U.S. patent application number 14/477961 was filed with the patent office on 2015-05-07 for method and arrangement in a telecommunication system.
The applicant listed for this patent is TELEFONAKTIEBOLAGET L M ERICSSON (PUBL). Invention is credited to Erik Dahlman, Ylva Jading, Niklas Johansson, Stefan Parkvall.
Application Number | 20150124685 14/477961 |
Document ID | / |
Family ID | 40999998 |
Filed Date | 2015-05-07 |
United States Patent
Application |
20150124685 |
Kind Code |
A1 |
Dahlman; Erik ; et
al. |
May 7, 2015 |
METHOD AND ARRANGEMENT IN A TELECOMMUNICATION SYSTEM
Abstract
Method and apparatus for avoiding or reducing interference
between transmissions from a donor eNB to a relay node and downlink
transmissions from the relay node to at least one mobile terminal,
where the transmissions take place in overlapping frequency bands.
In the method, at least one interruption is created in a
transmission from the relay node to the mobile terminal(s), and
during the created interruption, a transmission from the donor eNB
is received. This may result in an improved reception of the
transmission from the eNB in the relay node.
Inventors: |
Dahlman; Erik; (Stockholm,
SE) ; Jading; Ylva; (Stockholm, SE) ;
Parkvall; Stefan; (Bromma, SE) ; Johansson;
Niklas; (Sollentuna, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TELEFONAKTIEBOLAGET L M ERICSSON (PUBL) |
Stockholm |
|
SE |
|
|
Family ID: |
40999998 |
Appl. No.: |
14/477961 |
Filed: |
September 5, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13120034 |
Mar 21, 2011 |
8861420 |
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PCT/SE2009/050416 |
Apr 22, 2009 |
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14477961 |
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61098367 |
Sep 19, 2008 |
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Current U.S.
Class: |
370/312 ;
370/315 |
Current CPC
Class: |
H04B 7/15528 20130101;
H04B 7/14 20130101; H04L 25/24 20130101; H04W 84/047 20130101; H04W
4/06 20130101; H04W 72/14 20130101; H04W 72/1231 20130101; H04B
7/2606 20130101; H04W 72/0446 20130101 |
Class at
Publication: |
370/312 ;
370/315 |
International
Class: |
H04W 72/04 20060101
H04W072/04; H04W 4/06 20060101 H04W004/06; H04B 7/14 20060101
H04B007/14 |
Claims
1. A method for operating a relay node in a wireless communication
system, wherein the system includes an evolved Node B (eNB) for
sending first transmissions to the relay node, the relay node being
adapted for sending second transmissions to at least one mobile
terminal connected to the relay node, the first and second
transmissions taking place in overlapping frequency bands, the
method comprising the steps of: creating at least one interruption
in said second transmissions from the relay node to the at least
one mobile terminal; and, receiving, by the relay node, first
transmissions from the eNB during said at least one
interruption.
2. The method according to claim 1, wherein the at least one
interruption is created by using a Multicast/Broadcast Single
Frequency Network (MBSFN) subframe format for the second
transmissions.
3. The method according to claim 1, wherein said at least one
interruption is created by using a Multicast/Broadcast Single
Frequency Network (MBSFN) subframe format that is backwards
compatible with legacy mobile terminals.
4. The method according to claim 1, wherein said at least one
interruption is created by using a Multicast/Broadcast Single
Frequency Network (MBSFN) subframe format in which the subframe
contents are limited to reference symbols and control signalling,
which are allocated in less than 3 OFDM symbols of the
subframe.
5. The method according to claim 1, wherein the subframes of the
transmission from the eNB to the relay node are time-shifted one or
more OFDM symbol durations relative to the subframes of the second
transmissions.
6. The method according to claim 5, wherein the number of OFDM
symbol durations of the time shift is selected based on the
duration of a control region used in subframes within the cells of
the relay node.
7. The method according to claim 5, wherein a last part of at least
one subframe of the first transmissions from the eNB to the relay
node is left unused for transmission.
8. The method according to claim 7, wherein the time length of the
unused part depends on the number of OFDM symbol durations of the
time shift of the subframe.
9. The method according to claim 1, wherein the number of said
interruptions of the second transmissions can vary from several
interruptions per radio frame to less than one interruption per
radio frame.
10. The method according to claim 1, wherein the relay node decides
at which point in time the interruptions should be created; and,
wherein the relay node informs the concerned mobile terminals and,
if necessary, the eNB during which time interval an interruption
will be created in the second transmissions.
11. The method according to claim 1, wherein the relay node is
informed by the eNB of at which point in time the interruptions
should be created; and, wherein the relay node informs the
concerned mobile terminals during which time interval an
interruption will be created in the second transmission.
12. A relay node for a wireless communication system, the relay
node adapted to receive first transmissions from an evolved Node B
(eNB), the relay node further adapted to send second transmissions
to at least one mobile terminal connected to the relay node,
wherein the first and second transmissions take place in
overlapping frequency bands, said relay node comprising: an
interference avoiding unit adapted to create at least one
interruption in said second transmissions from the relay node to
the at least one mobile terminal; and, a receiving unit adapted to
receive first transmissions from the eNB during said at least one
interruption.
13. The relay node according to claim 12, wherein said at least one
interruption is created by using a Multicast/Broadcast Single
Frequency Network (MBSFN) subframe format.
14. The relay node according to claim 12, wherein the interference
avoiding unit is further adapted to create said at least one
interruption by using a Multicast/Broadcast Single Frequency
Network (MBSFN) subframe format that is backwards compatible with
legacy mobile terminals.
15. The relay node according to claim 12, wherein the interference
avoiding unit is further adapted to create said at least one
interruption by using a Multicast/Broadcast Single Frequency
Network (MBSFN) subframe format in which the subframe contents are
limited to reference symbols and control signalling, which are
allocated in less than 3 OFDM symbols of the subframe.
16. The relay node according to claim 12, wherein the receiving
unit is further adapted to receive subframes of the first
transmissions from the eNB to the relay node, which are
time-shifted one or more OFDM symbol durations relative to the
subframes of the second transmissions.
17. The relay node according to claim 16, wherein the receiving
unit is further adapted to receive subframes in which the number of
OFDM symbol durations of the time shift is selected based on the
duration of a control region used in subframes within the cells of
the relay node.
18. The relay node according to claim 16, wherein the receiving
unit is further adapted to receive subframes in which a last part
of at least one subframe of the first transmissions from the eNB to
the relay eNB is left unused for transmission.
19. The relay node according to claim 18, wherein the receiving
unit is further adapted to receive subframes in which the time
length of the unused part depends on the number of OFDM symbol
durations of the time shift of the subframe.
20. The relay node according to claim 12, wherein the interference
avoiding unit is further adapted to being able to vary the number
of said interruptions from several interruptions per radio frame to
less than one interruption per radio frame.
21. The relay node according to claim 12, wherein the relay node is
adapted to decide at which point in time the interruptions should
be created; and, wherein the relay node is further adapted to
inform the concerned mobile terminals and/or the eNB during which
time interval an interruption will be created in the second
transmissions.
22. The relay node according to claim 12, wherein the relay node is
adapted to receive, from the eNB, information about at which point
in time the interruptions should be created, and/or wherein the
relay node is further adapted to inform the concerned mobile
terminals during which time interval an interruption will be
created in the second transmissions.
23. An arrangement for operating in a wireless communication system
comprising: an evolved Node B (eNB) controlling a donor cell; and,
a relay node; wherein the eNB is adapted to send first
transmissions to the relay node, and the relay node is adapted to
send second transmissions to at least one mobile terminal connected
to the relay node, the first and second transmissions taking place
in overlapping frequency bands; and, wherein the relay node is
configured to: create at least one interruption in second
transmissions to the mobile terminal(s); and, receive first
transmissions from the eNB controlling the donor cell during said
at least one interruption.
24. An evolved Node B (eNB) for a wireless communication system,
the eNB adapted to send first transmissions to a relay node, which
is adapted to send second transmissions to a least one terminal
connected to the relay node, wherein the first and second
transmissions take place in overlapping frequency bands, the eNB
being further adapted to send first transmissions to the relay node
during an interruption of the second transmissions.
25. The evolved Node B according to claim 24, wherein the at least
one interruption is created by using a Multicast/Broadcast Single
Frequency Network (MBSFN) subframe format for the second
transmissions.
26. The evolved Node B according to claim 24, wherein said at least
one interruption is created by using a Multicast/Broadcast Single
Frequency Network (MBSFN) subframe format that is backwards
compatible with legacy mobile terminals.
27. The evolved Node B according to claim 24, wherein said at least
one interruption is created by using a Multicast/Broadcast Single
Frequency Network (MBSFN) subframe format in which the subframe
contents are limited to reference symbols and control signalling,
which are allocated in less than 3 OFDM symbols of the
subframe.
28. The evolved Node B according to claim 24, wherein the eNB is
adapted to time-shift subframes of the first transmissions from the
eNB to the relay node for one or more OFDM symbol durations
relative to the subframes of the second transmissions.
29. The evolved Node B according to claim 28, wherein the number of
OFDM symbol durations of the time shift is selected based on the
duration of a control region used in subframes within the cells of
the relay node.
30. The evolved Node B according to claim 24, wherein a last part
of at least one subframe of the first transmissions from the eNB to
the relay node is left unused for transmission.
31. The evolved Node B according to claim 30, wherein the time
length of the unused part depends on the number of OFDM symbol
durations of the time shift of the subframe.
32. The evolved Node B according to claim 24, wherein the number of
said interruptions of the second transmissions can vary from
several interruptions per radio frame to less than one interruption
per radio frame.
33. The evolved Node B according to claim 24, wherein the relay
node decides at which point in time the interruptions should be
created; and, wherein the relay node informs the concerned mobile
terminals and the eNB during which time interval an interruption
will be created in the second transmissions, wherein the eNB is
adapted to receive corresponding information from the relay node
and/or to send first transmissions based on such information.
34. The evolved Node B according to claim 24, the eNB being adapted
to determine at which point in time the interruptions should be
created and/or to inform the relay node about the determined point
in time.
35. A method for operating an evolved Node B (eNB) in a wireless
communication system, wherein the eNB sends first transmissions to
a relay node, which is adapted to send second transmissions to a
least one terminal connected to the relay node, wherein the first
and second transmissions take place in overlapping frequency bands,
and the eNB sends first transmissions to the relay node during an
interruption of the second transmissions.
36. The method according to claim 35, wherein the at least one
interruption is created by using a Multicast/Broadcast Single
Frequency Network (MBSFN) subframe format for the second
transmissions.
37. The method according to claim 35, wherein said at least one
interruption is created by using a Multicast/Broadcast Single
Frequency Network (MBSFN) subframe format that is backwards
compatible with legacy mobile terminals.
38. The method according to claim 35, wherein said at least one
interruption is created by using a Multicast/Broadcast Single
Frequency Network (MBSFN) subframe format in which the subframe
contents are limited to reference symbols and control signalling,
which are allocated in less than 3 OFDM symbols of the
subframe.
39. The method according to claim 35, wherein the eNB time-shifts
the subframes of the first transmissions from the eNB to the relay
node for one or more OFDM symbol durations relative to the
subframes of the second transmissions.
40. The method according to claim 35, wherein the number of OFDM
symbol durations of the time shift is selected based on the
duration of a control region used in subframes within the cells of
the relay node.
41. The method according to claim 35, wherein a last part of at
least one subframe of the first transmissions from the eNB to the
relay node is left unused for transmission.
42. The method according to claim 41, wherein the time length of
the unused part depends on the number of OFDM symbol durations of
the time shift of the subframe.
43. The method according to claim 35, wherein the number of said
interruptions of the second transmissions can vary from several
interruptions per radio frame to less than one interruption per
radio frame.
44. The method according to claim 35, wherein the eNB is adapted to
receive, from the relay node, information about in which time
interval an interruption will be created in the second
transmissions, and/or wherein the eNB sends first transmissions
based on such information.
45. The method according to claim 35, wherein the eNB determines at
which point in time the interruptions should be created and/or
informs the relay node about the determined point in time.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S. patent
application Ser. No. 13/120,034 filed Mar. 21, 2011 which is a 371
of International Application No. PCT/SE2009/050416, filed Apr. 22,
2009, which claims the benefit of U.S. Provisional Patent
Application No. 61/098,367 filed on Sep. 19, 2008, the disclosures
of which are fully incorporated herein by reference.
TECHNICAL FIELD
[0002] The invention relates to a method and an arrangement in a
telecommunication system, in particular to enable backwards
compatible self-backhauling in an E-UTRAN (Evolved Universal
Terrestrial Radio Access Network).
BACKGROUND
[0003] In certain situations it may be advantageous to extend the
radio coverage of a cellular telecommunication system by using a
wireless relay node, which is connected to a base station. The
relay node may constitute one or more cells of its own, or may be
used to extend the cells covered by the base station.
[0004] In e-UTRAN (Evolved Universal Terrestrial Radio Access
Network), also known as LTE, self-backhauling is one of the
relaying techniques which are considered to be included in the
radio access network standard. The concept of self-backhauling
implies that a wireless base station is wirelessly connected to the
remaining part of a network via another cell, sometimes called the
anchor cell, here referred to as the donor cell. The donor cell is
controlled by an eNB (evolved Node B), which here will be referred
to as the donor eNB or donor node. The donor eNB may also be called
the anchor eNB. The wireless eNB will here be referred to as the
relay node (RN) or relay. The relay may also be called the
self-backhauled eNB or the s-eNB.
[0005] The use of wireless backhaul to a base station by means of,
for example, a specific radio-link technology such as MiniLink,
sometimes also called micro wave, has been used for many years.
These specific technologies may, however, require additional
transceiver equipment or specific, dedicated frequency bands to
operate in, and may also require line-of-sight conditions.
[0006] The concept of self-backhauling also implies that the link
between the donor eNB and the relay node, here referred to as the
self-backhaul link, should be possible to operate in the same
frequency spectrum, i.e. frequency-overlapped with, the radio
access links that provide access for mobile terminals, also known
as User Equipment (UEs), within the donor cell and the UEs within
the cell(s) controlled by the relay node. It is also typically
assumed that the radio technology used for the self-backhaul link
is basically similar to the one used within the donor cell and the
cell(s) of the relay node respectively, possibly with some
additional extensions to optimize for the backhaul application. For
example, in case the donor eNB and the relay node use the LTE radio
access technology for communicating with UEs within their cell(s),
the self-backhaul link should also be LTE-based, or at least based
on an LTE-like radio technology. Signals which overlap in frequency
interfere with each other, which may obstruct reception of the
signals.
SUMMARY
[0007] As it is desirable to obtain a satisfactory reception of the
self-backhaul link at the relay node the present invention provides
a mechanism for enabling avoidance or reduction of the interference
which may occur when a self-backhaul link between a donor eNB and a
relay node and radio access links within the cell(s) controlled by
the relay node operate in the same frequency spectrum. These
objects are met by a method and apparatus according to the attached
independent claims.
[0008] According to one aspect, a method is provided in a relay
node in a wireless communication system for avoiding or reducing
interference between transmissions from a donor eNB to the relay
node and downlink transmissions from the relay node to at least one
mobile terminal connected to the relay node. In the method, at
least one interruption is created in said transmission from the
relay node to the mobile terminal(s), and a transmission is
received from the donor eNB during said at least one created
interruption.
[0009] According to another aspect, a relay node is provided in a
wireless communication system, and adapted to avoid or reduce
interference between transmissions from a donor eNB to the relay
node and downlink transmissions from the relay node to at least one
mobile terminal connected to the relay node. The relay node
comprises an interference avoiding unit, which is adapted to create
at least one interruption in the transmission from the relay node
to the mobile terminal(s). The relay node further comprises a
receiving unit, which is adapted to receive a transmission from the
donor eNB during the interruption(s).
[0010] According to yet another aspect, a donor eNB connected to a
relay node, such as the one described earlier in a wireless
communication system, is adapted to avoid or reduce interference
between transmissions from the donor eNB to the relay node and
downlink transmissions from the relay node to at least one mobile
terminal connected to the relay node. The donor eNB comprises a
time-shifting unit which is adapted to shift subframes destined for
the relay node one or more OFDM symbol durations in time relative
to the relay node downlink subframes. The donor eNB further
comprises a transmitting unit, which is adapted to transmit the
time-shifted subframes or other subframes to the relay node.
[0011] According to yet another aspect, an arrangement is provided
and adapted to avoid or reduce interference in a wireless
communication system. The arrangement comprises an eNB controlling
a donor cell, and a relay node. When at least one mobile terminal
connected to the relay node, the relay node is configured to create
at least one interruption in a transmission to the mobile
terminal(s), and to receive a transmission from the eNB controlling
the donor cell during the interruption(s).
[0012] In the different aspects above, the transmissions from the
donor eNB to the relay node and the downlink transmissions from the
relay node to the mobile terminal(s) take place in overlapping
frequency bands, which is one reason why these transmissions can
interfere with each other.
[0013] Various embodiments are possible for the method, nodes and
arrangement described above. In one exemplary embodiment, the
transmission interruption is created by using a downlink
transmission subframe format that is known to legacy mobile
terminals. When the format is known to legacy users, the embodiment
is backwards compatible and may be used by both legacy users and
other users, which is an advantage since it may take some time
before all users have changed their legacy equipment to a new or
upgraded version after a system upgrade.
[0014] In another embodiment, the interruption could be created by
using a downlink transmission subframe format, in which the
subframe contents are limited to reference symbols and control
signalling, which are allocated in less than 3 OFDM symbols of the
subframe. The interruption could also be created by using the
MBSFN-subframe format, which is also known to legacy mobile
terminals, therefore not requiring modification of the legacy
mobile terminals.
[0015] In one embodiment, the subframes of the transmission from
the donor eNB to the relay node are time-shifted one or more OFDM
symbol durations relative to the downlink subframes. This
embodiment can enable avoidance or reduction of interference
between the first part of the subframes of the radio access link
and selected parts of the subframes of self-backhaul link. The
number of OFDM symbol durations of the time shift may for example
be selected based on the duration of a control region used in the
subframes within the cells of the relay node. Thereby, the first
part of the subframes of the self-backhaul link will basically not
be subject to interference from the first part of the subframes of
the radio access link, which may improve the performance. However,
some other part, e.g. the last part, of the subframes of the
self-backhaul link will be subject to interference instead.
[0016] Further, in one embodiment, a last part of at least one
subframe of the transmission from the donor eNB to the relay node
could be left unused for transmission. This embodiment can enable
further avoidance or reduction of interference between the
self-backhaul link and the radio access links. The time length of
the unused part may for example depend on the number of OFDM symbol
durations of a time shift of the subframe.
[0017] For any of the embodiments, the number of created downlink
transmission interruptions can vary from several interruptions per
radio frame to less than one interruption per radio frame.
[0018] In one embodiment, it is the relay node that decides at
which point in time the interruptions should be created and that
informs the concerned mobile terminals of during which time
interval an interruption will be created in the downlink
transmission. If necessary, the relay node also informs the donor
eNB of during which time interval an interruption will be created
in the downlink transmission. It may not be necessary to inform the
eNB if the relay node knows or is able to predict when the donor
eNB will transmit on the self-backhaul link.
[0019] In another embodiment, it is the donor eNB that decides at
which point in time the interruptions should be created and informs
the relay node about when the relay node should create
interruptions. In that case, the relay node informs the concerned
mobile terminals of during which time interval an interruption will
be created in the downlink transmission.
[0020] The different features of the exemplary embodiments above
may be combined in different ways according to need, requirements
or preference.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The invention will now be explained in more detail by means
of exemplary embodiments and with reference to the accompanying
drawings, in which:
[0022] FIG. 1 is a schematic view illustrating a self-backhaul link
being subject to interference.
[0023] FIG. 2 is a flow chart illustrating an embodiment of
procedure steps in a relay node for avoiding or reducing
interference.
[0024] FIG. 3a illustrates an ordinary LTE Release 8 subframe and
FIG. 3b illustrates an MBSFN, which can be used in the described
embodiments.
[0025] FIG. 4 illustrates an MBSFN-subframe.
[0026] FIG. 5, FIG. 6 and FIG. 7 each illustrate inter-link
relations when using embodiments of the described procedure for
avoiding or reducing interference.
[0027] FIG. 8 illustrates a relay node 800 in a wireless
communication system according to one embodiment.
[0028] FIG. 9 illustrates a donor eNB, which is connected to a
relay node (not shown) in a wireless communication system according
to one embodiment.
[0029] FIG. 10 is a schematic view illustrating an arrangement
according to one embodiment.
DETAILED DESCRIPTION
[0030] The invention can be used to avoid or reduce interference
between transmissions over a self-backhauling link and
transmissions between one of the nodes connected to the
self-backhaul link and the UEs served by the cell(s) controlled by
said node.
[0031] The invention is particularly useful where the
transmissions, at least partly, take place in the same frequency
spectrum and where it is desired that the communication is
backwards compatible for legacy UEs, i.e. UEs communicating
according to an earlier version of a transmission standard or
protocol or the like. The present invention may also be used to
avoid or reduce interference in other, similar situations.
[0032] It may be desirable for network operators to use the same or
overlapping frequency bands for the self-backhaul link and for the
communication within the cells of the donor and/or the relay node,
for several reasons. One of the reasons is that the need for access
to any additional frequency bands, dedicated to the backhaul link,
it set aside. Acquiring additional frequencies may not be possible
or may be expensive. Further, the need for additional
frequency-specific or link-specific equipment, dedicated for
communication over the backhaul link, is reduced. Further, the use
of self-backhauling may also enable non line-of-sight transmission,
which may be useful in many situations.
[0033] The invention addresses the problem of the interference
which would most likely occur when overlapping frequency bands are
used for the self-backhaul link and for the relay-to-UE
transmissions within the cell(s) controlled by the relay node
respectively. This problem is illustrated in FIG. 1 as follows:
[0034] A donor eNB 104 transmits to a relay node 106 on a
self-backhaul link 110 at the same time as the relay transmits to a
UE 108 within one of its own cells. The relay node then "overhears"
its own transmission 112 to the UE, which overheard transmission
112 then interferes 116 with the incoming transmission from the
donor cell. This results in that the relay node may not be able to
detect the incoming transmission from the donor cell properly, and
thereby may fail to secure important information.
[0035] The above described interference can, however, be avoided by
inserting transmission interruptions in the downlink transmission
112 from the relay node 106 to the UE 108. These interruptions can
be regarded as "holes" or "gaps" of a certain duration in the
transmission, during which "holes" or "gaps" the relay may receive
incoming transmissions on the self-backhaul link 110 without severe
interference from the downlink transmissions 112 within the cell(s)
controlled by the relay. This can also be described as time
multiplexing between the self-backhaul link and the access link in
the cell(s) of the relay node.
[0036] Transmission interruptions can be implemented in different
ways. However, it is highly desirable to make the implementation
backwards compatible for legacy UEs, i.e. fully aligned with
downlink transmission schemes as defined in earlier versions of a
transmission protocol, as for example in Release 8 of the
3GPP-specifications for the LTE standard, where the interference
problem described above did not occur, since no self-backhaul links
were considered in that version. Backwards compatibility enables
legacy UEs to act according to a previous version of the
transmission protocol, and still be able to communicate with UEs
and nodes which act according to a more recent, considerably
changed version of the transmission protocol, e.g. Release 10 of
the 3GPP-specifications for the LTE standard. In a backwards
compatible system, the legacy UEs do not necessarily have to "be
aware" of the new version or be upgraded or adapted to the new
version, which is an advantage.
[0037] Therefore, the interruptions in the downlink should
preferably be created in a way which is backwards compatible for
legacy UEs. The challenge with this is that the legacy UEs expect a
certain format in the downlink transmissions, which should not be
diverged from. Changing the expected format would require changes
to be made in the earlier version of the transmission protocol,
which is troublesome and undesirable.
[0038] An ordinary LTE Release 8 subframe is illustrated in FIG.
3a. This is the subframe format which is normally expected by the
legacy UEs. An LTE-subframe has a duration of 1 ms, which typically
equals the duration of 14 OFDM symbols (Orthogonal Frequency
Division Multiplexing). Typically, the first 1-3 OFDM symbols of
the subframe are used for control information. Further, in these
ordinary unicast subframes there are several mandatory reference
symbols, e.g. evenly distributed over the frequency-time-grid.
These reference symbols may be used by a receiving unit, e.g. for
estimating the channels over which the transmitted symbols
propagate.
[0039] In one embodiment, the interruptions in the relay downlink
transmission are created by the use of MBSFN-subframes
(Multicast/Broadcast Single Frequency Network). Certain downlink
subframes are then defined as being MBSFN-subframes. The
MBSFN-subframes are known to legacy UEs, e.g. Release 8, but are
known to be used in a very different situation, i.e. for
MBSFN-transmissions.
[0040] An MBSFN-subframe is illustrated in FIG. 3b and FIG. 4.
Typically, the first two OFDM-symbols of an MBSFN-subframe are
defined to comprise reference symbols and control information.
These two first symbols constitute the [cell specific] control
region, or unicast region. The contents of the remaining part of
the MBSFN-subframe are not specified. This means that it is
possible to leave out the distributed reference symbols, which are
mandatory in ordinary LTE-downlink-subframes. Thereby, a major part
406 of the MBSFN-subframe may be left empty, i.e. left unused for
transmission. This empty part 406 of the MBSFN-subframe may be
regarded as a transmission interruption or a "hole" or "gap" in the
transmission for a certain time interval. This interruption or
pause in the downlink transmission gives the relay an opportunity
to receive a transmission from the donor eNB during the
corresponding time interval, without suffering from interference
from the downlink.
[0041] The unicast region 404, comprises reference symbols in the
first OFDM-symbol of the subframe in the case of 2-antenna-port
transmission, and in the first and second OFDM-symbol of the
subframe in the case of 4-antenna-port transmission. In addition to
containing the reference symbols, this region is also completely or
partly used for L1/L2 control signalling, i.e., HARQ (Hybrid
Automatic Repeat reQuest) acknowledgements and scheduling grants.
If not told otherwise, the legacy UEs will ignore all but the
unicast region of the MBSFN-subframes.
[0042] The number of downlink subframes that are defined as
MBSFN-subframes can vary from several subframes per frame to less
than one subframe per frame, e.g. one subframe every fourth frame.
The number of MBSFN-subframes may for example vary in accordance
with the amount of communication on the self-backhauling link. In
general, one frame or radio frame comprises 10 subframes.
[0043] In one embodiment, the relay node decides which subframes
that are suitable to be defined as MBSFN-subframes. The relay node
then communicates to the donor eNB and the concerned UEs at which
point in time the MBSFN-subframes will be transmitted on the
downlink. Thereby, the donor eNB "knows" during which time interval
it is advantageous/suitable to transmit to the relay on the
self-backhaul link.
[0044] In another embodiment of the present invention, the donor
eNB decides when to transmit to the relay node on the self-backhaul
link and which subframes that should be defined as MBSFN-subframes
in the relay node. The donor eNB then communicates to the relay
node at which point in time to transmit MBSFN-subframes on the
downlink, and the relay node informs the UEs about the
MBSFN-subframes. The relay then "knows" during which time interval
or at which point in time to expect transmissions on the
self-backhauling link, since the donor eNB transmits on the
self-backhauling link during the time interval corresponding to the
relay downlink transmission of the MBSFN-subframes.
[0045] In another embodiment, the occurrences of transmissions from
the donor eNB on the self-backhaul link are known or predictable to
the relay node. For example, they may be scheduled in a certain
way, which is known to the relay node or can be predicted by the
relay node. The relay node may then adapt to the transmissions from
the donor eNB by inserting MBSFN-subframes in the downlink when an
incoming transmission on the self-backhaul link is expected. The
relay node also informs the UEs of at which point in time to expect
MBSFN-subframes. In this embodiment, the donor eNB may be unaware
of the insertion of MBSFN-subframes.
[0046] In cases when both the self-backhaul link and the RN-to-UE
links are LTE-based and have the same subframe structure, the
control region of the relay downlink transmissions 508 will
severely interfere with the corresponding part 506 of the
self-backhaul transmission as illustrated in FIG. 5. This could be
a problem, especially when the corresponding part of the
self-backhaul transmission is considered to be particularly
important. To avoid or reduce this interference between the first
parts of the subframes, the self-backhaul link can be staggered in
time, i.e. time-shifted, as outlined in FIG. 6. If the length of
the control region 608 in the subframes transmitted on the relay
downlink is one OFDM-symbol, the staggering 604 should be at least
one OFDM-symbol duration. Similarly, if the length of the control
region 608 in the subframes transmitted on the relay node downlink
is two OFDM-symbols the staggering 604 should be at least two
OFDM-symbol durations.
[0047] The use of staggering will avoid or reduce the interference
problem in the first part of the subframes on the self-backhaul
link, but it will move the interference to another part of the
subframe. For example, the last part 606 of a subframe on the
self-backhauling link may be severely interfered by a subsequent
subframe transmission within the cell(s) of the relay.
[0048] The above described interference can be avoided in another
possible embodiment, illustrated in FIG. 7. When the interference
from the relay downlink occurs in the last part of the subframes of
the self-backhaul link, the subframe length may be shortened on the
self-backhaul link in order to avoid or reduce the interference. In
other words, the length of the subframes may depend on the amount
of staggering 704, which in turn may depend on e.g. the length of
the unicast region 708 in the subframes of the relay downlink.
Thus, the donor eNB refrains from transmitting on the self-backhaul
link during said last part 706 of a regular subframe duration, as
illustrated in FIG. 7.
[0049] Alternatively, the donor eNB transmits also during the last
part of the subframe on the self-backhaul link and it is assumed
that the channel coding applied to the self-backhaul link will be
sufficient to overcome the interference.
[0050] FIGS. 5-7 show a plurality of consecutive MBSFN-subframes
and "self-backhaul-subframes", which are partially subject to
interference. However, the creation of interruptions in the
downlink and the transmission on the self-backhauling link is not
limited to this scenario, as stated earlier. The number of downlink
subframes which comprise an interruption can vary from several
subframes per frame to less than one subframe per frame. The number
of subframes received from the donor eNB on the self-backhaul link
may vary in a corresponding way.
[0051] FIG. 8 illustrates a relay node 800 in a wireless
communication system according to one embodiment. The relay node
800 is adapted to avoiding or reducing interference between
transmissions 808 from a donor eNB to the relay node and downlink
transmissions 806 from the relay node 800 to at least one mobile
terminal (not shown) connected to the relay node. The relay node
800 comprises an interference avoiding unit 802, which is adapted
to create at least one interruption in the transmission 806 from
the relay node 800 to the mobile terminal(s). The relay node 800
further comprises a receiving unit 804, which is adapted to receive
a transmission 808 from the donor eNB during the
interruption(s).
[0052] FIG. 9 illustrates a donor eNB 900, which is connected to a
relay node (not shown) in a wireless communication system according
to one embodiment. The donor eNB 900 is adapted to avoid or reduce
interference between transmissions 906 from the donor eNB to the
relay node and downlink transmissions (not shown) from the relay
node to at least one mobile terminal (not shown) connected to the
relay node. The donor eNB comprises a time-shifting unit 902, which
is adapted to shift subframes destined for the relay node one or
more OFDM symbol durations in time relative to the relay node
downlink subframes. The donor eNB 900 further comprises a
transmitting unit 904, which is adapted to transmit the
time-shifted subframes or other subframes to the relay node.
[0053] It should be noted that FIGS. 8 and 9 merely illustrate
various functional units in the relay node 800 and the eNB 900 in a
logical sense. However, the skilled person is free to implement
these functions in practice using any suitable software and
hardware means. Thus, the invention is generally not limited to the
shown structure of the relay node 800 and the eNB 900.
[0054] FIG. 10 illustrates an arrangement 1000 according to one
embodiment. The arrangement 1000 is adapted to avoiding or reducing
interference in a wireless communication system. The arrangement
comprises an eNB 1004 controlling a donor cell 1002, and a relay
node 1006. When at least one mobile terminal 1008 is connected to
the relay node, the relay node is configured to create at least one
interruption in a transmission 1012 to the mobile terminal(s) 1008,
and to receive a transmission 1010 from the eNB 1004 controlling
the donor cell 1002 during the created interruption(s).
* * * * *