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The wireless communication channel around/in the human body is a difficult propagation environment. This paper presents measurement and simulation results to characterize such a channel. A fluid human body model is employed to emulate the inside of a human body. The paper details the fluid human model and path loss model parameters at 400 MHz (MICS band). It is shown that the simulated and measured results are in a close agreement, for instance at a distance of 20 cm and a implant depth of 10 cm, the measurement results in a path loss of -42.1 dB and the simulation in -43.0 dB. The effect of human model shape on measured path loss is analyzed. Furthermore, simulations are employed to characterize this effect. Using the path loss model a top-level link budget is evaluated to determine the feasibility of a given implant device compliant to IEEE802.15.6-WBAN-400 MHz standard.

The introduction of the IEEE802.15.6 standard (15.6) for wireless-body-area networks signals the advent of new medical applications, where various wireless nodes in, on or around a human body monitor vital signs. Radio communication often dominates the power consumption in the nodes, thus low-power transceivers are desired. Most state-of-the-art low-power transceivers support only proprietary modes with OOK or FSK modulations, and have poor sensitivity or low data rate [1,2]. In this work, a 15.6-compliant transceiver with enhanced performance is proposed. First, the data-rate is extended to 4.5Mb/s to cover multi-channel EEG applications. Second, while a best-in-class energy efficiency of 0.33nJ/b is achieved in the high-speed mode, a dedicated low-power mode reduces the RX power further in low-data-rate operation. Third, a sensitivity 5 to 10dB better than the 15.6 specification is targeted to accommodate extra path loss due to shadowing effects from human bodies.

Impulse radio ultra-wideband (IR-UWB) is being employed in several IEEE standards for Wireless Sensor Network (WSN). This paper presents a battery model for small form factor, zinc-air button cell batteries with high energy density but also high internal impedance. Their usage in small form factor IR-UWB radios, requires accurate modeling to enable proper power management system design, avoiding system failure due to excessive supply voltage variation. In preamble synchronization phase all receiver blocks are used continuously, causing a current peak. The required battery model consists of seven resistor-capacitor (RC) sections.

ESA is investigating wireless cable replacement for intra-spacecraft (IS) applications to reduce cable weight, and add flexibility to the subsystem layout. The low emission limit and robustness to highly reflective environments make UWB a potential candidate for cable replacement. Therefore, to validate these assumptions, channel measurements have been conducted in a representative spacecraft; the ESA Venus Express mock-up, which is divided in separate compartments/cavities connected by openings. Channel measurements that cover the entire 3 to 10 GHz UWB spectrum, are conducted for all cavity combinations of the Venus Express. Channel statistics are derived from the measurements. Moreover, the raw channel measurements are used in a hardware-true physical layer (PHY) simulator, based on current Holst Centre - IMEC UWB hardware platform supporting IEEE 802.15.4a standard. The used hardware specification are from the non-coherent setting, employing power detection and integrate and dump in RX for easy synchronization in a highly reflective environment, insensitivity to clock jitter, and robustness against clock offsets at cost of reduced sensitivity. The PHY results correspond well to the outage probability derived from the channel measurements when taking the actual noncoherent setting receiver hardware sensitivity into account. Since most power is in the scattered power, the most dominating factor in IS UWB communication is not the actual position or distance between the antennas, but the minimum number of openings between the cavities. The low mean loss of the measured radio channel combined with the immunity of the UWB air-interface to small-scale-fading, ensures that the signal is always well above the noise floor of the non-coherent setting of the current Holst Centre - IMEC hardware.

In this paper, non-data aided (NDA) signal-to-noise ratio (SNR) estimation techniques for non-coherent on-off keying (OOK) receivers using non-equiprobable signal transmission is analyzed. Expectation-maximization (EM), M1M2 and M2M3 estimators are investigated. It is shown that the performance of moments based estimators degrade in high SNR region due to bad noise estimates. Moreover, lower moment based estimator, i.e., M1M2 is shown to be inoperable for equiprobable case. EM estimator is investigated and a noise recalibration stage is added for high SNR region. Hybrid estimators, i.e., M1M2-EM and M2M3 - EM are proposed to cover a wide range of SNR for equiprobable and non-equiprobable signal transmission. The normalized mean square error (NMSE) is evaluated for each estimator. Closed form analytical expressions are derived for each of the estimators and is found to be in good agreement with the simulations.

This paper discusses the system level considerations of low-power receivers targeting body area networks (BAN). Since low power consumption is of the utmost importance either OOK or FSK modulation have to be used. We compare the two modulation schemes and compare the system level design issues. Both receivers have a zero-IF architecture and thus have to deal with 1/f noise and DC offsets. The biggest challenge of envelope-detector based OOK receiver design is its poor interferer robustness; the signal-to-interferer-ratio need to be at least 16dB. Additionally the effect of limited ADC ENOB and OOK threshold level on the BER performance of OOK receivers are addressed. On the other hand FSK receivers require a stable local frequency reference which leads to higher power consumption. It can be concluded that in interferer-limited environments FSK receivers are the better choice. Whereas OOK receivers have a slightly lower power consumption.

In order to minimize power consumption without sacrificing much latency performance, wake-up radios are employed to assist the main radio for low power channel monitoring. This paper presents the design and implementation of an ultra-low power digital baseband (DBB) circuit for a wake-up radio. In a 90nm CMOS process, the circuit running at a 800kHz clock consumes 3.72μW with a standard 1.2V supply voltage, and achieves very good packet detection performance. The circuit is fully functional at 0.6V supply consuming 0.9μW.

In this paper we propose modulation diversity as a candidate diversity scheme for uncoded cooperative communication in wireless networks with decode-and-forward (DF) communication protocol. A performance analysis of such a scheme in Nakagami-m fading channels in the presence of additive white Gaussian noise (AWGN) is presented. An upper bound on the average probability of bit error (P b ) and average probability of symbol error (P s ) is derived for M-ary phase shift keying (MPSK) modulation schemes. It is shown that the system employing employing modulation diversity is able to provide a performance improvement of 5 dB at a bit error rate of 10−4 as compared to the conventional cooperative communication systems. We introduce a power allocation factor and show that equal power allocation is not the optimal solution. Furthermore, we also analyze the effect of different rotation angles and power allocation on the system performance.

Co-ordinate interleaving (also known as signal space diversity (SSO)) with the rotation of signal constellation of multilevel modulation schemes with bit interleaved coded modulation (BICM) is known to provide good performance for single carrier systems. This paper studies the extension of SSD with recursive systematic convolutional (RSC) coded BICM and constellation rotation in an orthogonal frequency division multiplexing (OFDM) system. Iterative demodulation and decoding (ID) is employed at the receiver. It is shown that for a signal constellation and labeling using SSD on a frequency-selective fading channel, a well considered choice of the rotation angle leads to a significant gain over the conventional BICM-ID OFDM system. Furthermore, the choice of the rotation angle for the system is found to be dependent upon the symbol labeling and the number of iterations performed between the demodulator and the decoder.

Signal space diversity (SSD) with the rotation of the signal constellation using multi-level modulation schemes is known to provide good performance gains over fading channels. This paper studies the extension of such schemes with iterative demodulation and decoding using convolutional codes for MPSK signal constellations with different symbol mappings. It is shown that for a specific signal constellation and labeling using SSD on a Rayleigh fading channel, a well considered choice of the rotation angle leads to a significant gain over conventional bit interleaved coded modulation with iterative decoding (BICM-ID). Furthermore, the optimum rotation angle for the coded system is found to be dependent upon the symbol labeling and the number of iterations carried out at the receiver.

For multi-level modulation methods, rotation of the signal constellation together with in-phase and quadrature phase channel interleaving (signal space diversity) are known to provide good performance gains over fading channels. This paper studies the extension of such schemes with a low density parity check (LDPC) code. It is shown that for both coded and uncoded Gray-mapped MPSK modulation formats with signal space diversity on a Rayleigh fading channel, a well-considered choice of the rotation angle may lead to a significant gain over the conventional unrotated constellation. However, the optimum rotation angle for the coded scheme may be different from the corresponding optimization angle of the uncoded scheme.

For design of reflectarray antennas, microstrip patches of varying length provide an attractive alternative. In this paper the analysis, design and measurement of reflectarray antenna based on variable size at Ka-band is presented. The design procedure and critical parameters are discussed. For our analysis we employ a full wave solution, i.e., method of moment (MoM). This solution is made efficient using threads and parallel processing techniques. To validate our analysis, number of arrays are built and measured, showing a good agreement with the simulation results.

Rotation of the signal constellation together with in-phase and quadrature channel interleaving (signal space diversity) is known to provide good performance gains over fading channels for multi level modulation methods. This paper studies the extension of such schemes with a low density parity check (LDPC) code. It is shown that for both coded and un-coded Gray-mapped MPSK modulation formats with signal space diversity on a Rayleigh fading channel, a well-considered choice of the rotation angle may lead to a significant gain over the conventional un-rotated constellation. However, the optimum rotation angle for the coded scheme may be different from the corresponding optimization angle of the un-coded scheme.