Ahmet G. Cepni

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.

Single antenna time reversal adaptive interference cancellation

This paper presents the time reversal adaptive interferer canceller (TRAIC), a novel algorithm that uses time reversal techniques to cancel the presence of interferers. TRAIC is developed for broadband signals and a single emitting antenna. Experimental tests in the electromagnetic domain show the viability and the power of TRAIC.

Time Reversal Detection in Clutter: Additional Experimental Results

Time reversal (TR) is a promising technique in detecting weak targets immersed in clutter. This paper reports a series of electromagnetic (EM) domain experiments on TR detection using a single antenna pair in a controlled scattering environment. The TR likelihood ratio detector is compared with the conventional energy detector and the matched filter. The EM experiments demonstrate the superiority of TR detection over conventional detection in rich multipath scattering environments.

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.

Single antenna microwave nulling using time-reversal techniques

In this paper, we describe a single antenna microwave nulling technique that makes use of time-reversal concepts. The time-domain experiments have shown that by using single antenna and time-reversal technique, we can have focusing as well as nulling at any point in space. We have done experiments at 2.45 GHz in a cylindrical cavity environment. The degree of nulling (or focusing) depends on the multipath components in the channel as well as the bandwidth of the signal. The cavity provides a multipath rich-environment where we can show focusing and nulling by using a relatively small bandwidth compared to free space.

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.

Single antenna target detection using broadband frequency selection time reversal method

In this paper, we present a broadband single antenna target detection scheme using frequency selection time reversal method to further improve the target detection in a cluttered environment. By re-transmitting time-reversed difference signal between reflections from the environment with and without the target, constructive interferences between the target and the background scatterers are utilized to enhance the return signal from target. Meanwhile, frequency selection time reversal emphasizes on the section of wavelengths with more constructive interferences and filters out the broadband white noise at the other spectrum. Thus, signal to noise ratio (SNR) is substantially increased. The effectiveness of the proposed detection scheme has been demonstrated by numerical simulation. The simulation results show that using frequency selection time reversal method, the detection probability is significantly enhanced and SNR can be improved 2-5 dB