U.S. patent application number 16/174749 was filed with the patent office on 2019-02-28 for wireless device and methods therein for an improved cell reselection procedure.
The applicant listed for this patent is Telefonaktiebolaget LM Ericsson (publ). Invention is credited to Ulf Handel, Olof Liberg, Marten Sundberg.
Application Number | 20190069209 16/174749 |
Document ID | / |
Family ID | 58503688 |
Filed Date | 2019-02-28 |
United States Patent
Application |
20190069209 |
Kind Code |
A1 |
Sundberg; Marten ; et
al. |
February 28, 2019 |
Wireless Device and Methods Therein for an Improved Cell
Reselection Procedure
Abstract
A wireless device and a method for providing an improved cell
reselection procedure. The wireless device is served in a serving
cell. At a first point in time, the wireless device determines a
first signal quality of a first signal received from the serving
cell. At a second point in time, it determines a second signal
quality of a second signal received from a neighbour cell. Based on
the determined first and second signal qualities, the wireless
device determines a first trigger condition for performing
measurements for cell reselection. At a third point in time, the
wireless device determines a third signal quality of a third signal
received from the serving cell. When a difference between the third
and first signal qualities has passed the trigger condition, the
wireless device performs at least one measurement for cell
reselection on at least one of the cells.
Inventors: |
Sundberg; Marten; ( rsta,
SE) ; Handel; Ulf; (Norsholm, SE) ; Liberg;
Olof; (Stockholm, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Telefonaktiebolaget LM Ericsson (publ) |
Stockholm |
|
SE |
|
|
Family ID: |
58503688 |
Appl. No.: |
16/174749 |
Filed: |
October 30, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15572533 |
Nov 8, 2017 |
10149222 |
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PCT/SE2017/050325 |
Mar 31, 2017 |
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16174749 |
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62326033 |
Apr 22, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 36/0094 20130101;
H04W 24/08 20130101; Y02D 70/142 20180101; H04W 36/30 20130101;
Y02D 70/1242 20180101; Y02D 70/146 20180101; Y02D 70/1226 20180101;
Y02D 70/1262 20180101; Y02D 70/21 20180101; H04W 52/0209 20130101;
Y02D 70/1224 20180101; Y02D 30/70 20200801 |
International
Class: |
H04W 36/30 20060101
H04W036/30; H04W 24/08 20060101 H04W024/08 |
Claims
1. A method performed by a wireless device for providing an
improved cell reselection procedure, wherein the wireless device is
served in a serving cell by a first Radio Network Node (RNN),
wherein the wireless device and the first RNN are operating in a
wireless communications network, and wherein the method comprises:
at a first point in time, determining a first parameter value
related to a first signal quality of a first signal received from
the serving cell; at a second point in time, determining a second
parameter value related to a second signal quality of a second
signal received from a neighbor cell; based on a difference between
the first parameter value and the second parameter value,
determining a first trigger condition for performing measurements
for cell reselection; at a third point in time, determining a third
parameter value related to a third signal quality of a third signal
received from the serving cell; and when a difference between the
third parameter value and the first parameter value has passed the
first trigger condition, performing one or more measurements for
cell reselection.
2. The method of claim 1, further comprising: based on a result of
the one or more measurements performed for cell reselection,
performing cell reselection to one out of one or more neighbor
cells.
3. The method of claim 1, wherein the second signal quality is a
second best signal quality after the first signal quality, and
wherein the second best signal quality is determined out of one or
more determined second signal qualities of one or more second
signals received from one or more neighbor cells.
4. The method of claim 1, wherein determining the first trigger
condition for performing measurements for cell reselection
comprises: determining the first trigger condition as one of: a
fraction of the difference between the first and second parameter
values; and a difference between the first and second parameter
values limited by a maximum or a minimum value.
5. The method of claim 1, wherein performing the one or more
measurements for cell reselection comprises: performing one or more
out of: a measurement of total signal strength, a measurement of
Signal-to-Interference-plus-Noise Ratio (SINR), and a measurement
of carrier signal strength.
6. The method of claim 5, further comprising: based on a result of
the one or more measurements performed for cell reselection,
performing cell reselection to one out of one or more neighbor
cells, wherein performing the cell reselection based on the result
comprises: performing the cell reselection to a neighbor cell
having the highest measured total signal strength, the highest
measured SINR, or the highest measured carrier signal strength, out
of the neighbor cells.
7. The method of claim 1, wherein each of the first parameter
value, the second parameter value and the third parameter value is
one of: a total signal strength, a
Signal-to-Interference-plus-Noise Ratio (SINR), and a carrier
signal strength.
8. The method of claim 1, wherein the first and second points in
time are equal or almost equal points in time.
9. The method of claim 1, wherein the third point in time is
different from the first and second points in time.
10. The method of claim 1, further comprising: based on a best
signal quality and a second best signal quality found when
performing the one or more measurements for cell reselection,
determining a second trigger condition for performing measurements
for cell reselection, wherein the second trigger condition is one
out of: same as the first trigger condition; and different from the
first trigger condition.
11. The method of claim 1, wherein the first and third signals are
the same signal transmitted on a broadcast channel at the first
point in time and the third point in time, respectively.
12. A wireless device configured to provide an improved cell
reselection procedure, wherein the wireless device is configured to
be served in a serving cell by a first Radio Network Node (RNN),
wherein the wireless device and the first RNN are configured to
operate in a wireless communications network, and wherein the
wireless device comprises: transceiver circuitry configured for
receiving signals from the serving cell and one or more neighbor
cells; and processing circuitry operatively associated with the
transceiver circuitry and configured to: at a first point in time,
determine a first parameter value related to a first signal quality
of a first signal received from the serving cell; at a second point
in time, determine a second parameter value related to a second
signal quality of a second signal received from a neighbor cell;
based on a difference between the first parameter value and the
second parameter value, determine a first trigger condition for
performing measurements for cell reselection; at a third point in
time, determine a third parameter value related to a third signal
quality of a third signal received from the serving cell; and
perform one or more measurements for cell reselection when a
difference between the third parameter value and the first
parameter value has passed the first trigger condition.
13. The wireless device of claim 12, wherein the processing
circuitry is configured to: perform cell reselection to one out of
one or more neighbor cells based on a result of the one or more
measurements performed for cell reselection.
14. The wireless device of claim 12, wherein the second signal
quality is a second best signal quality after the first signal
quality, and wherein the second best signal quality is determined
out of one or more determined second signal qualities of one or
more second signals received from one or more neighbor cells.
15. The wireless device of claim 12, wherein the processing
circuitry is configured to determine the first trigger condition
for performing measurements for cell reselection by: determining
the first trigger condition as one of: a fraction of the difference
between the first and second parameter values; and a difference
between the first and second parameter values limited by a maximum
or a minimum value.
16. The wireless device of claim 12, wherein the processing
circuitry is configured to perform the one or more measurements for
cell reselection by: performing one or more out of: a measurement
of total signal strength, a measurement of
Signal-to-Interference-plus-Noise Ratio (SINR), and a measurement
of carrier signal strength.
17. The wireless device of claim 16, wherein the processing
circuitry is configured to perform cell reselection based on a
result of the one or more measurements performed for cell
reselection by: performing the cell reselection to a neighbor cell
having the highest measured total signal strength, the highest
measured SINR, or the highest measured carrier signal strength, out
of the neighbor cells.
18. The wireless device of claim 12, wherein each of the first
parameter value, the second parameter value and the third parameter
value is one of: a total signal strength, a
Signal-to-Interference-plus-Noise Ratio (SINR), and a carrier
signal strength.
19. The wireless device of claim 12, wherein the first and second
points in time are equal or almost equal points in time.
20. The wireless device of claim 12, wherein the third point in
time is different from the first and second points in time.
21. The wireless device of claim 12, wherein the processing
circuitry is configured to: determine a second trigger condition
for performing measurements for cell reselection based on a best
signal quality and a second best signal quality found when
performing the one or more measurements for cell reselection,
wherein the second trigger condition is one out of: same as the
first trigger condition; and different from the first trigger
condition.
22. The wireless device of claim 12, wherein the first and third
signals are the same signal transmitted on a broadcast channel at
the first point in time and the third point in time,
respectively.
23. A method of operation by a wireless device configured for
operating in a wireless communication network in which a cell of
the wireless communication network is a serving cell with respect
to the wireless device, the method comprising: determining a first
signal quality value for the serving cell, based on signal-quality
measurements made with respect to the serving cell; determining a
second signal quality value for a neighboring cell of the serving
cell, based on signal-quality measurements made with respect to the
neighboring cell; determining a threshold value for triggering
cell-reselection measurements by the wireless device, in dependence
on a difference between the first and second quality values;
determining a third signal quality value for the serving cell,
based on subsequent signal-quality measurements made with respect
to the serving cell; and triggering cell-reselection measurements
responsive to a difference between the first and third signal
quality values exceeding the threshold value.
24. A method of operation by a wireless device configured for
operating in a wireless communication network in which a cell of
the wireless communication network is a serving cell with respect
to the wireless device, the method comprising: determining
respective signal quality metrics for the serving cell at first and
second points in time; and triggering cell-reselection measurements
by the wireless device in response to a difference between the
respective signal quality metrics for the serving cell exceeding a
threshold value; and determining the threshold value in dependence
on a difference between the signal quality metric determined for
the serving cell at the first point in time with a signal quality
metric determined for a neighboring cell of the serving cell.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 15/572,533 filed 8 Nov. 2017, which is a U.S. National Phase
Application of PCT/SE2017/050325 filed 31 Mar. 2017, which claims
benefit of U.S. Provisional Application No. 62/326,033 filed 22
Apr. 2016. The entire contents of each aforementioned application
is incorporated herein by reference.
TECHNICAL FIELD
[0002] Embodiments herein relate to a wireless device and methods
therein. Especially, embodiments herein relate to an improved cell
reselection procedure.
BACKGROUND
[0003] Communication devices such as terminals or wireless devices
are also known as e.g. User Equipments (UEs), mobile terminals,
wireless terminals and/or mobile stations. Such terminals are
enabled to communicate wirelessly in a wireless communication
system or a cellular communications network, sometimes also
referred to as a cellular radio system or cellular networks. The
communication may be performed e.g. between two terminals, between
a terminal and a regular telephone and/or between a terminal and a
server via a Radio Access Network (RAN) and possibly one or more
core networks, comprised within the cellular communications
network.
[0004] The above terminals or wireless devices may further be
referred to as mobile telephones, cellular telephones, laptops, or
tablets with wireless capability, just to mention some further
examples. The terminals or wireless devices in the present context
may be, for example, portable, pocket-storable, hand-held,
computer-comprised, or vehicle-mounted mobile devices, enabled to
communicate voice and/or data, via the RAN, with another entity,
such as another terminal or a server.
[0005] The cellular communications network covers a geographical
area which is divided into cell areas, wherein each cell area being
served by an access node such as a base station, e.g. a Radio Base
Station (RBS), which sometimes may be referred to as e.g. an "eNB",
an "eNodeB", a "NodeB", a "B node", or a Base Transceiver Station
(BTS), depending on the technology and terminology used. The base
stations may be of different classes such as e.g. macro eNodeB,
home eNodeB or pico base station, based on transmission power and
thereby also cell size. A cell is the geographical area where radio
coverage is provided by the base station at a base station site.
One base station, situated at the base station site, may serve one
or several cells. Further, each base station may support one or
several communication technologies. The base stations communicate
over the air interface operating on radio frequencies with the
terminals or wireless devices within range of the base stations. In
the context of this disclosure, the expression Downlink (DL) is
used for the transmission path from the base station to the mobile
station. The expression Uplink (UL) is used for the transmission
path in the opposite direction i.e. from the mobile station to the
base station.
[0006] In 3rd Generation Partnership Project (3GPP) Long Term
Evolution (LTE), base stations, which may be referred to as eNodeBs
or even eNBs, may be directly connected to one or more core
networks.
[0007] The 3GPP LTE radio access standard has been written in order
to support high bitrates and low latency both for uplink and
downlink traffic. All data transmission is in LTE controlled by the
radio base station.
[0008] In a wireless communications system, such as a cellular
network, a wireless device. e.g. a mobile station, is periodically
monitoring the surrounding radio environment, in order for the
mobile station to be connected to the most suitable cell. e.g. to
the most suitable radio base station serving the cell, or at least
to a suitable cell. The selection of the suitable cell may be based
on network decision or by autonomous mobile decision. It should be
understood that the expression "the mobile station is connected to
a cell" or similar is to be interpreted as the mobile station is
connected to a radio network node. e.g. a radio base station or a
similar device, that serves or provides radio coverage in a
geographical area referred to as the cell. Further, it should be
understood that sometimes herein reference is made to the cell and
the radio network node serving the cell interchangeably. Thus,
sometimes when a reference is made to the cell it should be
interpreted as a reference to the radio network node serving the
cell. However, it should be understood that several cells may be
served by the same radio network node.
[0009] The initial process to select a cell by searching possible
different alternatives is usually referred to as cell selection.
The process of periodically monitoring cells and, after an initial
cell selection, deciding to move to another cell based on the
information acquired through monitoring is usually referred to as a
cell reselection procedure.
[0010] For cell reselection the process typically involves
monitoring different signal strengths from different cells. e.g.
from different radio base stations or from different cells served
by the same radio base station, and ordering them in descending
order. That is, the stronger the signal strength from the cell is,
the more suitable is the cell to camp on. In case all cells being
monitored are weak in signal strength there is typically a minimum
allowed signal strength for a cell to be considered as a suitable
cell by the mobile station.
[0011] By the expression "camp on" when used in this disclosure is
meant that the mobile station is served by the radio network node
serving the cell the mobile station is camping on. Sometimes in
this disclosure, the cell the mobile station is camping on is
referred to as a serving cell. Further, sometimes herein the
expressions "cell camped on" and "serving cell" are used
interchangeably.
[0012] By frequently monitoring the surrounding radio environment
the mobile station may be ensured to be camping on the cell serving
the mobile station with the strongest signal strength, or at least
one of the stronger cells, given its current position. In case the
mobile station is moving around, the radio environment will change.
Hence, to be fully up to date on the surrounding radio environment,
the mobile station would have to frequently search for and monitor
neighboring cells and to monitor the serving cell, in order to
understand the changes over time. This procedure consumes energy,
and it will more quickly drain the battery, the more frequently
these search procedures are performed. That is a drawback for a
mobile station that is dependent on a battery for power.
[0013] Although there are mobile stations that benefit from
frequent cell-reselection procedures, there are other classes of
mobile stations that rather trade a longer battery lifetime for a
sub-optimum cell re-selection procedure. At the same time, it is
always of interest for any mobile station to be connected to the
best cell. e.g. to the cell having the highest signal strength, or
at least to a good cell, e.g. to a cell having a high signal
strength, to minimize interference levels in the communications
network, and hence minimize transmission and/or reception
times.
[0014] A possible change to the cell re-selection behavior is to
allow the mobile station to stay camped on a specific cell as long
as the cell is suitable, i.e. the minimum allowed signal strength
is fulfilled. In other words, as long as the minimum signal
strength is fulfilled, the mobile station would not search for
other cells to camp on. However, this would imply that a
significant degradation of signal strength of the camped cell would
be allowed while still not triggering cell re-selection. If this
occurs and better cells are available in the mobile station's
current location this would imply increased interference levels in
the communications network. Further, it would imply draining of
battery during activity by the mobile station since a reduced
experienced Signal-to-Interference-plus-Noise Ratio (SINR) would
imply a longer ON time for the mobile station both for transmission
and reception.
SUMMARY
[0015] According to developments of wireless communications
networks an improved cell reselection procedure is needed for
improving the performance of the wireless communications network in
terms of providing a sustainable balance between radio network
performance and device battery life.
[0016] Therefore, an object of embodiments herein is to overcome
the above-mentioned drawbacks among others and to improve the
performance in a wireless communications system. For example, an
object of embodiments herein is to provide an improved cell
reselection procedure.
[0017] According to a first aspect of embodiments herein, the
object is achieved by a method performed by a wireless device for
providing an improved cell reselection procedure. The wireless
device is served in a first cell, e.g. a serving cell, by a first
Radio Network Node (RNN). Further, the wireless device and the
first RNN are operating in a wireless communications network.
[0018] At a first point in time T1, the wireless device determines
a first signal quality of a first signal received from the serving
cell. Further, at a second point in time T2, e.g. a second point in
time T2 similar to the first point in time T1, the wireless device
determines a second signal quality of a second signal received from
a neighbour cell.
[0019] It should be understood that the first and second signal
qualities are determined at the same time or almost at the same
time, and thus they are determined at similar or corresponding
points in time. In other words, the first and second points in time
T1,T2 are equal or almost equal. Consequently, the first and second
points in time T1. T2 may be the same point in time.
[0020] Based on the determined first and second signal qualities,
the wireless device determines a trigger condition for performing
measurements for cell reselection.
[0021] At a third point in time T3, the wireless device determines
a third signal quality of a third signal received from the serving
cell.
[0022] Further, when a difference between the third signal quality
and the first signal quality has passed the trigger condition, the
wireless device performs one or more measurements for cell
reselection on one or more out of the serving cell and one or more
neighbour cells.
[0023] Furthermore, the wireless device may perform cell
reselection based on a result of the performed measurement for cell
reselection.
[0024] According to a second aspect of embodiments herein, the
object is achieved by a wireless device for providing an improved
cell reselection procedure. The wireless device is configured to be
served in a first cell, e.g. a serving cell, by a first Radio
Network Node (RNN). Further, the wireless device and the first RNN
are configured to operate in a wireless communications network.
[0025] The wireless device is configured to determine a first
signal quality of a first signal received from the serving cell at
a first point in time T1. Further, the wireless device is
configured to determine a second signal quality of a second signal
received from a neighbour cell at a second point in time T2, e.g. a
second point in time T2 similar to the first point in time T1.
[0026] Further, the wireless device is configured to determine a
trigger condition for performing measurements for cell reselection
based on the determined first and second signal qualities.
[0027] Furthermore, the wireless device is configured to determine
a third signal quality of a third signal received from the serving
cell at a third point in time.
[0028] Yet further, the wireless device is configured to perform
one or more measurements for cell reselection when a difference
between the third signal quality and the first signal quality has
passed the trigger condition.
[0029] The wireless device may be configured to perform cell
reselection based on a result of the performed measurement for cell
reselection on one or more out of the serving cell and one or more
neighbour cells.
[0030] According to a third aspect of embodiments herein, the
object is achieved by a computer program, comprising instructions
which, when executed on at least one processor, causes the at least
one processor to carry out the method performed by the wireless
device.
[0031] According to a fourth aspect of embodiments herein, the
object is achieved by a carrier comprising the computer program,
wherein the carrier is one of an electronic signal, an optical
signal, a radio signal or a computer readable storage medium.
Since the wireless device performs one or more measurements for
cell reselection when the difference between the third signal
quality and the first signal quality has passed the determined
trigger condition, and since the wireless device performs cell
reselection based on a result of the performed measurement for cell
reselection, the cell reselection procedure is improved. This
results in an improved performance in the wireless communications
system.
[0032] An advantage with embodiments herein is that they enable the
wireless device to be camped more frequently on the most suitable
cell. e.g. the most suitable serving cell, than what is currently
specified, while at the same time allowing for a substantial
reduction in power consumption compared to the behaviour of legacy
wireless devices for which measurements for cell reselection is
triggered much more frequently.
[0033] A further advantage with embodiments herein is that by
having the wireless device to camp on a suitable cell with limited
need to perform neighbour cell measurements, the battery power of
the wireless device will be saved since less power is needed to
reach a serving radio network node, e.g. base station.
[0034] A further advantage with embodiments herein is that a
reduced energy consumption is provided when the receiver and
transmitter ON time is reduced. In the interest of battery
conservation, a wireless device that is battery operated may search
for and monitor neighbour cells on a limited basis as long as the
current serving cell remains suitable.
[0035] The points in time where such a wireless device chooses to
re-evaluate the suitability of its current serving cell may also
serve as opportunities to determine if that serving cell is
deteriorating to an excessive degree. If such a determination is
made then the wireless device may begin searching for and
monitoring neighbour cells and then perform cell reselection if a
better cell is found.
[0036] Therefore, some embodiments herein identify a new
reselection trigger condition that may help to reduce interference
levels in the wireless network by lowering the wireless device's
transmit time and to conserve the wireless device's battery by
reducing the amount of energy consumed per transmission and/or
reception event by reducing the wireless communications device's on
time.
[0037] By the expression "transmit time" when used in this
disclosure is meant a period of time during which the wireless
device transmits information. Further, by the expression "ON time"
when used in this disclosure is meant a period of time during which
the wireless device receives and/or transmits information. The on
time may sometimes be referred to as an active time. The additional
energy consumed by the wireless device performing the additional
processing required to evaluate serving cell deterioration is seen
as being substantially less than the energy saved by reducing
wireless device transmit "on time".
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] Examples of embodiments herein will be described in more
detail with reference to attached drawings in which:
[0039] FIG. 1 is a schematic block diagram schematically
illustrating cell reselection in a wireless communications system
according to prior art;
[0040] FIG. 2 schematically illustrates embodiments of a wireless
communications system;
[0041] FIG. 3 is a combined flowchart and signalling scheme
schematically illustrating embodiments of a method performed in a
wireless communications network.
[0042] FIG. 4 is a flowchart depicting embodiments of a method
performed by a wireless device:
[0043] FIG. 5 is a schematic block diagram illustrating embodiments
of a wireless device; and
[0044] FIG. 6 is a schematic block diagram schematically
illustrating cell reselection according to some embodiments.
DETAILED DESCRIPTION
[0045] As part of developing embodiments herein, some problems with
the state of the art communications networks will first be
identified and discussed.
[0046] In Extended GSM Coverage for Internet-of-Things (EC-GSM-IoT)
feature, the current assumption is that a wireless device when
determining if it has to perform measurements for cell reselection
only triggers this under certain conditions. This is done in order
to save battery in the wireless device. One important condition is
that the signal strength of the cell the wireless device is camped
on has not changed more than a certain threshold, see for example
the 3GPP TS 45.008 v 13.1.0 subclause 6.6.1a.
[0047] For example, in a first scenario, assume that a wireless
device is camping on the strongest measured cell, and that the
strongest neighbour cell is 3 dB weaker in signal strength. In a
second scenario assume that the wireless device is camping on the
strongest measured cell, and that the strongest neighbour cell is
20 dB weaker in signal strength. In these two scenarios,
measurements for cell reselection should be triggered faster in the
first scenario if a change in the camped cell's signal strength is
detected, since this will indicate that the earlier measured
neighbour cell might have become stronger, and might be the more
suitable cell to camp on. With the current specification. e.g. the
3GPP TS 45.008 v.13.1.0, this is however not the case, and
measurements for cell reselection is instead triggered based on a
fixed relative change in measured signal strength of the camped
cell, irrespective of the neighbouring radio environment.
[0048] A problem with this approach is that the wireless device
will not adopt its cell reselection behaviour depending on the
surrounding radio environment.
[0049] FIG. 1 is a schematic block diagram schematically
illustrating cell reselection in a wireless communications system
according to prior art.
[0050] A Mobile Station (MS) first performs measurements at point 1
in time. The result is that a cell A is the strongest cell and
hence the MS camps on that cell. A difference in signal strength
between two measurements .DELTA.SS that triggers a cell reselection
is or has been broadcasted to the MS.
[0051] Next, the MS wakes up at point 2 in location and time. It
tries to confirm that the previously camped cell. e.g. the cell A,
is still strong enough comparing to the strongest signal measured
of the camped on cell, here the same as the one measured at point 1
in time. The Cell A is confirmed to be suitable since the signal
strength change relative the measurement at point 1 is lower than
the broadcasted threshold, e.g. the broadcasted .DELTA.SS.
Therefore, the MS continues to camp on cell A.
[0052] The MS wakes up at point 3 in time. It tries to confirm that
the previously camped cell, e.g. the cell A, is still strong
enough, but fails to confirm this since the change in signal
strength relative to point 1 is higher, i.e. larger, than the
broadcasted threshold, e.g. the broadcasted .DELTA.SS. Measurements
for cell reselection are triggered. It is found that cell C is the
strongest cell and hence the MS camps on that cell. The same
broadcasted threshold value, e.g. the broadcasted .DELTA.SS, is
used again as further trigger of measurements for further cell
reselection.
[0053] It should be noted that the MS moves through cell B without
ever selecting it, and this is despite the fact that cell B as
illustrated in FIG. 1 would provide better signal strength than
cell A.
[0054] An object addressed by embodiments herein is therefore how
to provide an improved performance in a wireless communications
system or a wireless communications network.
[0055] In order to overcome the above-mentioned drawbacks, some
embodiments herein provides for an improved cell reselection
procedure wherein a wireless device determines a first signal
quality of a serving cell and determines a second signal quality of
one or more neighbour cells, e.g. a strongest neighbour cell.
Further, the wireless device determines a trigger condition for
performing measurements for cell reselection based on the
determined first and second signal qualities. Furthermore, the
wireless device performs one or more measurements for cell
reselection when a difference between a third signal quality and
the first signal quality has passed the determined trigger
condition. Yet further, the wireless device performs cell
reselection based on a result of the performed measurement for cell
reselection.
[0056] Some embodiments herein provide a balance between reduced
requirements on monitoring and performing measurements for cell
reselection to facilitate long device battery life and the
requirements on selecting the most suitable cell at all times.
TERMINOLOGY
[0057] The following terminology is used in embodiments described
herein and is elaborated below:
[0058] Network Node:
[0059] In some embodiments a more general term "network node" is
used and it may correspond to any type of radio network node or any
network node, which communicates with a UE and/or with another
network node. Examples of network nodes are NodeB, MeNB, SeNB, a
network node belonging to a Master Cell Group (MCG) or a Secondary
Cell Group (SCG), Base Station (BS), Multi-Standard Radio (MSR)
radio node such as MSR BS, eNodeB, network controller, Radio
Network Controller (RNC), Base Station Controller (BSC), relay,
donor node controlling relay, Base Transceiver Station (BTS),
Access Point (AP), transmission points, transmission nodes, Remote
Radio Unit (RRU), Remote Radio Head (RRH), nodes in Distributed
Antenna System (DAS), core network node (e.g. Mobile Switching
Center (MSC). Mobility Management Entity (MME) etc.), Operations
and Maintenance (O&M), Operations Support System (OSS),
Self-organizing Network (SON), positioning node (e.g. Enhanced
Serving Mobile Location Center (E-SMLC)). Mobile Data Terminal
(MDT) etc.
[0060] User Equipment/Wireless Device:
[0061] In some embodiments the non-limiting terms wireless device.
Mobile Station (MS) and User Equipment (UE) are used and they refer
to any type of wireless device communicating with a network node
and/or with another UE in a cellular or mobile communication
system. Examples of UE/wireless device are Device-to-Device (D2D)
UE, machine type UE or UE capable of Machine to Machine (M2M)
communication, Personal Digital Assistant (PDA), Tablet, mobile
terminals, smart phone. Laptop Embedded Equipped (LEE). Laptop
Mounted Equipment (LME). Universal Serial Bus (USB) dongles etc. In
this disclosure the terms wireless device and UE are used
interchangeably.
[0062] General
[0063] Note that although terminology from Global System for Mobile
Communications (GSM)/GSM EDGE Radio Access Network (GERAN) has been
used in this disclosure to exemplify embodiments, this should not
be seen as limiting the scope of embodiments herein to only the
aforementioned system. Other wireless systems, including Wideband
Code Division Multiple Access (WCDMA), High Speed Packet Access
(HSPA). Worldwide Interoperability for Microwave Access (WiMax).
WiFi. Wireless Local Area Network (WLAN), and 3GPP LTE, may also
benefit from exploiting the ideas covered within this
disclosure.
[0064] Also note that terminology such as eNodeB and UE should be
considering non-limiting and does in particular not imply a certain
hierarchical relation between the two; in general "eNodeB" could be
considered as device 1 and "UE" device 2, and these two devices
communicate with each other over some radio channel.
[0065] Further, the description frequently refers to wireless
transmissions in the downlink, but embodiments herein are equally
applicable in the uplink.
[0066] In the following section, embodiments herein will be
illustrated in more detail by a number of exemplary embodiments. It
should be noted that these embodiments are not mutually exclusive.
Components from one embodiment may be assumed to be present in
another embodiment and it will be obvious to a person skilled in
the art how those components may be used in the other exemplary
embodiments.
[0067] FIG. 2 depicts an example of the wireless communications
system 200 in which embodiments herein may be implemented. The
wireless communications system 200 is a wireless communication
system such as a GERAN system, an LTE system, a WCDMA system, a GSM
system, any 3GPP cellular system, WiMAX system, or any wireless or
cellular network/system.
[0068] A core network 202 is comprised in the wireless
communications system 200. The core network 202 is a wireless core
network such as a GERAN core network, an LTE core network. e.g. a
Evolved Packet Core (EPC); a WCDMA core network: a GSM core
network; any 3GPP core network; WiMAX core network; or any wireless
or cellular core network.
[0069] A core network node 204 is comprised in the core network
202. The core network node 204 may be an MSC, an MME, an O&M
node, a Serving GateWay (S-GW), a Serving General Packet Radio
Service (GPRS) Node (SGSN), etc.
[0070] A wireless communications network 206 is comprised in the
wireless communications system 200. The wireless communications
network 206 is a wireless communications network such as a GERAN
network, an LTE communications network, e.g. an Evolved UMTS
Terrestrial Radio Access Network (E-UTRAN); a WCDMA communications
network: a GSM communications network; any 3GPP communications
network; WiMAX communications network; or any wireless or cellular
communications network.
[0071] It should be understood that in some embodiments the core
network 202 and the wireless communications network 206 are
combined into one single network or that the wireless
communications network 206 may comprise the core network 202.
[0072] A first Radio Network Node (RNN) 210 serving a first
geographical area. e.g. a first cell 212 such as a first serving
cell, a second RNN 220 serving a second geographical area, e.g. a
second cell 222 such as a second serving cell, and/or a third RNN
230 serving a third geographical area, e.g. a third cell 232 such
as a third serving cell, may be operating in the wireless
communications system 200. It should be understood that more than
one RNN may be operating in the wireless communications system 200
and that one RNN may be configured to serve several geographical
areas, e.g. cells. For example, as schematically illustrated in
FIG. 2, the first RNN 210 may be configured to serve two first
cells, e.g. a first first cell 212-1 and a second first cell 212-2.
In this disclosure, the first first cell 212-1 is sometimes
referred to as the serving cell 212-1. Further, in this disclosure,
the second first cell 212-2, the second cell 222 and the third cell
232 are sometimes referred to as neighbouring cell 212-2, 222,
232.
[0073] As previously mentioned, the first RNN 210 is configured to
operate in the wireless communications system 200. The second RNN
220 is configured to operate in the wireless communications system
200. Further, the third RNN 230 may be configured to operate in the
wireless communications system 200. The RNNs 210, 220, 230 may each
be a radio access node such as a radio base station, for example an
eNB, an eNodeB, or a Home Node B, a Home eNode B or any other
network node capable to serve a user equipment or a machine type
communication device in a wireless communications network.
[0074] The RNNs 210, 220, 230 may each be configured for wireless
communication with one or more wireless devices, such as the
wireless device 240, when the wireless device is located within the
geographical areas, e.g. the cells 212, 222, 232 served by the
respective RNN 210, 220, 230. Herein, this is also specified as the
respective RNN 210,220,230 manages or is configured to manage
communication with one or more wireless devices in the respective
geographical area. In this disclosure, the respective geographical
area is sometimes referred to as a respective coverage area,
cluster or cell. Further, when the wireless device is located
within the geographical area and served by the RNN serving the
geographical area, that geographical area may be referred to as a
serving geographical area, e.g. a serving cell. Thus, when the
wireless device 240 is located within the first geographical area
and is served by the first RNN 210, the first geographical area is
sometimes herein referred to as the serving cell.
[0075] A wireless device 240 is operating in the wireless
communications system 200. The wireless device 240 also referred to
as a user equipment or UE is located in the wireless communications
system 200. The wireless device 240 may e.g. be a user equipment, a
mobile terminal or a wireless terminal, a mobile phone, a computer
such as e.g. a laptop, a Personal Digital Assistants (PDAs) or a
tablet computer, with wireless capability, or any other radio
network units capable to communicate over a radio link in a
wireless communications network. It should be noted that the term
user equipment used in this document also covers other wireless
devices such as Machine to Machine (M2M) devices, even though they
are not handled by any user.
[0076] As schematically illustrated in FIG. 2, the wireless device
240 may be moving with a velocity v in a direction indicated by the
dotted arrow.
[0077] FIG. 3 is a combined flowchart and signalling scheme
schematically illustrating embodiments of a method performed in a
wireless communications network, such as the wireless
communications network 206. The methods comprise one or more of the
following actions. It should be understood that these actions may
be taken in any suitable order and that some actions may be
combined.
[0078] Action 301
[0079] A first signal is transmitted from a serving cell 212-1 to
the wireless device 240. The serving cell 212-1 is served by a
serving RNN, e.g. the first RNN 210. The first signal may be a GSM
signal transmitted over an GSM air interface. However, the first
signal may also be an NB-IoT signal, an LTE-M signal, or an LTE
signal. LTE-M is the LTE feature and/or radio interface for machine
to machine communication. Further, the first signal may be a
broadcast signal, such as a signal transmitted on a broadcast
channel. e.g. on a Broadcast Control Channel (BCCH) or on an
Extended Coverage BCCH (EC-BCCH).
[0080] Action 302
[0081] At a first point in time T1, the wireless device 240
determines a first signal quality of the serving cell 212-1. For
example, the wireless device 240 determines the first signal
quality based on the first signal transmitted from the serving cell
212-1, as described in Action 301, and received by the wireless
device 240. The signal quality may be a total signal strength, a
Signal-to-Interference-plus-Noise Ratio (SINR), or carrier signal
strength just to give some examples. For example, the wireless
device 240 may determine the signal quality by measuring the energy
in the total received signal.
[0082] The total signal strength may sometimes herein be referred
to as useful signal strength or wanted signal strength and it may
exclude noise and interference.
[0083] Action 303
[0084] A second signal is transmitted from a neighbouring cell
212-2, 222, 232 to the wireless device 240. The neighbouring cell
212-2, 222, 232 may be served by the first RNN 210, or by a
neighbouring RNN, e.g. the second RNN 220 or the third RNN 230.
[0085] Further, one or more further second signals may be
transmitted from one or more further neighbouring cells. The one or
more neighbouring cells may be served by the first RNN 210, or by
one or more neighbouring RNNs. e.g. the second RNN 220 or the third
RNN 230.
[0086] It should be understood that the second signal transmitted
from one of the neighbouring cell 212-2, 222, 232 may be different
from another second signal transmitted from another neighbouring
cell 212-2, 222, 232. Thus, two second signals transmitted from two
different neighbouring cell 212-2, 222, 232 may be two distinct and
different second signals.
[0087] The one or more second signals may be GSM signals
transmitted over an GSM air interface. However, the one or more
second signals may also be an NB-IoT signal, an LTE-M signal, or an
LTE signal. Further, the second signal may be a broadcast signal,
such as a signal transmitted on the broadcast channel e.g. on the
BCCH or on the EC-BCCH.
[0088] Action 304
[0089] At a second point in time T2, the wireless device 240
determines one or more second signal qualities of the one or more
neighbouring cells 212-2, 222, 232. For example, the wireless
device 240 determines the one or more second signal qualities based
on one or more second signals transmitted from the one or more
neighbouring cells 212-2, 222, 232 and received by the wireless
device 240. The neighbouring cells may be ranked in strength and
the second signal quality may be signal quality of the strongest
neighbour cell. As mentioned above, the signal quality may be a
signal strength, a SINR, or carrier signal strength just to give
some examples.
[0090] For example, the wireless device 240 may determine the
signal quality by measuring the energy in the total received
signal. Further, as previously mentioned, it should be understood
that the first and second signal qualities are determined at the
same time or almost at the same time, and thus they are determined
at similar or corresponding points in time. In other words, the
first and second points in time T1,T2 are equal or almost equal.
Consequently, the first and second points in time may be the same
point in time or almost the same point in time. e.g. T1=T2 or
T1.apprxeq.T2. Further, it should be understood that the first
point in time may precede the second point in time, or that the
second point in time may precede the first point in time.
[0091] Sometimes in this disclosure the first and second points in
time T1, T2 are referred to as a first point in time TA.
[0092] Action 305
[0093] The wireless device 240 determines a trigger condition for
performing measurements for cell reselection. The determination may
be based on the determined first and second signal qualities. For
example, the trigger condition may be a difference .DELTA.SS
between the first and second signal qualities, a fraction of the
difference .DELTA.SS between the first and second signal qualities,
or a difference .DELTA.SS between the first and second signal
qualities limited by a maximum and/or minimum value.
[0094] Action 306
[0095] At a third point in time T3, the wireless device 240
determines a third signal quality of the serving cell 212-1. For
example, the wireless device 240 determines the third signal
quality based on a third signal transmitted from the serving cell
212-1 and received by the wireless device 240. The third signal may
be a GSM signal transmitted over an GSM air interface. However, the
third signal may also be a an NB-IoT signal, an LTE-M signal, or an
LTE signal. Further, the third signal may be a broadcast signal,
such as a signal transmitted on the BCCH or the EC-BCCH.
[0096] As previously mentioned, the first signal may be transmitted
by the serving cell 212-1 on a broadcast channel. Thus, it should
be understood that the first and third signals transmitted by the
serving cell 212-1 may be the same signal transmitted on the
broadcast channel at two different points in time. e.g. the first
point in time and the third point in time, respectively.
[0097] The third point in time T3 is different from the first and
second points in time, e.g. T3>T1,T2. For example, the third
point in time T3 may correspond to the time it takes for the
wireless device 240 to travel from a first point A to a second
point B.
[0098] Sometimes in this disclosure the third point in time T3 are
referred to as a second point in time TB.
[0099] Action 307
[0100] The wireless device 240 performs one or more measurements
for cell reselection when the third signal quality has passed the
trigger condition. In other words, the wireless device 240 performs
the one or more measurements for cell reselection on one or more
neighbouring cells 212-2, 222, 232 when the trigger condition is
met. For example, when the third signal quality has the trigger
condition, e.g. when a difference .DELTA.SS in signal level between
the third signal quality and the first signal quality has passed
the trigger condition, the wireless device 240 may perform one or
more of: a measurement of total signal strength, a measurement of
SINR, or measurements of carrier signal strength. The measurement
may be performed on one or more neighbour cells 212-2, 222,
232.
[0101] Action 308
[0102] Based on the result of the performed measurements for cell
reselection, the wireless device 240 may perform or performs cell
reselection to the cell providing the best signal quality. For
example, based on the result of performed measurement of total
signal strength, SINR, or carrier signal strength, the wireless
device 240 may perform cell reselection to a most suitable cell.
e.g. to a cell having the best total signal strength, the best
SINR, or the best carrier signal strength.
[0103] An example of a method performed by the wireless device 240
for providing an improved cell reselection procedure will now be
described with reference to a flowchart depicted in FIG. 4. As
mentioned above, the wireless device 240 is served, in a first cell
212, e.g. the serving cell 212-1, by the first RNN 210, and the
wireless device 240 and the first RNN 210 are operating in the
wireless communications network 200.
[0104] The methods comprise one or more of the following actions.
It should be understood that these actions may be taken in any
suitable order and that some actions may be combined.
[0105] Action 401
[0106] At a first point in time T1, the wireless device 240
determines a first signal quality of the serving cell 212-1. As
previously mentioned, the wireless device 240 may determine the
first signal quality based on the first signal transmitted from the
serving cell 212-1 and received by the wireless device 240. This is
done in order to determine the signal quality of the serving cell
212-1.
[0107] As previously mentioned, the first signal quality may be a
total signal strength, a SINR or a carrier signal strength. The
total signal strength may sometimes herein be referred to as useful
signal strength or wanted signal strength and it may exclude noise
and interference. This relates to Action 302 previously
described.
[0108] Action 402
[0109] In order to be able to compare the first signal quality of
the serving cell 212-1 with a signal quality of a neighbour cell
212-2, 222, 232, the wireless device 240 may determine the signal
quality of the neighbour cell 212-2, 222, 232. Thus, at a second
point in time T2, e.g. at a point in time similar to the first
point in time T1, the wireless device 240 determines a second
signal quality of a neighbour cell 212-2, 222, 232. In some
embodiments, the wireless device 240 determines one or more second
signal qualities of one or more neighbouring cells 212-2, 222, 232.
As previously mentioned, the wireless device 240 may determine the
one or more signal qualities based on one or more second signals
transmitted from the one or more neighbouring cells 212-2, 222, 232
and received by the wireless device 240.
[0110] In some embodiments, the second signal quality is a second
best signal quality after the first signal quality. Further, the
second best signal quality may be determined out of the one or more
determined second signal qualities of one or more second signals
received from one or more neighbour cells 212-2, 222, 232.
[0111] In some embodiments, the second signal quality is determined
in order to be able to relate the first signal quality of the
serving cell 212-1 to the second best cell, e.g. to the best
neighbouring cell 212-2, 222, 232, having the second signal
quality.
[0112] The second signal quality may be a total signal strength, a
SINR or a carrier signal strength.
[0113] As also previously mentioned the second point in time T2 is
equal to or almost equal to the first point in time T1.
[0114] This relates to Action 304 previously described.
Action 403
[0115] Based on the determined first and second signal qualities,
the wireless device 240 determines a trigger condition for
performing one or more measurements for cell reselection. For
example, this may be done in order to be able to trigger one or
more measurements for cell reselection when the signal quality of
the serving cell 212-1 deteriorates over time in relation to the
signal quality of a strongest neighbour cell.
[0116] In some embodiments, the wireless device 240 determines the
first trigger condition as a difference .DELTA.SS between the first
and second signal qualities, as a fraction of the difference
.DELTA.SS between the first and second signal qualities, or as a
difference .DELTA.SS between the first and second signal qualities
limited by a maximum or a minimum value.
[0117] This relates to Action 305 previously described. Further,
examples will be described in more detail below.
[0118] Action 404
[0119] At a third point in time T3, the wireless device 240
determines a third signal quality of the serving cell 212-1. This
is done in order to determine whether or not the signal quality of
the serving cell 212-1 has changed during the period of time since
the determination of the first signal quality at the first point in
time T1. For example, this may be the case when the wireless device
240 has been moving between the first point in time T1 and the
third point in time T3.
[0120] As previously mentioned, the wireless device 240 may
determine the third signal quality based on the third signal
transmitted from the serving cell 212-1 and received by the
wireless device 240.
[0121] The third signal quality may be a total signal strength, a
SINR or a carrier signal strength.
[0122] The third point in time T13 may be different from the first
and second points in time T1, T2.
[0123] This relates to Action 306 previously described.
[0124] Action 405
[0125] The wireless device 240 performs one or more measurements
for cell reselection when a difference between the third signal
quality and the first signal quality has passed the trigger
condition. This is done in order to determine the signal quality of
one or more neighbouring cells 212-2, 222, 232, when the signal
quality of the serving cell 212-1 has been deteriorated.
Especially, this is done when the difference between the third and
first signal qualities of the serving cell 212-1 has exceeded a
trigger condition.
[0126] In some embodiments, the wireless device 240 performs the
one or more measurements for cell reselection as one or more out
of: a measurement of total signals strength, a measurement of SINR,
or a measurement of carrier signal strength.
[0127] This relates to Action 307 previously described.
[0128] Action 406
[0129] The wireless device 240 performs cell reselection based on a
result of the performed one or more measurements for cell
reselection.
[0130] This relates to Action 308 previously described. As
described in Action 308, based on the result of the performed
measurements for cell reselection, the wireless device 240 performs
cell reselection to the cell, e.g. one of the neighbouring cell
212-2, 222, 232 providing the best signal quality. For example,
based on the result of performed measurement of total signal
strength, SINR, or carrier signal strength, the wireless device 240
may perform cell reselection to a most suitable cell, e.g. to a
cell having the best total signal strength, the best SINR, or the
best carrier signal strength.
[0131] Further, based on a best signal quality and a second best
signal quality found when performing the one or more measurements
for cell reselection, the wireless device 240 may determine a
second trigger condition for performing measurements for cell
reselection. This may for example be the case when the wireless
device 240 has performed a cell reselection to the cell having the
best signal quality and thus a new trigger condition should be
determined. The second trigger condition may be the same as the
first trigger condition or it may be different from the first
trigger condition. One or more of the actions described above, may
then be repeated in order to determine signal qualities at
subsequent points in time and to perform one or measurements for
cell reselection when a difference between the signal qualities
from the serving cell has passed a trigger condition such as when
the difference exceeds a threshold value. This will be described in
more detail below with reference to the example of FIG. 6.
[0132] To perform the method for the improved cell reselection
procedure, the wireless device 240 may be configured according to
an arrangement depicted in FIG. 5. As previously described, the
wireless device 240 is served, in the first cell 212, by the first
RNN 210, and the wireless device 230 and the first RNN 210 are
configured to operate in the wireless communications network
200.
[0133] In some embodiments, the wireless device 230 comprises an
input and/or output interface 500 configured to communicate with
one or more wireless devices, one or more radio network nodes, e.g.
the RNN 210, 220, 230, and one or more other network nodes, e.g.
the core network node 204. The input and/or output interface 500
may comprise a wireless receiver (not shown) and a wireless
transmitter (not shown).
[0134] The wireless device 240 is configured to receive, by means
of a receiving module 501 configured to receive, a transmission,
e.g. a signal or information, from a RNN, e.g. from the first,
second and/or third RNN 210, 220, 230. The receiving module 501 may
be implemented by or arranged in communication with a processor 507
of the wireless device 240. The processor 507 will be described in
more detail below.
[0135] The wireless device 240 is configured to receive one or more
signals from one or more cells served by one or more RNNs. For
example, the wireless device 204 may receive a first signal
transmitted from a serving cell 212-1. The serving cell 212-1 is
served by a serving RNN, e.g. the first RNN 210.
[0136] Further, the wireless device 240 may receive a second signal
transmitted from a neighbouring cell 212-2, 222, 232. The
neighbouring cell 212-2, 222, 232 may be served by the first RNN
210, or by a neighbouring RNN. e.g. the second RNN 220 or the third
RNN 230. It should be understood that the neighbouring cell 212-2,
222, 232 is the second first cell 212-2 when served by the first
RNN 210, the second cell 222 when served by the second RNN 220, and
the third cell 232 when served by the third RNN 230.
[0137] Furthermore, it should be understood that the wireless
device 240 may receive one or more second signals transmitted from
one or more neighbouring cells. The one or more neighbouring cells
may be served by the first RNN 210, or by one or more neighbouring
RNNs. e.g. the second RNN 220 or the third RNN 230.
[0138] Yet further, the wireless device 240 may receive a third
signal transmitted from a serving cell 212-1 at a third point in
time.
[0139] It should be understood that the third signal may be the
same signal as the first signal but transmitted at a different
point in time, e.g. at the third point in time.
[0140] The wireless device 240 is configured to transmit, by means
of a transmitting module 502 configured to transmit, a
transmission, e.g. a signal or information, to the RNN, e.g. the
first, second, or third RNN 210, 220, 230. The transmitting module
502 may be implemented by or arranged in communication with the
processor 507 of the wireless device 240.
[0141] For example, the wireless device 240 may be configured to
transmit a request for cell reselection to the RNN, e.g. the first,
second, or third RNN 210,220,230.
[0142] However, in for example the EC-GSM-IoT, the cell reselection
is an autonomous cell reselection wherein the wireless device 240
decides by itself without telling the communications system or the
communications network, e.g. the communications system 200 or the
communications network 206, which cell to camp on.
[0143] The wireless device 240 is configured to determine, by means
of a determining module 503 configured to determine, a signal
quality. The determining module 503 may be implemented by or
arranged in communication with the processor 507 of the wireless
device 240.
[0144] As previously mentioned, the wireless device 140 is
configured to determine a first signal quality of the serving cell,
one or more second signal qualities of one or more neighbouring
cells, and a third signal quality of the serving cell. The signal
quality may be a signal strength, a SINR, or carrier signal
strength just to give some examples. For example, the wireless
device 240 may be configured to determine the signal quality by
measuring the energy in the total received signal.
[0145] Further, the wireless device 240 is configured to determine
a trigger condition based on determined first and second signal
qualities.
[0146] The wireless device 240 may further be configured to
perform, by means of a performing module 504 configured to perform,
one or more measurements and cell reselection. The performing
module 504 may be implemented by or arranged in communication with
the processor 506 of the wireless device 240.
[0147] The wireless device 240 may be configured to perform one or
more measurements for cell reselection. For example, this may be
done when the third signal quality of the serving cell 212-1 has
passed the trigger condition or based on the first and/or the one
or more second signal qualities. For example, the wireless device
240 may be configured to perform one or more of: a measurement of
total signal strength, a measurement of SINR, or a measurements of
carrier signal strength.
[0148] Further, the wireless device 240 may be configured to
perform a cell reselection from the serving cell to a neighbouring
cell based on a result of the performed measurement for cell
reselection.
[0149] In some embodiments, the wireless device 240 is configured
to perform, by means of one or more other modules 505 configured to
perform one or more further actions described herein. The one or
more other modules 505 may be implemented by or arranged in
communication with the processor 507 of the wireless device
240.
[0150] The wireless device 240 may also comprise means for storing
data. In some embodiments, the wireless device 240 comprises a
memory 506 configured to store the data. The data may be processed
or non-processed data and/or information relating thereto. The
memory 506 may comprise one or more memory units. Further, the
memory 506 may be a computer data storage or a semiconductor memory
such as a computer memory, a read-only memory, a volatile memory or
a non-volatile memory. The memory is arranged to be used to store
obtained information, data, configurations, and applications etc.
to perform the methods herein when being executed in the wireless
device 240.
[0151] Embodiments herein for improving the cell reselection
procedure may be implemented through one or more processors, such
as the processor 507 in the arrangement depicted in FIG. 5,
together with computer program code for performing the functions
and/or method actions of embodiments herein. The program code
mentioned above may also be provided as a computer program product,
for instance in the form of a data carrier carrying computer
program code for performing the embodiments herein when being
loaded into the wireless device 240. One such carrier may be in the
form of an electronic signal, an optical signal, a radio signal or
a computer readable storage medium. The computer readable storage
medium may be a CD ROM disc or a memory stick.
[0152] The computer program code may furthermore be provided as
program code stored on a server and downloaded to the wireless
device 240.
[0153] Those skilled in the art will also appreciate that the
input/output interface 500, the receiving module 501, the
transmitting module 502, the determining module 503, the performing
module 504, and the one or more other modules 505 above may refer
to a combination of analogue and digital circuits, and/or one or
more processors configured with software and/or firmware, e.g.
stored in the memory 506, that when executed by the one or more
processors such as the processors in the wireless device 240
perform as described above. One or more of these processors, as
well as the other digital hardware, may be included in a single
Application-Specific Integrated Circuitry (ASIC), or several
processors and various digital hardware may be distributed among
several separate components, whether individually packaged or
assembled into a System-on-a-Chip (SoC).
Some Exemplifying Embodiments
[0154] Below some exemplifying embodiments will be described. It
should be understood that one or more features or actions from one
embodiments may be combined with one or more features or actions
from one or more other embodiments. In the exemplifying embodiments
below, references is made to signal strength. However, it should be
understood that signal strength is just an example and that the
examples given below are equally applicable to other signal
qualities such as a SINR and carrier signal strength just to give
two examples.
[0155] In some first embodiments, measurements for cell reselection
performed by the wireless device 240 is triggered based on the
first signal quality such as the signal strength of the camped on
cell, e.g. the serving cell 212-1, and based on the second signal
quality such as the measured signal strength of one or more
neighbour cells 212-2, 222, 232, and how those measurements evolve
over time. This relates to Actions 301-308 and 401-406 described
above.
[0156] The signal strength may be any metric used to rank cells,
such as estimation of SINR and/or quality of each cell and/or total
signal strength on a specific RF channel.
[0157] The evolvement over time may be based on the change from one
measurement to the next, or for example relative to the highest or
lowest measured value after a pre-determined event, such as a
trigger to do measurements for cell reselection.
[0158] In some second embodiments, the measurements for cell
reselection performed by the wireless device 240 is triggered by
the measured signal strength difference between the camped on cell,
e.g. the serving cell 212-1, and the strongest neighbour cell, e.g.
one of the neighbour cells 212-2, 222, 232. Assume for example that
the wireless device 240 has measured the camped on cell. e.g. the
serving cell 212-1, to a strength of -80 dBm, and the strongest
neighbour cell 212-2, 222, 232 to -90 dBm, measurements for cell
reselection will then be triggered by a change in 10 dBm (-80--90))
of the camped on cell's signal strength.
[0159] In other words, if the third signal quality of the serving
cell 212-1 relative the first signal quality is larger than or
exceeds 10 dB, the difference between the third signal quality and
the first signal quality has passed the trigger condition, and thus
the wireless device 240 performs one or more measurements for cell
reselection.
[0160] In some third embodiments, the measurements for cell
reselection performed by the wireless device 240 is triggered by a
ratio of the measured signal strength difference between the camped
on cell, e.g. the serving cell 212-1, and the strongest neighbour
cell 212-2, 222, 232. Thus, the measurements for cell reselection
is triggered by a fraction of the difference between the first and
second signal qualities. Take the example from some second
embodiments but modify the trigger to happen after a change in 0.5
of the signal strength difference, i.e. when the camped on cell's
signal strength has by a change in 5 dB ((-80 dBm-(-90 dBm))*0.5)
of the camped on cell's signal strength.
[0161] In other words, the trigger condition for cell reselection
is triggered by the fraction 0.5 of the signal strength difference,
e.g. 0.5*10 dB=0.5*(-80 dBm-(-90 dBm)) equal to 5 dB in this
example. If the third signal quality of the serving cell 212-1
relative the first signal quality is larger than or exceeds 5 dB,
the difference between the third signal quality and the first
signal quality has passed the trigger condition, and thus the
wireless device 240 performs one or more measurements for cell
reselection.
[0162] In some fourth embodiments, the measurements for cell
reselection performed by the wireless device 240 is subject to a
condition that the signal strength need to change by at least a
minimum change, and at most a maximum change. In this case the
embodiment may be combined with one of the abovementioned
embodiments. Take the example from some second embodiments but add
a requirement that the change need to be at least 3 dB and at most
8 dB. In this case the trigger will not be determined at 10 dB, but
would be limited by the maximum allowed change of 8 dB.
[0163] In other words, the trigger condition for cell reselection
is equal to 8 dB in this example. If the third signal quality of
the serving cell 212-1 relative the first signal quality is larger
than or exceeds 8 dB, the difference between the third signal
quality and the first signal quality has passed the trigger
condition, and thus the wireless device 240 performs one or more
measurements for cell reselection.
[0164] In some fifth embodiments, the measured signal strength
difference triggering cell reselection is made dependent on the
absolute signal strength level measured in the camped on cell, e.g.
the serving cell 212-1. A first wireless device, e.g. the wireless
device 240, experiencing a high absolute signal level may tolerate
a higher degradation in experienced signal strength before
attempting to re-select to a new cell, than a second wireless
device experiencing a low absolute signal level. For example, a
first wireless device, e.g. the wireless device 240, just at the
edge of its coverage limit needs to trigger cell reselection as
soon as the camped on signal strength is degraded, and this
regardless of the magnitude of the degradation.
[0165] As in some first embodiments described above, assume that
the wireless device 240 has measured that the first signal quality
of the serving cell 212-1 is -80 dBm, and that the second signal
quality of the strongest neighbour cell 212-2, 222, 232 is -90 dBm.
Then the trigger condition for cell reselection is 10 dB
(-80-(-90)). However, in some fifth embodiments assume that the
wireless device 240 has measured that the first signal quality of
the serving cell 212-1 is -30 dBm, and that the second signal
quality of the strongest neighbour cell 212-2, 222. 232 is -40 dBm.
Since the absolute signal level in some fifth embodiments is -30
dBm as compared to -80 dBm in some first embodiments, the trigger
condition for cell reselection may also be made dependent on the
absolute signal level in order to take it into consideration. For
example, for a low absolute signal level, the trigger condition for
cell reselection may determine as a fraction of the trigger
condition determined for a high absolute signal level. If the third
signal quality of the serving cell 212-1 relative the first signal
quality is larger than or exceeds this fraction of the trigger
condition, the difference between the third signal quality and the
first signal quality has passed the trigger condition, and thus the
wireless device 240 performs one or more measurements for cell
reselection.
[0166] In some sixth embodiments, the measured signal strength
triggering cell reselection is made dependent on the data size of
its next uplink data message in queue. A first wireless device.
e.g. the wireless device 240, with a small uplink data message in
queue may tolerate lower experienced signal strength before
attempting to re-select to a new cell, than a second wireless
device with a larger uplink data message in queue. This enables the
wireless device to trade off the power consumption for attempting
to a transfer its next uplink data message on the current cell and
the power consumption for cell-reselection measurements.
[0167] As an example, in the current operation the wireless device,
e.g. the wireless device 240, is required to confirm its serving
cell 212-1 by evaluating how strong the serving cell is, and also
evaluate the change in signal strength. Since the wireless device
at this point knows it's payload size, it could adopt its threshold
to trigger measurements based on the size expected to be
transmitted. For a longer expected data transfer the wireless
device would more likely like to spend time on the best cell, than
if the data transfer is smaller, e.g. less amount of energy being
consumed, and the relative energy added from triggering
measurements is larger.
[0168] As in some first embodiments described above, assume that
the wireless device 240 has measured that the first signal quality
of the serving cell 212-1 is -80 dBm. and that the second signal
quality of the strongest neighbour cell 212-2, 222, 232 is -90 dBm.
In some first embodiments, the trigger condition for cell
reselection was then determined to be 10 dB (-80-(-90)). However,
in some sixth embodiments, the trigger condition is also made
dependent on the signal quality and on the size of the data to be
transmitted. Thus, if the signal quality is low and the data size
large the trigger condition may be lesser than 10 dB, whereas it
may be larger than 10 dB if the signal quality is high and the data
size small.
[0169] If the third signal quality of the serving cell 212-1
relative the first signal quality is larger than or exceeds the
trigger condition, the difference between the third signal quality
and the first signal quality has passed the trigger condition, and
thus the wireless device 240 performs one or more measurements for
cell reselection.
[0170] In some seventh embodiments the measured signal strength
difference triggering cell reselection is made dependent on the
data size of its next uplink data message in queue. A first
wireless device, e.g. the wireless device 240, with a small uplink
data message in queue may tolerate higher degradation in
experienced signal strength before attempting to re-select to a new
cell, than a second wireless device with a larger uplink data
message in queue. This enables the wireless device to trade off the
power consumption for attempting to a transfer its next uplink data
message on the current cell and the power consumption for
cell-reselection measurements.
[0171] In other words, the trigger condition for cell reselection
is in some seventh embodiments made dependent on the size of the
data to be transmitted. This is in contrast to some sixth
embodiments wherein the trigger condition also was made dependent
on the signal quality. Thus, in some seventh embodiments, when data
of a larger size is to be transmitted the trigger condition may be
set smaller than the trigger condition when data of a smaller size
is to be transmitted.
[0172] If the third signal quality of the serving cell 212-1
relative the first signal quality is larger than or exceeds the
trigger condition, the difference between the third signal quality
and the first signal quality has passed the trigger condition, and
thus the wireless device 240 performs one or more measurements for
cell reselection.
[0173] In some eighth embodiments, one or more of the above
mentioned embodiments are combined to form a set of conditions to
trigger measurements for cell reselection.
[0174] The conditions to trigger measurements, such as the
mentioned limits for minimum and maximum change, for cell
reselection mentioned above may be signalled by the serving RNN,
e.g. the first RNN 210, to the wireless device 240 in for example
the System Information or the conditions to trigger measurements
may be pre-defined in the standard.
[0175] FIG. 6 is a schematic block diagram schematically
illustrating cell reselection according to some embodiments.
[0176] As schematically illustrated in FIG. 6, the wireless device
240 performs measurements at a first point in time T1, and at a
second point in time T2 similar to the first point in time. The
result is that cell A. e.g. the first cell 212, is the strongest
cell and hence the wireless device 240 camps on that cell. In this
example, the first cell 212 is the serving cell. The signal
strength for other cells. e.g. other neighbouring cells 222, 232,
are also measured and it is found that cell B, e.g. the
neighbouring cell 222, is the second strongest cell. A first
difference between the two cells .DELTA.SS,1, e.g. a difference in
signal strengths between the serving cell 212 and the strongest
neighbouring cell 222, are stored in the wireless device 240 as a
trigger, e.g. a first trigger condition, for cell reselection
measurements. This relates to Actions 302, 304, 305, 401, 402 and
403 previously described.
[0177] The wireless device 240 wakes up at a third point in time
T3. As previously mentioned the third point in time T3 is sometimes
herein referred to as a second point in time TB. The wireless
device 240 tries to confirm that the previously camped cell, e.g.
the first cell 212, is still strong enough, but fails to confirm
this since the relative change in signal strength .DELTA.SS,2 is
more than the stored allowed change .DELTA.SS,1. e.g. the first
trigger condition has been passed. In other words, the first cell
212, e.g. the serving cell, fails to confirm that it is strong
enough since the relative change in signal strength .DELTA.SS,2
between a third signal transmitted from the first cell at the third
point in time and the first signal is exceeds the stored allowed
change .DELTA.SS,1. This may also be expressed as the difference
between the third signal quality and the first signal quality has
passed the first trigger condition. Therefore, one or more
measurements for cell reselection are triggered. This relates to
Actions 306, 307 and 404, 405 previously described. It is found
that cell B. e.g. the second cell 222, is the strongest cell and
hence the wireless device 240 camps on that cell, i.e. the wireless
device 240 performs a reselection to the second cell 222. The
signal strength for other cells 212, 232 are also measured and it
is found that cell A, e.g. the first cell 212, is now the second
strongest cell. A second difference between the two cells, e.g. the
second cell 222 and the first cell 212. .DELTA.SS,2. e.g. a second
trigger condition, is stored in the wireless device 240 as a
trigger for cell reselection measurements. The second difference
.DELTA.SS,2 does not need to be the same as the first difference
.DELTA.SS,1 but the first and second differences could be the same.
In other words, the first and second trigger conditions may be
different.
[0178] The wireless device 240 wakes up at fourth point in time T4.
The fourth point in time T4 may sometimes herein be referred to as
a third point in time TC. It tries to confirm that the previously
camped cell. e.g. the second cell 222, is still strong enough, but
fails to confirm this since the relative change in signal strength
is more than the stored allowed change .DELTA.SS,2. e.g. the stored
second trigger condition. In other words, the second cell 222, e.g.
the serving cell, fails to confirm that it is strong enough since
the relative change in signal strength .DELTA.SS,3 is exceeds the
stored allowed change .DELTA.SS,2. This may also be expressed as
the difference between two signal strengths from the second cell
222 at a respective point in time, e.g. the third and fourth points
in time T3, T4, has passed the first trigger condition. Therefore,
one or more measurements for cell reselection are triggered. It is
found that cell C, e.g. the third cell 232, is the strongest cell
and hence the wireless device 240 camps on that cell, i.e. the
wireless device 240 performs a reselection to the third cell 232.
The signal strength for other cells 212, 222 are also measured and
it is found that cell B is now the second strongest cell. A third
difference between the two cells, e.g. the third cell 232 and the
second cell 222, .DELTA.SS,3, e.g. a third trigger condition, is
stored in the wireless device 240 as a trigger for further cell
reselection measurements. The third difference .DELTA.SS,3 does not
need to be the same as the first difference .DELTA.SS,1 or the
second difference .DELTA.SS,2 but it could be the same as one or
both of them. In other words, the first, second and third trigger
conditions may be different or one or more of them may be the
same.
[0179] Although an ideal cell reselection procedure would require
too frequent measurements to be made, embodiments herein provides
an improved cell reselection procedure wherein the right, e.g. the
optimal, cell is selected at the points in time where measurements
are triggered and the wireless device 240 selects all cells it
moves around when it moves in the communications network. e.g. the
communications network 200.
[0180] When the word "comprise" or "comprising" is used in this
disclosure it shall be interpreted as non-limiting, i.e. meaning
"consist at least of".
[0181] Modifications and other variants of the described
embodiment(s) will come to mind to one skilled in the art having
the benefit of teachings presented in the foregoing descriptions
and the associated drawings. Therefore, it is to be understood that
the embodiment(s) herein is/are not be limited to the specific
examples disclosed and that modifications and other variants are
intended to be included within the scope of this disclosure.
Although specific terms may be employed herein, they are used in a
generic and descriptive sense only and not for purposes of
limitation.
* * * * *