Walter Hirt

Ultra-wideband radio technology: potential and challenges ahead

An unprecedented transformation in the design, deployment, and application of short-range wireless devices and services is in progress today. This trend is in line with the imminent transition from third- to fourth-generation radio systems, where heterogeneous environments are expected to prevail eventually. A key driver in this transition is the steep growth in both demand and deployment of WLANs/WPANs based on the wireless standards within the IEEE 802 suite. Today, these short-range devices and networks operate mainly standalone in indoor home and office environments or large enclosed public areas, while their integration into the wireless wide-area infrastructure is still nearly nonexistent and far from trivial. This status quo in the short-range wireless application space is about to be disrupted by novel devices and systems based on the emerging UWB radio technology with the potential to provide solutions for many of todays problems in the areas of spectrum management and radio system engineering. The approach employed by UWB radio devices is based on sharing already occupied spectrum resources by means of the overlay principle, rather than looking for still available but possibly unsuitable new bands. This novel radio technology has received legal adoption by the regulatory authorities in the United States, and efforts to achieve this status in Europe and Asia are underway. This article discusses both the application potential and technical challenges presented by UWB radio as an unconventional but promising new wireless technology.

A PRML system for digital magnetic recording

The realization of a digital recording system using partial-response class-IV signaling with maximum-likelihood sequence detection (MLSD) is described. To perform MLSD at the high data rates encountered in recording systems, a simple implementation of the Viterbi detector based on a difference-metric algorithm is developed. Decision-directed schemes for gain control and timing recovery, for tracking variations of the gain and timing phase during data readback, and for fast initial adjustment from a known preamble are presented. The dynamic behavior of the control algorithms was studied by computer simulations. Coding was used to facilitate timing recovery and gain control, to limit the path memory length of the Viterbi detector, and to allow fast and reliable startup of the receiver. The design and properties of rate 8/9 constrained codes are examined. The problem of equalization is addressed, and analog and combined analog/digital filter implementations are developed. A simple adaptive equalizer capable of compensating variations of the recording channel characteristics with track radius and/or head-to-medium distance is described. >

Capacity of the discrete-time Gaussian channel with intersymbol interference

The discrete-time Gaussian channel with intersymbol interference (ISI) where the inputs are subject to a per symbol average-energy constraint is considered. The capacity of this channel is derived by means of a hypothetical channel model called the N-circular Gaussian channel (NCGC), whose capacity is readily derived using the theory of the discrete Fourier transform. The results obtained for the NCGC are used further to prove that, in the limit of increasing block length N, the capacity of the discrete-time Gaussian channel (DTGC) with ISI using a per block average-energy input constraint (N-block DTGC) is indeed also the capacity when using the per symbol average-energy constraint. >

Robust noncoherent receiver exploiting UWB channel properties

Most UWB radio receivers discussed in the literature are coherent receivers, which can offer high signal sensitivity and support high data rates but require precise timing clock recovery and complex RAKE structures. For UWB radio systems requiring only lower data throughput, noncoherent receiver architectures offer a good performance-complexity tradeoff. In this paper, we describe a noncoherent receiver for 2PPM UWB signals. The key design parameter, the duration of signal integration, can be chosen such that a target BER is achieved for each element of a preselected set of channel realizations. Although the proposed receiver works without channel state information and complex RAKE frontend, its performance compares favorably with that of a coherent 2PAM RAKE receiver of low order. The simple noncoherent receiver exploits most of the multipath diversity offered by the channel and is robust to clock timing errors.

Noise-predictive maximum likelihood (NPML) detection

Sequence detectors for the digital magnetic recording channel that are based on noise-predictive partial-response equalization are described. Called Noise-Predictive Maximum Likelihood (NPML) detectors, they arise by imbedding a noise prediction/whitening process into the branch metric computation of a Viterbi detector. NPML detectors can be realized in a form that allows RAM table look-up implementation of the imbedded feedback. Alternatively, the noise prediction/whitening mechanism can be implemented as an infinite impulse response (IIR) filter. For a Lorentzian channel with operating points in the range 0.5<PW50/T<3.5, IIR predictors with at most two zeros and two poles offer the best possible performance. Simulation results obtained for Lorentzian channels show that a judicious tradeoff between performance and state complexity leads to practical schemes offering substantial performance gains over both PRML and extended PRML detectors. An important practical advantage of the family of NPML detectors is that they can be conveniently integrated into existing PRML architectures.

A low supply voltage SiGe LNA for ultra-wideband frontends

A low-power low-noise amplifier (LNA) for ultra-wideband (UWB) radio systems is presented. The microwave monolithic integrated circuit (MMIC) has been fabricated using a commercial 0.25-/spl mu/m silicon-germanium (SiGe) bipolar CMOS (BiCMOS) technology. The amplifier uses peaking and feedback techniques to optimize its gain, bandwidth and impedance matching. It operates from 3.4 to 6.9GHz, which corresponds with the low end of the available UWB radio spectrum. The LNA has a peak gain of 10dB and a noise figure less than 5dB over the entire bandwidth. The circuit consumes only 3.5mW using a 1-V supply voltage. A figure of merit (FoM) for LNAs considering bandwidth, gain, noise, power consumption, and technology is proposed. The realized LNA circuit is compared with other recently published low-power LNA designs and shows the highest reported FoM.

Low-power ultra-wideband wavelets generator with fast start-up circuit

A low-power fully integrated ultra-wideband (UWB) wavelet generator is presented. This UWB generator is intended for low-power and low-complexity UWB radio technology using the noncoherent energy collection approach. The wavelet generator is based on a cross-coupled inductance-capacitance (LC) oscillator. It can be directly driven by two digital signals, which can modulate the length, position, and phase of the output wavelet. An additional digital circuit improves the startup time of the oscillator so that the oscillator and output buffers can be switched off between each wavelet generation. The entire chip-including output buffers-uses a 0.18-/spl mu/m CMOS technology. When operating at 10 megapulses per second (Mp/s) with a 1.2-GHz bandwidth wavelet, the generator provides a typical average output power of -20 dBm and consumes only 1.8 mW. The differential output signal is a multicycle waveform centered at 4.5 GHz.

Noise-predictive maximum-likelihood (NPML) detection for the magnetic recording channel

Sequence estimation detectors for the digital magnetic recording channel are described that are based on noise-predictive partial-response equalization. Called noise-predictive maximum-likelihood (NPML) detectors, they arise by imbedding a noise prediction/whitening process into the branch metric computation of a Viterbi detector. NPML detectors can be realized in a form that allows easy RAM table look-up implementation of the imbedded feedback. The noise prediction/whitening mechanism can also be applied to detectors using finite delay tree search algorithms instead of the Viterbi algorithm. Simulation results obtained for Lorentzian channels show that a judicious tradeoff between performance and state complexity and/or the length of the decision feedback leads to practical schemes offering substantial performance gains over both PRML and EPRML detectors. An important practical advantage of the family of NPML detectors is that they can be conveniently integrated into existing PRML architectures.

Performance of binary antipodal signaling over indoor UWB MIMO channel

We generalize a suitable, known indoor UWB SISO channel model to obtain a new discrete-time model for the indoor UWB MIMO radio channel. The properties and potential benefits arising from the channels specific correlation features benefits arising form the channels specific correlation features are investigated by means of simulations. We chow that the indoor UWB channel can offer much lower ISI than would be expected for a given rms delay spread, and confirm that systems operating on this channel require a small-scale fading margin of only a few dB. It is further demonstrated that an uncoded MIMO communication scheme applied to the UWB channel can offer superior SVEP performance compared to its use on the i.i.d. Rayleigh flat fading channel. Moreover, it was found that such an UWB scheme can offer very low SVEP with several transmitting and only a single receiving antenna (MISO), in contrast to a similar narrowband system.

Dynamic Cell Planning for Wireless Infrared In-House Data Transmission

A simulation model for characterizing the geometry of infrared communication cells representing full connectivity has been developed. Measured spatial daylight distributions in a large open-plan office have been incorporated into the model. With a 1 Mbps transmission system based on 16-slot pulse-position modulation and a non-directed infrared source of 250 mW average optical power, cell sizes of up to 10 m and 20 m diameter can be achieved for peer-to-peer and client/server topologies, respectively. Daylight variations cause severe distortions and size reductions of the cells. A transmission system with adaptive data rate control (10 kbps to 10 Mbps) maintains full network connectivity within the cells at the expense of a graceful throughput degradation for terminals exposed to high levels of ambient light.