U.S. patent application number 14/102627 was filed with the patent office on 2017-06-01 for neighbour cell quality measurement in a telecommunications system.
This patent application is currently assigned to IDTP HOLDINGS, INC.. The applicant listed for this patent is IDTP HOLDINGS, INC.. Invention is credited to George Jongren, Muhammad Kazmi.
Application Number | 20170155480 14/102627 |
Document ID | / |
Family ID | 40756755 |
Filed Date | 2017-06-01 |
United States Patent
Application |
20170155480 |
Kind Code |
A9 |
Kazmi; Muhammad ; et
al. |
June 1, 2017 |
NEIGHBOUR CELL QUALITY MEASUREMENT IN A TELECOMMUNICATIONS
SYSTEM
Abstract
The present invention relates to methods and arrangements for
neighbour cell quality measurements using silent resource element
(RE) grids, and as well to a silent RE grid.
Inventors: |
Kazmi; Muhammad; (Bromma,
SE) ; Jongren; George; (Stockholm, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IDTP HOLDINGS, INC. |
Wilmington |
DE |
US |
|
|
Assignee: |
IDTP HOLDINGS, INC.
Wilmington
DE
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20140153425 A1 |
June 5, 2014 |
|
|
Family ID: |
40756755 |
Appl. No.: |
14/102627 |
Filed: |
December 11, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12921853 |
Sep 10, 2010 |
8693463 |
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PCT/SE2009/050244 |
Mar 9, 2009 |
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14102627 |
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61036198 |
Mar 13, 2008 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04J 11/0093 20130101;
H04L 5/0039 20130101; H04W 24/10 20130101; H04L 5/006 20130101;
H04W 24/08 20130101; H04W 36/0085 20180801; H04J 11/005
20130101 |
International
Class: |
H04L 5/00 20060101
H04L005/00; H04W 24/10 20060101 H04W024/10; H04W 24/08 20060101
H04W024/08 |
Claims
1-34. (canceled)
35. A first method, executed in a first network node of a wireless
communication system, for measuring a quality of a neighbor cell
for mobility purposes, the method comprising: deriving a
cell-specific silent grid, the cell-specific silent grid comprising
resource elements having no data allocation; measuring signal
interference over said grid during a measurement period; and
estimating the quality of the neighbor cell based on the measured
signal interference.
36. A first method according to claim 1, further comprising a step
of reporting said estimated quality of the neighbor cell to a
second network node.
37. A first method according to claim 1, further comprising
calculating the quality of the neighbor cell as an inter-cell
interference that is measured or estimated during the cell-specific
silent grid.
38. A first method according to claim 37, wherein the inter-cell
interference comprises noise and a received power from a data
channel or a control channel, or a combination thereof.
39. A first method according to claim 37, further comprising
calculating the quality of the neighbor cell using signal strength
and interference.
40. A first method according to claim 37, further comprising
calculating the quality of the neighbor cell as a Reference Symbol
Received Quality (RSRQ) using the following equation:
RSRQ=RSRP/(I.sub.inter-cell+N.sub.0), where RSRP=Reference Symbol
Received Power, I.sub.inter-cell=inter-cell interference measured
during the silent resource element grid used in cell i, and
N.sub.0=noise.
41. A first method according to claim 37, further comprising
defining a position in the cell-specific silent grid of the
resource elements having no data allocation, as a function of a
cell ID of the cell corresponding to the cell-specific silent
grid.
42. A first method according to claim 37, further comprising
deriving the cell-specific silent grid for the first network node,
from a cell ID of the neighbor cell; and making the cell-specific
silent grid known to the first network node.
43. A first method according to claim 37, further comprising
signaling or sending an index of the cell-specific silent grid, to
the first network node, via at least one control channel.
44. A first method according to claim 43, wherein the at least one
control channel is a broadcast channel mapped on, or sent via, a
physical downlink shared channel (PDSCH).
45. A first arrangement in a first network node, configured to:
derive a cell-specific silent grid to measure a quality of a
neighbor cell, the cell-specific silent grid comprising data
resource elements with no data allocation; measure an inter-cell
interference during said silent grid over a measurement period; and
estimate the quality of the neighbor cell based on the measured
signal interference.
46. A first arrangement according to claim 45, further configured
to report said estimated quality of the neighbor cell to a second
network node.
47. A first arrangement according to claim 45, wherein the first
arrangement is configured to estimate the quality of the neighbor
cell based on measuring the inter-cell interference during the
cell-specific silent grid.
48. A first arrangement according to claim 45, wherein the
inter-cell interference comprises noise and a received power from a
data channel or control channel, or a combination thereof.
49. A first arrangement according to claim 45, wherein the first
arrangement is configured to estimate the quality of the neighbor
cell based on measuring signal strength and interference, the
interference including the inter-cell interference and noise.
50. A first arrangement according to claim 45, wherein the first
arrangement is configured to estimate the quality of the neighbor
cell based on calculating a Reference Symbol Received Quality
(RSRQ) using the following equation:
RSRQ=RSRP/(I.sub.inter-cell+N.sub.0), where RSRP=Reference Symbol
Received Power, I.sub.inter-cell=inter-cell interference measured
during the cell-specific silent grid used in the neighbor cell and
N.sub.0=noise.
51. A first arrangement according to claim 45, further configured
to define the position in the cell-specific silent grid as a
function of a cell ID of the neighbor cell.
52. A first arrangement according to claim 45, wherein: the
cell-specific silent grid is derived from a cell ID of the neighbor
cell; and the cell-specific silent grid is made known to the first
network node.
53. A first arrangement according to claim 45, further configured
to transmit an index of the cell-specific silent grid to the first
network node, via one or more control channels.
54. A first arrangement according to claim 53, wherein the
arrangement is configured to transmit the index of the
cell-specific silent grid via a secondary or a dedicated broadcast
channel (D-BCH), or a physical downlink shared channel (PDSCH).
55. A second method executed in a second network node of a wireless
communication system, for configuring a cell-specific silent grid
for use in neighbor cell quality measurements by a first network
node of the wireless communication system, wherein the method
comprises at least one of the following steps: configuring at least
one of the resource elements in said cell-specific silent grid to
have no data allocation, thereby achieving a cell-specific silent
grid; configuring at least some of the resource elements in said
cell-specific silent grid which can be used for data transmission
to have no data allocation; randomizing the cell-specific silent
grid in consecutive, in frequency and time, resource blocks; or
changing the cell-specific silent grid randomly, in frequency and
time.
56. A second method according to claim 55, said cell-specific
silent grid comprising resource elements organized in resource
blocks, time slots, sub-frames and frames, and the method further
including grouping, suitably for each sub frame, the resource
blocks into resource windows, wherein each resource window suitably
comprises a group of resource blocks contiguous in frequency.
57. A second method according to claim 55, further comprising,
suitably for each resource window, enumerating all resource
elements that are not used for control or reference symbol
signaling.
58. A second method according to claim 57, further comprising
selecting, suitably in each resource window, a specified number of
silent resource elements from the set of the enumerated resource
elements using a pseudo-random number generator that generates
numbers uniformly in the range of the enumerated data resource
elements.
59. A second method according to claim 55, further comprising
signaling an index of the cell-specific silent grid used in a
neighbor cell to the first network node, via one or more control
channels.
60. A second method according to claim 59, wherein the one or more
control channels is a broadcast channel mapped on, or sent via, a
physical downlink shared channel (PDSCH).
61. A second arrangement in a second network node of a wireless
communication system, said arrangement comprising at least one
processor configured to: configure a cell-specific silent grid, for
use in neighbor cell quality measurements by a first network node
of a wireless communication system; configure at least one of the
resource elements in said cell-specific silent grid to have no data
allocation, thereby achieving a cell-specific silent grid;
configure at least some of the resource elements in said
cell-specific silent grid which can be used for data transmission,
to have no data allocation, thereby achieving a cell-specific
silent grid, randomize said cell-specific silent grid in
consecutive, in frequency and time, resource blocks, change said
cell-specific silent grid randomly, in frequency and time.
62. A second arrangement according to claim 61, said cell-specific
silent grid comprising resource elements organized in resource
blocks, time slots, sub-frames and frames, and wherein the at least
one processor is further configured to group, suitably for each sub
frame, the resource blocks into resource windows, wherein each
resource window suitably comprises a group of resource blocks
contiguous in frequency.
63. A second arrangement according to claim 61, wherein the at
least one processor is further configured to, for each resource
window, enumerate all resource elements that are not used for
control or reference symbol signaling.
64. A second arrangement according to claim 63, wherein the at
least one processor is further configured to select, in each
resource window, a specified number of silent resource elements
from the set of the enumerated resource elements by using a
pseudo-random number generator that generates numbers uniformly in
the range of the enumerated resource elements.
65. A second arrangement according to claim 61, wherein the at
least one processor is further configured to signal an index of the
cell-specific silent grid used in the neighbor cell to the first
network node via at least one control channel.
66. A second arrangement according to claim 65, wherein the index
of the cell-specific silent grid is sent via a secondary or a
dedicated broadcast channel (D-BCH) on, or a physical downlink
shared channel (PDSCH).
Description
TECHNICAL FIELD
[0001] The present invention relates to methods and arrangements in
a telecommunications system, in particular it relates to methods
and arrangements for neighbour cell quality measurements in a
telecommunications system.
BACKGROUND
[0002] In E-UTRAN (Evolved-Universal Terrestrial Radio Access
Network, also called 3GPP) Orthogonal Frequency Division Multiple
Access (OFDMA) technology is used in the downlink. OFDM is a
modulation scheme in which the data to be transmitted is split into
several sub-streams, where each sub-stream is modulated on a
separate sub-carrier. Hence, in OFDMA based systems, the available
bandwidth is sub-divided into several sub-channels called resource
blocks (RB) or units, in both uplink and downlink. A resource block
is defined in both time and frequency. According to the current
assumptions, used herein, a resource block size is 180 KHz and 0.5
ms (time slot) in the frequency and time domains, respectively. The
resource block size in the time domain, here 0.5 ms, is often
called time slot. One or more resource blocks are allocated to a
User Equipment (UE) for data transmission. The transmission time
interval (TTI) comprises 2 time slots, which correspond to a
sub-frame of 1 ms length in time. The radio frame is 10 ms long
i.e. comprising of 10 sub-frames. The overall uplink and downlink
cell transmission bandwidth can be as large as 20 MHz; other
typical bandwidths are 1.4, 3, 5, 10 and 15 MHz. In the case of 20
MHz bandwidth up to 100 resource blocks (RB) containing data and
control signalling can be transmitted by the UE in the uplink or by
the network, e.g., a base station, in the downlink. The UE can be
allocated a sub-set of the resource blocks for reception and
transmission of data and control signalling.
Downlink Neighbour Cell Measurements for Mobility
[0003] In WCDMA the following three downlink neighbour cell
measurement quantities are specified primarily for mobility
purposes: [0004] 1. Common PIlot CHannel (CPICH) Received Signal
Code Power (RSCP), the received power on one code after
de-spreading measured on the pilot bits of the CPICH. The reference
point for the RSCP is the antenna connector at the UE. [0005] 2.
CPICH Ec/No; CPICH Ec/No=CPICH RSCP/carrier RSSI, where
RSSI=Received Signal Strength Indicator. CPICH Ec/No can be
described as the received energy per chip divided by the power
density in the band. Measurement is suitably performed on the
CPICH. The reference point for CPICH Ec/No is the antenna connector
at the UE. [0006] 3. UTRA carrier RSSI, can be described as the
wide-band received power within the relevant channel bandwidth.
Measurement is suitably performed on a UTRAN downlink carrier. The
reference point for the RSSI is the antenna connector at the
UE.
[0007] Reference [1] describes downlink neighbour cell measurements
for WCDMA more in detail.
[0008] The RSCP is measured by the UE on cell level basis on the
common pilot channel (CPICH). The UTRA carrier RSSI is measured
over the entire carrier. The UTRA carrier RSSI is the total
received power and noise from all cells (including serving cells)
on the same carrier. The above CPICH measurements are quantities
that are often used for the mobility decisions.
[0009] In E-UTRAN the following three downlink neighbour cell
measurement quantities are specified also primarily for mobility
purposes: [0010] i. Reference symbol received power (RSRP) [0011]
ii. Reference symbol received quality (RSRQ): RSRQ=RSRP/carrier
RSSI [0012] iii. E-UTRA carrier RSSI
[0013] Reference [2] describes downlink neighbour cell measurements
for E-UTRAN more in detail.
[0014] The RSRP or RSRP part in RSRQ is solely measured by the UE
on cell level basis on reference symbols. As in the case of WCDMA,
the E-UTRA carrier RSSI is measured over the entire carrier. It is
also the total received power and noise from all cells (including
serving cells) on the same carrier. The two RS based measurement
quantities (i. and ii.) are often used for the mobility
decisions.
[0015] The neighbour cell measurements are averaged over a long
time period, in the order of 200 ms or even longer, to filter out
the effect of small scale fading.
[0016] There is also a requirement on the UE to measure and report
the neighbour cell measurements, e.g. of RSRP and/or RSRQ in
E-UTRAN, from a certain minimum number of cells. In both WCDMA and
E-UTRAN this number is often 8 cells (comprising one serving and
seven neighbour cells) on the serving carrier frequency. The
serving carrier frequency is commonly called intra-frequency.
Hence, the expression "neighbour cell" includes both the serving
cell of an UE and the neighbour cells of this serving cell.
Sampling of Neighbour Cell Measurements
[0017] The overall neighbour cell measurement quantity results
comprises non-coherent averaging of 2 or more basic non-coherent
averaged samples. An example of RSRP measurement averaging in
E-UTRAN is shown in FIG. 1. The figure illustrates that the UE
obtains the overall measurement quantity result by collecting four
non-coherent averaged samples or snapshots, each of 3 ms length in
this example, during the physical layer measurement period, e.g.
200 ms. Every coherent averaged sample is 1 ms long. In this
example a 3 ms non-coherent sample comprises 3 consecutive coherent
samples. The measurement accuracy of the neighbour cell measurement
quantity, e.g. RSRP or RSRQ, is specified over the physical layer
measurement period. It should be noted that the sampling rate is UE
implementation specific. Therefore in another implementation a UE
may use only 3 snap shots over a 200 ms interval or measurement
period. Regardless of the sampling rate, it is important that the
measured quantity fulfils the performance requirements in terms of
the specified measurement accuracy.
[0018] In case of RSRQ both RSRP, numerator, and carrier RSSI,
denominator, should be sampled at the same time or instant to
follow similar fading profiles on both components.
Mobility Scenarios
[0019] There are basically, or at least, two kinds of mobility:
[0020] a. Idle mode mobility: cell reselection [0021] b. Connected
mode mobility: handover
[0022] The cell reselection is mainly a UE autonomous function
without any direct intervention of the network. But to some extent
the behaviour of the UE in this mobility scenario could still be
controlled by some broadcasted system parameters and performance
specification.
[0023] The handover is on the other hand often fully controlled by
the network through explicit UE specific commands and by
performance specification.
[0024] In both idle and connected modes the mobility decisions are
mainly based on the same kind of downlink neighbour cell
measurements, which were discussed previously.
[0025] Both WCDMA and E-UTRAN are frequency reuse-1 systems. This
means that the geographically closest or physically adjacent
neighbour cells operate on the same carrier frequency. An operator
may also deploy multiple frequency layers within the same coverage
area. Therefore, idle mode and connected mode mobility in both
WCDMA and E-UTRAN could be broadly classified into three main
categories: [0026] Intra-frequency mobility (idle and connected
modes) [0027] Inter-frequency mobility (idle and connected modes)
[0028] Inter-RAT mobility (idle and connected modes)
[0029] In intra-frequency mobility the UE moves between the cells
belonging to the same carrier frequency. This is an important,
maybe even the most important, mobility scenario since it involves
less cost in terms of delay due. This mobility scenario involves
shorter delay since UE measurements are not done during the
measurement gaps. Secondly most handovers and cell reselections are
carried out between the cells operating over the same carrier
frequency. In addition, an operator would have at least one carrier
at its disposal that it would like to be efficiently utilized.
[0030] In inter-frequency mobility the UE moves between cells
belonging to different carrier frequencies but of the same access
technology. This could be considered as a less important mobility
scenario than intra-frequency mobility. This is because handover
and cell reselection between cells belonging to different carriers
are carried out when no suitable cell is available on the serving
carrier frequency. Furthermore, UE measurements for inter-frequency
mobility are done in gaps. This increases measurement delay and
consequently involves longer handover delay compared to that in
case of intra-frequency scenario.
[0031] In inter-RAT mobility the UE moves between cells that belong
to different access technologies such as between WCDMA and GSM or
vice versa. This scenario is particularly important in case an
operator does not have full coverage of all the supported RATs in
its network. During an initial deployment an operator may have
limited coverage of the newly deployed technology. Thus inter-RAT
handover would ensure ubiquitous service to the users even if all
RATs don't have full coverage. Furthermore, an operator may
optimize different RATs for different services e.g. GSM for speed,
UTRAN for packet data and E-UTRAN for both speech and packet data.
Thus if UE switches between speech and packet data or requires both
type of services at the same time then if necessary, an inter-RAT
handover can be used by the operator to select the most appropriate
technology for offering the requested service to the prospective
subscriber.
Objectives of Quality Measurements
[0032] As indicated above, CPICH Ec/No and RSRQ are so-called
neighbour cell quality measurement quantities used in WCDMA and
E-UTRAN respectively.
[0033] In general the quality measurement (Q.sub.rx) can be
expressed as follows:
Q rx = P rx I + N o ( 1 ) ##EQU00001##
[0034] Where, P.sub.rx is the received power of the pilot or
reference signal or channel, i.e. signal strength part, I is the
interference and N.sub.o is the noise. Depending upon the type of
quality measurement the component I can be interference on the
pilot channel or the total interference on the entire carrier or
simply inter-cell interference plus noise. In current quality
measurements in WCDMA and in E-UTRAN the interference measurement
constitutes the entire interference on the carrier i.e. from the
serving and all non serving cells. In reality the noise and the
interference within the same measurement bandwidth cannot be
separated. This means that the interference measured by the UE
would incorporate both the actual interference and the noise i.e.
the measured part is the entire denominator (I+N.sub.O) in (1).
[0035] The goal of the neighbour cell quality measurement is to
estimate and predict the long term downlink quality that can be
experienced by the UE in a particular cell. It should indeed
indicate the signal quality or throughput that the UE will achieve
in a cell. This prediction enables the UE and the network to choose
the most appropriate cell when performing cell reselection and
handovers, respectively. In E-UTRAN any set of resource blocks
(i.e. part of the cell bandwidth) can be assigned to the UE for
transmission. Therefore the quality measurement should capture the
overall long term average quality over the entire bandwidth or at
least over the largest possible portion of the bandwidth. This is
in contrast with E-UTRAN CQI measurement, which typically depicts
short term quality of possibly a sub-set of the resource blocks
from the serving cell.
Problems with Existing Solutions
[0036] As noted above, the quality measurements include the total
interference on the entire carrier in their denominator e.g.
RSRQ=RSRP/carrier RSSI. This means that the quality measurement
also includes a contribution from the serving-cell signal.
Especially in a OFDM based system like E-UTRAN the serving-cell
signal introduces negligible intra-cell interference due to good
orthogonality between the sub-carriers across the cell bandwidth.
In order to correctly track the cell quality the contribution from
the serving-cell signal should hence be excluded from the
interference measurement part of the neighbour cell quality
measurement.
[0037] Furthermore, the statistical characteristics of the
inter-cell interference may be significantly different, depending
on whether the inter-cell interference originates from: [0038] 1.
reference symbols from neighbouring cells [0039] 2. data signaling
from neighbouring cells [0040] 3. control signaling from
neighbouring cells
[0041] Each of these three categories can have different
transmission power and spatial characteristics.
[0042] For accurate neighbour cell quality measurement or
estimation the UE must have good, statistics, or suitably should
obtain statistics or statistical characteristics, of the inter-cell
interference that is hitting or affecting the resource elements
(RE) in the data channel, which is a mixture of the three
categories mentioned above, here referred to as I_d. One may also
use the expression, the inter-cell interference from the resource
elements (RE) in neighbor cells, where the REs suitably should
belong only to the data channel. But the REs may also be a mixture
of one or more of the three categories of REs; data signaling,
control signaling and reference symbol containing REs.
[0043] The statistical characteristics of the inter-cell
interference is here referred to as I_d.
[0044] In reality, at least often, the inter-cell interference that
is hitting or affecting the resource elements (RE) in the data
channel is a mixture of the three categories 1, 2 and 3 mentioned
above.
[0045] Ultimately or suitably, this interference statistics should
be measured, or measured and calculated, on the data channel
itself. However, this measurement is limited to resource entities,
i.e. or e.g. time-frequency resource elements, that contain data
scheduled to the particular user or UE doing the measurement since
there is only or mainly a good chance of removing the contribution
from the serving-cell signal for resources where the UE doing the
measurement is scheduled. One may also say, for resources over
which the UE is receiving data sent by these resource entities. The
limited number of interference samples can significantly penalize
the accuracy of the statistics estimate, or of the measured or
estimated interference statistics. Moreover, in multiuser-MIMO
(MIMO=Multiple Input Multiple Output), i.e. or e.g. spatial
division multiple access, systems, several users may be assigned
the same data resource elements (RE), which in effect prohibits the
UE to separate the inter-cell interference from the intra-cell
interference, if the measurement is performed on data REs.
[0046] Alternatively, the interference measurement can be performed
on REs containing reference symbols (RS). However, the statistics,
or the statistical characteristics, e.g. average interference, of
the interference measurement on the neighbour cell RS,
corresponding to I_RS, may have significantly different statistics
than the interference on the data channel, or the control channel.
It may also be the case that the statistical characteristics of the
interference measurement, I_RS, on the neighbour cell RS is
different, or significantly different, than the statistical
characteristics of the interference measurement on the data
channel, or of the interference measurement on the control channel.
The interference measurement on the neighbour cell RS gives or
yields the interference from the neighbour cell RS. There is a
limited set of RS:s and in particular for MIMO, where the position
holding a RS on one antenna is empty for a neighbouring antenna.
Alternatively, one may say that for MIMO the time-frequency
resources, i.e. the resource elements, containing the RS on
different antennas are different. Therefore the interference
hitting a RS will to a larger extent, or mainly, come from, or be
contributed by, the RSs of the neighbouring cells. For example in
lightly loaded systems, I_RS may be significantly different,
typically or often substantially larger, than I_d, because possibly
data is not allocated to all resource blocks (RB) in the
neighbouring cells. The statistics of the measured interference
term may therefore deviate significantly from the interference that
hits the data channel. The RS grid for a RB in case of 1, 2 and 4
transmit antennas is illustrated in FIGS. 2a-2c4 Between cells, the
RS grid may be shifted in the frequency domain. This is because the
standard allows the possibility of configuring three possible
shifts in frequency domain to allow the randomization of the
interference. The frequency shift used in a cell is mapped on to
primary synchronization sequence (PSS). Therefore three unique PSS
are possible. The frequency shift is detected by the UE during the
cell synchronization phase, which requires the detection of PSS.
One RS grid may often span over a time slot, 0.5 ms, or a
sub-frame, 1 ms, in the time domain and over the entire cell
bandwidth (BW) in the frequency domain. In the frequency domain
that is over multiple RBs, e.g. 50 RBs in a cell with 10 MHz BW or
100 RB:s in a cell with 20 MHz BW and so forth. Reference sign 202
indicates a resource element, which may be identified by an index
(k,l) where 1 ranges from 0-6 and k from 0 to 12.
[0047] For 2 transmitting antennas only three frequency shifts for
common RSs exists. This will lead to that not all data interference
can be measured. Furthermore, the first three OFDM symbols might
see control channel interference instead of data interference.
Since control signaling may be differently power controlled than
the data signalling, the interference estimate obtained on these RS
s may not reflect the interference present when data is
transmitted. If common RSs in the later part of a sub-frame is
removed, for example because dedicated RSs are inserted instead, it
might be necessary to measure interference on data REs.
SUMMARY
[0048] The expression "neighbour cell quality measurement" includes
measurements performed on or in the serving cell of an UE as well
as measurements performed on or in neighbour cells of said serving
cell.
[0049] In this description, the term "base station" is used to
generally represent any network node capable of wireless
communication with a user terminal.
[0050] A cell specific grid of resource elements wherein a subset
of the resource elements are intentionally planned and/or
configured to be silent, i.e. to not have data or any type of
transmission allocated therein, is called a silent resource element
grid.
[0051] The first network node may e.g. be a user equipment
(UE).
[0052] The second network node may e.g. be a base station.
[0053] It is an object of the present invention to provide a
solution for neighbour cell quality measurements in a
communications system that at least to a certain extent alleviates
one or more of the problems indicated above.
[0054] It is also an object of the present invention to provide a
solution for neighbour cell quality measurements, which avoids
including serving cell contributions in the relevant interference
measurements.
[0055] At least one of the above objects is achieved with the
method/s, arrangement/s, network node/s or resource element grid
according to the example aspects and embodiments of the invention
herein described.
[0056] Further objects and advantages are evident from the
following.
[0057] Generally there is provided a method, executed in a first
network node of a wireless communication system, for measuring
neighbour cell quality for mobility purposes. Said method may
comprise the following steps: [0058] Deriving a cell specific grid
comprising resource elements having no data allocation, i.e. a
silent grid, of a neighbour cell i whose quality is to be measured,
[0059] Measuring signal interference during said grid over a
measurement period, [0060] Estimating the quality of the neighbour
cell i based on the measured signal interference.
[0061] According to one embodiment there is provided a first
method, comprising the step of reporting said estimated quality of
the neighbour cell i to a second network node.
[0062] According to another embodiment there is provided a first
method, comprising calculating, measuring and/or estimating the
quality of the neighbour cell i as the inter-cell interference that
is measured or estimated during the silent resource element grid
used in cell i.
[0063] According to a further embodiment there is provided a first
method, wherein the inter-cell interference comprises the noise and
the received power from a data- or control channel, or a
combination thereof.
[0064] According to yet a further embodiment there is provided a
first method, comprising calculating, measuring and/or estimating
the quality of the neighbour cell i using signal strength, e.g.
Reference Symbol Received Power (RSRP), and interference, e.g.
inter-cell interference plus or including noise.
[0065] According to yet another embodiment there is provided a
first method, comprising calculating, measuring and/or estimating
the quality of the neighbour cell i as the Reference Symbol
Received Quality (RSRQ) using the following equation:
RSRQ=RSRP/(I.sub.inter-cell+N.sub.0)
[0066] Where RSRP=Reference Symbol Received Power,
I.sub.inter-cell=inter cell interference measured during the silent
resource element grid used in cell i and N.sub.0=noise.
[0067] According to one embodiment there is provided a first
method, comprising defining the position in the silent resource
element grid of the data resource elements having no data
allocation, as a function of the cell ID of the cell of the silent
resource element grid.
[0068] According to a further embodiment there is provided a first
method, comprising deriving the silent resource element grid for
the first network node from the neighbour cell ID of the cell of
the silent resource element grid. As an alternative, or in
addition, it may be comprised the step of making the silent
resource element grid known to the first network node from the
neighbour cell ID of the cell of the silent resource element
grid.
[0069] According to another embodiment there is provided a first
method, comprising signaling or sending an index of the silent
resource element grid used in a neighbour cell i, to the concerned
first network node(s). The index may be sent via at least one
control channel, e.g. a primary or a physical broadcast channel
(PBCH) and/or a secondary or a dedicated broadcast channel
(D-BCH).
[0070] According to yet another embodiment there is provided a
first method, wherein the secondary or the dedicated broadcast
channel (D-BCH) is mapped on, or sent via, a physical downlink
shared channel (PDSCH).
[0071] Generally there is provided a first arrangement in a first
network node. Said first arrangement may comprise at least one of
the following elements or means: [0072] Grid deriving means for
deriving a cell specific silent grid, comprising data resource
elements with no data allocation, of a neighbour cell i to be
quality measured, [0073] Measuring means for measuring signal
interference during said silent grid over a measurement period,
[0074] Computing means for calculating, measuring and/or estimating
the quality of the neighbour cell i based on the measured signal
interference.
[0075] According to one embodiment there is provided a first
arrangement, comprising reporting means for reporting said
estimated quality of the neighbour cell i to a second network
node.
[0076] According to another embodiment there is provided a first
arrangement, wherein the computing means is adapted for
calculating, measuring and/or estimating the quality of the
neighbour cell i as the inter-cell interference that is measured or
estimated during the silent resource element grid used in cell
i.
[0077] According to yet another embodiment there is provided a
first arrangement, wherein the inter-cell interference comprises
the noise and the received power from a data- or control channel,
or a combination thereof.
[0078] According to a further embodiment there is provided a first
arrangement, wherein the computing means is adapted for
calculating, measuring and/or estimating the quality of the
neighbour cell i using signal strength, e.g. Reference Symbol
Received Power (RSRP), and interference, e.g. inter-cell
interference plus or including noise.
[0079] According to one embodiment there is provided a first
arrangement, wherein the computing means is adapted for
calculating, measuring and/or estimating the quality of the
neighbour cell i as the Reference Symbol Received Quality (RSRQ)
using the following equation:
RSRQ=RSRP/(I.sub.inter-cell+N.sub.0)
[0080] Where RSRP=Reference Symbol Received Power,
I.sub.inter-cell=inter cell interference measured during the silent
resource element grid used in cell i and N.sub.0=noise.
[0081] According to another embodiment there is provided a first
arrangement, comprising defining means for defining the position in
the silent resource element grid of the data resource elements
having no data allocation, as a function of the cell ID of the cell
of the silent resource element grid (210).
[0082] According to a further embodiment there is provided a first
arrangement, wherein the computing means is adapted for deriving
the silent resource element grid for the first network node from
the neighbour cell ID of the cell of the silent resource element
grid. As an alternative, or in addition, said computing means is
adapted for making the silent resource element grid known to the
first network node, from the neighbour cell ID of the cell of the
silent resource element grid.
[0083] According to one embodiment there is provided a first
arrangement, comprising transmitting means for signaling or sending
an index of the silent resource element grid used in a neighbour
cell i, to the concerned first network node/s, via at least one
control channel, e.g. a primary or a physical broadcast channel
(PBCH) and/or a secondary or a dedicated broadcast channel
(D-BCH).
[0084] According to a further embodiment there is provided a first
arrangement, wherein the transmitting means is adapted to mapp the
secondary or the dedicated broadcast channel (D-BCH) on, or send it
via, a physical downlink shared channel (PDSCH).
[0085] Generally there is provided a second method executed in a
second network node, e.g. a base station, of a wireless
communication system. Said second method comprises configuring or
designing a silent resource element grid, for use in neighbour cell
quality measurements by a first network node of a wireless
communication system. Said second method comprises at least one of
the following steps; [0086] configuring at least one of the
resource elements in said silent resource element grid to have no
data allocation, thereby achieving a silent resource element grid,
[0087] configuring at least some of the resource elements in said
silent resource element grid which, i.e. the RE, can be used for
data transmission, to have no data allocation, [0088] randomizing
the silent resource element grid in consecutive, in frequency and
time, resource blocks, [0089] changing the silent resource element
grid, e.g. randomly, in frequency and time.
[0090] According to one embodiment there is provided a second
method, wherein said silent resource element grid comprises
resource elements organized in resource blocks, time slots,
sub-frames and frames. Further said second method involves
grouping, suitably for each sub frame, the resource blocks into
resource windows. Suitably each resource window comprises a group
of resource blocks contiguous in frequency.
[0091] According to another embodiment there is provided a second
method, comprising enumerating all resource elements that are not
control or reference symbol signaling. Suitably said enumeration is
made for each resource window.
[0092] According to a further embodiment there is provided a second
method, comprising selecting a specified number of silent resource
elements from the set of enumerated resource elements. Said step of
selecting may be performed using a pseudo-random number generator
that generates numbers uniformly in the range of the enumerated
data resource elements. Suitably said step of selecting is made in,
or for, each resource window.
[0093] According to yet another embodiment there is provided a
second method, comprising signaling an index of the silent resource
element grid used in a neighbour cell i, to the concerned first
network node(s). Said signaling may be made via at least one
control channel, e.g. a primary or a physical broadcast channel
(PBCH) and/or a secondary or a dedicated broadcast channel
(D-BCH).
[0094] According to one embodiment there is provided a second
method, wherein the secondary or the dedicated broadcast channel
(D-BCH) is mapped on, or sent via, a physical downlink shared
channel (PDSCH).
[0095] Generally there is provided a second arrangement in a second
network node, e.g. a base station, of a wireless communication
system. Said second arrangement comprises at least one of the
following means; [0096] First configuring means for configuring or
designing a silent resource element grid, for use in neighbour cell
quality measurements by a first network node of a wireless
communication system, [0097] Second configuring means for
configuring at least one of the resource elements in said silent
resource element grid to have no data allocation, thereby achieving
a silent resource element grid, [0098] Third configuring means for
configuring at least some of the resource elements in said silent
resource element grid which, i.e. the RE, can be used for data
transmission, to have no data allocation, [0099] Randomizing means
for randomizing said silent resource element grid in consecutive,
in frequency and time, resource blocks, [0100] Changing means for
changing said silent resource element grid, e.g. randomly, in
frequency and time.
[0101] According to one embodiment there is provided a second
arrangement, wherein said silent resource element grid comprises
resource elements organized in resource blocks, time slots,
sub-frames and frames. Said second arrangement may comprise
organizing means for grouping, suitably for each sub frame, the
resource blocks into resource windows. Suitably each resource
window comprises a group of resource blocks contiguous in
frequency.
[0102] According to another embodiment there is provided a second
arrangement, comprising enumerating means for, suitably for each
resource window, enumerating all resource elements that are not
control or reference symbol signaling.
[0103] According to a further embodiment there is provided a second
arrangement, comprising selecting means for selecting, suitably in
each resource window, a specified number of silent resource
elements from the set of enumerated resource elements. Suitably
said selecting means is adapted to use e.g. using a pseudo-random
number generator that generates numbers uniformly in the range of
the enumerated data resource elements.
[0104] According to yet another embodiment there is provided a
second arrangement, comprising transmitting means for signaling or
sending an index of the silent resource element grid used in a
neighbour cell i, to the concerned first network node/s. Said
transmitting means is suitably adapted for signaling or sending
said index via at least one control channel, e.g. a primary or a
physical broadcast channel (PBCH) and/or a secondary or a dedicated
broadcast channel (D-BCH).
[0105] According to one embodiment there is provided a second
arrangement, wherein the transmitting means is adapted to map the
secondary or the dedicated broadcast channel (D-BCH) on, or send it
via, a physical downlink shared channel (PDSCH).
[0106] Generally there is provided a silent resource element grid
in a second network node of a wireless communication system,
wherein said silent resource element grid is configured to comprise
resource elements, e.g. data resource elements, having no data
allocation. Said silent resource element grid may be adapted for
use in neighbour cell quality measurements by a first network node
of said wireless communication system.
[0107] According to one embodiment there is provided a silent
resource element grid which is randomized in consecutive, in
frequency and time, resource blocks.
[0108] The present invention may as well, complementary or
alternatively be described as in the following.
[0109] A first aspect of the present invention relates to a method
in a network node, such as a user equipment (UE), of a wireless
communication system, for measuring neighbour cell quality.
[0110] A first method step of the first aspect of the invention
involves deriving a cell specific grid of data resource elements
(REs) with no data allocation, of a neighbour cell i to be quality
measured.
[0111] This provides the advantage that the assigned base station,
e.g. NodeB or eNodeB, will be silent on this grid, hereinafter
referred to as the silent RE grid, which cell specific grid is also
made known to the assigned node(s), e.g. UE.
[0112] Note that the silent RE grid refers to a grid of resource
elements (REs) wherein a subset of the resource elements are
intentionally planned/configured to be silent, i.e. to not have
data allocated therein. This is a definition of the silent grid as
it is to be understood throughout the whole description of the
present invention.
[0113] A second method step of the first aspect of the invention
involves measuring signal interference during this silent RE
grid.
[0114] Here the node measures the statistics of the signal(s) that
is/are received on, or during, this silent RE grid. Such signal(s),
e.g. denoted I.sub.inter-cell-data and I.sub.inter-cell-control,
originates completely from inter-cell signals that interfere with
the data- and/or control channel.
[0115] The statistics measurement is computationally trivial,
because no data must be decoded to obtain the residual noise and
interference.
[0116] The interference that hit the control channel,
I.sub.inter-cell-control, may be estimated in a similar way as that
on the data channel by introducing another silent RE grid on the
control channel, i.e., potentially up the first three ODFM symbols
in the sub-frame. This is because according to the E-UTRAN standard
the first three symbols in a time slot can be allocated for
transmitting the control channels e.g. PDCCH or PHICH.
[0117] In a third method step of the first aspect of the invention
the quality of the neighbour cell i is estimated based on the
measured signal interference, i.e. the inter-cell interference.
[0118] More specifically, the neighbour cell quality measurement
for cell i may be derived based on the inter-cell interference
estimated or measured during the silent RE grid used in cell i. The
inter-cell interference may comprise the received power from the
data or control channel or a combination thereof. As an example the
RSRQ may be measured or calculated according to Equation (2) below.
Both RSRP and the interference parts should be sampled during the
same period.
R S R Q = R S R P I inter - cell + N o ( 2 ) ##EQU00002##
[0119] Using the silent grid for neighbour cell quality
measurements thereby avoids including serving-cell contributions in
the relevant interference measurements.
[0120] As previously stated, in reality the noise and interference
cannot be separated. This means that the inter-cell interference
measured by the node, e.g. the UE, would incorporate both the
actual inter-cell interference and the noise i.e. the measured part
comprises the entire denominator (I.sub.int er-cell+N.sub.O) in
(2).
[0121] According to one embodiment of this aspect of the invention,
the silent RE grid is derived or made known to the network node,
e.g. the UE, from the neighbour cell ID. The silent resource
element grid may be derived from the neighbour cell ID e.g. by the
use of predefined rules, e.g. in the form of a table or a formula.
In this context the neighbor cell ID is the cell ID of the cell of
the silent resource element grid.
[0122] This has the advantage of providing little or no signaling
overhead.
[0123] Alternatively, an index of the silent grid used in a
neighbour cell is signaled to the concerned network node(s), e.g.
via a primary or a physical broadcast channel (PBCH) and/or a
secondary or a dedicated broadcast channel (D-BCH). The secondary
or dedicated broadcast channel may be sent via a physical downlink
shared channel (PDSCH).
[0124] A second aspect of the present invention relates to a
network node, such as a user equipment (UE) or a base station (BS),
e.g. NodeB or eNodeB, of a wireless communication system, capable
of measuring neighbour cell quality, wherein the node comprises
means arranged to perform the method according to the first aspect
of the invention.
[0125] A third aspect of the present invention relates to a method
of configuring, i.e. or e.g. designing, a silent resource element
(RE) grid for use in neighbour cell quality measurements by a
network node of a wireless communication system, e.g. for use in a
neighbour cell quality measurement according to the first aspect of
the present invention.
[0126] A first method step of the third aspect of the present
invention involves grouping, for each sub frame, the resource
blocks (RBs) into resource windows (RWs).
[0127] Here each resource windows (RW) is preferably a group of
contiguous, in frequency, resource blocks (RBs). The number of RBs
in each RW is preferably or suitably configured semi-statically. As
special cases, there could be only one RW that represent the entire
system bandwidth, or there could be a RW for each RB. For neighbour
cell quality measurements it should preferably, or may suitably, be
over the entire system bandwidth.
[0128] A second method step of this aspect of the invention
involves enumerating all REs that do not carry, or are not, control
signaling, e.g. physical downlink control channel (PDCCH), or
reference signal (RS) signaling, for each RW. In other words
enumerate all REs that only contain data.
[0129] A third method step of this aspect of the invention involves
selecting, in each RW, a specified number of silent REs from the
set of enumerated REs using a pseudo-random number generator that
generates numbers uniformly in the range of the enumerated data
REs.
[0130] Here the first method step of grouping into RWs will ensure
that clustering of silent REs is sufficiently limited. The number
of selected silent REs may be fixed, derived from the number of RBs
in each RW or semi-statically configured.
[0131] According to one embodiment of the third aspect of the
invention, the silent RE grid is randomized in consecutive, in
frequency and time, resource blocks.
[0132] This has the advantage of minimizing the effects of
potentially overlapping grids of neighbouring cells.
[0133] The grid in each cell can be randomly changed in each cell.
This enables that interference is not always measured through the
same grid rather on the average over larger number of RE.
[0134] A fourth aspect of the present invention relates to a
resource element (RE) grid configured to be silent, e.g. according
to the third aspect of the invention, for use in a method for
measuring neighbour cell quality, e.g. according to the first
aspect of the present invention.
[0135] The present invention may further be described as in the
following.
[0136] According to one aspect there is provided a first method
executed in a first network node, e.g. a user equipment, of a
wireless communication system, for measuring neighbour cell quality
for mobility purposes. Said first method may comprise one or more
of the following steps; [0137] Deriving a cell specific grid
comprising data resource elements with no data allocation, i.e. a
silent grid, of a neighbour cell i whose quality is to be measured,
[0138] Measuring signal interference during said grid, [0139]
Estimating the quality of the neighbour cell i based on the
measured signal interference.
[0140] According to one embodiment there is provided a first
method, comprising the step of reporting said estimated quality of
the neighbour cell i to a second network node.
[0141] According to a further embodiment there is provided a first
method, wherein the neighbour cell quality measurement for cell i
is derived based on the inter-cell interference estimated or
measured during the silent resource element grid used in cell
i.
[0142] According to another embodiment there is provided a first
method, wherein the inter-cell interference comprises he received
power from a data- or control channel, or a combination
thereof.
[0143] According to yet a further embodiment there is provided a
first method, wherein the quality of the neighbour cell i is
calculated, measured and/or estimated as Reference Symbol Received
Quality (RSRQ).
[0144] According to one embodiment there is provided a first
method, wherein the Reference Symbol Received Quality (RSRQ) is
calculated using the following equation:
RSRQ=RSRP/(I.sub.inter-cell+N.sub.0)
[0145] Where RSRP=Reference Symbol Received Power and
N.sub.0=Noise.
[0146] According to a further embodiment there is provided a first
method, wherein the silent resource element (RE) grid is derived or
made known to the first network node, e.g. a user equipment, from
the neighbour cell identity (ID).
[0147] According to one embodiment there is provided a first
method, wherein an index of the silent grid used in a neighbour
cell i is signaled to the concerned first network node(s), e.g. a
user equipment, via e.g. a primary broadcast channel (PBCH) and/or
a secondary broadcast channel (D-BCH).
[0148] According to a second aspect there is provided a first
arrangement in a first network node, e.g. a user equipment,
comprising first means arranged to perform the mentioned first
method according to any of its embodiments.
[0149] According to a third aspect there is provided a second
method, executed in a second network node, e.g. a base station, of
a wireless communication system.
[0150] Said second method may comprise configuring i.e. designing,
a silent resource element (RE) grid for use in neighbour cell
quality measurements by a first network node of a wireless
communication system. Said second method may comprise at least one
of the following steps; [0151] Configuring said silent resource
element grid to comprise a subset of data resource elements which
are planned/configured to be silent, i.e. to not have data
allocated therein, [0152] Randomizing the silent resource element
grid in consecutive, in frequency and time, resource blocks, [0153]
Changing said silent resource element grid over time and/or
frequency.
[0154] According to one embodiment there is provided a second
method wherein said silent resource element (RE) grid comprises sub
frames. Further, said second method suitably involves grouping, for
each sub frame, the resource blocks (RBs) into resource windows
(RW). Preferably each resource window (RW) is a group of
contiguous, in frequency, resource blocks (RB).
[0155] According to one embodiment there is provided a second
method involving, for each resource window, enumerating all
resource elements that are not control or reference symbol
signaling.
[0156] According to a further embodiment there is provided a second
method, involving selecting, in each resource window, a specified
number of silent resource elements from the set of enumerated
resource elements. Suitably this is performed using a pseudo-random
number generator that generates numbers uniformly in the range of
the enumerated data resource elements.
[0157] According to a fourth aspect there is provided a resource
element grid configured to be silent, e.g. according to any of the
aspects or embodiments of the second method, for use in a method
for measuring neighbour cell quality, e.g. according to any of the
aspects or embodiments of the first method.
[0158] The present invention according to the aspects and
embodiments thereof herein described provides the advantage of
allowing more accurate interference estimation or measurement i.e.
substantially only inter-cell interference which is experienced by
the UE in practice. Also, or another advantage is that, the
neighbour cell quality measurement provides a more accurate
prediction of the actual quality of the downlink in a particular
cell. A further advantage of the present invention is the
improvement of the mobility performance, i.e. or e.g. the improved
cell reselection and handovers.
[0159] The present invention provides the advantages of: [0160]
allowing more accurate interference estimation i.e. only, or
substantially only, inter-cell interference which is experienced by
the UE in practice. [0161] enabling more accurate prediction of the
actual quality of the downlink in a particular cell. [0162]
improving the mobility performance, i.e. or e.g. cell reselection
and handovers.
[0163] Herein described method steps and other features of the
invention may be implemented by software executed by a processor in
one or several network nodes, such as a mobile terminal also called
UE or mobile station, and/or a radio base station also called NodeB
or eNodeB.
[0164] One suitable example of a silent RE grid is a RE grid where
some of the resource elements, such REs which could potentially
contain data, are unused, i.e. forming a silent grid.
[0165] Any examples and terminology relating to 3GPP LTE standard
being used herein should not be seen as limiting the scope of the
invention, the methodology of which in principle may be applied to
other systems as well, including e.g. WCDMA. It should also be
noted that the present invention is in principle equally applicable
both in the downlink as well as the uplink of a wireless
system.
[0166] The features described above in relation to the method/s
according to the invention may, where applicable, also be
implemented in a arrangement/s according to the invention with the
same advantages as described in relation to the method/s.
[0167] It goes without saying that all of the above mentioned
aspects, embodiments and features of the invention may be freely
combined, e.g. in the same embodiment.
BRIEF DESCRIPTION OF DRAWINGS
[0168] FIG. 1 is an exemplary illustration of RSRP measurement
averaging in E-UTRAN.
[0169] FIGS. 2a, 2b1b, 2b2 and 2c1-2c4 illustrates one example of a
reference symbol (RS) or resource grid 200 for a size of two
resource blocks (RB) in the time domain in case of 1, 2 and 4
transmitting antennas.
[0170] FIG. 2d is an exemplary illustration of a silent grid in the
case of one antenna port, illustrating that some of the resource
elements, which could potentially contain data are unused, i.e.
forming a silent grid.
[0171] FIGS. 2e, 2f and 2g are figures where OFDM symbol, time
slot, RB, RW, sub frame, frame are schematically illustrated in
schematically illustrated resource element grid/s. The symbols . .
. :
[0172] indicate that not all elements are shown. In FIGS. 2e, 2f
and 2g these symbols are used to indicate that not all REs or
resource element grids are shown, this for sake of clarity.
[0173] FIG. 3 is an exemplary schematic drawing of a network where
the present methods and arrangements may be used.
[0174] FIG. 4 is a flowchart schematically illustrating a method,
e.g. according to the first aspect, which may be performed in the
first, or third, network node. Said method may also be performed in
a network node of similar type.
[0175] FIG. 5a is a drawing schematically illustrating one example
of a first arrangement, which e.g. may be present in a first
network node, and/or in a network node according to the second
aspect.
[0176] FIG. 5b is a drawing schematically illustrating another
example of a first arrangement, which e.g. may be present in a
first network node, and/or in a network node according to the
second aspect.
[0177] FIG. 6 is a drawing schematically illustrating one example
of a user equipment (UE),
[0178] FIG. 7 is a flowchart schematically illustrating a method,
e.g. according to the third aspect, which may be performed in the
second network node. Said method may also be performed in a network
node of similar type.
[0179] FIG. 8 is a drawing schematically illustrating one example
of a second arrangement, which e.g. may be present in a second
network node, and/or in a network node according to the second
aspect.
[0180] FIG. 9 is a drawing schematically illustrating one example
of a base station (BS),
ABBREVIATIONS
[0181] UE User Equipment [0182] RB Resource Block [0183] RE
Resource Element [0184] RW Resource Window [0185] I_d Interference
on data symbols [0186] I_RS Interference on reference symbols
[0187] CPICH Common pilot channel [0188] RSRP Reference symbol
received power [0189] RSRQ Reference symbol received quality [0190]
RSSI Received signal strength indicator [0191] PBCH Physical or
primary broadcast channel [0192] PDSCH Physical downlink shared
channel [0193] D-BCH Dedicated or secondary broadcast channel
[0194] P-SCH Primary synchronization channel [0195] S-SCH Secondary
synchronization channel [0196] PSS Primary synchronization sequence
[0197] SSS Secondary synchronization sequence
DETAILED DESCRIPTION
[0198] The, or one, general idea is to measure or estimate the
interference part of the neighbour cell quality measurement (e.g.
RSRQ) from serving and neighbour cells during silent grid of
resource element, or during a silent resource element grid.
Currently, or in the background art, the interference part of
neighbour cell quality measurement, e.g. RSRQ, includes
contribution from the serving cell as well. The methods and
arrangements in, or according to, the present invention will ensure
that neighbour cell quality measurement, e.g. RSRQ, contains only,
or substantially only, inter-cell interference. This will enable
more accurate estimation or calculation of RSRQ or quality since in
OFDMA intra-cell interference is often negligible.
[0199] In the following, various embodiments and alternatives of
the invention and its features will be described.
[0200] Briefly described, the present invention involves a method/s
and arrangement/s for neighbour cell quality measurements in a
telecommunications system, using a silent resource element
grid.
[0201] In more detail, the invention includes the following general
steps and features, and example realizations. In the following
focus is put on the data channel, but the same approach, with
straightforward modifications, may be also applied to estimate the
interference that hits the control channel. The invention will
partly be described with reference to the drawings but the
information stated is not limited to any specific example or
embodiment but can be generally deployed or used.
Designing the Silent Grids
[0202] Several aspects should be kept, or are suitable to keep, in
mind when designing the silent resource element grid.
[0203] 1. The interference on, or hitting, the silent resource
element grid should suitably reflect the interference statistics of
the data channel as a whole. Therefore the distribution of silent
REs over the data channel should suitably be as uniform as
possible. But also if the distribution of silent REs over the data
channel is not as uniform as it could be, using a silent resource
element grid is advantageous.
[0204] 2. The silent resource element grid should preferably or
suitably be pseudo-random in the sense that it suitably should
change over time and/or frequency to avoid significant long-term
overlap with silent grids of neighbouring cells. The silent
resource element grid may also be used without being changing over
time and/or frequency, e.g. being pseudo-random.
[0205] It should be noted that, concerning silent resource element
grids changing over time and/or frequency, the invention is not
limited to pseudo-random silent resource element grids; for
example, an alternative method is to coordinate the silent resource
element grids of neighbouring cells such that no significant
overlap occur. Such an approach does, or may, however result in
significant deployment difficulties as it typically requires
careful planning.
[0206] 3. The UEs should preferably, or suitably, be able to
readily derive which silent resource element grid that is being
used with little or preferably no control signaling overhead.
[0207] Note that the invention is not limited to this constraint,
even though it is preferable or suitable; it is conceivable to use
explicit signaling of the silent resource element grid layout.
[0208] 4. Clustering of the silent REs in one or a few RBs should
preferably or suitably be avoided for improved sample statistics.
This is illustrated by an example below. [0209] a. For example
assume there are 2 silent resource elements (RE) every 5.sup.th
resource block (RB) in a cell and maximum of 4 silent RE are
allowed in one RB. Hence out of 12 RE in a RB, 4 are silent RE.
This means in total there are 4 silent RE per RB in all cells. In
case of 10 MHz cell, i.e. containing 50 RB, the entire silent grid
per cell comprises of 20 RE i.e. 2 RE every 5.sup.th RB. Thus in
total there are: 10.times.2=20 unique silent RE grids, which can be
used in different cells. This is because in different cells the
resource blocks containing the silent RE could be different. For
instance in one cell the first RB containing the silent RE is also
the first RB in numerological order, the next one is 5.sup.th and
so on. But in another cell the first RB containing the silent RE
can be the second RB in numerological order, the next one is
6.sup.th and so on. This means a silent grid is to be reused after
every 20.sup.th cell in this example.
[0210] One scheme that achieves these four criteria is as follows:
[0211] For each sub frame the RBs are suitably grouped into
resource windows (RW). [0212] Each RW is suitably a group of
contiguous, e.g. in frequency, RBs. [0213] The number of RBs in
each RW is suitably configured semi-statically. [0214] As special
cases, there could be only one RW that represents the entire system
bandwidth, or there could be a RW for each RB. For neighbour cell
quality measurement it should preferably or suitably be over the
entire system bandwidth. That is, it is suitable that one RW
represents the entire system bandwidth. [0215] For each RW,
suitably all REs that are not control or RS signaling are
enumerated [0216] In each RW, suitably a specified number of silent
REs are selected from the set of enumerated REs, e.g.; [0217] using
a pseudo-random number generator that generates numbers uniformly
in the range of the enumerated REs, e.g. data REs. The grouping
into RWs will ensure that clustering of silent REs is sufficiently
limited. [0218] As an alternative to using a pseudo-random number
generator it is also possible that the silent resource element grid
is altered periodically in all cells. Suitably the UE knows, or is
informed of, the current pattern for this periodical alteration in
the serving cell. For example a certain pattern may start every
frame number k in serving cell `s` whose cell ID is known. The UE
can then derive the current pattern for a silent resource element
grid in a neighbour cell i from its cell ID, i.e. the cell ID of
the neighbor cell i. For example, when cell `s` uses a certain
silent resource element grid N, then at the same time cell i uses a
certain silent resource element grid M. This relation [0219] The
number of selected silent REs may e.g. be a) fixed, b) derived from
the number of RBs in each RW or c) semi-statically configured.
[0220] In alternative a) the number of silent REs depends upon how
many REs that it is acceptable to use or sacrifice for the
inter-cell interference measurement, instead of using them for e.g.
data transmission. The number of silent REs also depends on the
cell BW. One may say that the number of silent REs is proportional
to the cell BW and/or to the total number of RBs. [0221] In
alternative b) this may e.g. be implemented as follows: assuming
that it is allowed to have 2 silent REs every 5.sup.th RB in a cell
and a maximum of 4 silent RE in one RB. Then there are a total of 4
silent REs per RB. Hence, out of 12 RE in a RB, 4 are silent RE.
Then, if the cell BW is 10 MHz, meaning 50 RBs are present, then
the entire silent resource element grid per cell comprises 20
silent? RE. [0222] In total there are: 10.times.2=20 silent RE
grids available. They suitably should be reused after every
20.sup.th cell. [0223] In alternative c) this may e.g. be
implemented as follows: By manual configuration or by an operation
and maintenance function which connects to the base station (BS)
for configuring various parameters. Another possibility is to use a
self optimized network (SON), which automatically configures
various BS parameters and which also could configure the silent
resource element grid.
[0224] The scheme can also readily be generalized to let a RW
constitute only a part of a RB in the time domain. For example, the
OFDM symbols in the RB can be grouped so that symbols including RS
symbols, and data symbols, are mapped to RW_RS and OFDM symbols
carrying only data are mapped to RW_d. For example, the OFDM
symbols in the RB can be grouped so that symbols including RS
symbols, and data symbols, are mapped to RW_RS and OFDM symbols
carrying only data are mapped to RW_d. Hence, RW_RS represents a
set or group of OFDM symbols which contain only RS in a RB.
[0225] It is also conceivable to use a different number of silent
REs in RW_RS and, or than in, RW_d. Such a separation of the OFDM
symbols can be useful since the inter-cell interference that hit
RW_RS and RW_d will have different interference statistics. This in
turn would lead to different estimation of downlink quality. For
instance from neighbor cell measurement perspective, the
interference statistics based on RW_d is beneficial as it would
depict the actual cell quality.
[0226] Another advantage of the present invention is that the power
that may be saved by remaining silent on some REs may be
redistributed to boost the power on other REs that carry data or
reference symbols. Such power reallocation combined by the
preceding method of, or part on, assigning different OFDM symbols
to different RW categories, can be a useful approach to reallocate
the power within OFDM symbols. This for example in order to support
different powers on the REs carrying RS and the REs carrying data
in the same OFDM symbol.
Determining the Silent RE Grid
[0227] As indicated in the preceding, it is, or may be, beneficial
to let the silent RE grid be generated pseudo-randomly to
transparently avoid consistent grid-overlap, or overlap of silent
resource element grids, with neighbouring cells. It is therefore
necessary or suitable to synchronize the pseudo-random generators
used at the NodeB, or base station, with those in the UEs. A simple
or straight forward scheme for synchronizing the pseudo-random
generators is to reinitialize the pseudo-random generators in each
frame using a seed that is derived from: [0228] 1. Cell identity
(cell ID) to provide uniqueness for each cell. [0229] 2. Frame
index to provide hopping over time.
[0230] Both the cell ID and the frame index are available at the
UEs. In E-UTRAN the cell ID is mapped on the synchronization
channel, SCH, (P-SCH or PSS and S-SCH or SSS) as well as on the
reference symbols. Therefore the UE acquires the entire cell ID
from P-SCH or PSS and S-SCH or SSS signals during the
synchronization procedure of each cell. The UE has to acquire the
cell ID of all the necessary neighbour cells. This means it, or the
UE, can easily derive the silent RE grid used in all the neighbour
cells without reading any additional information such as a/the
broadcast channel. In this case the procedure is, or can be, as
follows: The UE first acquires the silent RE grid in a cell and
then measures the interference during this silent RE grid. This in
turn is used to measure or calculate the neighbour cell quality of
this particular cell.
[0231] Note that any re-initialization interval of the
pseudo-random number generator can be used as long as there is a
suitable index available at the UE and that can be used to progress
the seed over time; this includes, but is not limited to, a sub
frame, or groups of frames.
[0232] Another possibility is that in E-UTRAN the seed or the index
of the silent RE grid used in a cell is signaled via the primary or
the physical broadcast channel (P-BCH or PBCH) rather than being
mapped to the cell ID. It is relatively easier for the UE to read
the P-BCH or the PBCH compared to the full fledge dedicated
broadcast channel (D-BCH), which is mapped on to downlink shared
channel, i.e. PDSCH (Physical Downlink Shared CHannel). The D-BCH
contains the entire system information, which is transmitted in the
form of blocks of data called as system information blocks (SIB).
But in principle the seed or index of the silent RE grid can also
be transmitted via D-BCH. In another embodiment, or as an
alternative, the silent grid RE, or silent resource element grid,
information sent in a cell can be split into two parts: one static
part mapped on cell ID and one semi-static part transmitted via a
broadcast channel i.e. P-BCH, PBCH or D-BCH. In either of these
methods or cases, which use P-BCH, PBCH, or D-BCH, the UE will have
to first read the P-BCH, PBCH or D-BCH, depending on where it is
sent or which channel that is used, of a neighbour cell to acquire
the complete information about the silent RE grid used in that
cell. After acquiring the silent grid RE pattern, or the pattern of
the silent resource element grid, the UE shall perform the
neighbour cell quality measurement.
[0233] An, or one, important aspect of the invention is, as already
mentioned, that the inter-cell interference for neighbour cell
quality measurement from, or regarding, cell i is measured during
the silent RE grid in cell i, thus avoiding the contribution from
serving-cell signal into the interference statistic. The inter-cell
interference estimation is further elaborated in the following.
Measuring the Inter-Cell Interference
[0234] The silent RE grid is used by the UEs to collect statistics
of the inter-cell interference that hit the data channel or the
control channel. If the silent RE grid is uniformly distributed
over the data channel, as suggested in the preceding, the
interference samples collected in the silent RE grid will, over
time, be the same as the interference that hit the data channel as
a whole. These samples can thus be utilized by the UE to estimate:
[0235] The inter-cell interference power that hits the data
channel. [0236] The co-variance matrix of the inter-cell
interference that hits the data channel. This is particularly
useful if the UE has multiple antennas
[0237] The full probability distribution of the inter-cell
interference.
[0238] The measured statistics can be averaged over time and
frequency, in a similar manner as the approach proposed in
reference [3]. One important difference is that in case of the
neighbor cell quality measurement the averaging in time is done
over considerably longer period of time compared to that used for
CQI estimation. In case of CQI the averaging is over one or more
sub-frames. This is further explained below.
[0239] The silent resource element grid is suitably continuously
available, e.g. in every sub-frame, i.e. every 1 ms. But the
neighbour cell quality measurement is done over a certain
measurement period using periodical samples e.g. over a measurement
period of 200 ms where each sample may be of 2 ms and may be taken
with 50 ms periodicity, i.e. 4 samples of 2 ms in a 200 ms
measurement period in this example.
[0240] As explained in the preceding sections, this inter-cell
interference measurement sample will be used in Equation (1) or
more specifically in Equation (2) to obtain the cell quality
measurement i.e. or e.g. RSRQ. But the invention is applicable to
any type of quality measurement which incorporates the interference
component.
[0241] The described subject matter is of course not limited to the
above described embodiments, alternatives and examples, but can be
modified within the scope of the general concept of the
invention.
REFERENCES
[0242] [1] 3GPP TS 25.215, "Physical layer measurements (FDD)".
[0243] [2] 3GPP TS 36.214, "Evolved Universal Terrestrial Radio
Access (E UTRA); Physical layer measurements". [0244] [3]
R1-074855, CQI Measurement Methodology, Ericsson, 3GPP RAN1#51,
Korea.
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