U.S. patent application number 14/493607 was filed with the patent office on 2015-01-08 for techniques for radio link problem and recovery detection in a wireless communication system.
The applicant listed for this patent is APPLE INC.. Invention is credited to Taeyoon KIM, Ian WONG.
Application Number | 20150012783 14/493607 |
Document ID | / |
Family ID | 42131261 |
Filed Date | 2015-01-08 |
United States Patent
Application |
20150012783 |
Kind Code |
A1 |
WONG; Ian ; et al. |
January 8, 2015 |
Techniques for Radio Link Problem and Recovery Detection in a
Wireless Communication System
Abstract
A technique for radio link detection in a wireless communication
system includes estimating a first error rate of an indicator
channel. In this case, the indicator channel includes an indication
of a number of symbols in a control channel. A second error rate of
the control channel is also estimated. The first and second error
rates are then combined to provide a performance metric. Based on
the performance metric, a determination is made as to whether a
radio link problem exists.
Inventors: |
WONG; Ian; (CUPERTINO,
CA) ; KIM; Taeyoon; (CUPERTINO, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
APPLE INC. |
Cupertino |
CA |
US |
|
|
Family ID: |
42131261 |
Appl. No.: |
14/493607 |
Filed: |
September 23, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14336735 |
Jul 21, 2014 |
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14493607 |
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12263998 |
Nov 3, 2008 |
8787177 |
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14336735 |
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Current U.S.
Class: |
714/708 ;
714/704 |
Current CPC
Class: |
H04W 24/00 20130101;
H04B 17/336 20150115; G06F 11/0793 20130101; H04W 24/08 20130101;
H04W 24/10 20130101; H04J 11/0023 20130101; H04L 1/203 20130101;
G06F 11/076 20130101 |
Class at
Publication: |
714/708 ;
714/704 |
International
Class: |
G06F 11/07 20060101
G06F011/07 |
Claims
1-20. (canceled)
21. A method, comprising: at a subscriber station, estimating a
first error rate for an indicator channel; estimating a second
error rate for a control channel; comparing one of the first error
rate and the second error rate to a first threshold to determine a
radio link problem; and comparing one of the first error rate and
the second error rate to a second threshold to determine a radio
link recovery.
22. The method of claim 21, further comprising: combining the first
and second error rates to generate a performance metric, wherein
the comparing is based on the performance metric.
23. The method of claim 21, further comprising: providing an
indication when the comparing indicates a radio link problem.
24. The method of claim 21, further comprising: providing an
indication when the comparing indicates a radio link recovery.
25. The method of claim 21, wherein the indicator channel occupies
a first frequency band and estimating of the first error rate is
based on a first reference signal occupying a first frequency
adjacent to the first frequency band and a second reference signal
occupying a second frequency adjacent to the first frequency band,
wherein the first ad second frequencies are on opposite sides of
the first frequency bands.
26. The method of claim 25, wherein the first error rate is based
on a first quality metric of the first reference signal and a
second quality metric of the second reference signal.
27. The method of claim 26, wherein the first error rate is based
on interpolating the first quality metric and the second quality
metric.
28. The method of claim 21, wherein the indicator channel includes
an indication of a number of symbols in the control channel.
29. The method of claim 23, further comprising: determining when
the radio link problem exists for a period of time; indicating a
radio link failure when the radio link problem exists for the
period of time.
30. The method of claim 21, wherein the method is performed for a
plurality of indicator channels and a corresponding plurality of
control channels and when a predetermined number of radio link
problems exist, the method further comprises: powering down a
transmitter of the subscriber station.
31. A wireless communication device, comprising: a processor
configured to: estimate a first error rate for an indicator
channel; estimate a second error rate for a control channel;
compare one of the first error rate and the second error rate to a
first threshold to determine a radio link problem; and compare one
of the first error rate and the second error rate to a second
threshold to determine a radio link recovery.
32. The wireless communication device of claim 31, wherein the
processor is further configured to: combine the first and second
error rates to generate a performance metric, wherein the comparing
is based on the performance metric.
33. The wireless communication device of claim 31, wherein the
processor is further configured to: provide an indication when the
comparing indicates a radio link problem.
34. The wireless communication device of claim 31, wherein the
processor is further configured to: provide an indication when the
comparing indicates a radio link recovery.
35. The wireless communication device of claim 31, wherein the
indicator channel occupies a first frequency band and the processor
estimates the first error rate based on a first reference signal
occupying a first frequency adjacent to the first frequency band
and a second reference signal occupying a second frequency adjacent
to the first frequency band, wherein the first and second
frequencies are on opposite sides of the first frequency bands.
36. The wireless communication device of claim 35, wherein the
processor estimates the first error rate based on a first quality
metric of the first reference signal and a second quality metric of
the second reference signal.
37. The wireless communication device of claim 36, wherein the
processor estimates the first error rate by interpolating the first
quality metric and the second quality metric.
38. The wireless communication device of claim 31, wherein the
indicator channel includes an indication of a number of symbols in
the control channel.
39. The wireless communication device of claim 33, wherein the
processor is further configured to: determine when the radio link
problem exists for a period of time; indicate a radio link failure
when the radio link problem exists for the period of time.
40. The wireless communication device of claim 31, wherein the
processor estimates and compares for a plurality of indicator
channels and a corresponding plurality of control channels and when
a predetermined number of radio link problems exist, the processor
is further configured to: power down a transmitter of the wireless
communication device.
Description
BACKGROUND
[0001] 1. Field
[0002] This disclosure relates generally to a wireless
communication system and, more specifically, to techniques for
radio link problem and recovery detection in a wireless
communication system.
[0003] 2. Related Art
[0004] As is well known, a wireless channel provides an arbitrary
time dispersion, attenuation, and phase shift in a transmitted
signal. While the implementation of orthogonal frequency division
multiplexing (OFDM) with a cyclic prefix in a wireless
communication system mitigates the effect of time dispersion caused
by a wireless channel, in order to apply linear modulation schemes
it is also usually necessary to remove amplitude and phase shift
caused by the wireless channel. Channel estimation is typically
implemented in a wireless communication system to provide an
estimate (from available pilot information) of an amplitude and
phase shift caused by a wireless channel. Equalization may then be
employed in the wireless communication system to remove the effect
of the wireless channel and facilitate subsequent symbol
demodulation. Channel tracking is also usually employed to
periodically update an initial channel estimation. For example,
channel tracking may be employed to facilitate periodic
frequency-domain and time-domain channel correlation and periodic
updating of channel signal-to-noise ratio (SNR), channel delay
spread, and channel Doppler effect.
[0005] Known approaches for detecting a radio link problem (RLP)
and a radio link recovery (RLR) in wireless communication systems
suffer from significant shortcomings that affect the accuracy
and/or testability of a detection approach. Unfortunately, without
a good RLP/RLR metric that is both accurate, easily implementable,
and testable, wireless communication system performance inevitably
degrades. For example, in a third-generation partnership project
long-term evolution (3GPP LTE) compliant wireless communication
system, user equipment (UE) must be able to accurately detect a
radio link problem (RLP) and a radio link recovery (RLR) to prevent
performance degradation of the system.
[0006] A known first approach for determining an RLP and an RLR at
a UE in an LTE compliant wireless communication system has proposed
using a physical control format indicator channel (PCFICH) and a
pseudo-error rate that is based on received symbols. Unfortunately,
the first approach may be inaccurate as there is no clear
indication of whether the decoded message is correct due to the
absence of an error detection code (e.g., a cyclic redundancy check
(CRC)) and the small number of subcarriers associated with the
PCFICH (e.g., 16 subcarriers in an LTE system). A known second
approach for determining an RLP and an RLR at a UE in an LTE
compliant wireless communication system has proposed using a
combination of an actual PCFICH and an actual physical downlink
control channel (PDCCH) to detect radio link failure.
Unfortunately, a UE may not always get a PDCCH grant and, thus,
logging a CRC error rate is usually inaccurate as the UE cannot
distinguish between a true decoding error and the absence of a
PDCCH grant. In addition, the second approach also uses the actual
PCFICH which does not have an associated CRC.
[0007] A known third approach for determining an RLP and an RLR at
a UE in a wireless communication system has proposed using a
hypothetical PDCCH transmission to map to an estimate of a block
error rate (BLER) as the metric for RLF detection. While overcoming
most of the shortcomings in the above-referenced approaches, the
third approach still neglects the fact that a successful PCFICH
decoding is necessary before a PDCCH can be decoded correctly. As
such, the third approach may provide an overly optimistic result,
which could be problematic in environments with low
signal-to-interference and noise ratios (SINRs) where radio link
failure (RLF) is expected to occur. Furthermore, the third approach
is not particularly feasible from a conformance testing point of
view as a PDCCH error rate is not observable without PCFICH errors.
As such, a UE may experience behavior consistency problems when the
third approach is employed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The present invention is illustrated by way of example and
is not limited by the accompanying figures, in which like
references indicate similar elements. Elements in the figures are
illustrated for simplicity and clarity and have not necessarily
been drawn to scale.
[0009] FIG. 1 is a diagram of a relevant portion of an example
downlink (DL) frame transmitted from a serving base station (BS) in
a long-term evolution (LTE) compliant wireless communication
system.
[0010] FIG. 2 is an example diagram of a relevant portion of a
frequency spectrum that depicts a channel (e.g., a physical control
format indicator channel (PCFICH) or a physical downlink control
channel (PDCCH)) that is to be estimated based on reference signals
(RSs) located on opposite sides of the channel, according to one
embodiment of the present invention.
[0011] FIG. 3 is a flowchart of an example process for performing
radio link problem (RLP), radio link failure (RLF), and radio link
recovery (RLR) detection, according to one aspect of the present
invention.
[0012] FIG. 4 is a flowchart of an example process for performing
RLP, RLF, and RLR detection, according to another aspect of the
present invention.
[0013] FIG. 5 is a block diagram of an example wireless
communication system that includes wireless communication devices
that may perform RLP, RLF, and RLR detection according to various
embodiments of the present invention.
DETAILED DESCRIPTION
[0014] In the following detailed description of exemplary
embodiments of the invention, specific exemplary embodiments in
which the invention may be practiced are described in sufficient
detail to enable those skilled in the art to practice the
invention, and it is to be understood that other embodiments may be
utilized and that logical, architectural, programmatic, mechanical,
electrical and other changes may be made without departing from the
spirit or scope of the present invention. The following detailed
description is, therefore, not to be taken in a limiting sense, and
the scope of the present invention is defined only by the appended
claims and their equivalents. In particular, although the preferred
embodiment is described below in conjunction with a subscriber
station (SS), such as a cellular handset, it will be appreciated
that the present invention is not so limited and may potentially be
embodied in various wireless communication devices.
[0015] As used herein, the term "channel" includes one or more
subcarriers, which may be adjacent or distributed across a
frequency band. Moreover, the term "channel" may include an entire
system bandwidth or a portion of the entire system bandwidth. As
used herein, the term "reference signal" is synonymous with the
term "pilot signal." As is also used herein, the term "subscriber
station" is synonymous with the term "user equipment," which
includes a wireless communication device that may (or may not) be
mobile. In general, a reference signal (RS), when received at a
subscriber station (SS), is utilized by the SS to perform channel
estimation. The disclosed techniques are contemplated to be
applicable to systems that employ a wide variety of signaling
techniques, e.g., orthogonal frequency division multiplex (OFDM)
signaling and single-carrier frequency division multiple access
(SC-FDMA) signaling. As used herein, the term "coupled" includes a
direct electrical connection between blocks or components and an
indirect electrical connection between blocks or components
achieved using one or more intervening blocks or components.
[0016] In general, accurate channel estimation is desirable to
achieve acceptable performance for SSs in a wireless communication
system (e.g., a long-term evolution (LTE) wireless communication
system) as downlink (DL) performance is determined by the accuracy
of channel estimation. In an LTE compliant system, RSs are
distributed in a subframe and, as such, interpolation may be used
to perform channel estimation for an entire time-frequency grid of
an OFDM signal. In the case of an LTE compliant system having a 1.4
MHz system bandwidth, only twelve downlink reference signal (DLRS)
subcarriers are currently allocated (in a first symbol of each
subframe) for channel estimation. It should be appreciated that
while the discussion herein is directed to an LTE compliant system,
the techniques disclosed herein are broadly applicable to improving
radio link failure and recovery detection in any wireless
communication system that employs an indicator channel that
includes an indication of a number of symbols in an associated
control channel.
[0017] In a 3GPP-LTE wireless communication system, it is desirable
(for proper system operation) for an SS to accurately detect a
radio link problem (RLP) and a radio link recovery (RLR). The
detection of an RLP may lead to a radio link failure (RLF)
detection, i.e., an RLP for a sustained period of time, at which
point an SS can shut off an associated transmitter independent from
network commands and, in this manner, prevent the SS from causing
excessive interference on an uplink (UL). On the other hand, an RLR
detection results in the SS switching the associated transmitter
back on to facilitate a UL connection. According to various aspects
of the present disclosure, techniques are disclosed that accurately
and efficiently detect an RLP and an RLR.
[0018] According to various embodiments of the present disclosure,
a hypothetical physical control format indicator channel (PCFICH)
transmission and a hypothetical physical downlink control channel
(PDCCH) transmission are combined (e.g., added or scaled and then
added) to provide a quality metric for RLP, RLF, and RLR detection.
The quality metric may take various, forms, e.g., a
signal-to-interference and noise ratio (SINR) or a signal-to-noise
ratio (SNR). The quality metric for the hypothetical channels may
be estimated by performing interpolation based on reference signals
(pilot signals) that are, for example, located on opposite sides of
the hypothetical channels.
[0019] In one embodiment, a two-step exponential effective SINR
mapping (EESM) is employed to map an estimated SINR for resource
elements for which the PCFICH would be transmitted to an error rate
and map an estimated SINR for resource elements for which the PDCCH
would be transmitted to an error rate. The error rates for the
hypothetical PCFICH and PDDCH may then be combined (e.g., added or
scaled and then added) to estimate a combined (PCFICH and PDCCH)
error rate. The estimated combined error rate may be averaged over
time (e.g., 200 milliseconds for RLP and 100 milliseconds for RLR)
after which the averaged combined error rate may be compared
against thresholds (e.g., Qin and Qout, respectively) to determine
RLP and RLR, respectively. That is, if the average combined error
rate is greater than Qout, an RLP is detected. Similarly, if the
average combined error rate is less than Qin, an RLR is detected.
In an alternative embodiment, quality metrics for the PCFICH and
the PDDCH may be combined and then mapped to an error rate. In the
alternative embodiment, the quality metrics may be scaled prior to
being combined. In yet another alternative embodiment, a combined
quality metric is derived for the PCFICH and the PDDCH. The
combined quality metric is then mapped to an error rate.
[0020] It should be appreciated that a wide variety of transmission
formats for both PCFICH and PDCCH may be employed for determining a
quality metric. A control format indicator (CFI) transmitted on
PCFICH may be set to, for example, three (CFI=3), which implies
three orthogonal frequency division multiplexing (OFDM) symbols for
control if a bandwidth (BW) configuration has greater than six
resource blocks (RBs) and four OFDM symbols otherwise. As one
example, a `format 0` PDCCH transmission in eight control channel
elements (CCEs) for RLP detection and a `format 1C` PDCCH
transmission in four CCES for RLR detection may be assumed.
[0021] In general, when an SS cannot decode even the most reliable
control message, an RLP should be declared. If an SS can
successfully decode a broadcast message, which is typically
transmitted in `format 1C` for an LTE compliant system, then the SS
can be considered to be in synchronization with a serving base
station (BS). Alternatively, a same format, e.g., `format 0` may be
assumed for both RLP and RLR detection while performing the
estimates. For ease of understanding herein, a same format is
assumed for both RLP and RLR. In a typical implementation, a table
of constants that determine a specific mapping function from
subcarrier SINRs into an effective SINR (that can be used to
estimate an error rate (e.g., a block error rate (BLER)) for both
PCFICH and PDCCH) is developed off-line. For example, using an EESM
approach a beta (.beta.) value for each transmission configuration
(e.g., 1.times.2, 2.times.2 space frequency block coding (SFBC),
and 4.times.2 SFBC) and for each format for a PCFICH and a PDCCH
may be computed off-line and stored in a look-up table.
[0022] For each subframe `n` in a connected mode, the SS estimates
a received SINR (.gamma.i) for each subcarrier corresponding to a
hypothetical PCFICH transmission and computes an effective SINR
(.gamma.eff), e.g., using an EESM approach, as follows:
.gamma. eff = - .beta. ln ( 1 N i = 1 N - .gamma. i .beta. )
##EQU00001##
where N is the number of subcarriers for a channel and beta
(.beta.) is a constant that depends on a channel format and a
system configuration. The effective SINR (.gamma.eff) may then be
used to determine the PCFICH BLER in additive white Gaussian noise
(AWGN), which is the BLER estimate for the PCFICH transmission
(referred to herein as PCFICH_BLER). In a typical implementation,
the above steps are then performed for the PDCCH to estimate the
PDCCH BLER (referred to herein as PDCCH_BLER). A running average of
both the PCFICH_BLER and PDCCH_BLER may then be performed. For
example, one can either use a true average, an exponential average,
or a weighted average as set forth below:
PCFICH_BLER(n)=.alpha.PCFICH_BLER(n-1)+(1-.alpha.)PCFICH_BLER
PDCCH_BLER(n)=.alpha.PCFICH_BLER(n-1)+(1-.alpha.)PDCCH_BLER
where 0<.alpha.<1 is an averaging constant related to the
averaging window length (e.g., 200 subframes, which may correspond
to 200 milliseconds in an LTE compliant system).
[0023] After an initial period of the window length and at an end
of each reporting period (e.g., 10 frames, which may correspond to
100 milliseconds in an LTE compliant system) thereafter, a combined
(PCFICH/PDCCH) error rate may be estimated, for example, as
follows:
Combined_BLER(n)=1-(1-PCFICH_BLER(n))*(1-PDCCH_BLER(n))
[0024] A routine for reporting an RLP may be implemented, for
example, using the following code:
TABLE-US-00001 while Combined_BLER(n) > Qout Report radio link
problem to higher layers if Combined_BLER(n) < Qin Radio link
recovery detected break from reporting RLP end end
[0025] Since a true successful PDCCH decoding requires a likewise
successful PCFICH decoding, the techniques described herein provide
a more accurate performance metric for RLF and RLR detection than
known approaches, especially in environments with low SINRs where
RLP is expected to occur. Furthermore, the disclosed techniques are
readily testable as PDCCH can only be tested when PCFICH is also
present and the presence of a PDCCH CRC can accurately determine a
true error rate, which can be used as the benchmark for the
accuracy of the RLP or RLR detected by the SS in conformance
testing.
[0026] According to one embodiment of the present disclosure, a
technique for radio link detection in a wireless communication
system includes estimating a first error rate of an indicator
channel. In this case, the indicator channel includes an indication
of a number of symbols in a control channel. A second error rate of
the control channel is also estimated. The first and second error
rates are then combined to provide a performance metric. Based on
the performance metric, a determination is made as to whether a
radio link problem exists.
[0027] According to another embodiment of the present disclosure, a
wireless communication device includes a receiver and a processor
coupled to the receiver. The processor is configured to estimate a
first error rate of an indicator channel. In this case, the
indicator channel includes an indication of a number of symbols in
a control channel. The processor is also configured to estimate a
second error rate of the control channel. The processor is further
configured to combine the first and second error rates to provide a
performance metric. The processor is also configured to determine
whether a radio link problem exists based on the performance
metric.
[0028] According to another aspect of the present disclosure, a
technique for radio link detection in a wireless communication
system includes estimating a combined effective
signal-to-interference and noise ratio for a control channel and an
indicator channel, which includes an indication of a number of
symbols in the control channel. The combined effective
signal-to-interference and noise ratio is then mapped to a block
error rate. Based on the block error rate, a determination is made
as to whether a radio link problem, a radio link failure, or a
radio link recovery exists.
[0029] With reference to FIG. 1, a relevant portion of an example
downlink frame 100, which is transmitted from a serving base
station (BS) in an LTE compliant system, is illustrated. As is
shown, the frame 100 (which is 10 milliseconds in length) includes
ten subframes (each of which are 1 millisecond in length). Each of
the subframes begins with a symbol that includes, among other
items, one or more reference signals (RSs), a physical control
format indicator channel (PCFICH) and one or more physical downlink
control channels (PDCCH) (labeled `DLRS/PCFICH/PDCCH`). In the
illustrated example, a DL subframe includes two slots, each of
which include seven long blocks (LBs) which encode a symbol. It
should be appreciated that the techniques disclosed herein are
broadly applicable to UL subframes that employ more or less than
the illustrated number of LBs. With reference to Slot0, a 1.sup.st
secondary synchronization channel (SSCH) is assigned to LB 6 and a
primary synchronization channel (PSCH) is assigned to LB 7. With
reference to Slot11, a 2.sup.nd SSCH is assigned to LB 6 and the
PSCH is also assigned to LB 7. With reference to Slot1, a primary
broadcast channel (PBCH) is assigned to LB 1 (labeled `DLRS/PBCH`)
and LBs 2-4.
[0030] With reference to FIG. 2, an example diagram of a relevant
portion of a frequency spectrum 200 that depicts a channel 206
(e.g., a physical control format indicator channel (PCFICH) or a
physical downlink control channel (PDCCH)) that is to be estimated
based on reference signals (RSs) 202 and 204, which are located on
opposite sides of the channel, is illustrated. As mentioned above,
a quality metric for the channel 206 may be derived through
interpolation of quality metrics associated with the RSs 202 and
204. Alternatively, a quality metric for the channel 206 may
derived in another manner.
[0031] Turning to FIG. 3, an example process 300 for performing
radio link problem (RLP), radio link failure (RLF), and radio link
recovery (RLR) detection, according to one aspect of the present
invention, is depicted. The process 300 is initiated at block 302,
at which point control transfers to block 304. In block 304, a
control unit (e.g., a processor or an application specific
integrated circuit (ASIC)) of an SS estimates a first error rate
(e.g., a block error rate (BLER)) for an indicator channel, which
includes an indication of a number of symbols in a control channel.
As noted above, the first error rate may be estimated based on
various quality metrics (e.g., SNR or SINR) associated with
reference signals (RSs) located on opposite sides of the indicator
channel. For example, the control unit may estimate an effective
SINR for the indicator channel (based on interpolation of the SINRs
of respective RSs located on opposite sides of the indicator
channel) and map the estimated SINR for the indicator channel to
the first error rate. Next, in block 306, the control unit of the
SS estimates a second error rate (e.g., a BLER) for the control
channel. As mentioned above, the second error rate may also be
based on interpolation of various quality metrics associated with
RSs located on opposite sides of the control channel. For example,
the control unit may estimate an effective SINR for the control
channel using interpolation of the SINRs associated with respective
RSs located on opposite sides of the control channel and map the
estimated SINR for the control channel to the second error
rate.
[0032] Then, in block 308, the first and second error rates (which
may be BLERs) are combined (e.g., added together or scaled and then
added together) to provide a performance metric (e.g., a combined
BLER). Next, in decision block 310, the control unit determines
whether an RLP is indicated by the performance metric (e.g.,
whether the combined BLER is above a first threshold). If an RLP is
indicated in block 310, control transfers to block 316, where the
RLP is reported, e.g., to a higher layer. For example, when
multiple RLPs have been reported, the higher layer may initiate
power-down of a transmitter of an SS such that the SS does not
cause excessive interference on a UL. Then, in decision block 318,
the processor determines whether the RLP has been persistent for a
first time period (e.g., whether the combined BLER has exceeded the
first threshold for the first time period).
[0033] If an RLP is not persistent for the first time period,
control transfers from block 318 to block 322 where the process 300
terminates and control returns to a calling routine. If an RLP is
persistent for the first time period, control transfers to block
320 where an RLF is reported. From block 320 control transfers to
block 322. If an RLP is not indicated in block 310, control
transfers to decision block 312, where the control unit determines
if an RLR is indicated by the performance metric (e.g., whether the
combined BLER is below a second threshold). If an RLR is indicated
in block 312, control transfers to block 314, where the RLR is
reported. Following block 314, control transfers to block 322. If
an RLR is not indicated in block 312, control transfers to block
322.
[0034] With reference to FIG. 4, a process 400 for radio link
detection in a wireless communication system, according to another
embodiment of the present disclosure, is illustrated. In block 402
the process 400 is initiated at which point control transfers to
block 404. In block 404, a combined quality metric (e.g., an SNR or
an SINR) for a control channel and an indicator channel, which
includes an indication of a number of symbols in the control
channel, is estimated. The combined quality metric may, for
example, be based on interpolation of quality metrics associated
with respective RSs located on opposite sides of the channels. The
quality metrics for the control and indicator channels may, for
example, be combined by addition or may be scaled and then added
together. Next, in block 406, the quality metric is mapped to an
error rate (e.g., a BLER). Then, in block 408, based on the error
rate, a determination is made (based on whether the error rate is
above a first threshold, above the first threshold for a first time
period, or below a second threshold) as to whether a radio link
problem, a radio link failure, or a radio link recovery exists.
From block 408 control transfers to block 410 where the process 400
terminates and control returns to a calling routine.
[0035] With reference to FIG. 5, an example wireless communication
system 500 is depicted that includes a plurality of subscriber
stations or wireless communication devices 502, e.g., hand-held
computers, personal digital assistants (PDAs), cellular telephones,
etc., that may perform radio link problem (RLP), radio link failure
(RLF), and radio link recovery (RLR) detection according to one or
more embodiments of the present disclosure. In general, the devices
502 include a processor 508 (e.g., a digital signal processor (DSP)
or an ASIC), a transceiver (including a receiver and a transmitter)
506, and one or more input/output devices 504 (e.g., a camera, a
keypad, display, etc.), among other components not shown in FIG. 5.
As is noted above, according to various embodiments of the present
disclosure, techniques are disclosed that generally improve RLP,
RLF, and RLR detection. The devices 502 communicate with a base
station controller (BSC) 512 of a base station subsystem (BSS) 510,
via one or more base transceiver stations (BTS) 514, to receive or
transmit voice and/or data and to receive control signals. In
general, the BSC 512 may also be configured to choose a modulation
and coding scheme (MCS) for each of the devices 502, based on
channel conditions.
[0036] The BSC 512 is also in communication with a packet control
unit (PCU) 516, which is in communication with a serving general
packet radio service (GPRS) support node (SGSN) 522. The SGSN 522
is in communication with a gateway GPRS support node (GGSN) 524,
both of which are included within a GPRS core network 520. The GGSN
524 provides access to computer(s) 526 coupled to Internet/intranet
528. In this manner, the devices 502 may receive data from and/or
transmit data to computers coupled to the Internet/intranet 528.
For example, when the devices 502 include a camera, images may be
transferred to a computer 526 coupled to the Internet/intranet 528
or to another one of the devices 502. The BSC 512 is also in
communication with a mobile switching center/visitor location
register (MSC/VLR) 534, which is in communication with a home
location register (HLR), an authentication center (AUC), and an
equipment identity register (EIR) 532. In a typical implementation,
the MSC/VLR 534 and the HLR, AUC, and EIR 532 are located within a
network and switching subsystem (NSS) 530, which performs various
functions for the system 500. The SGSN 522 may communicate directly
with the HLR, AUC, and EIR 532. As is also shown, the MSC/VLR 534
is in communication with a public switched telephone network (PSTN)
542, which facilitates communication between wireless devices 502
and land telephone(s) 540.
[0037] As used herein, a software system can include one or more
objects, agents, threads, subroutines, separate software
applications, two or more lines of code or other suitable software
structures operating in one or more separate software applications,
on one or more different processors, or other suitable software
architectures.
[0038] As will be appreciated, the processes in preferred
embodiments of the present invention may be implemented using any
combination of computer programming software, firmware or hardware.
As a preparatory step to practicing the invention in software, the
computer programming code (whether software or firmware) according
to a preferred embodiment will typically be stored in one or more
machine readable storage mediums such as fixed (hard) drives,
diskettes, optical disks, magnetic tape, semiconductor memories
such as read-only memories (ROMs), programmable ROMs (PROMs), etc.,
thereby making an article of manufacture in accordance with the
invention. The article of manufacture containing the computer
programming code is used by either executing the code directly from
the storage device, by copying the code from the storage device
into another storage device such as a hard disk, random access
memory (RAM), etc., or by transmitting the code for remote
execution. The method form of the invention may be practiced by
combining one or more machine-readable storage devices containing
the code according to the present invention with appropriate
standard computer hardware to execute the code contained therein.
An apparatus for practicing the invention could be one or more
computers and storage systems containing or having network access
to computer program(s) coded in accordance with the invention.
[0039] Although the invention is described herein with reference to
specific embodiments, various modifications and changes can be made
without departing from the scope of the present invention as set
forth in the claims below. For example, many of the techniques
disclosed herein are broadly applicable to a wide variety of
wireless communication systems. Accordingly, the specification and
figures are to be regarded in an illustrative rather than a
restrictive sense, and all such modifications are intended to be
included with the scope of the present invention. Any benefits,
advantages, or solution to problems that are described herein with
regard to specific embodiments are not intended to be construed as
a critical, required, or essential feature or element of any or all
the claims.
[0040] Unless stated otherwise, terms such as "first" and "second"
are used to arbitrarily distinguish between the elements such terms
describe. Thus, these terms are not necessarily intended to
indicate temporal or other prioritization of such elements.
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