U.S. patent application number 10/170015 was filed with the patent office on 2003-02-06 for system and method for coordination of wireless maintenance channel power control.
This patent application is currently assigned to Tantivy Communications, Inc.. Invention is credited to Proctor, James A. JR..
Application Number | 20030027587 10/170015 |
Document ID | / |
Family ID | 23147941 |
Filed Date | 2003-02-06 |
United States Patent
Application |
20030027587 |
Kind Code |
A1 |
Proctor, James A. JR. |
February 6, 2003 |
System and method for coordination of wireless maintenance channel
power control
Abstract
In a wireless communication system, wireless channels are
maintained for communication between users and the base station.
Often, a wireless user may be switched on, but not actively sending
or receiving data. Accordingly, wireless users may be "active," and
currently allocated a wireless traffic channel for sending or
receiving, or "idle," and not currently sending or receiving. A
wireless user may be maintained in an idle state through a periodic
sequence of synchronization messages. A method for controlling a
power level of a wireless message includes determining the presence
of data to be transmitted, and adjusting the power level of the
synchronization message depending on the presence of data. The
synchronization messages corresponding to the idle state employ a
lower power level than the active state transmissions which employ
a higher power level. The system therefore controls the power
accordingly such that synchronization messages are sent at a lower
power level when no data is present, thereby reducing power
consumption and interference.
Inventors: |
Proctor, James A. JR.;
(Melbourne Beach, FL) |
Correspondence
Address: |
HAMILTON, BROOK, SMITH & REYNOLDS, P.C.
530 VIRGINIA ROAD
P.O. BOX 9133
CONCORD
MA
01742-9133
US
|
Assignee: |
Tantivy Communications,
Inc.
Melbourne
FL
|
Family ID: |
23147941 |
Appl. No.: |
10/170015 |
Filed: |
June 11, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60297839 |
Jun 13, 2001 |
|
|
|
Current U.S.
Class: |
455/522 ;
455/13.4 |
Current CPC
Class: |
H04W 52/0245 20130101;
H04W 52/325 20130101; H04W 52/44 20130101; H04W 52/248 20130101;
H04W 52/322 20130101; H04W 52/243 20130101; H04W 52/0219 20130101;
H04W 52/0238 20130101; H04W 52/287 20130101; H04W 28/0221 20130101;
H04W 52/16 20130101; H04W 40/08 20130101; Y02D 30/70 20200801; H04W
52/241 20130101 |
Class at
Publication: |
455/522 ;
455/13.4 |
International
Class: |
H04Q 007/20 |
Claims
What is claimed is:
1. A method for wireless communication comprising: defining at
least one wireless maintenance channel operable to transmit
synchronization messages, the synchronization messages having a
power level; determining the presence of data to be transmitted
from a wireless access terminal; and adjusting the power level of
the synchronization message sent from the access terminal via the
maintenance channel as a result of the determining the presence of
data.
2. The method of claim 1 further comprising determining a data
transmission state indicative of the presence or absence of data to
be transmitted from a wireless access terminal.
3. The method of claim 2 further comprising computing the power
level of the synchronization message in response to the data
transmission state.
4. The method of claim 3 further comprising transmitting at a first
power level in a first data transmission state and transmitting at
a second power level in a second data transmission state.
5. The method of claim 4 wherein the first power level corresponds
to an idle state wherein the synchronization messages are operable
to maintain synchronization between the wireless access terminal
and the base station.
6. The method of claim 1 further comprising establishing a
maintenance connection over the maintenance channel, the
maintenance connection operable for wireless communication of the
synchronization message between a wireless access terminal and a
base station.
7. The method of claim 6 wherein the maintenance channel is a pilot
channel operable to transmit pilot information.
8. The method of claim 7 wherein the pilot channel is operable to
transmit unmodulated signals corresponding to time tracking and
power control.
9. The method of claim 1 further comprising defining at least one
wireless data traffic channel operable to transmit data payload
messages.
10. The method of claim 9 wherein the data traffic channels are
operable to transmit modulated information corresponding to a data
payload.
11. The method of claim 4 wherein the second power level
corresponds to an active state wherein the synchronization messages
correspond with a wireless traffic message on at least one of the
data traffic channels.
12. The method of claim 4 wherein transmitting at the second power
level further comprises transmitting messages having phase
reference information.
13. The method of claim 2 further comprising detecting a change in
the data transmission state.
14. The method of claim 2 further comprising receiving return
messages in response to the synchronization messages, the return
messages indicative of power control.
15. The method of claim 14 wherein the return messages are power
control messages indicative of a target power level for successive
messages.
16. The method of claim 15 wherein sending the synchronization
messages further comprises sending from an access terminal to a
base station, and sending the power control messages further
comprises sending from the base station to an access terminal.
17. The method of claim 15 wherein the target power level further
comprises an idle target power level and an active target power
level, the idle target power level corresponding to the idle state
and the active target power level corresponding to the active
state.
18. The method of claim 17 wherein the active target power level is
a multiple of the idle target power level.
19. The method of claim 14 further comprising ignoring the return
messages for a predetermined interval after changing the data
transmission state.
20. The method of claim 19 wherein the predetermined interval
corresponds to a number of power control groups.
21. The method of claim 1 wherein the synchronization messages are
sent in a gated manner at a gating rate.
22. The method of claim 21 wherein sending the synchronization
messages in a gated manner occurs during the idle period.
23. The method of claim 1 wherein sending the synchronization
messages further comprises sending over a reverse link in a
wireless CDMA system.
24. The method of claim 1 wherein the maintenance channel and the
data traffic channels are orthogonal wireless channels.
25. The method of claim 15 wherein the target power level is
computed in response to at least one of received signal quality,
Signal-to-Noise (SNR) Ratio, and Carrier-to-Interference (C/I)
ratio.
26. A communication system comprising: at least one wireless
maintenance channel operable to transmit synchronization messages,
the synchronization messages having a power level; a wireless
access terminal operable to determine the presence of data to be
transmitted; and a power level controller operable to adjust the
power level of the synchronization message sent from the access
terminal via the maintenance channel as a result of the determining
the presence of data.
27. The system of claim 26 further comprising a data transmission
state indicative of the presence or absence of data to be
transmitted from a wireless access terminal.
28. The system of claim 27 wherein the wireless access terminal is
further operable to compute the power level of the synchronization
message in response to the data transmission state.
29. The system of claim 28 wherein the power level controller is
responsive to the data transmission state and operable to transmit
at a first power level in a first data transmission state and
transmit at a second power level in a second data transmission
state.
30. The system of claim 29 wherein the first power level
corresponds to an idle state wherein the synchronization messages
are operable to maintain synchronization between the wireless
access terminal and the base station.
31. The system of claim 26 wherein the maintenance channel is
operable to maintain a maintenance connection, the maintenance
connection operable for regular, periodic wireless communication of
the synchronization message between the wireless access unit and a
base station.
32. The system of claim 31 wherein the maintenance channel is a
pilot channel operable to transmit pilot information.
33. The system of claim 32 wherein the pilot channel is operable to
transmit unmodulated signals corresponding to time tracking and
power control.
34. The system of claim 29 further comprising defining at least one
wireless data traffic channel operable to transmit data payload
messages.
35. The system of claim 34 wherein the data traffic channels are
operable to transmit modulated information corresponding to a data
payload.
36. The system of claim 35 wherein the second power level
corresponds to an active state wherein the synchronization messages
correspond with a data payload message on at least one of the data
traffic channels.
37. The system of claim 36 wherein the second power level is
operable to transmit synchronization messages having phase
reference information.
38. The system of claim 27 further comprising a return message, the
return message responsive to the synchronization messages and
indicative of power control of successive messages.
39. The system of claim 38 further comprising a target power level
wherein the return messages are indicative of a target power level
for successive messages.
40. The system of claim 39 wherein the target power level further
comprises an idle target power level and an active target power
level, the idle target power level corresponding to an idle data
transmission state and the active target power level corresponding
to an active data transmission state.
41. The system of claim 39 wherein the return message further
comprises a power step corresponding to increments of the target
power level.
42. The system of claim 39 wherein the base station is further
operable to detect a change in the data transmission state and
recompute the target power level accordingly.
43. The system of claim 38 wherein the wireless access terminal is
further operable to ignore the return messages for a predetermined
interval after changing the data transmission state.
44. The system of claim 43 wherein the predetermined interval
corresponds to a number of power control groups.
45. The system of claim 26 wherein the wireless access terminal is
further operable to send the synchronization messages in a gated
manner at a gating rate.
46. The system of claim 26 wherein the wireless access terminal is
further operable to send the synchronization messages during a data
transmission state of idle.
47. The system of claim 26 wherein the maintenance channel further
comprises a reverse link in a wireless CDMA system.
48. The system of claim 34 wherein the maintenance channel and the
data traffic channels are orthogonal wireless channels.
49. The system of claim 39 wherein the base station is further
operable to compute the target power level in response to at least
one of received signal quality, signal strength, perceived signal
strength, Signal-to-Noise (SNR) Ratio, and Carrier-to-Interference
(C/I) ratio.
50. A method for controlling a power level of a wireless signal
over a maintenance channel comprising: providing a subscriber unit
and a base station operable for wireless communications; defining a
plurality of channels for wireless communication between the base
station and the subscriber unit; establishing a maintenance link
over at least one of the channels for maintaining the channel in at
least an idle state, the maintenance channel operable for
transmitting synchronization messages, the synchronization messages
having a power level; determining a data transmission state
indicative of the presence or absence of data to be transmitted
from a wireless access terminal; computing a power level of the
synchronization message based on the data transmission state; and
adjusting the power level of a message sent from the subscriber
unit as a result of the computed power level.
51. A computer program product having computer program code for
controlling a power level of a wireless message comprising:
computer program code for defining at least one wireless
maintenance channel operable to transmit synchronization messages,
the synchronization messages having a power level; computer program
code for determining the presence of data to be transmitted from a
wireless access terminal; and computer program code for adjusting
the power level of the synchronization message sent from the access
terminal via the maintenance channel as a result of the determining
the presence of data.
52. A computer data signal having program code for controlling a
power level of a wireless message comprising: program code for
defining at least one wireless synchronization channel operable to
transmit synchronization messages, the synchronization messages
having a power level; program code for determining the presence of
data to be transmitted from a wireless access terminal; and program
code for adjusting the power level of the synchronization message
sent from the access terminal via the maintenance channel as a
result of the determining the presence of data.
53. A system for controlling the power level of a signal sent over
a wireless maintenance channel comprising: means for defining at
least one wireless maintenance channel operable to transmit
synchronization messages, the synchronization messages having a
power level; means for determining the presence of data to be
transmitted from a wireless access terminal; and means for
adjusting the power level of the synchronization message sent from
the access terminal via the maintenance channel as a result of the
determining the presence of data.
Description
RELATED APPLICATION(S)
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/297,839, filed on Jun. 13, 2001. The entire
teachings of the above application(s) are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] In a wireless communication system, a number of radio
channels provide a connection between users and a central location,
such as a base station or access point. In such a system, the
wireless channels are a scarce resource which must typically be
shared. In a Code Division Multiple Access (CDMA) system, a number
of different channels can be transmitted on a single radio
frequency carrier by applying different codes to each signal.
However, even in a CDMA system, demand for access to channels is so
great that the base station must allocate and switch the channels
among multiple users.
[0003] Often, a wireless user may be switched on, but not actively
sending or receiving data. Accordingly, wireless users may be in an
"active" mode, and currently allocated a wireless data traffic
channel for sending or receiving data, or in an "idle" mode, and
not currently sending or receiving data. An idle user may, for
example, have just sent or received a data traffic transmission and
is therefore deemed likely to soon request a data traffic channel
for further transmissions. A maintenance message may therefore be
employed to maintain a user in a synchronized but idle state to
facilitate allocation of a wireless traffic channel when needed.
When a user requests a channel, the idle state allows the user to
be allocated a wireless traffic channel more quickly than for a
user who was not being maintained in a synchronized idle state. For
more information concerning one way to implement a system, please
refer to U.S. Pat. No. 6,222,832, entitled "Fast Acquisition of
Traffic Channels for a Highly Variable Data Rate Reverse Link of a
CDMA Wireless Communication System," (Attorney's Docket No.
2479.1008-000) assigned to Tantivy Communications, Inc., assignee
of the present application.
[0004] A number of users, therefore, may be maintained in an idle
state through a periodic sequence of maintenance messages. In the
idle state, the maintenance messages typically provide time
tracking and power control, and do not require phase reference
information employed when in the active state. Time tracking and
power control signaling requires less power than the maintenance
messages sent during active data payload transmission. The
maintenance messages, however, are typically sent at a similar
power level during both the idle and active states. Accordingly,
the maintenance messages can increase interference and battery
power drain during the idle state.
SUMMARY OF THE INVENTION
[0005] In a wireless communications system, synchronization
maintenance messages are often employed to maintain a user in an
idle state by providing time tracking and power control. According
to the present invention, a method for controlling the power level
of a wireless message which defines a maintenance channel operable
to transmit synchronization maintenance messages (synchronization
messages) includes determining the presence of data to be
transmitted from a wireless access terminal to a base station. The
power level of the synchronization message sent from the access
terminal via the maintenance channel is adjusted depending on the
presence of data to be sent. Synchronization messages for idle
state synchronization provide time tracking and power control
signaling, while synchronization messages corresponding to active
data traffic transmissions also provide phase reference for the
data traffic transmissions.
[0006] The synchronization messages corresponding to the idle state
employ a lower power level than the active state transmissions
which employ a higher power level.
[0007] In this manner, the system monitors the presence of data and
controls the power level accordingly such that synchronization
messages are sent at a lower power level in the idle state, when no
data is present, thereby reducing power consumption and
interference.
[0008] More specifically, a data transmission state is maintained
at the wireless access terminal to indicate the presence of data to
transmit via a data traffic channel on a reverse link. The power
level of a synchronization message is computed in response to the
data transmission state. Target power levels are maintained for the
idle state and the active state. The synchronization messages are
sent from the access terminal to the base station at the
corresponding power level. Power control messages (return messages)
sent in response from the base station manage the power level
towards the applicable target power level.
[0009] A maintenance channel connection is maintained for
transmission of the synchronization messages. The maintenance
channel typically transmits unmodulated, or pilot, signals for
maintaining synchronization. Since the maintenance channel is not a
dedicated data traffic channel, a plurality of access terminals may
be maintained over a single maintenance channel using a plurality
of time slots.
[0010] The synchronization messages are typically sent at
predetermined intervals from each of the access terminals. In the
idle state, synchronization messages are sent according to a gating
rate. In the active state, synchronization messages are sent
continuously in order to maintain a phase reference for a
corresponding data traffic transmission. Return power control
messages are sent in response to the synchronization messages
including power control and time tracking information according to
a power control group.
[0011] The access terminal determines the data transmission state,
either ON (active) or OFF (idle), and adjusts transmission power
accordingly. The base station, in turn, determines the data
transmission state and adjusts information in the return messages
accordingly to control the power level toward one of an active
power control target and an idle power control target. Further, the
access terminal disregards return messages for a predetermined
interval after a change in the data transmission state to allow for
recognition and adjustment of the data transmission state change by
the base station. The target power level is determined by the base
station using factors including the received signal strength,
received signal quality, Carrier-to-Interference (C/I) ratio, and
the Signal to Noise Ratio (SNR).
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of preferred embodiments of the invention, as
illustrated in the accompanying drawings in which like reference
characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention.
[0013] FIGS. 1a-1c are diagrams of prior art maintenance messages
for a wireless maintenance channel;
[0014] FIG. 2 is a diagram of a wireless communication system
employing the invention as defined by the present claims;
[0015] FIG. 3 shows the forward and reverse links between a
wireless access terminal and a base station for message
transmission;
[0016] FIG. 4 is a diagram of wireless synchronization messages as
defined by the present claims;
[0017] FIG. 5 shows idle and active power levels;
[0018] FIG. 6 is a flowchart of message transmission;
[0019] FIG. 7 is a flowchart of a power control loop for managing
transmission power according to the target power levels; and
[0020] FIG. 8 is a message transmission sequence diagram showing
the transition between data transmission states.
DETAILED DESCRIPTION OF THE INVENTION
[0021] A description of preferred embodiments of the invention
follows.
[0022] The wireless system as disclosed herein employs a reverse
link maintenance channel for maintaining synchronization and other
state information for a plurality of subscriber access terminals.
The subscriber access terminals support users by providing a
wireless link to a base station processor for communication with a
data network such as the Internet. The wireless link is provided by
one or more wireless channels managed by the base station. The
wireless channels are dynamically allocated by the base station
among the multiple access terminals depending on data transmission
needs, and typically do not remain dedicated to a single user.
[0023] A maintenance channel, therefore, is employed to maintain an
access terminal in synchronization with the base station when it is
not actively sending data. Such a maintenance channel is capable of
maintaining a plurality of access terminals at the same time. This
synchronization allows an access terminal to be allocated a data
traffic channel more readily when needed for data traffic
transmission than that which would be required to set up and tear
down a reverse link wireless channel each time the access terminal
was to send or receive data messages.
[0024] FIGS. 1a-1c show a diagram of several different types of
maintenance messages used in the prior art. Referring to FIGS.
1a-1c, the power level of the maintenance messages are shown for
three different gating rates--1, 1/2 and 1/4, respectively. When an
access terminal is in an idle state and not actively sending or
receiving data, as shown by the "data off/gated" period 10, a
maintenance message is sent to maintain time tracking and power
control. The idle state message need not be continuous. It is sent
in a time slotted or gated manner according to a gating rate
14a-14c, for the duration of a 20 ms power control group 18. As
shown in FIGS. 1a-1c, respectively, several different gating rates
have been used. During a "data on" period 12, the maintenance
message is sent continuously, as shown by the continuous
transmissions 16a-16c. However, during each power control group 18
gated messages are sent at the same power level, as shown by the
power level on axis 20. As the maintenance messages sent during the
data off period 10 are employed for time tracking and power
control, they need not be sent at the same power level afforded to
the maintenance messages sent during the data on period 12, which
are used also for phase reference for a corresponding data traffic
channel.
[0025] FIG. 2 is a diagram of a wireless communication system 22
employing the invention as defined by the present claims. A
plurality of subscriber terminals 24 (access terminals) are in
wireless communication with a base station processor 26 (base
station) via wireless links 30. The base station 26 is also
connected to the Internet 28 via a wired link 32 to act as a
gateway for the access terminals 24. The access terminals 24
provide wireless Internet access to customer premises equipment
(CPE) 32 generally, such as desktop PCs 32a, 32c, personal digital
assistants (PDAs) 32b, wireless phones 32d, and other devices such
as laptops, pagers, and automotive telematics devices, not shown.
It should be noted that the wireless functionality provided by the
access terminal 24 may be in a stand alone device such as a
subscriber access unit or embedded in the CPE 32 unit. In either
case the CPE is operable to communicate with the Internet 28 via
the wireless link 30 and the base station 26.
[0026] FIG. 3 shows forward and reverse links between an access
terminal and a base station for message transmission. Referring to
FIGS. 2 and 3, the wireless links include both a forward link 34
and a reverse link 36 to permit duplex communication. The forward
link supports wireless channels for carrying messages from the base
station 26 to the access terminal 24, and the reverse link 36
supports wireless channels for carrying messages from the access
terminal 24 to the base station.
[0027] Each of the access terminals 24 periodically sends a
synchronization message via the reverse link 36 to the base station
26. The synchronization message includes time tracking and power
control information sufficient to maintain the access terminal in
at least an idle state, and therefore synchronized with the base
station 26. The base station responds with a power control message
via the forward link 34. The power control message includes power
control commands to direct the power level of subsequent messages
to allow the access terminal 24 to remain synchronized with the
base station 26. The power level is determined by a power level
controller 38 at the base station for computing a target power
level for both the idle and active data transmission states.
[0028] The forward 34 and reverse 36 links further comprise data
traffic channels for transmitting wireless messages having a data
payload. The data traffic channels are allocated by the base
station 26 to an access terminal 24 when the access terminal 24 is
to send or receive data. A data transmission state, described
further below, is indicative of whether the access terminal 24 is
allocated a data traffic channel. When the data transmission state
is active, the synchronization messages provide a phase reference
for the messages transmitted on the data traffic channels, in
addition to time tracking and power control.
[0029] Synchronization messages employed for only for time tracking
synchronization and power control, however, do not require as much
power as the synchronization messages used to provide phase
reference during the active data transmission state. Therefore,
according to the present invention, synchronization messages are
sent at a reduced power level in the idle data transmission state.
Additional power is provided for the synchronization message when
it is also employed for phase reference. Accordingly, the
synchronization messages are sent at a lower power level in the
idle data transmission state than in the active data transmission
state.
[0030] FIG. 4 is a power level diagram for the invention. Referring
to FIGS. 4 and 2, during an idle (OFF) data transmission state 40,
the synchronization messages are sent in a gated manner according
to a gating rate. A gating rate of 1/4 is shown as exemplary; other
gating rates could be employed. The power level of the message is
shown by the axis 44. When the data transmission state transitions
to active (ON) 42, the power level 44 is increased to allow the
synchronization messages to be employed for phase reference as
well.
[0031] As indicated above, synchronization messages are transmitted
at one of two power levels. The power level is managed by the base
station 26 and transmitted to the access terminal 24 via the power
control messages. The access terminal 24 responds by transmitting
at the power level proscribed by the base station. The base station
26 computes a target power level, described further below,
indicative of the power level at which the access terminal should
transmit. Typically, the power level is expressed as effective
radiated power in decibels (dB), however, other metrics could be
employed. The base station, therefore, maintains target power
levels for each of the data transmission states. An active target
power level corresponds to the ON data transmission state and an
idle target power level corresponds to the OFF data transmission
state.
[0032] FIG. 5 shows idle and active power levels in more detail.
Periods 46 correspond to OFF data transmission state, and period 48
corresponds to ON data transmission state. The power level 44
indicates the power level of the synchronization messages. The idle
target power level, shown by dotted line 50, indicates the power
level at which synchronization messages should be sent during OFF
data transmission state. The active target power level, shown by
dotted line 52, indicates the power level at which synchronization
messages should be sent during ON data transmission state.
[0033] The access terminal 24 maintains the idle and active target
power levels 50, 52. The base station 26 manages the transmission
power of the messages sent by the access terminal 24 by the power
control messages, which are sent by the base station 26 to adjust
the idle and active target power levels 50, 52. The access terminal
24 determines when the data transmission state changes and toggles
between the active and idle transmission power levels, and
transmits according to the corresponding power level. The base
station 26 determines a change in the data transmission state,
described further below, and adjusts the power control messages
accordingly.
[0034] While the data transmission state affects whether
transmission occurs at the active or idle power level, other
factors affect the perceived power level as well. The distance from
the access terminal 24 to the base station 26, intervening objects,
interference from other sources, and other factors all can affect
the perceived power level of the wireless messages. Accordingly,
the base station 26 examines the received signal quality,
indicative of the power level of a received message, and computes
the power control message accordingly. If a message from the access
terminal 24 is being received at too low a perceived power level,
the base station will transmit power control messages indicative of
a higher power level at which to transmit. Similarly, if a message
is received from the access terminal 24 at too high a perceived
power level, the base station will transmit power control messages
indicative of a lower power level at which to transmit. The base
station, therefore, manages the power level of messages transmitted
from the access terminal by focusing on a target power level.
[0035] Accordingly, when the access terminal 24 changes data
transmission states, the base station will receive messages at a
different power level. The base station determines that the change
in power level is due to a change in data transmission state, and
not to other factors described above, and continues to compute the
idle and active power levels accordingly. Further, as the power
control messages are typically sent according to power control
groups of 16 every 20 ms, or every 1.25 ms, the base station may
not determine the data transmission state until several power
control message cycles. Accordingly, the access terminal 24 may
disregard power control messages for a predetermined period after
toggling data transmission states. The access terminal, therefore,
may toggle between the active and idle power levels without the
base station 26 countering with power control messages which would
otherwise undermine the transmission of reduced power
synchronization messages.
[0036] FIG. 6 is a flowchart of synchronization message
transmission according to a particular embodiment of the invention.
Referring also to FIG. 2 again, an access terminal 24 determines if
there is data ready to be transmitted on a traffic channel, as
depicted at step 100. A check is performed to set or maintain the
data transmission state accordingly, as shown at step 102. If there
is no data waiting to be transmitted, the access terminal 24 enters
or maintains the data transmission state of idle, as depicted at
step 104. If there is data waiting to be transmitted, the access
terminal 24 enters or maintains the data transmission state of
active, as shown at step 106.
[0037] In the idle data transmission state, the access terminal
sets 24 the transmission power level at the idle target power
level, as disclosed at step 108. The access terminal then
determines the gating rate of the idle state message, as determined
at step 110. In the idle mode, the message is sent in a gated, or
periodic manner, such as 1/4, 1/2, or 1. The gating rate results in
a periodic delay, prior to sending the next synchronization
message
[0038] In the active data transmission state, the access terminal
24 set sets the transmission power level at the active target power
level, as shown at step 112. The access terminal then sets the
message as continuous, with no gating, as shown at step 114.
[0039] The access terminal 24 then sends a synchronization message
to a base station 26, as depicted at step 116. The base station 26
receives the synchronization message, as disclosed at step 118, and
determines the data transmission state, as shown at step 120.
[0040] Determination of the data transmission state is discussed
further below with respect to FIG. 7. A check is performed to
examine the determined data transmission state, as disclosed at
step 122. If the data transmission state is idle, then the base
station computes or maintains a new idle target power level, as
depicted at step 124. If the data transmission state is active,
then the base station computes a new active target power level, as
shown at step 126. The base station 26 then sends a power control
message indicative of the computed target power level to the access
terminal 24, as shown at step 128.
[0041] The access terminal 24 receives the power control message,
including the new target power level, as shown at step 130. The
access terminal 24 then determines when to send the next
synchronization message, depending on gating rate, as depicted at
step 132, and control reverts to step 100.
[0042] In a gated manner, the access terminal 24 periodically sends
the synchronization message depending on the gating rate.
Accordingly, the access terminal 24 may wait for one or more power
control group intervals of 1.25 ms each to elapse before sending
the next synchronization message, as shown above in FIG. 4.
Alternatively, in the active data transmission state, the
synchronization messages are sent in a continuous manner, also as
shown in FIG. 4.
[0043] FIG. 7 is a flowchart of a power control loop for managing
transmission power according to the determined target power levels.
Referring to FIG. 2 as well, the determination of the data
transmission state is shown. The base station 26 receives the
synchronization message from the access terminal 24, as shown at
step 150. The base station determines which metric to employ to
determine the data transmission state at the access terminal 24, as
shown at step 152. As the access terminal toggles the data
transmission state between active and idle, the base station
determines the current data transmission state from the
synchronization messages as they are received. The base station 26
then attempts to set the target power level reflected in the power
control messages accordingly.
[0044] The base station 26 examines the received quality level of
the synchronization message to determine the power level at which
it was sent, and hence the data transmission state of either idle
or active, as depicted at step 154. As indicated above, the access
terminal 24 transmits at one of the idle or active power levels
depending on the data transmission state. However, the base station
26 attempts to adjust the target power level such that access
terminal transmissions are received uniformly at the base station
26. Accordingly, the base station 26 determines a transmission
quality based on a link quality metric. Since the received quality
level may be affected by other factors in addition to transmission
power employed by the access terminal 24, such as noise,
interference, and reflection, other metrics may be used to assess
received signal quality and determine the sending power level.
[0045] Alternatively, the base station may receive a separate data
transmission state indication according to a periodic interval, as
shown at step 156. Such a predetermined interval may be according
to the gating rate, or according to a predetermined interval agreed
to by the base station and the access terminal, as described in
copending U.S. patent application No. 60/346,527, entitled
"Coordination of Pilot Power Level Based on Periodic Intervals"
(Attorney's Docket No. 2479.2141-000), filed Jan. 8, 2002 and
incorporated herein by reference.
[0046] The base station 26 may also receive the data transmission
state encapsulated in the synchronization message, as shown at step
158. A detectable signal encapsulated in the synchronization
message is detected by the base station, and employed to set the
data transmission state, and the associated target power control
level, at the base station 26 accordingly.
[0047] In another embodiment, the base station employs a MAC (media
access control) state to determine the data transmission state, as
disclosed at step 160. The MAC state transitions are indicated by a
signal in the synchronization message. The base station detects the
MAC state change, as described in copending U.S. patent application
No. 60/346,525, entitled "Coordination of Pilot Power Level Based
on MAC State" (Attorney's Docket No. 2479.2140-000), filed Jan. 8,
2002, incorporated herein by reference, and sets the data
transmission state accordingly.
[0048] In alternate embodiments, other methods may be employed to
detect a change in data transmission state at the base station 26.
The base station 26 therefore, determines the data transmission
state from the synchronization message, and sets its own indicator
accordingly, as depicted at step 162. The indicator is employed in
determining the target power level to set in the power control
message, as disclosed at step 164. Other factors which affect the
target power level include the C/I (Carrier to Interference) ratio
or the SNR (Signal-to-Noise ratio), in addition to the received
power level. Further discussion of power control messages and power
control groups is disclosed in copending U.S. patent application
Ser. No. 09/999,172, filed Nov. 30, 2001, entitled "Antenna Control
System and Method" (Attorney's Docket No. 2479.2065-002),
incorporated herein by reference. Once the target power level is
determined, corresponding to a data transmission state of idle or
active at the access terminal 24, control resumes at step 120 in
FIG. 6.
[0049] FIG. 8 is a message transmission sequence diagram showing a
transition between data transmission states. A timing diagram 60 of
a maintenance channel is shown. A plurality of synchronization
messages 62a-62g are sent from an access terminal 24 to a base
station 26. A complementary plurality of power control messages
64a-64g are sent from the base station 26 to the access terminal
24. The data transmission state (DT) at the access terminal 24 is
shown by the hatched bars 66, and the DT state at the base station
are shown by the hatched bars 68. At an initial time T=0, the DT
state 66 at the access terminal 24 is idle (I), as shown by hatched
area 70, and the DT state at the base station 26 is also idle for
this user, as shown by hatched area 72. The synchronization message
62a is sent at a power level (PL) corresponding to the idle power
level, and is sent in a gated (G=Y) manner since only
synchronization information need be transmitted. The base station
26 responds with a power control message 64a indicating power
control (PC) is to be maintained at the Idle level. The access
terminal 24 receives the power control message 64a to maintain the
Idle power level. The next synchronization message 62b is sent,
also PL=I and G=Y, and the base station 26 responds with power
control message 64b, PC=I. A series of idle state (DT=I) messages
may continue, described above with respect to FIGS. 6 and 7, as
shown by dotted line 90.
[0050] The access terminal 24 detects data present to be
transmitted on a data traffic channel (not shown), and changes the
DT state 66 to active (ON), as shown by hatched area 74. The
synchronization message 62c is now transmitted at a power level of
"A" (Active) and is sent in a constant (non-gated) manner G=N. Upon
receiving the synchronization message, the base station 26
determines that there is data traffic present, and toggles the DT
state 68 to A, as shown by hatched bar 76. The base station
responds with power control message 64c, indicating power control
is to target the active level (PC=A). The synchronization message
62d is transmitted at PL=A and G=N, and a power control message 64d
is received for PC=A. A series of active state (DT=A) messages may
continue, as described above with respect to FIGS. 6 and 7, as
shown by dotted line 92. Synchronization message 62e is then sent,
which corresponds to the last active state message in this sequence
62c-62e.
[0051] Power control message 64e is sent, and the access terminal
24 determines that there is currently no more data to transmit.
Accordingly, the DT state 66 toggles to "I," (Idle) as shown by
hatched area 78, and synchronization message 62f is sent, at PL=I
and G=Y. The base station 26 receives the message 62f, determines
that there is no data presently being transmitted, and toggles the
DT state 68 to "I," as shown by hatched area 80. Power control
message 64f is sent in response, at PC=I. Idle mode messages 62g
and 64g follow in order, to continue the synchronization
maintenance cycle, until the next active DT state.
[0052] The embodiment described above includes two power control
levels of idle and active as illustrative. Multiple power level
thresholds could be maintained between a access terminal 24 and a
base station 26. Accordingly, the invention as described herein may
be employed to provide multiple levels of standby or idle status,
depending on the level of signaling capability employed at each
level, for the purpose of minimizing interference and maintaining
synchronization between an access terminal 24 and a base station
26.
[0053] Those skilled in the art should readily appreciate that the
system and methods for synchronization message power control as
defined herein are deliverable to a wireless device in many forms,
including but not limited to a) information permanently stored on
non-writeable storage media such as ROM devices, b) information
alterably stored on writeable storage media such as floppy disks,
magnetic tapes, CDs, RAM devices, and other magnetic and optical
media, or c) information conveyed to a computer through
communication media, for example using baseband signaling or
broadband signaling techniques, as in an electronic network such as
the Internet or telephone modem lines. The operations and methods
may be implemented in a software executable by a processor or as a
set of instructions embedded in a carrier wave. Alternatively, the
operations and methods may be embodied in whole or in part using
hardware components, such as Application Specific Integrated
Circuits (ASICs), state machines, controllers or other hardware
components or devices, or a combination of hardware, software, and
firmware components.
[0054] While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
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