U.S. patent application number 14/769884 was filed with the patent office on 2016-01-07 for communication system.
The applicant listed for this patent is NEC Corporation. Invention is credited to Yassin Aden AWAD, Vivek SHARMA, Meng WANG.
Application Number | 20160007255 14/769884 |
Document ID | / |
Family ID | 48483432 |
Filed Date | 2016-01-07 |
United States Patent
Application |
20160007255 |
Kind Code |
A1 |
SHARMA; Vivek ; et
al. |
January 7, 2016 |
COMMUNICATION SYSTEM
Abstract
A gateway is described which facilitates a change of
communication cell for a mobile device in a communication system,
which includes a core network. The gateway receives messages from a
base station operating a cell and forwards the messages received
from the base station to the core network. The gateway intercepts a
message relating to a change of communication cell, from a source
cell in which the mobile communication device is located to a
target cell, to determine if the core network needs to be notified
of the change of cell. When it is determined that the core network
needs to be notified, the gateway generates a message for providing
information relating to the change of cell to the core network and
transmits the message to the core network.
Inventors: |
SHARMA; Vivek; (Sutton,
GB) ; WANG; Meng; (Guildford, GB) ; AWAD;
Yassin Aden; (London, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NEC Corporation |
Minato-ku, Tokyo |
|
JP |
|
|
Family ID: |
48483432 |
Appl. No.: |
14/769884 |
Filed: |
March 28, 2014 |
PCT Filed: |
March 28, 2014 |
PCT NO: |
PCT/JP2014/059910 |
371 Date: |
August 24, 2015 |
Current U.S.
Class: |
370/331 |
Current CPC
Class: |
H04W 36/08 20130101;
H04W 92/045 20130101; H04W 84/045 20130101; H04W 88/12 20130101;
H04W 36/04 20130101 |
International
Class: |
H04W 36/04 20060101
H04W036/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 5, 2013 |
GB |
1306216.1 |
Claims
1. A gateway apparatus configured to facilitate a change of
communication cell for a mobile communication device in a
communication system, the gateway apparatus being operable to
receive messages from at least one base station operating a
respective cell of said communication system and to forward the
messages received from the at least one base station to a
communication entity in a core network, the gateway apparatus
comprising: a receiver configured to receive, from at least one of
a source base station that operates a source cell in which said
mobile communication device is located and a target base station
that operates a target cell for said change of communication cell,
at least one message relating to said change of communication cell;
an interceptor configured to intercept and process said message
relating to said change of communication cell to determine if said
communication entity in the core network needs to be notified of
information relating to said change of communication cell; a
generator configured to generate, when it is determined that said
communication entity in the core network needs to be notified of
information relating to said change of communication cell, a
message for providing said information relating to said change of
communication cell to said core network entity; and a transmitter
configured to transmit, to said communication entity in the core
network, said message for providing said information relating to
said change of communication cell; wherein each of the receiver,
the interceptor, the generator, and the transmitter are implemented
by a hardware processor.
2. Gateway apparatus according to claim 1 wherein said interceptor
is operable to determine whether or not said message relating to
said change of communication cell should be forwarded to said
communication entity in the core network.
3. Gateway apparatus according to claim 2 wherein said interceptor
is operable to determine whether messages relating to a change of
communication cell should be forwarded to said communication entity
in the core network based on a number of cell changes that have
occurred since messages relating to a change of communication cell
were previously forwarded to said communication entity in the core
network.
4. Gateway apparatus according to claim 3 said interceptor is
operable to determine that messages relating to a change of
communication cell should not be forwarded to said communication
entity in the core network when the number of cell changes that
have occurred since messages relating to a change of communication
cell were previously forwarded to said communication entity in the
core network has not exceeded a predetermined value.
5. Gateway apparatus according to claim 3 said interceptor is
operable to determine that messages relating to a change of
communication cell should be forwarded to said communication entity
in the core network when the number of cell changes that have
occurred since messages relating to a change of communication cell
were previously forwarded to said communication entity in the core
network has reached or exceeded the predetermined value.
6. Gateway apparatus according to claim 1 wherein said generator is
operable to generate, responsive to said message relating to said
change of communication cell, a further message for progressing
said change of communication cell; and said transmitter is operable
to transmit said further message for progressing said change of
communication cell to said source base station or to said target
base station.
7. Gateway apparatus according to claim 6 wherein said generator is
operable to generate said further message for progressing said
change of communication cell without forwarding the message
relating to said change of communication cell to the communication
entity in the core network.
8. Gateway apparatus according to claim 6 wherein said generator is
operable to generate said further message for progressing said
change of communication cell based on information obtained by said
interceptor from messages previously forwarded to or from said
communication entity in said core network.
9. Gateway apparatus according to claim 1, wherein said interceptor
is operable to determine if said communication entity in the core
network needs to be notified of information relating to said change
of communication cell comprising location information; and wherein
said message for providing said information relating to said change
of communication cell to said communication entity in the core
network comprises a location report for providing said location
information.
10. Gateway apparatus according to claim 1 wherein said interceptor
is operable to determine if said communication entity in the core
network needs to be notified of information relating to said change
of communication cell comprising information identifying
communication bearers that the target base station has failed to
set up; and wherein said message for providing said information
relating to said change of communication cell to said communication
entity in the core network comprises a message identifying said
communication bearers that the target base station has failed to
set up.
11. Gateway apparatus according to claim 10 wherein said receiver
is operable to receive, from said communication entity in the core
network in response to said message identifying said communication
bearers that the target base station has failed to set up, a
message for initiating a modification in a communication parameter
for communication by said mobile communication device in said
target cell.
12. Gateway apparatus according to claim 11 wherein said message
for initiating a modification in a communication parameter is
configured to initiate a change in an aggregate maximum bit
rate.
13. Gateway apparatus according to claim 1 wherein said interceptor
is operable to determine, from a message relating to said change of
communication cell received from said source base station, whether
direct data forwarding is possible for at least one communication
bearer of said mobile communication device.
14. Gateway apparatus according to claim 13 wherein said generator
is operable to generate, responsive to said determination of
whether direct data forwarding is possible, a message indicating
whether direct data forwarding is possible for sending to said
target base station.
15. Gateway apparatus according to claim 13 wherein said generator
is operable to generate, responsive to a determination that direct
data forwarding is possible, a message comprising parameters for
establishing a direct communication tunnel for forwarding data
directly between said source and target base stations.
16. Gateway apparatus according to claim 13 wherein said gateway
apparatus is operable, responsive to a determination that direct
data forwarding is not possible, to facilitate establishment of an
indirect communication tunnel for forwarding data indirectly
between said source and target base stations via said gateway
apparatus.
17. Gateway apparatus according to claim 16 wherein said gateway
apparatus is operable to facilitate said establishment of an
indirect communication tunnel using a tunnel creation request and a
corresponding response message.
18. Gateway apparatus according to claim 1 wherein said gateway
apparatus is operable to terminate messages related to said change
of communication cell, received from said source base station or
from said target base station and destined for said communication
entity in the core network, without forwarding them to said
communication entity in the core network.
19. Gateway apparatus according to claim 1 wherein said gateway
apparatus is a small cell gateway apparatus.
20. Gateway apparatus according to claim 1 wherein said gateway
apparatus comprises at least one of a home base station gateway
(HeNB-GW) function, a security gateway (SeGW), and an X2 gateway
(X2-GW) function.
21. Gateway apparatus according to claim 1 wherein said
communication entity in the core network is a mobility management
entity (MME).
22. Gateway apparatus according to claim 1 wherein each said base
station comprises a low power node (LPN) operating a small
cell.
23. Gateway apparatus according to claim 1 wherein said at least
one message relating to said change of communication cell is a
message in accordance with the S1 application protocol (S1AP).
24. A gateway apparatus configured to facilitate a change of
communication cell for a mobile communication device in a
communication system, the gateway apparatus comprising: a storage,
implemented by a memory, the storage being configured to store at
the gateway apparatus, context information for the mobile
communication device relating to a communications connection
between the mobile communication device and a source base station
that operates a source cell in which said mobile communication
device is located; a receiver configured to receive, from at least
one of a source base station that operates a source cell in which
said mobile communication device is located and a target base
station that operates a target cell for said change of
communication cell, at least one message relating to said change of
communication cell; a generator configured to generate at least one
further message for progressing said change of communication cell
responsive to said at least one message relating to said change of
communication cell using said context information; and a
transmitter configured to transmit, to at least one of said source
base station and said target base station, said at least one
further message for progressing said change of communication cell;
wherein each of the receiver, the generator, and the transmitter
are implemented by a hardware processor.
25. Gateway apparatus according to claim 24 wherein said at least
one further message for progressing said change of communication
cell comprises a message for transferring said context information
to said target base station.
26. Gateway apparatus according to claim 24 wherein said context
information comprises security context information relating to the
communications connection between the mobile communication device
and the source base station.
27. Gateway apparatus according to claim 26 wherein said gateway
apparatus is operable to determine whether or not to initiate the
transfer of said context information, including said security
context information, based on a number of cell changes that have
occurred since the security context information was last
updated.
28. Gateway apparatus according to claim 27 wherein said gateway
apparatus is operable to determine to initiate the transfer of said
context information, including said security context information,
when the number of cell changes that have occurred since the
security context information was last updated has not exceeded a
predetermined value.
29. Gateway apparatus according to claim 27 wherein said gateway
apparatus is operable to determine not to initiate the transfer of
said context information, including said security context
information, when the number of cell changes that have occurred
since the security context information was last updated has reached
or exceeded said predetermined value.
30. Gateway apparatus according to claim 29 wherein said gateway
apparatus is operable to initiate an update to said security
context information when the number of cell changes that have
occurred since the security context information was last updated
has reached or exceeded said predetermined value.
31. A gateway apparatus configured to facilitate a change of
communication cell for a mobile communication device in a
communication system, the gateway apparatus being operable to
receive messages from at least one base station operating a
respective cell of said communication system and to forward the
messages received from the at least one base station to a
communication entity in a core network, the gateway apparatus
comprising: a receiver configured to receive, from at least one of
a source base station that operates a source cell in which said
mobile communication device is located and a target base station
that operates a target cell for said change of communication cell,
at least one message relating to said change of communication cell;
an interceptor configured to intercept and process said message
relating to said change of communication cell to determine whether
said message relating to a change of communication cell should be
forwarded to said communication entity in the core network based on
a number of cell changes that have occurred since messages relating
to a change of communication cell were previously forwarded to said
communication entity in the core network; a generator configured to
generate, when it is determined that said message relating to a
change of communication cell should not be forwarded to said
communication entity in the core network, a further message for
progressing said change of communication cell; a transmitter
configured to transmit, when it is determined that said message
relating to a change of communication cell should not be forwarded
to said communication entity in the core network, to said source
base station or to said target base station, said further message
for progressing said change of communication cell; and a forwarded
configured to forward said message relating to a change of
communication cell to said communication entity in the core
network, when it is determined that said message relating to a
change of communication cell should be forwarded to said
communication entity in the core network; wherein each of the
receiver, the interceptor, the generator, the transmitter and the
forwarder are implemented by a hardware processor.
32. A gateway apparatus for configured to facilitate change of
communication cell for a mobile communication device in a
communication system, the gateway apparatus being operable to
receive messages from at least one base station operating a
respective cell of said communication system and to forward the
messages received from the at least one base station to a
communication entity in a core network, the gateway apparatus
comprising: a receiver configured to receive, from at least one of
a source base station that operates a source cell in which said
mobile communication device is located and a target base station
that operates a target cell for said change of communication cell,
at least one message relating to said change of communication cell;
an interceptor configured to intercept and process said message
relating to said change of communication cell to determine, from a
message relating to said change of communication cell received from
said source base station, whether direct data forwarding is
possible for at least one communication bearer of said mobile
communication device; a generator configured to generate,
responsive to said determination of whether direct data forwarding
is possible, a message indicating whether direct data forwarding is
possible for sending to said target base station; and a transmitter
configured to transmit, said message indicating whether direct data
forwarding is possible to said target base station; wherein each of
the receiver, the interceptor, the generator, and the transmitter
are implemented by a hardware processor.
33. A gateway apparatus configured to facilitate a change of
communication cell for a mobile communication device in a
communication system, the gateway apparatus being operable to
receive messages from at least one base station operating a
respective cell of said communication system and to forward the
messages received from the at least one base station to a
communication entity in a core network, the gateway apparatus
comprising a processor and transceiver circuitry, wherein: said
transceiver circuitry is configured to receive, from at least one
of a source base station that operates a source cell in which said
mobile communication device is located and a target base station
that operates a target cell for said change of communication cell,
at least one message relating to said change of communication cell;
said processor is configured to: i) intercept and process said
message relating to said change of communication cell to determine
if said core network entity needs to be notified of information
relating to said change of communication cell; and ii) generate,
when it is determined that said communication entity in the core
network needs to be notified of information relating to said change
of communication cell, a message for providing said information
relating to said change of communication cell to said communication
entity in the core network; and said transceiver circuitry is
configured to transmit, to said communication entity in the core
network, said message for providing said information relating to
said change of communication cell.
34. A gateway apparatus configured to facilitate a change of
communication cell for a mobile communication device in a
communication system, the gateway apparatus comprising a processor,
a memory, and transceiver circuitry, wherein: said processor is
configured to store in said memory context information for the
mobile communication device relating to a communications connection
between the mobile communication device and a source base station
that operates a source cell in which said mobile communication
device is located; said transceiver circuitry is configured to
receive, from at least one of a source base station that operates a
source cell in which said mobile communication device is located
and a target base station that operates a target cell for said
change of communication cell, at least one message relating to said
change of communication cell; said processor is configured to
generate at least one further message for progressing said change
of communication cell responsive to said at least one message
relating to said change of communication cell using said context
information; and said transceiver circuitry is configured to
transmit, to at least one of said source base station and said
target base station, said at least one further message for
progressing said change of communication cell.
35. A gateway apparatus configured to facilitate a change of
communication cell for a mobile communication device in a
communication system, the gateway apparatus being operable to
receive messages from at least one base station operating a
respective cell of said communication system and to forward the
messages received from the at least one base station to a
communication entity in a core network, the gateway apparatus
comprising a processor and transceiver circuitry, wherein: said
transceiver circuitry is configured to receive, from at least one
of a source base station that operates a source cell in which said
mobile communication device is located and a target base station
that operates a target cell for said change of communication cell,
at least one message relating to said change of communication cell;
said processor is configured to: i) intercept and process said
message relating to said change of communication cell to determine
whether said message relating to a change of communication cell
should be forwarded to said communication entity in the core
network based on a number of cell changes that have occurred since
messages relating to a change of communication cell were previously
forwarded to said communication entity in the core network; and ii)
generate, when it is determined that said message relating to a
change of communication cell should not be forwarded to said
communication entity in the core network, a further message for
progressing said change of communication cell; said transceiver
circuitry is configured to transmit, when it is determined that
said message relating to a change of communication cell should not
be forwarded to said communication entity in the core network, to
said source base station or to said target base station, said
further message for progressing said change of communication cell;
and said transceiver circuitry is configured to forward said
message relating to a change of communication cell to said
communication entity in the core network, when it is determined
that said message relating to a change of communication cell should
be forwarded to said communication entity in the core network.
36. A gateway apparatus configured to facilitate a change of
communication cell for a mobile communication device in a
communication system, the gateway apparatus being operable to
receive messages from at least one base station operating a
respective cell of said communication system and to forward the
messages received from the at least one base station to a
communication entity in a core network, the gateway apparatus
comprising a processor and transceiver circuitry, wherein: said
transceiver circuitry is configured to receive, from at least one
of a source base station that operates a source cell in which said
mobile communication device is located and a target base station
that operates a target cell for said change of communication cell,
at least one message relating to said change of communication cell;
said processor is configured to: i) intercept and process said
message relating to said change of communication cell to determine,
from a message relating to said change of communication cell
received from said source base station, whether direct data
forwarding is possible for at least one communication bearer of
said mobile communication device; and generate, responsive to said
determination of whether direct data forwarding is possible, a
message indicating whether direct data forwarding is possible for
sending to said target base station; and said transceiver circuitry
is configured to transmit, said message indicating whether direct
data forwarding is possible to said target base station.
37. A communication system comprising a gateway apparatus according
to claim 1, at least one mobile communication device, a source base
station and a target base station.
38. A method performed by a gateway apparatus for facilitating a
change of communication cell for a mobile communication device in a
communication system, the gateway apparatus being operable to
receive messages from at least one base station operating a
respective cell of said communication system and to forward the
messages received from the at least one base station to a
communication entity in a core network, the method comprising:
receiving, from at least one of a source base station that operates
a source cell in which said mobile communication device is located
and a target base station that operates a target cell for said
change of communication cell, at least one message relating to said
change of communication cell; intercepting and processing said
message relating to said change of communication cell to determine
if said communication entity in the core network needs to be
notified of information relating to said change of communication
cell; generating, when it is determined that said communication
entity in the core network needs to be notified of information
relating to said change of communication cell, a message for
providing said information relating to said change of communication
cell to said communication entity in the core network; and
transmitting, to said communication entity in the core network,
said message for providing said information relating to said change
of communication cell.
39. A method performed by a gateway apparatus for facilitating a
change of communication cell for a mobile communication device in a
communication system, the method comprising: storing, at the
gateway apparatus, context information for the mobile communication
device relating to a communications connection between the mobile
communication device and a source base station that operates a
source cell in which said mobile communication device is located;
receiving, from at least one of a source base station that operates
a source cell in which said mobile communication device is located
and a target base station that operates a target cell for said
change of communication cell, at least one message relating to said
change of communication cell; generating at least one further
message for progressing said change of communication cell
responsive to said at least one message relating to said change of
communication cell using said context information; and
transmitting, to at least one of said source base station and said
target base station, said at least one further message for
progressing said change of communication cell.
40. A method performed by a gateway apparatus for facilitating a
change of communication cell for a mobile communication device in a
communication system, the gateway apparatus being operable to
receive messages from at least one base station operating a
respective cell of said communication system and to forward the
messages received from the at least one base station to a
communication entity in a core network, the method comprising:
receiving, from at least one of a source base station that operates
a source cell in which said mobile communication device is located
and a target base station that operates a target cell for said
change of communication cell, at least one message relating to said
change of communication cell; intercepting and processing said
message relating to said change of communication cell to determine
whether said message relating to a change of communication cell
should be forwarded to said communication entity in the core
network based on a number of cell changes that have occurred since
messages relating to a change of communication cell were previously
forwarded to said communication entity in the core network;
generating, when it is determined that said message relating to a
change of communication cell should not be forwarded to said
communication entity in the core network, a further message for
progressing said change of communication cell; transmitting, when
it is determined that said message relating to a change of
communication cell should not be forwarded to said communication
entity in the core network, to said source base station or to said
target base station, said further message for progressing said
change of communication cell; and forwarding said message relating
to a change of communication cell to said communication entity in
the core network, when it is determined that said message relating
to a change of communication cell should be forwarded to said
communication entity in the core network.
41. A method performed by a gateway apparatus for facilitating a
change of communication cell for a mobile communication device in a
communication system, the gateway apparatus being operable to
receive messages from at least one base station operating a
respective cell of said communication system and to forward the
messages received from the at least one base station to a
communication entity in a core network, the method comprising:
receiving, from at least one of a source base station that operates
a source cell in which said mobile communication device is located
and a target base station that operates a target cell for said
change of communication cell, at least one message relating to said
change of communication cell; intercepting and processing said
message relating to said change of communication cell to determine,
from a message relating to said change of communication cell
received from said source base station, whether direct data
forwarding is possible for at least one communication bearer of
said mobile communication device; generating, responsive to said
determination of whether direct data forwarding is possible, a
message indicating whether direct data forwarding is possible for
sending to said target base station; and transmitting, said message
indicating whether direct data forwarding is possible to said
target base station.
42. A computer implementable instructions product comprising
computer implementable instructions for causing a programmable
communications device to perform the method of claim 38.
Description
TECHNICAL FIELD
[0001] The present invention relates to a communication system and
to components thereof for providing communication services to
mobile or fixed communication devices. The invention has particular
but not exclusive relevance to the implementation of so-called
`small` cells or Low Power Nodes (LPNs) in Long Term Evolution
(LTE) communication systems currently being developed by the
3.sup.rd Generation Partnership Project (3GPP).
BACKGROUND ART
[0002] In 3GPP LTE networks, a base station (i.e. evolved NodeB,
eNB) of a Radio Access Network (RAN) transmits data and signalling
between a core network (CN) and User Equipment (UEs) located within
the base station's coverage area.
[0003] Recent developments in communication networks have seen
increased deployment of so called `small` cells operated by Low
Power Nodes (LPNs), such as pico eNBs, femto cells, Home eNBs
(HeNBs) or the like, which cells have a smaller coverage area than
existing macro cells operated by a higher power macro base station.
Networks comprising a number of different cell types, for example a
network comprising a macro cell and a femto cell, are referred to
as Heterogeneous Networks, or HetNets.
[0004] The LPNs/small cell base stations that operate small cells
can typically communicate with the core network and with macro base
stations by a small cell gateway (`small cell GW`). A small cell GW
typically has so called home evolved nodeB gateway (HeNB-GW)
functionality to provide connectivity from the LPN/small cell base
station, to the core network, and X2-GW functionality effectively
to provide X2 interface connectivity (albeit indirect) from the
LPN/small cell base station to the macro base stations.
[0005] More recently the need to make further enhancements to small
cells using low-power nodes, has been identified as one of the most
important topics for further development of 3GPP standards
compliant communication systems in order to enable such
communication systems to cope with increases in mobile traffic
especially for hotspot deployments in indoor and outdoor scenarios.
According to this interest in small cell enhancements, scenarios
and requirements for small cell enhancements were studied and
captured in a 3GPP technical report (3GPP TR 36.932) the contents
of which are herein incorporated by reference. TR 36.932 defines a
low-power node as generally meaning a node whose transmit power is
lower than that of macro node and base station classes. For
example, as indicated above, both pico eNB and femto HeNBs are
considered to be low power nodes.
[0006] Small cell enhancements for E-UTRA and E-UTRAN will focus on
additional functionalities for enhanced performance in hotspot
areas for indoor and outdoor using such low power nodes.
[0007] Currently, the average geographic density of macro cells is
5-7 macro cells per square kilometre. However, it is predicted that
the number of small cells in urban areas will reach 40 small cells
per square kilometre. The increasing geographic density of small
cells presents challenges in achieving successful and efficient
handover procedures in HetNets.
[0008] R1-130748, the contents of which are herein incorporated by
reference, is a 3GPP text proposal for TR36.923, on `Small Cell
Enhancement Scenarios`, which describes a number of scenarios for
further evaluation including, for example: a scenario in which
macro and small cells are provided on the same carrier frequency
(intra-frequency); a scenario in which macro and small cells are
provided on different carrier frequencies (inter-frequency); and a
scenario in which macro cell coverage is not present, resulting in
the presence of only small cells, on one or more carrier
frequency.
[0009] In each scenario, the cells are considered to be connected
via a non-ideal backhaul (e.g. a typical backhaul widely used in
the market such as xDSL, microwave, and other backhauls like
relaying) as opposed to via an ideal backhaul (e.g. a very high
throughput and very low latency backhaul such as dedicated
point-to-point connection using optical fiber).
[0010] 3GPP technical document R2-130845, the contents of which are
herein incorporated by reference, comprises the basis for a 3GPP
technical report (3GPP TR 36.842) that highlights a number of
issues that need resolving for each of these scenarios including,
inter alias [0011] a) mobility robustness; [0012] b) difficulties
in improving system capacity by utilising radio resources in more
than one base station; [0013] c) increased signalling load (e.g.,
to CN) due to frequent handover; [0014] d) difficulties in
improving per-user throughput by utilising radio resources in more
than one base station; [0015] e) network planning and configuration
effort;
[0016] Referring, for example, to issue (c) relating to increased
signalling load (e.g., to CN) due to frequent handover, handover
between the small cells may comprise a so called `S1` based
handover involving S1 signalling with a mobility management entity
(MME) in the core network, which MME is responsible for controlling
mobility of a UE between cells (e.g. where there is no X2
connectivity between the small cells). Alternatively, handover
between the small cells may comprise an `X2` based handover
involving X2 signalling with the target small cell base station and
which involves S1AP path switch messages being exchanged via the
core network.
[0017] In the case of the former, S1 based handover situation, for
example, the following messages typically need to be exchanged for
inter small cell handover involving the core network: [0018] S1: HO
Required to MME [0019] S1: HO Request to another small cell [0020]
S1: HO Request Ack from small cell to MME [0021] S1: HO Command
from MME to small cell [0022] Handover Notify [0023] UE Context
Release Command [0024] UE Context Release Complete
[0025] And optional messages of: [0026] eNB Status Transfer [0027]
MME Status Transfer [0028] Location Report
[0029] Thus, MME signalling load for every handover includes at
least seven messages related to the radio access network. Moreover,
further signalling from a further core network entity (a serving
gateway (S-GW)) is required to switch the communication tunnel with
the core network (GTP tunnel) from source small cell to target
small cell.
[0030] In the case of the former, X2 based handover situation, for
example, MME signalling load for every handover comprises two
messages and the MME will also ensure that the communication tunnel
with the core network (GTP tunnel) is switched from the source cell
to target cell (requiring another two messages--namely an S1AP PATH
SWITCH REQUEST and an S1AP PATH SWITH REQUEST ACK message).
[0031] In the case of the scenario in which macro cell coverage is
not present, whilst the absence of a macro cell may reduce
interference from the macro on the same carrier as one or more of
the small cells, the absence of a macro cell can also add to the
complexity of addressing the issues highlighted above.
SUMMARY OF INVENTION
[0032] Accordingly, preferred exemplary embodiments of the present
invention aim to provide methods and apparatus which overcome or at
least alleviate the above issues.
[0033] In one aspect, the invention provides a gateway apparatus
for facilitating a change of communication cell for a mobile
communication device in a communication system, the gateway
apparatus being operable to receive messages from at least one base
station operating a respective cell of said communication system
and to forward the messages received from the at least one base
station to a communication entity in a core network, the gateway
apparatus comprising: receiving means for receiving, from at least
one of a source base station that operates a source cell in which
said mobile communication device is located and a target base
station that operates a target cell for said change of
communication cell, at least one message relating to said change of
communication cell; means for intercepting and processing said
message relating to said change of communication cell to determine
if said communication entity in the core network needs to be
notified of information relating to said change of communication
cell; generating means for generating, when it is determined that
said communication entity in the core network needs to be notified
of information relating to said change of communication cell, a
message for providing said information relating to said change of
communication cell to said core network entity; and transmitting
means for transmitting, to said communication entity in the core
network, said message for providing said information relating to
said change of communication cell.
[0034] The means for intercepting and processing may be operable to
determine whether or not said message relating to said change of
communication cell should be forwarded to said communication entity
in the core network.
[0035] The means for intercepting and processing may be operable to
determine whether messages relating to a change of communication
cell should be forwarded to said communication entity in the core
network based on a number of cell changes that have occurred since
messages relating to a change of communication cell were previously
forwarded to said communication entity in the core network. In this
case, the means for intercepting and processing may be operable to
determine that messages relating to a change of communication cell
should not be forwarded to said communication entity in the core
network when the number of cell changes that have occurred since
messages relating to a change of communication cell were previously
forwarded to said communication entity in the core network has not
exceeded a predetermined value. The means for intercepting and
processing may also be operable to determine that messages relating
to a change of communication cell should be forwarded to said
communication entity in the core network when the number of cell
changes that have occurred since messages relating to a change of
communication cell were previously forwarded to said communication
entity in the core network has reached or exceeded the
predetermined value.
[0036] The generating means may be operable to generate, responsive
to said message relating to said change of communication cell, a
further message for progressing said change of communication cell;
and said transmitting means may be operable to transmit said
further message for progressing said change of communication cell
to said source base station or to said target base station. In this
case, the generating means may be operable to generate said further
message for progressing said change of communication cell without
forwarding the message relating to said change of communication
cell to the communication entity in the core network. The
generating means may be operable to generate said further message
for progressing said change of communication cell based on
information obtained by said means for intercepting and processing
from messages previously forwarded to or from said communication
entity in said core network.
[0037] The means for intercepting and processing may be operable to
determine if said communication entity in the core network needs to
be notified of information relating to said change of communication
cell comprising location information. In this case, the message for
providing said information relating to said change of communication
cell to said communication entity in the core network may comprise
a location report for providing said location information.
[0038] The means for intercepting and processing may be operable to
determine if said communication entity in the core network needs to
be notified of information relating to said change of communication
cell comprising information identifying communication bearers that
the target base station has failed to set up. In this case, the
message for providing said information relating to said change of
communication cell to said communication entity in the core network
may comprise a message identifying said communication bearers that
the target base station has failed to set up.
[0039] The receiving means may be operable to receive, from said
communication entity in the core network in response to said
message identifying said communication bearers that the target base
station has failed to set up, a message for initiating a
modification in a communication parameter for communication by said
mobile communication device in said target cell. In this case, the
message for initiating a modification in a communication parameter
may be configured to initiate a change in an aggregate maximum bit
rate.
[0040] The means for intercepting and processing may be operable to
determine, from a message relating to said change of communication
cell received from said source base station, whether direct data
forwarding is possible for at least one communication bearer of
said mobile communication device. In this case, the generating
means may be operable to generate, responsive to said determination
of whether direct data forwarding is possible, a message indicating
whether direct data forwarding is possible for sending to said
target base station.
[0041] The generating means may be operable to generate, responsive
to a determination that direct data forwarding is possible, a
message comprising parameters for establishing a direct
communication tunnel for forwarding data directly between said
source and target base stations.
[0042] The gateway apparatus may be operable, responsive to a
determination that direct data forwarding is not possible, to
facilitate establishment of an indirect communication tunnel for
forwarding data indirectly between said source and target base
stations via said gateway apparatus. The gateway apparatus may also
be operable to facilitate said establishment of an indirect
communication tunnel using a tunnel creation request (e.g. a Create
Indirect Data Forwarding Tunnel Request message) and a
corresponding response message (e.g. a Create Indirect Data
Forwarding Tunnel Response message).
[0043] The gateway apparatus may be operable to terminate messages
related to said change of communication cell, received from said
source base station or from said target base station and destined
for said communication entity in the core network, without
forwarding them to said communication entity in the core
network.
[0044] The gateway apparatus may be a small cell gateway apparatus.
The gateway apparatus may comprise at least one of a home base
station gateway (HeNB-GW) function, a security gateway (SeGW), and
an X2 gateway (X2-GW) function. The communication entity in the
core network may be a mobility management entity (MME). The base
station may comprise a low power node (LPN) operating a small cell
(e.g. a pico, femto or micro cell). The at least one message
relating to said change of communication cell may be a message in
accordance with the S1 application protocol (S1AP).
[0045] In another aspect, the invention provides a gateway
apparatus for facilitating a change of communication cell for a
mobile communication device in a communication system, the gateway
apparatus comprising: means for storing, at the gateway apparatus,
context information for the mobile communication device relating to
a communications connection between the mobile communication device
and a source base station that operates a source cell in which said
mobile communication device is located; means for receiving, from
at least one of a source base station that operates a source cell
in which said mobile communication device is located and a target
base station that operates a target cell for said change of
communication cell, at least one message relating to said change of
communication cell; means for generating at least one further
message for progressing said change of communication cell
responsive to said at least one message relating to said change of
communication cell using said context information; and means for
transmitting, to at least one of said source base station and said
target base station, said at least one further message for
progressing said change of communication cell.
[0046] In this case, the at least one further message for
progressing said change of communication cell may comprise a
message for transferring said context information to said target
base station. The context information may comprise security context
information relating to the communications connection between the
mobile communication device and the source base station (e.g.
including at least one security key). The gateway apparatus may be
operable to determine whether or not to initiate the transfer of
said context information, including said security context
information, based on a number of cell changes that have occurred
since the security context information was last updated. The
gateway apparatus may be operable to determine to initiate the
transfer of said context information, including said security
context information, when the number of cell changes that have
occurred since the security context information was last updated
has not exceeded a predetermined value.
[0047] The gateway apparatus may be operable to determine not to
initiate the transfer of said context information, including said
security context information, when the number of cell changes that
have occurred since the security context information was last
updated has reached or exceeded said predetermined value. In this
case, the gateway apparatus may be operable to initiate an update
to said security context information when the number of cell
changes that have occurred since the security context information
was last updated has reached or exceeded said predetermined
value.
[0048] In yet another aspect, the invention provides a gateway
apparatus for facilitating a change of communication cell for a
mobile communication device in a communication system, the gateway
apparatus being operable to receive messages from at least one base
station operating a respective cell of said communication system
and to forward the messages received from the at least one base
station to a communication entity in a core network, the gateway
apparatus comprising: means for receiving, from at least one of a
source base station that operates a source cell in which said
mobile communication device is located and a target base station
that operates a target cell for said change of communication cell,
at least one message relating to said change of communication cell;
means for intercepting and processing said message relating to said
change of communication cell to determine whether said message
relating to a change of communication cell should be forwarded to
said communication entity in the core network based on a number of
cell changes that have occurred since messages relating to a change
of communication cell were previously forwarded to said
communication entity in the core network; means for generating,
when it is determined that said message relating to a change of
communication cell should not be forwarded to said communication
entity in the core network, a further message for progressing said
change of communication cell; means for transmitting, when it is
determined that said message relating to a change of communication
cell should not be forwarded to said communication entity in the
core network, to said source base station or to said target base
station, said further message for progressing said change of
communication cell; and means for forwarding said message relating
to a change of communication cell to said communication entity in
the core network, when it is determined that said message relating
to a change of communication cell should be forwarded to said
communication entity in the core network.
[0049] In a further aspect, the invention provides a gateway
apparatus for facilitating a change of communication cell for a
mobile communication device in a communication system, the gateway
apparatus being operable to receive messages from at least one base
station operating a respective cell of said communication system
and to forward the messages received from the at least one base
station to a communication entity in a core network, the gateway
apparatus comprising: means for receiving, from at least one of a
source base station that operates a source cell in which said
mobile communication device is located and a target base station
that operates a target cell for said change of communication cell,
at least one message relating to said change of communication cell;
means for intercepting and processing said message relating to said
change of communication cell to determine, from a message relating
to said change of communication cell received from said source base
station, whether direct data forwarding is possible for at least
one communication bearer of said mobile communication device; means
for generating, responsive to said determination of whether direct
data forwarding is possible, a message indicating whether direct
data forwarding is possible for sending to said target base
station; and means for transmitting, said message indicating
whether direct data forwarding is possible to said target base
station.
[0050] In another aspect, the invention provides a gateway
apparatus for facilitating a change of communication cell for a
mobile communication device in a communication system, the gateway
apparatus being operable to receive messages from at least one base
station operating a respective cell of said communication system
and to forward the messages received from the at least one base
station to a communication entity in a core network, the gateway
apparatus comprising a processor and transceiver circuitry,
wherein: said transceiver circuitry is configured to receive, from
at least one of a source base station that operates a source cell
in which said mobile communication device is located and a target
base station that operates a target cell for said change of
communication cell, at least one message relating to said change of
communication cell; said processor is configured to: i) intercept
and process said message relating to said change of communication
cell to determine if said core network entity needs to be notified
of information relating to said change of communication cell; and
ii) generate, when it is determined that said communication entity
in the core network needs to be notified of information relating to
said change of communication cell, a message for providing said
information relating to said change of communication cell to said
communication entity in the core network; and said transceiver
circuitry is configured to transmit, to said communication entity
in the core network, said message for providing said information
relating to said change of communication cell.
[0051] In another aspect, the invention provides a gateway
apparatus for facilitating a change of communication cell for a
mobile communication device in a communication system, the gateway
apparatus comprising a processor, a memory, and transceiver
circuitry, wherein: said processor is configured to store in said
memory context information for the mobile communication device
relating to a communications connection between the mobile
communication device and a source base station that operates a
source cell in which said mobile communication device is located;
said transceiver circuitry is configured to receive, from at least
one of a source base station that operates a source cell in which
said mobile communication device is located and a target base
station that operates a target cell for said change of
communication cell, at least one message relating to said change of
communication cell; said processor is configured to generate at
least one further message for progressing said change of
communication cell responsive to said at least one message relating
to said change of communication cell using said context
information; and said transceiver circuitry is configured to
transmit, to at least one of said source base station and said
target base station, said at least one further message for
progressing said change of communication cell.
[0052] In another aspect, the invention provides a gateway
apparatus for facilitating a change of communication cell for a
mobile communication device in a communication system, the gateway
apparatus being operable to receive messages from at least one base
station operating a respective cell of said communication system
and to forward the messages received from the at least one base
station to a communication entity in a core network, the gateway
apparatus comprising a processor and transceiver circuitry,
wherein: said transceiver circuitry is configured to receive, from
at least one of a source base station that operates a source cell
in which said mobile communication device is located and a target
base station that operates a target cell for said change of
communication cell, at least one message relating to said change of
communication cell;
[0053] said processor is configured to: i) intercept and process
said message relating to said change of communication cell to
determine whether said message relating to a change of
communication cell should be forwarded to said communication entity
in the core network based on a number of cell changes that have
occurred since messages relating to a change of communication cell
were previously forwarded to said communication entity in the core
network; and ii) generate, when it is determined that said message
relating to a change of communication cell should not be forwarded
to said communication entity in the core network, a further message
for progressing said change of communication cell; means for
transmitting, when it is determined that said message relating to a
change of communication cell should not be forwarded to said
communication entity in the core network, to said source base
station or to said target base station, said further message for
progressing said change of communication cell; and said transceiver
circuitry is configured to forward said message relating to a
change of communication cell to said communication entity in the
core network, when it is determined that said message relating to a
change of communication cell should be forwarded to said
communication entity in the core network.
[0054] In another aspect, the invention provides a gateway
apparatus for facilitating a change of communication cell for a
mobile communication device in a communication system, the gateway
apparatus being operable to receive messages from at least one base
station operating a respective cell of said communication system
and to forward the messages received from the at least one base
station to a communication entity in a core network, the gateway
apparatus comprising a processor and transceiver circuitry,
wherein: said transceiver circuitry is configured to receive, from
at least one of a source base station that operates a source cell
in which said mobile communication device is located and a target
base station that operates a target cell for said change of
communication cell, at least one message relating to said change of
communication cell; said processor is configured to: i) intercept
and process said message relating to said change of communication
cell to determine, from a message relating to said change of
communication cell received from said source base station, whether
direct data forwarding is possible for at least one communication
bearer of said mobile communication device; and ii) generate,
responsive to said determination of whether direct data forwarding
is possible, a message indicating whether direct data forwarding is
possible for sending to said target base station; and said
transceiver circuitry is configured to transmit, said message
indicating whether direct data forwarding is possible to said
target base station.
[0055] The invention also provides a communication system
comprising the above described gateway apparatus, at least one
mobile communication device, a source base station and a target
base station.
[0056] In another aspect, the invention provides a method performed
by a gateway apparatus for facilitating a change of communication
cell for a mobile communication device in a communication system,
the gateway apparatus being operable to receive messages from at
least one base station operating a respective cell of said
communication system and to forward the messages received from the
at least one base station to a communication entity in a core
network, the method comprising: receiving, from at least one of a
source base station that operates a source cell in which said
mobile communication device is located and a target base station
that operates a target cell for said change of communication cell,
at least one message relating to said change of communication cell;
intercepting and processing said message relating to said change of
communication cell to determine if said communication entity in the
core network needs to be notified of information relating to said
change of communication cell; generating, when it is determined
that said communication entity in the core network needs to be
notified of information relating to said change of communication
cell, a message for providing said information relating to said
change of communication cell to said communication entity in the
core network; and transmitting, to said communication entity in the
core network, said message for providing said information relating
to said change of communication cell.
[0057] In another aspect, the invention provides a method performed
by a gateway apparatus for facilitating a change of communication
cell for a mobile communication device in a communication system,
the method comprising: storing, at the gateway apparatus, context
information for the mobile communication device relating to a
communications connection between the mobile communication device
and a source base station that operates a source cell in which said
mobile communication device is located; receiving, from at least
one of a source base station that operates a source cell in which
said mobile communication device is located and a target base
station that operates a target cell for said change of
communication cell, at least one message relating to said change of
communication cell; generating at least one further message for
progressing said change of communication cell responsive to said at
least one message relating to said change of communication cell
using said context information; and transmitting, to at least one
of said source base station and said target base station, said at
least one further message for progressing said change of
communication cell.
[0058] In another aspect, the invention provides a method performed
by a gateway apparatus for facilitating a change of communication
cell for a mobile communication device in a communication system,
the gateway apparatus being operable to receive messages from at
least one base station operating a respective cell of said
communication system and to forward the messages received from the
at least one base station to a communication entity in a core
network, the method comprising: receiving, from at least one of a
source base station that operates a source cell in which said
mobile communication device is located and a target base station
that operates a target cell for said change of communication cell,
at least one message relating to said change of communication cell;
intercepting and processing said message relating to said change of
communication cell to determine whether said message relating to a
change of communication cell should be forwarded to said
communication entity in the core network based on a number of cell
changes that have occurred since messages relating to a change of
communication cell were previously forwarded to said communication
entity in the core network; generating, when it is determined that
said message relating to a change of communication cell should not
be forwarded to said communication entity in the core network, a
further message for progressing said change of communication cell;
transmitting, when it is determined that said message relating to a
change of communication cell should not be forwarded to said
communication entity in the core network, to said source base
station or to said target base station, said further message for
progressing said change of communication cell; and forwarding said
message relating to a change of communication cell to said
communication entity in the core network, when it is determined
that said message relating to a change of communication cell should
be forwarded to said communication entity in the core network.
[0059] In another aspect, the invention provides a method performed
by a gateway apparatus for facilitating a change of communication
cell for a mobile communication device in a communication system,
the gateway apparatus being operable to receive messages from at
least one base station operating a respective cell of said
communication system and to forward the messages received from the
at least one base station to a communication entity in a core
network, the method comprising: receiving, from at least one of a
source base station that operates a source cell in which said
mobile communication device is located and a target base station
that operates a target cell for said change of communication cell,
at least one message relating to said change of communication cell;
intercepting and processing said message relating to said change of
communication cell to determine, from a message relating to said
change of communication cell received from said source base
station, whether direct data forwarding is possible for at least
one communication bearer of said mobile communication device;
generating, responsive to said determination of whether direct data
forwarding is possible, a message indicating whether direct data
forwarding is possible for sending to said target base station; and
transmitting, said message indicating whether direct data
forwarding is possible to said target base station.
[0060] Aspects of the invention extend to computer program products
such as computer readable storage media having instructions stored
thereon which are operable to program a programmable processor to
carry out a method as described in the aspects and possibilities
set out above or recited in the claims and/or to program a suitably
adapted computer to provide the apparatus recited in any of the
claims.
[0061] Although for efficiency of understanding for those of skill
in the art, the invention will be described in detail in the
context of a 3G system (UMTS, LTE), the principles of the invention
can be applied to other systems (such as WiMAX) in which (home)
base stations communicate via a signalling gateway with the
corresponding elements of the system changed as required.
BRIEF DESCRIPTION OF DRAWINGS
[0062] Exemplary embodiments of the invention will now be
described, by way of example, with reference to the accompanying
drawings in which:
[0063] FIG. 1 schematically illustrates a mobile telecommunication
system of a type to which the invention is applicable;
[0064] FIG. 2 schematically illustrates a mobile telecommunication
system of another type to which the invention is applicable;
[0065] FIG. 3 is a block diagram illustrating the main components
of a mobile communication device forming part of the system shown
in FIG. 1 or FIG. 2;
[0066] FIG. 4 is a block diagram illustrating the main components
of a base station forming part of the system shown in FIG. 1 or
FIG. 2;
[0067] FIG. 5 is a block diagram illustrating the main components
of a small cell gateway forming part of the system forming part of
the system shown in FIG. 1 or FIG. 2;
[0068] FIG. 6 is an exemplary timing diagram illustrating a method
performed by components of the mobile telecommunication system of
FIG. 1 whilst carrying out an embodiment of the invention;
[0069] FIG. 7 is an exemplary timing diagram illustrating another
method performed by components of the mobile telecommunication
system of FIG. 1 whilst carrying out an embodiment of the
invention;
[0070] FIG. 8 is an exemplary timing diagram illustrating another
method performed by components of the mobile telecommunication
system of FIG. 1 whilst carrying out an embodiment of the
invention;
[0071] FIG. 9 is an exemplary timing diagram illustrating another
method performed by components of the mobile telecommunication
system of FIG. 1 whilst carrying out an embodiment of the
invention;
[0072] FIG. 10 illustrates an architecture for a small cell
gateway;
[0073] FIG. 11 illustrates another architecture for a small cell
gateway;
[0074] FIG. 12 shows an exemplary control plane architecture for an
exemplary communication system;
[0075] FIG. 13 shows an exemplary user plane architecture for an
exemplary communication system;
[0076] FIG. 14 is an exemplary timing diagram for an initial RRC
connection establishment by a mobile communication device; and
[0077] FIG. 15 is an exemplary timing diagram illustrating a
handover scenario in a communication system configured for virtual
dual connectivity.
MODE FOR CARRYING OUT THE INVENTION
Overview
[0078] FIGS. 1 and 2 each schematically illustrates a mobile
(cellular) telecommunication system 1 including a mobile
communication device 3 comprising a mobile telephone (or other
compatible user equipment) and a plurality of small cell base
stations 5-1 to 5-3 (which may be any suitable small cell base
station for example, Home evolved NodeBs (HeNBs), pico or femto
base stations or the like) but which may be any suitable small cell
base station) each of which operates an associated small cell 10-1
to 10-3 arranged in a cluster.
[0079] Each base station 5 is coupled to a core network 7 via a
small cell gateway 14 and the core network 7 is also coupled to
other networks (e.g. the Internet) via one or more gateways (not
shown). The core network 7 includes a mobility management entity
(MME) 12, a serving gateway (S-GW) 16 (and other communication
entities such as a Packet Data Network (PDN) Gateway (PGW), which
have also been omitted for sake of simplicity). The mobile
communication device 3 is served via a small cell 10-2 operated by
one of the base stations 5-2.
[0080] The backhaul from the base stations 5 to the core network 7
is considered to be non-ideal (e.g. comprising a typical backhaul
such as xDSL or microwave). Further, in the arrangement of cells
shown in FIG. 1 there is no macro cell, within the vicinity, which
the mobile communication device 3 can connect to or can receive
information (such as system information) or reference signals from.
Accordingly, this conforms with the scenario, described in
R1-130748, in which macro cell coverage is not present, resulting
in the presence of only small cells, on one or more carrier
frequency
[0081] Communication between the base stations 5 and the MME 12 is
via a so-called `S1` interface. An `X2` interface is also provided
for communication between neighbouring base stations 5 to
facilitate data exchange between them. As those skilled in the art
will appreciate, whilst one mobile communication device 3 and three
base stations 5 are shown in FIG. 1 for illustration purposes,
additional user equipment and/or base stations may be present in a
deployed system. As illustrated, the mobile communication device 3
is located within cell 10-2, and base station 5-2 acts as a serving
cell for the mobile communication device 3. Connection of the
mobile communication device 3 with a serving base station 5-2
allows the mobile communication device 3 to perform communication
actions such as registering with the network, updating its
registration, and establishing a data session or a voice call.
[0082] However, when the mobile communication device 3 approaches
the edge of cell 10-2, or when the signal conditions within this
cell begin to deteriorate, for example due to path loss, physical
environment or power limitation, it becomes necessary for the
mobile communication device 3 to handover to another cell, such as
cell 10-1 or 10-3, or any other suitable cell.
[0083] Further reasons for handover becoming necessary may include,
for example, the presence of regions where the signals from the
serving base station 5-2 cannot be decoded by the mobile
communication device 3. Also, in uplink, because a base station may
communicate with many mobile communication devices, its resources
may become limited or insufficient. Such limited cell coverage or
lack of base station resources results in fewer services for users
and on-going communication/applications may suffer, for example
experiencing increased latency.
[0084] The serving base station 5-2 receives information from the
mobile communication device 3 which it uses to determine when
handover becomes necessary for the mobile communication device 3,
and to identify a plurality of suitable candidate target cells. The
information received by the base station 5-2 could be any
information measured by the mobile communication device 3 or
information deduced from the measurements performed by the mobile
communication device 3.
[0085] The mobile communication device 3 is therefore configured
(by or via base station 5-2) to perform signal measurements with
respect to its neighbouring cells and/or serving cell and to report
the results based on these measurements when certain predetermined
signal conditions are met.
[0086] The small cell base stations 5 and MME 12 are operable in
accordance with the so-called S1 application protocol (S1AP) in
accordance with 3GPP TS 36.413 the contents of which are herein
incorporated by reference. SLAP provides the signalling service
between the small base stations 5 of the E-UTRAN and the evolved
packet core (EPC) that is required to fulfil a number of S1AP
functions including, inter alia: [0087] Evolved Radio Access Bearer
(E-RAB) management functions for setting up, modifying and
releasing E-RABs, which are triggered by the MME 12. The release of
E-RABs may be triggered by the base station 5 as well. [0088]
Initial Context Transfer functions to establish an S1 context for
the mobile communication device 3 in the base station 5, to setup
the default IP connectivity, to setup one or more E-RAB(s) if
requested by the MME 12, and to transfer non-access stratum (NAS)
signalling related information to the base station 5 if needed.
[0089] UE Capability Information Indication functions to provide
the capability information for the mobile communication device 3,
when received from the mobile communication device 3 to the MME 12.
[0090] Mobility Functions for mobile communication devices 3
operating in an active mode to enable a change of base station via
the S1 interface and/or a change of radio access network (RAN)
nodes between different radio access technologies (RATs) via the S1
interface. [0091] Paging functionality which allows the EPC the
capability to page the mobile communication device 3. [0092] S1
interface management functions including: reset functionality to
ensure a well defined initialisation on the S1 interface; error
Indication functionality to allow a proper error reporting/handling
in cases where no failure messages are defined; an overload
function to indicate the load situation in the control plane of the
S1 interface; a load balancing function to ensure equally loaded
MMEs 12 within an MME pool area; S1 setup functionality for initial
S1 interface setup for providing configuration information; base
station 5 and MME 12 configuration update functions are to update
application level configuration data needed for the base station 5
and MME 12 to interoperate correctly on the S1 interface. [0093]
Non-Access Stratum (NAS) signalling transport functionality between
the mobile communication device 3 and the MME 12: to transfer NAS
signalling related information and to establish the S1 context for
the mobile communication device 3 in the base station 5; to
transfer NAS signalling related information when the S1 context for
the mobile communication device 3 in the base station 5 is already
established. [0094] S1 UE context release functionality to manage
the release of a mobile communication device specific context in
the base station 5 and the MME 12. [0095] UE context modification
functionality to modify the established context for the mobile
communication device 3 partly. [0096] Status transfer functionality
for transferring Packet Data Convergence Protocol (PDCP) Sequence
Number (SN) status information from a source base station to a
target base station in support of in-sequence delivery of data and
duplication avoidance for intra LTE handover. [0097] Location
reporting functionality to allow the MME 12 to be aware of the
mobile communication devices current location.
[0098] The small cell gateway 14 is provided both: with
conventional HeNB-GW functionality for receiving and forwarding S1
signalling between the base station 5 and the MME 12; and with
X2-GW functionality for receiving and forwarding X2 signalling
between base stations.
[0099] Beneficially, in one exemplary embodiment (as illustrated in
FIG. 1), S1 mobility related signalling for the purposes of
handover is terminated in the small cell gateway 14 as opposed to
the MME 12 as is conventionally the case, thereby avoiding
additional signalling with the core network 7.
[0100] Specifically, the small cell gateway 14 is able to receive
S1 signalling, from the base station 5-2 of a source small cell
10-2, that indicates that handover is required. The small cell
gateway 14 is, advantageously, able to determine, based on this S1
signalling, without involving the core network 7 (e.g. without
involving the MME 12), that handover is required. Further, the
small cell gateway 14 is able to generate, when it is determined
that handover is required, appropriate S1 signalling for
communicating with the base stations 5 of a target cell (e.g. cell
10-1 or cell 10-3) and the source cell 10-2, (and for receiving
associated response signalling from the respective base stations 5
of the target cell (e.g. cell 10-1 or cell 10-3) and the source
cell 10-2) in pursuit of handover of the mobile communication
device 3 from the source small cell 5-2, to the target small cell
(e.g. cell 10-1 or cell 10-3) without additional, unnecessary
signalling directed to the MME 12.
[0101] It is noted, however, that termination of handover
signalling in the small cell gateway 14 does not, by itself,
provide the flexibility to handle some more complex situations that
may become increasingly prevalent as small cell scenarios become
more ubiquitous.
[0102] In this exemplary embodiment, greater flexibility is
beneficially provided, by allowing some communication between the
small cell gateway 14 and the core network 7 even where handover is
terminated at the small cell gateway 14.
[0103] Advantageously, for example, greater flexibility is
beneficially provided by having the small cell gateway 14 monitor
whether set up of any communication bearers supported at the source
small cell base station 5-2 has failed at the target base station
5-1 or 5-3. If set up of any communication bearers supported at the
source small cell base station has failed at the target base
station 5-1 or 5-3, then the small cell gateway 14 communicates
with the MME 12, and the target small cell base station 5-1 or 5-3
in order to initiate an appropriate change in the aggregate maximum
bit rate for the mobile communication device 3.
[0104] The aggregate maximum bit rate (UE-AMBR) limits the
aggregate bit rate that can be expected to be provided across all
non-guaranteed bit rate (non-GBR) bearers for a mobile
communication device. Accordingly, updating the UE-AMBR as
described above allows for better utilisation of the resources,
when communication bearers are rejected, because it allows the
UE-AMBR to be dynamically reduced so that resources can be
allocated to other mobile communication devices.
[0105] Moreover, in this exemplary embodiment, greater flexibility
is beneficially provided by having the small cell gateway 14
monitor whether location reporting is required, when there is a
change in the serving cell, to store an indicator that the location
reporting is required in response to a change in the serving cell,
and to generate a location report and send it to the core network 7
accordingly. Hence, the core network 7 is advantageously able to
maintain is ability to keep track of the mobile communication
device's location, when required, in response to the change of cell
despite other S1 signalling being terminated in the small cell
gateway 14.
[0106] This exemplary embodiment also provides greater flexibility
by providing a mechanism for supporting both direct and indirect
forwarding of downlink data from the source cell 10-2 to the target
cell 10-1, 10-3 during handover in order to avoid, or at least
mitigate, potential loss of downlink data. This mechanism involves
the small cell gateway 14 receiving an indication, from the source
cell base station 5-2, as to whether direct data forwarding is
supported or not and then providing a corresponding indication to
the target cell base station 5-1, 5-3. In the case of direct
forwarding, the downlink data can then be forwarded directly from
the source cell base station 5-2 to the target cell base station
5-1, 5-3 without further involvement of the small cell gateway 14
in the data forwarding process. In the case of indirect forwarding,
the small cell gateway 14 manages the setup and configuration of a
communication tunnel for forwarding the downlink data from the
source cell base station 5-2 to the target cell base station 5-1,
5-2.
[0107] It will be appreciated that although this exemplary
embodiment has been introduced with reference to S1 interface based
handover a similar approach can also be applied for signalling,
during an X2 based handover, directed towards the core network
(e.g. the MME/Se-GW). One difference, compared to the S1 based
handover will, of course, be the presence of X2-GW assisting in X2
signalling between small cells in pursuance of the handover.
[0108] Beneficially, in another exemplary embodiment (as
illustrated in FIG. 2), instead of terminating S1 signalling in the
small cell gateway 14 in the manner introduced above, the small
cell gateway is operable to provide `virtual` dual connectivity in
which the mobile communication device 3 can have simultaneous
`connectivity` to two cells: a secondary cell (SCell) which, in
this exemplary embodiment, is the small cell 10-2 operated by the
small cell base station 5-2 via which the mobile communication
device 3 is connected to the network; and a `virtual` primary cell
(PCell) 15 which appears, to the mobile communication device 3, to
be a `virtual macro cell` via which the small cell is connected to
the network.
[0109] Specifically, the `virtual` dual connectivity is implemented
by storing a `virtual macro cell` context in the small cell gateway
14. The mobile communication device 3 is, effectively, provided
with a `virtual` association to the `virtual macro cell` 15 but
does not have a physical association.
[0110] Accordingly, since the source small cell 10-2 is in the
effective coverage of the `virtual` macro cell 15, a dual
connection can be used for handover in order to simplify the
inter-node signalling exchange. Thus, when small cell to small cell
handover occurs this is dealt with at the small cell gateway 14 and
no signalling is required towards the core network 7.
Mobile Communication Device
[0111] FIG. 3 is a block diagram illustrating the main components
of the mobile communication device 3 shown in FIGS. 1 and 2. As
shown, the mobile communication device 3 includes a transceiver
circuit 310 which is operable to transmit signals to, and to
receive signals from, the base station 5 and/or other mobile
communication devices (not illustrated in FIG. 1) via at least one
antenna 312. The mobile communication device 3 may of course have
all the usual functionalities of a conventional mobile
communication device (such as a user interface 314 which may
comprise input and output devices such as microphones, touch
screen, keypad, speaker and/or the like) and this may be provided
by any combination of hardware, software and firmware, as
appropriate. The operation of the transceiver circuit 310 is
controlled by a controller 316 in accordance with software stored
in memory 318. The software includes, among other things, an
operating system 318, a communication control module 322 and a
measurement module 325.
[0112] The communication control module 322 is operable to handle
(e.g. generate, send and receive) control signals for controlling
the connections between the mobile communication device 3 and other
user equipment or various network nodes, such as the serving base
station 5-2.
[0113] The measurement module 325 is operable to perform desired
signal measurements (e.g. CRS or CSI-RS measurements), to determine
associated signal quality values (e.g. RSRP and RSRQ) and to
generate and send associated measurement reports as appropriate
under the control of the communication control module 322.
Base Station
[0114] FIG. 4 is a block diagram illustrating the main components
of one of the small cell base stations 5 shown in FIGS. 1 and 2,
such as serving base station 5-2. As shown, the base station 5
includes a transceiver circuit 410 which is operable to transmit
signals to, and to receive signals from, the mobile communication
device 3 via at least one antenna 412. The base station 5 is also
operable to transmit signals to and to receive signals from nodes
in the core network 7 (such as the MME 12 or the S-GW 16), via the
small cell gateway 14, using network interface 414 which comprises
the S1 interface. The base station 5 is also operable to transmit
signals to and to receive signals from other base stations (macro
or small) either using the functionality of the small cell gateway
14 or via a dedicated eNB (X2) interface 415. The operation of the
transceiver circuit 410 is controlled by a controller 416 in
accordance with software stored in memory 418. The software
includes, among other things, an operating system 420, a
communication control module 422, a measurement configuration
module 423, and a handover management module 425 comprising a
handover signalling module 426 and a data forwarding module
427.
[0115] The communication control module 422 is operable to control
communications between the base station 5 and the mobile
communication device 3, between the base station 5 and the network
devices such as the MME 12, SGW 16 via the small cell gateway 14,
and between the base station 5 and other base stations via the X2
interface 415 or via the X2-GW functionality of the small cell
gateway 14.
[0116] The measurement configuration module 423 is operable to
configure the mobile communication device 3 to perform required
signal measurements (for example CRS or CSI-RS measurements) and to
sending associated information in a measurement report as
appropriate (e.g. in response to a specific event).
[0117] The handover management module 425 is operable to manage
aspects of handover procedures performed at the base station 5
including generation and transmission of appropriate handover
signalling by the handover signalling module 426 and managing the
forwarding of downlink data via the data forwarding module 427.
Small Cell Gateway
[0118] FIG. 5 is a block diagram illustrating the main components
of the small cell gateway 14 shown in FIGS. 1 and 2. As shown, the
small cell gateway 14 includes a transceiver circuit 510 which is
operable to transmit signals to, and to receive signals from, nodes
in the core network 7 (such as the MME 12 or the SGW 16), via an
associated network interface 514 comprising the S1 interface. The
small cell gateway 14 is also operable to transmit signals to and
to receive signals from base stations 5 via an eNB interface 515
including both an S1 and X2 interface. The operation of the
transceiver circuit 510 is controlled by a controller 516 in
accordance with software stored in memory 518. The software
includes, among other things, an operating system 520, a
communication control module 522, a handover management module 525
comprising a handover signalling module 526 and a data forwarding
module 527, an S1AP termination module 528, an HeNB-GW module 529
and X2-GW module 530.
[0119] The communication control module 522 is operable to control
communications between the small cell gateway 14 and the base
stations via the eNB interface 515 and between the small cell
gateway 14 and network devices such as the MME 12 and SGW 16 via
the network interface 514.
[0120] The handover management module 525 is operable to manage
aspects of handover procedures performed at the small cell gateway
14 including generation and transmission of appropriate handover
signalling by the handover signalling module 526 and managing the
forwarding of downlink data via the data forwarding management
module 527.
[0121] The S1AP termination module 528 provides S1AP functionality
at the small cell gateway thereby allowing the small cell gateway
to terminate S1 signalling at the small cell gateway (e.g. for
implementing the embodiment in which S1 signalling is terminated at
the gateway), and in particular handover related signalling. The
S1AP functionality includes the ability to process S1 messages
received from the base station 5 and to generate appropriate 51
response messages without the involvement of the core network. It
will be appreciated that although this module may not be necessary
for the exemplary embodiment of FIG. 5 it may, nevertheless, be
present to allow the flexibility to terminate of signalling if
required.
[0122] The HeNB-GW module 529 provides the HeNB-GW functionality to
allow the small cell gateway to continue to act as an intermediary
between the base station 5 and the core network 7 (e.g. for S1
signalling that is not terminated at the small cell gateway 14 such
as the exemplary embodiment in which S1 signalling is not
terminated at the gateway) and the X2-GW module 530 provides the
X2-GW functionality to allow the small cell gateway to act as an
intermediary between the base station 5 and other base stations for
X2 based signalling.
[0123] In the above description, the mobile communication device 3,
the base station 5 and the small cell gateway 14 are each described
for ease of understanding as having a number of discrete modules
(such as the communications control modules, the reporting module,
and the handover command module). Whilst these modules may be
provided in this way for certain applications, for example where an
existing system has been modified to implement the invention, in
other applications, for example in systems designed with the
inventive features in mind from the outset, these modules may be
built into the overall operating system or code and so these
modules may not be discernible as discrete entities. These modules
may also be implemented in software, hardware, firmware or a mix of
these.
Operation--Normal Handover
[0124] FIG. 6 illustrates operation of the exemplary embodiment in
which S1 handover related signalling is terminated at the gateway
during a normal handover from one small cell to another.
[0125] As seen in FIG. 6, when a handover becomes necessary (at
S600), the source small cell base station 5-2 generates and sends
an S1 message towards the core network 7 (i.e. to the small cell
gateway 14) (at S612) to indicate that handover is required and to
request that handover takes place (e.g. an S1AP: Handover Required
message).
[0126] The small cell gateway 14 intercepts the message indicating
that handover is required and does not forward it to the MME 12 but
instead processes it in the small cell gateway 14 and generates a
message requesting handover (e.g. an S1AP: Handover Request
message) and sends it (at S614) to the base station 5-1, 5-3 of the
target cell 10-1, 10-3 and informing the base station 5-1, 5-3 of
the target cell 10-1, 10-3 of relevant information such as a list
providing details of each Radio Access Bearer (E-RAB) that needs to
be set up.
[0127] In order to allow the small cell gateway 14 to provide the
relevant information to encode the S1AP Handover Request message
that are sent to small cell base station directly, the relevant
information (UE context) is stored at the small cell gateway 14
(e.g. information identifying the E-RABs that have been
established, transport layer address, E-RAB level quality of
service parameters, Aggregate Maximum Bit Rate) in association with
information identifying the mobile communication device to which
the information relates. This information is obtained by
intercepting appropriate S1 messages that are forwarded to and from
the MME 12 during normal operation (e.g. operation to set up
communication, establish radio access bearers etc.) and storing
relevant message contents for later use while preparing messages,
like the S1: Handover Request, for facilitating small gateway
terminated handover procedures. It will be appreciated that if the
small cell gateway 14 is unable to fill in all the relevant
information it can revert to forwarding the S1 messages to the MME
12 for the MME 12 to handle the handover signalling
appropriately.
[0128] The base station 5-1, 5-3 of the target cell 10-1, 10-3
responds (at S616) with a suitable acknowledgement (e.g. an S1AP:
Handover Request Acknowledgement message) which may indicate that
the appropriate communication bearers have been successfully set
up.
[0129] The small cell gateway 14 intercepts the acknowledgement
message and does not forward it to the MME 12 but instead processes
it in the small cell gateway 14 and generates and sends a message
instructing handover (e.g. an S1AP: Handover Command message) to
the base station 5-2 of the source cell 5-2 (at S628).
[0130] At this point forwarding of undelivered downlink data takes
place (if possible and if required) between the base station 5-2 of
the source cell 10-2 and the base station 5-1, 5-3 of the target
cell 10-1, 10-3 (at S630).
[0131] The target small cell base station 5-1, 5-3 sends an
appropriate notification message (e.g. an S1AP: Handover Notify
message) (at S632), once the mobile communication device 3 subject
to the handover has been identified in the target cell 10-1, 10-3
and that S1 handover has been completed at the target end.
[0132] The small cell gateway 14 intercepts the notification
message and does not forward it to the MME 12 but instead processes
it in the small cell gateway 14 and generates and sends a message
instructing release of the mobile communication device's context at
the source cell 10-2 (e.g. an S1AP: UE Context Release Command
message) to the base station 5-2 of the source cell 5-2 (at
S636).
[0133] The base station 5-2 of the source cell 10-2 responds by
releasing the mobile communication device's context and confirms
that the mobile communication device's context has been released at
the source cell 10-2 by sending an appropriate message (e.g. an
S1AP: UE Context Release Complete message) to the small cell
gateway 14 (at S638).
[0134] It will be appreciated that in the above operation, the
security context is not updated between MME 12 and small cell
gateway 14 after the mobile device has moved from one small cell to
another small cell because there is no signalling towards the core
network 7. In order to mitigate the security risk that this might
cause, a number of handovers or `hops` can beneficially be defined
(e.g. by the operator) during which handover signalling will
terminate in the small cell gateway. Once this predefined number of
`hops` has been reached the next small cell gateway 14 routes
handover signalling via the core network for the next handover in
order to ensure that the security context is updated. The small
cell gateway 14 can return to small cell gateway terminated
signalling for another set of `hops` and so on. Accordingly, in
this way security is compromised for a configurable number of hops
only. Information identifying the predetermined number of hops can
be exchanged between MME 12 and small cell gateway 14 using S1
signalling or can be provided by an operation and maintenance (OAM)
function.
Operation--Partial Rejection
[0135] FIG. 7 illustrates operation of the exemplary embodiment in
which S1 handover related signalling is terminated at the gateway
during a handover from one small cell to another in which handover
is partially rejected, e.g. due to a failure in the set up of some
radio access bearers at the base station 5-1, 5-3 of the target
cell 10-1, 10-3.
[0136] As seen in FIG. 7, when a handover becomes necessary (at
S700), the source small cell base station 5-2 proceeds much in the
same way as in FIG. 6 by generating and sending an S1 message to
the small cell gateway 14 (at S712) to indicate that handover is
required and to request that handover takes place (e.g. an S1AP:
Handover Required message).
[0137] The small cell gateway 14 intercepts the message indicating
that handover is required and does not forward it to the MME 12 but
instead processes it in the small cell gateway 14 and generates a
message requesting handover (e.g. an S1AP: Handover Request
message) and sends it (at S714) to the base station 5-1, 5-3 of the
target cell 10-1, 10-3 and informing the base station 5-1, 5-3 of
the target cell 10-1, 10-3 of relevant information such as a list
providing details of each Radio Access Bearer (E-RAB) that needs to
be set up.
[0138] The base station 5-1, 5-3 of the target cell 10-1, 10-3
responds (at S716) with a suitable acknowledgement (e.g. an S1AP:
Handover Request Acknowledgement message) which indicates that the
some of the communication bearers have not been successfully set up
(e.g. in an E-RABs Failed to Setup List information element).
[0139] The small cell gateway 14 intercepts the acknowledgement
message and does not forward it to the MME 12 but instead processes
it in the small cell gateway 14 and determines that handover has,
in effect, been partially rejected. The small cell gateway 14
responds to this determination (at S718) by sending a message to
the MME 12 identifying the bearers that have failed to set up (e.g.
in a E-RABs Released List information element (IE) in an S1AP:
E-RAB Release Indication message).
[0140] The MME 12 may respond by determining a new aggregate
maximum bit rate and by notifying the small cell gateway 14 (at
S720) of the new aggregate maximum bit rate in an appropriate
message (e.g. S1AP: UE Context Modification Request with a UE
Aggregate Maximum Bit Rate IE set appropriately). The small cell
gateway 14 forwards the message carrying the new aggregate maximum
bit rate to the base station 5-1, 5-3 of the target cell 10-1, 10-3
(at S722).
[0141] The base station 5-1, 5-3 of the target cell 10-1, 10-3
responds to the message carrying the new aggregate maximum bit rate
by modifying the context of the mobile communication device 3 in
the target cell 10-1, 10-3 by changing the aggregate maximum bit
rate appropriately and by generating and sending a corresponding
response message (e.g. an S1AP: UE Context Modification Response
message) to the small cell gateway 14 (at S724).
[0142] The small cell gateway 14 also generates and sends a message
instructing handover (e.g. an S1AP: Handover Command message) to
the base station 5-2 of the source cell 5-2 (at S728). At this
point forwarding of undelivered downlink data takes place (if
possible and if required) between the base station 5-2 of the
source cell 10-2 and the base station 5-1, 5-3 of the target cell
10-1, 10-3 (at S730).
[0143] The target small cell base station 5-1, 5-3 sends an
appropriate notification message (e.g. an S1AP: Handover Notify
message) (at S732), once the mobile communication device 3 subject
to the handover has been identified in the target cell 10-1, 10-3
and that S1 handover has been completed at the target end.
[0144] The small cell gateway 14 intercepts the notification
message and does not forward it to the MME 12 but instead processes
it in the small cell gateway 14 and generates and sends a message
instructing release of the mobile communication device's context at
the source cell 10-2 (e.g. an S1AP: UE Context Release Command
message) to the base station 5-2 of the source cell 5-2 (at
S736).
[0145] The base station 5-2 of the source cell 10-2 responds by
releasing the mobile communication device's context and confirms
that the mobile communication device's context has been released at
the source cell 10-2 by sending an appropriate message (e.g. an
S1AP: UE Context Release Complete message) to the small cell
gateway 14 (at S738).
Operation--Location Reporting
[0146] FIG. 8 illustrates operation of the exemplary embodiment in
which S1 handover related signalling is terminated at the gateway
during a normal handover from one small cell to another but in
which the MME 12 requires location information.
[0147] As seen in FIG. 8, before handover becomes necessary, the
MME 12 indicates (at S802) that location reporting is required by
sending an appropriate location reporting control message
indicating that location reporting is required in the event of a
change of serving cell) (e.g. an S1AP Location Reporting Control
message with a Request Type IE set to Event IE in the Request Type
IE set to "Change of service cell"). It will be appreciated that an
inbound mobility request (e.g. an S1AP: Handover Request message)
from MME 12 could be similarly configured to indicate that location
reporting is required.
[0148] The small cell gateway 14 stores an indication that location
reporting is required in the event of a change of serving cell at
S804.
[0149] When a handover becomes necessary (at S800), the source
small cell base station 5-2 proceeds much in the same way as in
FIG. 6 by generating and sending an S1 message to the small cell
gateway 14 (at S812) to indicate that handover is required and to
request that handover takes place (e.g. an S1AP: Handover Required
message).
[0150] The small cell gateway 14 intercepts the message indicating
that handover is required and does not forward it to the MME 12 but
instead processes it in the small cell gateway 14 and generates a
message requesting handover (e.g. an S1AP: Handover Request
message) and sends it (at S814) to the base station 5-1, 5-3 of the
target cell 10-1, 10-3 and informing the base station 5-1, 5-3 of
the target cell 10-1, 10-3 of relevant information such as a list
providing details of each Radio Access Bearer (E-RAB) that needs to
be set up.
[0151] The base station 5-1, 5-3 of the target cell 10-1, 10-3
responds (at S816) with a suitable acknowledgement (e.g. an S1AP:
Handover Request Acknowledgement message) which may indicate that
the appropriate communication bearers have been successfully set
up.
[0152] The small cell gateway 14 intercepts the acknowledgement
message and does not forward it to the MME 12 but instead processes
it in the small cell gateway 14 and generates and sends a message
instructing handover (e.g. an S1AP: Handover Command message) to
the base station 5-2 of the source cell 5-2 (at S828).
[0153] At this point forwarding of undelivered downlink data takes
place (if possible and if required) between the base station 5-2 of
the source cell 10-2 and the base station 5-1, 5-3 of the target
cell 10-1, 10-3 (at S830).
[0154] The target small cell base station 5-1, 5-3 sends an
appropriate notification message (e.g. an S1AP: Handover Notify
message) (at S832), once the mobile communication device 3 subject
to the handover has been identified in the target cell 10-1, 10-3
and that S1 handover has been completed at the target end.
[0155] The small cell gateway 14 intercepts the notification
message and does not forward it to the MME 12 but instead processes
it in the small cell gateway 14 and determines that location
reporting is now required as a result of the change of cell.
Accordingly, the small cell gateway 14 generates and sends a
location report (e.g. an S1AP: LOCATION REPORT message) as S834 to
the MME 12 in accordance with the earlier request and associated
stored information.
[0156] The small cell gateway 14 then generates and sends a message
instructing release of the mobile communication device's context at
the source cell 10-2 (e.g. an S1AP: UE Context Release Command
message) to the base station 5-2 of the source cell 5-2 (at S836).
The base station 5-2 of the source cell 10-2 responds by releasing
the mobile communication device's context and confirms that the
mobile communication device's context has been released at the
source cell 10-2 by sending an appropriate message (e.g. an S1AP:
UE Context Release Complete message) to the small cell gateway 14
(at S838).
Operation--Status Transfer
[0157] FIG. 9 illustrates operation of the exemplary embodiment in
which S1 handover related signalling is terminated at the gateway
during a normal handover from one small cell to another but in
which a transfer of status information (e.g. uplink/downlink Packet
Data Convergence Protocol (PDCP) Sequence Number (SN) and/or hyper
frame number (HFN)) is required in support of in-sequence delivery
of data and duplication avoidance for the handover. Such a status
transfer may be required, for example, for each respective E-RAB
for which PDCP-SN and HFN status preservation applies.
[0158] As seen in FIG. 9, when a handover becomes necessary (at
S900), the source small cell base station 5-2 proceeds much in the
same way as in FIG. 6 wherein the steps labelled using the format
S6nn in FIG. 6 correspond to steps sharing the same last two digits
but labelled using the format S9nn in FIG. 9.
[0159] Unlike FIG. 6, however, in FIG. 9 the base station 5-2 of
the source cell 10-2 determines, after any data forwarding at S930,
that a transfer of status information (e.g. uplink/downlink Packet
Data Convergence Protocol (PDCP) Sequence Number (SN) and/or hyper
frame number (HFN)) is required in support of in-sequence delivery
of data and duplication avoidance for the handover. The base
station 5-2 of the source cell 10-2 generates and sends an
appropriate status transfer message (e.g. an S1AP: eNB Status
Transfer Message) towards the core network 7 at S920.
[0160] The small cell gateway 14 intercepts the status transfer
message and does not forward it to the MME 12 but instead processes
it in the small cell gateway 14 and in response to the message
generates an appropriate status transfer message (e.g. an S1AP: MME
Status Transfer Message) for sending to the base station 5-1, 5-3
of the target cell 10-1, 10-3.
[0161] The remaining procedure then continues much in the same way
as in FIG. 6.
Operation--Data Forwarding
[0162] There are two data forwarding schemes which are supported by
the small cell gateway 14 for S1 based Small Cell to Small Cell
handover. The two schemes include direct data forwarding and
indirect data forwarding and these are described below.
[0163] Moreover, in the case of indirect data forwarding, two
different methods are described below depending on the architecture
chosen for the small cell gateway 14. The two different
architectures are illustrated in FIGS. 10 and 11.
[0164] In the architectures shown in FIGS. 10 and 11 the LTE Femto
cells correspond to the small cells 10 described above and these
are connected to small cell gateway apparatus 14 (in this example a
HeNB gateway system). The HeNB gateway system in each case
comprises security gateway (SeGW) to which the small cells are
connected into the small cell gateway apparatus 14 via the internet
and an S1 interface. The SeGW is connected via an IP router to a
home location register (HLR) via an Authentication, Authorization
and Accounting (AAA) function, to Operation and Maintenance
(OA&M) network, and to a HeNB GW function. In each of the
architectures shown in FIGS. 10 and 11 control plane signalling is
routed, from the IP router, to the MME 12 of the core network 7 via
an S1-MME interface and the HeNB GW function. In the architecture
shown in FIG. 11 user plane signalling is also routed, from the IP
router, to the core network 7 (to the SGW 16) via the HeNB GW
function (and an S1-U interface). In the architecture shown in FIG.
10, however, user plane signalling is not routed, from the IP
router, via the HeNB GW function but is instead routed directly,
from the IP router, via an S1-U interface to the SGW 16 of the core
network 7. The SeGW may be a physically separate communication
entity to the HeNB GW.
[0165] Accordingly, in the architecture of FIG. 10, the user plane
is terminated in the SeGW and the control plane is terminated in
the HeNB GW whereas, in the architecture of FIG. 11, the user and
control planes are each terminated in the HeNB GW.
[0166] Similarly, in the architecture of FIG. 10, GPRS Tunnelling
Protocol (GTP) functions are provided in the SeGW whereas, in the
architecture of FIG. 11, these are provided in the HeNB GW.
Direct Data Forwarding
[0167] If the direct forwarding is available from the source small
cell 10-2 to the target small cell 10-1, 10-3, then the base
station 5-2 of the source small cell 10-2 indicates this in the S1
message sent to the small cell gateway 14 to indicate that handover
is required and to request that handover takes place (e.g. by
setting a Direct Forwarding Path Availability IE to "Direct Path is
Available" in the S1AP: Handover Required message sent at S612 in
FIG. 6 or corresponding steps in FIGS. 7 to 9).
[0168] The small cell gateway 14 processes the message indicating
that handover is required, determines that direct forwarding is
available, and hence informs the base station 5-1, 5-3 of the
target small cell 10-1, 10-3 of this in the message requesting
handover (e.g. in the S1AP: Handover Request message sent at S614
in FIG. 6 or corresponding steps in FIGS. 7 to 9). Specifically,
the small cell gateway 14 indicates that direct forwarding is
available by deliberately not configuring, in the S1AP: Handover
Request message, the "Data forwarding not possible IE" for each
bearer represented in the "E-RABs To Be Setup Item IEs" for which
direct forwarding is available.
[0169] When the small cell gateway 14 sends the message instructing
handover (e.g. an S1AP: Handover Command message) to the base
station 5-2 of the source cell 5-2 (e.g. at S628 in FIG. 6 or
corresponding steps in FIGS. 7 to 9). The small cell gateway 14
configures the message instructing handover to identify the
addresses allocated, and associated tunnelling identities (TEIDs),
for each radio access bearer subject to forwarding, for example by
configuring the "E-RABs Subject to Forwarding List" IE in the S1AP:
Handover Command message to include a list of addresses and TEIDs
allocated for forwarding. The E-RABs to Release List IE include a
list of all the bearers to be released.
[0170] After this, the base station 5-2 of the source cell 5-2 can
start forwarding downlink data towards the base station 5-1, 5-3 of
the target small cell 10-1, 10-3 (e.g. at S630 in FIG. 6 or
corresponding steps in FIGS. 7 to 9). During this data forwarding
process, therefore, the base station 5-2 of the source cell 5-2
forwards downlink data directly to the base station 5-1, 5-3 of the
target small cell 10-1, 10-3. The SeGW in the case of the variant
shown in FIG. 10 and the HeNB-GW function in the case of the
variant shown in FIG. 11 is not involved.
Indirect Data Forwarding
[0171] If the direct forwarding is not available from the source
small cell 10-2 to the target small cell 10-1, 10-3, then the base
station 5-2 of the source small cell 10-2 indicates this in the S1
message sent to the small cell gateway 14 to indicate that handover
is required and to request that handover takes place (e.g. by
setting a Direct Forwarding Path Availability IE to "Direct Path is
Not Available" in the S1AP: Handover Required message sent at S612
in FIG. 6 or corresponding steps in FIGS. 7 to 9).
[0172] The small cell gateway 14 processes the message indicating
that handover is required, determines that direct forwarding is not
available, and hence informs the base station 5-1, 5-3 of the
target small cell 10-1, 10-3 of this in the message requesting
handover (e.g. in the S1AP: Handover Request message sent at S614
in FIG. 6 or corresponding steps in FIGS. 7 to 9). Specifically,
the small cell gateway 14 indicates that direct forwarding is not
available by deliberately configuring, in the S1AP: Handover
Request message, the "Data forwarding not possible IE" for each
bearer represented in the "E-RABs To Be Setup Item IEs" for which
direct forwarding is not available.
[0173] In the case of the architecture in FIG. 10, the HeNB-GW uses
parameters (target Small Cell addresses, TEID and E-RAB pair for
forwarding) for setting up the forwarding path tunnel by sending a
forwarding tunnel creation request (e.g. a Create Indirect Data
Forwarding Tunnel Request message) to SeGW to initiate
configuration of an appropriate communication tunnel for forwarding
the data. The SeGW responds with a corresponding response message
(e.g. a Create Indirect Data Forwarding Tunnel Response message)
comprising SeGW addresses, TEID and information identifying the
E-RAB pair for forwarding.
[0174] In the case of the architecture in FIG. 11 the HeNB-GW
function uses appropriate parameters (target Small Cell addresses
and TEIDs for forwarding) for setting up the forwarding path
tunnel.
[0175] When the small cell gateway 14 sends the message instructing
handover (e.g. an S1AP: Handover Command message) to the base
station 5-2 of the source cell 5-2 (e.g. at S628 in FIG. 6 or
corresponding steps in FIGS. 7 to 9). The small cell gateway 14
configures the message instructing handover to identify the
addresses allocated, and associated tunnelling identities (TEIDs),
for each radio access bearer subject to forwarding, for example by
configuring the "E-RABs Subject to Forwarding List" IE in the S1AP:
Handover Command message to include a list of addresses and TEIDs
allocated for forwarding. The E-RABs to Release List IE include a
list of all the bearers to be released.
[0176] After this, the base station 5-2 of the source cell 5-2 can
start forwarding downlink data towards the base station 5-1, 5-3 of
the target small cell 10-1, 10-3 (e.g. at S630 in FIG. 6 or
corresponding steps in FIGS. 7 to 9). During this data forwarding
process, therefore, the base station 5-2 of the source cell 5-2
forwards downlink data indirectly to the base station 5-1, 5-3 of
the target small cell 10-1, 10-3 via the forwarding path
tunnel.
[0177] In the case of the architecture in FIG. 10, during the data
forwarding process, the SeGW effectively works as the U-plane
anchor point for forwarding the U-plane packets from the source
small cell 10-2 to the target small cell 10-1, 10-3.
[0178] In the case of the architecture in FIG. 11, during the data
forwarding process, the HeNB-GW effectively works as the U-plane
anchor point to forward the U-plane packets from the source small
cell 10-2 to the target small cell 10-1, 10-3.
[0179] On receipt of the notification message (e.g. an S1AP:
Handover Notify message) informing the small cell gateway that
handover has effectively been completed at the target end (e.g. at
S632 in FIG. 6 or corresponding steps in FIGS. 7 to 9), the HeNB-GW
starts a timer for releasing the data forwarding resource.
[0180] In the case of the architecture in FIG. 10, after the timer
has expired the HeNB-GW generates a message to initiate release of
the temporary resources used for indirect forwarding (e.g. a Delete
Indirect Data Forwarding Tunnel Request message) and sends it to
the SeGW to initiate the release.
[0181] In the case of the architecture in FIG. 11, after the timer
expires, the HeNB-GW releases the temporary resources used for
indirect forwarding itself.
Dual Connectivity
[0182] As explained above FIG. 2 illustrates an embodiment in which
a `virtual` dual connectivity is advantageously provided even
though there is no physical macro cell in the vicinity. It will be
appreciated that although this is described as a different
embodiment some (or all) of the features of both embodiments could,
potentially, be implemented in the same communication device as
appropriate in order to provide different options to an end user.
FIGS. 12 and 13 respectively show a control plane architecture and
a user plane architecture in a communication system in which
`virtual` dual connectivity is provided by having the small cell
gateway 14 administer a virtual macro cell which acts to terminate
X2 signalling.
[0183] In order to achieve `virtual` dual connectivity the
`virtual` macro cell context is stored in the small cell gateway
14, and the mobile communication device 3 has a virtual association
to the virtual macro cell 15 but not a physical association. This
virtual macro cell 15 acts as a primary cell (PCell) whilst the
small cells 10 operate as secondary cells (SCells) in which control
signalling is limited.
[0184] As seen in FIGS. 12 and 13, in the control plane, the mobile
communication device 3 has a radio resource control (RRC) and other
control connections to the small cell base station 5 as normal. No
RRC state machine is provided in the small cell gateway 14 but the
gateway maintains the RRC context for the mobile communication
device 3. Small cells may be added/deleted as secondary cells in a
manner similar to Scell addition/deletion as defined, for example
in section 5.3.10.3b of TS 36.331.
[0185] The mobile communication device 3 maintains security keys
derived from the initial connection with the first small cell 10
operating as a secondary cell (SCell) to the virtual macro cell 15
acting as the PCell. The mobile communication device 3 is
configured to store and maintain these keys in response to an
indication that these keys should be preserved provided by the base
station 5 operating the first cell via which the mobile
communication device 3 connects (e.g. following initial
configuration of the non access stratum (NAS) and access stratum
(AS) security contexts).
[0186] More specifically, the mobile communication device 3 is
explicitly informed that the virtual macro cell 15 exists and
stores security keys (AS and NAS) accordingly. During a move from
one small cell to another, the source small cell base station 5
transfers the security keys to small cell gateway 14 as part of the
security context for that mobile communication device and the
gateway continues to transfer these keys to the respective base
station 5 of each small cell 10 to which the mobile communication
device 3 moves. The number of times that the security keys are
transferred in this way is limited to a predetermined number of
`hops` which may be reconfigurable or fixed. It will be appreciated
that where all the small cells in one hop use the same tracking
area identity there is no issue related to NAS mobility information
reference.
[0187] When the number of `hops` reaches its limit, normal security
handling shall be performed to re-initialise the security context
with new keys thereby limiting any security risk associated with
the re-use of keys and the transfer of keys between small cell base
station 5 and the small cell gateway 14.
[0188] Unlike existing methods for adding Scells, the addition of
SCells for the purposes of virtual dual connectivity involves the
setting up of a Packet Data Convergence Protocol (PDCP), Radio Link
Control (RLC) and Medium Access Control (MAC) configuration during
adding another small cell 10 as SCell by including PDCP, RLC and
MAC information in the RRC message.
[0189] In order to alleviate the additional signalling overhead
associated with the need to setting up the PDCP, RLC and MAC
configurations the `delta` signalling may be used to signal only
modifications to the configurations (e.g. only new/modified
parameters compared to an existing configuration).
[0190] The mobile communication device 3 continues to receive
system information in connected mode from the base station 5 of the
small cell 10 via which it is connected. The virtual Pcell 15 does
not send any system information because no system information
exists for such a Pcell 15. Similarly, Earthquake and Tsunami
Warning System (ETWS)/Commercial Mobile Alert System (CMAS)
notifications are provided from via the small cell 10 acting as an
Scell only because no such information is available from the
virtual Pcell 15. The mobile communication device 3 also receives
paging information from the base station 5 of the small cell
10.
[0191] Unlike current systems in which a Pcell Cell Radio Network
Temporary Identifier (C-RNTI-- an identifier allocated by a base
station, to a mobile communication device, to be unique within one
cell controlled by that base station) is used in SCells as well.
The C-RNTI for an SCell to a virtual PCell is carried out by the
base station 5 of the small cell 10. Whilst the same C-RNTI
allocation could be kept throughout multiple `hops` from one small
cell to another this may restrict the number of available C-RNTIs
and could potentially cause C-RNTI collision. Accordingly, in this
embodiment, the C-RNTI is not kept when a move to a new small cell
10 occurs.
Operation--Dual Connectivity
[0192] Typical operation in a communication system configured for
virtual dual connectivity will now be described, by way of example
only, with reference to FIGS. 14 and 15 in which FIG. 14 is a
timing diagram for an initial RRC connection establishment by a
mobile communication device 3 in a small cell 10 and FIG. 15 is a
timing diagram illustrating a handover scenario in a communication
system configured for virtual dual connectivity.
[0193] Referring to FIG. 14 an initial RRC connection setup
procedure begins at S1400. The mobile communication device 3
generates and sends an initial UE message to the base station 5-2
of a small cell 10-2. The initial UE message is propagated to the
MME 12 via the small cell gateway 14 using S1 signalling (at S1402
and S1403). The MME 12 sets up of an NAS security context for the
mobile communication device 3 at S1405 before initiating setup of
an AS context for the mobile communication device 3 by sending an
initial UE context setup message to the small cell gateway at S1407
which is then forwarded to the base station 5-2 of the small cell
10-2 at S1408. A reconfiguration message to configure bearer
establishment and inform the mobile communication device that the
control and user planes are virtually split between the small cell
10-2 and the virtual macro cell 15. Once reconfiguration is
complete the mobile communication device confirms this to the base
station 5-2 of the small cell 10-2 at S1411 and the base station
5-2 of the small cell 10-2 responds by sending an initial context
setup response message to the small cell gateway 14 at S1412. The
small cell gateway 14 forwards the initial context setup response
message to the MME 12 at S1413 to complete set up of the initial
connection. GTP communication tunnels are thus setup (S1415 and
S1417) between the base station 5-2 of the small cell 10-2 and the
small cell gateway 14 and between the small cell gateway 14 and the
MME 12.
[0194] Referring to FIG. 15 a measurement report is sent to the
base station 5-2 of a source small cell 10-2 at S1501. The base
station 5-2 of the source small cell 10-2 determines that a
transfer of cell may be necessary and prepares for this by
transferring the mobile communication device's context (RRC, 51 and
GTP) to the small cell gateway 14 at S1503 (e.g. using appropriate
X2/X3 signalling such as an X3-AP: Context Transfer message) before
forwarding the measurement report to the small cell gateway 14,
using appropriate X2/X3 signalling including a target identifier
for the target cell 10-1, 10-3 at S1504 (e.g. using appropriate
X2/X3 signalling such as an X3-AP: Measurement Report message). The
small cell gateway 14 stores the context for the mobile
communication device 3 and, on receipt of the measurement report,
initiates setup of a corresponding context for the mobile
communication device 3 at the base station 5-1, 5-3 of the target
small cell 10-1, 10-3 (e.g. using appropriate X2/X3 signalling such
as an X3-AP: Context Setup message). The base station 5-1, 5-3 of
the target small cell 10-1, 10-3 responds at 51507 to indicate that
the context has been set up successfully. The small cell gateway 14
then responds, at S1509, appropriately to the original context
transfer message from the base station 5-2 of the source small cell
10-2. On receipt of the response from the small cell gateway 14 the
base station 5-2 of the source small cell 10-2 reconfigures the
mobile communication device 3 by providing, at S1511, appropriate
information to allow the mobile communication device 3 to connect
to the base station 5-1, 5-3 of the target cell 10-1, 10-3 (e.g. in
an SCell INFO information element or the like). Once the
reconfiguration has completed successfully this is indicated
directly to the base station 5-1, 5-3 of the new (target) cell
10-1, 10-3 at S1513. The base station 5-1, 5-3 of the new (target)
cell 10-1, 10-3 notifies the small cell gateway 14 of this at S1515
and the small cell gateway 14 notifies the base station 5-2 of the
old (source) cell 10-2.
[0195] In order to support the dual connectivity, the target small
cell base station is added by using an Scell addition/deletion
procedure (in contrast to the approach for a normal mobility
procedure). For this procedure, security keys can advantageously be
reused (without involving key derivation with the core
network).
[0196] Based on the GTP context (e.g. E-RAB information of E-RAB
ID, Transport layer address and GTP-TEID) exchanged during the
51505, 51507, the GTP tunnel is set up between the target small
cell base station and the small cell gateway at S1519. Hence, user
data packets can be transferred from the target small cell base
station to the small cell gateway and then to the S-GW.
[0197] Referring to steps S1521 and S1523, the small cell gateway
14 is operable to terminates S1AP messages from the MME 12 (such as
the S1AP Bearer Modification Request shown at S1521) so that the
small cell gateway 14 can update the information stored at the
gateway 14 (e.g. in a database) with the latest context for the
mobile communication device according to the received S1AP message.
The small cell gateway 14 then forwards the message to the correct
small cell base station based on the context information for the
mobile communication device (at S1523).
Modifications and Alternatives
[0198] A number of detailed exemplary embodiments have been
described above. As those skilled in the art will appreciate, a
number of modifications and alternatives can be made to the above
exemplary embodiments whilst still benefiting from the inventions
embodied therein.
[0199] Referring to the exemplary embodiment shown in FIG. 2 it
will be appreciated that data forwarding could be implemented by
having the source cell base station transfer the PDCP SN and
Service Data Units (SDUs) for which no acknowledgement has been
received, to the small cell gateway and having the small cell
gateway forward this information to the target small cell base
station. Such information can be transferred over an X3, a new
interface, or an existing S1/X2 interface.
[0200] It will be appreciated that the MME may transfer the context
to small cell gateway in a new S1 message instead of having a small
cell transfer it as described with reference to FIG. 15. The small
cell gateway may still intercept S1 messages so that when it
receives an S1 message to modify a communication bearer the gateway
knows where to route it to.
[0201] In the above exemplary embodiments, a mobile telephone based
telecommunications system was described. As those skilled in the
art will appreciate, the signalling techniques described in the
present application can be employed in other communications system.
Other communications nodes or devices may include user devices such
as, for example, personal digital assistants, laptop computers, web
browsers, etc.
[0202] In the exemplary embodiments described above, the base
station and the home base station each include transceiver
circuitry. Typically this circuitry will be formed by dedicated
hardware circuits. However, in some exemplary embodiments, part of
the transceiver circuitry may be implemented as software run by the
corresponding controller.
[0203] In the above exemplary embodiments, a number of software
modules were described. As those skilled in the art will
appreciate, the software modules may be provided in compiled or
un-compiled form and may be supplied to the HENB or to the mobile
telephone as a signal over a computer network, or on a recording
medium. Further, the functionality performed by part or all of this
software may be performed using one or more dedicated hardware
circuits. However, the use of software modules is preferred as it
facilitates the updating of the base stations, gateways, and the
mobile telephones in order to update their functionalities.
[0204] Various other modifications will be apparent to those
skilled in the art and will not be described in further detail
here.
[0205] This application is based upon and claims the benefit of
priority from United Kingdom patent application No. 1306216.1,
filed on Apr. 5, 2013, the disclosure of which is incorporated
herein in its entirety by reference.
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