HK1078718A - Power control of point to multipoint physical channels - Google Patents

Description

Power control for point-to-multipoint physical channels

Technical Field

The present invention relates to wireless communications. More particularly, the present invention relates to power control for point-to-multipoint (PtM) services.

Background

The need for using point-to-point services in wireless communication systems is growing, in point-to-multipoint (PtM) services, a service originating from a single point, such as a base station, to multiple points, such as multiple wireless transmit/receive units (WTRUs), one example of which is multimedia broadcast and multicast services.

In conventional point-to-point (PtP) services, power control allows a particular wireless transmit/receive unit (WTRU) to receive the PtP service at a desired quality of service (QoS) while minimizing interference to other WTRUs.

In PtP, such as the third generation partnership project (3GPP), when the WTRU dedicated downlink physical channel is power controlled, the WTRU typically determines a target value for a signal-to-interference ratio (SIR) based on the received block error rate (BLER) of the dedicated physical channel, which the WTRU predicts, a closest decision for the SIR is, for example, the ratio of Received Signal Code Power (RSCP) divided by Interference Signal Code Power (ISCP).

When the WTRU determines that the SIR target value is greater than the calculated estimated received SIR value, the WTRU signals a Transmit Power Control (TPC) command to the base station to increase the transmit power of the downlink dedicated channel, and when the SIR target value is less than the calculated estimated received SIR value, the TPC command is generated to decrease the DL transmit power.

It is proposed that a channel with potential support for PtM services be the Forward Access Channel (FACH), which is a channel broadcast throughout a cell, and that the FACH be maintained at a power level such that any user of the cell can receive the FACH. As a final result, the adaptive power control mechanism is not used for FACH, and one problem is that FACH power control suffers from the disadvantage that a high data rate service is transmitted through FACH with considerable interference, and the FACH transmit power level must be set at a power level such that a WTRU located at the cell edge can receive the high data rate service at an acceptable quality.

Therefore, it becomes desirable for PtM services to have adaptive power control.

Disclosure of Invention

Data is sent from a transmitter to a plurality of receivers over a particular channel, which is received at the plurality of receivers. Each of the receivers sends power control information to the transmitter based on a measured reception quality and a reception quality request of each receiver. The transmitter uses the power control information from each receiver and adjusts a transmit power level of the particular channel so that if any receiver requests an increase in transmit power level to satisfy the reception quality request, the transmit power level is increased and if all receivers exceed their quality requests, the transmit power level is decreased.

Drawings

Fig. 1 is a flow diagram of power control for PtM services using associated dedicated channels.

Figure 2 is a diagram of a base station and WTRU for power control using PtM services associated with dedicated channels.

Fig. 3 is a flow diagram of power control for PtM services using an associated dedicated channel.

Figure 4 is a diagram of a base station and WTRU for power control that does not use the PtM service associated with dedicated channels.

Detailed Description

Although the preferred embodiment is described in conjunction with a third generation partnership project (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 reference numerals are used to refer to like elements throughout. A wireless transmit/receive unit (WTRU) may include, 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 invention will be described next in three different general embodiments. In a first embodiment, each WTRU receiving the PtM service has an associated dedicated channel to support the PtM service. In a second embodiment, WTRUs receiving the PtM service do not have dedicated channels to support the service. In a third embodiment, some users have a dedicated channel to support the service, while others do not.

Fig. 1 is a flow chart of adaptive power control PtM service when associated dedicated channels exist. Figure 2 is a simplified block diagram of a base station 54 and WTRU56 for sending and receiving the service, the PtM service data may be sent over one of various channels, such as a common channel, high speed common channel as mentioned for W-CDMA, or a common channel. For the PtM service, multiple WTRUs56 registered with the service receive the service simultaneously over the PtM channel.

For each WTRU56 that enters the PtM service area and is registered with the service, an uplink and a downlink dedicated physical channel are established, step 20. The dedicated physical channel may stand alone or comprise a separate dedicated physical channel for control and data, or simply a physical control channel.

Like the Downlink (DL) dedicated channel associated with the PtM channel shown in fig. 2, a DL dedicated channel transmitter 30 generates the channel, an amplifier adjusts the transmit power level of the DL dedicated channel, and an antenna 42 or antenna array transmits the DL dedicated channel over the radio interface 44. At the WTRU56, a DL dedicated channel receiver 50 coupled to the WTRU antenna 46 receives the channel.

Each WTRU56 evaluates a reception quality, such as a received signal-to-interference ratio (SIR), of the DL dedicated channel, step 22. The SIR may be measured using the Received Signal Code Power (RSCP) and Interference Signal Code Power (ISCP) associated with the DL dedicated physical channel, and the estimated received quality is compared to a nominal received quality, such as a nominal SIR. Based on the comparison, Transmit Power Control (TPC) commands are generated by a TPC command generator 52, which are sent to the base station 54, e.g., using the uplink dedicated channel or a layer 3 message such as a normal uplink channel.

A TPC receiver 40 at the base station 54 receives the command, which is used to adjust the transmit power of the DL dedicated command for the required quality of service (QoS) to achieve the indicated reception level, such as indicated SIR and block error rate (BLER) requests, as the pa 34 of the DL dedicated channel changes accordingly.

For each power-controlled PtM physical channel or set of physical channels, the base station equipment maintains a database of how many WTRUs56 the particular WTRU56 receives the PtM channel, the group of WTRUs56 associated with each PtM channel being treated as a PtM group (PtM-G), and a WTRU56 may be a member of more than one PtM-G.

The transmit power of each DL dedicated channel or set of dedicated channels for WTRUs is adjusted to the minimum necessary power to achieve the respective QoS requirements for the WTRU 56. Preferably, for each WTRU5, the transmit power of the PtM physical channel or set of physical channels is derived from the current transmit power of the associated DL dedicated channel in PtM-G, step 26. A closer approximation to determine the PtM channel power required by a WTRU56 in the PtM-G is according to equations 1 and 2.

PtM _ TxPwr ═ DL _ DchPwr + PtM _ Power _ Offset equation 1

Ptmtxpwr ═ DL _ DchPwr ═ PtM _ Power _ Ratio equation 2

PtM _ TxPwr is the desired transmit power of the PtM channel of the WTRU 56. DL _ DcgPwr is the transmit power of the WTRU's DL dedicated channel, which is adjusted based on TPC commands and the configured TPC step size. PtM Power Offset is an adjustment or compensation for differences between the DL dedicated channel and PtM channel, such as coding rate, QoS, etc. The PtM _ Power _ Ratio is a Ratio to correct for differences between DL dedicated channels and PtM channels.

The PtM power compensation and the PtM power ratio are preferably derived using multiple factors as shown in equation 3 for PtM power compensation and as shown in equation 4 for PtM power ratio.

PtM _ Power _ Offset ═ RelDch + RelTF + RelQoS + X equation 3

Ptm _ Power _ Ratio ═ RelDch ═ RelTF · RelQoS × equation 4

RelDch is a factor configured by the operator to correct for the difference in power compensation between the dedicated channel and the PtM channel. RelTF is a factor to compensate for the difference in transmitted data block size and coding rate between dedicated and PtM channels, RelQoS is a factor to compensate for the difference in the BLER requests between the dedicated and PtM channels, and X is a general factor to any other related transmit power correction/scaling that may be implemented.

The PtM transmit power (PtM _ Tx _ Pwr _ PtM-G) is calculated by determining the maximum WTRU PtM transmit power request within PtM-G, via equation 6.

PtM _ Tx _ Pwr _ PtM-G ═ MAX (PtM _ txpwr (wtru)) equation 6

Ptmtxpwr (wtru) is a set of determined PtM transmit power levels, ptmtx Pw for each user in group G. MAX (ptmtxpwr) (WTRU)) is the maximum PtM transmit power level outside the group, ensuring that all other WTRUs56 in the group (which require less transmit power) will be able to receive the PtM signal, using the maximum PtM transmit power level required by any WTRU56 in the group, step 28. The PtM transmission power may be recalculated and adjusted on a slot, radio frame, or Transmission Time Interval (TTI) basis during other time periods for best performance.

A PtM transmitter (Xmitter)32 generates the PtM channel, and a transmit power calculation device 38 adjusts the transmit power of the PtM channel to a desired transmit power level, such as by altering the gain of the power amplifier 36. The base station transmit power level is adjusted in accordance with the highest WTRU transmit power request, and TPC commands from all WTRUs56 in the group are processed to determine the power adjustment. In fact, only a single WTRU56 is required to request an increase in transmit power in order to increase the PtM transmit power, and all WTRUs56 in the group are required to request a decrease in transmit power in order to decrease the transmit power.

Equation 7 is one possible equation for determining the PtM transmission power adjustment.

New_PtM_Power_PtM-G＝Current_PtM_Power_PtM-G+Ptpc+Pbal

Equation 7

Current _ PtM _ Power _ PtM-G is the Current PtM transmit Power, ptp c is increased or decreased by a step size, preferably an allocated Power control step size (0.5, 1, 1.5 or 2dB), which is increased or decreased in accordance with the received TPC command. Pbal is an optional correction to forward balance the general reference power.

Fig. 3 is a flow diagram for adaptive power control for PtM services when dedicated channels are not present or used to support the PtM services. Figure 4 is a simplified block diagram of base station 54 and WTRU56 for transmitting and receiving a service.

A PtM transmitter (Xmitter) generates a PtM channel whose transmission power level is controlled, for example, by an amplifier 36. The initial PtM transmission power level may be a pre-configured power level by an operator. The operator considers the total cell coverage or is based on the RSCP and ISCP measurements of WTRUs56 in the PtM group. The PtM channel is transmitted via an antenna 42 or antenna array of the base station 54 over a wireless interface 44, each WTRU56 associated with the PtM service receives the PtM channel via an antenna 46, and a PtM receiver recovers the data from the PtM channel.

A TPC command generator sends TPC commands to the base station 54 for PtM, which may be based on the SIR values of the received PtM channels or other channels received by the WTRU56, e.g., a channel received by multiple ones of the WTRUs56 in the group, steps 58 and 60. The SIR values may be obtained using RSCP and ISCP values, path loss and/or the measured channel.

A preferred technique for obtaining these measurements is by physical control signaling. These measurements, such as RSCP, ISCP and/or path loss, are signaled either in physical control signaling or directly in the header message of L2 sent on the uplink common channel, as is the case with the procedure for setting the initial power of the PtM channel. The updating of the measurements is preferably provided on a "best possible" basis, based on the availability of the uplink channels for the WTRUs. For example, a "persistent" indication to send and an "access service level" partitioning technique for the general channel on the upstream path may be used.

Equation 8 is one possible equation for such a general channel to calculate the PtM transmit power, ptmtxpwr.

PtM_TxPwr＝DL_PtM_Pwr*a*(Target RSCP/ISCP)/(Measured RSCP/ISCP)

Equation 8

DL _ PtM _ Pwr is the previous PtM transmission power setting. a is an operator control factor that affects the RSCP/ISCP ratio. The path loss may alternatively replace the RSCP/ISCP ratio in equation 8.

A TPC receiver at base station 54 receives the TPC command, step 62. Using the received TPC commands, a transmit power calculation device adjusts the transmit power level of the base station 54, which is adjusted based on the highest WTRU transmit power request, the TPC commands from all WTRUs56 in the group being processed to determine the power adjustment. In fact, only a single WTRU56 is required to request an increase in transmit power in order to increase the PtM transmit power, and all WTRUs56 in the group are required to request a decrease in transmit power in order to decrease the transmit power, step 64.

In another embodiment, some of the WTRUs56 have dedicated channels for power control of the PtM channel, while others do not. In such an embodiment, power control may be implemented without the use of dedicated channels as in fig. 3 and 4. Preferably, however, the WTRU56 with the dedicated channel uses these channels to generate TPC commands, and the WTRU56 without the dedicated channel uses other channels, such as the PtM channel or the common channel, to multiple WTRUs56 in the group to generate the TPC commands. The base station 54 sets its transmit power level based on the commands from all WTRUs in a particular PtM group, in fact, only a single WTRU56 is required to request an increase in transmit power in order to increase the PtM transmit power, and all WTRUs56 in the group are required to request a decrease in transmit power in order to decrease the transmit power.

Claims (28)

1. A method for transmitting data in a wireless communication system, the method comprising:

transmitting data from a transmitter to a plurality of receivers via a specific channel;

receiving the specific channel at the plurality of receivers;

each receiver transmitting power control information to the transmitter based on a measured reception quality and a reception quality request of each receiver;

the transmitter uses the power control information from each receiver and adjusts a transmit power level for the particular channel so that if any receiver needs to increase the transmit power level to meet the receiver quality request, the transmit power level is increased and if all receivers exceed their quality requests, the transmit power level is decreased.

2. The method of claim 1 wherein the specific channel is a common channel.

3. The method of claim 1 wherein the specific channel is a high speed shared channel.

4. The method of claim 1 wherein the power control information transmitted by each receiver is a transmit power control command.

5. The method of claim 1 wherein the measured reception quality is a signal-to-interference ratio and the receiver quality request is a beacon signal-to-interference ratio.

6. The method of claim 1 wherein the measured reception quality is the reception quality of a particular channel.

7. The method of claim 1 wherein for at least one of the receivers, the particular channel has an associated dedicated channel and the measured reception quality belongs to the associated dedicated channel.

8. The method of claim 1 wherein for each receiver, the particular channel has an associated dedicated channel and the measured reception quality belongs to the associated dedicated channel.

9. A base station for transmitting data to a plurality of users over a particular channel, the base station comprising:

a transmitter and an antenna for generating a specific channel to be simultaneously transmitted to a plurality of users;

a power control receiver for receiving power control information from each of the users;

a transmission power control means for using the power control information from each of the plurality of users and adjusting a transmission power level of an amplifier of the particular channel so that the transmission power level is increased if any user requests the transmission power level to be increased and is decreased if all users exceed their quality requests.

10. The base station of claim 9 wherein the particular channel is a shared channel.

11. The base station of claim 9 wherein the particular channel is a high speed shared channel.

12. The base station of claim 9 wherein the power control information received from each user is a transmit power control command.

13. The base station of claim 9 wherein the base station establishes a dedicated channel for each subscriber associated with the particular channel.

14. The base station of claim 9 wherein the base station has a dedicated channel associated with the particular channel for at least one of the subscribers.

15. A base station for transmitting data to a plurality of users over a particular channel, the base station comprising:

means for generating a specific channel for simultaneous transmission to a plurality of users;

means for receiving power control information from each of the users;

means for using the power control information from each of the plurality of users and adjusting a transmit power level of an amplifier of the particular channel such that if any user requests an increase in the transmit power level, the transmit power level is increased and if all users exceed their quality requests, the transmit power level is decreased.

16. The base station of claim 15 wherein the particular channel is a shared channel.

17. The base station of claim 15 wherein the particular channel is a high speed shared channel.

18. The base station of claim 15 wherein the power control information received from each user is a transmit power control command.

19. The base station of claim 15 wherein the base station establishes a dedicated channel for each subscriber associated with the particular channel.

20. The base station of claim 15 wherein the base station has a dedicated channel associated with the particular channel for at least one of the subscribers.

21. A wireless transmit/receive unit (WTRU) for receiving data over a particular channel, the WTRU comprising:

a receiver for receiving the specific channel, the specific channel being simultaneously received by a plurality of WTRUs;

a power control information generator for sending power control information based on a measured reception quality and a reception quality request of the WTRU; and

wherein the particular channel has a transmit power level setting such that if any of the plurality of WTRUs requests an increase in the transmit power level to satisfy the reception quality request, the transmit power level is increased and if all of the plurality of WTRUs drop below their quality request, the transmit power level is decreased.

22. The WTRU of claim 21 wherein the measured reception quality is a signal to interference ratio and the reception quality request is a beacon signal to interference ratio.

23. The WTRU of claim 21 wherein the measured reception quality is a reception quality of the particular channel.

24. The WTRU of claim 21 further comprising a dedicated channel receiver wherein the measured reception quality is of the dedicated channel.

25. A wireless transmit/receive unit (WTRU) for receiving data over a particular channel, the WTRU comprising:

means for receiving the particular channel, the particular channel being simultaneously received by a plurality of WTRUs;

means for sending power control information based on a measured reception quality and a reception quality request of the WTRU; and

wherein the particular channel has a transmit power level setting such that if any of the plurality of WTRUs requests an increase in the transmit power level to satisfy the reception quality request, the transmit power level is increased and if all of the plurality of WTRUs drop below their quality request, the transmit power level is decreased.

26. The WTRU of claim 25 wherein the measured reception quality is a signal to interference ratio and the reception quality request is a beacon signal to interference ratio.

27. The WTRU of claim 25 wherein the measured reception quality is a reception quality of the particular channel.

28. The WTRU of claim 25 further comprising means for receiving a dedicated channel to which the measured reception quality belongs.