Los Angeles FOT Spread Spectrum Radio Traffic Signal Interconnect Evaluation Task: Final Report on Full Deployment

Problem

Spread spectrum radio networks (SSRN) are an alternative to hard-wired methods of traffic monitoring and control which take less time and money to build and maintain. How well do they work? Los Angeles needs to connect 2000 intersections to its existing traffic control system (which already controls 2000 intersections via hard-wired links) so USC set up a field operation test in the Mar Vista area to implement and test the reliability and cost effectiveness of SSRN.

The radio links are arranged in a network of cells, each consisting of one headend radio hard-wired to the control center and up to 31 remote radios hard-wired to intersection controllers.

Findings

The overall performance of the system is satisfactory. It can send large amounts of information reliably through the network, with an average signal throughput of 90 percent, which is satisfactory, but can be improved. The automatic network reconfiguration in the presence of failed and poor links also worked well.

Some channels are busier and less reliable than others; in fact one particular channel (7) was very busy with other radio traffic and so was eliminated from the choices used in this area. Some antenna locations work better than others, and antennas that were mounted high enough to create visual line-of-sight connection provided high quality links between units. Some mounting options work better than others, depending on the particular location, although sometimes a choice must be made between signal loss or durability and ease of maintenance. Also, some units had a problem with polarization, which was solved with the use of a special antenna.

Recommendations include the use of an exclusive radio band to increase throughput, and taller posts for antennas to get the best possible line-of-sight connection.