U.S. patent application number 14/651905 was filed with the patent office on 2015-11-05 for controlled synchronization group selection.
The applicant listed for this patent is NOKIA TECHNOLOGIES OY. Invention is credited to Juha S. KORHONEN, Cassio RIBEIRO.
Application Number | 20150319723 14/651905 |
Document ID | / |
Family ID | 51209081 |
Filed Date | 2015-11-05 |
United States Patent
Application |
20150319723 |
Kind Code |
A1 |
KORHONEN; Juha S. ; et
al. |
November 5, 2015 |
CONTROLLED SYNCHRONIZATION GROUP SELECTION
Abstract
Methods, apparatuses, and computer program products for
synchronization in a network are provided. One method includes
configuring a first node for joining a first timings
synchronization group with a second node on a lowest stratum,
receiving at least one synchronization signal comprising
information on at least an identity of the second node, and
synchronizing the first node to the first synchronization group
based on the synchronization signal.
Inventors: |
KORHONEN; Juha S.; (Espoo,
FI) ; RIBEIRO; Cassio; (Espoo, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NOKIA TECHNOLOGIES OY |
Espoo |
|
FI |
|
|
Family ID: |
51209081 |
Appl. No.: |
14/651905 |
Filed: |
January 17, 2014 |
PCT Filed: |
January 17, 2014 |
PCT NO: |
PCT/IB2014/058361 |
371 Date: |
June 12, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61754269 |
Jan 18, 2013 |
|
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Current U.S.
Class: |
370/350 |
Current CPC
Class: |
H04W 72/005 20130101;
H04W 4/08 20130101; H04W 56/0015 20130101; H04W 56/001 20130101;
H04W 72/042 20130101; H04J 3/0679 20130101; H04W 56/002
20130101 |
International
Class: |
H04W 56/00 20060101
H04W056/00; H04W 72/00 20060101 H04W072/00; H04W 72/04 20060101
H04W072/04; H04W 4/08 20060101 H04W004/08 |
Claims
1-35. (canceled)
36. A method, comprising: searching for synchronization sources in
a network; determining a group with a highest preference that can
be joined from a preference list; and joining the determined
group.
37. The method according to claim 36, further comprising reporting
the synchronization sources.
38. The method according to claim 36, further comprising, when it
is determined that none of the groups listed in the preference list
can be joined, joining an unlisted group.
39. The method according to claim 36, further comprising observing
a synchronization conflict, and reporting the conflict to a
network.
40. The method according to claim 36, further comprising receiving
an updated preference list for synchronization.
41. The method according to claim 36, wherein the preference list
comprises synchronization sources on several preference levels.
42. The method according to claim 36, wherein the preference list
comprises multiple, mutually synchronized sources on a same
preference level.
43. The method according to claim 36, further comprising receiving
a stratum information from at least one of the synchronization
sources.
44. The method according to claim 43, wherein the stratum
information is a broadcast information.
45. The method according to claim 43, wherein the stratum
information is carried in a physical broadcast channel or a
physical downlink shared channel resources.
46. An apparatus, comprising: at least one processor; and at least
one memory including computer program code, wherein the at least
one memory and the computer program code are configured, with the
at least one processor, to cause the apparatus at least to search
for synchronization sources in a network; determine a group with a
highest preference that can be joined from a preference list; and
join the determined group.
47. The apparatus according to claim 46, wherein the at least one
memory and the computer program code are further configured, with
the at least one processor, to cause the apparatus at least to
report the synchronization sources.
48. The apparatus according to claim 46, wherein the at least one
memory and the computer program code are further configured, with
the at least one processor, to cause the apparatus at least to,
when it is determined that none of the groups listed in the
preference list can be joined, join an unlisted group.
49. The apparatus according to claim 46, wherein the at least one
memory and the computer program code are further configured, with
the at least one processor, to cause the apparatus at least to
observe a synchronization conflict, and report the conflict to a
network.
50. The apparatus according to claim 46, wherein the at least one
memory and the computer program code are further configured, with
the at least one processor, to cause the apparatus at least to
receive an updated preference list for synchronization.
51. The apparatus according to claim 46, wherein the preference
list comprises synchronization sources on several preference
levels.
52. The apparatus according to claim 46, wherein the preference
list comprises multiple, mutually synchronized sources on a same
preference level.
53. The apparatus according to claim 46, wherein the apparatus
comprises at least one of a user equipment, a base station, an
evolved node B, or an access point.
54. The apparatus according to claim 46, wherein the at least one
memory and the computer program code are further configured, with
the at least one processor, to cause the apparatus at least to
receive a stratum information from at least one of the
synchronization sources.
55. The apparatus according to claim 54, wherein the stratum
information is a broadcast information.
56. The apparatus according to claim 54, wherein the stratum
information is carried in a physical broadcast channel or a
physical downlink shared channel resources.
57. A computer program, embodied on a computer readable medium, the
computer program configured to control a processor to perform a
process, comprising: searching for synchronization sources in a
network; determining a group with a highest preference that can be
joined from a preference list; and joining the determined group.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application No. 61/754,269, filed on Jan. 18, 2013. The entire
contents of this earlier filed application is hereby incorporated
by reference in its entirety.
BACKGROUND
[0002] 1. Field
[0003] Embodiments of the invention generally relate to wireless
communication systems, such as, but not limited to, the Universal
Mobile Telecommunications System (UMTS) Terrestrial Radio Access
Network (UTRAN), Long Term Evolution (LTE) Evolved UTRAN (E-UTRAN),
and/or LTE-Advanced (LTE-A).
[0004] 2. Description of the Related Art
[0005] Universal Mobile Telecommunications System (UMTS)
Terrestrial Radio Access Network (UTRAN) refers to a communications
network including base stations, or Node Bs, and for example radio
network controllers (RNC). UTRAN allows for connectivity between
the user equipment (UE) and the core network. The RNC provides
control functionalities for one or more Node Bs. The RNC and its
corresponding Node Bs are called the Radio Network Subsystem (RNS).
In case of E-UTRAN (enhanced UTRAN) no RNC exists and most of the
RNC functionalities are contained in the eNodeB (evolved Node B,
also called E-UTRAN Node B).
[0006] Long Term Evolution (LTE) or E-UTRAN refers to improvements
of the UMTS through improved efficiency and services, lower costs,
and use of new spectrum opportunities. In particular, LTE is a 3rd
generation partnership project (3GPP) standard that provides for
uplink peak rates of at least 50 megabits per second (Mbps) and
downlink peak rates of at least 100 Mbps. LTE supports scalable
carrier bandwidths from 20 MHz down to 1.4 MHz and supports both
Frequency Division Duplexing (FDD) and Time Division Duplexing
(TDD). Advantages of LTE are, for example, high throughput, low
latency, FDD and TDD support in the same platform, an improved
end-user experience, and a simple architecture resulting in low
operating costs.
[0007] Further releases of 3GPP LTE (e.g., LTE Rd-11, LTE-Rel-12)
are targeted towards future international mobile telecommunications
advanced (IMT-A) systems, referred to herein for convenience simply
as LTE-Advanced (LTE-A). LTE-A is directed toward extending and
optimizing the 3GPP LTE radio access technologies. A goal of LTE-A
is to provide significantly enhanced services by means of higher
data rates and lower latency with reduced cost. LTE-A will be a
more optimized radio system fulfilling the international
telecommunication union-radio (ITU-R) requirements for IMT-Advanced
while keeping the backward compatibility.
SUMMARY
[0008] One embodiment is directed to a method including configuring
a first node for joining a first synchronization group with a
second node on a lowest stratum, receiving at least one
synchronization signal comprising information on at least an
identity of the second node, and synchronizing the first node to
the first synchronization group based on the synchronization
signal.
[0009] In one embodiment, the synchronization signal comprises an
indication of a stratum ordinal, and the stratum ordinal may
comprise the lowest ordinal among the at least one synchronization
signal from the first synchronization group.
[0010] According to an embodiment, the receiving may comprise
receiving the at least one synchronization signal from a third
node, and the third node may be a member of the first
synchronization group.
[0011] In an embodiment, the method may further comprise
transmitting another synchronization signal comprising an
indication of the second node of the first synchronization group.
In another embodiment, the method may further comprise reporting
synchronization sources, and the synchronization sources may
comprise a list of observed strata originating from different macro
cells and ordinals of the strata the first node can join.
[0012] According to an embodiment, the method may further comprise
reporting a node on the lowest stratum to a network or a network
device. In an embodiment, the method may further comprise receiving
a configuration for the first node to join a second synchronization
group, and the configuration may be based on the reporting.
[0013] In an embodiment, the second synchronization group may be
different from the first synchronization group. According to one
embodiment, the method may further comprise reporting resource
utilization.
[0014] According to another embodiment, the method may further
comprise observing a synchronization conflict, and reporting the
conflict to a network or a network device. In one embodiment, the
first node may be a base station, an enhanced node B, an access
point, or a user equipment.
[0015] Another embodiment is directed to an apparatus including at
least one processor, and at least one memory comprising computer
program code. The at least one memory and the computer program code
are configured, with the at least one processor, to cause the
apparatus at least to configure a first node or the apparatus for
joining a first synchronization group with a second node on a
lowest stratum, receive at least one synchronization signal
comprising information on at least an identity of the second node,
and synchronize the first node to the first synchronization group
based on the synchronization signal.
[0016] In some embodiments, the apparatus may be a unit, device,
component, function, and/or means allocated within the first node.
In other embodiments, the apparatus may be the first node
itself.
[0017] Another embodiment is directed to a computer program
embodied on a computer readable medium. The computer program is
configured to control a processor to perform a process including
configuring a first node for joining a first synchronization group
with a second node on a lowest stratum, receiving at least one
synchronization signal comprising information on at least an
identity of the second node, and synchronizing the first node to
the first synchronization group based on the synchronization
signal.
[0018] Another embodiment is directed to an apparatus including
means for configuring a first node or the apparatus for joining a
first synchronization group with a second node on a lowest stratum,
means for receiving at least one synchronization signal comprising
information on at least an identity of the second node, and means
for synchronizing the first node to the first synchronization group
based on the synchronization signal.
[0019] Another embodiment is directed to a method including
configuring, for example by a network function, a first node for
joining a first synchronization group with a second node on a
lowest stratum. In one embodiment, the configuring may be based on
the first node's reports on synchronization sources or
synchronization conflicts. In some embodiments, the network
function may run or be comprised in an eNB. In other embodiments,
the network function may run or be comprised in a UE (e.g., cluster
head).
[0020] Another embodiment is directed to an apparatus including at
least one processor, and at least one memory comprising computer
program code. The at least one memory and the computer program code
are configured, with the at least one processor, to cause the
apparatus at least to configure a first node for joining a first
synchronization group with a second node on a lowest stratum. In
one embodiment, the configuring may be based on the first node's
reports on synchronization sources or synchronization conflicts. In
some embodiments, the apparatus may comprise a network function
that may run or be comprised in an eNB. In other embodiments, the
apparatus may comprise a network function that may run or be
comprised in a UE (e.g., cluster head).
[0021] Another embodiment is directed to a computer program
embodied on a computer readable medium. The computer program is
configured to control a processor to perform a process including
configuring, for example by a network function, a first node for
joining a first synchronization group with a second node on a
lowest stratum. In one embodiment, the configuring may be based on
the first node's reports on synchronization sources or
synchronization conflicts. In some embodiments, the network
function may run or be comprised in an eNB. In other embodiments,
the network function may run or be comprised in a UE (e.g., cluster
head).
[0022] Another embodiment is directed to an apparatus including
configuring means for configuring a first node for joining a first
synchronization group with a second node on a lowest stratum. In
one embodiment, the configuring means may configure the first node
based on the first node's reports on synchronization sources or
synchronization conflicts. In some embodiments, apparatus may
comprise a network function that may run or be comprised in an eNB.
In other embodiments, the apparatus may comprise a network function
that may run or be comprised in a UE (e.g., cluster head).
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] For proper understanding of the invention, reference should
be made to the accompanying drawings, wherein:
[0024] FIG. 1 illustrates a system according to one embodiment;
[0025] FIG. 2 illustrates a system according to another
embodiment;
[0026] FIG. 3 illustrates a system according to another
embodiment;
[0027] FIG. 4 illustrates a flow diagram of a method according to
an embodiment;
[0028] FIG. 5 illustrates a flow diagram of a method according to
another embodiment;
[0029] FIG. 6a illustrates an apparatus according to one
embodiment; and
[0030] FIG. 6b illustrates an apparatus according to another
embodiment.
DETAILED DESCRIPTION
[0031] It will be readily understood that the components of the
invention, as generally described and illustrated in the figures
herein, may be arranged and designed in a wide variety of different
configurations. Thus, the following detailed description of
embodiments of methods, systems, apparatuses, and computer program
products for synchronization of cells, as represented in the
attached figures, is not intended to limit the scope of the
invention, but is merely representative of selected embodiments of
the invention.
[0032] If desired, the different functions discussed below may be
performed in a different order and/or concurrently with each other.
Furthermore, if desired, one or more of the described functions may
be optional or may be combined. As such, the following description
should be considered as merely illustrative of the principles,
teachings and embodiments of this invention, and not in limitation
thereof.
[0033] Certain embodiments of the invention relate to mutual
synchronization of small cells, including small cells that are in
the presence of multiple synchronization sources provided by macro
cells.
[0034] Small cell enhancements have been subject to a 3GPP
RAN-level study item (SI) and considerations on the small cell
scenarios and requirements have been collected in the technical
report (TR) 36.932. This TR includes the following statement: "Both
synchronized and un-synchronized scenarios should be considered
between small cells as well as between small cells and macro
cell(s). For specific operations e.g. interference coordination,
carrier aggregation and inter-eNB COMP, small cell enhancement can
benefit from synchronized deployments with respect to small cell
search/measurements and interference/resource management. Therefore
time synchronized deployments of small cell clusters are
prioritized in the study and new means to achieve such
synchronization shall be considered." An example of a system
benefitting from synchronized small and macro cells is operating
all type of cells at the same carrier and with the time division
duplex (TDD) method. An example of a system where small cells layer
benefits from synchronization but macro cells are asynchronous is
operating small and macro cells on different carriers in the manner
that TDD is used with small cells while frequency division duplex
(FDD) is used with macro cells.
[0035] FIG. 1 illustrates a system including macro cells 101 and
small cells 105, according to one embodiment. One scenario of
interest, according to certain embodiments, is displayed in the
lower left corner of FIG. 1 where a group of small cells 105 are
only partly in the coverage area of macro cells 101 of one eNB 100.
The small cells 105 that are not on the coverage of the macro cells
101 of eNB 100 could be under the coverage of the macro cells of
another eNB or some of them could be without any macro cell
coverage or with coverage of multiple macro cells.
[0036] One solution that has been considered for the
synchronization of TDD home eNodeBs (HeNBs) is stratified
over-the-air synchronization. According to this solution, the
lowest stratum is the macro cells that are assumed to be
synchronized, for instance by a global navigation satellite system
(GNSS), the second lowest stratum are the small cells that are able
to synchronize directly to a macro cell by listening the macro
cell's signal, and, generally, a cell on stratum N can synchronize
to a cell on stratum N-1 but not to any cell on a stratum below
N-1. It has been assumed that macro cells are synchronized or small
cells are isolated inside a macro cell. Therefore, this method does
not provide solution in the case of asynchronous macro cells.
Furthermore, these earlier considerations were done for co-channel
macro and small cells, in which the synchronization between small
and macro cells is essential.
[0037] Some embodiments consider the case where small and macro
cells are on different bands (or carriers). Accordingly, it may not
be essential to maintain common timing in the macro and small
cells, but small cells within a macro cell can join a small cell
group that is mainly under another macro cell.
[0038] There are multiple examples of distributed synchronization
methods, i.e., methods where synchronization is obtained without an
external synchronization source. One example is WiFi independent
basic service set (IBSS) synchronization that is based on
over-the-air exchange of time stamps in such a manner that a node
adopts the timing of another node if the other node' s time is
later than the node's own time. That method could be used for
synchronizing locally a layer of small cells.
[0039] In view of the above, small cell synchronization can pose a
number of challenges. For example, small cells are not equipped
with global positioning system (GPS) receivers or they are deployed
outside the coverage of GPS signals, e.g., indoors. Also, backhaul
connections of the small cells cannot always be assumed to be
suitable for utilizing precision time protocol. In the absence of
GPS receivers and good enough backhaul, cell synchronization could
be based on signals that are received over-the-air from other
cells, as it has been proposed for the synchronization of TDD
HeNBs. However, macro cells cannot always provide a coherent time
reference because the small cells to be synchronized may hear
different asynchronous macro cells. Macro cells on an FDD band are
typically assumed to be asynchronous.
[0040] FIG. 2 illustrates an example of a system where over-the-air
synchronization is assumed and the synchronization configuration of
small cells is shown in the presence of asynchronous macro cells 1
and 2. It would be natural to specify that small cells synchronize
to the macro cell with the strongest signal or, when lacking a
macro cell signal, to the small cell at lowest stratum. However,
such an approach would not allow any steering of the small cell
synchronization, which would be completely defined by the
deployment of the cells. Therefore, a more flexible synchronization
system would be desirable in order to control how the synchronized
groups form such that the effect of conflicting small cell
synchronizations are avoided or minimized In the example of FIG. 2,
specifying that a small cell synchronizes to the macro cell with
the strongest signal or to a small cell at the lowest stratum leads
to synchronization conflicts between small cells as some adjacent
small cells belong to different synchronization groups that are
depicted by the different colors in the figure. In this example, a
better grouping would be such that all the small cells, except the
three separated cells in the coverage of macro cell 2, would belong
to the same synchronization group. The three cells could form a
different synchronization group because of their separation from
the rest of the small cells.
[0041] Certain embodiments of the invention include procedures and
signaling for controlling cell synchronization, for example, in the
presence of multiple synchronization sources. Some embodiments
relate to cells being configured with a preference list of
synchronization sources, cells broadcasting information of their
source of synchronization, cells reporting observations on
synchronization sources, as well as a synchronization conflict
resolving method.
[0042] One aspect of the invention modifies the above proposed
stratified synchronization system in such a way that the small
cells can be instructed to join a synchronization group with a
particular cell on the lowest stratum. FIGS. 3a and b illustrate
synchronization of small cells in the presence of asynchronous
macro cells that are formed by different eNBs.
[0043] An example of conventional stratified synchronization of
three small cells in the presence of two macro eNBs is illustrated
in FIG. 3a, where the lines with arrow heads are drawn from the
source of synchronization. Assuming the small cells 1 and 2 can
hear macro cells formed by eNBs 1 and 2 respectively,
correspondingly, they synchronize to each of those macro cells
covered by eNBs 1 and 2 because, conventionally, the source of
synchronization should be a node on the lowest heard stratum. Small
cell 3 might not hear any macro cells and could then synchronize,
for example, to small cell 2. If the macro cells were not
synchronized, the neighboring cells 1 and 3 would be asynchronous.
Accordingly, in the example of FIG. 3a, the small cells synchronize
to the cell with lowest stratum. The situation can be improved if
the network can configure the small cells to synchronize, directly
or through strata, to a certain macro cell. The small cells would
then indicate, for example via synchronization signal, their
stratum ordinal and also the identity of the synchronization source
on the lowest stratum.
[0044] An improved synchronization configuration is shown in FIG.
3b. The small cell 1 has been configured to join preferably the
stratified synchronization with macro eNB2 on the lowest stratum.
Therefore, if it hears small cell 3, it chooses that as a
synchronization source although that would lead it to the fourth
lowest stratum instead of the second lowest that would have been
provided by synchronization to eNB1. The configuration of FIG. 3b
could be desired, for instance, if the three small cells were
coupled strongly together but to a lesser extent to the small cells
in the surroundings. This could be the case, for instance, if the
three small cells were indoors in the same building or were
deployed for a hotspot without other small cells in the
vicinity.
[0045] Accordingly, one embodiment provides a preference list of
synchronization sources to cells. In an embodiment, instead of just
a single most preferred timing reference, the preference list could
contain multiple, mutually synchronized sources on the same
preference level.
[0046] Another embodiment is directed to deployment of the small
cells with the best macro cell on the lowest stratum. In some
cases, for example with small cells in an office building or
shopping mall, the operator could know rather well the coverage of
macro cells within the small cell covered region, and could base
selection of the preferred macro cell on this prior knowledge by,
for example, choosing the macro cell covering the largest number of
small cells as the reference with highest preference.
[0047] However, utilizing only prior knowledge may not always be
sufficient, and reaching the optimal configuration could require
small cell measurements and creating a report about the possible
synchronization sources. For instance, such a report could include
a list of the observed strata originating from different macro
cells and the corresponding ordinals of the strata the small cell
could join. Based on the signaling, the network could keep a record
on the relative timings of the small cells, advise a small cell to
join the most suitable synchronization group, and optimize the use
of frequency and carrier resources for mitigating the effect of
conflicting timings.
[0048] The approach of controlling the formation of synchronization
groups can be generalized to all kinds of synchronization
procedures. For instance, instead of the selection between
synchronization groups with different macro cells in the lowest
stratum (like in FIGS. 3a and b), the selection could as well be
between a group of cells maintaining stratified synchronization and
another group of cells maintaining distributed synchronization
based on, for instance, WiFi IBSS type synchronization method.
Another generalization is that also a small cell could be assigned
to act as the synchronization source in the lowest stratum.
[0049] FIG. 4 illustrates a flow diagram of an example of a
synchronization method, according to one embodiment. In an
embodiment, the method of FIG. 4 may be performed by a base
station, eNB, and/or access point (AP) for a small cell, for
example. As shown in FIG. 4, a small cell is switched on at 400. At
410, the method includes searching for synchronization sources. The
method may then include, at 420, reporting the synchronization
sources to the network. At 430, the method includes receiving a
preference list for synchronization.
[0050] In certain embodiments, the step of reporting
synchronization sources to network, at 420, may be optional. As a
result, in some embodiments, the preference list may be updated
even without any preceding reporting.
[0051] When the preference list is made, several factors may be
taken into account besides the information reported by a cell at
step 420. There may be prior knowledge about the possible
synchronization sources based on knowledge of the location of
cells. Cells in a dense group could be preferably configured with
the same most preferred synchronization source. On the other hand,
even neighboring small cells could in some cases be configured with
different most preferred synchronization source if it is seen
reasonable to make a border of two synchronization groups between
the two cells. Configuring a cell with a preference list containing
sources on several preference levels could be important if the cell
is located on the coverage border region of macro cells. The
highest priority could be given for the macro cell where most of
the small cells in the neighborhood can synchronize to while lower
priorities are given for other macro cells that the cell might be
able to synchronize to if for instance interference occasionally
prevents synchronization to the most preferred source.
[0052] Returning to FIG. 4, at 440, it is determined whether the
cell can join the group with the highest preference from the
preference list. If it can, at 445, the cell maintains the
synchronization to the group with the highest preference from the
preference list. If it cannot join the group with the highest
preference from the preference list, then, at 450, it is determined
whether the cell can join the group with the second highest
preference from the preference list. If it can, at 455, the cell
maintains the synchronization to the group with the second highest
preference from the preference list. If it cannot join the group
with the second highest preference from the preference list, the
method continues with the cell attempting to join the group with
the next highest preference until at 460, it is determined whether
the cell can join the group with the lowest preference from the
preference list. If it can, at 465, the cell maintains the
synchronization to the group with the lowest preference from the
preference list. If none of the preferred and listed
synchronization groups can be joined, at 470, it is determined
whether the cell can synchronize with an unlisted group. If it can
synchronize with an unlisted group, at 475, the cell may join to an
unlisted synchronization group that could maintain synchronism with
a stratified synchronization method or with a distributed method,
such as WiFi IBSS mode synchronization. If it is determined that it
cannot synchronize with an unlisted group, the method returns to
step 410.
[0053] After a cell has joined to a synchronization group at steps
445, 455, 465, or 475, it may from time to time return to the step
410 of searching synchronization sources in order check if changes
have taken place. Such changes may happen, for instance, when new
small cells are deployed to the system or earlier deployed cells
are switched on or off, or when cell coverage areas are tuned or
changing when load and interference level are changing in the
system. The return to searching of synchronization sources 410 may
take place periodically as configured by the network, or be
triggered by the network when changes are supposed to take place,
or be based on an event observed by the synchronizing cell. An
example of an event causing the return to step 410 is the cell
losing the connection to its synchronization group. Another example
is the cell observing severe synchronization conflict either
directly, or based on UE reporting or by over-the-air or backhaul
signaling from other cells.
[0054] According to an embodiment, each small cell that can act as
a synchronization source may broadcast information about its
stratum, as well as the macro eNB used as the reference. Such
information can be included, for example, in a physical broadcast
channel (PBCH) or similar channel, or else transmitted using
physical downlink shared channel (PDSCH) resources. In this case,
the utilized PDSCH resources can be pre-defined or scheduled using
proper identifiers.
[0055] According to an embodiment, in order to save radio
resources, a small cell may send information on its stratum and
synchronization reference through backhaul instead of broadcasting.
A small cell hearing another small cell could contact the other
cell through backhaul to ask the other cell's information or to
send its own information to the other cell.
[0056] There may be situations where synchronization cannot be
achieved within the small cell cluster due to deployment
characteristics and configuration of preferred synchronization
sources. For example, if the small cell 1 in FIG. 3b is configured
to use macro eNB1 as preferred synchronization source, while small
cell 3 is configured to use macro eNB2 as the preferred
synchronization source, then a conflict exists. In this case, small
cell 1 can send synchronization reports to macro eNB 1 indicating
this conflict, and corresponding action can be taken in the network
to handle it, for example, reconfiguring any of the small cells in
FIG. 3b to use a common synchronization source.
[0057] FIG. 5 illustrates a flow diagram of a method for reporting
and resolving synchronization conflicts, according to one
embodiment. The method may include, at 500, searching for
synchronization sources. At 510, the method includes observing a
synchronization conflict and, at 520, reporting the conflict to the
network. The method may also include, at 530, receiving an updated
preference list for synchronization.
[0058] In some situations this conflict resolution procedure may
not be possible, for example, if the Macro eNBs in FIG. 3 belong to
different operators, which are sharing the spectrum for the small
cells. In order to handle these remaining conflicts, the small
cells can transmit information about their resource utilization,
either together with the synchronization information or as a
separate message. The resource utilization can include the
frequency resources utilized by the small cell, such as which
carriers are utilized. This information can be included in the
synchronization reports sent to each corresponding macro eNB, which
in turn can utilize this information for interference
management.
[0059] Hence, the information broadcast or sent through backhaul by
small cells can, for example, include: [0060] For synchronization:
[0061] Stratum number [0062] Reference macro cell used for
synchronization [0063] Optional, for interference management in
critical synchronization situations: [0064] Resource utilization
[0065] Transmit power [0066] Maximum transmit power
[0067] Information contained in the synchronization report can, for
example, include: [0068] ID of identified small cells, together
with: [0069] Stratum number [0070] Reference macro cell used for
synchronization [0071] Resource utilization [0072] Received power,
estimated path loss, or similar
[0073] It should be noted that many combinations are possible for
the report, according to different embodiments. For example, the
small cells may order the detected small cells according to their
reference macro eNBs and report only the most relevant small cell
in each group. As another example, in case two small cells are
detected in strata 1 and 2, both using macro eNB2 as reference, the
report may include only the small cell belonging to stratum 1.
Other small cells using other Macro eNBs as reference would still
be included in the report.
[0074] In an embodiment, if the synchronization group selection
method is generalized to also cover selection between stratified
and distributed synchronization systems, the broadcast information
and synchronization report would indicate the synchronization
method used by the cells.
[0075] While the description above focuses on the roles of eNBs in
the synchronization and conflict reporting, the UEs may also
provide assistance, in particular in identifying and reporting
synchronization conflicts. For example, the UE may be required to
listen to neighboring cells and report to the network the
synchronization report. This can be particularly useful if the
synchronization groups are loosely connected, implying that the
eNBs may not be able to decode each other signals but UEs on cell
edge could receive signals from two or more cells belonging to
different synchronization groups. Such reporting could be
periodical or triggered by the network.
[0076] The information on the synchronization reports may also be
used by the eNB receiving the reports to adjust its own
synchronization according to synchronization groups reported by the
UEs.
[0077] In some embodiments, the functionality of any of the methods
described herein, such as those illustrated in FIGS. 4 and 5
discussed above, may be implemented by software and/or computer
program code stored in memory or other computer readable or
tangible media, and executed by a processor. In other embodiments,
the functionality may be performed by hardware, for example through
the use of an application specific integrated circuit (ASIC), a
programmable gate array (PGA), a field programmable gate array
(FPGA), or any other combination of hardware and software.
[0078] FIG. 6a illustrates an example of an apparatus 10 according
to an embodiment. In one embodiment, apparatus 10 may be a base
station (BS), such as an eNB, or access point (AP). It should be
noted that one of ordinary skill in the art would understand that
apparatus 10 may include components or features not shown in FIG.
6a. Only those components or feature necessary for illustration of
the invention are depicted in FIG. 6a.
[0079] As illustrated in FIG. 6a, apparatus 10 includes a processor
22 for processing information and executing instructions or
operations. Processor 22 may be any type of general or specific
purpose processor. While a single processor 22 is shown in FIG. 6a,
multiple processors may be utilized according to other embodiments.
In fact, processor 22 may include one or more of general-purpose
computers, special purpose computers, microprocessors, digital
signal processors (DSPs), field-programmable gate arrays (FPGAs),
application-specific integrated circuits (ASICs), and processors
based on a multi-core processor architecture, as examples.
[0080] Apparatus 10 further includes a memory 14, which may be
coupled to processor 22, for storing information and instructions
that may be executed by processor 22. Memory 14 may be one or more
memories and of any type suitable to the local application
environment, and may be implemented using any suitable volatile or
nonvolatile data storage technology such as a semiconductor-based
memory device, a magnetic memory device and system, an optical
memory device and system, fixed memory, and removable memory. For
example, memory 14 can be comprised of any combination of random
access memory (RAM), read only memory (ROM), static storage such as
a magnetic or optical disk, or any other type of non-transitory
machine or computer readable media. The instructions stored in
memory 14 may include program instructions or computer program code
that, when executed by processor 22, enable the apparatus 10 to
perform tasks as described herein.
[0081] Apparatus 10 may also include one or more antennas 25 for
transmitting and receiving signals and/or data to and from
apparatus 10. Apparatus 10 may further include a transceiver 28
configured to transmit and receive information. For instance,
transceiver 28 may be configured to modulate information on to a
carrier waveform for transmission by the antenna(s) 25 and
demodulates information received via the antenna(s) 25 for further
processing by other elements of apparatus 10. In other embodiments,
transceiver 28 may be capable of transmitting and receiving signals
or data directly.
[0082] Processor 22 may perform functions associated with the
operation of apparatus 10 including, without limitation, precoding
of antenna gain/phase parameters, encoding and decoding of
individual bits forming a communication message, formatting of
information, and overall control of the apparatus 10, including
processes related to management of communication resources.
[0083] In an embodiment, memory 14 stores software modules that
provide functionality when executed by processor 22. The modules
may include, for example, an operating system that provides
operating system functionality for apparatus 10. The memory may
also store one or more functional modules, such as an application
or program, to provide additional functionality for apparatus 10.
The components of apparatus 10 may be implemented in hardware, or
as any suitable combination of hardware and software.
[0084] As mentioned above, according to one embodiment, apparatus
10 may be a BS or AP. In an embodiment, apparatus 10 may be
controlled, by memory 14 and processor 22, to search for
synchronization sources, report the synchronization sources to the
network, receive a preference list of synchronization sources from
the network, determine a group with the highest preference from the
preference list that can be joined, and join the determined group.
If it is determined that none of the groups listed in the
preference list can be joined, apparatus 10 may be controlled, by
memory 14 and processor 22, to join an unlisted group.
[0085] FIG. 6b illustrates an example of an apparatus 20 according
to another embodiment. In an embodiment, apparatus 20 may be
network element. It should be noted that one of ordinary skill in
the art would understand that apparatus 20 may include components
or features not shown in FIG. 6b. Only those components or feature
necessary for illustration of the invention are depicted in FIG.
6b.
[0086] As illustrated in FIG. 6b, apparatus 20 includes a processor
32 for processing information and executing instructions or
operations. Processor 32 may be any type of general or specific
purpose processor. While a single processor 32 is shown in FIG. 6b,
multiple processors may be utilized according to other embodiments.
In fact, processor 32 may include one or more of general-purpose
computers, special purpose computers, microprocessors, digital
signal processors (DSPs), field-programmable gate arrays (FPGAs),
application-specific integrated circuits (ASICs), and processors
based on a multi-core processor architecture, as examples.
[0087] Apparatus 20 further includes a memory 34, which may be
coupled to processor 32, for storing information and instructions
that may be executed by processor 32. Memory 34 may be one or more
memories and of any type suitable to the local application
environment, and may be implemented using any suitable volatile or
nonvolatile data storage technology such as a semiconductor-based
memory device, a magnetic memory device and system, an optical
memory device and system, fixed memory, and removable memory. For
example, memory 34 can be comprised of any combination of random
access memory (RAM), read only memory (ROM), static storage such as
a magnetic or optical disk, or any other type of non-transitory
machine or computer readable media. The instructions stored in
memory 34 may include program instructions or computer program code
that, when executed by processor 32, enable the apparatus 20 to
perform tasks as described herein.
[0088] Apparatus 20 may also include one or more antennas 35 for
transmitting and receiving signals and/or data to and from
apparatus 20. Apparatus 20 may further include a transceiver 38
configured to transmit and receive information. For instance,
transceiver 38 may be configured to modulate information on to a
carrier waveform for transmission by the antenna(s) 35 and
demodulates information received via the antenna(s) 35 for further
processing by other elements of apparatus 20. In other embodiments,
transceiver 38 may be capable of transmitting and receiving signals
or data directly.
[0089] Processor 32 may perform functions associated with the
operation of apparatus 20 including, without limitation, precoding
of antenna gain/phase parameters, encoding and decoding of
individual bits forming a communication message, formatting of
information, and overall control of the apparatus 20, including
processes related to management of communication resources.
[0090] In an embodiment, memory 34 stores software modules that
provide functionality when executed by processor 32. The modules
may include, for example, an operating system that provides
operating system functionality for apparatus 20. The memory may
also store one or more functional modules, such as an application
or program, to provide additional functionality for apparatus 20.
The components of apparatus 20 may be implemented in hardware, or
as any suitable combination of hardware and software.
[0091] As mentioned above, according to one embodiment, apparatus
20 may be a network element. In this embodiment, apparatus 20 may
be controlled by memory 34 and processor 32 to receive information,
from one or more small cells, about stratum number and macro eNB(s)
used as reference for synchronization. Apparatus 20 may then be
controlled by memory 34 and processor 32 to create a preference
list including a ranking of the preference of the groups, and to
send the preference list to the small cell(s).
[0092] One embodiment is directed to a method for synchronization.
The method may include searching for synchronization sources, and
reporting the synchronization sources to the network. The method
may further include receiving a preference list of synchronization
sources from the network. The method may also include determining a
group with a highest preference that can be joined from the
preference list, and joining the determined group. The method can
include, if it is determined that none of the groups listed in the
received preference list can be joined, joining an unlisted
group.
[0093] Another embodiment is directed to a synchronization method
including receiving information about stratum number and macro
eNB(s) used as reference for synchronization from one or more small
cells. The method may then include creating a preference list
including a ranking of the preference of the groups, and sending
the preference list to the small cell(s).
[0094] Another embodiment is directed to a synchronization conflict
reporting and resolving method. The method may include searching
for synchronization sources, observing a synchronization conflict,
and reporting the conflict to the network. The method may also
include receiving an updated preference list for
synchronization.
[0095] Another embodiment is directed to an apparatus including at
least one processor and at least one memory including computer
program code. The at least one memory and the computer program code
may be configured, with the at least one processor, to cause the
apparatus at least to search for synchronization sources, report
the synchronization sources to the network, and receive a
preference list of synchronization sources from the network. The at
least one memory and the computer program code may be further
configured, with the at least one processor, to cause the apparatus
at least to determine a group with a highest preference that can be
joined from the preference list, and join the determined group. If
it is determined that none of the groups listed in the received
preference list can be joined, the apparatus may be controlled to
join an unlisted group.
[0096] Another embodiment is directed to an apparatus including at
least one processor and at least one memory including computer
program code. The at least one memory and the computer program code
may be configured, with the at least one processor, to cause the
apparatus at least to receive information about stratum number and
synchronization source(s) used as reference for synchronization
from one or more small cells, create preference lists including a
ranking of the preference of the groups, and send the preference
lists to the small cell(s).
[0097] Another embodiment is directed to an apparatus including at
least one processor and at least one memory including computer
program code. The at least one memory and the computer program code
may be configured, with the at least one processor, to cause the
apparatus at least to search for synchronization sources, observe a
synchronization conflict, report the conflict to the network, and
receive an updated preference list for synchronization.
[0098] In view of the above, certain embodiments provide
flexibility for steering small cell synchronization when different
synchronization sources are available. Embodiments can provide a
simpler and more stable method because each cell only needs to
follow timing of a single cell, instead of exchanging time stamps
with multiple cells the way that is done, for example, in the WiFi
IBSS mode synchronization.
[0099] One having ordinary skill in the art will readily understand
that the invention as discussed above may be practiced with steps
in a different order, and/or with hardware elements in
configurations which are different than those which are disclosed.
Therefore, although the invention has been described based upon
these preferred embodiments, it would be apparent to those of skill
in the art that certain modifications, variations, and alternative
constructions would be apparent, while remaining within the spirit
and scope of the invention.
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