BARRACLOUGH, Kristan (1 Bell Court, Romsey Hampshire SO51 8JR, GB)
CHAPMAN, Thomas Malcolm (68 Montgomery Road, Bitterne, Southampton Hampshire SO18 4RY, GB)
BARRACLOUGH, Kristan (1 Bell Court, Romsey Hampshire SO51 8JR, GB)
| CLAIMS
1. A counting method for a single frequency broadcast network comprising at least one base station and a plurality of terminals, the method comprising counting the number of terminals in a cell of the base station, which terminals require broadcast services; counting the number of terminals in surrounding cells of surrounding base stations, which terminals require broadcast services; and determining whether the number of terminals in any of the cells is sufficient for the base station to use a broadcast transmission.
2. A method according to claim 1, wherein the base station first counts terminals in its own cell; then counts terminals in one or more surrounding cells; and wherein a base station of any cell which determines that it has insufficient terminals to justify a broadcast transmission notifies base stations in the surrounding cells that it will use a point to point transmission in its cell.
3. A method according to claim 1 or claim 2, wherein the surrounding cell is an adjacent cell.
4. A method according to any preceding claim, wherein in the synchronised single frequency networks a count occurs at a specified time, such that surrounding cells reduce their transmissions and listen to a count in the cell.
5. A method according to claim 4, wherein the base station notifies surrounding base stations that it is about to perform a count at the specified time, in order that the surrounding base stations can listen to the counting responses
6. A method according to any preceding claim, wherein power levels of counting responses from each terminal are predetermined and known to each base station and surrounding base stations are able to use received power levels of the counting responses, together with the number of terminals counted, to determine whether a broadcast is required.
7. A method according to any preceding claim, whereby the broadcast is transmitted using the Multimedia Broadcast & Multicast (MBMS) protocols. |
ACOUNTING METHOD FOR A MOBILE BROADCAST NETWORK
This invention relates to a counting method for a single frequency broadcast network. For broadcast soft combining in single frequency network (SFN), for example as applied in Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN) long term evolution (LTE), or evolved UTRAN, there may be a need for a particular cell to make a broadcast, generally by transmitting point to multipoint (PtM) even though there are no terminals in the cell. An example of a broadcast service is multimedia broadcast multicast service (MBMS), although the present invention is not limited to services of this type. There may be terminals within neighbouring cells that are benefiting from the MBMS power from the target cell using soft combining. If the target cell were to stop transmitting MBMS and start transmitting something else, then there would be a double penalty for such user equipments (UEs), arising from the loss of broadcast signal energy and the increase in neighbour cell interference from any other signal that is sent instead. If there are no nearby UEs that would benefit from SFN from the target cell then it is a waste of resources to transmit PtM MBMS unnecessarily.
In wideband code division multiple access (WCDMA) MBMS, it is only possible to count UEs in the Node Bs own cell. However, the architecture of WCDMA means that a radio network controller (RNC) is able to co-ordinate such information.
In accordance with the present invention, a counting method for a single frequency broadcast network comprising at least one base station and a plurality of terminals comprises counting the number of terminals in a cell of the base station, which terminals require broadcast services; counting the number of terminals in surrounding cells of surrounding base stations, which terminals require broadcast services; and determining whether the number of terminals in any of the cells is sufficient for the base station to use a broadcast transmission.
Even if there are no terminals in its own cell, if there are sufficient terminals in a surrounding cell that require broadcast services, a base station in an empty cell of a single frequency network may still make a point to multipoint broadcast transmission to give those terminals the benefit of constructive combining of the signal.
Preferably, the base station first counts terminals in its own cell; then counts terminals in one or more surrounding cells; and wherein a base station of any cell which determines that it has insufficient terminals in its own, or surrounding cells to justify a broadcast transmission notifies base stations in the surrounding cells that it will use a point to point transmission in its cell.
Situations where a cell has no terminals itself and very few in its immediately surrounding cells are unlikely to justify the use of point to multipoint, or broadcast transmission, so the base stations in the vicinity communicate to agree that only a point to point transmission is required from that base station to the terminal in the surrounding cell.
Preferably, the surrounding cell is an adjacent cell. Surrounding cells are not limited to being adjacent, but adjacent cells will typically have more impact than those further away.
Preferably, in the synchronised single frequency networks a count occurs at a specified time, such that surrounding cells reduce their transmissions and listen to a count in the cell.
Preferably, the base station notifies surrounding base stations that it is about to perform a count at the specified time, in order that the surrounding base stations can listen to the counting responses Preferably, power levels of counting responses from each terminal are predetermined and known to each base station and surrounding base stations are able to use received power levels of the counting responses, together with the number of terminals counted, to determine whether a broadcast is required.
If a terminal's counting response has a very weak power when received, indicating that it is further away, the surrounding base station is more likely to ignore that terminal in determining whether it should use a broadcast transmission, than if a strong response is received, so in combination with the straight count, an improved decision is made on whether to use a point to multipoint, or broadcast transmission in an otherwise empty cell. Preferably, the broadcast is transmitted using the Multimedia Broadcast &
Multicast (MBMS) protocols.
These protocols are defined in 3GPP.
An example of a counting method for a single frequency broadcast network in accordance with the present invention will now be described with reference to the accompanying drawings in which:
Figure 1 illustrates a first scenario in which the method of the present invention is applied;
Figure 2 illustrates a second scenario in which the method of the present invention is applied; and,
Figure 3 illustrates a third scenario in which the method of the present invention is applied. In the present invention, a counting method is applied in order to determine whether a base station of a cell should transmit a broadcast, a point to point transmission, or no transmission. If a cell has any terminals within it, then a broadcast would be made by that cell. However, for surrounding cells, the decision is less clear- cut, so the method of the present invention is applied. Surrounding cells can include cells which have no direct border with a cell containing a terminal, but might still have some impact on that terminal if the base station of the surrounding cell transmits.
The examples described below are made with reference to MBMS for UTRAN LTE or eUTRAN, but the invention also applies to other systems with a similar broadcast protocol defined, for example wireless interoperability for microwave access (WiMAX), or wireless local area network (LAN). Another possible application is in broadcast systems currently using SFN without counting, such as digital video broadcast - handheld (DVB-H).
In Fig. 1, there are a number of cells 1 to 10, all of which either contain a terminal, or are close enough to a terminal in a bordering cell to need to transmit, even although the cell itself is empty. For example, cells 1, 3, 4, 7 have terminals within them, so they will transmit. The other cells 2, 5, 6, 8, 9, 10 have a boundary with a cell which contains a terminal. When the base stations of one of the surrounding cells 8, 9, 10 transmit, there is some benefit to terminals 12, 13 in cell 1 as well as to terminals 14, 15, 16 in neighbouring cells 3, 4. The effect of the transmission from surrounding cells 8, 9, 10 is reduced for terminal 11 in cell 7 which is somewhat further away.
In Fig. 2, another example is given in which terminals 17, 18, 19 are clustered in cell 3 and one terminal is present in cell 4. In this case lower cells 6, 7 have no terminals nearby, so do not need to participate in the single frequency network
transmission, but cells 1, 2 and 5 are close enough to have some effect, so the base stations in those cells do transmit a broadcast for the benefit of the terminals.
Fig. 3 illustrates an example where, in addition to terminals 23, 24, 25, 22 in cells 3, 4 there is a single terminal 21 present at the bottom of cell 6. Since only that one terminal 21 would benefit from SFN signals from the lower cells 6, 7 then terminal 21 is served by a point to point transmission from cell 6 in order that the lower cells do not need to broadcast using point to multipoint.
In the present invention, the decision on whether or not to broadcast from a cell is based on counting the number of terminals in the cell and in surrounding cells. In addition, the received power level provides further refinement.
Neighbouring base stations or Node Bs of the cell are made aware of when another Node B plans to undertake an MBMS counting procedure. When the counting is due to take place, the neighbouring cells reduce the amount of uplink transmissions in their own cells and listen for counting responses in the counting cell. UEs transmit counting responses at a known power level. Hence by listening to the counting responses and examining the received power levels, neighbour Node Bs are able to determine how many UEs there are in neighbour cells that would benefit from the cell transmitting PtM MBMS in SFN.
The advantage is a more efficient management of radio resources, in which Node Bs in an SFN network do not transmit SFN MBMS where not necessary, but are able to take into account the reception requirements of UEs in neighbour cells, but close to the cell borders.
Typically, the UEs transmit counting responses with a known power level. The information obtained on the number and positions of MBMS UEs in neighbour cells can be used by a cell in order to decide whether it is helpful to transmit point to multipoint MBMS.
The present invention provides a counting procedure, which can be used for MBMS, or for other defined broadcast protocols, in which the counting base station informs base stations in surrounding cells of the proposed timing of the count and the surrounding base stations respond by reducing the amount of uplink transmissions in their own cells during the counting time and listening to the responses of terminals in the counting cell. Other examples of applications for such a counting and power level related procedure include WiMAX, WLAN, or DVB-H.
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