U.S. patent application number 14/856119 was filed with the patent office on 2016-01-07 for power control of point to multipoint physical channels.
This patent application is currently assigned to SIGNAL TRUST FOR WIRELESS INNOVATION. The applicant listed for this patent is SIGNAL TRUST FOR WIRELESS INNOVATION. Invention is credited to Stephen E. Terry.
Application Number | 20160007303 14/856119 |
Document ID | / |
Family ID | 29736726 |
Filed Date | 2016-01-07 |
United States Patent
Application |
20160007303 |
Kind Code |
A1 |
Terry; Stephen E. |
January 7, 2016 |
POWER CONTROL OF POINT TO MULTIPOINT PHYSICAL CHANNELS
Abstract
A method and apparatus are used to determine an efficient
transmit power for point to multipoint (PtM) transmissions by
maintaining a database at a base station which specifies which of a
plurality of wireless transmit/receive units (WTRUs) are members of
each PtM group. The transmit power of each WTRU's downlink
dedicated channel is adjusted to the minimum required power
necessary and the PtM transmit power for each PtM group is set such
that the PtM transmit power of a PtM group is equal to the greatest
of a WTRU in the PtM group plus a PtM power offset.
Inventors: |
Terry; Stephen E.;
(Northport, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SIGNAL TRUST FOR WIRELESS INNOVATION |
Wilmington |
DE |
US |
|
|
Assignee: |
SIGNAL TRUST FOR WIRELESS
INNOVATION
WILMINGTON
DE
|
Family ID: |
29736726 |
Appl. No.: |
14/856119 |
Filed: |
September 16, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14080250 |
Nov 14, 2013 |
9144027 |
|
|
14856119 |
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Current U.S.
Class: |
455/522 |
Current CPC
Class: |
H04W 52/08 20130101;
H04W 52/143 20130101; H04W 52/247 20130101; H04W 52/327 20130101;
H04W 52/06 20130101; H04W 52/28 20130101; H04W 72/005 20130101;
H04W 52/322 20130101; H04W 52/267 20130101 |
International
Class: |
H04W 52/32 20060101
H04W052/32; H04W 52/26 20060101 H04W052/26; H04W 72/00 20060101
H04W072/00; H04W 52/14 20060101 H04W052/14 |
Claims
1. A base station configured to transmit point to multipoint (PtM)
channels in wireless communications, the base station comprising: a
receiver configured to receive transmit power control (TPC)
commands from a plurality of wireless transmit receive units
(WTRUs); a processor configured to: categorize each WTRU of the
plurality of WTRUs according to the TPC commands and a database
created on the basis of an association of a WTRU with a Ptm
channel, wherein the database includes groups of WTRUs from the
plurality of WTRUs that are associated with each PtM channel;
adjust a transmit power level of a downlink (DL) channel associated
with each WTRU of the plurality of WTRUs; set a transmission power
level for each of the groups of WTRUs wherein the transmission
power level for a PtM channel equals a maximum transmission power
level required for a WTRU of the group adjusted by an offset
parameter; a PtM transmitter configured to produce a PtM channel
with the transmission power level; an amplifier configured to
control the transmission power level of the PtM channel; and an
antenna configured to radiate the PtM channel from a wireless
interface.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/080,250 filed Nov. 14, 2013, which is a
continuation of U.S. patent application Ser. No. 12/758,330 filed
Apr. 12, 2010, which issued on Dec. 10, 2013 as U.S. Pat. No.
8,606,282, which is a continuation of U.S. patent application Ser.
No. 12/169,739 filed Jul. 9, 2008, which issued on Jun. 15, 2010 as
U.S. Pat. No. 7,738,895, which is a continuation of U.S. patent
application Ser. No. 10/632,776 filed Aug. 1, 2003, which issued on
Jul. 15, 2008 as U.S. Pat. No. 7,400,861, which claims the benefit
of U.S. Provisional Application No. 60/400,602 filed Aug. 1, 2002,
which are incorporated by reference as if fully set forth.
FIELD OF INVENTION
[0002] The present invention relates to wireless communications.
More specifically, the present invention relates to power control
for point to multipoint (PtM) services.
BACKGROUND
[0003] There is a growing desire to use point to multi-point
services in wireless communication systems. In point to multi-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.
[0004] 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.
[0005] 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 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 (ISCP).
[0006] When the WTRU determines that the SIR target value is
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 are generated to decrease DL
transmit power.
[0007] 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 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 level so that a WTRU at the periphery of the
cell can receive the high data rate service at an acceptable
quality.
[0008] Accordingly, it is desirable to have adaptive power control
for PtM services.
SUMMARY
[0009] A method and apparatus are used to determine an efficient
transmit power for point to multipoint (PtM) transmissions by
maintaining a database at a base station which specifies which of a
plurality of wireless transmit/receive units (WTRUs) are members of
each PtM group. The transmit power of each WTRU's downlink
dedicated channel is adjusted to the minimum required power
necessary and the PtM transmit power for each PtM group is set such
that the PtM transmit power of a PtM group is equal to the greatest
of a WTRU in the PtM group plus a PtM power offset.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0010] FIG. 1 is a flow chart for power control of a PtM service
using associated dedicated channels;
[0011] FIG. 2 is a simplified diagram of a base station and a WTRU
for power control of a PtM service using associated dedicated
channels;
[0012] FIG. 3 is a flow chart for power control of a PtM service
using associated dedicated channels; and
[0013] 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 EMBODIMENT(S)
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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 antenna 42 or
antenna array radiates the DL dedicated channel through the
wireless interface 44. At the WTRU 56, a DL dedicated channel
receiver 50 coupled to the WTRU antenna 46 receives the
channel.
[0020] Each WTRU 56 estimates a reception quality of the DL
dedicated channel, such as a received signal to interference ratio
(SIR), 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 channels. The estimated
reception quality is compared with a target reception quality, such
as a target SIR. Based on the comparison, transmit power control
(TPC) commands are generated by a TPC command generator 52. The TPC
commands are sent to the base station 54, such as using the uplink
dedicated channel or as a layer 3 message on a common uplink
channel.
[0021] A TPC receiver 40 at the base station 54 receives the
commands. The TPC commands are used to adjust the transmit power of
the DL dedicated channel to achieve the target reception levels,
such as target SIR and block error rate (BLER) requirements, for
the quality of service (QoS) desired. The power amplifier 34 of the
DL dedicated channel is changed accordingly.
[0022] For each power controlled PtM physical channel or set of
physical channels, the base station equipment maintains a database
of which specific WTRUs 56 receive which particular PtM channels.
The group of WTRUs 56 associated with each PtM channel is referred
to as a PtM Group (PtM-G). A WTRU 56 can be member of more than one
PtM-G.
[0023] The transmit power of each WTRU's DL dedicated channel or
set of dedicated channels is adjusted to the minimum required power
to the minimum required power necessary to achieve the respective
QoS requirement for that WTRU 56. Preferably, for each WTRU 56, the
transmit power of the PtM physical channel or set of physical
channels is derived from the current transmit powers of the
associated DL dedicated channels within the PtM-G, step 26. One
approach to determine the required PtM channel power for a WTRU 56
of the PtM-G is according to Equation 1 or Equation 2.
PtM.sub.--TxPwr=DL.sub.--DchPwr+PtM_Power_Offset Equation 1
PtM.sub.--TxPwr=DL.sub.--DchPwr*PtM_Power_Ratio Equation 2
[0024] PtM_TxPwr is the desired transmit power of the PtM channel
for that WTRU 56. DL_DchPwr is the transmission power of that
WTRU's DL dedicated channel or channels, adjusted according to TPC
commands and the configured TPC step size. PtM_Power_Offset is an
adjustment to correct for differences between the DL dedicated
channel and the PtM channel, such as coding rate, QoS, etc.
PtM_Power_Ratio is a ratio to correct for differences between the
DL dedicated channel and the PtM channel.
[0025] The PtM power offset and the PtM power ratio are,
preferably, derived using multiple factors as illustrated in
Equation 3 for the PtM power offset and Equation 4 for the PtM
Power Ratio.
PtM_Power_Offset=RelDch+RelTF+RelQoS+X Equation 3
PtM_Power_Ratio=RelDch*RelTF*RelQos*X Equation 4
RelDch is a factor configured by the operator to correct between
the power offset between the dedicated channel and the PtM channel.
RelTF is a factor to compensate for the difference in transport
data block set size and coding rate between the dedicated and the
PtM channel. RelQoS is a factor to compensate between the BLER
requirements between the dedicated and the PtM channel. X is a
general factor for any other relative transmit power offsets/ratios
which may be applied.
[0026] The PtM transmit power (PtM_Tx_Pwr_PtM-G) is calculated by
determining the maximum WTRU PtM transmit power requirement within
the PtM-G per Equation 6.
PtM.sub.--Tx.sub.--Pwr.sub.--PtM-G=MAX(PtM.sub.--TxPwr(WTRU))
Equation 6
PtM_TxPwr(WTRU) is the set of determined PtM transmission power
levels, PtM_TxPwr, for each user of the group, group G.
MAX(PtM_TxPwr(WTRU)) is the maximum PtM transmission power level
out of this group. By using the maximum PtM transmission power
level required by any WTRU 56 in the group, it ensures that all the
other WTRUs 56 in the group (which require less PtM transmit power)
will be able to receive the PtM signal, step 28. The PtM transmit
power may be recalculated and adjusted on a slot, radio frame, or
transmission time interval (TTI) basis, among other time periods,
for optimal performance.
[0027] A PtM transmitter (Xmitter) 32 produces the PtM channel. A
transmit power calculation device 38 adjusts the transmit power of
the PtM channel, such as by changing a gain of a power amplifier
36, to the desired transmission power level. The base station's
transmission power level is adjusted in accordance with the highest
WTRU transmission power requirement. The TPC commands from all the
WTRUs 56 in the group are processed to determine the power
adjustment. Essentially, to increase the transmission power of the
PtM requires only a single WTRU 56 to request an increase in
transmission power. For the transmission power to decrease, all the
WTRUs 56 in the group need to request a decrease in power.
[0028] Equation 7 is one possible equation for determining the
power adjustments for the PtM transmission.
New.sub.--PtM_Power.sub.--PtM-G=Current.sub.--PtM_Power.sub.--PtM-G+Ptpc-
+Pbal Equation 7
Current_PtM_Power_PtM-G is the current PtM transmit power. Ptpc is
either an increase or decrease by a step size. The Ptpc adjustment
is preferably a configured power control step size (0.5, 1, 1.5 or
2 dB), which either increases or decreases the transmission power
level based on the received TPC commands. Pbal is an optional
correction for balancing towards a common reference power.
[0029] FIG. 3 is a flow chart for adaptive power control for a PtM
service when dedicated channels are not available or are not used
to support the PtM service. FIG. 4 is a simplified block diagram of
a base station 54 and WTRU 56 for sending and receiving such a
service.
[0030] A PtM transmitter (Xmitter) produces a PtM channel. The
transmission power level of the PtM channel is controlled, such as
by an amplifier 36. The initial PtM transmission power level may be
a power level preconfigured by an operator that allows for full
cell coverage or be based on RSCP and ISCP measurements of WTRUs 56
in the PtM group. The PtM channel is radiated by an antenna 42 or
antenna array of the base station 54, though a wireless interface
44. The PtM channel is received by an antenna 46 of each WTRU 56
associated with the PtM service. A PtM receiver recovers data from
the PtM channel.
[0031] A TPC command generator sends TPC commands to the base
station 54 for the PtM. The TPC commands may be based on the SIR of
the received PtM channel or another channel received by the WTRU
56, such as a channel received by multiple ones of the WTRUs 56 in
the group, steps 58 and 60. The SIR may be derived using the RSCP
and ISCP values, pathloss and/or BLER of the measured channel.
[0032] One preferred technique for getting these measurements is to
use physical control signaling. The measurements, such as RSCP,
ISCP and/or pathloss, are signaled directly in physical control
signaling or within L2 header information of uplink common channel
transmissions. This procedure is similar to the procedure that the
initial power of the PtM channel is set. The measurements updates
would, preferably, be provided on a "best effort" basis, depending
on the availability of the uplink channels to the WTRUs. For
example, a "persistency" indication for transmission and "access
service class" partitioning of the uplink common channel may be
used.
[0033] Equation 8 is one possible equation for use with this common
channel, for calculating the PtM transmission power, PtM_TxPwr.
PtM.sub.--TxPwr=DL.sub.--PtM.sub.--Pwr*a*(TargetRSCP/ISCP)/(Measured(RSC-
P/ISCP) Equation 8
DL_PtM_Pwr is the previous PtM transmission power setting. "a" is
an operator controlling factor effecting the RSCP/ISCP ratio.
Alternately, the pathloss may replace the RSCP/ISCP ratio in
Equation 8.
[0034] A TPC receiver at the base station 54 receives the TPC
commands, step 62. Using the received TPC commands, a transmit
power calculation device adjusts the transmit power level of the
base station 54. The base station's transmission power level is
adjusted in accordance with the highest WTRU transmission power
requirement. The TPC commands from all the WTRUs 56 in the group
are processed to determine the power adjustment. Essentially, to
increase the transmission power of the PtM requires only a single
WTRU 56 to request an increase in transmission power. For the
transmission power to decrease, all the WTRUs 56 in the group need
to request a decrease in power, step 64. In another implementation,
some of the WTRUs 56 have dedicated channels for use in power
control of the PtM channel and others may not. In such an
implementation, power control can be performed without using the
dedicated channels such as per FIGS. 3 and 4. However, preferably,
WTRUs 56 having dedicated channels use those channels to generate
TPC command and the WTRUs 56 not having dedicated channels use
other channels, such as the PtM channel or a channel common to
multiple WTRUs 56 in the group to generate the TPC commands. The
base station 54 sets its transmission power level based on the
commands from all the WTRUs in a particular PtM group. Essentially,
to increase the transmission power of the PtM requires only a
single WTRU 56 to request an increase in transmission power. For
the transmission power to decrease, all the WTRUs 56 in the group
need to request a decrease in power.
* * * * *