Vit Sipal

Twenty years of ultrawideband: Opportunities and challenges

It has been 20 years since the word ultrawideband (UWB) has first been used in the open literature. In these 20 years, ideas have been transformed into real products. Yet, some might object that UWB has not yet lived upto the promises of gigabit wireless. This review shows that despite some drawbacks, UWB is not only needed because of the spectrum gridlock but it can still deliver its promises, including gigabit wireless. To do so, the gap between the potential, which is achievable, and the current performance must be closed. Thus, this review identifies some main issues of UWB (range, bit error rate performance, data rate, chip complexity and issues associated by strong narrowband interference). It shows that their reasons are well understood and addressed by erudite research, which includes low complexity chip design, alternative modulation schemes, multiple antenna systems, UWB radio-over-fibre, higher band UWB and interferer detection and suppression techniques. A specific feature of this review is the cross-layer approach. The latest findings from different system layers, for example, wave propagation, are linked to the system performance or complexity.

Effects of antenna impulse response on wideband wireless channel

This paper presents wideband measurements in a laboratory environment. These measurements provide further evidence in support of the previously published hypothesis that the clusters within the Saleh-Valenzuela propagation model are manifestations of antenna impulse responses. The issue caused by frequency variations of the antenna radiation pattern of wideband antennas and by the selection of antenna type are discussed. It is shown that due to limited movement in target applications of extremely wideband systems, the variation of antenna impulse responses due to the change of mutual antenna position does not significantly change. Thus, the deterministic nature of the antenna impulse responses can be exploited in the design of more efficient receivers.

Adaptive OFDM for Wireless Interconnect in Confined Enclosures

This letter considers and recommends OFDM with adaptive subcarrier modulation as a suitable candidate for wireless UWB communication in computer chassis. A rigorous measurement campaign studies the guaranteed spectral efficiency. It concludes that enhancement of the existing WiMedia OFDM systems with a bandwidth of 528 MHz in order to support adaptive OFDM would enable data-rates above 1 Gbps over short ranges, i.e. the spectral efficiency would be doubled. Moreover, the guaranteed spectral efficiency is shown to increase with bandwidth, i.e. the guaranteed data-rate increases better than linearly with bandwidth.

Multi-tone frequency shift keying for ultrawideband wireless communications

This paper is a preprint of a paper submitted to and accepted for publication in IET Communications and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at IET Digital Library (http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=06261621)

Bandwidth requirement for suppression of grating lobes in ultrawideband antenna arrays

Sparse ultrawideband antenna arrays suppress the grating lobes due to the fact that the duration of pulses processed by individual antenna elements is too short to constructively superpose them in the time domain. Such arrays represent an attractive option for design of many low-comlexity low-cost ultrawideband systems, where narrow beamwidth is achieved by increase of element spacing. This paper empirically explores the minimum bandwidth required for suppression of the grating lobes. It is found that the relative bandwidth required to suppress grating lobes is independent on the centre frequency, element spacing, and number of elements. There is a weak dependency of the bandwidth on the type of the pulse used, but the general conclusion is that the relative bandwidth has to exceed 100% in order to suppress the grating lobes. It is, however, noted that whilst sparse array with a low number of antenna elements can suppress the grating lobes and posses a narrow beam, the compromise for this feature is a reduction of the level of spatial filtering between the main lobe and other directions, when compared to arrays where grating lobes are suppressed by dense spacing.

Exploration and analysis of fade depth scaling

This paper presents a study of fade depth scaling properties of extremely wideband wireless links. The behaviour effects robustness of communication system and needs to be considered in system design as it influences the required link budget fade margin. This paper introduces a new simplified model of fade depth scaling as a function of bandwidth. It is based on higher number of measurements compared to preceding works. As a result, thorough exploration of fade depth dependency on frequency and distance has been conducted. The results provide more insight into the issue of fade depth scaling, which can be used in the design of wideband wireless communication systems.

Impact of confined environments on WiMedia UWB systems

This paper explores the performance of a commercial WiMedia Multi-Band OFDM Ultrawideband development kit in a confined environment. It confirms previous predictions that the forward error correction schemes of WiMedia systems might not be sufficient for confined environments with a high number of multipaths. A carefully designed environment is shown to be able to alleviate the issue and improve the performance by reducing the packet-error rates. Analysis of packet-error-rates obtained for various antenna orientations and polarisations enables us to propose design rules to assist deployment of WiMedia Multi-Band OFDM Ultrawideband wireless systems in confined environments.

Effect of Substrate Dimensions on Zeroth-Order Resonator Antennas

This letter focuses on the design of electrically small transmission line zeroth-order resonator antennas (ZORAs). These antennas represent a known concept. However, previous works seem to neglect the size of the substrate. A small antenna that requires a large ground plane loses its competitive advantage. Thus, this letter studies the relation between substrate dimensions and the antenna properties on the example of a ZORA using e-negative transmission line (ENG TL). It was found out that antenna radiation properties deteriorate as the substrate is reduced. Thus, a simple measure based on use of metallic walls to overcome this issue is also introduced in this letter.

On the range of Wimedia OFDM UWB wireless

We show a significant discrepancy between the range estimates and the actual performance of an ultrawideband wireless system based on the Wimedia standard. We also show this discrepancy to be linked to the combination of frequency selectivity of the ultrawideband channel and the low dynamic range available to ultrawideband receiver. We propose an alternative means of range estimation combining the statistics of frequency selective fading and the path-loss and we show that this algorithm provides significantly more accurate estimation.

Optimisation of low power Radio-over-fibre links for UWB systems

This paper focuses on the design of Radio-over-fibre (ROF) links for ultrawideband (UWB) applications. Due to strict regulations, network architecture and technical feasibility, UWB ROF links must have 0 dB gain, low noise figure and low DC power dissipation. Due to the low power of UWB signals, pre-amplification is possible. Design rules for UWB ROF links with a pre-amplifier are presented. If followed, these rules enable design of links with a lower noise figure and power dissipation than previous design rules yield for general purpose ROF links. This is illustrated by a ROF link for UWB channel sounding that requires only 27.3% of DC power compared to a commercial link with similar gain and noise figure.