U.S. patent application number 14/014629 was filed with the patent office on 2014-01-02 for system and method for determining air interface information for radio resource management in wireless communications.
This patent application is currently assigned to InterDigital Technology Corporation. The applicant listed for this patent is InterDigital Technology Corporation. Invention is credited to Christopher R. Cave, Angelo A. Cuffaro, Teresa J. Hunkeler, Maged M. Zaki, Guodong Zhang, Juan Carlos Zuniga.
Application Number | 20140004871 14/014629 |
Document ID | / |
Family ID | 33555562 |
Filed Date | 2014-01-02 |
United States Patent
Application |
20140004871 |
Kind Code |
A1 |
Cave; Christopher R. ; et
al. |
January 2, 2014 |
SYSTEM AND METHOD FOR DETERMINING AIR INTERFACE INFORMATION FOR
RADIO RESOURCE MANAGEMENT IN WIRELESS COMMUNICATIONS
Abstract
A radio resource control unit configured to determine values for
use by radio resource management functions includes a measurement
reception and storing unit and a measurement processing unit. The
measurement reception and storing unit is configured to obtain and
store air interface actual values and predictive values; and
generate and store a timestamp indicating a time when each actual
or predictive value is obtained. The measurement processing unit is
configured to process the actual and predictive values to provide
an output value; determine an occurrence of a transient period,
which is a period of time when a radio link is unstable; and
determine whether the actual value is valid by comparing the
timestamp of the actual value to the occurrence of the transient
period, and on a condition that the timestamp is within the
transient period, then the actual value is determined to be not
valid.
Inventors: |
Cave; Christopher R.;
(Dollard-des-Ormeaux, CA) ; Cuffaro; Angelo A.;
(Laval, CA) ; Hunkeler; Teresa J.; (Montreal,
CA) ; Zaki; Maged M.; (San Diego, CA) ; Zhang;
Guodong; (Syosset, NY) ; Zuniga; Juan Carlos;
(Montreal, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
InterDigital Technology Corporation |
Wilmington |
DE |
US |
|
|
Assignee: |
InterDigital Technology
Corporation
Wilmington
DE
|
Family ID: |
33555562 |
Appl. No.: |
14/014629 |
Filed: |
August 30, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13164052 |
Jun 20, 2011 |
8542627 |
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14014629 |
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|
11318402 |
Dec 23, 2005 |
7978642 |
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13164052 |
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10748015 |
Dec 30, 2003 |
7050412 |
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11318402 |
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60480844 |
Jun 23, 2003 |
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Current U.S.
Class: |
455/452.2 |
Current CPC
Class: |
H04W 72/085 20130101;
H04L 41/147 20130101; H04W 24/10 20130101; H04L 43/106
20130101 |
Class at
Publication: |
455/452.2 |
International
Class: |
H04W 72/08 20060101
H04W072/08 |
Claims
1. A radio resource control (RRC) unit configured to determine
values for use by radio resource management functions, the RRC unit
comprising: a measurement reception and storing unit, configured
to: obtain air interface actual values and predictive values; store
the actual values and the predictive values; and generate and store
a timestamp indicating a time when each actual value or predictive
value is obtained; and a measurement processing unit, configured
to: process the actual values and the predictive values to provide
an output value, wherein the output value includes any one of: an
actual value, a predictive value, a combination of the actual value
and the predictive value, a default value, or the actual value plus
a margin; determine an occurrence of a transient period, wherein
the transient period is a period of time when a radio link is
unstable; and determine whether the actual value is valid by
comparing the timestamp of the actual value to the occurrence of
the transient period, and on a condition that the timestamp is
within the transient period, then the actual value is determined to
be not valid.
2. The RRC unit according to claim 1, wherein the measurement
processing unit is further configured to determine whether the
actual value or the predictive value is valid by comparing the
corresponding timestamp with a threshold, and on a condition that
the timestamp is older than the threshold, then the actual value or
the predictive value is determined to be not valid.
3. The RRC unit according to claim 1, wherein: the measurement
reception and storing unit is further configured to store the
actual value with a corresponding indicator, which indicates
whether the actual value was obtained during the transient period;
and the measurement processing unit is further configured to
evaluate the indicator to determine whether the actual value is
valid.
4. The RRC unit according to claim 1, wherein the measurement
processing unit is further configured to use the actual value to
provide the output value on a condition that the actual value is
available and valid.
5. The RRC unit according to claim 1, wherein the measurement
processing unit is further configured to combine the actual value
and the predictive value to provide the output value on a condition
that the actual value is available but not valid and the predictive
value is available.
6. The RRC unit according to claim 1, wherein the measurement
processing unit is further configured to provide the output value
using any one of: the default value, the combination of the actual
value and the default value, the actual value plus the margin, or
declaring air interface resources to be unavailable on a condition
that the actual value is available but not valid and the predictive
value is not available.
7. The RRC unit according to claim 1, wherein the measurement
processing unit is further configured to use the predictive value
to provide the output value on a condition that the actual value is
not available and the predictive value is available.
8. The RRC unit according to claim 1, wherein the measurement
processing unit is further configured to use the default value to
provide the output value on a condition that the actual value is
not available and the predictive value is not available.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/164,052, filed Jun. 20, 2011, which is a
continuation of U.S. patent application Ser. No. 11/318,402, filed
Dec. 23, 2005, now U.S. Pat. No. 7,978,642, issued Jul. 12, 2011,
which is a continuation of U.S. patent application Ser. No.
10/748,015, filed Dec. 30, 2003, now U.S. Pat. No. 7,050,412,
issued May 23, 2006, which claims priority from U.S. Provisional
Patent Application No. 60/480,844, filed Jun. 23, 2003, which are
all incorporated by reference as if fully set forth herein.
FIELD OF INVENTION
[0002] The present invention relates generally to wireless
communication systems. More particularly, the invention is useful
for wireless communication systems which use air interface values
for radio resource management.
BACKGROUND
[0003] The purpose of radio resource management (RRM) in wireless
communication systems is to efficiently manage the use of resources
over the air interface (i.e., radio resources). Intelligent
management of radio resources is essential for maximizing the air
interface capacity, ensuring connection reliability and network
stability and reducing the battery consumption of wireless
transmit/receive units (WTRUs).
[0004] Typical RRM functions include: (1) call admission control,
which accepts or rejects requests for new radio links based on the
system load and quality targets; (2) handover control, which
ensures that a call (connection) is not dropped when a WTRU moves
from the coverage area of one cell to the coverage area of another
cell; (3) power control, which maintains interference levels at a
minimum while providing acceptable link quality; (4) radio link
maintenance, which ensures that quality of service requirements for
individual radio links are satisfied; and (5) congestion control,
which maintains network stability in periods of high
congestion.
[0005] RRM functions are triggered, and make decisions, based upon
a variety of inputs. Among these inputs, air interface measurements
observed by the WTRU and the Node B are extensively used. Air
interface measurements can originate from either the WTRU or the
Node B. WTRU measurements and radio link specific Node B
measurements are referred to as dedicated measurements.
Cell-specific Node B measurements are referred to as common
measurements. Both types of measurements are employed to precisely
evaluate the current state of the radio environment. For example,
interference measurements can be used to decide the allocation of
physical resources in a timeslot or frequency band.
[0006] Typical measurements which RRM functions rely upon for
evaluating the status of the radio environment include:
interference signal code power (ISCP); received power measurements
(both individual radio link and received total wideband power
(RTWP)); received signal strength indicator (RSSI); transmission
power, (including individual radio link power and total power); and
signal-to-interference ratio (SIR) measurements. These measurements
are just several examples of the many measurements that are
applicable with the proposed invention.
[0007] As will be described hereinafter, some of these measurements
may be predicted and a combination of their latest reports and
their predictions may be used when the system is in a transient
phase.
[0008] Unfortunately, there is a drawback in the manner in which
current RRM functions are performed. There are several conditions
that may cause the aforementioned measurements to be unavailable or
invalid. First, it is possible that measurements are simply not
reported, or measurement reports are corrupted over the air
interface. For example, WTRU measurement reports are eventually
encapsulated into transport blocks (TBs) to which cyclic redundancy
check (CRC) bits are attached. The Node B physical layer determines
whether an error occurred by examining the CRC bits. In the event
of an error, the Node B physical layer may either deliver the
erroneous TB to upper layers with an error indication, or simply
indicate to upper layers that an erroneous TB was received on a
particular transport channel or a set of transport channels. Such a
scenario is particularly relevant when considering WTRU
measurements since they are sent over the air interface.
[0009] Secondly, measurements generally have an age threshold,
after which the measurement is considered invalid. If measurement
reports are not frequent enough, it is possible that valid
measurements will eventually become invalid, and thus unavailable
to RRM functions.
[0010] Finally, it is possible that measurements are simply invalid
because the radio link or the system has entered a transient phase
that is undergoing stabilization. For example, interference
measurements are unstable for a certain period of time (up to 1/2
second) following the configuration or reconfiguration of a radio
link due to the transient phase of the power control. Such
measurements should not be used to trigger RRM functions or to make
decisions since the current state of the radio link or the system
is unstable.
[0011] Accordingly, an improved system and method for obtaining
measurements for more effective radio resource management is
needed.
SUMMARY
[0012] The present invention is a radio resource control system and
method which manage air interface resources. According to the
present invention, a wireless communication system obtains RRM data
by determining availability and validity of certain system
measurements. First it is determined whether actual system
measurements and predicted measurements are available, and it is
also determined whether the actual system measurements are valid.
Depending upon the results of the determination, a selective
combination of actual air interface measurements, predicted values
and default values are used. Alternatively, the radio resources for
which the RRM measurement is desired may not be allocated for
use.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] A more detailed understanding of the invention may be had
from the following description of preferred embodiments, given by
way of example and to be understood in conjunction with the
accompanying drawing wherein:
[0014] FIG. 1 is a flow diagram showing the use of different types
of values for RRM functions in accordance with the present
invention;
[0015] FIGS. 2A and 2B are time varying weighting functions used in
accordance with the present invention; and
[0016] FIG. 3 is a centralized measurement control unit made in
accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] The preferred embodiments are described herein in
conjunction with an application of the invention for voice or data
utilizing regular and HSDPA transmissions according to the Third
Generation Partnership Project (3GPP) wideband code division
multiple access (W-CDMA) communication system, which is an
implementation of a Universal Mobile Telecommunications System
(UMTS). Although 3GPP terminology is employed throughout this
application, the 3GPP system is used only as an example and the
invention may be applied to other wireless communications systems
where measurement-based RRM is feasible.
[0018] As used throughout the current specification, the
terminology "wireless transmit/receive unit" (WTRU) includes, but
is not limited to, a user equipment, mobile station, fixed or
mobile subscriber unit, pager, or any other type of device capable
of operating in a wireless environment. These exemplary types of
wireless environments include, but are not limited to, wireless
local area networks and public land mobile networks. The
terminology "Node B" includes, but is not limited to, a base
station, site controller, access point or any other type of
interfacing device in a wireless environment.
[0019] FIG. 1 is a flow diagram of a procedure 20 for determining
measurement values for use by RRM functions in accordance with the
present invention. First, actual measurements and predictive values
are received and stored in a database along with a timestamp of
when they were received (step 22). These measurements and values
are received from different RRM functions such as call admission
control, handover control, power control, and radio link
maintenance. Regardless of whether they are actual system
measurements or predictive values (such as, for example, in the
case of the call admission control function which predicts the
system impact upon acceptance of a new call), they are stored in a
database. The RNC maintains the database of both the measurements
and values and when they were stored.
[0020] Each time the RNC receives a measurement or value, it stores
it in the database along with a timestamp corresponding to the time
at which it is received. By doing so, the RNC can subsequently
determine if measurements or values are available (i.e., stored in
the database) and if so, if they are valid with respect to their
age (i.e., their age is less than a certain age threshold).
[0021] If an RRM measurement request has not been received as
determined at step 30, no further action is taken other than to
continue to receive and store actual measurements and predictive
values at step 22. If a request for an RRM measurement has been
received as determined at step 30, the RNC reviews the database for
the requested RRM measurement to determine whether the requested
RRM measurement is available. Measurements may be unavailable
(i.e., they are not stored in the database) either because no
measurement report was sent or the measurement report was corrupted
over the air interface. If actual system measurements are not
available as determined at step 34, a determination is made as to
whether predictive values are available (step 36).
[0022] The predictive values (M.sub.PREDICTED) are determined as
follows. When certain RRM functions perform an action, they can
predict what certain system measurements, (such as interference or
power), will be once the action is performed. For example, one RRM
function is the Call Admission Control (CAC) algorithm. The CAC
algorithm predicts what the interference and power will become once
a call is added. If the predicted levels are acceptable, then the
call is added; if the predicted levels are unacceptable, then the
call is denied. In accordance with the present invention, these
predicted interference and power values (along with other types of
predicted values) are then stored and used as predicted values for
interference and power. Since the prediction of RRM values is well
known in the prior art for many different types of RRM functions,
and the particular prediction method is not central to the present
invention, it will not be described in detail hereinafter.
[0023] If predictive values are available, the predictive values
are used (step 38), and if not, a default value is used (step
40).
[0024] A default value is a predetermined value which is
established by historical conditions and or a series of
measurements or evaluations. In essence, a default value is a
predetermined value which is pre-stored and retrieved when desired.
The default value is typically chosen such that RRM functions
behave in a conservative way.
[0025] If actual system measurements are available as determined at
step 34, then it is determined whether the actual system
measurements are valid (step 42). As aforementioned, with respect
to the validity of actual system measurements, these measurements
may be invalid because they are too old, or may be invalid because
the system is in a transient phase and hence, the measurements do
not accurately represent the state of the system.
[0026] With respect to the age of a measurement, when a measurement
report is received in the RNC database, it is assigned a timestamp.
The timestamp corresponds to the time at which the measurement
report was received. When the measurement is retrieved from memory,
its timestamp is read. If the timestamp indicates that the
measurement is older than a certain measurement age threshold
(e.g., one second), then the measurement is deemed invalid.
[0027] With respect to the invalidity of a measurement because it
is taken when the system is in a transient period, as
aforementioned, each RRM function is associated with one or more
RRM measurements. Each time an RRM function performs an action on
the system, it determines the time at which the action was taken.
This time corresponds to the start of the "transient period." The
transition period lasts for a certain duration, after which point
the system is considered stable again. The duration of the
transient period depends on the type of action that was performed
by the RRM function. The duration of the transient period is a
design parameter.
[0028] If a particular RRM measurement is taken during the
transient period of the RRM function, it is deemed to be invalid.
This can be determined in several ways. In a first alternative,
associated with each RRM measurement stored in the database is an
indication of whether or not the RRM measurement was taken during
the transient period. Although these measurements are stored, they
will be deemed invalid.
[0029] In a second alternative, a timestamp for the beginning of
each RRM transient is stored separately. When an RRM measurement is
retrieved from the database, its timestamp may be compared to the
timestamp of the transient period. If the timestamp of the
retrieved RRM measurement is within the transient period (i.e., the
timestamp of the beginning of the RRM transient plus the duration
of the transient), the retrieved RRM measurement is determined to
be invalid.
[0030] In a third alternative, actual measurements may be declared
invalid by simply determining if a predicted measurement is in the
database and if so, determining its timestamp. This alternative
assumes that the transient period begins exactly when predicted
measurements are written to the database. These alternatives are
intended to be illustrative, not limiting, as there are many
different ways that such a determination of invalidity may be
effected.
[0031] The system determines the validity of an actual measurement
in view of both age of the actual measurement and the stability of
the system. If the actual measurement is valid as determined at
step 42, then the actual measurement is used (step 44).
[0032] If the actual measurement is deemed not valid at step 42, a
determination is made as to whether a predictive value is available
(step 46). If a predictive value is available as determined at step
46, the actual measurement is combined with the predictive value
(step 48).
[0033] The combination of actual measurements and predictive values
as performed at step 48 will now be described. Although those of
skill in the art realize that they are many different ways to
combine the values, in one preferred embodiment, the present
invention uses a combination of actual measurements (M.sub.ACTUAL)
and predicted values (M.sub.PREDICTED) as follows:
M(t)=.alpha.(t)M.sub.PREDICTED+(1-.alpha.(t))M.sub.ACTUAL; Equation
(1)
where .alpha.(t) is a time-varying weighting function and t
represent the amount for time elapsed since the initiation of the
transient period (i.e., transient period starts at t=0).
M(t)represents the combined measurement at time t which is provided
to the RRM function. Typically, .alpha. is a monotonically
decreasing function between one (1) and zero (0). Preferably
.alpha. should equal 1 at t=0, immediately following the beginning
of the transient period and .alpha. should equal 0 at the end of
the transient period, once actual measurements are considered
stable.
[0034] Example .alpha. weighting functions are shown in FIGS. 2A
and 2B for a transient phase of 1 second duration. In FIG. 2A, the
variation over time is a substantially straight line function,
whereas in FIG. 2B the variation over time results in .alpha.
initially diminishing at a slow rate, followed by a rapidly
diminishing rate. This may be approximated by an exponential or
geometric change, depending on the nature of .alpha..
[0035] It is possible that succeeding actions take place during the
transient period (i.e., before .alpha. has reached zero). When a
subsequent action is taken by an RRM function, the system enters a
"new" transient period. Since certain RRM functions typically
predict what a value would be following an action that is taken at
time t.sub.1, the predicted value is based on M (t.sub.1). In this
case, M.sub.PREDICTED is made based on M (t.sub.1), where ti is the
time when the succeeding action is triggered.
[0036] Furthermore, t is reset to zero at the completion of the
succeeding action (i.e., a new transient period is started). If a
new transient period is started, any subsequent RRM function that
acts at t.sub.2 would use t.sub.1 as the beginning of the transient
phase. As a result, t in Equation 1 would be t=t.sub.2-t.sub.1.
[0037] Referring back to FIG. 1, if it has been determined that the
actual measurement is not valid as determined at step 42 and
predictive values are not available as determined at step 46, then
the RNC may implement one of the following four options (step 50):
(1) use a default value as in step 40; (2) combine the actual
measurement with a default value; (3) add a margin to the actual
measurement; or (4) declare the resources at issue to be
unavailable.
[0038] With respect to the first option, use of the default value,
this was explained with reference to step 40.
[0039] With respect to the second option, combining the actual
measurement and a default value, the RNC combines these in
different ways depending upon the reason why the measurement is
invalid. If the measurement is invalid because the latest actual
measurement in the database is too old, then an equation similar to
Equation 1 can be used:
M(t)=.alpha.(t)M.sub.ACTUAL+(1-.alpha.(t))M.sub.DEFAULT Equation
(2)
[0040] In Equation 2, the time-decaying a term is applied to
M.sub.ACTUAL and t is the elapsed time since the measurement was
stored in the database. Preferably this .alpha. function differs
from the one used in Equation 1 in that it is chosen to decay much
more slowly.
[0041] If the actual measurement is declared invalid because the
system is in a transient state, but fresh actual measurements are
available, a weighted combination of the actual measurement and the
default value is used:
M=AM.sub.ACTUAL+BM.sub.DEFAULT; Equation (3)
where A+B=1 and the weighting factors A and B are configurable
parameters that are optimized based on simulations or observations
of the system. Note that different measurements could have
different weighting factors.
[0042] With respect to the third option of adding a margin to the
actual measurement, preferably a time-varying error margin is added
to the actual measurement, as described by:
M=M.sub.ACTUAL.+-.MARGIN; Equation (4)
where MARGIN is a time-varying margin which is large at time zero,
immediately following the initiation of the transient period, and
monotonically decreases toward zero as the transient period ends.
As is the case with Equation (1), Equation (4) is executed when the
actual measurements are available, but are deemed not to be valid
due to a transient period or an expired timestamp. Note that this
option is only valid in the case where measurements or metrics
monotonically increase or decrease towards the converged value. In
the case where measurements or metrics oscillate around the
converged value, this option is not optimum.
[0043] This option has the advantage that predictive measurements
need not be presumed to exist during the transient period. It is
further possible to execute Equation (1) when predictive
measurements are available and execute Equation (4) when MARGIN is
considered the best "prediction."
[0044] With respect to the last option of step 50 regarding
declaring resources to be unavailable, if it has been determined
that actual measurements, predictive values, adding a margin to an
actual measurement or a combination of any of these options is
undesirable, the system may simply decline to send an RRM
measurement and those resources for which the RRM measurement was
requested will be deemed by the assistant to be unavailable.
Accordingly, those resources will not be used.
[0045] The result of the determination as to whether to use the
actual value at step 44, a predictive value at step 38, a default
value at step 40, a combined actual measurement with a predictive
value at step 48, or one of the options in step 50, is then used to
provide the requested RRM measurement.
[0046] To facilitate the management of measurements, a centralized
measurement control unit is utilized at the RNC. The centralized
measurement control unit implements the following functions: (1)
storing received measurements within a central structure; and (2)
measurement processing, including measurement filtering, tracking
measurement age, and validity (e.g., assigning timestamp upon
reception, and age threshold comparison) and selecting between or
combining predicted values and actual measurements.
[0047] A centralized measurement control unit 80 made in accordance
with the present invention is shown in FIG. 3. The measurement
control unit 80 includes a measurement setup unit 81, a measurement
reception and storing unit 82, a measurement processing unit 83 and
a measurement output unit 84.
[0048] The measurement setup unit 81 implements the measurement
setup procedures with respect to the WTRU and the Node B. It is
responsible for the setup and configuration of measurements. More
specifically, it communicates with the Node B and the WTRU RRC
layers to setup, modify, and end measurements, giving all
measurement configuration details (e.g., averaging period,
reporting criterion/period).
[0049] The measurement reception and storing unit 82 stores the
actual and predicted WTRU and Node B measurements in an organized
structure. This includes assigning timestamp information upon
reception of a measurement in order to track the age of the
measurement.
[0050] The measurement processing unit 83 filters received
measurements, verifies measurement validity and/or availability and
combining actual measurements, predicted values and default as
appropriate. The measurement processing unit 83 is responsible for
all of the measurement processing that is described in the present
invention.
[0051] The measurement output unit 84 provides proper measurements
to RRM functions upon request (i.e., providing actual measurements
when valid, predicted measurements when unavailable or invalid or a
combination of actual measurements, predicted values and default
values, such as are illustrated in FIG. 1 at steps 38, 40, 44, 48,
and 50). Moreover, this measurement output unit 84 can optionally
be responsible for triggering RRM functions when measurements
exceed a predetermined threshold.
* * * * *