U.S. patent application number 11/086958 was filed with the patent office on 2005-07-28 for adaptive gain adjustment control.
Invention is credited to Saifuddin, Ahmed.
Application Number | 20050163068 11/086958 |
Document ID | / |
Family ID | 29734303 |
Filed Date | 2005-07-28 |
United States Patent
Application |
20050163068 |
Kind Code |
A1 |
Saifuddin, Ahmed |
July 28, 2005 |
Adaptive gain adjustment control
Abstract
Systems and techniques are disclosed relating to
telecommunications which include transmitting a plurality of data
groups to a receiver at a first power level, retransmitting a first
one of the data groups to the receiver at a second power level
lower than the first power level, providing feedback from the
receiver relating to the retransmission of the first one of the
data groups, and retransmitting a second one of the data groups to
the receiver at a third power level different from the second power
level, the third power level being a function of the feedback. It
is emphasized that this abstract is provided to comply with the
rules requiring an abstract which will allow a searcher or other
reader to quickly ascertain the subject matter of the technical
disclosure. It is submitted with the understanding that it will not
be used to interpret or limit the scope or the meaning of the
claims.
Inventors: |
Saifuddin, Ahmed; (San
Diego, CA) |
Correspondence
Address: |
Qualcomm Incorporated
Patents Department
5775 Morehouse Drive
San Diego
CA
92121-1714
US
|
Family ID: |
29734303 |
Appl. No.: |
11/086958 |
Filed: |
March 21, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11086958 |
Mar 21, 2005 |
|
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10177132 |
Jun 20, 2002 |
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6898193 |
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Current U.S.
Class: |
370/326 ;
455/522 |
Current CPC
Class: |
H04L 1/1825 20130101;
H04W 52/50 20130101; H04W 52/48 20130101 |
Class at
Publication: |
370/326 ;
455/522 |
International
Class: |
H04B 007/00; H04B
001/69 |
Claims
What is claimed is:
1. A method of communications, comprising: transmitting a plurality
of data groups to a receiver at a first power level; decoding the
plurality of data groups by the receiver; and retransmitting one of
the data groups at a second power level lower than the first power
level if the one of the data groups is unsuccessfully decoded by
the receiver.
2. The method of claim 1 further comprising retransmitting another
of the data groups at third power level different from the second
power level if the another of the data groups is unsuccessfully
decoded by the receiver.
3. The method of claim 2 further including adjusting the third
power level as a function of the second power level.
4. The method of claim 3 further including: lowering the third
power level relative to the second power level if the one of the
data groups is successfully decoded; and increasing the third power
level relative to the second power level if the one of the data
groups is unsuccessfully decoded.
5. A method of communications, comprising: transmitting a plurality
of data groups to a receiver at a first power level; retransmitting
a first one of the data groups to the receiver at a second power
level lower than the first power level; providing feedback from the
receiver relating to the retransmission of the first one of the
data groups; and retransmitting a second one of the data groups to
the receiver at a third power level different from the second power
level, the third power level being a function of the feedback.
6. The method of claim 5 wherein the third power level is set
relative to the second power level as a function of the
feedback.
7. The method of claim 5 wherein each of the data groups comprises
a data frame.
8. The method of claim 5 wherein the third power level is less than
the first power level.
9. The method of claim 5 further comprising encoding each of the
data groups, and wherein the feedback indicates whether the
retransmission of the first one of the data groups was successfully
decoded by the receiver.
10. The method of claim 9 wherein the third power level is set
higher than the second power level if the feedback indicates that
the retransmission of the first one of the data groups was not
successfully decoded by the receiver, and the third power level is
set lower than the second power level if the feedback indicates
that the retransmission of the first one of the data groups was
successfully decoded by the receiver.
11. The method of claim 10 wherein the third power level is set
half-way between the first power level and the second power level
if the feedback indicates that the retransmission of the first one
of the data groups was not successfully decoded by the receiver,
and the third power level is set half-way between a minimum power
level and the second power level if the feedback indicates that the
retransmission of the first one of the data groups was successfully
decoded by the receiver, the minimum power level being less than
the second power level.
12. The method of claim 5 further comprising computing a reference
power level for transmitting a reference signal with each of the
data groups, computing a first power ratio as function of a
parameter, setting the first power level as a function of the
reference power level and the first power ratio, deriving a second
power ratio, setting of the second power level as a function of the
reference power level and the second power ratio, deriving a third
power ratio as a function of the feedback, and setting the third
power level as a function of the reference power level and the
power ratio.
13. The method of claim 12 wherein the third power ratio is set
relative to the second power ratio as a function of the
feedback.
14. The method of claim 12 wherein the first power ratio is defined
as the first power level divided by the reference power level, the
second power ratio is defined as the second power level divided by
the reference power level, and the third power ratio is defined as
the third power level divided by the reference power level.
15. The method of claim 14 wherein the third power ratio is less
than the first power ratio.
16. The method of claim 12 further comprising encoding each of the
data groups, and wherein the feedback indicates whether the
retransmission of the first one of the data groups was successfully
decoded by the receiver.
17. The method of claim 16 wherein the first power ratio is defined
as the first power level divided by the reference power level, the
second power ratio is defined as the second power level divided by
the reference power level, and the third power ratio is defined as
the third power level divided by the reference power level, the
third power ratio being set higher than the second power ratio if
the feedback indicates that the retransmission of the first one of
the data groups was not successfully decoded by the receiver, and
third power ratio being set lower than the second power ratio if
the feedback indicates that the retransmission of the first one of
the data groups was successfully decoded by the receiver.
18. The method of claim 17 wherein the third power ratio is set
half-way between the first power ratio and the second power ratio
if the feedback indicates that the retransmission of the first one
of the data groups was not successfully decoded by the receiver,
and the third power ratio is set half-way between a minimum power
ratio and the second power ratio if the feedback indicates that the
retransmission of the first one of the data groups was successfully
decoded by the receiver, the minimum power ratio being less than
the second power ratio.
19. Computer-readable media embodying a program of instructions
executable by a computer program to perform a method of
communications, the method comprising: transmitting a plurality of
data groups to a receiver at a first power level; decoding the
plurality of data groups by the receiver; and retransmitting one of
the data groups at a second power level lower than the first power
level if the one of the data groups is unsuccessfully decoded by
the receiver.
20. The computer-readable media of claim 19 wherein the method
further comprising retransmitting another of the data groups at
third power level different from the second power level if the
another of the data groups is unsuccessfully decoded by the
receiver.
21. The computer-readable media of claim 20 wherein the method
further including adjusting the third power level as a function of
the second power level.
22. The computer-readable media of claim 21 wherein the method
further including: lowering the third power level relative to the
second power level if the one of the data groups is successfully
decoded; and increasing the third power level relative to the
second power level if the one of the data groups is unsuccessfully
decoded.
23. An apparatus, comprising: a transmitter; a buffer configured to
provide a plurality of data groups to the transmitter for initial
transmission to a receiver, and provide at least first and second
ones of the data groups to the transmitter for retransmission to
the receiver; and a gain control configured to set each of the data
groups to a first power level for initial transmission, set the
first one of the data groups to a second power level lower than the
first power level, receive feedback from the receiver relating to
the first one of the data groups, and set the second one of the
data groups to a third power level as a function of the
feedback.
24. The apparatus of claim 23 wherein the gain control is further
configured to set the third power level relative to the second
power level as a function of the feedback.
25. The apparatus of claim 23 wherein each of the data groups
comprises a data frame.
26. The apparatus of claim 23 wherein the gain control is further
configured to set the third power level lower than the first power
level.
27. The apparatus of claim 23 further comprising an encoder
configured to encode each of the data groups from the buffer before
transmission, and wherein the feedback indicates whether the
retransmission of the first one of the data groups was successfully
decoded by the receiver.
28. The apparatus of claim 27 wherein the gain control is further
configured to set the third power level higher than the second
power level if the feedback indicates that the retransmission of
the first one of the data groups was not successfully decoded by
the receiver, and set the third power level lower than the second
power level if the feedback indicates that the retransmission of
the first one of the data groups was successfully decoded by the
receiver.
29. The apparatus of claim 28 wherein the gain control is further
configured to set the third power level half-way between the first
power level and the second power level if the feedback indicates
that the retransmission of the first one of the data groups was not
successfully decoded by the receiver, and set the third power level
half-way between a minimum power level and the second power level
if the feedback indicates that the retransmission of the first one
of the data groups was successfully decoded by the receiver, the
minimum power level being less than the second power level.
30. The apparatus of claim 23 further comprising a reference signal
generator configured to generate a reference signal and provide it
to the transmitter for transmission with each of the data groups,
the reference signal having a reference power level, and wherein
the gain control is further configured to compute a first power
ratio as function of a parameter, set the first power level as a
function of the reference power level and the first power ratio,
derive a second power ratio, set the second power level as a
function of the reference power level and the second power ratio,
derive a third power ratio as a function of the feedback, and set
the third power level as a function of the reference power level
and the power ratio.
31. The apparatus of claim 30 wherein gain control is further
configured to set the third power ratio relative to the second
power ratio as a function of the feedback.
32. The apparatus of claim 30 wherein the first power ratio is
defined as the first power level divided by the reference power
level, the second power ratio is defined as the second power level
divided by the reference power level, and the third power ratio is
defined as the third power level divided by the reference power
level.
33. The apparatus of claim 32 wherein the gain control is further
configured to set the third power ratio lower than the first power
ratio.
34. The apparatus of claim 30 further comprising an encoder
configured to encode each of the data groups from the buffer before
transmission, and wherein the feedback indicates whether the
retransmission of the first one of the data groups was successfully
decoded by the receiver.
35. The apparatus of claim 34 wherein the first power ratio is
defined as the first power level divided by the reference power
level, the second power ratio is defined as the second power level
divided by the reference power level, and the third power ratio is
defined as the third power level divided by the reference power
level, and wherein the gain control is further configured to set
the third power ratio higher than the second power ratio if the
feedback indicates that the retransmission of the first one of the
data groups was not successfully decoded by the receiver, and set
the third power ratio lower than the second power ratio if the
feedback indicates that the retransmission of the first one of the
data groups was successfully decoded by the receiver.
36. The apparatus of claim 35 wherein the gain control is further
configured to set the third power ratio half-way between the first
power ratio and the second power ratio if the feedback indicates
that the retransmission of the first one of the data groups was not
successfully decoded by the receiver, and set the third power ratio
half-way between a minimum power ratio and the second power ratio
if the feedback indicates that the retransmission of the first one
of the data groups was successfully decoded by the receiver, the
minimum power ratio being less than the second power ratio.
37. An apparatus, comprising: a transmitter; a buffer configured to
provide a plurality of data groups to the transmitter, and identify
whether each of the data groups provided to the transmitter is an
initial transmission or retransmission to a receiver; and a gain
control configured to set each of the data groups identified as an
initial transmission to an initial power level, receive feedback
from the receiver related to each of the data groups identified as
a retransmission, and adjust the power level for each of the data
groups identified as a retransmission based on the feedback from
the respective previous retransmission.
38. The apparatus of claim 37 wherein the gain control is further
configured to adjust the power level for each of the data groups
identified as a retransmission based on both the feedback for the
respective previous retransmission and the adjusted power level for
that previous retransmission.
39. The apparatus of claim 38 wherein each of the data groups
comprises a data frame.
40. The apparatus of claim 37 wherein the adjusted power level is
less than the initial power level.
41. The apparatus of claim 37 further comprising an encoder
configured to encode each of the data groups from the buffer before
transmission, and wherein the feedback indicates whether the
retransmission of each of the data groups was successfully decoded
by the receiver.
42. The apparatus of claim 41 wherein the gain control is further
configured to adjust the power level upward relative to the
adjusted power level for the previous retransmission if the
feedback indicates that the previous retransmission was not
successfully decoded by the receiver, and adjust the power level
downward relative to the adjusted power level for the previous
retransmission if the feedback indicates that the previous
retransmission was successfully decoded by the receiver.
43. The apparatus of claim 42 wherein the adjusted power level is
less than the initial power level, and wherein the gain control is
further configured to adjust the power level half-way between the
initial power level and the adjusted power level for the previous
retransmission if the feedback indicates that the previous
retransmission was not successfully decoded by the receiver, and
adjust the power level half-way between a minimum power level and
the adjusted power level for the previous retransmission if the
feedback indicates that the previous retransmission was
successfully decoded by the receiver, the minimum power level being
less than the adjusted power level for the previous
retransmission.
44. The apparatus of claim 37 further comprising a reference signal
generator configured to generate a reference signal and provide it
to the transmitter for transmission with each of the data groups,
the reference signal having a reference power level, and wherein
the gain control is further configured to compute an initial power
ratio as function of a parameter, set the initial power level as a
function of the reference power level and the initial power ratio,
adjust the power ratio as a function of the feedback for the
previous retransmission, and adjust the power level as a function
of the reference power level and the adjusted power ratio.
45. The apparatus of claim 44 wherein gain control is further
configured to adjust the power ratio as a function of both the
feedback for the previous retransmission and the adjusted power
ratio for that retransmission.
46. The apparatus of claim 44 wherein the initial power ratio is
defined as the initial power level divided by the reference power
level, and the adjusted power ratio is defined as the adjusted
power level divided by the reference power level.
47. The apparatus of claim 46 wherein the gain control is further
configured to adjust the power level lower than the initial power
ratio.
48. The apparatus of claim 44 further comprising an encoder
configured to encode each of the data groups from the buffer before
transmission, and wherein the feedback indicates whether the
respective retransmission was successfully decoded by the
receiver.
49. The apparatus of claim 48 wherein the initial power ratio is
defined as the initial power level divided by the reference power
level, and the adjusted power ratio is defined as the adjusted
power level divided by the reference power level, and wherein the
gain control is further configured to adjust the power ratio upward
with respect to the adjusted power ratio for the previous
retransmission if the feedback indicates that the previous
retransmission was not successfully decoded by the receiver, and
adjust the power ratio downward with respect to the adjusted power
ratio for the previous transmission if the feedback indicates that
the previous retransmission was successfully decoded by the
receiver.
50. The apparatus of claim 49 wherein the adjusted power level is
less than the initial power level, and wherein the gain control is
further configured to adjust the power level half-way between the
initial power level and the adjusted power level for the previous
retransmission if the feedback indicates that the previous
retransmission was not successfully decoded by the receiver, and
adjust the power level half-way between a minimum power level and
the adjusted power level for the previous retransmission if the
feedback indicates that the previous retransmission was
successfully decoded by the receiver, the minimum power level being
less than the adjusted power level for the previous
retransmission.
51. An apparatus for communications, comprising: means for
transmitting a plurality of data groups to a receiver at a first
power level; means for receiving feedback from the receiver; and
means for retransmitting one of the data groups at a second power
level lower than the first power level if the one of the data
groups is unsuccessfully decoded by the receiver.
52. The apparatus of claim 51 further comprising means for
retransmitting another of the data groups at third power level
different from the second power level if the another of the data
groups is unsuccessfully decoded by the receiver.
53. The apparatus of claim 52 further including means for adjusting
the third power level as a function of the second power level.
54. The apparatus of claim 53 further including: means for lowering
the third power level relative to the second power level if the one
of the data groups is successfully decoded; and means for
increasing the third power level relative to the second power level
if the one of the data groups is unsuccessfully decoded.
55. An apparatus, comprising: a transmitter; means for providing a
plurality of data groups to the transmitter for initial
transmission to a receiver; means for providing at least first and
second ones of the data groups to the transmitter for
retransmission to the receiver; means for setting each of the data
groups to a first power level for initial transmission; means for
setting the first one of the data groups to a second power level
lower than the first power level; means for receiving feedback from
the receiver relating to the first one of the data groups; and
means for setting the second one of the data groups to a third
power level as a function of the feedback.
56. The apparatus of claim 55 wherein the third power level is set
relative to the second power level as a function of the
feedback.
57. The apparatus of claim 55 wherein each of the data groups
comprises a data frame.
58. The apparatus of claim 55 wherein the third power level is set
below the first power level.
59. The apparatus of claim 55 further comprising means for encoding
each of the data groups before transmission, and wherein the
feedback indicates whether the retransmission of the first one of
the data groups was successfully decoded by the receiver.
60. The apparatus of claim 59 wherein the third power level is set
above the second power level if the feedback indicates that the
retransmission of the first one of the data groups was not
successfully decoded by the receiver, and the third power level is
set lower than the second power level if the feedback indicates
that the retransmission of the first one of the data groups was
successfully decoded by the receiver.
61. The apparatus of claim 60 wherein the third power level is set
half-way between the first power level and the second power level
if the feedback indicates that the retransmission of the first one
of the data groups was not successfully decoded by the receiver,
and the third power level is set half-way between a minimum power
level and the second power level if the feedback indicates that the
retransmission of the first one of the data groups was successfully
decoded by the receiver, the minimum power level being less than
the second power level.
62. The apparatus of claim 55 further comprising means for
generating a reference signal having a reference power level, means
for providing the reference signal to the transmitter for
transmission with each of the data groups, and means for computing
a first power ratio as function of a parameter, wherein the first
power level is set as a function of the reference power level and
the first power ratio, the apparatus further comprising means for
deriving second and third power ratios, the third power ratio being
a function of the feedback, and wherein the second power level is
set as a function of the reference power level and the second power
ratio, and the third power ratio is set as a function of the
reference power level and the power ratio.
63. The apparatus of claim 62 wherein the third power ratio is set
relative to the second power ratio as a function of the
feedback.
64. The apparatus of claim 62 wherein the first power ratio is
defined as the first power level divided by the reference power
level, the second power ratio is defined as the second power level
divided by the reference power level, and the third power ratio is
defined as the third power level divided by the reference power
level.
65. The apparatus of claim 64 wherein the third power ratio is set
lower than the first power ratio.
66. The apparatus of claim 62 further comprising means for encoding
each of the data groups before transmission, and wherein the
feedback indicates whether the retransmission of the first one of
the data groups was successfully decoded by the receiver.
67. The apparatus of claim 66 wherein the first power ratio is
defined as the first power level divided by the reference power
level, the second power ratio is defined as the second power level
divided by the reference power level, and the third power ratio is
defined as the third power level divided by the reference power
level, and wherein the third power ratio is set higher than the
second power ratio if the feedback indicates that the
retransmission of the first one of the data groups was not
successfully decoded by the receiver, and the third power ratio is
set lower than the second power ratio if the feedback indicates
that the retransmission of the first one of the data groups was
successfully decoded by the receiver.
68. The apparatus of claim 67 wherein the third power ratio is set
half-way between the first power ratio and the second power ratio
if the feedback indicates that the retransmission of the first one
of the data groups was not successfully decoded by the receiver,
and set the third power ratio half-way between a minimum power
ratio and the second power ratio if the feedback indicates that the
retransmission of the first one of the data groups was successfully
decoded by the receiver, the minimum power ratio being less than
the second power ratio.
Description
CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn.120
[0001] The present Application for Patent is a Continuation and
claims priority to patent application Ser. No. 10/177,132 entitled
"Adaptive Gain Adjustment Control" filed Jun. 20, 2002, now
allowed, and assigned to the assignee hereof and hereby expressly
incorporated by reference herein.
BACKGROUND
[0002] 1. Field
[0003] The present invention relates generally to communications
systems, and more specifically, to systems and techniques for
adaptively controlling the gain of one or more channels in a
communications system.
[0004] 2. Background
[0005] Modern communications systems are designed for multiple user
access to a common communications medium. Numerous multiple-access
techniques are known in the art, such as time division
multiple-access (TDMA), frequency division multiple-access (FDMA),
space division multiple-access, polarization division
multiple-access, code division multiple-access (CDMA), and other
similar multi-access techniques. The multiple-access concept is a
channel allocation methodology which allows each user to access a
common communications medium without interfering with others.
[0006] In multi-access communications systems, techniques to reduce
mutual interference between multiple users are often utilized to
increase user capacity. By way of example, power control techniques
are currently employed to limit the transmission power of each user
to that necessary to achieve a desired quality of service. This
approach ensures that each user transmits only the minimum power
necessary, but no higher, thereby making the smallest contribution
to the total noise seen by others. However, as user demands for
multi-access capability increases, techniques to further reduce the
transmission power of each user without compromising the quality of
service are needed.
SUMMARY
[0007] In one aspect of the present invention, a method of
communications includes transmitting a plurality of data groups to
a receiver at a first power level, retransmitting a first one of
the data groups to the receiver at a second power level lower than
the first power level, providing feedback from the receiver
relating to the retransmission of the first one of the data groups,
and retransmitting a second one of the data groups to the receiver
at a third power level different from the second power level, the
third power level being a function of the feedback.
[0008] In another aspect of the present invention,
computer-readable media embodying a program of instructions
executable by a computer program performs a method of
communications, the method includes setting a plurality of data
groups to a first power level for transmission to a receiver,
setting a first one of the data groups to a second power level
lower than the first power level for retransmission to the
receiver, receiving feedback from the receiver relating to a
retransmission of the first one of the data groups, and setting a
second one of the data groups to a third power level for
retransmission to the receiver, the third power level being a
function of the feedback.
[0009] In yet another aspect of the present invention, an apparatus
includes a transmitter, a buffer configured to provide a plurality
of data groups to the transmitter for initial transmission to a
receiver, and provide at least first and second ones of the data
groups to the transmitter for retransmission to the receiver, and a
gain control configured to set each of the data groups to a first
power level for initial transmission, set the first one of the data
groups to a second power level lower than the first power level,
receive feedback from the receiver relating to the first one of the
data groups, and set the second one of the data groups to a third
power level as a function of the feedback.
[0010] In a further aspect of the present invention, an apparatus
includes a transmitter, a buffer configured to provide a plurality
of data groups to the transmitter, and identify each of the data
groups provided to the transmitter as an initial transmission or
retransmission to a receiver, and a gain control configured to set
each of the data groups identified as an initial transmission to an
initial power level, receive feedback from the receiver related to
each of the data groups identified as a retransmission, and adjust
the power level for each of the data groups identified as a
retransmission based on the feedback from the respective previous
retransmission.
[0011] In yet a further aspect of the present invention, an
apparatus includes a transmitter, means for providing a plurality
of data groups to the transmitter for initial transmission to a
receiver, means for providing at least first and second ones of the
data groups to the transmitter for retransmission to the receiver,
means for setting each of the data groups to a first power level
for initial transmission, means for setting the first one of the
data groups to a second power level lower than the first power
level, means for receiving feedback from the receiver relating to
the first one of the data groups, and means for setting the second
one of the data groups to a third power level as a function of the
feedback.
[0012] It is understood that other embodiments of the present
invention will become readily apparent to those skilled in the art
from the following detailed description, wherein it is shown and
described only exemplary embodiments of the invention by way of
illustration. As will be realized, the invention is capable of
other and different embodiments and its several details are capable
of modification in various other respects, all without departing
from the spirit and scope of the present invention. Accordingly,
the drawings and detailed description are to be regarded as
illustrative in nature and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Aspects of the present invention are illustrated by way of
example, and not by way of limitation, in the accompanying
drawings, wherein:
[0014] FIG. 1 is a conceptual overview of an exemplary CDMA
communications system;
[0015] FIG. 2 is a simplified functional block diagram of a
subscriber station configured to operate in a CDMA communications
system;
[0016] FIG. 3 is a flow diagram illustrating an exemplary algorithm
for a gain control function in a subscriber station; and
[0017] FIG. 4 is a graphical illustration of an exemplary adaptive
traffic-pilot ratio used to implement the gain control
function.
DETAILED DESCRIPTION
[0018] The detailed description set forth below in connection with
the appended drawings is intended as a description of exemplary
embodiments of the present invention and is not intended to
represent the only embodiments in which the present invention can
be practiced. The term "exemplary" used throughout this description
means "serving as an example, instance, or illustration," and
should not necessarily be construed as preferred or advantageous
over other embodiments. The detailed description includes specific
details for the purpose of providing a thorough understanding of
the present invention. However, it will be apparent to those
skilled in the art that the present invention may be practiced
without these specific details. In some instances, well-known
structures and devices are shown in block diagram form in order to
avoid obscuring the concepts of the present invention.
[0019] In an exemplary communications system, power control
techniques can be used to limit the power of each user to that
necessary to achieve a desired quality of service. If the
communications system supports packet data services with
retransmission capability for corrupted data, the retransmission
power can be further limited by using the information received from
the corrupted data to decode the retransmitted data. More
specifically, the soft decisions from the corrupted data can be
soft combined with the retransmitted data to reduce the energy per
bit (EbNt) required to maintain the desired quality of service. As
a result, user capacity of the system may be increased.
[0020] The application of these power control techniques can be
illustrated with reference to an exemplary CDMA communications
system as shown in FIG. 1. CDMA is a modulation and multiple access
technique based on spread-spectrum communications. In a CDMA
communications system, a large number of signals share the same
frequency spectrum. This is achieved by transmitting each signal
with a different code that modulates a carrier, and thereby,
spreads the spectrum of the signal waveform. The transmitted
signals are separated in the receiver by a demodulator that uses a
corresponding code to despread the desired signal's spectrum. The
undesired signals, whose codes do not match, are not despread in
bandwidth and contribute only to noise.
[0021] Although various aspects of these power control techniques
will be described in the context of a CDMA communications system,
those skilled in the art will appreciate that these techniques are
equally applicable to various other communications environments.
Accordingly, any reference to a CDMA communications system is
intended only to illustrate the inventive aspects of the present
invention, with the understanding that such inventive aspects have
a wide range of applications.
[0022] Turning to FIG. 1, a base station controller 102 can be used
to provide an interface between a network 104 and all base stations
dispersed throughout a geographic area. The geographic area is
divided into coverage regions known as cells or sectors. A base
station is generally assigned to serve all subscriber stations in a
coverage region. For ease of explanation, only one base station 106
is shown. A subscriber station 108 may access the network 104, or
communicate with other subscriber stations (not shown), through one
or more base stations under control of the base station controller
102.
[0023] The exemplary CDMA communications system supports two-way
communications between the base station 106 and the subscriber
station 108. Transmissions from the base station 106 to the
subscriber station 108 are referred to as forward link
transmissions, and transmissions from the subscriber 108 to the
base station 106 are referred to as reverse link transmissions. The
base station 106 typically controls the reverse link power of a
reference or pilot signal transmitted from the subscriber station
108 using various power control techniques well known in the art.
The subscriber station 108 also transmits traffic over the reverse
link. The reverse link power of the traffic can be set by the
subscriber station 108 based on the power of the pilot signal using
a traffic-pilot ratio. The traffic-pilot ratio may be set based on
any number of parameters such as the carrier frequency, chip rate,
data rate, modulation scheme, frame length, or any other
parameters. In at least one embodiment of the CDMA communications
system, the base station 106 can be configured to provide feedback
to the subscriber station 108 indicating whether the reverse link
traffic can be successfully decoded. This can be accomplished by
transmitting the reverse link traffic in data groups, typically
known as frames, and sending an acknowledgement (ACK) response over
the forward link for each frame that can be successfully decoded by
the base station 106. For those frames that cannot be successfully
decoded, a negative acknowledgement (NACK) response can be sent to
the subscriber station 108 over the forward link requesting a
retransmission of that frame. Because the base station 106 can use
the information from the unsuccessfully decoded frame, the
subscriber station 108 can reduce the transmission power of the
frame being retransmitted by reducing the traffic-pilot ratio. In a
manner to be described in greater detail later, the level of power
reduction for retransmitted frames can be adaptively adjusted to
optimize performance.
[0024] FIG. 2 is a functional block diagram of an exemplary
subscriber station. The subscriber station 108 includes a data
buffer 202 which partitions the reverse link traffic into data
groups for transmission to the base station. The data groups can be
data frames, or any other type of data groups such as a data
packets. The data buffer 202 includes a data queue 203 and a frame
synchronizer 204. The data queue 203 can be used to buffer data
from an external data source (not shown), and the frame
synchronizer 204 can be used to control, the release of data frames
sequentially from the data queue 203 to an encoder 206. The encoder
206 provides error correction coding and interleaving of the data
within each frame. The encoded frames can be provided to the
modulator 208 where they are spread with a Walsh cover and
amplified with a gain signal computed by a gain control 210. The
Walsh covered frames can then be combined with other overhead
signals, each having a unique Walsh code, spread with a long
pseudo-random noise (PN) code generated by a unique user address
mask, and quadrature modulated with short PN codes identifying the
base station. The quadrature modulated signal can then be provided
to a transmitter 212 where it is upconverted, filtered and
amplified for over the air transmission through an antenna 214 to
the base station.
[0025] Following the transmission of each data frame, a response
may be transmitted from the base station to the subscriber station
over the forward link indicating whether the data frame was
successfully decoded. The response may be an ACK indicating that
the data frame was successfully decoded. Conversely, the response
may be a NACK indicating that the data frame was corrupted and
requesting a retransmission of that data frame. The response can be
sent from the base station in a separate transmission or
accompanying the forward link traffic. Where the response is
transmitted with the forward link traffic, the response can be
time-division multiplexed, frequency-division multiplexed,
code-division multiplexed, or multiplexed using any other scheme
known in the art. Alternatively, the response can be transmitted
with the forward link pilot signal. This approach ensures timely
delivery of the response to the subscriber station even when the
forward link traffic is not present. Typically, the response will
be covered with a unique Walsh function so that it can be combined
with other forward link transmissions before being quadrature
modulated with the short PN codes.
[0026] The forward link transmission is received by the antenna 214
and provided to a receiver 216. The receiver 216 filters,
amplifies, and downconverts the forward link transmission to a
baseband signal. The baseband signal can be coupled to a
demodulator 218 where it is quadrature demodulated with the short
PN codes and decovered by the Walsh codes to separate the various
signals. The forward link traffic can then be despread using the
long PN code and provided to a decoder 220 for de-interleaving and
decoding. The ACK or NACK response can be coupled from the
demodulator 218 to the frame synchronizer 204. The frame
synchronizer 204 initiates the retransmission of the data frame in
response to a NACK response by re-releasing the data frame from the
data queue 203 after a predetermined retransmission delay. By way
of example, if data frames 1, 2, 3, 4, 5, 6 and 7 are queued to be
released sequentially from the data queue 203, and a NACK response
is generated from data frames 1, 3 and 4, then the frame
synchronizer 204 will insert frame repeats in the sequence such
that data frames 1, 2, 3, 1, 4, 3, 5, 4, 6 and 7 are sequentially
released from the data queue 203 if the retransmission delay is set
for two data frames.
[0027] The transmission power for each data frame can be controlled
by a gain signal computed by the gain control 210 based on the
traffic-pilot ratio. The traffic-pilot ratio is typically
predetermined during the call set up based on any number of
parameters such as the carrier frequency, chip rate, data rate,
modulation scheme, frame length, or any other parameters. The gain
signal applied to the data frames can be computed by means well
known in the art from the predetermined traffic-pilot ratio and the
reverse link transmission power of the pilot signal. In existing
CDMA communications systems, the reverse link transmission power of
pilot signal is computed with two power control loops: an open loop
control and a closed loop control. The open loop control is
designed to control the reverse link transmission power of the
pilot signal as a function of path loss, the effect of base station
loading, and environmentally induced phenomena such as fast fading
and shadowing. The closed loop control is designed to correct the
open loop estimate to achieve a desired signal-to-noise ratio. This
can be achieved by measuring the reverse link power of the pilot
signal at the base station and providing feedback to the subscriber
station to adjust the reverse link transmission power for the pilot
signal.
[0028] The gain applied to the data frames during retransmission
can be reduced by reducing the traffic-pilot ratio. To optimize
performance, the traffic-pilot ratio should be reduced to the point
where the transmission power is limited to that necessary to
successfully decode the retransmitted frame at the base station
using the soft decisions of the same frame previously transmitted.
An adaptive algorithm can be used to maintain an optimal
traffic-pilot ratio for retransmission frames despite changing data
rates and environmental conditions. The adaptive algorithm can be
implemented to adjust the traffic-pilot ratio during retransmission
frames based on whether or not the previous retransmission frame
was successfully decoded by the base station. The previous
retransmission frame can be either the same frame, or
alternatively, a retransmission of an entirely different data
frame. To illustrate this concept using the earlier example, if
data frames 1, 2, 3, 4, 5, 6 and 7 are queued to be released
sequentially from the data queue 203, and a NACK response is
generated from data frames 1, 3 and 4, then the frame synchronizer
204 will insert frame repeats in the sequence such that data frames
1, 2, 3, 1, 4, 3, 5, 4, 6 and 7 are sequentially released from the
data queue 202. In this case, the traffic-pilot ratio used to
compute the gain signal for the retransmission of frame 3 will be
based on the feedback from the base station for the retransmission
of frame 1.
[0029] A flag 204a set by the frame synchronizer 204 can be used by
the gain control 210 to identify the retransmission frames. If the
frame synchronizer 204 releases a data frame from the data queue
203 for initial transmission, the flag 204a is cleared, and the
gain control 210 uses the predetermined traffic-pilot ratio to
compute the gain signal. Conversely, if the frame synchronizer 204
releases a data frame from the data queue 203 for retransmission,
the flag 204a is set, and the gain control 210 adjusts the
traffic-pilot ratio to some level below the predetermined level,
computes the gain signal applied to the data frame in the modulator
208 based on the adjusted traffic-pilot ratio, and listens for
feedback from the base station for the retransmitted data frame.
The feedback 218a can be provided to the gain control 210 from the
demodulator 218. When the next retransmission frame is released
from the data queue 203, the feedback for the previous
retransmission frame can be used to adjust the traffic-pilot ratio
to compute a new gain signal.
[0030] Various algorithms can be implemented by the gain control
depending on the particular application and overall design
requirements. FIG. 3 is a flow diagram illustrating an exemplary
algorithm. In step 302, a predetermined traffic-pilot ratio is
established based on various parameters such as the carrier
frequency, chip rate, data rate, modulation scheme, frame length,
or any other parameters. This is typically done during call set up.
In step 304, the flag from the frame synchronizer is checked to
determine whether the data frame released from the data queue is a
retransmission frame. If the data frame is not a retransmission
frame, the traffic-pilot ratio is set to the predetermined value to
compute the gain signal in step 306. Conversely, if the data frame
released from the data queue is a retransmission frame, then a
determination is made as to whether the data frame is the first
retransmission frame of the call in step 308. If the data frame is
the first retransmission of the call, then the traffic-pilot ratio
is set to a minimum value to compute the gain signal in step
310.
[0031] Assuming that the data frame is not the first retransmission
of the call, then a determination is made as to whether the
previous retransmission frame was successfully decoded by the base
station in step 312. If the previous retransmission frame was
successfully decoded, then the traffic-pilot ratio for the current
retransmission frame is reduced in step 314. The magnitude of the
traffic-pilot ratio reduction is application dependent and those
skilled in the art will be readily able to determine the
appropriate magnitude based on the overall design parameters. The
reduced traffic-pilot ratio is then compared with the minimum value
in step 316. If the reduced traffic-pilot is greater than or equal
to the minimum value, then the reduced traffic-pilot ratio is used
to compute the gain signal in step 318. Conversely, if the reduced
traffic-pilot ratio is below the minimum value, then the
traffic-pilot ratio is set to the minimum value and the gain signal
is computed at the minimum value in step 320.
[0032] Assuming that the previous retransmission frame was not
successfully decoded at the base station, then the traffic-pilot
ratio for the current retransmission frame is increased in step
322. The magnitude of the traffic-pilot ratio increase is
application dependent and those skilled in the art will be readily
able to determine the appropriate magnitude based on the overall
design parameters. The increased traffic-pilot ratio is then
compared with a maximum value in step 324. If the increased
traffic-pilot is less than or equal to the maximum value, then the
increased traffic-pilot ratio is used to compute the gain signal in
step 326. Conversely, if the increased traffic-pilot ratio is above
the maximum value, then the traffic-pilot ratio is set to the
maximum value and the gain signal is computed at the maximum value
in step 328.
[0033] An exemplary application of the algorithm can be illustrated
using the earlier example with data frames 1, 2, 3, 4, 5, 6 and 7
queued to be released sequentially from the data queue, and a NACK
response generated from data frames 1, 3 and 4, resulting in data
frames 1, 2, 3, 1, 4, 3, 5, 4, 6 and 7 being sequentially released
from the data queue. For the purposes of explanation, the
predetermined traffic-pilot ratio is equal to the maximum
traffic-pilot ratio which is equal to 5 dB. The magnitude of any
increase in the traffic-pilot ratio will be equal to 1/2 of the
magnitude in dB between the traffic-pilot ratio for the previous
retransmission frame and the maximum traffic-pilot ratio. In
addition, the minimum traffic-pilot ratio is equal to 1 dB, and the
magnitude of any reduction in the traffic-pilot ratio is equal to
1/2 the magnitude in dB between the traffic-pilot ratio for the
previous retransmission frame and the minimum traffic-pilot
ratio.
[0034] A graphical illustration of the adaptive traffic-pilot ratio
under these conditions is shown in FIG. 4. The initial transmission
of data frames 1, 2, and 3 would be transmitted with a
traffic-pilot ratio of 5 dB. The retransmission of data frame 1,
being the first retransmission for the call, would be transmitted
at the minimum traffic-pilot ratio, i.e., 1 dB. The initial
transmission of frame 4 following the retransmission of frame 1
would be at the predetermined traffic-pilot ratio, i.e., 5 dB. The
traffic-pilot ratio used for the retransmission of frame 3 would
depend on whether the retransmission of frame 1 was successfully
decoded at the base station. If the retransmission of frame 1 was
not successfully decoded, then the traffic-pilot ratio for the
retransmission of frame 3 would be adjusted to 3 dB as shown in
FIG. 4, i.e., half the magnitude between the traffic-pilot ratio
for the retransmission of frame 1 and the maximum value.
Conversely, if the retransmission of frame 1 was successfully
decoded at the base station, then the traffic-pilot ratio for the
retransmission of frame 3 would be adjusted to 1 dB. Either way,
the initial transmission of frame 5 following the retransmission of
frame 3 would be at the predetermined traffic-pilot ratio, i.e., 5
dB.
[0035] The retransmission of frame 4 would depend on whether the
retransmission of frame 3 was successfully decoded at the base
station. Assuming that the retransmission of frame 3 occurred with
a traffic-pilot ratio of 3 dB and was successfully decoded at the
base station, then the traffic-pilot ratio for the retransmission
of frame 4 would be adjusted to 2 dB as shown in FIG. 4, i.e., half
the magnitude between the traffic-pilot ratio for the
retransmission of frame 3 and the minimum value. Assuming that the
retransmission of frame occurred with a traffic-pilot ratio of 3 dB
and was not successfully decoded at the base station, then the
traffic-pilot ratio for the retransmission of frame 4 would be
adjusted to 4 dB, i.e., half the magnitude between the
traffic-pilot ratio for the retransmission of frame 3 and the
maximum value. Either way, the initial transmission of frames 6 and
7 following the retransmission of frame 4 would be at the
predetermined traffic-pilot ratio, i.e., 5 dB.
[0036] The various illustrative logical blocks, modules, and
circuits described in connection with the embodiments disclosed
herein may be implemented or performed with a general purpose
processor, a digital signal processor (DSP), an application
specific integrated circuit (ASIC), a field programmable gate array
(FPGA) or other programmable logic device, discrete gate or
transistor logic, discrete hardware components, or any combination
thereof designed to perform the functions described herein. A
general-purpose processor may be a microprocessor, but in the
alternative, the processor may be any conventional processor,
controller, microcontroller, or state machine. A processor may also
be implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0037] The methods or algorithms described in connection with the
embodiments disclosed herein may be embodied directly in hardware,
in a software module executed by a processor, or in a combination
of the two. A software module may reside in RAM memory, flash
memory, ROM memory, EPROM memory, EEPROM memory, registers, hard
disk, a removable disk, a CD-ROM, or any other form of storage
medium known in the art. An exemplary storage medium is coupled to
the processor such the processor can read information from, and
write information to, the storage medium. In the alternative, the
storage medium may be integral to the processor. The processor and
the storage medium may reside in an ASIC. The ASIC may reside in a
user terminal. In the alternative, the processor and the storage
medium may reside as discrete components in a user terminal.
[0038] The previous description of the disclosed embodiments is
provided to enable any person skilled in the art to make or use the
present invention. Various modifications to these embodiments will
be readily apparent to those skilled in the art, and the generic
principles defined herein may be applied to other embodiments
without departing from the spirit or scope of the invention. Thus,
the present invention is not intended to be limited to the
embodiments shown herein but is to be accorded the widest scope
consistent with the principles and novel features disclosed
herein.
* * * * *