U.S. patent application number 12/076349 was filed with the patent office on 2008-07-10 for hard handover method, controller and communication system.
This patent application is currently assigned to Nokia Corporation. Invention is credited to Juha Sipila.
Application Number | 20080167043 12/076349 |
Document ID | / |
Family ID | 33306096 |
Filed Date | 2008-07-10 |
United States Patent
Application |
20080167043 |
Kind Code |
A1 |
Sipila; Juha |
July 10, 2008 |
Hard handover method, controller and communication system
Abstract
The invention is related to a controller of a communication
system, the controller comprising: means for determining user
terminal time delay between delivery and acknowledgement of a
transmission; means for conveying the user terminal time delay;
means for calculating switching time delay; and means for
transferring user terminal data conveyance to the handover target
network controller at a moment based on the switching time
delay.
Inventors: |
Sipila; Juha; (Nokia,
FI) |
Correspondence
Address: |
SQUIRE, SANDERS & DEMPSEY L.L.P.
8000 TOWERS CRESCENT DRIVE, 14TH FLOOR
VIENNA
VA
22182-6212
US
|
Assignee: |
Nokia Corporation
|
Family ID: |
33306096 |
Appl. No.: |
12/076349 |
Filed: |
March 17, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11142666 |
Jun 2, 2005 |
7359708 |
|
|
12076349 |
|
|
|
|
Current U.S.
Class: |
455/436 |
Current CPC
Class: |
H04W 36/00837 20180801;
H04W 36/10 20130101 |
Class at
Publication: |
455/436 |
International
Class: |
H04Q 7/20 20060101
H04Q007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 6, 2004 |
FI |
20045375 |
Claims
1. A method, comprising: determining user terminal time delay
between delivery and acknowledgement of a transmission, in a
handover source network controller; conveying the user terminal
time delay to a handover target network controller; and
transferring user terminal data conveyance to the handover target
network controller based on the switching time delay.
2. The method of claim 1, further comprising: calculating a
switching time delay in the handover target network controller.
3. The method of claim 2, wherein the switching time delay is
calculated by using an equation comprising, round - trip time 2 +
UE cell changeover time , ##EQU00002## wherein the UE corresponds
to a user terminal or a user equipment, and the UE cell changeover
time is a previously known parameter or is estimated during an
intra-RNC hard handover, where a round-trip time is measured during
a configuration management and subtracted from the switching time
delay caused by the hard handover target network controller.
4. The method of claim 1, wherein the conveying comprises conveying
by adding a new field to a container that is passed to the handover
target network controller during an inter-RNC hard handover.
5. An apparatus, comprising: a determiner configured to determine
user terminal time delay between delivery and acknowledgement of a
transmission; a conveyer configured to convey and receiving the
user terminal time delay; and a transferor configured to transfer
user terminal data conveyance to a handover target network
controller based on the switching time delay.
6. The apparatus of claim 5, further comprising: calculator
configured to calculate a switching time delay.
7. The apparatus of claim 6, wherein the calculator is configured
to calculate the switching time delay by using an equation
comprising round - trip time 2 + UE cell changeover time ,
##EQU00003## wherein the UE corresponds to a user terminal or a
user equipment, and the UE cell changeover time is a previously
known parameter or is estimated during an intra-RNC hard handover,
where a round-trip time is measured during a configuration
management and subtracted from the switching time delay caused by
the hard handover target network controller.
8. The apparatus of claim 6, wherein the calculator is further
configured to calculate the switching time delay using user
terminal cell changeover time and the user terminal time delay
between the delivery and the acknowledgement of the
transmission.
9. The apparatus of claim 5, wherein the conveyer is further
configured to receive the user terminal time delay.
10. The apparatus of claim 5, wherein the conveyer is configured to
convey the user terminal time delay by adding a new field to a
container that is passed to the handover target network controller
during an inter-radio network controller hard handover.
11. The apparatus of claim 5, wherein the determiner is further
configured to determine a round-trip time as the user terminal time
delay between the delivery and the acknowledgement of the
transmission.
12. The apparatus of claim 5, further comprising: a controller
configured to control the switching time delay by delaying sending
of a relocation detect message from a target radio network
controller (RNC).
13. A computer program embodied on a computer-readable medium, the
computer program configured to control a processor to perform
operations comprising: determining user terminal time delay between
delivery and acknowledgement of a transmission, in a handover
source network controller; conveying the user terminal time delay
to a handover target network controller; and transferring user
terminal data conveyance to the handover target network controller
based on the switching time delay.
14. A system, comprising: a controller configured to, determine
user terminal time delay between delivery and acknowledgement of a
transmission; convey the user terminal time delay; calculate a
switching time delay; and transfer user terminal data conveyance to
a handover target network controller based on the switching time
delay.
15. A method, comprising: receiving a user terminal time delay from
a handover source network controller; calculating a switching time
delay in the handover target network controller using the user
terminal time delay; and transferring a user terminal data
conveyance to the handover target network controller based on the
switching time delay.
16. The method of claim 15, wherein the switching time delay is
calculated using user terminal cell changeover time and the user
terminal time delay between the delivery and the acknowledgement of
the transmission.
17. The method of claim 15, wherein a round-trip time is determined
as the user terminal time delay between the delivery and the
acknowledgement of the transmission.
18. The method of claim 15, wherein the switching time delay is
controlled by delaying sending of a relocation detect message from
a target radio network controller.
19. An apparatus, comprising: a receiver configured to receive a
user terminal time delay from a handover source network controller;
a calculator configured to calculate a switching time delay in the
handover target network controller using the user terminal time
delay; and a transferor configured to transfer a user terminal data
conveyance to the handover target network controller based on the
switching time delay.
20. The apparatus of claim 19, the calculator is configured to
calculate the switching time delay using a user terminal cell
changeover time and the user terminal time delay between the
delivery and the acknowledgement of the transmission.
21. The apparatus of claim 19, wherein a round-trip time is
determined as the user terminal time delay between the delivery and
the acknowledgement of the transmission.
22. The apparatus of claim 19, wherein the switching time delay is
controlled by delaying sending of a relocation detect message from
a target radio network controller.
23. A computer program embodied on a computer-readable medium, the
computer program configured to control a processor to perform
operations comprising: receiving a user terminal time delay from a
handover source network controller; calculating a switching time
delay in the handover target network controller using the user
terminal time delay; and transferring a user terminal data
conveyance to the handover target network controller based on the
switching time delay.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation application of U.S. patent
application Ser. No. 11/142,666, filed on Jun. 2, 2005. The
disclosure of the prior application is hereby incorporated by
reference in its/their entirety.
FIELD
[0002] The invention relates to a hard handover method, a
controller of a communication system and a communication
system.
BACKGROUND
[0003] The handover (or handoff) procedure is a means to continue a
call when a user terminal crosses the border of one cell into
another. In a cellular network, a cell has typically several
neighbouring cells. The basic concept of a handover is that when
the user terminal moves from the coverage area of one cell to
another, a new connection is set up with a target cell and the
connection with the old cell may be released. In many cases, an
inter radio network controller hard handover is carried out.
[0004] In inter radio network controller (radio network
controller=RNC) hard handovers, the main problem is to find a right
time for switching from a handover source RNC to a handover target
RNC due to delays in the handover process.
BRIEF DESCRIPTION
[0005] According to an aspect of the invention, there is provided a
hard handover method in a communication system, the method
comprising: determining user terminal time delay between delivery
and acknowledgement of a transmission, in a handover source network
controller; conveying the user terminal time delay to a handover
target network controller; calculating switching time delay in the
handover target network controller using the user terminal time
delay; and transferring user terminal data conveyance to the
handover target network controller at a moment based on the
switching time delay.
[0006] According to another aspect of the invention, there is
provided a hard handover method in a communication system, the
method comprising: determining user terminal time delay between
delivery and acknowledgement of a transmission, in a handover
source network controller; conveying the user terminal time delay
to a handover target network controller; calculating switching time
delay in the handover target network controller; and transferring
user terminal data conveyance to the handover target network
controller at a moment based on the switching time delay.
[0007] According to another aspect of the invention, there is
provided a controller of a communication system, the controller
comprising: means for determining user terminal time delay between
delivery and acknowledgement of a transmission; means for conveying
the user terminal time delay; means for calculating switching time
delay; and means for transferring user terminal data conveyance to
the handover target network controller at a moment based on the
switching time delay.
[0008] According to another aspect of the invention, there is
provided a controller of a communication system, the controller
being configured to: determine user terminal time delay between
delivery and acknowledgement of a transmission; convey the user
terminal time delay; calculate switching time delay; and transfer
user terminal data conveyance to the handover target network
controller at a moment based on the switching time delay.
[0009] According to another aspect of the invention, there is
provided a communication system, the system comprising: means for
determining user terminal time delay between delivery and
acknowledgement of a transmission; means for conveying the user
terminal time delay; means for calculating switching time delay;
and means for transferring user terminal data conveyance to the
handover target network controller at a moment based on the
switching time delay.
[0010] According to another aspect of the invention, there is
provided a communication system, the system being configured to:
determine user terminal time delay between delivery and
acknowledgement of a transmission; convey the user terminal time
delay; calculate switching time delay; and transfer user terminal
data conveyance to the handover target network controller at a
moment based on the switching time delay.
[0011] Embodiments of the invention are described in the dependent
claims.
[0012] The method and system of the invention provide several
advantages. An embodiment provides a method for determining a hard
handover RNC switching time taking delays in to account, which
gives a more accurate estimate of the switching time.
LIST OF DRAWINGS
[0013] In the following, the invention will be described in greater
detail with reference to the preferred embodiments and the
accompanying drawings, in which
[0014] FIG. 1 shows an example of a communication system,
[0015] FIG. 2 is a flow chart,
[0016] FIG. 3 shows an example of message communications, and
[0017] FIG. 4 is a block diagram illustrating an example of the
radio network controller's logical structure.
DESCRIPTION OF EMBODIMENTS
[0018] With reference to FIG. 1, we examine an example of a
communication system in which embodiments of the invention can be
applied. The present invention can be applied in various
communication systems. One example of such a communication system
is Universal Mobile Telecommunications System (UMTS) radio access
network. It is a radio access network which includes wideband code
division multiple access (WCDMA) technology and can also offer
real-time circuit and packet switched services. Another example is
Global System for Mobile Communications (GSM). The embodiments are
not, however, restricted to the systems given as examples but a
person skilled in the art may apply the solution in other
communication systems provided with the necessary properties.
[0019] It is clear to a person skilled in the art that the method
according to the invention can be applied to systems utilizing
different modulation methods or air interface standards.
[0020] FIG. 1 is a simplified illustration of a digital data
transmission system to which the solution according to the
invention is applicable. This is a part of a cellular radio system,
which comprises a base station (or a node B) 100, which has
bi-directional radio links 102 and 104 to user terminals 106 and
108. The user terminals may be fixed, vehicle-mounted or portable.
The base station includes transceivers, for instance. From the
transceivers of the base station, there is a connection to an
antenna unit that establishes the bidirectional radio links to the
user terminal. The base station is further connected to a
controller 110, a radio network controller (RNC) or a base station
controller (BSC), which transmits the connections of the terminals
to the other parts of the network. The base station controller
controls in a centralized manner several base stations connected to
it. The base station controller or the radio network controller is
further connected to core network 112 (CN). Depending on the
system, the counterpart on the CN side can be a mobile services
switching centre (MSC), a media gateway (MGW) or a serving GPRS
(general packet radio service) support node (SGSN).
[0021] The cellular radio system can also communicate with other
networks, such as a public switched telephone network or the
Internet.
[0022] The handover (or handoff) procedure is a means to continue a
call when a user terminal crosses the border of one cell into
another. In a cellular network, a cell has typically several
neighbouring cells. The basic concept of a handover is that when
the user terminal moves from the coverage area of one cell to
another, a new connection is set up with the target cell and the
connection with the old cell is released.
[0023] In WCDMA systems (Wide Band Code Division Multiple Access),
like UMTS (Universal Mobile Telecommunication System), there are
several different types of hard handovers, such as intra-frequency
handovers, interfrequency handovers and inter-system handovers. For
performing a successful handover, the user terminal has to perform
measurements to find out whether the signal of a base station (or
node B) to which it is connected is strong enough or would there
possibly be a stronger signal in another cell.
[0024] There is also another type of handovers called soft
handover. In a soft handover, the user terminal is connected to
more than one base station simultaneously. A softer handover is a
soft handover between two sectors of a cell.
[0025] There are many reasons for a handover. The basic reason
behind a handover is that the air interface connection no longer
fulfils the criteria set for it. The most typical criteria for a
handover are, for instance, signal quality, user mobility and
traffic distribution.
[0026] A signal quality handover is made when the quality of the
radio signal deteriorates below parameters defined in the radio
network controller. The deterioration is detected by the signal
measurements carried out by mobile stations or base stations.
[0027] A traffic distribution handover occurs when the traffic
capacity of a cell has reached the maximum or is approaching it. In
that situation, a mobile station near the edge of the cell with a
high load may be transferred to a neighbouring cell with a smaller
load.
[0028] The embodiment depicted by means of FIG. 2, is related to
the inter radio network controller hard handover. Before a
handover, the user terminal measures selected cells and/or
frequencies in the cells to find an appropriate handover target
cell. For measuring, the RNC reduces the used bit rate to give the
user terminal time to carry out measurements. The reducing of the
bit rate releases time slots. The reduced bit rate is called a
compressed mode. The radio network controller (RNC) commands the
user terminal to enter the compressed mode and provides downlink
and uplink compressed mode parameters.
[0029] In the prior art, when a handover source RNC (the user
terminal's current RNC) informs a handover target RNC that the
connection switching should be carried out, the source RNC does not
know the exact time when the user terminal is going to transmit or
is able to receive signals via the new cell. The main source of
delay is that hard handover messages are transmitted via the source
RNC. Naturally, the delays vary according to radio conditions.
[0030] The basic idea of an embodiment of the inter-RNC hard
handover method according to the invention is to estimate the delay
of the channel change of a user terminal. In the embodiment, the
switching time instant is controlled by delaying the sending of a
"Relocation Detect" message from the target RNC. The delay is
mainly due to the transmission and processing time of hard handover
signalling messages from the handover source RNC over the air
interface to the user terminal, the cell changeover time of the
user terminal and the transmission time of user data in the uplink
direction. Since the delay may vary according to the circumstances,
the handover source RNC measures, in the embodiment, a user
terminal round-trip time before a handover during compressed mode
signalling. The handover source RNC sends the measured value to the
handover target RNC within a new field of a signalling message. The
time when the target RNC sends a "Relocation Detect" message to the
CN is adjusted on the basis of the round-trip time and estimated
(or previously known) user terminal cell changeover time.
[0031] An embodiment of the handover method begins in block 200. In
block 202, a user terminal time delay between delivery and
acknowledgement of a transmission is determined in a handover
source network controller. The determination can be carried out in
different ways, but typically the time delay is measured. This kind
of time delay is usually called round-trip time. The round-trip
time is typically measured during the compressed mode transmission
explained above.
[0032] In block 204, the determined user terminal time delay is
conveyed to a handover target network controller. The user terminal
time delay can be delivered by adding a new field to a container
that is passed to the handover target RNC during an inter-RNC hard
handover.
[0033] In block 206, a switching time delay is calculated in the
handover target network controller. The switching time is typically
calculated by using the user terminal time delay and a user
terminal changeover time. Therefore, the target RNC may calculate
the switching time delay by using the following equation:
round - trip time 2 + UE cell changeover time ( 1 )
##EQU00001##
[0034] wherein
[0035] UE means a user terminal (also user equipment),
[0036] round-trip time is determined in block 202 and
the UE cell changeover time is a previously known parameter or it
can be estimated in several ways, for instance during an intra-RNC
hard handover: a round-trip time is measured during configuration
management and subtracted from the corresponding delay caused by a
hard handover.
[0037] In block 208, user terminal data conveyance is transferred
(or switched) to the hand-over target network controller at a
moment based on the switching time delay. Typically, during the
inter-RNC hard handover, the source RNC informs the target RNC of
the drifting RNC change by sending a "relocation commit" message.
After receiving the message, the target RNC (the new drifting RNC)
may re-route data by sending a "relocation detect" message to the
core network.
[0038] The embodiment ends in block 210. The method can be repeated
when a next hard handover is carried out.
[0039] It is also possible that a handover does not succeed. Then,
typically, the user terminal returns to the old channel or the call
is terminated. If the user terminal returns to the old channel, it
is possible to try again to carry out a handover.
[0040] In the following, an example of messaging during the
compressed mode according to the embodiment described above is
explained in further detail by means of FIG. 3. The source RNC
typically makes the decision to start the compressed mode. It is
possible that also other hard handover messages are conveyed in
addition to those mentioned in the example.
[0041] According to FIG. 3, source RNC 110 sends a relocation
required message to core network (CN) 112 after it has noticed that
the user terminal has left the cells controlled by it. The message
type is radio access network application (RANAP). The RANAP means a
radio access network signalling protocol that consists of
mechanisms that handle the procedures between the core network and
the radio access network (RAN). The message is Relocation
Required.
[0042] Then core network 112 sends an "RANAP: Relocation Request"
message to relocation target RNC 300. The target RNC sends an
"RANAP: Relocation request Ack" message (Ack=acknowledgement)
meaning that it has received the "Relocation Request" message.
[0043] "RANAP: Relocation command" message is sent from core
network 112 to source RNC 110. The source RNC sends an RRC:
Physical Channel Reconfiguration message to the user terminal. The
RRC means radio resource control. In the UMTS, RRC is a sub-layer
of radio interface layer 3 and it provides information transfer
services. RRC functions are typically responsible for controlling
the configuration of radio interface layers 1 and 2.
[0044] The source RNC transmits an "RNSAP: Relocation commit"
message to the target RNC. RNSAP means a radio network subsystem
application part. RNSAP is a radio network subsystem signalling
protocol for an lur interface.
[0045] Next, the target RNC sends an "RANAP: Relocation Detect"
message to the core network (CN). The "RANAP: Relocation Detect"
message is typically sent after the expiration of a switch timer
(usually timers give time limits for sending messages).
[0046] The user terminal informs the target RNC that it has
completed the physical channel reconfiguration by sending a
"Physical Channel Reconfiguration Complete" message.
[0047] The target RNC sends an "RANAP: Relocation Complete" message
to the core network. The core network in turn sends an "lu Release
command" message to the source RNC. The Source RNC releases the lu
connection and sends an "RANAP: lu Release Complete" message to the
core network.
[0048] Referring to FIG. 4, a simplified block diagram illustrates
an example of the radio network controller's (RNC) logical
structure. A network controller is taken herein as an example of a
controller. Both the source RNC and the target RNC may have the
logical structure depicted in the example.
[0049] RNC is the switching and controlling element of UTRAN. The
switching 400 takes care of connections between the core network
and the user terminal. The radio network controller is located
between lub 402 and lu 414 interfaces. The network controller is
connected to these interfaces via interface units 404, 412. There
is also an interface for inter-RNC transmission called lur 416.
[0050] The functionality of the radio network controller can be
classified into two classes: UTRAN radio resource management 406
and control functions 410. An operation and management interface
function 408 serves as a medium for information transfer to and
from network management functions.
[0051] The radio resource management is a group of algorithms used
to share and manage the radio path connection so that the quality
and capacity of the connection are adequate. The most important
radio resource management algorithms are handover control, power
control, admission control, packet scheduling, and code
management.
[0052] The UTRAN control functions take care of functions related
to the setup, maintenance and release of a radio connection between
the base stations and the user terminals. Therefore, the
embodiments of the hard handover method described above are
typically carried out in radio resource block 406 and UTRAN control
block 410. The radio resource block 406 and control functions block
410 can be combined for forming a radio resource control (RRC) unit
of a serving radio network controller (SRNC-RRC).
[0053] The precise implementation of the radio network controller
(RNC) is vendor-dependent.
[0054] The disclosed functionalities of the embodiments of the
invention can be advantageously implemented by means of software in
appropriate parts of a radio network controller. Other
implementation solutions are also possible such as different
hardware implementations, e.g. a circuit built of separate logics
components or one or more client-specific integrated circuits
(Application-Specific Integrated Circuit, ASIC). A hybrid of these
implementations is also feasible.
[0055] Even though the invention is described above with reference
to an example according to the accompanying drawings, it is clear
that the invention is not restricted thereto but it can be modified
in several ways within the scope of the appended claims.
* * * * *