System Feature Overview 51
68007024085 April 2011
2.4.3.5 Enhanced GPS Revert Channel
The Enhanced GPS Revert channel is an enhancement of the GPS Revert channel functionality
that supports higher throughput and increased reliability. Similar to the former feature, a subscriber
offloads location responses routed to a server, to a revert channel. The primary difference lies in
the method a subscriber accesses the channel. In the GPS Revert channel feature, subscribers
access a channel in a desynchronized manner and may therefore cause transmission collisions.
The probability of collision increases with the number of transmissions made over the channel and
collisions adversely affect the reliability of transmissions.
This enhanced feature enables subscribers to access a channel in a synchronized manner, which
eliminate collisions and allow them to use the channel efficiently. The synchronization between
subscribers is achieved by a repeater that divides a logical channel into groups of contiguous
bursts defined as “windows”. This allows subscribers to make reservations for these windows in
which GPS data can be transmitted. This is a slot wide configuration. The windowed data structure
consists of an eight minute data superframe. Within the eight minute data superframe, there are 16
data frames, each 30-second in duration This data superframe is repeated over and over again.
Both the data frame and superframe always have the same size for every windowed GPS Revert
channel.
Within a 30-second data frame, there are windows that can be reserved by subscribers for GPS
data transmission. The number of windows within a 30-second data frame depends on the size of
each window. A window consists of an announcement slot in the beginning followed by bursts of
GPS data. The diagram below illustrates the windowed data structure for a window size of six (one
announcement + five bursts of GPS data).
Enabled Enabled None
GPS Chip: Enabled
Presence: Enabled
Location: Disabled
Enabled Enabled
Selected (Channel1)
GPS Chip: Enabled
Presence: Enabled
Location: TX on Channel1
GPS1
GPS Chip: Enabled
Presence: Enabled
Location: TX on GPS1
Note: Not Selectable means the setting cannot be configured as the option is grayed out.
General
Settings: GPS
Channels:
Zone1
Channel1
ARS
Channels:
Zone1
Channel1
GPS Revert
Result
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