U.S. patent application number 09/777338 was filed with the patent office on 2002-01-17 for diversity reception employing periodic testing.
Invention is credited to Burneske, Gregory W., Melewski, Brian John, Murphy, Timothy Patrick, Sullivan, Daniel Thomas, Thyes, Todd Robert, Wagner, Keely Anne.
Application Number | 20020006159 09/777338 |
Document ID | / |
Family ID | 26895060 |
Filed Date | 2002-01-17 |
United States Patent
Application |
20020006159 |
Kind Code |
A1 |
Wagner, Keely Anne ; et
al. |
January 17, 2002 |
Diversity reception employing periodic testing
Abstract
The quality of a channel for each of a plurality of receive
antennas is determined in part by examining data collected during
reception of test data. Substantially simultaneously, payload data
is also used to evaluate channel quality for at least one antenna.
A quality metric calculated for any given antenna is the result of
measurements made upon the test and payload data. Parameters used
to calculate the quality metric are preferably divided into two
sets of non-identical parameters, those based on the test data and
those based on the payload data. These parameters preferably
include jitter, received signal strength, CRC errors and
synchronization errors. By continuously updating quality metrics
based on both test and payload data, more reliable assessments can
be made of the various antennas being used. As a result, antenna
selection is rendered commensurately more reliable thereby
improving received signal quality.
Inventors: |
Wagner, Keely Anne; (Neenah,
WI) ; Melewski, Brian John; (Appleton, WI) ;
Murphy, Timothy Patrick; (Menasha, WI) ; Sullivan,
Daniel Thomas; (New London, WI) ; Thyes, Todd
Robert; (Appleton, WI) ; Burneske, Gregory W.;
(Sherwood, WI) |
Correspondence
Address: |
BANNER & WITCOFF, LTD.
TEN SOUTH WACKER DRIVE
SUITE 3000
CHICAGO
IL
60606
US
|
Family ID: |
26895060 |
Appl. No.: |
09/777338 |
Filed: |
February 6, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09777338 |
Feb 6, 2001 |
|
|
|
09629115 |
Jul 31, 2000 |
|
|
|
09777338 |
Feb 6, 2001 |
|
|
|
09628850 |
Jul 31, 2000 |
|
|
|
09777338 |
Feb 6, 2001 |
|
|
|
09628851 |
Jul 31, 2000 |
|
|
|
09777338 |
Feb 6, 2001 |
|
|
|
09629117 |
Jul 31, 2000 |
|
|
|
60159069 |
Oct 12, 1999 |
|
|
|
60193141 |
Mar 29, 2000 |
|
|
|
60193153 |
Mar 29, 2000 |
|
|
|
60193142 |
Mar 29, 2000 |
|
|
|
60193862 |
Mar 30, 2000 |
|
|
|
60159069 |
Oct 12, 1999 |
|
|
|
60193141 |
Mar 29, 2000 |
|
|
|
60193153 |
Mar 29, 2000 |
|
|
|
60193142 |
Mar 29, 2000 |
|
|
|
60193862 |
Mar 30, 2000 |
|
|
|
60159069 |
Oct 12, 1999 |
|
|
|
60193141 |
Mar 29, 2000 |
|
|
|
60193153 |
Mar 29, 2000 |
|
|
|
60193142 |
Mar 29, 2000 |
|
|
|
60193862 |
Mar 30, 2000 |
|
|
|
60159069 |
Oct 12, 1999 |
|
|
|
60193141 |
Mar 29, 2000 |
|
|
|
60193153 |
Mar 29, 2000 |
|
|
|
60193142 |
Mar 29, 2000 |
|
|
|
60193862 |
Mar 30, 2000 |
|
|
|
60193142 |
Mar 29, 2000 |
|
|
|
60193141 |
Mar 29, 2000 |
|
|
|
60193153 |
Mar 29, 2000 |
|
|
|
60193862 |
Mar 30, 2000 |
|
|
|
Current U.S.
Class: |
375/224 ;
375/267 |
Current CPC
Class: |
H04L 1/20 20130101; H04B
7/0808 20130101; H04B 7/0811 20130101 |
Class at
Publication: |
375/224 ;
375/267 |
International
Class: |
H04Q 001/20; H04B
003/46; H04B 017/00; H04L 001/02; H04B 007/02 |
Claims
What is claimed is:
1. In a wireless communication device, a method for evaluating
signal sources of a plurality of signal sources, the method
comprising steps of: determining at least one test quality metric
uniquely corresponding to at least one test signal source of the
plurality of signal sources; determining at least one payload
quality metric uniquely corresponding to a payload signal source of
the plurality of signal sources substantially simultaneously with
the step of determining the at least one test quality metric; and
evaluating at least some of the plurality of signal sources based
at least upon the at least one test quality metric and the at least
one payload quality metric.
2. The method of claim 1, wherein the plurality of signal sources
comprises a plurality of antennas.
3. The method of claim 1, further comprising a step of: selecting a
new payload signal source from the plurality of signal sources
based at least upon the at least one test quality metric and the at
least one payload quality metric.
4. The method of claim 3, wherein the step of selecting further
comprises selecting the new payload signal source based at least
upon a previous payload quality metric corresponding to the payload
signal source comparing unfavorably with a threshold.
5. The method of claim 3, wherein the step of selecting further
comprises selecting the new payload signal source at least based
upon the at least one payload quality metric comparing unfavorably
with a threshold.
6. The method of claim 1, wherein the at least one test quality
metric is based at least upon a jitter value measured during the
reception of test data.
7. The method of claim 1, wherein the at least one test quality
metric is based at least upon received signal strength value
measured during the reception of test data.
8. The method of claim 1, wherein the at least one test quality
metric is based at least upon any of: at least one previous jitter
value measured during the reception of previous test data, at least
one previous received signal strength value measured during the
reception of the previous test data, at least one previous CRC
error value calculated during the reception of the previous test
data, and at least one previous synchronization error value
calculated during the reception of the previous test data.
9. The method of claim 1, wherein the at least one payload quality
metric is based at least upon an error value calculated during the
reception of payload data.
10. The method of claim 1, wherein the at least one payload quality
metric is based at least upon a synchronization error value
calculated during the reception of payload data.
11. The method of claim 1, wherein the at least one payload quality
metric is based at least upon any of: at least one previous CRC
error value calculated during the reception of previous payload
data and at least one previous synchronization error value
calculated during the reception of the previous payload data.
12. In a wireless communication device, a method for determining a
quality metric for at least one signal source, the method
comprising steps of: calculating a first set of quality parameters
for the at least one signal source based on reception of test data;
calculating a second set of quality parameters for the at least one
signal source based on the reception of payload data, wherein the
first set of quality parameters are not identical to the second set
of quality parameters; and determining the quality metric based at
least upon the first and second sets of quality parameters.
13. The method of claim 12, wherein the first set of quality
parameters comprises any of: a jitter value measured during the
reception of the test data and a received signal strength value
measured during the reception of the test data.
14. The method of claim 13, wherein the quality metric is at least
based upon any of: at least one previous jitter value measured
during the reception of previous test data and at least one
previous received signal strength value measured during the
reception of the previous test data.
15. The method of claim 12, wherein the second set of quality
parameters comprises any of: a CRC error value calculated during
the reception of the payload data and a synchronization error value
calculated during the reception of the payload data.
16. The method of claim 15, wherein the quality metric is at least
based upon any of: at least one previous CRC error value calculated
during the reception of previous payload data and at least one
previous synchronization error value calculated during the
reception of the previous payload data.
17. The method of claim 12, wherein the at least one signal source
is at least one antenna.
18. In a wireless communication device, a method for evaluating a
plurality of signal sources, the method comprising steps of:
evaluating each of the plurality of signal sources based upon
reception of test data to provide a plurality of quality metrics;
selecting a payload signal source based on the plurality of quality
metrics; and updating a quality metric corresponding to the payload
signal source based upon the reception of payload data to provide
an updated quality metric.
19. The method of claim 18, wherein the step of selecting further
comprises selecting the payload signal source based at least upon a
previous quality metric corresponding to a previous payload signal
source comparing unfavorably with a threshold.
20. The method of claim 18, wherein the step of selecting further
comprises selecting the payload signal source at least based upon a
quality metric of the plurality of quality metrics corresponding to
a previous payload signal source comparing unfavorably with a
threshold.
21. The method of claim 18, further comprising a step of: selecting
a new payload signal source based at least upon the updated quality
metric.
22. The method of claim 21, wherein the step of selecting the new
payload signal source further comprises selecting the new payload
signal source based at least upon the updated quality metric
comparing unfavorably with a threshold.
23. The method of claim 18, wherein the plurality of signal sources
comprises a plurality of antennas.
24. A wireless communication device comprising: a plurality of
antennas; and a signal processing unit, operably coupled to the
plurality of antennas, that substantially simultaneously determines
at least one test quality metric uniquely corresponding to at least
one test antenna of the plurality of antennas and at least one
payload quality metric uniquely corresponding to a payload antenna
of the plurality of antennas, and that selects a new payload
antenna from the plurality of antennas at least based upon the at
least one test quality metric and the at least one payload quality
metric.
25. The wireless communication device of claim 24, wherein the
signal processing unit selects the new payload antenna based at
least upon a previous payload quality metric corresponding to the
payload antenna comparing unfavorably with a threshold.
26. The wireless communication device of claim 24, wherein the
signal processing unit selects the new payload antenna at least
based upon the at least one payload quality metric comparing
unfavorably with a threshold.
27. The wireless communication device of claim 24, further
comprising: a wireless receiver, operably coupled to the plurality
of antennas and the signal processing unit, operating in a U-NII
band.
28. The wireless communication device of claim 24, wherein at least
some of the plurality of antennas are directional antennas.
29. The wireless communication device of claim 24, wherein the
plurality of antennas comprises at least one omnidirectional
transmit antenna.
30. A wireless communication device comprising: a plurality of
antennas; and a signal processing unit, operably coupled to the
plurality of antennas, that calculates a first set of quality
parameters for one of the plurality of antennas based on reception
of test data and a second set of quality parameters for the one of
the plurality of antennas based on the reception of payload data,
and that determines a quality metric for the one of the plurality
of antennas based on the first and second sets of quality
parameters, wherein the first set of quality parameters are not
identical to the second set of quality parameters.
31. The wireless communication device of claim 30, wherein the
signal processing unit calculates the first set of quality
parameters comprising any of: a jitter value measured during the
reception of the test data and a received signal strength value
measured during the reception of the test data.
32. The wireless communication device of claim 30, wherein the
signal processing unit determines the quality metric at least based
upon any of: at least one previous jitter value measured during the
reception of previous test data and at least one previous received
signal strength value measured during the reception of the previous
test data.
33. The wireless communication device of claim 30, further
comprising: a wireless receiver, operably coupled to the plurality
of antennas and the signal processing unit, operating in a U-NII
band.
34. The wireless communication device of claim 30, wherein at least
a portion of the plurality of antennas are directional
antennas.
35. The wireless communication device of claim 3 0, wherein the
plurality of antennas comprises at least one omnidirectional
transmit antenna.
36. A wireless communication device comprising: a plurality of
antennas; and a signal processing unit, operably coupled to the
plurality of antennas, that evaluates each of the plurality of
antennas based upon reception of test data to provide a plurality
of quality metrics, selects a payload antenna based on the
plurality of quality metrics, and that updates a quality metric
corresponding to the payload antenna based upon the reception of
payload data to provide an updated quality metric.
37. The wireless communication device of claim 36, wherein the
signal processing unit selects the payload antenna based at least
upon a previous quality metric corresponding to a previous payload
antenna comparing unfavorably with a threshold.
38. The wireless communication device of claim 36, wherein the
signal processing unit selects the payload antenna at least based
upon a quality metric of the plurality of quality metrics
corresponding to a previous payload antenna comparing unfavorably
with a threshold.
39. The wireless communication device of claim 36, wherein the
signal processing unit selects a new payload antenna based at least
upon the updated quality metric.
40. The wireless communication device of claim 39, wherein the
signal processing unit selects the new payload signal source based
at least upon the updated quality metric comparing unfavorably with
a threshold.
41. The wireless communication device of claim 36, further
comprising: a wireless receiver, operably coupled to the plurality
of antennas and the signal processing unit, operating in a U-NII
band.
42. The wireless communication device of claim 36, wherein at least
a portion of the plurality of antennas are directional
antennas.
43. The wireless communication device of claim 36, wherein the
plurality of antennas comprises at least one omnidirectional
transmit antenna.
44. An integrated circuit for use in selecting a signal source from
amongst a plurality of signal sources, comprising: at least one
signal source input; means, coupled to the at least one signal
source input, for substantially simultaneously determining at least
one test quality metric uniquely corresponding to at least one test
signal source of the plurality of signal sources and at least one
payload quality metric uniquely corresponding to a payload signal
source of the plurality of signal sources; and means, coupled to
the means for determining, that selects a new payload signal source
from the plurality of signal sources at least based upon the at
least one test quality metric and the at least one payload quality
metric.
45. The integrated circuit of claim 44, wherein the means for
selecting selects the new payload signal source based at least upon
a previous payload quality metric corresponding to the payload
signal source comparing unfavorably with a threshold.
46. The integrated circuit of claim 44, wherein the means for
selecting selects the new payload signal source at least based upon
the at least one payload quality metric comparing unfavorably with
a threshold.
47. The integrated circuit of claim 44, wherein the means for
determining measures a jitter value during the reception of test
data, and wherein the at least one test quality metric is based at
least upon the jitter value.
48. The integrated circuit of claim 52, further comprising: a
signal strength input, coupled to the means for determining,
wherein the at least one test quality metric is based at least upon
a received signal strength value received via the signal strength
input.
49. An integrated circuit for determining a quality metric for one
of a plurality signal sources, comprising: at least one signal
source input; means, coupled to the at least one signal source
input, for calculating a first set of quality parameters for the
one of the plurality of signal sources based on reception of test
data; means, coupled to the at least one signal source input, for
calculating a second set of quality parameters for the one of the
plurality of signal sources based on the reception of payload data,
wherein the first set of quality parameters and the second set of
quality parameters are not identical; and means, coupled to the
means for calculating the first set of quality parameters and the
means for calculating the second set of quality parameters, for
determining the quality metric based on the first and second sets
of quality parameters.
50. The integrated circuit of claim 49, wherein the first set of
quality parameters comprises a jitter value measured during the
reception of the test data.
51. The integrated circuit of claim 49, further comprising: a
signal strength input, coupled to the means for calculating the
first set of quality parameters, wherein the first set of quality
parameters comprises a received signal strength value measured
during the reception of the test data and received via the signal
strength input.
52. The integrated circuit of claim 49, wherein the second set of
quality parameters comprises any of: a CRC error value calculated
during the reception of the payload data and a synchronization
error value calculated during the reception of the payload
data.
53. An integrated circuit for use in evaluating a plurality of
signal sources, comprising: at least one signal source input;
means, coupled to the at least one signal source input, for
evaluating each of the plurality of signal sources based upon
reception of test data to provide a plurality of quality metrics;
and means for selecting a payload signal source based on the
plurality of quality metrics, wherein the means for evaluating
updates a quality metric corresponding to the payload antenna based
upon the reception of payload data to provide an updated quality
metric.
54. The integrated circuit of claim 53, wherein the means for
selecting selects the payload signal source based at least upon a
previous quality metric corresponding to a previous payload signal
source comparing unfavorably with a threshold.
55. The integrated circuit of claim 53, wherein the means for
selecting selects the payload signal source at least based upon a
quality metric of the plurality of quality metrics corresponding to
a previous payload signal source comparing unfavorably with a
threshold.
56. The integrated circuit of claim 53, wherein the means for
selecting selects a new payload signal source based at least upon
the updated quality metric.
57. The integrated circuit of claim 56, wherein the means for
selecting selects the new payload signal source based at least upon
the updated quality metric comparing unfavorably with a threshold.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The instant application claims priority under 35 U.S.C.
119(e) from U.S. Provisional Patent Application Ser. No. 60/199,712
filed on Apr. 26, 2000.
TECHNICAL FIELD
[0002] The present invention relates generally to wireless
communication systems and, in particular, to the selection of
receiving antennas in wireless communication devices having a
plurality of antennas.
BACKGROUND OF THE INVENTION
[0003] Wireless communication systems are well known in the art. In
such systems, wireless communication devices typically communicate
information (such as voice and data) with each other via one or
more wireless channels, e.g., radio frequency (RF) channels. A
fundamental performance limitation on such wireless systems,
however, arises from the fact that the wireless channels used to
convey information are typically subjected to a variety of noise
and interference sources. These impairments to the wireless
channels degrade overall system performance, for example, by
introducing errors into signals demodulated by wireless receivers.
While such degradations may be corrected and/or mitigated through a
variety of techniques, system designers continue to develop new
approaches to combat this problem.
[0004] One well-known technique in this regard is sometimes
referred to as diversity reception. Such diversity receivers
generally comprise a single receiver (meaning, in this case, a
device capable of comparing a plurality of received signals)
provided with multiple receiving sources in order to receive a
given transmitted signal. One type of diversity receiver then
attempts to consistently pick the most reliable receiving source,
i.e., the signal with the best reception. Thus, if performance of a
given receiving source is intermittently impaired, the diversity
receiver can optimally identify a better signal source, thereby
maintaining or improving receiver performance.
[0005] The benefits of diversity receivers are provided, in part,
by virtue of spatial diversity between the multiple receiving
sources. For example, in wide-area communication systems, diversity
receivers often comprise a device referred to as a comparator
coupled to a plurality of geographically diverse receivers. The
comparator continuously compares the quality of the signals
received from each of the diverse receivers and attempts to select
the best signal. The resulting signal output by the comparator
optimally represents the best possible signal at all times.
[0006] A variation of this technique is used in conjunction with
portable or mobile communication devices. For mobile applications,
spatial diversity through geographically diverse receivers is not
possible. Instead, spatial diversity is achieved by equipping the
portable or mobile device with a plurality of directional antennas.
As known in the art, a directional antenna provides optimal
coverage along a specific direction, in contrast to an
omindirectional antenna that provides equal coverage in all
directions. By diversely aligning the optimal receive paths of the
directional antennas, the probability of the wireless device
receiving at least one acceptable signal source is increased. The
best possible signal is provided at all times by switching between
antennas when appropriate. For this reason, this technique is often
referred to as antenna switching. Antenna switching as described
herein is particularly effective in applications where it is
anticipated that reflected signals would be prevalent; for example,
indoor applications.
[0007] While diversity reception may be employed to improve system
performance, a continuing challenge when implementing diversity
receivers is how to determine which source should be used at any
given moment in order to ensure that received errors are minimized.
For example, when the currently used source degrades, the receiver
should ideally switch to the best available source. However, it may
be that the current source is actually the best available at that
moment and switching would only worsen performance. Conversely,
even though the current source is acceptable, it may be
advantageous to switch to another source that is currently
performing even better. Overall, the goal of any diversity
reception scheme, including antenna switching, is to minimize the
number of errors occurring at a receiver. Ideally, the number of
such errors would be zero; however, in reality this goal is
unattainable using only diversity reception or, more particularly,
antenna switching, because it is entirely possible for a wireless
channel to severely degrade during reception of a signal thereby
resulting in completely unpredictable errors. The goal, therefore,
of any diversity reception technique is actually to reduce the
number of errors detected to be the number of undetectable, and
therefore unavoidable, errors. Techniques that help system
designers achieve this goal would represent an advancement of the
art.
SUMMARY OF THE INVENTION
[0008] The present invention provides a technique for a wireless
communication device to select a signal source with which to
receive payload data from amongst a plurality of signal sources.
Preferably, each signal source is a directional antenna. Each
signal source effectively represents a receive channel. The quality
of the channel for each receive signal source is determined in part
by examining data collected during reception of test data.
Substantially simultaneously, payload data is also used to evaluate
channel quality for at least one signal source. Thus, a quality
metric calculated for any given signal source is preferably the
result of measurements made upon test and payload data. In one
embodiment of the invention, the parameters used to calculate the
quality metric are divided into two sets of parameters, those based
on the test data and those based on the payload data. Preferably,
the types of parameters in the first set are not identical to the
types of parameters as in the second set. Parameters preferably
used to determine the quality metric for a signal source comprise
jitter, received signal strength, CRC errors and synchronization
errors. Selection of anew signal source preferably occurs only when
the current payload signal source compares unfavorably with a
threshold. By continuously updating quality metrics based on both
test and payload data, more reliable assessments can be made of the
various signal sources being used. As a result, signal source
selection is rendered commensurately more reliable thereby
improving received signal quality. These and other advantages will
be apparent from the detailed description that follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] In the detailed description of presently preferred
embodiments of the present invention which follows, reference will
be made to the drawings comprised of the following figures, wherein
like reference numerals refer to like elements in the various views
and wherein:
[0010] FIG. 1 is a block diagram of a wireless communications
system in accordance with the present invention;
[0011] FIG. 2 is a block diagram of a wireless communication device
in accordance with the present invention;
[0012] FIG. 3 is a functional block diagram of a wireless receiver
front-end in accordance with the present invention;
[0013] FIG. 4 is a flow chart illustrating a generalized method for
antenna selection in accordance with the present invention;
[0014] FIG. 5 is a flow chart illustrating one embodiment of a
method for antenna selection in accordance with the present
invention;
[0015] FIGS. 6A and 6B are a flow chart illustrating a preferred
embodiment of a method for antenna selection in accordance with the
present invention;
[0016] FIG. 7 illustrates a structured packet in accordance with
the present invention that is used to implemented the method
illustrated in FIGS. 6A and 6B;
[0017] FIG. 8 illustrates a test packet in accordance with a
preferred embodiment of the present invention; and
[0018] FIG. 9 illustrates exemplary waveforms for determining a
parameter that, in turn, is used to establish quality metrics in
accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0019] The present invention may be more fully described with
reference to FIGS. 1-9. FIG. 1 illustrates a block diagram of a
wireless communication system 100 comprising a wireless
transmitting device 102 and a wireless receiving device 104 that
communicate with each other via at least one wireless channel 103.
While only a single transmitting device and a single receiving
device are shown, such systems typically comprise a plurality of
transmitting and receiving devices. The transmitting device 102 and
receiving device 104 may comprise stationary or mobile devices or
both and, in a preferred embodiment, both comprise mobile devices
used in an in-home environment. For the sake of simplicity, various
infrastructure devices (e.g., repeaters, base stations, etc.) that
are often used to facilitate wireless communications are not
depicted in FIG. 1. However, it is understood that the present
invention may be equally applied to wireless communication systems
employing such infrastructure devices. The at least one wireless
channel 103 may comprise any wireless media including, but not
limited to, one or more infrared carriers, RF carriers, etc.
Furthermore, the present invention is not limited by the manner in
which the at least one wireless channel 103 is modulated. In a
preferred embodiment, the at least one wireless channel 103
comprises a frequency modulated RF carrier in the so-called
Unlicensed-National Information Infrastructure (U-NII) band located
at 5.15-5.35 GHz and 5.725-5.825 GHz.
[0020] The receiving device 104 also preferably comprises a
plurality of antennas 106 used for diversity reception. While any
number of antennas may be used, the plurality of antennas 106
preferably comprises at least one transmitting antenna and a
plurality of receiving antennas. Furthermore, while any one type or
combination of types of antennas may be used, transmitting antennas
preferably comprise omnidirectional antennas and receiving antennas
preferably comprise directional antennas, such as linearly or
circularly polarized patch antennas. In one embodiment of the
present invention, the plurality of antennas 106 comprises one
omnidirectional transmitting antenna and four linearly polarized
patch receiving antennas. Where directional antennas are used,
their particular orientation relative to each other is a matter of
design choice. However, in a preferred embodiment, they are
oriented to be maximally diverse, i.e., such that the Euclidean
distance between the respective optimized receive directions of
each antenna is maximized, and such that all potential receive
vectors (i.e., 360 degrees) are covered by the directional
antennas. In the case of four equivalent directional antennas, this
implies that each directional antenna has a beamwidth of at least
90 degrees.
[0021] The present invention is primarily described in terms of
multiple antennas. However, those having ordinary skill in the art
will appreciate that antennas are a single case of what may be
referred to as signal sources. In the context of the present
invention, a signal source may be defined as any means whereby a
transmitted signal is provided for use in diversity reception. As
such, signal sources may include antennas coupled to a single
wireless receiver through an antenna switch. Alternatively, signal
sources may comprise multiple wireless receivers (each having one
or more antennas) providing baseband data for diversity reception
analysis. Further examples of signal sources may be readily
apparent to those having ordinary skill in the art. Although the
present invention is described hereinafter in terms of antennas, it
is understood that signal sources, as broadly defined herein, may
be substituted equally.
[0022] Turning now to FIG. 2, there is illustrated a block diagram
of a wireless communication device 200 in accordance with the
present invention. The wireless communication device 200 comprises
the plurality of antennas 106 described above, an antenna switch
202, a wireless receiver 204, a wireless transmitter 206, and a
control and signal processing unit 208 arranged as shown. The
antenna switch 202 comprises a solid-state or mechanical switching
device that at least routes any of the antenna inputs to its
receiving output. Where more than one transmitting antenna is
provided, the antenna switch 202 may similarly route signals from
one or more transmitters (only one shown) to any of the
transmitting antennas. The wireless receiver 204 demodulates
signals received via the antenna switch 202. In a preferred
embodiment, the wireless receiver 204 is an RF receiver operating
within the U-NII band. However, other types of receivers are well
known in the art and may be equally employed. Likewise, the
wireless transmitter 206 modulates a wireless carrier, preferably
an RF carrier in the U-NII band. For both the transmitter 206 and
receiver 204, any of a variety of well-known modulation and
demodulation techniques may be used; the present invention is not
limited in this regard.
[0023] The control and signal processing unit 208 preferably
provides control of the antenna switch 202 and, optionally, the
receiver 204 and transmitter 206 as illustrated by the dashed
lines. However, it is understood that such control may be provided
by and incorporated within, or shared with, other components, e.g.,
the receiver 204 or transmitter 206 or both. The control
functionality and the signal processing functionality embodied by
the control and signal processing unit 208 may be incorporated into
separate devices, rather than a signal device.
[0024] The control and signal processing unit 208 may be a
microprocessor, microcontroller, digital signal processor or the
like, or a combination of such devices operating under the control
of software routines and operational data stored in volatile or
non-volatile digital storage devices or both as known in the art.
In a preferred embodiment, however, the control and signal
processing unit 208 is at least partially implemented in hardware
using, for example, one or more application specific integrated
circuits (ASICs) or field-programmable gate arrays (FPGAs). A more
detailed description of such a hardware embodiment is further
described below with respect to FIG. 3.
[0025] The control and signal processing unit 208 implements
control and processing functions for the wireless communication
device 200. In part, the control and signal processing unit 208,
and the functionality it implements, operates to take demodulated
baseband data from the receiver 204 as input and to provide
processed data as output. Processing performed on the demodulated
baseband data is well known in the art and includes error
correction decoding, etc. In particular, as described below,
processing on the demodulated baseband data also includes analysis
used for antenna switching purposes. Some or all of this type of
processing may be incorporated into the receiver 204 as a matter of
design choice. In the opposite direction, the control and signal
processing unit 208 takes as input data to be transmitted and,
after processing the transmit data in accordance with known
techniques (e.g., error correction encoding), provides the transmit
data to the transmitter 206 for modulation onto the wireless
carrier. Once again, some or all of this functionality may be
incorporated into the transmitter 206 as a matter of design
choice.
[0026] A more detailed depiction of a wireless receiver front-end
300 in accordance with the present invention is illustrated in FIG.
3. As shown, the wireless receiver front-end 300 comprises a
plurality of receiving antennas 301 of the type described above
coupled to an antenna switch 302. The antenna switch 302
selectively provides input signals received from the antennas 301
as an output 303 as determined by a control signal 310. The antenna
switch 302 is coupled to a demodulator 304 that is, in turn,
coupled to a signal processor 308. The signal processor 308
provides a control signal 309 and a data output 310. When
implemented, the functionality represented by the demodulator 304
and signal processor 308 may be distributed among separate elements
or combined, in whole or in part, within one or more elements. To
illustrate with reference to FIG. 2, the demodulator 304 may be
implemented entirely by the receiver 204 and the signal processor
308 may be implemented entirely within the control and signal
processing unit 208. Alternatively, the receiver 204 may carry out
a portion of the signal processor 308 functionality or the control
and signal processing unit 208 may carry out a portion of the
demodulator 304 functionality. Those having ordinary skill in the
art will appreciate that implementation of the functions
illustrated in FIG. 3 is a matter of design choice and that the
present invention is not limited in this regard.
[0027] As known in the art, the demodulator 304 functions to
extract data that has been modulated onto a wireless carrier
signal. Regardless of how it is implemented, the demodulator 304
takes as input a received modulated carrier signal 303 and provides
as output a received baseband signal 305. Further, in a presently
preferred embodiment, the demodulator 304 also provides as output
received signal strength data 306 indicative of the signal strength
of the received wireless carrier. In practice, a variety of
techniques for implementing the functionality of the demodulator
304 are well known in the art and typically depends upon the manner
in which the carrier signal was modulated.
[0028] The signal processor 308 operates upon the received baseband
signal 305 and, preferably, upon the received signal strength data
306 so as to provide the control output 309 used to control the
antenna switch 302. That is, the control output 309 causes the
antenna switch 302 to selectively route the signal provided by one
of the antennas to its output 303. The present invention improves
determination of the control output 309 such that the data output
310 optimally represents the best possible received data. The
manner in which this is done is further described with reference to
FIGS. 4-9. Furthermore, in a preferred embodiment, at least the
functionality in the signal processor 308 relating to antenna
switching is implemented in hardware using FPGAs, ASICs or the
like. Optionally, and as depicted in the implementation illustrated
in FIG. 3, the signal processor 308 provides the data output 309
comprising reconstructed information representative of the
information originally transmitted. To this end, the signal
processor 308 may implement a variety of functions well known in
the art, such as decryption, error correction decoding, signal
conditioning (e.g., filtering), etc.
[0029] Referring now to FIG. 4, a generalized method for selecting
an antenna in accordance with the present invention is illustrated.
In particular, steps 402 through 410 illustrate a continuous loop
whereby quality metrics Q are continuously determined and assessed
for N different receiving antennas. In particular, the present
invention provides techniques whereby a given quality metric
Q.sub.j is determined based on test data and payload data, thereby
providing a more reliable indication of the "quality" of signals
provided by the j.sup.th receiving antenna. Hereinafter, the
variable T is used to indicate an antenna that is currently being
tested through the reception of test data, whereas the variable P
is used to indicate an antenna that is currently being used to
receive payload data, i.e., the antenna whose signal is currently
being routed to the output of the antenna switch during payload
reception. As used herein, test data indicates data that is used
for the purpose of testing the quality of a channel provided by a
receiving antenna. Otherwise, test data conveys no information
intended for reconstruction or consumption by a user at the
receiver. In contrast, payload data is the information that is
conveyed with the intent that it will be reconstructed for
consumption at the receiver and, in accordance with the present
invention, is also used to test the quality of channels provided by
receiving antennas.
[0030] Thus, at step 402, the quality metric, Q(T), for the antenna
currently chosen to receive the test data (the test antenna) is
updated based on the received test data and, at step 404, the
quality metric, Q(P), for the antenna currently selected to receive
payload data (the payload antenna) is updated based on the received
payload data. Because channel conditions can change rapidly, it is
preferable to perform steps 402 and 404 as closely in time as
possible. Furthermore, it is possible for T and P to have the same
value, implying that the antenna currently under test is also the
same antenna being used to receive payload data.
[0031] At step 406, it is determined whether the quality metric for
the payload antenna is currently favorable. In the context of the
present invention, a favorable quality metric indicates that the
channel provided by the antenna to which the quality metric
corresponds is performing well enough to provide reliable data
output, e.g., data output 309. This step is preferably included so
that a good channel will not be abandoned until its performance
degrades to the point that a reliable data output (i.e.
substantially error free) can no longer be assured. If Q(P) is
currently favorable, the processing continues at step 410 where T
is incremented and the process is repeated. If, however, Q(P) is no
longer favorable, processing continues at step 408 where a new
antenna P is selected based on all of the current quality metrics.
In other words, when performance of the current payload antenna
degrades sufficiently, a new payload antenna is selected based on
the current state of the quality metrics. Thereafter, T is
incremented so that the process of updating quality metrics may
continue. Although the thresholding test of step 406 is preferably
implemented, it is understood that step 406 could be eliminated, in
which case it is possible that a new payload antenna will be
selected for each iteration of test data.
[0032] Regardless, it should be noted that the particular order of
steps 402 through 410 might be varied as a matter of design choice.
That is, the order of steps 402 and 404 could be reversed with
little or no effect. As another example, steps 406 and 408 could be
performed at any time relative to steps 402 and 404, even between
steps 402 and 404. In essence, because of the continuous nature of
the process of evaluating quality metrics and selecting a payload
antenna based thereon, the particular order in which these steps
are performed can be arbitrary. In a presently preferred
embodiment, all test data for each antenna is sequentially received
at step 402, prior to the reception of payload data at step 404. In
this embodiment, the determination of step 406 is performed twice;
once after the reception of all of the test data and again after
the reception of payload data. This preferred embodiment is
described in further detail with reference to FIG. 6 below.
[0033] Referring now to FIG. 5, one embodiment of a method for
selecting an antenna in accordance with the present invention is
illustrated. In particular, the method illustrated in FIG. 5 relies
on the use of packetized data transmission in which test data
packets are transmitted before each payload packet. The use of
packet data systems is well known in the art and need not be
described in further detail.
[0034] At step 502, the antenna currently selected to receive a
test packet, Ant(T), is evaluated based on reception of a test
packet. In the context of the present invention, this evaluation
consist of measuring and/or calculating the values of various
receive parameters based on the received test data, presently
preferred examples of which are described in greater detail below.
Preferably, the parameters measured/calculated at step 502 comprise
a first set of parameters. Using the first set of parameters, the
quality metric, Q(T), of the test antenna is updated and stored at
step 504. Thereafter, at step 506, T is incremented in anticipation
of the next test packet. Because the identity of the test antenna
is continuously incremented, the present invention causes quality
metrics to be continuously updated, thereby providing greater
reliability when using the quality metrics to select an
antenna.
[0035] At step 508, it is determined whether the quality metric,
Q(P), of the current payload antenna is favorable or not, as
described above relative to step 406. If not, a new payload antenna
P is selected at step 512 based on all of the current quality
metric values. The selection of a new antenna may then be
manifested through the issuance of a control signal used to control
an antenna switch. In a preferred embodiment, the quality metrics
values may vary within a fixed range, for example, from 0 to 1023
where a value of 0 represents the best possible (most favorable)
quality metric and a value of 1023 represents the worst possible
(least favorable) quality metric. Thus, as shown in FIG. 5, P is
set to the value of j based on finding the minimum quality metric
Q(j) for j=1 to N.
[0036] Processing continues at step 510 after selecting a new value
for P at step 512 or after determining that Q(P) is favorable at
step 508. At step 510, the antenna currently selected as the
payload antenna, Ant(P), is evaluated based on reception of a
payload (or data) packet. In one embodiment of the present
invention, the payload packet occurs immediately after the test
packet such that testing based on both occurs substantially
simultaneously. As before, the evaluation of the payload packet
consist of measuring and/or calculating the values of various
receive parameters based on the received payload data, presently
preferred examples of which are described in greater detail below.
Preferably, the parameters measured/calculated at step 510 comprise
a second set of parameters that are not identical to the types of
parameters in the first set of parameters measured/calculated at
step 502. Using the second set of parameters, the quality metric,
Q(P), of the payload antenna is updated and stored at step 514.
Thereafter, processing continues at step 502 in anticipation of new
test and payload packets. The method illustrated in FIG. 5 is
particularly suited for implementations in which forward error
correction (FEC) is not used to ensure the integrity of the payload
data. However, in practice, it is desirable and often necessary to
implement FEC in wireless systems.
[0037] Referring now to FIG. 6, there is illustrated a preferred
embodiment of a method for antenna selection in accordance with the
present invention. As noted above, the method illustrated in FIG. 6
is preferably implemented in hardware using ASICs, FPGAs or the
like. The method illustrated in FIG. 6 is particularly suited for
use in packet data systems in which structured packets,
incorporating FEC, are used. A preferred form of packet structure
is illustrated in FIG. 7.
[0038] As shown in FIG. 7, a structured packet 700 comprises a
packet sync segment 702 and a plurality of payload segments 704.
Preferably, the structured packet 700 is transmitted or otherwise
conveyed by sequentially transmitting the packet sync segment 702
followed by each of the plurality of payload segments 704. The
packet sync segment 702 comprises, at its beginning, an antenna
switching buffer period 706, followed by a packet sync 708, a
closed loop refresh period 710 and a plurality of antenna test
packets 712. The antenna switching buffer period 706 is a period of
time in which no data is actually transmitted and provides an
interval in which an antenna switch may be reliably configured to
connect a given antenna input to an output of the antenna switch.
In a presently preferred embodiment, the buffer period 706 has
duration equivalent to the amount of time normally required to
transmit four bytes of data. In practice, the length of the buffer
period is a function of the minimum settling time of the antenna
switch as well as the data transmission rate.
[0039] The packet sync 708 is a predefined length (preferably,
eight bytes) data field comprising known data. The packet sync 708
provides large-scale synchronization for the entire structured
packet 700. The remainder of the structured packet 700 cannot be
received if the packet sync 708 is not found. Because the packet
sync 708 is transmitted and received with known periodicity, it is
not necessary to receive the entire packet sync 708 with perfect
accuracy. In a preferred embodiment, the packet sync 708 may be
skewed two bits (to account for phase shifts caused by switching
antennas) in either direction and still be detected. This five-bit
window allows the packet sync 708 to be robust to channel
degradations and still received with high confidence.
[0040] Like the buffer period 706, no data is transmitted during
the closed loop refresh period 710. The duration of the refresh
period 710 is a matter of transmitter and receiver implementation.
In a preferred embodiment, the refresh period is equivalent to the
transmission time of 141 bytes of data. This accounts for a closed
loop refresh of 75 usec. at the transmitter, as well as 15 usec. of
phase locked loop programming and wait time at the receiver. It is
understood that the length of the refresh period 710 is design
dependent and may be adjusted according to the needs of the
particular implementation.
[0041] The packet sync segment 702 concludes with a plurality of
antenna test packets 712. In a preferred embodiment, four antenna
test packets (one for each antenna) are transmitted; a greater or
lesser number of antenna test packets may be used as a matter of
design choice. In general, each test packet 712 (including those
used in conjunction with the embodiments illustrated in FIGS. 4 and
5) must at least include known data. By comparing the data received
during a test packet against the known data corresponding to that
test packet, the performance of a particular antenna may be
evaluated. A preferred structure for each of the antenna test
packets 712 is illustrated in FIG. 8. As shown, the test packet
comprises various fields. The bit lengths shown relative to each
field represent presently preferred lengths but, in practice, such
lengths are a matter of design choice.
[0042] As shown in FIG. 8, each antenna test packet begins with a
first wait or buffer period 802 during which no information is
transmitted to allow for switching to the desired test antenna. In
a preferred embodiment, duration of the first wait period is the
time required to transmit four bytes of data. A preamble 804
comprises a succession of alternating bits (AAAA in hexadecimal
notation) which carry no information. They allow the receiver to
lock onto the transmitter and recover a clock signal, as known in
the art. Similar to the packet sync 708, the antenna or test sync
806 is a series of bits that needs to be received correctly to
align the receiver to the transmitted bit stream. If the antenna
sync 806 is not found, no information in the packet is found. As
described in greater detail below, the antenna sync 806 is also
used to derive parameters useful in calculating an antenna quality
metric. The test word 810 is a known, fixed bit pattern having, for
example, the value (in hexadecimal notation) A5A6B654D5929A5A. As
described in further detail below, the deterministic nature of the
test word 810 allows various measurements to be performed, thereby
allowing a quality metric to be determined for the antenna being
tested. Finally, an antenna or test cyclic redundancy check 812 is
determined based on the test word 810 and is included as way to
determine whether there were any errors in the test word 810. The
use of CRCs in general is well known in the art and is not
described in further detail herein.
[0043] Referring again to FIG. 7, the structured packet 700 is
shown comprising the preferred number (twelve) of payload segments.
Preferably, each of the payload segments comprises the identical
structure to all other payload segments, as illustrated in FIG. 7.
Each payload segment begins with the identical buffer period 706 to
allow for antenna switching between the packet sync segment 702 and
the initial payload segment, or for antenna switching between
payload segments. The buffer period 706 is followed by a segment
sync 714. Preferably, the segment sync 714 is a known bit pattern
having a length of one byte. Like the packet sync 708 and the test
sync 806, the segment sync 714 ensures that the receiver continues
to be aligned with the transmitted bit stream. A one byte header
716 is preferably included in each payload segment. Each header 716
comprises information regarding the type of packet being
transmitted and, optionally, version information. A payload segment
718 follows each header 716. Preferably, each payload segment 718
comprises 207 bytes of interleaved data and parity information. The
parity information is the result of FEC coding and serves to
correct errors in the received data. Finally, each payload segment
concludes with a segment CRC 720. The segment CRC 720 is determined
relative to the payload segment 718. The segment CRC 720 serves as
a means for updating quality metrics determined during reception of
the antenna test packets 712, as will be described in greater
detail below.
[0044] Before describing FIG. 6 in detail, it is noted that the
method illustrated therein is based on several quality parameters
used to determine quality metrics for receiving antennas. In
particular, the quality parameters used include a synchronization
(Sync) error parameter, a correlation quality (CQ) parameter, a
received signal strength (RSS) parameter and an antenna or test
cyclical redundancy code (aCRC) error parameter and a segment
cyclical redundancy code (sCRC) error parameter. Those having
ordinary skill in the art will recognize that other parameters
could be used in place of, or in addition to, the parameters
described herein. Regardless of the types of parameters used, a
complete set of such parameters is maintained for each antenna
under consideration. The measurement of each of these parameters is
preferably based, in the case of the Sync, CQ, RSS and aCRC
parameters, on test data and, in the case of the sCRC parameter, on
payload data. Those having ordinary skill in the art will recognize
that other combinations of the test and payload data may be used to
determine the various parameters. Each of these parameters and the
manner in which the quality metrics are calculated based on these
parameters is discussed in greater detail below. Various particular
values and thresholds relative to the implementation of these
parameters are described below for exemplary purposes. However, it
is understood that other values could be equally used as a matter
of design choice. The use of penalty adders, etc. below assumes
that quality metrics may range from low to high values, with low
being favorable and high being unfavorable. However, other
comparison methods could be used. For example, higher values could
be considered favorable and lower values unfavorable. In this case,
rather than using penalty adders, penalty subtractors could be
used. Those having ordinary skill in the art will doubtless be able
to create a variety of such methods without departing from the
scope of the present invention. Additionally, particular techniques
for maintaining memory of previous parameter values are described
below. However, it is understood that a variety of techniques may
be used to implement such memory.
[0045] The Sync error parameter is based on the number of errors
detected in a received antenna sync 806. Techniques for determining
the occurrence and number of errors are well known in the art. The
preferred maximum value of the Sync parameter is 511. Additionally,
in accordance with the present invention, the Sync error parameter
is preferably maintained as a running sum that incorporates memory
of its previous values. To this end, if a Sync error is detected
(i.e., a test packet is not found), a total equal to the number of
detected bit errors multiplied by 64 is added to one half the
previous value of the running sum. In the optimal case in which no
errors are detected, the update to the Sync parameter defaults to
dividing the running sum by two. Note that in accordance with a
presently preferred embodiment, test packets will be detected if
the number of errors in the test packet is less than twelve.
[0046] During the reception of each test packet, the correlation
between the received test word and the known test word is measured
to determine the CQ parameter. In a presently preferred
implementation, each bit of the received test word is over-sampled
by a factor of 8. Thus, each bit of the received test word will
ideally comprise eight samples that, if perfectly received, would
correlate exactly with eight samples of the corresponding bit in
the known test word. By comparing the received test word samples
with the known test word samples, it is possible to obtain a
measurement of the jitter induced by the channel in the received
test word. Thus, the samples for each bit in the received test word
are treated as a set and compared with a corresponding set from the
ideal test word. The number of consecutive errors (i.e.,
non-matching samples) is counted for each set. This is illustrated
in FIG. 9 where waveforms representative of a known test word 902
and a received test word 904 are shown. In particular, two bits
906, 908 of each waveform are shown. The dotted lines illustrate
the eight-times over-sampling done on each bit to provide a set of
samples for each bit. Relative to the first bit 906, one of the
samples 910 is in error; relative to the second bit 908, two
consecutive bits 912 are in error. Although consecutive errors are
illustrated at the beginning of the second bit 908, in practice
consecutive errors may occur anywhere within a single bit period.
The number of consecutive errors arising from each set causes the
addition of a corresponding penalty value to the CQ parameter. Each
penalty value represents how far off the received edges are from
the expected edges. Exemplary penalty values are illustrated in
Table 1 below. The values illustrated in Table 1 assume that CQ is
an eight-bit number, and that any penalty values that cause CQ to
go above 255 will be ignored.
1 TABLE 1 Number of Consecutive Errors Adder 1 1 2 32 3 64 4 or
more 128
[0047] Tests have shown that CQ does predict bit errors. However,
it tends to be noisy in that the value can jump from very high to
very low between packets. It is possible for an antenna to have a
high CQ several packets before a data packet with errors, followed
by a very low CQ immediately before the bad packet. If some memory
of the high CQ is kept, tests have shown that it is sometimes
possible to switch off of the bad antenna before the bit error is
detected. Thus, a running sum of old (previous) CQ values is
preferably maintained. In particular, after every antenna test, the
running sum is first divided by two and the current value of CQ is
then added to the running sum. In this way, the old values have a
continually decreasing influence on the choice of receive antenna.
An additional benefit of this memory is the smoothing out of the CQ
factor, preventing some unnecessary switching between antennas.
[0048] As its name would imply, the received signal strength
parameter describes the strength of received signal over the
channel currently being tested. Techniques for assessing received
signal strength are well known in the art. In a presently preferred
embodiment, an RSS of 0 ideally corresponds to no signal and an RSS
of 240 ideally corresponds to a very strong signal. Note that this
range of values is dependent upon current implementations and is,
essentially, an arbitrary range. Other ranges of value may be
equally employed as a matter of design choice. Where the RSS value
is determined based on a conversion of an analog signal to digital
values, changing the voltage reference on the analog-to-digital
converter can increase the dynamic range of measured RSS values.
Regardless, the RSS value is used to derive a received signal
strength quality (RQ) factor that is, essentially, a penalty value.
Tests have shown that changes in received signal strength, whether
increasing or decreasing, are a strong indicator of poor channel
quality. In a presently preferred embodiment, the RQ factor is
determined as follows. First, the absolute value of the difference
between the previous RSS and current RSS, minus one to allow room
for noise, is determined, as shown in Equation 1 below:
.vertline.RSSI.sub.k-1-RSSI.sub.k.vertline.-1 Eq. (1)
[0049] To determine the RQ, the value derived from Equation 1 is
multiplied by a constant to determine RQ. Note that the lack of
change in RSS values (i.e., that the previous RSS value is the same
as the current RSS) will result in RQ being set to zero. Otherwise,
the multiplier constant is chosen based on the current RSS value.
Exemplary multiplier constants are illustrated in Table 2
below.
2 TABLE 2 Current RSS RQ Multiplier 220 <= RSS 0 185 <= RSS
< 220 1 150 <= RSS < 185 2 115 <= RSS < 150 4 80
<= RSS < 115 8 RSS < 80 16
[0050] The values illustrated in Table 2 assume that RQ is an
eight-bit number, and that any difference value or multiplier that
causes RQ to go above 255 will be ignored. Additionally, the RQ
parameter is maintained as a running sum in a manner similar to the
other parameters-the new RQ penalty is added to one half of a
running sum to derive the new running sum.
[0051] It is possible for the channel in use to change within a
single test or data packet. In this case, there is no prior
notification that the data will be bad; therefore, this type of
error cannot be avoided by antenna switching. However, since
packets containing bit errors tend to come in groups, the antenna
that received data containing a bit error should be penalized so
that the antenna switching algorithm will be disposed to switch to
a different antenna. This situation is addressed in part by the
aCRC error parameter. The antenna CRC 812 included in each test
packet 712 serves as the basis for the aCRC parameter. Techniques
for determining the occurrence of CRC errors are well known in the
art. In accordance with the present invention, the aCRC error
parameter preferably maintains memory of previous values using a
running sum. To this end, if a CRC error is detected during the
reception of a test packet, the running sum representative of the
aCRC error parameter is preferably incremented by 128, with the
maximum possible value of the CRC error parameter set to 255. Each
time a test packet is received without CRC errors, the running sum
representative of the aCRC error parameter is preferably divided by
two.
[0052] While the present invention incorporates the use of antenna
test packets 712 to evaluate the antennas in order to select the
optimal antenna, it is recognized that channel conditions may
change rapidly, particularly during the reception of payload data.
To this end, the segment CRCs 720 are used to derive the sCRC error
parameter. As described below, the sCRC error parameter is used to
update quality metrics corresponding to antennas used to receive
the payload data. In accordance with the present invention, the
aCRC error parameter preferably maintains memory of previous values
using a running sum. To this end, if a CRC error is detected during
the reception of a payload segment 718, the running sum
representative of the sCRC error parameter is preferably
incremented by 64, with the maximum possible value of the sCRC
error parameter set to 255. Each time a payload segment 718 is
received without CRC errors, the running sum representative of the
sCRC error parameter is preferably divided by two. Additionally, as
described below, the sCRC error parameter is also used as a means
to reflect any failures to detect a segment sync 714. To this end,
if a segment sync 714 is not found, the running sum representative
of the sCRC error parameter is preferably incremented by 32.
Although it is presently preferred to reflect errors during a
segment sync 714 in the sCRC error parameter, it is understood that
such errors could be reflected in another, separate parameter.
[0053] The quality metric (Q) for each antenna is preferably the
sum of all the penalty adders (parameters), although it is
understood that other combinations of the parameters may be used.
In a preferred embodiment, each quality metric is represented as a
10-bit number. In this embodiment, each quality metric is limited
to 1023 regardless of whether the sum of the factors is greater
than 1023. Adhering to the protocol that lower quality metrics are
more favorable than higher quality metrics, the most favorable
antenna will be initially chosen as the antenna with the lowest Q.
Thereafter, antennas having the lowest quality metrics are
continuously identified and selected. In a preferred embodiment,
such selection occurs only when the current antenna's quality
metric has become sufficiently unfavorable as determined by a
threshold comparison. Preferably, this threshold is set at 127.
This is preferably implemented to prevent a switch from a very good
antenna to a less favorable one due to noise in the quality
metrics.
[0054] Referring again to FIG. 6, a more detailed embodiment of the
present invention is now described. In a packet-based communication
system, it is possible to anticipate the reception of certain data,
such as the structured packet 700 illustrated in FIG. 7. Thus, at
step 602, the antenna referenced by the index P is used to detect
the packet sync 708. If the packet sync 708 is not detected one
time, it is ignored and attempts are made to receive the remainder
of the packet 700. However, if the packet sync 708 is not detected
for two consecutive packets 700, then a search mode is entered and
the method of FIG. 6 is ignored. Assuming that packet sync 708 is
found, processing continues at step 604 where the refresh period
710 is allowed to expire. At step 606, the test antenna index, T,
is initialized. In a preferred embodiment, the four antennas used
are logically labeled 0 through 3, and the index T is initialized
to 0 and incremented thereafter. Of course, other indexing schemes
could be used as a matter of design choice. At step 608, the
running sums representative of the sCRC error parameter for each
antenna is initialized to zero. Note that steps 606 and 608, rather
than being performed subsequent to step 604, may be performed
simultaneous to step 604.
[0055] Regardless, at step 610, and after the expiration of the
refresh period 710, the receiving device knows to look for a test
packet at a predetermined time. In particular, the receiving device
inspects baseband data received via the current test antenna (T)
looking for preamble 804 and synchronization 806 fields indicative
of the beginning of a new received test packet. If the test packet
is not found at step 612, processing continues at step 614 where
the Sync parameter for the test antenna is incremented (penalized)
by a preferred value of 511. Furthermore, the failure to detect the
synchronization field also has an effect on the RQ and CQ
parameters, as well as the CRC parameter. In particular, the
running sums representing the RQ and CQ parameters (shown in FIG. 6
as oldRQ and oldCQ, respectively) are updated as described above,
e.g., the running sum is divided by two and then incremented by the
preferred value of 128. In this manner, the failure to receive a
test packet synchronization field imparts a substantial penalty on
the antenna currently being tested. Processing then continues at
step 630 where the aCRC parameter is divided by two. This helps
ensure that the aCRC parameter and the Sync parameter remain
independent of each other, thereby preventing the loss of test sync
from doubly penalizing an antenna. Subsequently, at step 632, the
quality metric for the antenna being tested, Q(T), is updated based
on the now-updated values of the RQ, CQ, aCRC and Sync parameters,
as well as the current sCRC parameter. In particular, the test
antenna quality metric is preferably calculated as the sum of the
CQ, RQ, aCRC, sCRC and Sync parameters (all represented as running
sums).
[0056] Referring once again to step 612, if the test packet is
found, i.e., if the synchronization field is correctly received,
processing continues at step 616 where it is determined whether any
errors were found in the detected test sync. If not, the Sync
parameter for the test antenna is divided by two at step 622.
Processing then continues at step 620 where current values for the
CQ and RSS/RQ parameters are determined as described above.
Thereafter, at step 624, the running sums for the CQ (oldCQ) and RQ
(oldRQ) parameters are updated. However, at step 618, if errors
were found in the detected test sync, the number of bit errors
found is multiplied by 64 and the resulting product added to one
half the running sum representative of the Sync parameter for the
test antenna. Thereafter steps 620 and 624 are performed as
previously described.
[0057] At step 620, it is determined whether a CRC error was
detected during the reception of the test packet. To this end, the
test CRC 812 is received and compared with a CRC value calculated
based on the received test word 810. If a CRC error is detected,
the aCRC parameter for the test antenna is incremented by the
preferred value of 128 at step 628. If no CRC error is detected,
the aCRC parameter is divided by two at step 630. Subsequently, the
test antenna quality metric is thereafter updated in accordance
with step 632, as previously described.
[0058] At step 634, it is determined whether all antennas have been
tested. Stated another way, it is determined whether all of the
test packets 712 have been received. If not, the test index T is
incremented at step 636 so that the next test packet will be used
to test another antenna. Note that step 634 could be implemented at
other points within the sequence of steps shown in FIG. 6 as a
matter of design choice.
[0059] As described above, it is a feature of the present invention
that a new payload antenna will not be chosen (based on the quality
metrics) unless the current payload antenna is performing
sufficiently unfavorably. This is shown at step 638 as a comparison
of the current payload antenna's quality metric, Q(P), against a
predetermined threshold. (Recall that the payload antenna index P
is independent of the test antenna index T, although they can have
the same value at any given time.) In a preferred embodiment, the
threshold is set to 127. Thus, if the quality metric is not greater
than the threshold, indicating a favorable channel via the
currently selected payload antenna, the payload antenna remains
unchanged at step 640. If the quality metric is above the
threshold, indicating an unfavorable channel, processing continues
at step 642 where a new payload antenna is selected. In a preferred
embodiment, the selection is accomplished by comparing the quality
metrics for each of the receive antennas and selecting the antenna
corresponding to the quality metric having the minimum value.
Having selected a new antenna P in this manner, a control signal
may be generated for use in controlling an antenna switch. As noted
previously, the correspondence of minimum and maximum value quality
metrics with favorable and unfavorable antenna performance,
respectively, is but one possible scheme and those having ordinary
skill in the art can readily devise other such schemes still within
the scope of the present invention.
[0060] Regardless of whether the payload antenna index P is newly
selected or the previously used value, processing continues at step
640 by switching (if necessary) to the payload antenna specified by
the index P. As with the test packet at step 610, the receiving
device now looks for a payload segment at step 644 (FIG. 6B).
Preferably, the payload segments 704 occur immediately after the
packet sync segments 702 such that evaluations based on both occur
substantially simultaneously. In the context of the present
invention, "substantially simultaneously" means within the time
period defined by a packet having test and payload data. In looking
for the payload segment, the receiving device inspects baseband
data received via the payload antenna looking for a segment sync
714 indicative of the beginning of a new received payload segment.
If the segment sync 714 is not found at step 646, processing
continues at step 650 where the sCRC parameter for the payload
antenna is incremented (penalized) by the preferred value of 32. In
a presently preferred embodiment, there is a five-bit window on the
segment sync detection, i.e., the segment sync can be detected if
it is +/-two bits from its expected position. If it is not found
within this window, the algorithm defaults to assuming that the
segment sync is in the expected position when attempting to receive
the data.
[0061] If the segment sync 714 is detected, or after incurring a
penalty for failure to detect it, processing continues at step 648
where attempts are made to receive the payload segment 718. After
that payload segment has been received, the segment CRC 720 is
received. As with the test CRC 812, the segment CRC 720 is compared
with a CRC calculated based on the received payload segment 718. If
any errors are detected through this comparison, at step 652,
processing continues at step 658 where the sCRC parameter for the
payload antenna is incremented (penalized) by the preferred value
of 64. Conversely, if no CRC errors are detected, processing
continues at step 654 where the running sum representing the sCRC
parameter for the payload antenna is divided by two, subject to the
condition that the segment sync 714 was previously detected. If the
segment sync was not previously detected and no CRC errors were
detected, the sCRC parameter is unchanged. Stated another way, the
failure to find the segment sync at step 646 causes incurrence of a
penalty at step 650; allowing the error free reception of the
segment CRC to divide the running sum would effectively undo the
penalty for failure to receive the segment sync 714.
[0062] Regardless of whether the segment CRC was received with our
without errors, processing continues at step 656 where the quality
metric for the payload antenna, Q(P), is updated based on the
now-updated value of the sCRC parameter, and the previous values of
the CQ, RQ aCRC and Sync parameters. As before, the test antenna
quality metric is preferably calculated as the sum of the CQ, RQ,
aCRC, sCRC and Sync parameters (all represented as running
sums).
[0063] Incorporating the updated quality metric resulting from the
reception of the payload segment, the decision and selection
process described above relative to steps 638 through 642 is
repeated at steps 660 through 664. That is, if the current payload
antenna's quality metric, Q(P) compares favorably with the
predetermined threshold, the payload antenna remains unchanged. If
the quality metric compares unfavorably with the threshold, a new
payload antenna is selected corresponding to the quality metric
having the minimum (most favorable) value. Having selected a new
antenna P in this manner, a control signal may be generated for use
in controlling an antenna switch.
[0064] Finally, at step 666, it is determine whether all payload
segments 718 have been received. Recall that, in a preferred
embodiment, each structured packet 700 comprises twelve payload
segments. If further payload segments remain, processing continues
at step 644 where searching is performed for the next payload
segment. In this manner, each payload segment offers the
opportunity to update the sCRC parameter and, consequently, the
opportunity to switch payload antennas in the event that the
current payload channel degrades. If, however, all segments have
already been received, processing continues at step 602 where
searching is performed for the next structured packet 700.
[0065] The present invention provides a technique for a wireless
communication device to select an antenna with which to receive
payload data from amongst a plurality of antennas. Using test data
and payload data, quality metrics for each of the plurality of
antennas are determined. The quality metrics are then used to
select an antenna for receiving the payload data. By continuously
updating quality metrics based on both test and payload data, more
reliable assessments can be made of the various antennas being
used. As a result, antenna selection is rendered commensurately
more reliable thereby improving received signal quality.
[0066] While the foregoing detailed description sets forth
presently preferred embodiments of the invention, it will be
understood that many variations may be made to the embodiments
disclosed herein without departing from the true spirit and scope
of the invention. This true spirit and scope of the present
invention is defined by the appended claims, to be interpreted in
light of the foregoing specifications.
* * * * *