U.S. patent application number 12/072962 was filed with the patent office on 2008-08-21 for method and arrangement for controlling cell change and a terminal of a cellular system.
This patent application is currently assigned to Nokia Corporation. Invention is credited to Lars Dalsgaard.
Application Number | 20080200173 12/072962 |
Document ID | / |
Family ID | 8558008 |
Filed Date | 2008-08-21 |
United States Patent
Application |
20080200173 |
Kind Code |
A1 |
Dalsgaard; Lars |
August 21, 2008 |
Method and arrangement for controlling cell change and a terminal
of a cellular system
Abstract
The invention relates to an improved method and arrangement for
controlling a cell change performed by a terminal of a cellular
radio system. In particular the invention relates to a cell change
in a situation where the terminal is connected to a special service
provided by its current cell, e.g. to the GPRS service (General
Packet Radio Service). An essential idea of the invention is that
in conjunction with a cell change order a base station sends to the
terminal information about whether the terminal is allowed not to
carry out the cell change order if the terminal does not know the
timing information of the new cell assigned to it. This information
is advantageously sent in a signalling message of a certain
service, such as the GPRS service. It is an advantage of the
invention that a terminal connected to a certain service will not
make unnecessary cell change attempts which are doomed to fail. The
invention helps direct the cell change in such a manner that the
load caused by possible repeated cell change attempts on the
terminal and radio signalling is low.
Inventors: |
Dalsgaard; Lars; (Oulu,
FI) |
Correspondence
Address: |
HARRINGTON & SMITH, PC
4 RESEARCH DRIVE
SHELTON
CT
06484-6212
US
|
Assignee: |
Nokia Corporation
|
Family ID: |
8558008 |
Appl. No.: |
12/072962 |
Filed: |
February 29, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11469579 |
Sep 1, 2006 |
|
|
|
12072962 |
|
|
|
|
09812932 |
Mar 20, 2001 |
7133383 |
|
|
11469579 |
|
|
|
|
Current U.S.
Class: |
455/436 |
Current CPC
Class: |
H04W 36/36 20130101;
H04W 56/00 20130101 |
Class at
Publication: |
455/436 |
International
Class: |
H04Q 7/20 20060101
H04Q007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 2000 |
FI |
20000675 |
Claims
1-24. (canceled)
25. A method comprising: sending, to a terminal, a first message
comprising first identification information for a plurality of
target cells and a command to change a communication link from a
source cell to a first target cell of the plurality of target
cells; and receiving, from the terminal, a second message
indicating a failure to change the communication link, wherein the
second message further comprises second identification information
for at least one target cell of the plurality of target cells with
which the terminal is synchronized.
26. A method as in claim 25, wherein the first message comprises a
RR_CELL_CHANGE_ORDER message sent on a common control channel
(CCCH) or a stand-alone dedicated control channel (SDCCH) in a
global system for mobile communications (GSM) network.
27. A method as in claim 25, wherein the first message comprises a
PACKET_CELL_CHANGE_ORDER message sent on a packet common control
channel (PCCCH) or a packet associated control channel (PACCH) in a
general packet radio services (GPRS) network.
28. A method as in claim 25, wherein the first message comprises a
system information message or a packet system information
message.
29. A method as in claim 25, wherein the second message comprises a
CELL_CHANGE_FAILURE message, a PACKET_CELL_CHANGE_FAILURE message,
or a HANDOVER_FAILURE message.
30. A method as in claim 25, wherein the second message further
indicates a cause of the failure to change the communication link
from the source cell to the target cell.
31. A method as in claim 25, wherein the at least one target cell
with which the terminal is synchronized comprises at least one
target cell for which timing information is known.
32. A method as in claim 25, further comprising: using the second
information to select a second target cell from the at least one
target cell with which the terminal is synchronized; and sending,
to the terminal, a third message comprising a second command to
change the communication link from the source cell to the second
target cell.
33. A computer program product comprising program instructions
embodied on a tangible computer-readable medium, execution of the
program instructions by a control unit of an electronic device
resulting in operations comprising: sending, to a terminal, a first
message comprising first identification information for a plurality
of target cells and a command to change a communication link from a
source cell to a first target cell of the plurality of target
cells; and receiving, from the terminal, a second message
indicating a failure to change the communication link, wherein the
second message further comprises second identification information
for at least one target cell of the plurality of target cells with
which the terminal is synchronized.
34. A computer program product as in claim 33, wherein the first
message comprises a RR_CELL_CHANGE_ORDER message, a
PACKET_CELL_CHANGE_ORDER message, a system information message or a
packet system information message.
35. A computer program product as in claim 33, wherein the second
message comprises a CELL_CHANGE_FAILURE message, a
PACKET_CELL_CHANGE_FAILURE message, or a HANDOVER_FAILURE
message.
36. A computer program product as in claim 33, wherein the second
message further indicates a cause of the failure to change the
communication link from the source cell to the target cell.
37. A computer program product as in claim 33, wherein the at least
one target cell with which the terminal is synchronized comprises
at least one target cell for which timing information is known.
38. A computer program product as in claim 33, execution of the
program instructions resulting in operations further comprising:
using the second information to select a second target cell from
the at least one target cell with which the terminal is
synchronized; and sending, to the terminal, a third message
comprising a second command to change the communication link from
the source cell to the second target cell.
39. An electronic device comprising: a transmitter configurable to
send, to a terminal, a first message comprising first
identification information for a plurality of target cells and a
command to change a communication link from a source cell to a
first target cell of the plurality of target cells; and a receiver
configurable to receive, from the terminal, a second message
indicating a failure to change the communication link, wherein the
second message further comprises second identification information
for at least one target cell of the plurality of target cells with
which the terminal is synchronized.
40. An electronic device as in claim 39, wherein the first message
comprises a RR_CELL_CHANGE_ORDER message, a
PACKET_CELL_CHANGE_ORDER message, a system information message or a
packet system information message.
41. An electronic device as in claim 39, wherein the second message
further indicates a cause of the failure to change the
communication link from the source cell to the target cell.
42. An electronic device as in claim 39, wherein the at least one
target cell with which the terminal is synchronized comprises at
least one target cell for which timing information is known.
43. An electronic device as in claim 39, execution of the program
instructions resulting in operations further comprising: using the
second information to select a second target cell from the at least
one target cell with which the terminal is synchronized; and
sending, to the terminal, a third message comprising a second
command to change the communication link from the source cell to
the second target cell.
44. A method comprising: sending, to a mobile station, a cell
re-selection command message comprising first identification
information for a plurality of target cells and a command to change
a communication link from a source cell to a first target cell of
the plurality of target cells, wherein the target cell comprises a
global system for mobile communications (GSM) cell with which the
mobile station is not synchronized; and receiving, from the mobile
station, a packet cell change failure message indicating a failure
to change the communication link, wherein the packet cell change
failure message further comprises second identification information
for at least one target cell of the plurality of target cells with
which the mobile station is synchronized.
45. A method as in claim 44, wherein the packet cell change failure
message further indicates a cause of the failure to change the
communication link from the source cell to the target cell.
46. A method as in claim 44, further comprising: using the second
information to select a second target cell from the at least one
target cell with which the mobile station is synchronized; and
sending, to the mobile station, a third message comprising a second
command to change the communication link from the source cell to
the second target cell.
47. A base station comprising: a transmitter configurable to send,
to a mobile station, a cell re-selection command message comprising
first identification information for a plurality of target cells
and a command to change a communication link from a source cell to
a first target cell of the plurality of target cells, wherein the
target cell comprises a global system for mobile communications
(GSM) cell with which the mobile station is not synchronized; and a
receiver configurable to receive, from the mobile station, a packet
cell change failure message indicating a failure to change the
communication link, wherein the packet cell change failure message
further comprises second identification information for at least
one target cell of the plurality of target cells with which the
mobile station is synchronized.
48. A base station as in claim 47, wherein the packet cell change
failure message further indicates a cause of the failure to change
the communication link from the source cell to the target cell.
49. A base station as in claim 47, further comprising: a control
unit configurable to use the second information to select a second
target cell from the at least one target cell with which the mobile
station is synchronized, and wherein the transmitter is further
configurable to send, to the mobile station, a third message
comprising a second command to change the communication link from
the source cell to the second target cell.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a continuation of copending U.S. patent application
Ser. No. 11/469,579, filed on Sep. 1, 2006, which is a continuation
of U.S. Pat. No. 7,133,383, filed on Mar. 20, 2001, which claims
priority to Finnish Application No. 20000675, filed on Mar. 22,
2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a method for controlling cell
change in a service network, in which method a terminal performs
neighbour cell measurements for cell change, the network makes a
decision about the cell change on the basis of the results of said
measurements, current network load and the service needs of the
terminal, and the network sends to the terminal a cell change order
instructing it to switch over to a new cell. The invention
additionally relates to a base station of a cellular radio system,
which base station comprises means for providing service and means
for receiving signalling messages from a terminal as well as means
for generating signalling messages and sending them to terminals.
Furthermore, the invention relates to a terminal of cellular radio
system, which terminal is equipped with means for connecting to a
certain service and which comprises means for receiving signalling
messages from base stations and means for performing cell specific
measurements in order to find a suitable serving cell. In addition,
the invention relates to a cellular radio system comprising base
stations and associated cells as well as terminals, wherein the
base stations are equipped with means for conveying signaling
messages between the base station and a terminal, and the terminals
are equipped so as to operate at a certain service level and to
convey signalling messages between the terminal and base
station.
[0004] 2. Brief Description of Related Developments
[0005] To provide background for the invention we will next
describe some examples of prior-art solutions for changing the
active cell in USM (Global System for Mobile telecommunications)
and in the General Packet Radio Service (GPRS) associated with it.
FIG. 1 illustrates the basic structure of a GSM network. The mobile
communication network typically comprises at least one core network
(CN) and one or more radio access networks (RAN). Core networks
comprise various switching systems which may offer different
value-added services in addition to the versatile communications
features. A core network comprises mobile services switching
centres (MSC), other network elements, which in GSM include e.g.
the serving GPRS support node (SGSN) and gateway GPRS support node
(GGSN), and the associated transmission systems. The radio access
networks are located between the core network and the terminals. A
radio access network comprises base stations (BS) and a radio
network controller (RNC). Each base station is connected via a
fixed line to the radio network controller. The radio network
controllers in turn are connected via fixed lines to at least one
core network node. Between the terminals and core networks there
may operate one or more radio access networks, and a terminal may
be connected to a plurality of core networks via a radio access
network.
[0006] A terminal of a cellular radio system always attempts to
choose a base station in the coverage area, or cell, of which it
camps. In the exemplary situation depicted by FIG. 2, a need for a
change of cells arises at least at points P2 to P7. Conventionally,
the cell change has been based on measuring the strength of the
received radio signal from neighbouring cells 1 to 11 either at the
terminal or base station. In GSM, for example, each base station
broadcasts, at a so-called broadcast frequency, a signal which has
different frequencies for the adjacent base stations. In GSM, a
base station sends to a terminal, on the so-called broadcast
control channel (BCCH), the parameters used by the terminal to
calculate the so-called C values. Most commonly, the so-called C1
value is used in the calculation. The calculation of the C1 value
is described in more detail in Michel Mouly, Marie-Bernadette
Pautet, "The GSM System for Mobile Communications", section
7.1.2.2.
[0007] Terminals have to measure the reception levels of the
received broadcast signals in order to be able to calculate the C1
values of the cells. The cell with the highest C1 value is the most
advantageous for the radio connection. In order to optimize cell
changes the network may also send additional parameters which make
possible to use so-called C2 values. A more detailed description of
the use of these parameters is given in reference [1]. The base
stations also send to terminals information about the BCCH
frequencies used in the adjacent cells so that the terminals know
what frequencies they have to listen to in order to find the BCCH
broadcasts of the adjacent cells.
[0008] GSM system cells provide users with basic services: audio
transmission, slow data transmission, and various short message
services. GSM operation has been standardized by the European
Telecommunication Standardization Institute (ETSI). In GSM, the
cells overlap with respect to their coverage areas, so at a cell
boundary a decision has to be made about which one of the cells the
terminal is to use. In addition to the quality of the connection
the decision is based on other factors, too, such as the traffic
load of the different cells of the network, for instance. In the
active state, the decision about which cell the terminal is to use,
as well as the decision about the cell change timing is made by the
network, which then informs the terminal. According to an ETSI
standard, a terminal in the active state cannot by itself make a
decision to start using the service of another cell. A terminal in
the idle state makes the decision about which cell it belongs to
based on the cells' C1/C2 values which it has calculated. From the
terminal's standpoint the moment of cell change is then not of
great significance as all the system's cells offer the same basic
services and the user of the terminal will not notice the cell
change.
[0009] FIG. 3 shows as an example a flow diagram of prior-art
operation in a cell change situation in connection with a basic GSM
service and GPRS service. While in the idle/active state 30 the
terminal performs, in the example case depicted by FIG. 3,
neighbour cell measurements on the basis of which the network may
estimate 31 the need for a cell change. If the result of the
estimation is that a cell change is not needed, operation returns
to the initial state 30. If a cell change is needed the network
chooses in step 32 one of the neighbour cells as the new target
cell and sends to the terminal a cell change order 33. This order
may be conveyed to the terminal in the basic GSM on the common
control channel (CCCH) or Slow Dedicated Control Channel (SDCCH)
advantageously using a RR_CELL_CHANGE_ORDER message, in which the
new serving cell is described in more detail by means of a base
station identity code (BSIC) and at least the information about the
absolute radio frequency number (ARFCN) of the new cell's base
station. If the terminal at the initial stage 30 is connected to a
GPRS service on a cell supporting PCCCH, the cell change order is
conveyed on the packet common control channel (PCCCH),
advantageously using a PACKET_CELL_CHANGE_ORDER message. Having
received one of the above-mentioned messages the terminal must
immediately attempt 34 a cell change if the operation takes place
in a system according to the prior art. If the terminal does not
know the timing information of the new cell, it is not possible to
immediately get synchronized to the timing used by the new cell,
which is indicated at step 35. In this situation the terminal
returns to using the original cell and informs 37 the network that
the cell change was unsuccessful using e.g. a
PACKET_CELL_CHANGE_FAILURE message if the terminal is connected to
a GPRS service. After that the network may give a new cell change
order to the terminal, possibly targeted at the same cell. In the
worst case, there may be several failed cell change attempts and
returns to the original cell before a successful cell change. If,
however, the terminal knows the new cell's timing information and
is thus able to immediately synchronize to the cell's timing, it
starts to use the new cell already at step 34. Successful step 35
is then followed by the active/idle state 36.
[0010] The prior--an approach described above has many drawbacks.
The cell change fails if the terminal does not know the timing
information of the new cell. If the cell change fails, a service
used by the terminal, which is above the basic service, such as
e.g. GPRS, may be disconnected because of the failed cell change.
In any case the terminal may have to make several attempts to
change cells, which adds to the cell change related signalling
between the terminal and the base station in the serving cell.
[0011] An object of this invention is to provide a cell change
procedure which minimizes unsuccessful cell change attempts to
cells with which the operation of the terminal cannot be
immediately synchronized at the moment of receiving the cell change
order.
SUMMARY OF THE INVENTION
[0012] The objects of the invention are achieved by a procedure in
which a terminal constantly monitors the timing information of the
neighbour cells known to it and conveys that information to the
network if the network orders the terminal to switch over to a cell
the timing information of which is unknown to the terminal. As soon
as the network becomes aware of the conflict, it selects on the
basis of the neighbour cell information sent by the terminal
another cell to which the terminal can immediately switch over
without problems. The network may then consequently send to the
terminal a new cell change order, instructing it to switch over to
a cell with which the terminal has internal synchronization and
thereby can be synchronized without problems.
[0013] It is characteristic of the cell change method according to
the invention that if the new serving cell assigned to a terminal
in a cell change order is a cell the timing information of which is
unknown to the terminal after neighbour cell measurements, the cell
change may not take place but instead the terminal may send to the
base station a cell change failure message which may include
various information such as the cause of the failure as well as
neighbour cell information.
[0014] It is characteristic of the base station according to the
invention that it comprises means for receiving and processing
information coming from a terminal, which information is adapted so
as to convey to the base station information about those neighbour
cells known to the terminal the internal timing information of
which is known to the terminal.
[0015] It is characteristic of the terminal according to the
invention that it is equipped with means for determining neighbour
cell timing information and means for sending neighbour cell
information to the base station of its current cell when the timing
information of the base station of the new cell assigned in a cell
change order to the terminal by the serving base station is unknown
to the terminal.
[0016] It is characteristic of the cellular radio system according
to the invention that it comprises information, which is known to a
terminal, about a set of neighbour cells of said terminal, the
timing information of the base stations of which neighbour cells
the terminal has determined, whereby said system is adapted so as
to convey, after a cell change order addressed to the terminal,
said information from the terminal to a base station in a
signalling message for the purpose of selecting a new serving cell
if the target cell assigned to the terminal in the cell change
order is not included in the set of neighbour cells determined by
the terminal.
[0017] Advantageous embodiments of the invention are presented in
the dependent claims.
[0018] The basic idea of the invention is as follows: A cellular
phone is allowed not to make a cell change attempt to a cell the
timing information of which is unknown to it. This behaviour may be
either set as a default in the terminal or it may be enabled in the
terminal separately for each case by means of a message sent to it
by the network. In practical operation, a cellular phone measures
the neighbour cell information according to the prior art. This way
it determines the transmission frequencies used by the base
stations of neighbour cells, as well as the timing information, if
possible. Thus it is possible for the terminal at any given time to
know which base stations in the network can be chosen as new
serving cells without problems. As a cell change order comes from
the network, the switch can be performed without problems and in
accordance with the prior art to a cell the timing information of
which is known to the terminal and with which it is thus possible
to synchronize without problems. In the case where the switch
should be made to a cell with which terminal has no internal
timing, the terminal, instead of attempting a cell change, uses a
cell change failure message according to the invention to inform
the network about the cells/base stations with which a cell change
would be immediately successful. At this stage the terminal stays
with the original cell until either the network assigns to it by
means of a new cell change order another cell with which the
terminal can synchronize immediately or until other cell change
constraints/rules are fulfilled. After that, the cell change takes
place as in the prior art.
[0019] An advantage of the invention is that the number of failed
cell change attempts is reduced.
[0020] Another advantage of the invention is that the load caused
by failed cell change attempts on network signalling is
reduced.
[0021] A further advantage of the invention is that possible
service breaks caused by failed cell change attempts are
reduced.
[0022] A yet further advantage of the invention is that the
availability of certain services (such as GPRS) is improved as
unnecessary failed cell change attempts are eliminated or reduced
and the terminal can be directly assigned to a cell that can
immediately provide the service needed by the terminal.
DESCRIPTION OF THE DRAWINGS
[0023] The invention is described in detail in the following.
Reference is made to the attached drawings in which
[0024] FIG. 1 shows by way of example the principal elements of a
GSM network,
[0025] FIG. 2 shows by way of example a cell change according to
the prior art in the GSM system,
[0026] FIG. 3 shows by way of example a flow diagram of a cell
change according to the prior art in the GSM system,
[0027] FIG. 4 shows by way of example a flow diagram of a cell
change according to the invention in the GSM system, and
[0028] FIG. 5 shows by way of example the essential structure of a
terminal according to the invention.
DETAILED DESCRIPTION
[0029] FIGS. 1, 2 and 3 were discussed in connection with the
description of the prior art. FIG. 4 shows by way of example an
advantageous method of realizing the improved cell change according
to the invention. Operation according to the invention may be set
as a default in a terminal or the terminal may be enabled to
operate according to the invention by means of a special message
sent by the network. The cell change starts from the active/idle
state 40 in which the cell change need is from time to time
estimated 41. In the example case depicted by FIG. 4 it is the
network that performs said estimation of the cell change need. If
there is no need to change cells, operation returns to step 40. If
a cell change is required the network selects in step 42 one of the
possible neighbour cells as the new target cell. In the active
state the network issues a cell change order in step 43 and in the
basic GSM this order is conveyed on the CCCH or SDCCH to the
terminal advantageously using a RR_CELL_CHANGE_ORDER message and in
GPRS on the PCCCH or on the PACCH advantageously using a
PACKET_CELL_CHANGE_ORDER message. When the terminal has received
the order, it will not attempt a cell change immediately but finds
out in step 44 whether the timing information of the new cell is
known. If immediate synchronization with the timing of the new cell
is impossible the terminal transmits advantageously a modified
PACKET_CELL_CHANGE_FAILURE message 47 or another message used in
connection with cell change failures. The message in question
advantageously includes additional information about those
neighbour cells to which the terminal can switch over immediately
without synchronization problems. Having received the message the
network makes a new cell change decision among the cells that were
included in the message 47 from the terminal. The network sends a
new cell change order 43, and in step 44 it is found that a cell
change can be performed, and in step 45 the terminal immediately
makes a cell change attempt. The success of the cell change attempt
is tested in the step 45. If the cell change is not successful the
terminal transmits advantageously a modified
PACKET_CELL_CHANGE_FAILURE message in the step 47. If the cell
change is successful the operation ends up in the active/idle state
48, and the procedure starts over from the beginning 40.
[0030] When a terminal according to the invention sends a message
about the fact that it does not know the timing information of the
cell assigned to it, the terminal may convey said information
advantageously using a CELL_CHANGE_FAILURE,
PACKET_CELL_CHANGE_FAILURE or HANDOVER_FAILURE message. Into the
message the terminal adds information about the neighbour cells the
timing information of which the terminal knows and with which a
cell change would be immediately successful. On the basis of this
information the network can address to the terminal a new cell
change order in which the target cell is one of the neighbour cells
indicated by the terminal.
[0031] Below it is shown by way of example how the
permission/information enabling operation according to the
invention can be conveyed to a terminal in a RR_CELL_CHANGE_ORDER
or PACKET_CELL_CHANGE_ORDER message. The information may also be
conveyed in other messages used in the communication between the
terminal and the network, such as e.g. system information (SI) and
packet system information (PSI) messages. The following shows by
way of example how the additional information required by the
invention can be conveyed in the GPRS service to a terminal in a
PACKET_CELL_CHANGE_ORDER, as expressed by its information
elements:
TABLE-US-00001 <Packet Cell Change Order message content>::=
<PAGE_MODE : bit(2) { {0<Global TFI :Global TFI IE>> |
10<TLLI:bit (32)>} {0-Message escape {IMMEDIATE_REL:bit>
<ARFCN: bit (10) <BSIC: bit (6) <NC Measurement
Parameters:<NC measurement Parameters struct>>
<Packet_cell_change_order_options: bit (3)> <padding
bits> | <Non-distribution part error: bit(*)=<no
string>>} | <message escape: 1 bit(*) = <no
string>>} | Address information part error: bit(*) = <no
string>>} |<Distribution part error: bit(*) = <no
string>>;
[0032] The message tells, using three bits in the information
element "Packet_cell_change_order_options" according to the
invention, how the terminal is allowed to operate when it receives
a cell change order. The other information elements comply with the
standard. The bit combinations in the additional information
according to the invention may be interpreted advantageously
according to Table 1, for instance.
TABLE-US-00002 TABLE 1 Information element
"Packet_cell_change_order_options" according to the invention Bits
3 2 1 0 0 0 MS shall obey the cell change order 0 0 1 MS shall
without cell change reply with PACKET_CELL_CHANGE_FAILURE . . . 1 0
0 MS shall without cell change reply with
PACKET_CELL_CHANGE_FAILURE 1 0 1 Reserved . . . 1 1 0 Reserved 1 1
1 MS shall without cell change reply with
PACKET_CELL_CHANGE_FAILURE
[0033] Bit combination 0-0-0 in Table 1 corresponds to operation
according to the prior art, whereby the terminal shall obey the
cell change order it has received. If one of bit combinations from
0-0-1 to 1-0-0 is assigned to the terminal, the terminal shall not
in uncertain cases perform a cell change but shall instead send a
PACKET_CELL_CHANGE_FAILURE message to the network. The received bit
combination determines the maximum number of neighbour cells the
information of which shall be included by the terminal in said
reply message. Combination 0-0-1 means that the information of one
neighbour cell will be sent, combination 0-1-0 means that the
information of two neighbour cells will be sent, combination 0-1-1
means that the information of three neighbour cells will be sent,
and combination 1-0-0 means that the information of four neighbour
cells will be sent. Combination 1-1-1 causes the transmission of a
PACKET_CELL_CHANGE_FAILURE message that does not include neighbour
cell measurement data. The other combinations may be used for other
cell change related functions if necessary.
[0034] The Packet_cell_change_order_options information element may
be shorter than the three bits mentioned above. In that case the
number of different bit combinations naturally becomes smaller, and
the number of possible neighbour cells included in the message may
advantageously be none for a certain bit combination and e.g. three
for a certain second bit combination.
[0035] Below it is shown by way of example how the information
according to the invention can be conveyed from a terminal to the
network in a PACKET_CELL_CHANGE_FAILURE or HANDOVER_FAILURE
message, expressed as their information elements, in a situation
where the probability of a successful cell change is small because
the timing information of the new cell is unknown to the
terminal.
TABLE-US-00003 <Packet Cell Change Failure message
content>::= <TLLI:bit (32)>} <ARFCN: bit (10) <BSIC:
bit (6) <Neighbour_cell_reporting: <neighbour cell reporting
struct> <spare padding>
[0036] The new information element "Neighbour_cell_reporting"
according to the invention may have the same basic structure as
that described in a table presented in the ETSI document Reference
[2]. In the operation according to the invention the information
element in question has then the structure illustrated in Table
2:
TABLE-US-00004 TABLE 2 "Neighbour_cell_reporting" information
element according to the invention 8 7 6 5 4 3 2 1 CAUSE NO-OF-
BCCH- octet 1 NCELLS FREQ- NCELL 1 BCCH-FREQ-NCELL 1 BSIC-NCELL 1
octet 2 BSIC- RXLEV-NCELL 1 BCHH octet 3 NCELL FREQ 1 NCELL 2
BCCH-FREQ-NCELL 2 BSIC-NCELL 2 octet 4 BSIC-NCELL 2 RXLEV-NCELL 2
octet 5 BCCH-FREQ-NCELL 3 BSIC-NCELL 3 octet 6 BSIC-NCELL 3
BCCH-FREQ-NCELL-3 octet 7 RXLEV octet 8 NCELL 3
[0037] Table 2 shows a measurement report according to the
invention which report advantageously comprises eight octets. The
first four bits of the first octet advantageously indicate the
cause of the cell change failure. Operation according to the
invention can possibly use the already existing cause codes but it
is possible to add to them a new code for the operation according
to the invention. The next two bits in the first octet indicate the
number of those neighbour cells NO-OF-NCELLS in the report the
timing information of which is known to the terminal on the basis
of the neighbour cell measurements performed by it. In this example
case the data of three neighbour cells are advantageously
transmitted. The last two bits in the first octet are used to
convey the frequency information of a first neighbour cell
BCCH-FREQ-NCELL 1, and the first three bits in the second octet are
also used for this same purpose. The frequency information can be
advantageously conveyed through either the absolute radio frequency
carrier number ARFCN the different values of which refer to certain
predetermined frequencies or as indexes to the list of neighbours
given by the network to the terminal. The rest of the bits in the
second octet are used to convey part of the neighbour cell identity
information BSIC-NCELL 1, and the rest of that information is
conveyed through the first bit of the third octet. Next six bits in
the third octet are used to convey the level measurement data of
the first neighbour cell RXLEV5 NCELL 1. The data for the two other
neighbour cells are transmitted in the following octets in the
order described above. The last octet to be used is octet number
eight, and its first bit is used to convey the last bit of the
level measurement data of the third neighbour cell RXLEV 3.
[0038] In an advantageous embodiment no ARFCN information is
transmitted as such in the measurement report but the ARFCN data in
question are indexed in the cellular system in a manner known to
both the terminal and the network. In this case it suffices to
include the indices in question in the measurement report according
to the invention transmitted to the base station.
[0039] In another advantageous embodiment the terminal arranges the
neighbour cell data in the measurement report advantageously in the
order according to the received RX level (RXLEV) measured by it. In
that case the level measurement data may either be included in the
measurement report according to the invention or they may be left
out of it. By leaving the level measurement data out it is possible
to reduce the amount of data transmitted in the cellular system,
while still being able to convey to the network the information
about the order which from the cell change standpoint is best for
the terminal.
[0040] FIG. 5 shows in the form of simplified block diagram a
terminal 500, advanta-geously a mobile station, according to the
invention and its connection to a cellular telephone network. The
mobile station comprises an antenna 501 for receiving
radio-frequency (RF) signals transmitted by base stations. A
received RF signal is directed by a switch 502 to a RF receiver 511
where the signal is amplified and converted digital. The signal is
then detected and demodulated in block 512. Block 513 performs
decryption and deinterleaving. Then follows signal processing in
block 530. Received data may be stored as such in the mobile
station's memory 504 or, alternatively, the processed packet data
are taken after the signal processing to a potential external
device such as a computer. A control unit controls the
above-mentioned reception blocks in accordance with a program
stored in the unit. Transmission from the mobile station is
performed e.g. as follows. Controlled by the control unit 503,
block 533 performs possible signal processing on the data and block
521 performs interleaving and encryption on the processed signal to
be transmitted. Bursts are generated from the encoded data, block
522, which are modulated and amplified into a RF signal to be
transmitted, block 523. The RF signal to be transmitted is led to
the antenna 501 through the switch 502. Also these processing and
transmission functions are controlled by the control unit 503. Also
illustrated in FIG. 5 are a keypad 531 for inputting information or
commands which may be stored in memory 504. A display 532 can be
used to display data stored in the memory 504.
[0041] In the terminal of FIG. 5, the parts that are essential from
the invention's perspective include the prior-art reception blocks
511-513, by means of which the terminal receives, demodulates and
decodes the messages transmitted by base stations and measures the
received signal power levels, as well as the control unit 503 which
processes the information contained in the messages and controls
the operation of the terminal. Additional features required by the
operation according to the invention have to be added to the
operation of the control unit in order to implement the message
indicating cell change failure. Part of the memory 504 of the
terminal must be allocated to information relating to neighbour
cell selection, such as e.g. information about neighbour cells'
BCCH frequencies received from base stations, information about the
received signal level, information about the neighbour cells'
timing information, and information about the quality of service
provided by the neighbour cells. For this purpose it is naturally
possible to use a detachable memory device in connection with the
terminal, say a SIM card which is known as such. By means of the
transmission blocks 521-523 the terminal sends the cell change
messages, both those according to the standards and those according
to the invention, to base stations.
[0042] The hardware requirements caused by the invention on prior
art base stations are minimal. Base station 551 and/or base station
controller 552, and switching center 553, have access to a database
(not shown in FIG. 5) containing neighbour cell information about
the BCCH frequencies and service levels, such as the ability of
neighbour cells to provide GPRS service, for example. To this
database it is possible to add information according to the
invention sent by the terminal about the cells for which the
terminal indicates that a cell change to them is impossible at that
moment, and also information about the cells to which a cell change
could be successfully performed at that moment. On the basis of the
information received the base station can then assign another cell
to the terminal. The base station 551 is coupled to the terminal
500 via antenna 550.
[0043] Naturally the embodiments described above are exemplary only
and do not limit the application of the invention. Particularly it
should be noted that although the examples described above relate
to the GSM and GPRS systems, the invention is applicable to any
other digital cellular system as well. Especially we could mention
the DCS1800 (Digital Communications System at 1800 MHz), IS-54
(Interim Standard 54) and PDC (Personal Digital Cellular) and in
particular the forthcoming third-generation digital cellular UMTS
(Universal Mobile Telecommunications System). In addition, the
inventional idea can be applied in many ways within the limits
defined by the claims.
REFERENCES
[0044] [1] ETSI 05.08 version 6.4.0 [0045] [1] ETSI 04.08 version
6.2.0 section 10.5.2.20 FIG. 10.5.47
* * * * *