Enhanced GPS

Enhanced GPS, or more broadly, Enhanced GNSS (Global Navigation Satellite System) is an enhancement of the GPS Revert Channel functionality that supports higher throughput and increased reliability for location updates. It specifically aims to reduce over the air collisions among radios sending location data, that normally occurs when standard GPS Revert Channel is used due to desynchronized access. It ensures effective and efficient channel use by ensuring radios access the channel in a synchronized manner.

This synchronization is achieved by a repeater by dividing a logical channel into groups of contiguous bursts defined as "windows", allowing radios to make reservations for transmitting location data.

Functionality and Mechanism

• The repeater creates a windowed data structure consisting of an eight-minute data superframe, which contains 16 data frames, each 30 seconds long. This superframe repeats continuously.
• Within each 30-second data frame, there are "windows" that subscribers can reserve for GPS data transmission. The number of windows depends on the size of each window.
• A window typically includes an announcement slot followed by bursts of GPS data.
• Before sending location data, a subscriber requests a window from the repeater (either for a one-time or periodic update). The repeater allocates available window(s) and informs the subscriber. The subscriber then stores this timing, reverts to the Enhanced GPS Revert Channel before its allocated window, verifies the reservation with a confirmation grant from the repeater, and finally sends its location response in the reserved window.
• Since subscribers only transmit in their reserved windows, collisions are eliminated.

The benefits of using Enhanced GPS include:

• Drastic reduction of collisions among subscribers sending GPS data leads to increased reliability.
• Supports a higher number of location responses per minute per repeater (e.g., up to 360 location responses per minute per repeater using both slots at 90% capacity for IP data, or 900 for High Efficiency Data).
• By offloading location responses to a dedicated revert channel, it frees up the primary (selected) channel for increased voice loads and other traffic, enhancing user experience by reducing channel busies.
• Allows users to choose the most appropriate window size based on location response characteristics.

Enhanced GPS is supported exclusively in repeater mode - both trunked and conventional.

See Also

• Data Revert Channel
• GNSS
• LRRP