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In this paper, we study the performance of three handover priority schemes--the pure guard channel method (GCM), GCM with first-in-first-out (GCM-FIFO), and dynamic priority queuing (DPQ)--and, for the first time, compare them for different scenarios and provide guidelines as to which scheme to use under which scenario. In the first scenario, the channel holding time is assumed to follow an exponential distribution. For this scenario, we derive new accurate formulas to evaluate the performance of GCM and GCM-FIFO schemes. Our results show that existing analytical frameworks for GCM and GCM-FIFO overestimate the handover failure probability. Recent field measurements have shown that the best fits to measured data for channel holding time are lognormal and mixed lognormal distributions rather than an exponential distribution. We quantify and compare the handover performance of GCM, GCM-FIFO, and DPQ for ideal (i.e., exponential channel holding time distribution) and for practical (i.e., lognormal and mixed lognormal channel holding time distributions) scenarios. Our results show that, depending on the cell type, the number of channels per cell, and the traffic load, the operator should use either DPQ or GCM. For example, for high handover traffic and high traffic load, the operator should use GCM-FIFO; for light-to-moderate traffic load and a high number of channels per cell (40 or more), DPQ seems to be the best option. To make the handover scheme adaptive, a switching mechanism can be used such that, depending on the time of the day, traffic load, number of channels per cell, and cell type, the handover scheme that provides the best performance is selected. The guidelines provided in our paper are, in most cases, valid for both exponential and pure/mixed lognormal distributions. Index Terms--Cellular networks, dynamic priority queuing (DPQ), guard channel method (GCM), handover.

In this paper, we report theoretical and experimental channel-capacity estimates of heating, ventilation, and air conditioning (HVAC) ducts based on multicarrier transmission that uses M-ary quadrature amplitude modulation and measured channel responses at the 2.4-GHz industrial, scientific, and medical band. It is shown theoretically that data rates in excess of 1 Gb/s are possible over distances up to 500 m in straight ducts in which reflections have been suppressed. Our experimental results also show that even in the case of more complex HVAC duct networks (i.e., HVAC duct networks that include bends, tees, etc.) data rates over 2 Gb/s are possible. Our estimations in this case are valid for distances of up to 22 m, which was the maximum distance of our experimental setup. These experimental results, measured with a large-scale testbed set up at Carnegie Mellon University, Pittsburgh, PA, albeit limited in terms of transmitter-receiver separation distance, provide further evidence on the potential of HVAC systems as an attractive solution for providing communications in indoor wireless networks. Index Terms--Heating, ventilation, and air conditioning (HVAC) systems for wireless transmission, indoor propagation, internet access, multicarrier transmission, orthogonal frequency-division multiplexing (OFDM).

In this paper, we present a simple path-loss prediction model for link budget analysis in indoor wireless local area networks that use heating, ventilation, and air conditioning (HVAC) cylindrical ducts in the 2.4-2.5-GHz industrial, scientific, and medical band. The model we propose predicts the average power loss between a transmitter-receiver pair in an HVAC duct network. This prediction model greatly simplifies the link budget analysis for a complex duct network, making it a convenient and simple tool for system design. The accuracy of our prediction model is verified by an extensive set of experimental measurements. Index Terms--Heating, ventilation, and air conditioning (HVAC) systems, indoor wireless local area networks (WLANs), Internet access, path-loss prediction model.

This paper presents a novel technique for analyzing the mode content excited by antennas placed in multimode waveguides. The technique is based on measuring the frequency response between the two antennas coupled into a waveguide and using that information to extract the mode content generated by the transmitting antenna. The technique is applicable to cases in which the mode amplitudes are approximately constant over the frequency range of interest. This method is valuable for determining the mode mix generated by arbitrary transmitting antennas in a multimode waveguide propagation environment. An example of such an environment is heating, ventilation, and air-conditioning (HVAC) ducts used for indoor communications, where an important antenna characteristic is the mode sensitivity (analogous to the antenna directive gain in free space). We validate our technique with the example of a monopole probe antenna coupled into a multimode cylindrical HVAC duct. Index Terms--Antennas, indoor radio communication, microwave measurements, multimode waveguides.

Heating, ventilation, and air conditioning (HVAC) ducts in buildings behave as multimode waveguides when excited at radio frequencies and thus, can be used to distribute radio signals. The channel properties of the ducts are different from the properties of a usual indoor propagation channel. In this paper, we describe physical mechanisms which affect the HVAC channel impulse response and analyze their influence on the delay spread. Those mechanisms include antenna coupling, attenuation, and three types of dispersion: intramodal, intermodal, and multipath. We analyze each type separately and explore the behavior of the delay spread as a function of distance in straight ducts. Experimental channel measurements taken on real ducts confirm the validity of our model. Index Terms--Dispersive channels, indoor radio communication, multimode waveguides, wireless local-area network (LAN).

Heating, ventilation, and air conditioning (HVAC) ducts in buildings are typically hollow metal pipes which can be used as waveguides to carry signals and provide the network access to offices. Knowledge of channel properties is crucial to designing such a communication system. This paper presents a propagation model for a straight HVAC duct terminated at both ends. At high frequencies this duct behaves as a multimode waveguide with a transmitting antenna coupling in and a receiving antenna coupling out. We derive a simple analytical expression for the frequency response of this channel using conventional techniques. Experimental data taken on real circular ducts excited by monopole probe antennas confirm theoretical results. This model represents an initial step toward the development of a tool for planning a wireless distribution system using building HVAC ducts. Index Terms--Indoor radio communication, monopole antennas, multimode waveguides, radio propagation, wireless LAN.