A Wireless Alternative to Traffic Management LVACTS Project

The future of wireless traffic management systems has been installed in the city of Las Vegas. The Las Vegas Area Computer Traffic System (LVACTS) is designed to monitor and control 48 of the busiest intersections in the city. Developed by AML Wireless Networks in partnership with the Nevada DOT, Barton-Aschman Associates and Fischbach and Moore Traffic Systems Group, the microwave trunk network was accepted by the customer July 29, 1997 after successfully completing a 30 day system verification test. The network delivered a reliability of 99.99% over the test period.

The Las Vegas microwave trunk network is comprised of 10 control zones and one master control center. Using technology developed and supplied by AML Wireless Networks, 18 GHz microwave radios are used to transport 27 channels using QPSK digital modulation. The decision to use microwave for the network backbone expedited the deployment of the traffic system, while providing the reliability required by the Nevada DOT.

This microwave system represents a landmark for future ITS systems. State-of-the-art broadband wireless technology is used to provide a two-way, full duplex monitoring and control system at a fraction of the cost of a hard-wired network. The real time multi-channel video provides the Nevada DOT an advantage in improving the city's traffic logistics. The design has the flexibility to expand the microwave portion to surrounding areas, and integrates with existing fiber and coaxial networks. The system is also ready for digital video should the need arise in the future.

The LVACTS microwave trunking network operates in the 18.14 - 18.58 GHz spectrum, allocated by the FCC for private video transmission. The spectrum can be used to carry video, voice, or data for distances up to 10 miles. Based on the NTSC channel system, the spectrum has the capacity for 72 video channels. Microwave signals tend to be hindered somewhat by atmospheric absorption and rain attenuation, but these effects can be minimized through proper system design.

AML Wireless Networks (formerly Hughes AML) has over 30 years of experience in providing solutions to any video, voice, or data signal distribution requirement. This is not a new or untried technology, this same technology has been used by the CATV industry for years to provide signal distribution in cable systems. AML Wireless pioneered this technology in 1969 and has built and installed 100's of systems worldwide. This is just a natural progression of this technology into emerging markets.

The advantage of using 18 GHz for ITS applications is the available bandwidth, lower equipment costs, and a simplified set-up. The LVACTS system uses monopoles with outdoor microwave radios mounted directly behind the antennas. A cabinet at the base of each zone's monopole houses the video and data processing equipment. Frequency diversification and alternating polarizations provide the system with a two-way capability in a fully redundant design. The redundancy option ensures that the system meets the customer's requested reliability.

Live roadside video feeds are interconnected with the controllers at each zone using existing twisted pair infrastructure. Where no twisted pair wire exists, narrowband FM microwave radios have been deployed to transport the video and audio signals. The wireless links provide LVACTS with a low cost alternative to a traditionally hard-wired solution. Single-channel 31 GHz radios with their integrated antennas are ideally suited to traverse the short distances between the remote traffic cameras and the control zone cabinets. A video matrix switch at the control zone cabinet consolidates the video feeds.

Compared to negotiating right-of-ways and installing hard-wired systems, the broadband wireless alternative requires minimal infrastructure costs and offers a quick implementation. It also provides an alternative for integrating areas with terrain constraints into existing ITS networks. Wireless technology has a proven track record within other industries and projects like LVACTS are providing its viability within the ITS market.

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