Ultra-wideband (UWB) radio is a fast emerging technology with many unique attractive features that promotes major advances in wireless communications, networking, radar, imaging, and positioning systems. Research in UWB is still in its infancy stages, offering limited resources in handling the challenges facing the UWB communications. Understanding the unique properties and challenges of UWB communications as well as its application in competent signal processing techniques are vital in conquering the obstacles towards developing exciting UWB applications. UWB research and development has to cope with the challenges that limit their performance, capacity, throughput, network flexibility, implementation complexity, and cost. This tutorial focuses on UWB wireless communications at the physical layer. It overviews the state-of-the-art UWB in channel modeling, transmitters, and receivers of UWB radios, and outlines the research directions and challenges that needs to be overcome. Since a signal processing expertise is expected to have major impact in research and development of UWB systems, emphasis is placed on the DSP aspects.

Ultra-wideband communications: an idea whose time has come

This paper reports a 128-channel neural recording integrated circuit (IC) with on-the-fly spike feature extraction and wireless telemetry. The chip consists of eight 16-channel front-end recording blocks, spike detection and feature extraction digital signal processor (DSP), ultra wideband (UWB) transmitter, and on-chip bias generators. Each recording channel has amplifiers with programmable gain and bandwidth to accommodate different types of biological signals. An analog-to-digital converter (ADC) shared by 16 amplifiers through time-multiplexing results in a balanced trade-off between the power consumption and chip area. A nonlinear energy operator (NEO) based spike detector is implemented for identifying spikes, which are further processed by a digital frequency-shaping filter. The computationally efficient spike detection and feature extraction algorithms attribute to an auspicious DSP implementation on-chip. UWB telemetry is designed to wirelessly transfer raw data from 128 recording channels at a data rate of 90 Mbit/s. The chip is realized in 0.35 mum complementary metal-oxide-semiconductor (CMOS) process with an area of 8.8 times 7.2 mm2 and consumes 6 mW by employing a sequential turn-on architecture that selectively powers off idle analog circuit blocks. The chip has been tested for electrical specifications and verified in an ex vivo biological environment.

A 128-Channel 6 mW Wireless Neural Recording IC With Spike Feature Extraction and UWB Transmitter

Summary form only given. Ultra-wideband (UWB) refers to bandwidths in excess of 2 GHz, whose utilization by radar systems dates back to the late '60s. The renewed and rapidly growing interest for UWB was sparked by the spectral mask released by FCC in February 2002, and is well motivated by the attractive features UWB brings to commercial communications: low-power carrier-free transmissions, ample multipath diversity, enhanced penetration capability, low-complexity transceivers, ability to overlay existing systems, and a potential for increase in capacity. This article outlines features and challenges unique to UWB, with emphasis on timely signal processing issues that focus on synchronization, channel estimation, multiple access, and suppression of interference UWB systems cause to (and suffer from) co-existing narrowband systems. Application areas include shortrange indoor wireless links at home, and in the workplace for low-cost multimedia communications and storage, as well as secure connectivity for ranging, and covert communications.

The high time resolution of ultra-wide-band (UWB) signals facilitates very precise position estimation in many scenarios, which makes a variety applications possible. This paper reviews the problem of position estimation in UWB systems, beginning with an overview of the basic structure of UWB signals and their positioning applications. This overview is followed by a discussion of various position estimation techniques, with an emphasis on time-based approaches, which are particularly suitable for UWB positioning systems. Practical issues arising in UWB signal design and hardware implementation are also discussed.

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Position Estimation via Ultra-Wide-Band Signals

The high time resolution of ultra-wideband (UWB) signals facilitates very precise position estimation in many scenarios, which makes a variety applications possible. This paper reviews the problem of position estimation in UWB systems, beginning with an overview of the basic structure of UWB signals and their positioning applications. This overview is followed by a discussion of various position estimation techniques, with an emphasis on time-based approaches, which are particularly suitable for UWB positioning systems. Practical issues arising in UWB signal design and hardware implementation are also discussed.

Position Estimation via Ultra-Wideband Signals

Ultra-wideband communications systems offer unique challenges and opportunities for RF circuit design. Proper understanding of the trade-offs that system specifications impose upon the circuit designer is essential in optimizing a system for UWB. The defining attribute of UWB is the wide fractional bandwidth of the signal. This wide bandwidth can be achieved in several ways: with carrierless systems, with a wide-bandwidth single carrier spread-spectrum system, with a multi-carrier system such as OFDM, via frequency hopping, or via some combination of these methods. This paper provides detailed impact analysis of wide fractional bandwidth on RF frontend circuits and examines the various tradeoffs. In particular, wide-bandwidth channels limit the instantaneous Q allowable in the signal path. This requires modifications of the traditional narrowband design methods. Some of the issues discussed in this paper include: issues of broadbanding, power impact, fast hopping tradeoffs, power amplifier, and antenna issues.

Analog/RF physical layer issues for UWB systems

This paper presents a low power impulse generator design for ultra-wideband (UWB) impulse radio (IR) applications. Simple digital delay elements and a NAND gate are used to generate short duration pulses. A varactor controls the pulse width of the generated signal. The low-end of the spectrum of the generated pulse is attenuated using an integrated high-pass filter while the high-end of the spectrum is extended using a peaking inductor. This makes efficient use of the FCC spectral mask. The designed pulse generator in 0.18 /spl mu/m TSMC CMOS technology consumes 0.4 mW at 100 MHz pulse repetition rate, and the spectral efficiency is more than 55%. The proposed IR generator topology gives a spectral efficiency improvement of more than 14% relative to the topology without the peaking inductor.

Pulse generator design for UWB IR communication systems

This paper presents a DC-coupled 900-MHz ISM band RF front-end for a short-range wireless receiver. The front-end, fabricated in a 0.5-/spl mu/m CMOS process, is intended as a test vehicle to verify the proposed DC-coupled topology. In this topology, a low-frequency feedback circuit suppresses the DC offset and low-frequency noise at the mixer output. The DC-coupled topology is compared with traditional AC coupling. We show that there is a tradeoff between bandwidth and midband loss in a fully integrated AC-coupled system. The proposed DC-coupling technique does not impose this tradeoff. The DC-coupled topology was verified via simulation and measurements from the test vehicle.

DC-coupled IF stage design for a 900-MHz ISM receiver

The analysis of a quadrature mixer based on the CMOS double-balanced mixer is presented. The noise, image rejection, conversion gain, and linearity of the quadrature mixer are compared to that of a Gilbert mixer under square wave and sinusoidal LO drive. It is shown that the quadrature mixer exhibits a 3 dB improvement in noise and conversion gain, and improved image rejection, compared to a pair of Gilbert mixers when the LO signal is a large amplitude sine wave.

Analysis and design of an integrated quadrature mixer with improved noise, gain, and image rejection

The analysis of a quadrature mixer based on the CMOS double-balanced mixer is presented The noise, image rejection, conversion gain, and linearity of the quadrature mixer are compared to that of a Gilbert mixer under square wave and sinusoidal LO drive It is shown that the quadrature mixer exhibits a 3 dB improvement in noise and conversion gain, and improved image rejection, compared to a pair of Gilbert mixers when the LO signal is a large amplitude sine wave

J. Harvey

Papers

Analog/RF physical layer issues for UWB systems

Pulse generator design for UWB IR communication systems

DC-coupled IF stage design for a 900-MHz ISM receiver

Analysis and design of an integrated quadrature mixer with improved noise, gain, and image rejection

Analysis and design of an integrated quadrature mixer with improved noise, gain and image rejection