Performance evaluation of non-prefiltering vs. time reversal prefiltering in distributed and uncoordinated IR-UWB ad-hoc networks

Time Reversal (TR) is a prefiltering scheme mostly analyzed in the context of centralized and synchronous IR-UWB networks, in order to leverage the trade-off between communication performance and device complexity, in particular in presence of multiuser interference. Several strong assumptions have been typically adopted in the analysis of TR, such as the absence of Inter-Symbol / Inter-Frame Interference (ISI/IFI) and multipath dispersion due to complex signal propagation. This work has the main goal of comparing the performance of TR-based systems with traditional non-prefiltered schemes, in the novel context of a distributed and uncoordinated IR-UWB network, under more realistic assumptions including the presence of ISI/IFI and multipath dispersion. Results show that, lack of power control and imperfect channel knowledge affect the performance of both non-prefiltered and TR systems; in these conditions, TR prefiltering still guarantees a performance improvement in sparse/low-loaded and overloaded network scenarios, while the opposite is true for less extreme scenarios, calling for the developement of an adaptive scheme that enables/disables TR prefiltering depending on network conditions

A low-cost time-hopping impulse radio system for high data rate transmission

We present an efficient, low-cost implementation of time-hopping impulse radio that fulfills the spectral mask mandated by the FCC and is suitable for high-data-rate, short-range communications. Key features are: (i) all-baseband implementation that obviates the need for passband components, (ii) symbol-rate (not chip rate) sampling, A/D conversion, and digital signal processing, (iii) fast acquisition due to novel search algorithms, (iv) spectral shaping that can be adapted to accommodate different spectrum regulations and interference environments. Computer simulations show that this system can provide 110Mbit/s at 7-10m distance, as well as higher data rates at shorter distances under FCC emissions limits. Due to the spreading concept of time-hopping impulse radio, the system can sustain multiple simultaneous users, and can suppress narrowband interference effectively.Comment: To appear in EURASIP Journal on Applied Signal Processing (Special Issue on UWB - State of the Art

Implementation Aspects of a Transmitted-Reference UWB Receiver

In this paper, we discuss the design issues of an ultra wide band (UWB) receiver targeting a single-chip CMOS implementation for low data-rate applications like ad hoc wireless sensor networks. A non-coherent transmitted reference (TR) receiver is chosen because of its small complexity compared to other architectures. After a brief recapitulation of the UWB fundamentals and a short discussion on the major differences between coherent and non-coherent receivers, we discuss issues, challenges and possible design solutions. Several simulation results obtained by means of a behavioral model are presented, together with an analysis of the trade-off between performance and complexity in an integrated circuit implementation

A Genetic Algorithm Based Finger Selection Scheme for UWB MMSE Rake Receivers

Due to a large number of multipath components in a typical ultra wideband (UWB) system, selective Rake (SRake) receivers, which combine energy from a subset of multipath components, are commonly employed. In order to optimize system performance, an optimal selection of multipath components to be employed at fingers of an SRake receiver needs to be considered. In this paper, this finger selection problem is investigated for a minimum mean square error (MMSE) UWB SRake receiver. Since the optimal solution is NP hard, a genetic algorithm (GA) based iterative scheme is proposed, which can achieve near-optimal performance after a reasonable number of iterations. Simulation results are presented to compare the performance of the proposed finger selection algorithm with those of the conventional and optimal schemes.Comment: To appear in the Proc. IEEE International Conference on Ultrawideband (ICU-2005

Optimal and Suboptimal Finger Selection Algorithms for MMSE Rake Receivers in Impulse Radio Ultra-Wideband Systems

Convex relaxations of the optimal finger selection algorithm are proposed for a minimum mean square error (MMSE) Rake receiver in an impulse radio ultra-wideband system. First, the optimal finger selection problem is formulated as an integer programming problem with a non-convex objective function. Then, the objective function is approximated by a convex function and the integer programming problem is solved by means of constraint relaxation techniques. The proposed algorithms are suboptimal due to the approximate objective function and the constraint relaxation steps. However, they can be used in conjunction with the conventional finger selection algorithm, which is suboptimal on its own since it ignores the correlation between multipath components, to obtain performances reasonably close to that of the optimal scheme that cannot be implemented in practice due to its complexity. The proposed algorithms leverage convexity of the optimization problem formulations, which is the watershed between `easy' and `difficult' optimization problems.Comment: To appear in IEEE Wireless Communications and Networking Conference (WCNC 2005), New Orleans, LA, March 13-17, 200

Impulse Radio Systems with Multiple Types of Ultra-Wideband Pulses

Spectral properties and performance of multi-pulse impulse radio ultra-wideband systems with pulse-based polarity randomization are analyzed. Instead of a single type of pulse transmitted in each frame, multiple types of pulses are considered, which is shown to reduce the effects of multiple-access interference. First, the spectral properties of a multi-pulse impulse radio system is investigated. It is shown that the power spectral density is the average of spectral contents of different pulse shapes. Then, approximate closed-form expressions for bit error probability of a multi-pulse impulse radio system are derived for RAKE receivers in asynchronous multiuser environments. The theoretical and simulation results indicate that impulse radio systems that are more robust against multiple-access interference than a "classical" impulse radio system can be designed with multiple types of ultra-wideband pulses.Comment: To be presented at the 2005 Conference on Information Sciences and System

On the Effects of Estimation Error and Jitter in Ultra-Wideband Communication

The opening of the 3.6 - 10.1 GHz frequency spectrum below the \u27noise-floor\u27 by the FCC in 2002 has made possible the prospect of reusing this frequency spectrum through ultra-wideband (UWB) communication. In this thesis, we compare the performance of several UWB systems in the presence of estimation error and jitter. We then develop two alternative decision schemes to combat the effect of jitter in the UWB system. Numerical results show that one of the schemes provides significantly better performance in the presence of severe jitter than maximal ratio combining and minimal degradation of performance if jitter is not present. A generalized maximal ratio combining decision scheme to combat the presence of estimation error is also proposed. It is shown that the generalized scheme outperforms traditional maximal ratio combining

Performance Evaluation of 802.15.4 UWB PHY for High Speed Data Rate under IEEE Channel Mode

In modern day society the increase of data generation and transfer has been an issue that researchers are working on. This generated and shared data might have a different purpose but one thing is certain, the reception. This communication can cover continents, countries, cities or even just a few meters. For the purpose of the later, personal area networks (PAN) have been created with a main focus to lower the energy consumption. The protocol that is created under IEEE is 802.15.4 and it has multiple applications in the context of next generation sensor networks. This thesis investigates the performance IEEE 802.15.4 UWB PHY for high data rates over IEEE multipath fading channels and introduces receivers aiming to diversity and to mitigate the intersymbol interference (ISI) that might appear. We simulate the protocols highest mandatory data rate over slow, block faded, realistic IEEE channel models such as, residential, office, outdoor and industrial. The simulation includes Reed Solomon (RS) channel coding, optimal successive erasure decoding (SED), and coherent RAKE receivers. We verify that the selective RAKE (sRAKE) perform better than the nonselective RAKE (n-sRAKE) in all environments and also the increase of fingers is mandatory in order to improve performance. In cases with low number of fingers the ISI mitigation techniques like Maximum-Likehood Sequence Estimator (MLSE) & RAKE combination or Maximum Ration Combining (MRC) ISI cancellation receivers, can provide some gain in large delay spread environments. In cases with high number of ingers the MRC received employs its full diversity since the received power is arger than before. Overall the apply of optimal errors and erasures decoding can urther improve the system performance by adding a small gain, lowering existing it Error Probability (BEP) even more.A huge percentage of data has been generated in the last two years and it will grow more, as every one of us is constantly producing and releasing data. The latest years has been an extensive research on capacity maximization, bit rate increment and power optimization. That research lead to the development of various protocols for cellular and personal area networks (PAN), where they each utilizes the frequency spectrum differently. Even if cellular networks have the ability to cover large area, development of multiple personal area networks can be developed for the purpose to offload data from the cellular network. Keeping in mind the research needs, 802.15.4 UWH PHY is a solid candidate when it comes to data transfer in a small area. This protocol offers various mandatory transmission modes that can be selected depending the channel parameters and various data rate needs. Time hopping and spreading sequence offers the existence of multiuser environment where multiple transceivers can co-exist. Overall the complexity, cost and energy consumption for transmission and reception can be kept low, matching the research needs. The main issues regarding 802.15.4 UWH PHY and high speed data rates is first, the energy dispersion of the transmitted symbol to multiple bins and second, the appearance of Inter Symbol Interference (ISI) in high delay profile environments. The solution in the former problem is the necessary implementation of a RAKE receiver. Regarding the latter, literature offers multiple ways to mitigate the ISI but the aim should be to keep the lowest complexity possible regarding the implementation. In this thesis we evaluate the performance of 802.15.4 UWB PHY for high speed data rates under IEEE channel models. Various receivers has been build for the purpose of this thesis, Maximum Ratio Combining (MRC), MRC with Inter Symbol Interference and MLSE & RAKE combination receiver. The MRC is a simple RAKE receiver with maximum diversity, MRC with ISI cancellation is based on the MRC receiver with the ability to mitigate ISI, and MLSE & RAKE combination is an optimum ISI mitigation receiver without the diversity of the MRC

Time Domain Equalizer Design Using Bit Error Rate Minimization for UWB Systems

Ultra-wideband (UWB) communication systems occupy huge bandwidths with very low power spectral densities. This feature makes the UWB channels highly rich in resolvable multipaths. To exploit the temporal diversity, the receiver is commonly implemented through a Rake. The aim to capture enough signal energy to maintain an acceptable output signal-to-noise ratio (SNR) dictates a very complicated Rake structure with a large number of fingers. Channel shortening or time domain equalizer (TEQ) can simplify the Rake receiver design by reducing the number of significant taps in the effective channel. In this paper, we first derive the bit error rate (BER) of a multiuser and multipath UWB system in the presence of a TEQ at the receiver front end. This BER is then written in a form suitable for traditional optimization. We then present a TEQ design which minimizes the BER of the system to perform efficient channel shortening. The performance of the proposed algorithm is compared with some generic TEQ designs and other Rake structures in UWB channels. It is shown that the proposed algorithm maintains a lower BER along with efficiently shortening the channel

Comparison between Coherent and Noncoherent Receivers for UWB Communications

We present a comparison between coherent and noncoherent UWB receivers, under a realistic propagation environment, that takes into account also the effect of path-dependent pulse distortion. As far as coherent receivers are concerned, both maximal ratio combining (MRC) and equal gain combining (EGC) techniques are analyzed, considering a limited number of estimated paths. Furthermore, two classical noncoherent schemes, a differential detector, and a transmitted-reference receiver, together with two iterative solutions, recently proposed in the literature, are considered. Finally, we extend the multisymbol approach to the UWB case and we propose a decision-feedback receiver that reduces the complexity of the previous strategy, thus still maintaining good performance. While traditional noncoherent receivers exhibit performance loss, if compared to coherent detectors, the iterative and the decision-feedback ones are able to guarantee error probability close to the one obtained employing an ideal RAKE, without requiring channel estimation, in the presence of static indoor channel and limited multiuser interference