U.S. patent application number 13/591085 was filed with the patent office on 2013-02-07 for handling of idle gap commands in a telecommunication system.
This patent application is currently assigned to Telefonaktiebolaget LM Ericsson (publ). The applicant listed for this patent is Muhammad Ali Kazmi. Invention is credited to Muhammad Ali Kazmi.
Application Number | 20130034008 13/591085 |
Document ID | / |
Family ID | 39536853 |
Filed Date | 2013-02-07 |
United States Patent
Application |
20130034008 |
Kind Code |
A1 |
Kazmi; Muhammad Ali |
February 7, 2013 |
Handling of Idle Gap Commands in a Telecommunication System
Abstract
The invention relates to methods and arrangements for the
reliability handling of idle gap commands received in a unit of a
mobile telecommunication system. A user equipment located in a cell
of a mobile telecommunication network receives signaling gap
commands used to activate or deactivate idle gaps for downlink
measurements in the neighbor cells. It is determined whether the
received gap command is reliable or not. Downlink measurements are
then performed in accordance with a predefined rule in case the
received gap command is determined as unreliable.
Inventors: |
Kazmi; Muhammad Ali;
(Bromma, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kazmi; Muhammad Ali |
Bromma |
|
SE |
|
|
Assignee: |
Telefonaktiebolaget LM Ericsson
(publ)
Stockholm
SE
|
Family ID: |
39536853 |
Appl. No.: |
13/591085 |
Filed: |
August 21, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12520099 |
Jun 19, 2009 |
8270340 |
|
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PCT/SE2007/050961 |
Dec 7, 2007 |
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13591085 |
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Current U.S.
Class: |
370/252 |
Current CPC
Class: |
H04W 36/0088
20130101 |
Class at
Publication: |
370/252 |
International
Class: |
H04W 24/00 20090101
H04W024/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2006 |
SE |
0602769-2 |
Claims
1. A method for handling idle gap commands, the method performed by
a user equipment located in a cell of a mobile telecommunication
network and comprising: determining whether a signaling gap command
received from a base station is reliable or unreliable; and
performing downlink measurements on a neighbor cell during an idle
gap according to a predefined rule if the gap command is
unreliable.
2. A method for handling idle gap commands, the method performed by
a radio base station operating in a cell of a mobile
telecommunication network and comprising: sending gap commands to a
user equipment indicating a function to be performed by the user
equipment during idle gaps corresponding to the gap commands; and
configuring the user equipment to perform a predetermined function
responsive to the user equipment determining that a received gap
command is unreliable.
3. A user equipment located in a cell of a mobile telecommunication
network, the user equipment comprising: a logic unit configured to:
determine whether a signaling gap command received from a base
station is reliable or unreliable; and perform downlink
measurements on a neighbor cell during an idle gap according to a
predefined rule if the gap command is unreliable.
4. A radio base station operating in a cell of a mobile
telecommunication network, the radio base station comprising: a
logic unit configured to: send gap commands to a user equipment
indicating a function to be performed by the user equipment during
idle gaps corresponding to the gap commands; and configure the user
equipment to perform a predetermined function responsive to the
user equipment determining that a received gap command is
unreliable.
5. A user equipment located in a cell of a mobile telecommunication
network, the user equipment comprising: means for determining
whether a signaling gap command received from a base station is
reliable or unreliable; and means for determining downlink
measurements on a neighbor cell during an idle gap according to a
predefined rule if the gap command is unreliable.
6. A radio base station operating in a cell of a mobile
telecommunication network, the radio base station comprising: means
for sending gap commands to a user equipment indicating a function
to be performed by the user equipment during idle gaps
corresponding to the gap commands; and means for configuring the
user equipment to perform a predetermined function responsive to
the user equipment determining that a received gap command is
unreliable.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 12/520,099 entitled "Handling of Idle
Gap Commands in a Telecommunication System" filed Jun. 19, 2009.
This application claims priority from the '099 application, and
from International Application No. PCT/SE2007/050961, filed Dec. 7,
2007, and Foreign Application No. SE0602769-2, filed Dec. 19, 2006.
The '099, '961, and '769-2 applications are expressly incorporated
herein by reference in their entirety.
TECHNICAL FIELD
[0002] The present invention relates to methods and arrangements in
a telecommunication system, in particular to methods and
arrangements for the reliability handling of idle gap commands
received in a unit of a mobile telecommunication system.
BACKGROUND
[0003] Universal Terrestrial Radio Access Network (UTRAN) is a
conceptual term that identifies the part of the network consisting
of Radio Network Controllers (RNCs) and Node Bs. This communication
network is commonly referred to as 3G. Evolved UTRAN (E-UTRAN) is
an evolution of the 3G radio access network towards a high-data
rate, low-latency and packet-optimized radio access network.
[0004] As stated in the document 3GPP TR 25.913 "Requirements for
Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN)" issued by the
3rd Generation Partnership Project (3GPP), an evolved UMTS
Terrestrial Radio Access Network (E-UTRAN) is supposed to support
the mobility of user equipment (UE) within different E-UTRA carrier
frequency layers as well as support mobility between E-UTRAN and
legacy technologies (such as UTRAN and GERAN). In order to realize
such mobility scenarios, the UE should be able to perform downlink
measurements on other frequency or other access technologies
without significant performance degradation. These types of
measurements (i.e. outside serving frequency layer or outside intra
frequency) are performed during idle gaps. An idle gap implies a
time period that the UE for instance can use for performing such
measurements. When performing measurements, the UE does not receive
or transmit any data or signaling information.
[0005] Idle gap patterns can be scheduled in the following ways:
[0006] Static idle gaps [0007] Fully dynamic periodic gaps [0008]
Semi-dynamic periodic gaps
[0009] In static idle gap patterns the network configures all the
associated parameters at the time of measurement configuration. In
this approach the gaps occur periodically. The periodic pattern is
used throughout the measurement until modified by higher layer
signaling. The UE will not be scheduled during the gaps; instead it
will perform the requested measurements.
[0010] Dynamic idle gaps are generally created through negotiation
between UE and Node B.
[0011] In semi-dynamic gap allocation the gap pattern is initially
assigned to the UE at the start of each measurement via RRC
signaling in a Measurement Control message. But during the course
of the measurement the gaps can be altered by sending short
commands. The network can send information to the UE to indicate
whether the UE shall consider the gap pattern to be on or off. When
the gap pattern is off the UE may be scheduled during the gap
pattern and so will not use the gap to perform measurements. On the
other hand when the gap pattern is on, the UE will not be scheduled
and so can perform measurements during the gaps.
[0012] Most UEs have a single receiver chain, which can operate on
a single carrier frequency at a time. Therefore, in E-UTRAN the UE
can perform neighbor cell measurements without idle gaps on the
neighbor cells belonging to the serving carrier frequency provided
these cells are well aligned in the frequency domain.
[0013] Generally, cell identification and handover measurements
that are carried out on cells operating on a carrier frequency
outside the serving frequency layer, i.e. on inter-frequency,
require idle gaps. In E-UTRAN the following categories of handovers
will require a UE to perform neighbor cell measurements with idle
gaps: [0014] Handovers to E-UTRA inter-frequency cells, Frequency
Division Duplex (FDD); [0015] Handovers to E-UTRA inter-frequency
cells, Time Division Duplex (TDD); [0016] Handovers to UTRA
Frequency Division Duplex (FDD) cells; [0017] Handovers to UTRA
Time Division Duplex (TDD) cells; [0018] Handovers to GSM Edge
Radio Access Network (GERAN) cells; [0019] Handovers to non 3GPP
technologies, e.g. CDMA2000, Mobile Wimax, etc.
[0020] During an idle gap the UE tunes its receiver to another
E-UTRA carrier frequency or to a carrier frequency of another
access technology (e.g. UTRA or GERAN) for performing the neighbor
cell measurements and/or cell identification. The more general term
measurements is used which implies neighbor cell measurements as
well as cell identification. It should be noted that in order to be
able to perform neighbor cell measurements, the UE should first
identify the cell. The neighbor cell measurements are performed on
identified neighbor cells. While performing such measurements the
UE does not receive or transmit any data or signaling information
on the serving E-UTRA carrier frequency.
[0021] It is likely that at least some sort of semi-dynamic idle
gaps will be used in E-UTRAN. In a semi-dynamic idle gap pattern
assignment one or more gap patterns are initially assigned (or
pre-configured) to the UE at the time of measurement configuration
via higher layer signaling such as radio resource control (RRC).
During the course of measurement the gaps can be activated or
deactivated by sending short and fast commands, typically
"on"/"off"-signals, that are sent on a shared control channel (e.g.
L1/L2 control) as proposed in the document 3GPP TR 25.814 "Physical
layer aspect for Evolved Universal Terrestrial Radio Access
(UTRA)". The commands are sent just prior to the start of gaps.
Even if static idle gaps are used, on/off commands can still be
used for activating or deactivating an entire gap pattern, i.e. to
start or stop the idle gap pattern. Irrespective of the gap pattern
type, the on/off commands can also be used at the very beginning,
or activation, of the pattern and for terminating the pattern when
measurements are over. It should be noted that the conventional way
of activating or deactivating the entire pattern is via Radio
Resource Control (RRC) signaling, whereby the drawback is that it
is slow and therefore may cause performance degradation.
[0022] The main advantage of the "on"/"off"-commands is to provide
flexibility to the scheduler since it can schedule users during the
gaps if resources are available, if the quality of service is to be
met, and if there is sufficient traffic in the buffer. Another main
advantage is that HARQ (Hybrid Automatic Repeat Request) initial
transmission and especially retransmissions would not be delayed
due to measurements during the gap.
[0023] As shown in FIG. 6, each pre-configured idle gap pattern is
characterized by a start sub frame number (SSSFN), an end sub frame
number (ESSFN), and an inter-gap length (IGL). The typical gap
length can vary between 2 ms and 10 ms duration. The gap pattern
can be configured for a limited duration but also for infinite
amount of time, i.e. until the end of the session. During an idle
gap the UE can perform downlink measurements unless forbidden by
the network via shared control channel (L1/L2 control) as explained
above. In case a measurement is not allowed, e.g. by a gap
"off"-command, the UE expects to be scheduled for data
transmission.
TABLE-US-00001 Shared control channel field Interpretation Action 0
Gap ON Perform measurement only 1 Gap OFF Skip measurement,
receive/transmit data
[0024] The table illustrates an example of the connotation of gap
commands and how gap commands can be interpreted. This, however, is
purely a matter of definition; alternative approaches could define,
for instance, the values 0 and 1 to be specified as gap "off" and
gap "on", respectively.
[0025] One particularly important issue in transmissions is the
reliability. I.e. the entire decision process relies upon one or
more simple commands, such as the "on"/"off"-signaling, up and down
commands, etc. Thus, unreliable commands may cause actions to occur
in reverse direction and in some cases may lead to unstable
behavior. Unreliabilities where a receiver cannot properly
interpret the correct meaning of a received command generally occur
due to bad radio conditions, low transmitted power level, poor
coverage, high system load, etc. FIG. 7 illustrates an example in
which an unreliable gap command leads to a missed HARQ
transmission.
[0026] To ensure reliable operations, four sets of functionalities
should be specified: [0027] Reliability check; [0028] Behavior or
action of UE and/or base station; [0029] Indication or reporting of
unreliability events to network; [0030] Prevention of
unreliability.
[0031] The reliability check can be based either on some signal
strength or quality thresholds. It can also be based on some bit
error rate (BER) target value. This means a received command is
regarded as unreliable in case the received signal quality or
strength falls between the thresholds or if the BER is higher than
the target.
[0032] The behavior of UE or base station in response to unreliable
command detection depends upon a particular functionality governed
by the on/off command. This is described with the following
examples from UTRAN.
[0033] Assuming for instance TPC commands ("on"/"off"-type
signaling) as used in WCDMA for inner loop power control in a soft
handover scenario. The UE is supposed to regard the UL TPC command
(received on the downlink) as unreliable in case TPC command error
rate exceeds a certain threshold, e.g. 30%. The immediate action or
behavior of the user equipment is to disregard such a command when
combining TPC commands in soft handover from more than one radio
link sets. Both reliability check and UE actions are generally
mandated by a suitable test case as is the case with TPC
combining.
[0034] Another example relates to the UE behavior in case of
unreliable scheduling grants in E-DCH transmission. An unreliable
up- or down-command is treated as a hold command by the UE. This
means that the UE in case of a detected unreliable grant will
neither increase nor decrease its current transmitted rate. This
well specified behavior ensures that a UE shall not transmit with
unnecessary higher power because this would otherwise increase the
noise rise at the base station.
[0035] In order to eliminate the unreliable behavior, the network
needs to take some corrective actions (such as increasing power
level, performing congestion control, doing handover, etc.), which
is generally possible if the network is made aware of the
"unreliable" behavior, preferably by reporting "successive
unreliable occurrences". Reliability of the received commands can
be improved by using redundant bits (e.g. sending 000 and 111 for 0
and 1 respectively). But this is not sufficient as this is almost
always done (e.g., 2 or more bits per TPC command) but still UE
behavior needs to be specified since redundant bits may also become
unreliable.
SUMMARY
[0036] Hence, the gap commands sent via shared control channel
signaling may be unreliable due to poor radio conditions,
insufficient transmit power setting, or, if the user is in the cell
border region, inter-cell interference. If, in such situations, an
unreliable gap "off"-command is interpreted incorrectly, there will
arise two problems: first, the UE will miss the scheduling commands
on the shared control channel and the corresponding data sent on
DL-SCH on the serving E-UTRA carrier frequency. This will obviously
delay the HARQ transmissions and retransmissions. Second, downlink
resources, which contain scheduling command and the data on the
DL-SCH, will be wasted.
[0037] Thus, it is an object of the invention to decrease unstable
behavior in the network due to incorrect interpretation of gap
commands.
[0038] According to a first aspect of the invention a method in a
user equipment located in a cell of a mobile telecommunication
network is provided. The method comprises the step of receiving
signaling gap commands used to activate or deactivate idle gaps for
downlink measurements in the neighbor cells. The signaling gap
commands may be MAC level gap on/off commands indicating whether or
not the user equipment can use the gap for measurements. According
to the method it is first determined whether the received gap
command is reliable or not. Then, downlink measurements are
performed in accordance with a predefined rule in case the received
gap command is determined as unreliable.
[0039] A second aspect of the invention provides a method in a
radio base station in a cell of a mobile telecommunication network.
The method comprises the steps of configuring idle gaps in a user
equipment in the cell for downlink measurements, and sending gap
commands indicating whether the user equipment should receive data
or perform downlink measurement during the corresponding gap. The
method also comprises the step of configuring a user equipment for
specifying a predetermined behavior when the received gap commands
are unreliable.
[0040] According to a third aspect of the invention, a user
equipment located in a cell of a telecommunication network is
provided. The user equipment is equipped for receiving signaling
gap commands used to activate or deactivate idle gaps for downlink
measurements on the neighbor cells. The user equipment comprises
means for determining whether the received gap command is reliable
or unreliable. Furthermore, it comprises means for performing
downlink measurements in accordance with a predefined rule, in case
the received gap command is determined as unreliable. The means
utilized according to this third aspect, such as antenna and radio
equipment, are all standard user equipment components well known to
a person skilled in the art. Also, the means for performing
downlink measurements in accordance with a predefined rule could be
partly implemented by for instance software that is run on one or
more processors in the user equipment. Alternatively it could
possibly be implemented by hardware, such as one or more ASICs.
[0041] A fourth aspect of the invention provides a radio base
station in a cell of a mobile telecommunication network. The radio
base station comprises means for configuring idle gaps in a user
equipment in the cell for downlink measurements. It also comprises
means for sending gap commands indicating whether the user
equipment should receive data or perform downlink measurement
during the corresponding gap. Furthermore, it comprises means for
configuring a user equipment for specifying correct behavior when
the received gap commands are unreliable. The means utilized
according to this fourth aspect, such as antenna and radio
equipment, are all standard radio base station components well
known to a person skilled in the art. Software run on e.g. a
processor in the radio base station could be used for logical
operations, such as how to configure the idle gaps and how to
specify correct behavior when the gap commands are unreliable.
[0042] A fifth aspect of the invention provides a method in a radio
base station in a cell of a mobile telecommunication network. The
method comprises the steps of configuring idle gaps in a user
equipment in the cell for downlink measurements, and sending gap
commands indicating whether the user equipment should receive data
or perform downlink measurement during the corresponding gap. The
method also comprises the step of configuring a user equipment for
specifying correct behavior when the received gap commands are
unreliable. Furthermore, the method comprises the step of
configuring a user equipment to be able to report results or events
pertaining to unreliable commands. It also comprises the step of
performing one or more actions to improve the reliability of the
received gap commands in response to the results or events reported
by the user equipment. Finally, it comprises the steps of
autonomously detecting that the transmitted gap commands are
received unreliably by the user equipment without explicit reports
from the user equipment and performing one or more actions to
improve the reliability of the transmitted gap commands.
[0043] According to a first embodiment the predetermined rule and
predetermined behavior imply that the UE assumes that the next gap
is "off", whereby it omits the gap (i.e. it does not perform any
measurements) and waits to be scheduled.
[0044] According to a second embodiment the predetermined rule and
predetermined behavior imply that the UE also assumes that the next
gap is initially "off" but after an expiration of a timer (starting
from start of the gap) it may perform measurement during the
remaining gap provided it has not received any data.
[0045] According to yet another embodiment the predetermined rule
and predetermined behavior imply that the UE assumes that the next
gap is "on", whereby it performs measurement during the entire
gap.
[0046] The UE may also report events or results pertaining to
unreliable events (or unreliable gap commands) to the network,
which in turn takes some corrective measures such as increase
transmit power, congestion control, etc.
[0047] It is an advantage of the present invention that the UE
behavior is specified in case of receiving unreliable gap commands,
whereby unstable behavior in the network is decreased.
[0048] It is a further advantage of the present invention that HARQ
transmissions will not be lost due to the reception of unreliable
gap command.
[0049] It is still another advantage of an embodiment of the
present invention that the network is able to take appropriate
action (e.g. adjusts transmit power etc.) when gap commands are
repeatedly received as unreliable.
[0050] A further advantage is that the embodiment concerning
non-static gaps (semi-dynamic or fully dynamic) provides such a
flexibility that would ensure that at least HARQ retransmissions
are not delayed due to gaps. As stated above, due to unreliable
behavior in the prior art solutions not only HARQ transmissions and
retransmissions are delayed but they can even be lost over the air
(waste of resources).
[0051] Further objectives, features, aspects and advantages of the
present invention will appear from the following detailed
disclosure, from the attached claims as well as from the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] Exemplifying embodiments of the invention will now be
described in more detail with reference to the accompanying
schematic drawings.
[0053] FIG. 1 schematically illustrates the general architecture in
which embodiments of the invention can be used.
[0054] FIG. 2 schematically illustrates a user equipment for which
embodiments of the invention can be used.
[0055] FIG. 3 schematically illustrates a radio base station for
which embodiments of the invention can be used.
[0056] FIG. 4 illustrates a block diagram of the general flow of a
method in a user equipment according to an embodiment of the
invention.
[0057] FIG. 5 illustrates a block diagram of the general flow of a
method in a base station according to an embodiment of the
invention.
[0058] FIG. 6 illustrates the principles of semi-dynamic gap
patterns.
[0059] FIG. 7 illustrates the impact of a misinterpretation of
unreliable idle gap commands.
[0060] FIG. 8 illustrates an unreliability region that is
determined by thresholds.
[0061] FIG. 9 illustrates an unreliability region that is based on
a BER target threshold.
[0062] FIG. 10 illustrates a first embodiment of the present
invention.
[0063] FIG. 11 illustrates a second embodiment of the present
invention.
[0064] FIG. 12 illustrates a third embodiment of the present
invention.
DETAILED DESCRIPTION
[0065] FIG. 1 shows the general architecture in which embodiments
of the invention may be used. A mobile station 10, or user
equipment (UE), is located within the coverage of a mobile
communications network. The UE communicates with base stations 20,
or E-UTRAN NodeBs (eNBs) in the case of LTE, which provides
wireless network coverage for a particular coverage area commonly
referred to as a cell. The eNBs 20 are interconnected, and are also
connected to the EPC (Evolved Packet Core), and more specifically
to the MME (Mobility Management Entity) and to the Serving Gateway
(S-GW). Radio Resource Control (RRC) terminates in eNB 20, and
measurement configuration is done via RRC, which resides in eNB 20.
FIG. 2 schematically shows a UE 10 that comprises standard wireless
device components, such as an antenna arrangement, radio equipment,
a logic unit that can be implemented for instance as a
microprocessor, a CPU, or similar processing or computer means, as
well as some kind of data storage unit or memory unit. The skilled
person will realize that a user equipment 10 comprises these and
other components, and they will therefore not be described further
in this application. The UE 10 in FIG. 2 comprises means 111 for
receiving signaling gap commands, means 112 for determining whether
a received gap command is reliable or unreliable, and means 113 for
performing downlink measurements in accordance to a predefined
rule, in case the received gap command is determined as
unreliable.
[0066] FIG. 3 schematically shows a network radio base station 20
that may be used in connection with the present invention. It
comprises standard radio base station components, such as network
interfaces, an antenna arrangement, radio equipment, a logic unit
that can be implemented for instance as a microprocessor, a CPU, or
similar processing or computer means, as well as some kind of data
storage unit or memory unit. The radio base station 20 in FIG. 3
comprises means 211 for configuring idle gaps in a UE, means 212
for sending gap commands, means 213 for configuring a UE for
specifying correct behavior when the received gap commands are
unreliable. It also comprises means 214 for configuring a UE 10 to
be able to report results or events pertaining to unreliable
commands. Furthermore, means 215 for performing one or more actions
to improve the reliability of the received gap commands in response
to the results or events reported by the UE 10 are comprised.
According to embodiments of the invention such actions are radio
resource management actions. Also, the radio base station 20
comprises means 216 for detecting autonomously that the transmitted
gap commands are received unreliably by the UE 10 without explicit
reports from the UE 10.
[0067] The invention determines whether a signaling gap command
used to activate or deactivate idle gaps for downlink measurements
in the neighbor cells transmitted from the network to the UE 10 is
reliable or unreliable. If it is determined that the signaling gap
command is unreliable, the downlink measurements are performed in
accordance with a predefined rule according to the present
invention.
[0068] According to embodiments of the invention, on/off commands
can also be used to start and/or stop the entire idle gap pattern.
Such gap commands, or gap pattern commands, regarding an entire gap
pattern are received in the user equipment. The base station may
send the on/off command to the user equipment to activate and/or
deactivate the idle gap pattern, whereby the user equipment is
configured for specifying a predetermined behavior when the
received gap pattern commands are unreliable. In such a case the
gap pattern on/off command will be sent via the MAC layer or via
the downlink physical layer control channel. An advantage is that
it is quicker than the conventional way of activating/deactivating
an entire pattern via RRC signaling, since gaps can be activated or
deactivated in just one or a few time slots, e.g. 0.5 ms or maximum
1 ms. The swift activation and deactivation of gap patterns would
speed up the measurement process and reduce throughput loss,
respectively.
[0069] FIG. 4 shows steps of a method in a UE 10 that are carried
out according to embodiments of the invention. First, the UE 10
receives signaling gap commands in s100. In s100 the UE 10 then
determines whether the received gap command is reliable or
unreliable. In case the received gap command is determined as
unreliable, the UE 10 performs downlink measurements in accordance
with a predefined rule in s120. In s130 the UE 10 also has the
possibility to report an event in case of receiving several
unreliable gap commands during a certain time period.
[0070] Thus, the UE 10 needs to check whether a received gap
command is reliable or unreliable. The UE 10 must check the
reliability of each and every gap command. FIG. 8 illustrates one
simple mechanism of reliability checking. The command is unreliable
in case its received signal strength is between lower (.mu..sub.1)
and upper (.mu..sub.2) thresholds. Another possibility, which is
illustrated in FIG. 9, is to map the measured quality of the
received command onto a certain bit error (BER) rate based on some
pre-defined lookup table. The received gap command is considered to
be unreliable in case the mapped BER is larger than the specified
threshold level (.gamma..sub.BER). The exact algorithm that
determines unreliability of the received command is generally
implementation dependent but in some cases it can partly be
specified such as BER target etc. Reliability checking and
appropriate behavior are ensured by a test case.
[0071] If it is determined that a received gap command is
unreliable, then the downlink measurements should according to the
present invention be performed in accordance with a predefined
rule.
[0072] In accordance with embodiments of the invention, there are
the following (possibly) mutually exclusive predefined rules, which
will be discussed in the following detailed description: [0073]
According to a first embodiment of the present invention the UE 10
skips the gap, i.e. no downlink measurements are performed during
the next gap; [0074] According to a second embodiment, the UE 10
partly skips the gap, i.e. it may perform downlink measurements
after time T.sub.0; [0075] According to a third embodiment, the UE
10 considers the next gap for downlink measurements.
[0076] According to the first embodiment, the UE 10 detects an
unreliable gap command and completely skips the next gap and awaits
instead a scheduling command from the network as shown in FIG. 10.
The main advantage of this solution is that HARQ transmissions will
not be lost and there will not be any wastage of downlink
transmission resources since UE 10 will be able to receive the
data.
[0077] According to the second embodiment, which is exemplified in
FIG. 11, the UE 10 partly skips the gap: as stated before the gap
can be typically between 2 ms and 10 ms long depending on the
number of measurements (e.g. number of cells) to be performed and
the desired measurement reporting delay. A longer gap (e.g. between
8 ms and 10 ms) would be inefficiently used (i.e. no measurements)
in response to unreliable gap command if the UE 10 neither performs
any measurement nor receives any HARQ transmission.
[0078] When the UE 10 receives an unreliable gap command, it sets a
gap activation timer (or counter) (T.sub.0) in the order of number
of TTIs according to the second embodiment. Another possibility is
to reset the timer after the UE 10 has been scheduled during the
gap. Until the expiration of the timer the UE 10 skips the gap and
waits for the data transmission from the network. After the
expiration of the timer the UE 10 starts the measurement, provided
it has not already been scheduled during time T.sub.0. This is
because the network is likely to schedule just after the start of
the gap. If the UE 10 is not scheduled within the time T.sub.0, it
may assume that the network sent a gap "on" command. This
embodiment implies the advantage that the UE 10 can use at least a
part of the gap more efficiently.
[0079] The behavior of the network can be specified, e.g., by
scheduling a user immediately after sending the gap "off" command.
The timer value should be settable by the network, e.g. via RRC
signaling. The network can use the timer option in case of long
gaps. In case the timer value is set to a very large value (larger
than the gap length), the solution becomes similar to embodiment to
fully skip the gap, which has been described above.
[0080] The third embodiment, which is exemplified in FIG. 12, uses
the gaps fully for measurements and is the converse embodiment to
the first embodiment (i.e. gap fully skipped). In case of
unreliably received gap command, the UE 10 will perform
measurements in the entire next gap. This means that the
measurement reports will not be delayed.
[0081] According to embodiments of the invention, a method in a
radio base station 20 comprises the following steps, which are
illustrated in FIG. 5. First, the radio base station 20 configures
idle gaps in a UE 10 in s200. In s210, the radio base station 20
sends gap commands to the UE 10. The UE 10 is then configured for
specifying correct behavior when the gap commands are unreliable in
s220. S230 and s235 shows two steps which can be carried out
separately or in combination. In s230 the UE 10 is configured to be
able to report results or events pertaining to unreliable commands.
In s235 the radio base station 20 autonomously detects that the
transmitted gap commands are received unreliably. Based on this the
radio base station 20 in s240 performs actions to improve the
reliability of transmitted gap commands.
[0082] The following section deals with the reporting of events
concerning unreliable gap commands and discloses two possible
methods, an explicit method based on UE 10 reports and an implicit
method. Irrespective which method is used to specify UE behavior
when receiving unreliable gap commands, it is advantageous that UE
10 reports unreliable events to the network. This could be either:
[0083] The number of unreliable gap commands received over time
period T.sub.1 where T.sub.1 is a network configurable parameter;
[0084] An event indicating that at least N consecutive gap commands
are unreliable, where N is settable by the network; [0085] An event
indicating that at least M gap commands are unreliable during time
T.sub.2, where T.sub.2 and M are network configurable
parameters.
[0086] In response to an event reporting the network will take
appropriate radio resource management action, which may include,
e.g. increase of the transmit power level, congestion control to
reduce interference, or, in the worst case, a cell change, etc.
This information can also be used for operational and maintenance
purposes, i.e. for long term network planning to set correct
transmission power levels, cell size dimensioning, etc. One or more
of these actions could be performed by eNBs 20.
[0087] The event reporting described above explicitly notifies the
network about the unreliable reception of gap commands. However,
this requires some signaling overheads used for event reporting in
the uplink. In some cases network can itself infer that the gap
commands sent by UE 10 are unreliable, without any event reporting.
For instance, in the embodiment where a gap is fully skipped the
fact that the measurement reporting delay is longer than expected
could implicitly imply that the UE 10 has omitted some gaps due to
unreliable commands. The network can then take an appropriate radio
resource management action, e.g. increase transmitted power level,
etc. Similar arguments can be used for the embodiment where gaps
are partly skipped. In the embodiment where gaps are fully used,
the network can presume that the received gap commands are
unreliable if the network does not repeatedly receive any UE
response (e.g. ACK or NACK) during those gaps where the UE 10 is
scheduled.
[0088] The above described embodiments of the invention are
intended to be examples only. Alterations, modification, and
variations may be effected to particular embodiments by those
skilled in the art without departing from the scope of the
invention, which is defined by the accompanying claims.
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