‐UWB. Based on this PFD IR‐UWB receiver, uncertain (search) regions are limited to one frame duration without any symbol‐level synchronization process. Performance of PFD and SD receivers are compared by computer simulations, showing that the proposed PFD receiver not only achieves significant bit error rate performance but also better and more robust results than the SD receiver in this literature. Copyright © 2012 John Wiley & Sons, Ltd.

IR-UWB 시스템 응용을 위한 시간- 및 주파수-영역에서의 앤티포달 비발디 안테나 성능 평가

본 논문에서는 IR-UWB(Impulse Radio Ultra Wideband) 시스템 응용을 위한 앤티포달 비발디 안테나를 설계하고, 시간 및 주파수 영역에서 나노 초 단위의 초광대역 임펄스 신호 전송을 위한 IR-UWB 안테나 성능 평가를 수행하였다. 설계된 앤티포달 비발디 안테나는 저가 생산이 가능한 두께 1.6 mm, 유전율 <TEX>${\epsilon}_r=4.7$</TEX>, <TEX>$tan{\delta}=0.002$</TEX>인 FR-4 기판을 이용하여 제작하였다. 제작된 안테나는 무반사실에서 주파수 영역 파라메타인 반사 손실, Far 필드방사 패턴을 측정하였다. 또한, 시간 영역에서 나노 초 단위의 임펄스 신호 전송에 따른 펄스 충실도 분석을 수행하여 UWB 대역에서 안정적으로 초광대역 신호 전송이 가능함을 증명하였다. 본 논문에서 설계/제작된 앤티포달 비발디 안테나는 낮은 왜곡과 양호한 방사 특성을 갖고, 나노 초 단위의 초광대역 임펄스를 방사 또는 수신할 수 있다. In this paper, we designed the antipodal vivaldi antenna for IR-UWB systems application and evaluated IR-UWB antenna performance for the ultra wideband impulse signal transmission in the time- and frequency-domain. The designed antipodal vivaldi antenna was fabricated using FR-4 substrate which thickness 1.6 mm, dielectric constant <TEX>${\epsilon}_r=4.7$</TEX> and <TEX>$tan{\delta}=0.002$</TEX>. We measured the return loss, far filed radiation pattern at the anechoic chamber in the frequency-domain. We also performed the pulse fidelity analysis in the time-domain using nano-second impulse signal transmission and demonstrated the feasibility of ultra wideband signal stable transmission in the UWB band. The designed and fabricated antipodal vivaldi antenna could be emitting and receiving the IR-UWB signal while preserving low pulse distortion and good radiation pattern in time- and frequency-domain.

A novel low complexity data demodulation algorithm for pulse position modulation

In this paper, a low complexity data demodulation algorithm is proposed that requires time of arrival information of the received signal exclusively. As an application example, the algorithm is applied to an ultra-wideband impulse radio communication system with pulse position modulation. The algorithm is insensitive to a common time delay for all pulses, that means, it does not require an accurate synchronization between the transmitter and the receiver. For the performance estimation, only a symbol synchronization is assumed, i.e., that there is a priori knowledge which pulse marks the beginning of a received data symbol. The performance of the proposed algorithm is evaluated for straightforward time of arrivals estimators, such as a maximum detector or a threshold detector. It is shown that the proposed algorithm outperforms a least squares algorithm in all considered scenarios. In particular, an increased robustness against additive white Gaussian noise, impulse like noise, and multiuser interference is demonstrated as well as an improved performance for multipath propagation channels.

Simplified structure of weighted energy detector for UWB-IR systems

Proposed is a simplified weighted energy detector (WED) receiver structure for ultra-wideband impulse radio (UWB-IR) systems. The performance improvement of the WED comes with the cost of increased hardware complexity when performing linear combination over the fractional energies. In this proposed scheme, multiplication for the combination process is replaced with a register-shifting operation based on simplified weighting coefficients. Simulations show that the proposed WED structure achieves the same BER performance as a multiplier-using WED structure with much lower hardware complexity.

GLRT-Based Combining Schemes for PPM IR-UWB Systems with Multiple Receive Antennas

This paper deals with impulse-radio ultra wide-band systems with multiple receive antennas. For binary PPM modulations, we propose various combining/detection schemes derived by the generalized likelihood ratio criterion. These schemes first combine delayed versions of the waveforms received at the different antennas and then compute the energies of the resulting signal over intervals smaller than half the symbol period. The decision statistic is finally obtained by a linear combination of these energies. The proposed algorithms can be implemented using currently available technology. They outperform a detection scheme that simply combines the decision statistics obtained (at each antenna) by means of a conventional energy-based detector. Their advantage increases with the number of antennas.

Group waveform-coded biorthogonal pulse position modulation with level cutting for ultra-wideband impulse radio communications

A new modulation scheme termed as group waveform-coded biorthogonal pulse position modulation (GWC-BPPM) is proposed for an ultrawideband (UWB) impulse radio communication system. The group waveform-coded signal, generated using several orthogonal waveform codes to transmit data simultaneously, is converted to pulse position and polarity to improve data rate and obtain processing gain in reception. In addition, the authors also suggest greatly boosting the data rate of the proposed scheme by introducing the level cutting concept. By restricting the maximum level of the group waveform-coded signal, the authors can boost the data rate without any degradation in error performance. To guarantee the benefit and the validity of the proposed scheme, the authors focus on the achievable data rate as a performance measure and analyse it theoretically. Simulations show that the achievable data rate of the proposed systems can be increased by GWC-BPPM and can be boosted via level cutting compared with other schemes such as M-ary BPPM and MBOK.

Investigation of blind detection mechanism for chaotic UWB system based on generalized negentrogy

A non-coherent blind detection method based on the generalized negative entropy mechanism for chaotic ultra-wideband system is proposed in this paper. In the case without knowing the transmission channel information, the chaotic impulse signals can be detected. The proposed method can overcome the practical application problem existing in the direct chaotic communication (DCC) scheme for impulse radio ultra-wideband (IR-UWB) communication system. Also, this method can overcome the complicated and unknown multipath channel effect. Analysis of simulation results show that the proposed approach has a good separating and detection performance in the case without the channel information. A new way for the noncoherent blind detection of chaotic UWB system under non-ideal unknown channel is established.

Comparison of Kurtosis and Fourth Power Detectors with Applications to IR-UWB OOK Systems

On-off keying (OOK) is one of the modulation schemes for non-coherent impulse radio Ultra-wideband systems. In this paper, the utilization of the kurtosis detector (KD) and fourth power detector (FD) receivers for OOK signaling is introduced. We investigate the effect of integration interval and the optimum threshold on the performance of energy detector (ED), KD and FD receivers. The semi analytic expression of BER is obtained by using generalized extreme value distribution function for KD and FD receivers. From performance point of view, the simulation results show that FD receiver outperforms KD and ED receivers. In contrast, the sensitivity to the optimum threshold is greatly reduced in KD receiver compared to ED and FD receivers.

Non-Coherent Fourth-Order Detector for Impulse Radio Ultra Wideband Systems: Empirical Evaluation Using Channel Measurements

Low-complex and low-power non-coherent energy detectors (EDs) are interesting for low data rate impulse radio (IR) ultra wideband (UWB) systems, but suffer from a loss in performance compared to coherent receivers. The performance of an ED also strongly depends on the integration interval (window size) of the integrator and the window position. This paper presents a non-coherent fourth-order detector (FD) which can discriminate between Gaussian noise signals and non-Gaussian IR-UWB signals by directly estimating the fourth-order moment of the received signal. The performance of the detectors is evaluated using realistic channels measured in a corridor, an office and a laboratory environment. The results show that bit-error-rate (BER) performance of the proposed FD receiver is slightly better than the ED in low signal-to-noise ratio (SNR) region and its performance improves as the SNR increases. In addition, BER of the FD receiver is less sensitive to overestimation of the integration interval making it relatively robust to variations of the channel delay spread. Finally, a criteria for the selection of integration time of the proposed detector is suggested.

Training-Based Synchronization and Demodulation With Low Complexity for UWB Signals

In this paper, we propose a low-complexity data-aided (DA) synchronization and efficient demodulation technique for an ultrawideband (UWB) impulse radio system. Depending on the autocorrelation property of a judiciously chosen training sequence, a redundance-included demodulation template (RDT) can be extracted from the received signal by separating, shifting, and realigning two connected portions in the observation window. After constructing the RDT, two receiver designs are available. One approach is to demodulate transmitted symbols by correlating the RDT in a straightforward manner, which does not require the explicit timing acquisition and, thus, considerably reduces the complexity of the receiver. An alternative approach is accomplished with the assistance of a non-RDT (NRDT). The NRDT-based receiver is able to remove the redundant noisy component of the RDT by acquiring timing offset via a simple synchronization scheme, therefore achieving a better bit error rate (BER) performance. Both the schemes can counteract the effects of interframe interference (IFI) and unknown multipath channels. Furthermore, analytical performance evaluations of the RDT- and NRDT-based receivers are provided. Simulations verify the realistic performance of the proposed receivers in the presence of multiuser interference (MUI) and timing errors.

Novel signaling and detection schemes for ultra-wideband transmitted-reference systems

Ultra-Wideband (UWB) impulse radio systems apply sub-nanosecond pulses and are able to resolve multipath due to their fine time-resolution capability. To take full advantage of the available signal energy, a Rake receiver with high hardware complexity is required. To remedy this difficulty, an improved scheme called the transmitted reference (TR) systems is proposed. TR systems do not require the complex task of channel estimation and render a simple receiver structure. However, the low-complexity detection in the conventional TR scheme is achieved at the cost of 50% energy/bandwidth disadvantage. This disadvantage has become the popular research focus of UWB TR systems. In this paper a performance-enhanced signal and detection scheme, namely the dual averaging N-bit differential transmitted reference/balanced transmitted reference (A2NDTR/BTR) system, is proposed to increase the data rate while still maintain the overall system performance. Numerical results suggest that this proposed scheme is able to achieve superior data rate while maintain the same or better bit error performance as compared with others.

Co-design of ESD protection and UWB RF front-end ICs

This paper discusses critical aspects for co-design of ultra wideband (UWB) system-on-chip (SoC) and on-chip electrostatic discharge (ESD) protection, which are beyond the considerations on data rate and bandwidth. Impulse radio UWB system architecture has been defined with critical building blocks proposed and verified, including pulse generator, transmitter, low noise amplifier (LNA) and multiplier based correlator. ESD protection is well considered for each related block. Design examples have been implemented in a commercial RFCMOS processes to demonstrate the working principles for key UWB transmitter and receiver circuit blocks. UWB-ESD co-design techniques, simulation and measurement results for these UWB RF modules are presented in detail.

Direct Sequence and Time-Hopping Sequence Designs for Narrowband Interference Mitigation in Impulse Radio UWB Systems

Direct sequence and time-hopping sequence designs are proposed for impulse radio ultra-wide bandwidth systems to suppress the mutual interference between ultra-wide bandwidth wireless and coexisting narrowband services. Notch frequencies are created in the ultra-wide bandwidth signal spectrum at bands where narrowband services operate. The direct sequence and the time-hopping sequence designs have low computational complexities and can be easily implemented in practical systems. When combined with the cognitive radio technique, these designs can adapt to channel conditions according to the spectral occupancy information provided by cognitive radio. Numerical results are provided to show that these designs can significantly suppress the mutual interference between ultra-wide bandwidth and narrowband services. Therefore, the integrity of both ultra-wide bandwidth and narrowband systems can be highly enhanced.

Reduce-complexity fuzzy-inference-based iterative multiuser detection for wireless communication systems

In recent years, combining multiuser detection and intelligence computer scheme have received considerable attention. In this paper, adaptive fuzzy-inference multistage matrix wiener filtering (FI-MMWF) techniques, based on the minimum mean-square error criterion, are proposed for ultra-wideband (UWB) impulse radio communication systems. These FI-MMWF-based algorithms employ a time-varying fuzzy-inference-controlled filter stage. Consequently, the proposed approaches accomplish a substantial saving in complexity without trading off the system performance and dynamic-tracking characteristic. In addition, the fuzzy-logic-controlled matrix conjugate gradient algorithm is adopted to reduce the system complexity without trading off the bit-error-rate (BER). Simulations are conducted to evaluate the convergence and tracking behavior of the proposed MMWF algorithm, and the BER of the time-hopping-UWB system in a realistic UWB channel is investigated. Copyright © 2011 John Wiley & Sons, Ltd.