Andrew Fort

A Comprehensive Standardized Model for Ultrawideband Propagation Channels

A comprehensive statistical model is described for ultrawideband (UWB) propagation channels that is valid for a frequency range from 3-10 GHz. It is based on measurements and simulations in the following environments: residential indoor, office indoor, builtup outdoor, industrial indoor, farm environments, and body area networks. The model is independent of the used antennas. It includes the frequency dependence of the path gain as well as several generalizations of the Saleh-Valenzuela model, like mixed Poisson times of arrival and delay-dependent cluster decay constants. A separate model is specified for the frequency range below 1 GHz. The model can thus be used for realistic performance assessment of UWB systems. It was accepted by the IEEE 802.15.4a Task Group as standard model for evaluation of UWB system proposals. This paper also presents a critical assessment of the applicability of the model and possible generalizations and improvements

Ultra-wideband channel model for communication around the human body

Using ultra-wideband (UWB) wireless sensors placed on a person to continuously monitor health information is a promising new application. However, there are currently no detailed models describing the UWB radio channel around the human body making it difficult to design a suitable communication system. To address this problem, we have measured radio propagation around the body in a typical indoor environment and incorporated these results into a simple model. We then implemented this model on a computer and compared experimental data with the simulation results. This paper proposes a simple statistical channel model and a practical implementation useful for evaluating UWB body area communication systems.

An ultra-wideband body area propagation channel Model-from statistics to implementation

Body worn wireless sensors for monitoring health information is a promising new application. In developing these sensors, a communication channel model is essential. However, there are currently few measurements or models describing propagation around the body. To address this problem, we have measured electromagnetic waves near the torso and derived relevant statistics. We find that components diffracting around the body are well modeled using correlated log normal variables, and a Nakagami-m distribution can be used to incorporate the influence of arm motions. We have implement this model and evaluated it in terms of important communication metrics. This paper describes body area propagation statistics and proposes a suitable computer model implementation.

Joint compensation of IQ imbalance and frequency offset in OFDM systems

Zero-IF receivers are gaining interest because they enable low-cost WLAN OFDM terminals. However, zero-IF receivers introduce IQ imbalance which may have a huge impact on performance. Rather than increasing component cost to decrease the IQ imbalance, an alternative is to tolerate the IQ imbalance and compensate it digitally. Current solutions converge too slowly for bursty WLAN communication. Moreover, the tremendous impact of a frequency offset on the IQ estimation/compensation problem is not considered. We analyze joint IQ-CFO estimation/compensation and propose a low-cost, highly effective compensation scheme. For large IQ imbalance (/spl epsi/=10%, /spl Delta//spl phi/=10/spl deg/) and large frequency offset, our solution results in an average remaining degradation below 0.5 dB compared to the reference case without IQ imbalance or frequency offset. It therefore enables the design of low-cost, low-complexity WLAN OFDM receivers.

Characterization of the ultra wideband body area propagation channel

Using wireless sensors placed on a person to continuously monitor health information is a promising new application. In developing these sensors, detailed knowledge of the communication channel is essential. However, there are currently very few measurements describing propagation around the body. To address this problem, we have measured electromagnetic waves traveling near the torso to derive a simple pathless law. The pathless law is then extended to include the influence of arm movements and a surrounding office environment. This paper describes our measurement campaign and the basic characteristics of the body area radio channel.

Ultra wide-band body area channel model

Using wireless sensors placed on a person to continuously monitor health information is a promising new application. However, there are currently no models describing the radio channel around the human body making it difficult to design a suitable communication system. To address this problem, we have simulated electromagnetic wave propagation around the body and incorporated these results into a simple model. We then compared this model with measurements taken around the human torso and with previous studies in the literature. This paper proposes a simple statistical channel model useful for evaluating both UWB and (after resampling) narrow-band body area communication systems.

A comprehensive model for ultrawideband propagation channels

This paper describes a comprehensive statistical model for UWB propagation channels that is valid for a frequency range from 3-10 GHz. It is based on measurements and simulations in the following environments: residential indoor, office indoor, built-up outdoor, industrial indoor, farm environments, and body area networks. The model is independent of the used antennas. It includes the frequency dependence of the pathloss, as well as several generalizations of the Saleh-Valenzuela model, like mixed Poisson times of arrival and delay dependent cluster decay constants. The model can thus be used for realistic performance assessment of UWB systems. It was accepted by the IEEE 802.15.4a working group (WG) as standard model for evaluation of UWB system proposals

A Body Area Propagation Model Derived From Fundamental Principles: Analytical Analysis and Comparison With Measurements

Using wireless sensors worn on the body to monitor health information is a promising new application. To realize transceivers targeted for these applications, it is essential to understand the body area propagation channel. Several numerical, simulated, and measured body area propagation studies have recently been conducted. While many of these studies are useful for evaluating communication systems, they are not compared against or justified by more fundamental physical models derived from basic principles. This type of comparison is necessary to provide better physical insights into expected propagation trends and to justify modeling choices. To address this problem, we have developed a simple and generic body area propagation model derived directly from Maxwells equations revealing basic propagation trends away, inside, around, and along the body. We have verified the resulting analytical model by comparing it with measurements in an anechoic chamber. This paper develops an analytical model of the body, describes the expected body area pathloss trends predicted by Maxwells equations, and compares it with measurements of the electric field close to the body.

A performance and complexity comparison of auto-correlation and cross-correlation for OFDM burst synchronization

A symbol timing synchronization scheme is critical in the design of an OFDM receiver. Large timing errors can result in a loss of orthogonality between subcarriers, ISI and severe bit error degradation. To minimize this degradation, standards incorporate preambles suitable for two kinds of synchronization algorithms: auto-correlation and crosscorrelation. Unfortunately, the performance and complexity tradeoffs between these algorithms have not been well explored. To address this problem, we have built an FPGA implementation of a synchronization system using both autocorrelation and cross-correlation. Based on our results, in this paper we propose a novel cross-correlation synchronizer and hardware architecture. We then compare its performance and complexity to auto-correlation algorithms for HiperLAN/2 and IEEE 802.11a preambles.

Selection of channel coding for low-power wireless systems

The wireless communications world is moving towards the so-called 4G pictures, by integrating many different subsystems. Some of them have to provide short-range connectivity at very low power, in order to enable battery-operated sensors or devices. This low-power requirement can be achieved by selecting channel codes of high coding gain. However, the power consumption of encoding and decoding operations also has to be taken into account. This paper analyzes this trade-off between coding gain and digital power consumption, considering different wireless scenarios. It shows that turbo codes can be used even for relatively low-power applications. For every low-power system, simple Hamming codes provide a good trade-off, as well as convolutional codes. The Golay code is another strong candidate, thanks to a very efficient implementation. Considering current CMOS technology, the different codes are in competition for systems sending bits with energy between 0.1 and 10 nJ. Systems working at lower values do not gain anything in coding, while systems working above will always advantageously use turbo-codes.