Achieving accurate and effective modeling of the vehicle-to-vehicle (V2V) communication channel has proven to be a challenging task, particularly owing to the highly dynamic nature of vehicular environments. V2V channels generally may have contributions from the line-of-sight path, reflections from large stationary and moving objects such as bridges and other vehicles, and a diffuse base from large numbers of small stationary objects in the environment. We propose a new geometrical model for the diffuse component based on scattering objects distributed along the roadside, and use this model to predict the Doppler spectrum and angle-of-arrival distribution associated with this component for various V2V scenarios. In contrast with previous roadside scattering models that sum the contributions from large numbers of randomly-generated scattering objects, our model assumes a uniform linear distribution along the roadside. This permits a computationally efficient, closed-form model. Comparisons with on-road measurement data as well as the double ring model demonstrate the validity and effectiveness of the proposed model.

A sensing technique to determine the height and orientation (pitch, roll) above a conducting half-space using magnetoquasistatic fields and complex image theory is presented. The technique is based on measuring the fields due to the complex image of a magnetic dipole source at different locations. Examples for use of this sensor include applications as diverse as aerial vehicle landing, take-off and hovering, terrain-relative navigation, and motion sensing or tracking.

An RF ranging sensor based on time-interleaved Dual Frequency Continuous Wave (DFCW) radar is proposed to measure the absolute distance between two shoes to aid a dead reckoning system for pedestrian navigation. Conventional single frequency Continuous Wave (CW) radar provides accurate but ambiguous range measurement, while DFCW techniques are employed to find the approximate range of the target and to remove the ambiguity of the single frequency CW radar. The two frequencies in the proposed DFCW radar work in a Time division Duplexing (TDD) manner so that they can share the same transceiver hardware. Such a composite DFCW/CW system can be implemented with a simple direct conversion receiver which is desirable for applications such as pedestrian navigation where compact and low power consumption devices are required. The feasibility of the proposed sensor is demonstrated by a sensor prototype based on Commercial Off The Shelf (COTS) components in a practical environment. An absolute accuracy (RMS) of 0.92 mm has been achieved for a maximum test range of 600 mm. The results show that the proposed ranging sensor is promising for measuring the distance in short range applications.

IEEE 802.11p-based Dedicated Short Range Communications (DSRC) is considered a promising wireless technology for enhancing transportation safety and improving highway efficiency. Here, using a large set of empirical measurement data taken in a rich variety of realistic driving environments, we attempt to characterize communication properties of DSRC as well as to analyze the causes of communication loss. Specifically, from a perspective of vehicular network engineers, the fundamental characteristic of DSRC communications is Packet Delivery Ratio (PDR). We investigate the impact of both uncontrollable environmental factors and controllable radio parameters on DSRC characteristics. Moreover, we also examine temporal correlation, spatial correlation and symmetric correlation of DSRC characteristics under realistic vehicular environments.

In this paper, the use of hollow metal heating, ventilating, and air-conditioning (HVAC) ducts as a potential communication channel between passive ultrahigh-frequency (UHF) radio-frequency identification (RFID) readers and tags is studied. HVAC ducts behave as electromagnetic waveguides with much lower signal attenuation compared to free-space propagation. This low-loss electromagnetic environment allows one to greatly increase the communication range of passive UHF RFID systems and build, for example, a long range passive sensor network spanning an entire infrastructure such as a large building. In this work, it is shown both theoretically and experimentally that the read range of passive UHF RFID systems can be increased by multiple times compared to operation in a free-space environment.

Direct sequence spread spectrum (DSSS) techniques are commonly used for characterizing RF communications channels. These techniques have relative immunity to interference and do not require a direct reference connection between the transmitter and receiver. Current DSSS propagation measurement systems use a pseudo noise (PN) sequence to probe the impulse response of the channel. However, the use of PN sequences can introduce noise into the measurements. This noise is caused by a bias term that is inversely proportional to the length of the PN-Sequence, and limits the dynamic range of the measurement system. In this paper it is shown that this bias term will not be present when zero correlation zone (ZCZ) sequences are used. Consequently the dynamic range of the measurement system is limited by the SNR instead of the sequence itself. This paper also provides test data to show the effects of the bias term and to compare and contrast the use of PN and ZCZ sequences.

Wireless channel emulators are important tools for testing radio devices, especially in mobile environments. Wireless network emulators give the same accuracy and control for testing radio network systems that traditional channel emulators give to point to point radio links. Network emulators require many more independent channels than traditional channel emulators. This problem is particularly challenging for the real time channel simulator in the emulator. The challenges of designing a wireless network channel simulator are discussed and a design is presented on a Xilinx Virtex-II Pro FPGA. This channel simulator can model 210 independent channels between 15 nodes with a bandwidth of 90 MHz. The performance of the design was verified by measuring transport-layer throughput between 802.11b radios transmitting through the channel simulator.

An experimental study of the Doppler coherence time properties of Vehicle-to-Vehicle (V2V) wireless channels at 5.9 GHz in both rural and highway environments is presented. Simultaneous RF and mobility measurements were conducted in environments near Pittsburgh, Pennsylvania. The average Doppler spread was observed to depend linearly on effective speed, defined as the square root of the sum of the squares of the ground speeds of the two vehicles. Sample spectrum is analyzed and comparisons with the double-ring models are presented. The coherence time was observed to vary inversely with effective speed, as expected. In addition, the coherence time was observed to decrease with vehicle separation out to about 100 m, followed by a relative peak at about 200 m. A possible interpretation of this peak in terms of a two-ray propagation model is presented. The observed Doppler spread should not be a problem for proposed V2V OFDM signal transmission formats, but the channel coherence time is much shorter than a typical packet suggesting that present equalization schemes may not be adequate.

This work presents fair comparisons of a ventilation duct based antenna system to a conventional wireless LAN access point installation, both inside and in areas around the outside of a building. We present comparisons of 3 different access point locations using signal strength measurements at nearly 100 different locations in the building for each location. We also present signal strength measurement comparisons as a user gets further and further away from the building outdoors. Lastly, we use this data to show that ventilation duct antenna systems can provide better signal strength inside a building resulting in improved user experience and in reduced system installation and life-cycle cost.

Broadband sounding of the vehicle-to-vehicle channel is reported in suburban, rural, and highway environments. A direct sequence spread spectrum waveform based on zero correlation zone sequences was used with an instantaneous bandwidth of about 40 MHz. Cumulative distribution functions are presented for the maximum excess delay, RMS delay spread, and coherence bandwidth using a threshold of 15 dB below the peak. The highway environment showed the largest median RMS delay spread (about 110 ns), the largest median maximum excess delay (about 600 ns) and the smallest median 90% coherence bandwidth (about 900 kHz). In general, the distributions of these quantities for the suburban environment were narrower than those for the rural and highway environments. This is interpreted in terms of the more restricted range of distances to scattering objects in the suburban environment.

The Gaussian quadrature rules (GQRs) are used to construct a wireless fading simulator based on the popular sum of sinusoids (SoS) method. The general statistics of the proposed simulator are given. This simulator is also shown to perform well for important design parameters. An extension of the GQRs is employed to build uncorrelated simulators, which are important in frequency selective and MIMO simulators. These simulation techniques are then applied to the mobile-to-mobile (MtM) spectrum and are compared with the best known SoS techniques for the MtM spectrum. Although the proposed method is more complex, the efficiency and accuracy are significantly better than the previously proposed methods.

A practical demonstration of IEEE 802.11g transmissions using time-reversal antenna arrays in MISO and MIMO configurations is presented in this work. Throughput measurements indicate significant channel improvement through the use of time-reversal array coefficients and illustrate the viability of increased access point (AP) capacity and co-channel interference reduction in multi-user scenarios.

This study presents narrow-band measurements of the mobile vehicle-to-vehicle propagation channel at 5.9 GHz, under realistic suburban driving conditions in Pittsburgh, Pennsylvania. Our system includes differential Global Positioning System (DGPS) receivers, thereby enabling dynamic measurements of how large-scale path loss, Doppler spectrum, and coherence time depend on vehicle location and separation. A Nakagami distribution is used for describing the fading statistics. The speed-separation diagram is introduced as a new tool for analyzing and understanding the vehicle-to-vehicle propagation environment. We show that this diagram can be used to model and predict channel Doppler spread and coherence time using vehicle speed and separation.

In this paper we derive the generalized likelihood ratio test (GLRT) for time reversal detection. We consider a multistatic array configuration with two antenna arrays, one for transmitting and one for receiving. We examine the time reversal GLRT performance with experimental measurements in the electromagnetic domain in a highly cluttered laboratory environment. The experiments show that time reversal provides significant performance gain over the conventional energy detector.

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.

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.

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.

In this paper, we present an innovative solution to the handover problem in multi-story buildings using HVAC ducts for wireless communications. The proposed solution is based on a new system architecture design of the indoor wireless networks that use the heating, ventilation, and air conditioning (HVAC) ducts as a communication channel. Exploiting the system architecture design and the time diversity at the mobile terminal, we show that intra-floor handover can be eliminated, while inter-floor handover can be substantially reduced due to the fact that multiple floors can be served via the same access point. Our results indicate that the mean number of handovers per call achieved in the indoor wireless networks that use HVAC ducts reduces; e.g., by up to a factor of nine for the illustrative example considered in this paper compared to that of indoor wireless networks that do not use HVAC ducts. The improvement; i.e., reduction in the mean number of handovers in multi-story building, depends on the number of access points used.

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.

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.

We report theoretical channel capacity estimates of heating, ventilation, and air-conditioning (HVAC) ducts based on multi-carrier transmission that uses M-QAM modulation and measured channel responses at 2.4 GHz Industrial, Scientific, and Medical (ISM) band. It is shown that, data rates in excess of 1 Gbps are possible over distances up to 500 m in "matched" ducts (one can think of "matched" ducts as user-friendly ducts, since "matching" can, in principle, eliminate all the multipath reflections in HVAC ducts). Our work also shows that data rates in excess of 300 Mbps are possible over distances up to 500 m even in the presence of significant multipath reflections.

High data rate wireless communications links use highly bandwidth efficient modulations to get the most from the limited spectrum available. Many of these schemes are complex, requiring large amounts of computation and hardware complexity to accomplish their tasks. This paper presents a method by which a high data rate, short-range, unlicensed wireless link is obtained using a modulation with low bandwidth efficiency to ensure that the radiated power spectral density is below maximum allowed levels. An experimental ultrawideband system is described that is capable of transmitting up to 600 Mbps over distances of a few meters.

There is an increasing presence of wireless LAN devices in the ISM band. Co-located operation of these devices causes mutual interference and performance degradation. This paper presents experimental results of interference measurements between sample Bluetooth and IEEE 802.11b DS-SS devices.