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This study presents a co-design approach to wireless network control systems (WNCS). Experimental studies are carried out to identify and analyse the delays inherent in WNCS, with a new inverse Gaussian model for their statistical distribution proposed. Two different packet-based predictive control schemes are presented. One uses dynamic matrix control (DMC), the other is a linear quadratic (LQ) controller incorporating multiple observers. Lyapunov stability is derived using linear matrix inequalities (LMIs) for the multi-observer LQ control whereas Monte-Carlo simulation results on a cart-mounted inverted pendulum are presented to confirm the performance advantages of packet-based DMC. Finally, results from a real-time implementation of the multi-observer LQ controller are also presented. [ABSTRACT FROM AUTHOR]

The performance of a new pointer-based medium-access control protocol that was designed to significantly improve the energy efficiency of user terminals in quality-of-service-enabled wireless local area networks was analysed. The new protocol, pointer-controlled slot allocation and resynchronisation protocol (PCSARe), is based on the hybrid coordination function-controlled channel access mode of the IEEE 802.11e standard. PCSARe reduces energy consumption by removing the need for power-saving stations to remain awake for channel listening. Discrete event network simulations were performed to compare the performance of PCSARe with the non-automatic power save delivery (APSD) and scheduled-APSD power-saving modes of IEEE 802.11e. The simulation results show a demonstrable improvement in energy efficiency without significant reduction in performance when using PCSARe. For a wireless network consisting of an access point and eight stations in power-saving mode, the energy saving was up to 39% when using PCSARe instead of IEEE 802.11e non-APSD. The results also show that PCSARe offers significantly reduced uplink access delay over IEEE 802.11e non-APSD, while modestly improving the uplink throughput. Furthermore, although both had the same energy consumption, PCSARe gave a 25% reduction in downlink access delay compared with IEEE 802.11e S-APSD. [ABSTRACT FROM AUTHOR]

Closing feedback loops using an IEEE 802.11b ad hoc wireless communication network incurs many challenges – sensitivity to varying channel conditions and lower physical transmission rates tend to limit the bandwidth of the communication channel. Given that the bandwidth usage and control performance are linked, a method of adapting the sampling interval based on an ‘a priori’, static sampling policy has been proposed and, more significantly, assuring stability in the mean square sense using discrete-time Markov jump linear system theory. Practical issues including current limitations of the 802.11 b protocol, the sampling policy and stability are highlighted. Simulation results on a cart-mounted inverted pendulum show that closed-loop stability can be improved using sample rate adaptation and that the control design criteria can be met in the presence of channel errors and severe channel contention. [ABSTRACT FROM AUTHOR]

Wireless enabled portable devices must operate with the highest possible energy efficiency while still maintaining a minimum level and quality of service to meet the user's expectations. The authors analyse the performance of a new pointer-based medium access control protocol that was designed to significantly improve the energy efficiency of user terminals in wireless local area networks. The new protocol, pointer controlled slot allocation and resynchronisation protocol (PCSAR), is based on the existing IEEE 802.11 point coordination function (PCF) standard. PCSAR reduces energy consumption by removing the need for power saving stations to remain awake and listen to the channel. Using OPNET, simulations were performed under symmetric channel loading conditions to compare the performance of PCSAR with the infrastructure power saving mode of IEEE 802.11, PCF-PS. The simulation results demonstrate a significant improvement in energy efficiency without significant reduction in performance when using PCSAR. For a wireless network consisting of an access point and 8 stations in power saving mode, the energy saving was up to 31% while using PCSAR instead of PCF-PS, depending upon frame error rate and load. The results also show that PCSAR offers significantly reduced uplink access delay over PCF-PS while modestly improving uplink throughput. [ABSTRACT FROM AUTHOR]

Objective: We examined the effect of three feeding conditions on cigarette smoking and coffee drinking in four healthy women. We hypothesized that food deprivation and changes in meal patterns would increase rates of smoking and coffee drinking based on extensive animal literature documenting this effect. Method: The conditions were: normal three meals per day containing usual energy intake, one meal per day (dinner time) containing 50% of usual energy intake, and three meals per day containing 50% of usual energy intake. Each condition lasted 3 days. Results: Neither reduction of energy intake nor alteration in the pattern of meals had any observable effect on number of cigarettes smoked, number of cups of coffee consumed, expired air carbon monoxide levels, or urges to smoke or drink coffee. Discussion: This study adds to the growing body of literature suggesting that the food deprivation effect observed in animals does not apply readily to humans. Reasons for the absence of this effect are discussed. (C) 1997 by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Closed-form expressions for the level crossing rate and average fade duration of a κ–μ distributed fading signal envelope are presented. The proposed equations are validated by reduction to known Rice, Rayleigh and Nakagami-m special cases. They are also compared with measured data obtained from field trials analysing human body to body radio channels and shown to provide good agreement. [ABSTRACT FROM AUTHOR]

Power deposition in the head of a user wearing metal-framed spectacles was calculated with a 450 MHz personal radio transmitting in close proximity. Peak tissue SAR in the head depended on lens shape—whether circular half-rim or rectangular—with 70 and 174% increases, respectively, compared to the spectacle-free case. However, localised screening occurred with square frames, with a 40% reduction of peak SAR in the eye closest to the antenna. [ABSTRACT FROM AUTHOR]