Efficient means of sending location information on a bandwidth limited channel
Original Publication Date: 2014-Oct-22
Included in the Prior Art Database: 2014-Oct-22
Henderson Jr, Alan: INVENTOR [+2]
The idea is to map the site coverage area onto a 255x255 grid. Depending on the coverage pattern, the grid may be square or rectangular to fit the coverage although other shapes could be considered for ease of distance calculations. The Trunking Control Channel station(s) at the site would transmit the GPS coordinates of the center grid location and the size of an individual grid. The subscriber would determine the grid it is located in based on the difference between the its GPS coordinates and the center grid's GPS coordinates and the size of the grid. This subscriber sends in its grid location with any registration or ptt request data or with its voice steam as a 2 byte grid number based on how many grids North(+)/South(-) it is from the station and how many grids East(+)/West(-) it is from the station. A coverage radial for a site can range from 5 miles to 30 miles. At 5 miles, the grid size is 103.5x103.5 ft (5*5280 ft per mile/255). At 30 miles, the grid size is 621x621 ft. From the site the location data can be sent to the ZSS with the RF quality information and then to TRACES. Another way to build this feature is to have the Site controller format the Unit ID, Computed location (based on the Site's location info and the grid number) and site time stamp and send it as a Datagram up to the PDG to feed other subscriber location apps.
By James Alan Henderson, Jr and George R Economy
Motorola Solutions, Inc.
This publication describes a method for a subscriber to send in its approximate location during a transmission using minimal channel bandwidth. Its grid location is based on a grid layout whose properties are transmitted by a central base station and the subscriber’s GPS-determined location. The method allows flexibility in designing a grid system to best describe the RF coverage area and provides tradeoffs between bandwidth efficiency and location resolution.
Today, subscriber location tracking on a Land Mobile Radio system is done via a data service. The subscribers send in their location data at a chosen cadence of between 30 seconds to 2 minutes using 9 byte data packets on a data channel. If the location of a subscriber during a voice transmission is required, a fixed end or dispatch user has to interpolate between the last location received and the next or one that follows the end of the current transmission. For other system managers, the cost to support additional data channels is both prohibitive and provides more precise data location than they require.
A method is needed to efficiently provide a subscriber’s location within a small bounded area while it is making any type of transmission.
The method described herein provides the means for a RF site to provide the subscriber with a grid-based description of its provided coverage area. It also provides the means for the subscriber to send in its approximate location within that grid system during any inbound transmission using very little RF bandwidth.
The most basic bandwidth efficient method has the site coverage area mapped onto a 255x255 grid. The grid is constructed such that the outer ring of cells is outside of the coverage area as shown in Figure 1. Depending on the coverage pattern, the grid may be square or rectangular to fit the coverage although other shapes could be considered for ease of distance calculations.
Periodically the Trunking Control Channel station(s) at the site transmits the GPS coordinates of the center grid location and the size and number of the individual grids.
The subscriber determines the grid it is located in based on the difference between its GPS coordinates and the center grid's GPS coordinates and the size of the grids.
The subscriber sends in its grid location with any inbound transmission as a 2 byte grid number based on how many grids North(+)/South(-) it is from the grid center and how many grids East(+)/West(-) it is from the grid center.
The process is shown in Figure 2.
. If the subscriber is outside of coverage, it will transmit in a location with at least one of the grid coordinates as +/-127. The receiving end can still determine a vector along with the user can be found but the user’s actual distance from the center would be unknown....