Provision of additional traffic capacity by slot punching
Original Publication Date: 2010-Jul-31
Included in the Prior Art Database: 2010-Jul-31
Chater-Lea, Dave: INVENTOR [+2]
TETRA is a TDMA system where information is carried in discrete slots of information. It already allows for slots to be stolen within circuit mode channels to send additional signalling or data, and the receiving radios can recover from missing audio frames caused by this, or by signal loss. This invention makes use of the ability of a receiving radio to recover from a frame loss. Slots are regularly punched out from many or all of the allocated downlink circuit mode traffic channels on a site in a regularly advancing pattern, and an extra one or more calls is allocated to the stolen pattern of frames.
Provision of additional channel capacity by slot punching
By Author’s Dave Chater-Lea, Dean Dyson
Government and Public Safety business
This concept provides a means of gaining additional channel capacity on a multiple channel base station on a digital trunked radio system. The concept relies on wanted information being carried in timeslots (or ‘slots’) of information, and therefore is particularly suited to a TDMA radio system, although it could be applied on an FDMA radio system if information on traffic channels is regularly segmented into discrete slots.
The concept operates by periodically punching out slots from existing calls (i.e. stealing information from those calls) in a round robin manner, and to use this capacity to build new virtual channels to carry additional calls, or to carry additional signalling information. The existing underlying calls mitigate for the lost capacity. The mitigation process may be assisted by information provided by the infrastructure.
Base stations are speech traffic capacity limited according to the number of available circuit mode traffic channels. Whereas the traffic channel capacity of a base station may be designed to provide a particular grade of service under normal peak loading conditions, there can be times of exceptional load which exceed the planned capacity of this site. These load excesses reduce the grade of service below the designed value, and cause calls to be excessively queued or dropped.
A related problem occurs where there is much demand for downlink channel capacity for speech calls, and much demand for uplink capacity for short data transmissions. In general, if the uplink and downlink of a physical channel can be allocated to separate calls, the uplink short data transmissions can be sent on the same physical channels as downlink speech group calls. However where the downlink is occupied with speech, there can be insufficient capacity available to acknowledge the uplink short data transmissions.
A solution is needed to allow some of the additional peak load to be absorbed by the base station without requiring the addition of extra physical channels, and to provide sufficient downlink control capacity to acknowledge uplink data messages within the existing physical channel capacity of the base station.
A TDMA system such as TETRA carries information in discrete slots. It already allows for slots to be stolen within circuit mode channels to send additional signalling or data, and the receiving radios can recover from missing audio frames caused by this, in the same way that they can recover from frames lost due to signal loss.
This invention makes use of the ability of a receiving radio to recover from a frame loss. Slots will be regularly punched out from many or all of the allocated downlink circuit mode traffic channels on a site in a regularly advancing pattern, and the capacity obtained can be used to allocate one o...