POWER CONTROL OF POINT TO
MULTIPOINT PHYSICAL CHANNELS
CROSS REFERENCE TO RELATED
This application claims priority from U.S. provisional application No. 60/400,602 which was filed on Aug. 1, 2002, which is incorporated by reference as if fully set forth.
FIELD OF INVENTION
The present invention relates to wireless communications. More specifically, the present invention relates to power control for point to multipoint (PtM) services. 15
BACKGROUND OF THE INVENTION
There is a growing desire to use point to multi-point services in wireless communication systems. In point to multi- 2o point (PtM) services, one service is sent from a single point, such as a base station, to multiple points, such as multiple wireless transmit/receive units (WTRUs). Examples of point to multi-point services are multimedia broadcasts and multicast services. 25
In traditional point to point (PtP) services, power control allows for efficient use of radio resources. Power control allows a particular wireless transmit/receive unit (WTRU) to receive the PtP service at a desired quality of service (QoS) and minimize interference to other WTRUs. 30
In PtP, such as for the third generation partnership project (3GPP), when the WTRU's dedicated downlink physical channel is power controlled, that WTRU typically determines a target signal to interference ratio (SIR) based on the received block error rate (BLER) of the dedicated physical 35 channel. The WTRU estimates the received dedicated physical channel's SIR. One approach to determine the SIR is as the ratio of received signal code power (RSCP) over the interference signal code power
When the WTRU determines that the SIR target value is 40 greater than the calculated estimate of the received SIR value, the WTRU signals via the transmit power control (TPC) commands to the base station to increase transmit power of the downlink dedicated channel. When the SIR target value is less then the received SIR calculated estimate, TPC commands 45 are generated to decrease DL transmit power.
One channel currently proposed for potentially supporting PtM services is the forward access channel (FACH). The FACH is a channel broadcast throughout a cell and the FACH is maintained at a power level so that any user in the cell can 50 receive the FACH. As a result, adaptive power control mechanisms are not used for the FACH. One problem with the lack of FACH power control is that a high data rate service sent over the FACH will generate considerable interference. The FACH transmission power level needs to be set at a power 55 level so that a WTRU at the periphery of the cell can receive the high data rate service at an acceptable quality.
Accordingly, it is desirable to have adaptive power control for PtM services.
Data is transmitted over a particular channel from a transmitter to a plurality of receivers. The particular channel is received at the plurality of receivers. Each of the receivers 65 sends power control information to the transmitter based on a measured reception quality and a reception quality require
ments of each receiver. The transmitter uses the power control information from each receiver and adjusts a transmission power level of the particular channel so that if any receiver requires an increase in the transmission power level to meet that receiver quality requirement, the transmission power level is increased and if all receivers exceed their quality requirement, the transmission power level is decreased.
BRIEF DESCRIPTION OF THE DRAWING(S)
FIG. 1 is a flow chart for power control of a PtM service using associated dedicated channels.
FIG. 2 is a simplified diagram of a base station and a WTRU for power control of a PtM service using associated dedicated channels.
FIG. 3 is a flow chart for power control of a PtM service using associated dedicated channels.
FIG. 4 is a simplified diagram of a base station and a WTRU for power control of a PtM service without using associated dedicated channels.
DETAILED DESCRIPTION OF THE PREFERRED
Although the preferred embodiments are described in conjunction with a third generation partnership program (3GPP) wideband code division multiple access (W-CDMA) system, the embodiments are applicable to any wireless system using PtM services.
The present invention will be described with reference to the drawing figures wherein like numerals represent like elements throughout. Hereafter, a wireless transmit/receive unit (WTRU) includes but is not limited to a user equipment, mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, a base station includes but is not limited to a base station, Node-B, site controller, access point or other interfacing device in a wireless environment.
The present invention is described subsequently for three different general implementations. In a first implementation, each WTRU receiving the PtM service has associated dedicated channels for use in supporting the PtM service. In a second implementation, the WTRUs receiving the PtM service do not have dedicated channels for use in supporting the service. In a third implementation, some of the users have dedicated channels for use in supporting the service and others do not.
FIG. 1 is a flow chart for adaptive power control for a PtM service when associated dedicated channels are available. FIG. 2 is a simplified block diagram of a base station 54 and WTRU 56 for sending and receiving such a service. The PtM service data may be sent over one of various channels, such as a shared channel, high speed shared channel as proposed for W-CDMA or a common channel. For the PtM service, multiple WTRUs 56 registered for the service receive that service over the PtM channel simultaneously.
For each WTRU 56 that enters the PtM service area and is registered for that service, an uplink and a downlink dedicated physical channels are established, step 20. The dedicated physical channel may be independent or comprised of separate dedicated physical channels for control and data, or just physical control channels.
As shown in FIG. 2 for the downlink (DL) dedicated channel associated with the PtM channel, a DL dedicated channel transmitter 30 produces the channel. An amplifier adjusts the transmission power level of the DL dedicated channel and an