Bert Gyselinckx

Ultra-wide-band transmitter for low-power wireless body area networks: design and evaluation

The successful realization of a wireless body area network (WBAN) requires innovative solutions to meet the energy consumption budget of the autonomous sensor nodes. The radio interface is a major challenge, since its power consumption must be reduced below 100 /spl mu/W (energy scavenging limit). The emerging ultra-wide-band (UWB) technology shows strong advantages in reaching this target. First, most of the complexity of an UWB system is in the receiver, which is a perfect scenario in the WBAN context. Second, the very little hardware complexity of a UWB transmitter offers the potential for low-cost and highly integrated solutions. Finally, in a pulse-based UWB scheme, the transmitter can be duty-cycled at the pulse rate, thereby reducing the baseline power consumption. We present a low-power UWB transmitter that can be fully integrated in standard CMOS technology. Measured performances of a fully integrated pulse generator are provided, showing the potential of UWB for low power and low cost implementations. Finally, using a WBAN channel model, we present a comparison between our UWB solution and state-of-the-art low-power narrow-band implementations. This paper shows that UWB performs better in the short range due to a reduced baseline power consumption.

Training sequence versus cyclic prefix-a new look on single carrier communication

Orthogonal frequency-division multiplexing (OFDM), with the help of a cyclic prefix, enables low complexity frequency domain equalization, but suffers from a high crest factor. Single carrier with cyclic prefix (SC-CP) has the same advantage with similar performance, but with a lower crest factor and enhanced robustness to phase noise. The cyclic prefix is overhead, so we put more information in it by implementing this cyclic prefix as a training sequence (TS). This new training aided frequency domain equalized single carrier (TASC) scheme offers us additional known symbols and enables better synchronization and (potentially) channel estimation, with the same performance as SC-CP.

A low-complexity ML channel estimator for OFDM

Orthogonal frequency-division multiplexing with cyclic prefix enables low-cost frequency-domain mitigation of multipath distortion. However, to determine the equalizer coefficients, knowledge of the channel frequency response is required. While a straightforward approach is to measure the response to a known pilot symbol sequence, existing literature reports a significant performance gain when exploiting the frequency correlation properties of the channel. Expressing this correlation by the finite delay spread, we build a deterministic model parametrized by the channel impulse response and, based on this model, derive the maximum-likelihood channel estimator. In addition to being optimal (up to the modeling error), this estimator receives an elegant time-frequency interpretation. As a result, it has a significantly lower complexity than previously published methods.

Human++: autonomous wireless sensors for body area networks

This paper gives an overview of the results of BMECs Human++ research program. This program aims to achieve highly miniaturized and autonomous sensor systems that enable people to carry their personal body area network. The body area network will provide medical, lifestyle, assisted living, sports or entertainment functions. It combines expertise in wireless ultra-low power communications, packaging, 3D integration technologies, MEMS energy scavenging techniques and low-power design techniques.

Training sequence vs. cyclic prefix a new look on single carrier communication

Frequency domain equalization has gained a lot of attention in the last decade, mainly pushed by the OFDM (orthogonal frequency division multiplexing) communication scheme. It has been adopted, in various flavours, for, among others, wireless LANs and xDSL. The technique is indeed leading to low complexity implementation, at the cost of a cyclic prefix, used to avoid inter block interference (IBI). The idea has been adapted to single carrier communication, almost as is, yielding the same computational advantages and avoiding the high crest factor of OFDM. We name this scheme CP-SC (cyclic prefix-single carrier). We take a new look at this single carrier scheme, and, with a slight modification, show that the cyclic prefix can be implemented as a training sequence, and hence play two important roles: avoid IBI and help in synchronisation and channel estimation. The latter topic is of utter importance in fast fading situations (e.g. mobile). This new training aided frequency domain equalized single carrier (we name it TASC) scheme offers these advantages at the expense of only a small fraction of a dB (in terms of E/sub b//N/sub 0/). All these arguments make TASC an interesting candidate in situations where multipath and fast fading are present, while in other situations it has hardly no drawback compared to CP-SC.

A 16mA UWB 3-to-5GHz 20Mpulses/s Quadrature Analog Correlation Receiver in 0.18/spl mu/m CMOS

A 3-to-5GHz quadrature analog correlation RX for UWB impulse radio draws 16mA at 20Mpulses/s, making it suitable for low-power low-data-rate applications. The RX is fully integrated in a CMOS 0.18mum process and comprises an LNA, quadrature LO generation and mixers, baseband filtering, an integrator, timing circuitry, and an ADC

Body-Heat Powered Autonomous Pulse Oximeter

A wireless pulse oximeter for non-invasive measurement of pulse and blood oxygen saturation has been realized. The device is powered by a thermoelectric generator in the form of a watch using the persons body heat and therefore achieves full energy autonomy. It does not require a battery, only a small (super-)capacitor as a short-time energy buffer. At 22degC ambient temperature, the generator produces more than 100muW of electrical power. All signal processing is done locally in the sensor. To our knowledge, this is the first realization of a non-trivial biomedical sensor fully powered by the patients body heat.

Technologies for highly miniaturized autonomous sensor networks

Recent results of the autonomous sensor research program HUMAN++ will be summarized in this paper. The research program aims to achieve highly miniaturized and (nearly) autonomous sensor systems that assist our health and comfort. Although the application examples are dedicated to human monitoring/assistance, the necessary technology development for this program is generic and can serve many wireless sensor applications. This multi-disciplinary program combines research on wireless ultra-low-power communications, research on 2D/3D integration and packaging platforms, energy scavenging techniques, as well as low-power and ultra-low-power sensor circuit design. An example sensor system is the wearable wireless EEG system.

A 10.6mW/0.8pJ power-scalable 1GS/s 4b ADC in 0.18/spl mu/m CMOS with 5.8GHz ERBW

We present a 4-bit power scalable flash analog-to-digital converter in digital 0.18-μm CMOS, targeting low power ultra-wide band receivers. To minimize static power consumption, we exploit dynamic comparators with built-in digitally tunable thresholds. The converter has been realized and tested outperforming recent comparable designs even in more advanced technologies. The main performance figures include 5.8GHz effective resolution bandwidth and 0.8pJ/conversion-step at 1-GS/s and Nyquist conditions.

A digital 72 Mb/s 64-QAM OFDM transceiver for 5 GHz wireless LAN in 0.18 /spl mu/m CMOS

OFDM forms the physical layer for upcoming broadband wireless LAN standards like IEEE 802.11a and ETSI Hiperlan/2. A throughput of 72Mb/s after coding within a 20MHz bandwidth requires spectrally-efficient modulation schemes up to 64-QAM. This requires transceiver implementations that extend the capabilities of classic OFDM signal processing to fast-burst communication in a multipath indoor environment. The presented ASIC includes a parameterizable interpolating equalizer architecture, clock offset tracking, and a robust programmable acquisition, covering all transmission modes from BPSK to 64-QAM.