Dagfin Brodtkorb

Propagation model for the HVAC duct as a communication channel

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 network access to offices. Knowledge of channel properties is crucial to designing such a communication system. The 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 the theoretical results. This model represents an initial step toward the development of a tool for planning a wireless distribution system using building HVAC ducts.

High-speed Internet access via HVAC ducts: a new approach

We report a novel technique for inexpensive high-speed Internet access in buildings. Our work shows that, one can use heating, ventilation, and air conditioning (HVAC) ducts for indoor wireless transmission systems and networks. Measurements and system calculations show that coverage distances in excess of 100 meters from the base station and data rates of up to 100 Mbps should be possible, when HVAC system is used in conjunction with OFDM technology.

Impulse response of the HVAC duct as a communication channel

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.

A simple path-loss prediction model for HVAC systems

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.

A novel mode content analysis technique for antennas in multimode waveguides

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.

An empirical path loss model for HVAC duct systems

We present a simple path loss prediction model for link budget analysis in indoor wireless local area networks (LANs) that use heating, ventilation, and air conditioning (HVAC) ducts. The model we propose predicts the average power at each location in an HVAC duct network. This prediction model greatly simplifies the analysis for a complex duct network, making it a convenient and simple tool for system design. Our prediction model Is verified by experimental measurements.

On the capacity limits of HVAC duct channel for high-speed Internet access

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.

Capacity of multi-antenna array systems for HVAC ducts

Multi-element antenna arrays at both transmitter and receiver systems have emerged as a new technique for wireless communication systems in rich multipath environments. HVAC ducts, viewed as over-moded waveguide network systems at RF frequencies, have the multipath richness through various propagating modes and reflections within the system. This paper studies multiple-input multiple-output (MIMO) systems for HVAC ducts. Computations based on measured channel responses of a 6/spl times/6 MIMO system in 0.3 m diameter HVAC ducts in the 2.4 GHz ISM band demonstrate a five-fold increase in mean capacity over single antenna systems for an SNR of 30 dB.

RF propagation in an HVAC duct system: impulse response characteristics of the channel

Usually, the heating, ventilation, and air conditioning (HVAC) duct system in buildings is a complex network of hollow metal pipes of rectangular or circular cross-section which behave as multimode waveguides when driven at RF and microwave frequencies. The impulse response in the HVAC duct system used as a wireless communication channel is shaped by three physical mechanisms: probe coupling, attenuation, and dispersion. Three types of dispersion exist in this channel that affect the RMS delay spread. In order of importance, they are multipath reflections, intermodal dispersion, and intramodal dispersion. We present a model for the power delay profile in a straight terminated duct which allows exploration of RMS delay spread parametric behavior. As an example, we calculate the delay spread as a function of distance in a straight duct and find it to be in good agreement with experimental data at distances up to 15 m. A real HVAC system has a complicated geometry, which may include bends, junctions, etc. Efficient modelling of its channel properties is a challenging task. Our model for straight ducts should be perceived as a first step towards that goal.

Novel mode content analysis technique for multimode waveguides

This paper presents a novel technique for analyzing the mode content in multimode waveguides. The technique is based on measuring the frequency response between the two antennas coupled into a multimode waveguide and using that information to extract the frequency-averaged mode content at the location of the transmitting antenna. The technique is applicable to cases in which the complex 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, such as HVAC duct system used for indoor wireless communications.