U.S. patent application number 11/341333 was filed with the patent office on 2007-08-02 for using the repetition of an erasure indicator bit to enhance a power control command during handoff.
Invention is credited to Dongzhe Cui, Yuan-Rong Shen.
Application Number | 20070177544 11/341333 |
Document ID | / |
Family ID | 38090996 |
Filed Date | 2007-08-02 |
United States Patent
Application |
20070177544 |
Kind Code |
A1 |
Cui; Dongzhe ; et
al. |
August 2, 2007 |
Using the repetition of an erasure indicator bit to enhance a power
control command during handoff
Abstract
A wireless communication network (20) includes a power control
technique that includes repeating an erasure indicator bit in a
transmission from a mobile station (22) to a base station (24, 30,
36). The repeated erasure indicator bit is transmitted on the
uplink to each base station. The base station then uses the
majority rule of those repeated erasure indicator bits to adjust
its transmit power. It results in a desired power control command
corresponding to the quality of a downlink between a base station
(24, 30, 36) and the mobile station (22). A disclosed example
includes using the repeated error indicator bit for deciding
whether a recent frame should be considered an erasure. If so, the
base station increases power on the downlink forward channel. If
not, the base station decreases the transmit power on the downlink
forward channel. A disclosed example includes alternative power
control adjustment techniques, depending on the recent history of
the quality of the downlink.
Inventors: |
Cui; Dongzhe; (Parsippany,
NJ) ; Shen; Yuan-Rong; (Randolph, NJ) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 W MAPLE RD
SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
38090996 |
Appl. No.: |
11/341333 |
Filed: |
January 27, 2006 |
Current U.S.
Class: |
370/331 ;
370/311 |
Current CPC
Class: |
H04W 52/40 20130101;
H04W 52/367 20130101; H04W 52/08 20130101; H04W 52/20 20130101;
H04W 52/58 20130101 |
Class at
Publication: |
370/331 ;
370/311 |
International
Class: |
G08C 17/00 20060101
G08C017/00; H04Q 7/00 20060101 H04Q007/00 |
Claims
1. A method of communicating, comprising using a repeated erasure
indicator bit within a frame as an indication of a power control
command.
2. The method of claim 1, comprising receiving the repeated erasure
indicator bit; and adjusting a forward link transmit power level in
a manner corresponding to a value of at least a majority of the
received repeated erasure indicator bit.
3. The method of claim 2, comprising automatically increasing the
transmit power level using a predetermined increment when the
repeated erasure indicator bit indicates a command for increased
transmit power.
4. The method of claim 2, comprising determining whether using a
predetermined increment for increasing the transmit power level
will result in the transmit power level exceeding a maximum level;
and increasing the transmit power level by the predetermined
increment if using the predetermined increment will not result in
the transmit power level exceeding the maximum level; or setting
the transmit power level to the maximum level if using the
predetermined increment will result in the transmit power level
exceeding the maximum level.
5. The method of claim 2, comprising automatically decreasing the
transmit power level using a predetermined amount when the repeated
erasure indicator bit indicates a command for decreased transmit
power.
6. The method of claim 5, comprising determining a number of
consecutive frames in which the repeated erasure indicator bit
indicates a command for decreased transmit power; and decreasing
the transmit power by the predetermined amount when the determined
number is below a threshold; or decreasing the transmit power by
the predetermined amount multiplied by a factor comprising the
determined number when the determined number exceeds the
threshold.
7. The method of claim 6, wherein the factor comprises the square
root of the determined number.
8. The method of claim 6, wherein the threshold comprises two
consecutive frames.
9. The method of claim 2, comprising determining whether using a
predetermined amount for decreasing the transmit power level will
result in a transmit power level that is below a lock threshold;
and decreasing the transmit power level by the predetermined amount
if decreasing the transmit power level by the predetermined amount
will result in a transmit power level exceeding the lock threshold;
or setting the transmit power level to the lock threshold level if
decreasing the transmit power level by the predetermined amount
will result in a transmit power level below the lock threshold.
10. The method of claim 1, comprising transmitting the repeated
erasure indicator bit.
11. The method of claim 1, wherein the erasure indicator bit is
repeated a number of times corresponding to an entire set of power
control groups within the frame.
12. The method of claim 1, wherein the erasure indicator bit is
repeated 16 times within the frame.
13. The method of claim 1, comprising using the repeated erasure
indicator bit during soft handoff.
14. The method of claim 1, wherein the repeated erasure indicator
bit has a value of 1 when a previous frame received at a mobile
station comprises an erasure and the repeated erasure indicator bit
has a value of 0 when a previous frame was successfully received at
the mobile station.
15. The method of claim 14, wherein the repeated erasure indicator
bit value of 1 corresponds to a power control command for
increasing transmit power on a forward link and the value of 0
corresponds to a power control command corresponding for decreasing
the transmit power.
16. The method of claim 14, comprising receiving the repeated
erasure indicator bit; and determining whether a number of the
received bits having the value 1 exceeds a number of the received
bits having the value 0.
17. The method of claim 16, comprising increasing a forward link
transmit power when the number of the received bits having the
value 1 exceeds the number having the value 0; or decreasing the
forward link transmit power when the number of the received bits
having the value 0 exceeds the number having the value 1.
Description
FIELD OF THE INVENTION
[0001] This invention relates to communications. More particularly,
this invention relates to wireless communications.
DESCRIPTION OF THE RELATED ART
[0002] Wireless communication systems are in widespread use.
Typical arrangements include a plurality of base stations
strategically positioned to provide wireless communication coverage
over selected geographic regions. A mobile station such as a cell
phone or notebook computer communicates with the wireless
communication network through a base station that serves the region
within which the mobile station is located. There are various
signaling techniques that are implemented to provide desired
service levels and signaling quality.
[0003] One technique includes power control. There are two-way
communications between a mobile station and a base station.
Communications from the base station to the mobile station are
typically referred to as downlink communications. Communications
from the mobile station to the base station are typically referred
to as uplink communications. One aspect of power control in
wireless communication systems includes the mobile station
reporting to the base station the quality of the downlink. It is
typical to include a specific power control command signal on a
reverse power control sub-channel. The base station responds by
adjusting the transmission power on the downlink. There are known
techniques for such power control.
[0004] As mobile stations travel, different base stations serve the
mobile station as it moves between the various regions covered by
the different base stations. In some situations, a mobile station
will be in soft handoff during which the mobile station
communicates simultaneously with more than one base station. Under
such circumstances, the mobile station typically reports the
quality of the downlink of each base station back to it. Each base
station then uses that information to adjust the transmit power on
the downlink to ensure that the link with the mobile station is not
lost before the mobile station completes a handoff, for
example.
[0005] There are situations where the power control commands
between the mobile station and a base station might be blurred
because of the fast fading channel such that the power control
command is not successfully received by the base station. If a base
station misinterprets a power control message, the wireless phone
call may be terminated contrary to the intentions of the mobile
user.
[0006] There is a need for an improved technique that will minimize
the chances of a base station not receiving a power control command
or erroneously interpreting a received power control command.
[0007] This invention provides an improved power control signaling
technique.
SUMMARY OF THE INVENTION
[0008] An exemplary method of communicating includes using a
repeated erasure indicator bit within a frame as an indication of a
power control command.
[0009] One example includes repeating an erasure indicator bit
sixteen times within a frame. A base station receives the frame and
determines whether a majority of the erasure indicator bits within
the frame corresponds to an erasure set by the mobile station. If
so, the base station interprets that as a power control command for
increased transmit power on the downlink. If not, the base station
responds by decreasing the transmit power on the downlink.
[0010] Using a repeated erasure indicator bit increases the
likelihood that the base station will receive the appropriate
information regarding the desirability of an increase or decrease
in downlink transmit power. The disclosed example does not rely
upon a power control command separate from the erasure indicator
bit. Instead, the repeated erasure indicator bit provides the
indication of the desired power control. Having a repeated erasure
indicator bit increases the likelihood that the base station will
receive the desired indication and respond appropriately with an
adjustment to the downlink transmit power.
[0011] The various features and advantages of this invention will
become apparent to those skilled in the art from the following
detailed description. The drawings that accompany the detailed
description can be briefly described as follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 schematically illustrates selected portions of a
wireless communication system that is useful with an embodiment of
this invention.
[0013] FIG. 2 is a flowchart diagram summarizing one example
approach.
DETAILED DESCRIPTION
[0014] This invention is useful for power control within wireless
communication systems. An example implementation of this invention
during a soft handoff procedure is described for purposes of
illustration. Those skilled in the art who have the benefit of this
description will realize applicable uses of the inventive power
control technique to meet the needs of their particular
situation.
[0015] FIG. 1 schematically illustrates selected portions of a
wireless communication system 20. A mobile station 22 communicates
with at least one base station 24. Communications between the
mobile station 22 and the base station 24 occur over a downlink 26
and an uplink 28.
[0016] The mobile station 22 may be a cellular phone, notebook
computer, personal digital assistant or other communication device
that is capable of communicating in a wireless communication
system. When the mobile station 22 is within the geographic region
served by the base station 24, for example, it communicates with
that base station.
[0017] At times, the mobile station 22 will handoff between base
stations. The illustration in FIG. 1 schematically shows a soft
handoff scenario. The mobile station 22 is simultaneously in
communication with the base station 24 and another base station 30.
Communications between the mobile station 22 and the base station
30 occur over a downlink 32 and an uplink 34. In the example of
FIG. 1, the mobile station 22 also communicates with a base station
36. Communications between the mobile station 22 and the base
station 36 occur over a downlink 38 and an uplink 40.
[0018] In the illustrated example, most of the communication links
are sufficiently strong to provide reliable communications between
the mobile station 22 and the base stations. The downlink 38 and
uplink 40 between the base station 36 and the mobile station 22,
however, are relatively weaker. The transmit power on the link 38
should be increased. The transmit power on the downlinks 26 and 32
may be decreased or held at a current level.
[0019] The mobile station 22 communicates with each of the base
stations using a signaling technique for providing an indication of
a desired power control that improves the reliability of
communicating power control commands between the mobile station 22
and each of the base stations 24, 30 and 36.
[0020] FIG. 2 includes a flowchart diagram 50 that summarizes one
example approach. For purposes of discussion, the example of FIG. 2
includes the mobile station 22 being in soft handoff and
communicating using the CDMA 2000 standard. The flowchart 50 begins
at 52 where a determination is made whether the mobile station is
in soft handoff. If not, the rest of the process in FIG. 2 need not
be carried out in this example.
[0021] Assuming that the mobile station 22 is in soft handoff mode,
at least one of the base stations sends a power control message to
the mobile station at 54 to set the forward power control mode to a
mode corresponding to desired communications during soft handoff.
In the illustrated example, this includes setting the forward power
control mode using the "011" FPC_MODE according to the CDMA 2000
standard. The mobile station 22 responds to this mode indication by
repeating an error indicator bit on the reverse power control
sub-channel. In one example, every power control group in each
frame (e.g., 16 power control bits) on the reverse power control
sub-channel is set to the error indicator bit. In one example, a 20
millisecond frame includes sixteen repetitions of the error
indicator bit. In other words, the error indicator bit is repeated
sixteen times in one example. This provides an effective feedback
rate of 50 bits per second in such an example.
[0022] At 56, the base station receives the frame including the
repeated error indicator bit. The base station determines how many
of the error indicator bits have a value of 1 and how many have a
value of 0. The base station then determines which is the majority.
In one example, the error indicator bit has a value of 1 for
situations where the mobile station did not properly receive the
most recent communication from the base station. An error indicator
bit value of 0 indicates that a good frame is received by the
mobile station 22.
[0023] In the example of FIG. 2, when there are more error
indicator bits with the value 1 than the value 0 received at a base
station, the process continues at the step indicated at 58 such
that the frame is treated as an erasure. Under such circumstances,
the repeated error indicator bit provides an indication of a power
control command corresponding to a desired increase in the transmit
power on the downlink or forward channel. In other words, the value
of the majority of the received erasure indicator bits results in a
desired power control command.
[0024] In one example, the transmit power on the fundamental
forward channel (e.g., on the downlink) is adjusted using a
preselected increment. One example includes adjusting the downlink
power P.sub.F-FCH using the equation
P.sub.new.sub.--.sub.F-FCH=P.sub.F-FCH+.DELTA..sub.up. In one
example, .DELTA..sub.up is 0.5 dB.
[0025] In FIG. 2, at 60, a determination is made whether the
adjustment to the downlink transmit power level makes it greater
than the maximum power allowable on the particular forward channel.
If not, then the adjusted value is used for the transmit power on
the forward channel. In the event that the adjustment to the
downlink transmit power level exceeds the maximum, the example of
FIG. 2 includes a step at 62 where the transmit power is set to the
maximum power level available. The process continues at 64 for the
next frame.
[0026] When the determination made at 56 is that there are more "0"
erasure indicator bits than those having the value "1", that frame
is treated as a "no erasure" at 70. When a majority of the received
erasure indicator bits within a frame have the value zero, the base
station interprets that as an indication of a power control command
allowing for a decrease in the transmit power on the downlink. The
example of FIG. 2 includes two options for decreasing the transmit
power. A determination is made at 72 whether there have been two or
more consecutive "no erasure" frames. If not, the process proceeds
at 74 to decrease the transmit power on the forward channel using a
preselected decrement. One example includes adjusting the downlink
transmit power P.sub.F-FCH using the equation
P.sub.new.sub.--.sub.F-FCH=P.sub.F-FCH-.DELTA..sub.down. In one
example, .DELTA..sub.down=0.02 dB.
[0027] When there are two or more consecutive "no erasure" frames,
that is an indication of a very good quality downlink. Accordingly,
the transmit power on the downlink may be accelerated down at a
faster rate. This is accomplished in the example of FIG. 2 at 76
where the transmit power on the forward channel is accelerated
down. One example includes using the equation
P.sub.new.sub.--.sub.F-FCH=P.sub.F-FCH- {square root over
(N)}.DELTA..sub.down, where N is the number of consecutive good or
"no erasure" frames. Using this number as a factor for multiplying
the amount by which the transmit power is decreased allows for
further decreasing the transmit power based upon the recent history
on that particular channel.
[0028] The example of FIG. 2 includes a determination at 78
regarding whether the decreased transmit power is within an
acceptable level. The determination at 60 assures that the transmit
power does not get too high. The determination at 78 assures that
the transmit power does not get too low. As known, a forward
channel transmit power for a base station should be greater than a
forward channel lock threshold to avoid dropping that link. The
determination at 78 includes determining whether the decreased
transmit power is greater than the lock threshold. If not, an
adjustment is made at 80 to ensure that the transmit power is at
least equal to the lock threshold value. If the decreased downlink
transmit power is greater than the lock threshold, then the
procedure continues at 64 without making the adjustment at 80.
[0029] Applying a repeated error indicator bit on a reverse power
control sub-channel improves the forward power control and provides
more robust and more reliable power control commands that can help
to eliminate mobile call drop in many situations. The disclosed
example is particularly useful during soft handoff, for
example.
[0030] The repeated error indicator bit is essentially cumulative
and combined at each base station over the number of power control
groups within which the error indicator bit is repeated (e.g., 16
power control groups over 20 milliseconds in the above example).
That provides more robust and reliable information regarding frame
erasure transmitted on the forward link by each base station. Even
for a base station with a weak link, the above-described example
improves the effective signal to noise ratio of the received error
indicator bit soft metric. The disclosed example results in a more
reliable decision regarding frame erasure.
[0031] The preceding description is exemplary rather than limiting
in nature. Variations and modifications to the disclosed examples
may become apparent to those skilled in the art that do not
necessarily depart from the essence of this invention. The scope of
legal protection given to this invention can only be determined by
studying the following claims.
* * * * *