Rooftop Antennas Research Articles

Empirical Study and Modeling of Vehicular Communications at Intersections in the 5 GHz Band

Event warnings are critical in the context of ITS, being dependent on reliable and low-delay delivery of messages to nearby vehicles. One of the main challenges to address in this context is intersection management. Since buildings will severely hinder signals in the 5 GHz band, it becomes necessary to transmit at the exact moment a vehicle is at the center of an intersection to maximize delivery chances. However, GPS inaccuracy, among other problems, complicates the achievement of this goal. In this paper we study this problem by first analyzing different intersection types, studying the vehicular communications performance in each type of intersection through real scenario experiments. Obtained results show that intersection-related communications depend on the distances to the intersection and line-of-sight (LOS) conditions. Also, depending on the physical characteristics of intersections, the presented blockages introduce different degrees of hampering to message delivery. Based on the modeling of the different intersection types, we then study the expected success ratio when notifying events at intersections. In general, we find that effective propagation of messages at intersections is possible, even in urban canyons and despite GPS errors, as long as rooftop antennas are used to compensate for poor communication conditions.

Experimental evaluation of theperformance of 2×2 MIMO-OFDM for vehicle-to-infrastructure communications

In this paper, a novel 2×2 multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) testbed based on an Analog Devices AD9361 highly integrated radio frequency (RF) agile transceiver was specifically implemented for the purpose of estimating and analyzing MIMO-OFDM channel capacity in vehicle-to-infrastructure (V2I) environments using the 920 MHz industrial, scientific, and medical (ISM) band. We implemented two-dimensional discrete cosine transform-based filtering to reduce the channel estimation errors and show its effectiveness on our measurement results. We have also analyzed the effects of channel estimation error on the MIMO channel capacity by simulation. Three different scenarios of subcarrier spacing were investigated which correspond to IEEE 802.11p, Long-Term Evolution (LTE), and Digital Video Broadcasting Terrestrial (DVB-T)(2k) standards. An extensive MIMO-OFDM V2I channel measurement campaign was performed in a suburban environment. Analysis of the measured MIMO channel capacity results as a function of the transmitter-to-receiver (TX-RX) separation distance up to 250 m shows that the variance of the MIMO channel capacity is larger for the near-range line-of-sight (LOS) scenarios than for the long-range non-LOS cases, using a fixed receiver signal-to-noise ratio (SNR) criterion. We observed that the largest capacity values were achieved at LOS propagation despite the common assumption of a degenerated MIMO channel in LOS. We consider that this is due to the large angular spacing between MIMO subchannels which occurs when the receiver vehicle rooftop antennas pass by the fixed transmitter antennas at close range, causing MIMO subchannels to be orthogonal. In addition, analysis on the effects of different subcarrier spacings on MIMO-OFDM channel capacity showed negligible differences in mean channel capacity for the subcarrier spacing range investigated. Measured channels described in this paper are available on request.

Video Over LTE: Exploring Efficiency in Distribution

Interest in LTE Broadcast technology is increasing rapidly. With consumer desire for Anywhere at an all-time high, more and more leading mobile operators are trialling the LTE Broadcast technology within their networks to start identifying different use-cases and scenarios globally to explore its business potential. Broadcasting is efficient usually if more than one user is receiving from one transmitter. Roof top reception enables a wide reach from High-Power High Tower (HPHT) transmitters, so that broadcasting is efficient for popular TV programs, particularly if transmitters operate in Single Frequency Network (SFN) mode. LTE, including LTE Broadcast, is currently designed to operate on Low Power Low Tower (LPLT) networks. This paper discusses the spectral efficiency and flexibility of LTE Broadcast, which is only efficient when several devices receive the same content stream. Unicast is much more efficient for less popular, so called long-tail content. At times when there is only low interest in a certain part of the network, the infrastructure can stop the broadcast and use the resources for unicast content delivery and use the spare resources for mobile broadband (MBB). Furthermore, the implications of differences in replacement cycles of fixed TV receivers and mobile devices are discussed. A signal adapted to the high radio signal quality of roof-top antennas should be used for the legacy technologies supporting fixed receivers, whereas a signal adapted to the low radio signal quality typical for mobile reception is required. Thus, it is essential to use the most efficient technologies soon after ratification of the standards. Finally, we outline a potential use of existing roof-top antenna installations for LTE modems that can be used for TV distribution and beyond.

Impact of Low-Frequency Radar Interference on Digital Terrestrial Television

This paper considers low-frequency radar cohabitation with digital video broadcasting terrestrial (DVB-T). The spatial and temporal radio frequency propagation characteristics of the terrestrial and air-to-ground channels are modeled using state-of-the-art 3-D ray tracing for real-world broadcast television scenarios. Rooftop DVB-T receivers are assumed at user locations in two different urban environments, namely, the cities of London and Bristol, U.K.. The propagation characteristics are combined with appropriately orientated 3-D antenna radiation patterns, which include full polarization information for the DVB-T rooftop antennas, the base-station antennas, and the airborne radar antennas. A radar waveform generator is used to synthesize a representative range of radar signals. A DVB-T physical layer simulator has been developed to predict the performance of the received broadcast stream at each rooftop location. Factors, such as additive noise, the power and structure of the wanted DVB-T and the interfering radar signals, and the nature of the radio channels, are shown to influence the DVB-T bit error rate results. Statistics for the probability of high-quality DVB-T reception are reported as a function of the modulation scheme, propagation environment, aircraft orientation, radar antenna array configuration, and radar waveform type.

Modeling the interference generated from car base stations towards indoor femto-cells

In future wireless networks, a significant number of users will be vehicular. One promising solution to improve the capacity for these vehicular users is to employ moving relays or car base stations. The system forms cell inside the vehicle and then uses rooftop antenna for backhauling to overcome the vehicular penetration loss. In this paper, we develop a model for aggregate interference distribution generated from moving/parked cars to indoor users in order to study whether indoor femto-cells can coexist on the same spectrum with vehicular communications. Since spectrum authorization for vehicular communications is open at moment, we consider two spectrum sharing scenarios (i) communication from mounted antennas on the roof of the vehicles to the infrastructure network utilizes same spectrum with indoor femto-cells (ii) in-vehicle communication utilizes same spectrum with indoor femto-cells while vehicular to infrastructure (V2I) communication is allocated at different spectrum. Based on our findings we suggest that V2I and indoor femto-cells should be allocated at different spectrum. The reason being that mounted roof-top antennas facing the indoor cells generate unacceptable interference levels. On the other hand, in-vehicle communication and indoor cells can share the spectrum thanks to the vehicle body isolation and the lower transmit power levels that can be used inside the vehicle.

On the Provisioning of Mobile Digital Terrestrial TV Services to Vehicles With DVB-T

Most of the DVB-T (Digital Video Broadcasting -Terrestrial) networks deployments worldwide have been designed for fixed rooftop antennas and high transmission capacity, not providing good coverage level for vehicular mobile reception. This letter analyses how to combine different technical solutions, so far studied individually, in order to increase the robustness of the transmission for vehicular reception to provide in-band mobile services. In particular, we consider: receive antenna diversity, hierarchical modulation, and Application Layer– Forward Error Correction (AL-FEC). Performance evaluation results have been obtained by means of simulations, laboratory tests, and field measurements in the commercial DVB-T network of the city of Valencia (Spain). The paper shows that the combined usage of these solutions can compensate the impairments caused by the mobility of the receivers, such as signal fast fading, Doppler shift, the poor coverage at ground level and the utilization of lower gain antennas; being possible to provide mobile DVB-T services to vehicles in networks dimensioned for fixed rooftop reception.

Information raining and optimal link-layer design for mobile hotspots

In this paper, we propose a link layer design for mobile hotspots. We design a novel system architecture that enables high-speed Internet access in railway systems. The proposed design uses a number of repeaters placed along the track and multiple antennas installed on the roof of a vehicle. Each packet is decomposed into smaller fragments and relayed to the vehicle via adjacent repeaters. We also use erasure coding to add parity fragments to original data. This approach is called information raining since fragments are rained upon the vehicle from adjacent repeaters. We investigate two instances of information raining. In blind information raining, all repeaters awaken when they sense the presence of the vehicle. The fragments are then blindly transmitted via awakened repeaters. A vehicle station installed inside the train is responsible for aggregating a large enough number of fragments. In the throughput-optimized information raining, the vehicle station selects a bipartite matching between repeaters and roof-top antennas and activates only a subset of the repeaters. It also dictates the amount of transmission power of each activated repeater. Both the bipartite matching and power allocations are individually shown to be NP-complete. Matching heuristics based on the Hungarian algorithm and Gale-Shapley algorithm are proposed. A simplex-type algorithm is proposed as the power allocation heuristics.

A new approach to 3-D ray tracing for propagation prediction in cities

A vertical-plane-launch (VPL) technique for approximating a full three dimensional (3-D) site-specific ray trace to predict propagation effects in cities for frequencies in the 300 MHz-3-GHz band is described and its predictions are compared with measurements for Rosslyn, VA. The VPL technique employs the standard shoot and bounce method in the horizontal plane while using a deterministic approach to find the vertical displacement of the unfolded ray paths. This approximation is valid since building walls are almost always vertical. The VPL method shows significant improvement compared with the slant-plane/vertical-plane (SP/VP) method for rooftop antennas. For a base station located at street level, the VPL method gives better predictions than the two-dimensional (2-D) method in locations where propagation over buildings is significant.

Versorgungsaspekte bei der digitalen terrestrischen Ton- und Fernsehrundfunkübertragung

For terrestrial broadcast services the reception situation at the border of the coverage area on principle is a problem which affects different coverage aspects. It is reasonable to have a graceful degradation for mobile reception of digital audio services at the edge of the coverage area, but for stationary reception it is only interesting whether a digital service can be received error-free or not at all. Furthermore, there is a big difference in the reception probability between portable receivers and receivers with directional roof-top antennas. This implies difficulties for the definition of a coverage area. The present contribution deals with coverage aspects of digital terrestrial audio and television broadcasting in general. Especially, it emphasises the possibility of the new specification for digital terrestrial video broadcasting (DVB-T) to increase the coverage probability for portable reception on the base of a hierarchical modulation. The coverage probability is determined for a regular single frequency network (SFN) on the basis of 'Monte Carlo' simulations.

A concept of digital terrestrial television broadcasting

The future terrestrial television broadcasting system should support the transmission of a digital HDTV signal with a high spectral efficiency. In addition, this system should maintain graceful degradation as the actual analog systems, and should be compatible with the SDTV. The system compatibility can be achieved by using a hierarchical HDTV source-coding scheme that can provide at least two (HDTV, SDTV) or three (HDTV, EDTV, SDTV) hierarchy levels: SDTV image quality will be expected for portable receivers, and HDTV/EDTV image quality will destinate to stationary receivers with roof-top antennas. Taking into account the receivers' antenna gains and the different channel conditions, there will be a difference of 25–30 dB between the received powers of the stationary and the portable receivers. Therefore, the design of a powerful and a suitable transmission scheme for the future broadcasting of the digital HDTV signal will be a technological challenge. In this article we describe a concept of a flexible reconfigurable hierarchical digital terrestrial TV broadcasting system for clear and taboo channels. The flexibility of the proposed scheme easily permits the receivers to support different reconfigurable modes: One HDTV program or multi-programming EDTV or SDTV (for fixed receivers up to 5 × SDTV in clear and up to 2 × SDTV in taboo channels; for portable receivers up to 2 × SDTV.) The system achieves a high interoperability with the Satellite Baseline system. It maintains a graceful degradation and provides a hierarchical complexity. It is based on a concatenated coding scheme. The inner code of the concatenated coding scheme is combined with multi-resolution modulation. The basic constellation is a 64-QAM, which will be operated in clear channels. It can be reconfigured to a 16-QAM in the case of taboo channels. The principle of OFDM with very rugged frequency/time synchronization mechanisms is used to combat the frequency selectivity and the co-channel interference (CCI) in the channel. Known pilot symbols are sent regularly in order to perform coherent detection.