U.S. patent application number 11/582303 was filed with the patent office on 2007-05-24 for data transmission method and mobile telephone system.
This patent application is currently assigned to NOKIA Corporation. Invention is credited to Zhi-Chun Honkasalo, Antti Toskala.
Application Number | 20070115875 11/582303 |
Document ID | / |
Family ID | 8552140 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070115875 |
Kind Code |
A1 |
Toskala; Antti ; et
al. |
May 24, 2007 |
Data transmission method and mobile telephone system
Abstract
A method for transmitting data from a radio network subsystem to
user equipment in a mobile telephone system, a radio network
subsystem and user equipment. In the method, the radio network
subsystem transmits a dedicated control channel to the user
equipment and a dedicated traffic channel of variable data
transmission rate to the user equipment. During transmission, the
radio network subsystem spreads each channel with a spreading code,
and the spreading code used to spread the traffic channel is
changed according to the required data transmission rate. According
to the invention, each control channel frame indicates the
spreading code with which the corresponding traffic channel is
spread when transmitted.
Inventors: |
Toskala; Antti; (Helsinki,
FI) ; Honkasalo; Zhi-Chun; (Kauniainen, FI) |
Correspondence
Address: |
PILLSBURY WINTHROP SHAW PITTMAN, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
NOKIA Corporation
Espoo
FI
|
Family ID: |
8552140 |
Appl. No.: |
11/582303 |
Filed: |
October 18, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11152084 |
Jun 15, 2005 |
7139260 |
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11582303 |
Oct 18, 2006 |
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09486821 |
Mar 2, 2000 |
6975615 |
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PCT/FI99/00581 |
Jun 30, 1999 |
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11152084 |
Jun 15, 2005 |
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Current U.S.
Class: |
370/328 ;
370/338; 375/E1.002 |
Current CPC
Class: |
H04J 13/20 20130101;
H04J 13/004 20130101; H04J 13/0044 20130101; H04B 1/707 20130101;
H04B 2201/70703 20130101; H04B 2201/70701 20130101; H04W 88/08
20130101; H04W 28/22 20130101 |
Class at
Publication: |
370/328 ;
370/338 |
International
Class: |
H04Q 7/00 20060101
H04Q007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 3, 1998 |
FI |
981546 |
Claims
1. A base station comprising a radio transmitter that includes a
control unit, and a transceiver, said base station for transmitting
a control channel to a user equipment; transmitting a traffic
channel of variable data transmission rate to the user equipment;
spreading each channel with a spreading code during transmission;
changing the spreading code used to spread the traffic channel
according to a required data transmission rate; indicating in each
control channel frame the spreading code with which a corresponding
traffic channel frame is spread when transmitted, and transmitting
the control channel and traffic channel frames associated with each
other on the same frequency, spread with different spreading codes,
and separated by one frame length at most.
2. The base station of claim 1, wherein said control unit is
configured to control said transceiver.
3. The base station of claim 1, wherein the control channel frame
comprises a transport format indicator into which the base station
is configured to enter the identification data of the spreading
code used to spread the traffic channel.
4. The base station of claim 1, wherein the spreading codes are
arranged into a code tree in such a manner that on the first level,
the code tree root comprises a one-bit spreading code, the second
level comprises two branches with mutually orthogonal two-bit
spreading codes, the third level comprises four branches with
mutually orthogonal four-bit spreading codes, the fourth level
comprises eight branches with mutually orthogonal eight-bit
spreading codes, the fifth level comprises sixteen branches with
mutually orthogonal sixteen-bit spreading codes, the sixth level
comprises thirty two branches with mutually orthogonal
thirty-two-bit spreading codes, the seventh level comprises sixty
four branches with mutually orthogonal sixty-four-bit spreading
codes, the eight level comprises one hundred and twenty eight
branches with mutually orthogonal 128-bit spreading codes, the
ninth level comprises two hundred and fifty six branches with
mutually orthogonal 256-bit spreading codes.
5. The base station of claim 4, wherein the base station is
configured to divide the code tree into sub-code trees, and one
branch in a level is a tree access point to a sub-code tree, and
the branches below the tree access point belong to the sub-code
tree in question.
6. The base station of claim 5, wherein the base station is
configured to change the data transmission rate of the traffic
channel by changing the length of its spreading code by moving
between the levels of the sub-code tree.
7. The base station of claim 6, wherein the base station is
configured to number each spreading code of a sub-code tree in an
agreed manner and to enter the number in question into a transport
format indicator.
8. The base station of claim 6, wherein the base station does not
expect an acknowledgement from the user equipment after
transmitting a transport format indicator to the user
equipment.
9. The base station of claim 1, wherein the base station is
configured to transmit signalling of the physical layer, data link
layer and network layer in the control channel.
10. The base station of claim 5, wherein the base station is
configured to signal the tree access point of the sub-code tree to
the user equipment and to await an acknowledgement to its
signalling from the user equipment.
11. The base station of claim 10, wherein the base station is
configured to perform the signalling of the tree access point of
the sub-code tree as signalling of the MAC sub-layer in the data
link layer.
12. The base station of claim 1, wherein the base station is
configured to transmit the traffic channel frames in a synchronized
manner to the units of user equipment which belong to the same
sub-code tree.
13. The base station of claim 1, wherein the base station is
configured to set the data transmission rate of the control channel
as low as possible.
14. The base station of claim 1, wherein the base station is
configured to place pilot bits into the traffic channel for channel
estimation.
15. The base station of claim 1, wherein the base station is
configured to place only useful load in the traffic channel.
16. The base station of claim 1, wherein the base station is
configured to transmit the control channel frames of different user
equipment as non-simultaneously as possible.
17. The base station of claim 1, wherein the base station is
configured to place data or speech in free capacity of the control
channel frame.
18. The base station of claim 1, wherein the base station is
configured to transmit the control channel at a fixed data
transmission rate.
19. The base station of claim 1, wherein the base station is a part
of a universal mobile telecommunication system using a
direct-sequence wideband code division multiple access method.
20. A software product having computer executable instructions,
said computer executable instructions being stored on a computer
readable medium, said instructions being executable by a network
element to perform a method for transmitting data from the network
element to a user equipment, the method comprising: transmitting a
control channel to the user equipment; transmitting a traffic
channel of variable data transmission rate to the user equipment;
spreading each channel with a spreading code during transmission;
changing the spreading code used to spread the traffic channel
according to a required data transmission rate; indicating in each
control channel frame the spreading code with which a corresponding
traffic channel frame is spread when transmitted, and transmitting
the control channel and traffic channel frames associated with each
other on the same frequency, spread with different spreading codes,
and separated by one frame length at most.
21. The software product of claim 20, wherein said network element
is a base station.
22. A radio network controller comprising a control unit, said
radio network controller, in conjunction with a transmission of a
control channel and a traffic channel of variable data transmission
rate to user equipment, for allocating a spreading code for each
channel during transmission; changing the spreading code used to
spread the traffic channel according to a required data
transmission rate, and indicating in each control channel frame the
spreading code with which a corresponding traffic channel frame is
spread when transmitted, wherein the control channel and traffic
channel frames associated with each other are transmitted on the
same frequency, spread with different spreading codes, and
separated by one frame length at most.
23. The radio network controller of claim 22, wherein the spreading
codes are arranged into a code tree in such a manner that on the
first level, the code tree root comprises a one-bit spreading code,
the second level comprises two branches with mutually orthogonal
two-bit spreading codes, the third level comprises four branches
with mutually orthogonal four-bit spreading codes, the fourth level
comprises eight branches with mutually orthogonal eight-bit
spreading codes, the fifth level comprises sixteen branches with
mutually orthogonal sixteen-bit spreading codes, the sixth level
comprises thirty two branches with mutually orthogonal
thirty-two-bit spreading codes, the seventh level comprises sixty
four branches with mutually orthogonal sixty-four-bit spreading
codes, the eight level comprises one hundred and twenty eight
branches with mutually orthogonal 128-bit spreading codes, the
ninth level comprises two hundred and fifty six branches with
mutually orthogonal 256-bit spreading codes.
24. The radio network controller of claim 23, wherein the radio
network controller is configured to reserve a part of the spreading
codes in the code tree for the use of the control channels.
25. The radio network controller of claim 23, wherein the radio
network controller is configured to divide the code tree into
sub-code trees, and one branch in a level is a tree access point to
a sub-code tree, and the branches below the tree access point
belong to the sub-code tree in question.
26. The radio network controller of claim 25, wherein the radio
network controller is configured to change the data transmission
rate of the traffic channel by changing the length of its spreading
code by moving between the levels of the sub-code tree.
27. The radio network controller of claim 26, wherein the radio
network controller is configured to number each spreading code of a
sub-code tree in an agreed manner and to enter the number in
question into a transport format indicator.
28. The radio network controller of claim 7, wherein the number
refers to at least two parallel spreading codes.
29. The radio network controller of claim 25, wherein the radio
network controller is configured to use the various spreading codes
of the same sub-code tree for at least two different units of user
equipment.
30. The radio network controller of claim 29, wherein the radio
network subsystem is configured to allocate the spreading
codes.
31. The radio network controller of claim 30, wherein when the
sub-code tree becomes congested, the radio network controller is
configured to transfer the user equipment to another sub-code
tree.
32. The radio network controller of claim 22, wherein the radio
network controller is configured to always use the same spreading
code in spreading the control channel.
33. A software product having computer executable instructions,
said computer executable instructions being stored on a computer
readable medium, said instructions being executable by a network
controller to perform a method for transmitting data from a network
element to a user equipment, said network element being configured
to transmit a control channel to the user equipment, and to
transmit a traffic channel of variable data transmission rate to
the user equipment, the method comprising: allocating a spreading
code for each channel during transmission; changing the spreading
code used to spread the traffic channel according to a required
data transmission rate, and indicating in each control channel
frame the spreading code with which a corresponding traffic channel
frame is spread when transmitted, wherein the control channel and
traffic channel frames associated with each other are transmitted
on the same frequency, spread with different spreading codes, and
separated by one frame length at most.
34. A software product having computer executable instructions,
said computer executable instructions being stored on a computer
readable medium, said instructions being executable by a user
equipment to perform a method for receiving data from a network
element, said method comprising: receiving a control channel
transmitted by a radio network subsystem; receiving a traffic
channel of variable data transmission rate transmitted by the
network element, wherein a spreading code used by the network
element to spread the traffic channel during transmission is
changed according to a required data transmission rate; removing
the spreading of each channel with the spreading code; reading from
each control channel frame the spreading code with which a
corresponding traffic channel frame is spread, and receiving the
control channel frames and traffic channel frames associated with
each other transmitted by the network element on the same
frequency, spread with different spreading codes, and separated by
one frame length at most.
35. A communication system comprising a network element and a user
equipment, (a) said network element for: (i) transmitting a control
channel to the user equipment; (ii) transmitting a traffic channel
of variable data transmission rate to the user equipment; (iii)
spreading each channel with a spreading code during transmission;
(iv) changing the spreading code used to spread the traffic channel
according to a required data transmission rate; (v) indicating in
each control channel frame the spreading code with which a
corresponding traffic channel frame is spread when transmitted, and
(vi) transmitting the control channel and traffic channel frames
associated with each other on the same frequency, spread with
different spreading codes, and separated by one frame length at
most; and (b) said user equipment for (i) receiving the control
channel transmitted by the network element; (ii)-receiving the
traffic channel of variable data transmission rate transmitted by
the network element, wherein a spreading code used by the network
element to spread the traffic channel during transmission is
changed according to a required data transmission rate;
(iii)-removing the spreading of each channel with the spreading
code; (iv) reading from each control channel frame the spreading
code with which a corresponding traffic channel frame is spread,
and (v) receiving the control channel frames and traffic channel
frames associated with each other transmitted by the network
element on the same frequency, spread with different spreading
codes, and separated by one frame length at most.
36. The communication system of claim 35, wherein said network
element is a base station.
37. A processor for use in a base station of a communication
system, said processor being configured to execute computer
executable instructions for transmitting data from a radio network
subsystem to a user equipment according to a method comprising:
transmitting a physical control channel to the user equipment;
transmitting a physical traffic channel of variable data
transmission rate to the user equipment; spreading each channel
with a spreading code during transmission; changing the spreading
code used to spread the traffic channel according to a required
data transmission rate; indicating in each control channel frame
the spreading code with which a corresponding traffic channel frame
is spread when transmitted, and transmitting the control channel
and traffic channel frames associated with each other on the same
frequency, spread with different spreading codes, and separated by
one frame length at most.
38. An apparatus for use in a network element of a communications
system comprising a transmitter and a control unit, said apparatus
for: transmitting a control channel to user equipment; transmitting
a traffic channel of variable data transmission rate to the user
equipment; spreading each channel with a spreading code during
transmission; changing the spreading code used to spread the
traffic channel according to a required data transmission rate;
indicating in each control channel frame the spreading code with
which a corresponding traffic channel frame is spread when
transmitted, and transmitting the control channel and traffic
channel frames associated with each other on the same frequency,
spread with different spreading codes, and separated by one frame
length at most.
39. An apparatus for use in a user equipment of a communications
system comprising a receiver and a control unit, said apparatus
for: receiving a control channel transmitted by a radio network
subsystem; and receiving a traffic channel of variable data
transmission rate transmitted by the radio network subsystem,
wherein a spreading code used by the radio network subsystem to
spread the traffic channel during transmission is changed according
to a required data transmission rate; removing the spreading of
each channel with a spreading code, wherein the apparatus-reads
from each control channel frame the spreading code with which a
corresponding traffic channel frame is spread, and wherein the
apparatus receives the control channel frames and traffic channel
frames associated with each other transmitted by the radio network
subsystem on the same frequency, spread with different spreading
codes, and separated by one frame length at most.
40. User equipment comprising: a receiver for receiving a control
channel transmitted by a radio network subsystem; and receiving a
traffic channel of variable data transmission rate transmitted by
the radio network subsystem, wherein a spreading code used by the
radio network subsystem to spread the traffic channel during
transmission is changed according to a required data transmission
rate; and a control part for removing the spreading of each channel
with a spreading code, wherein the user equipment is configured to
read from each control channel frame the spreading code with which
a corresponding traffic channel frame is spread, and wherein the
user equipment receives the control channel frames and traffic
channel frames associated with each other transmitted by the radio
network subsystem on the same frequency, spread with different
spreading codes, and separated by one frame length at most.
Description
[0001] This is a continuation of U.S. patent application Ser. No.
11/152,084, filed on Jun. 15, 2006 (Issue Fee Paid), which is a
continuation of U.S. patent application Ser. No. 09/486,821, filed
on Mar. 2, 2002 (U.S. Pat. No. 6,975,615), which is the U.S.
National Stage of International Patent Application No. [[:]]
PCT/FI99/00581, filed Jun. 30, 1999, which, in turn, relies for
priority upon Finnish Application No. 981546, filed Jul. 3, 1998,
the contents of all of which are incorporated herein by reference
in their entireties.
FIELD OF THE INVENTION
[0002] The invention relates to a method for transmitting data from
a radio network subsystem to user equipment in a mobile telephone
system. The invention relates in particular to changing the data
transmission rate of a traffic channel, especially a packet traffic
channel during a radio link in a universal mobile telephone
system.
BACKGROUND OF THE INVENTION
[0003] One of the biggest problems in mobile telephone systems is
an efficient use of a limited radio capacity. In present systems, a
certain amount of capacity is reserved for each user for a
circuit-switched call during the entire radio link. When using
packet-switched transmission, in which the data to be transmitted
is typically generated in bursts, it is a waste of radio capacity
to keep the radio capacity reserved all the time according to the
greatest momentary data transmission need.
[0004] In systems using the code division multiple access (CDMA)
method, in a downlink from a radio network subsystem to user
equipment, different users use the same code tree in which the
spreading codes used in the system are arranged mutually
orthogonally. If a spreading code having a small spreading factor
allowing a high transmission rate is reserved for one user, the
code in question can reserve a large part of the capacity of the
radio network subsystem in question, or its base transceiver
station. In a code tree used by one base transceiver station, one
sector of the base transceiver station can use sixteen mutually
orthogonal sixteen character-long spreading codes, for instance, in
which case the entire capacity of the base transceiver station can
at one moment be in use and a new user will not have access to any
data transmission resources for a downlink.
[0005] On an uplink, this problem does not exist, since each user
has access to the entire code tree of the base transceiver station.
Various users are distinguished from each other with a scrambling
code which is specific for each transmitter. For instance, a
universal mobile telecommunication system (UMTS) using a
direct-sequence wideband code division multiple access method (DS
W-CDMA) can have 512 different scrambling codes and 256 different
spreading codes on a downlink. On an uplink, the number of
scrambling codes can be much higher, even millions of different
codes. It is interesting to note that a base transceiver station
normally uses only one scrambling code for each transmitter.
[0006] In present mobile telephone systems, the data transmission
rates used for both speech and data have been relatively low, and
it has been possible to keep the resource problem under control. In
new mobile telephone systems, the data transmission rates used will
be considerably higher than in the present systems due to the
wireless remote, use of various computer applications. The computer
applications include various database applications, e-mail, WWW
browser, etc.
[0007] For instance, the CDMA2000 system discloses a solution in
which fundamental channels and supplementary channels are used. The
fundamental channel transmits the signalling of the MAC (Medium
Access Control) sub-layer of the data link layer, which indicates
whether a supplementary channel with a higher transmission rate is
used in addition to the fundamental channel. A problem with this
solution is that it does not support fast changing of the channel
transmission rate by changing the spreading code, since MAC
sublayer signalling is used to change the spreading code and it is
a relatively slow process.
BRIEF DESCRIPTION OF THE INVENTION
[0008] It is thus an object of the invention to develop a method
and an apparatus implementing the method so as to solve the above
problems. This is achieved by the method described in the
following. The method in question is a method for transmitting data
from a radio network subsystem to user equipment in a mobile
telephone system, comprising: the radio network subsystem transmits
a dedicated control channel to the user equipment; the radio
network subsystem transmits a dedicated traffic channel of variable
data transmission rate to the user equipment; during transmission,
the radio network subsystem spreads each channel with a spreading
code; the spreading code used to spread the traffic channel is
changed according to the required data transmission rate. In the
method in question, each frame of the control channel indicates the
spreading code with which the corresponding traffic channel frame
is spread when transmitted.
[0009] The invention also relates to a radio network subsystem
which is adapted to: transmit a dedicated control channel to the
user equipment; transmit a dedicated traffic channel of variable
data transmission rate to the user equipment; spread each channel
with a spreading code during transmission; change the spreading
code used to spread the traffic channel according to the required
data transmission rate. The radio network subsystem is adapted to
indicate in each control channel frame the spreading code with
which the corresponding traffic channel frame is spread when
transmitted.
[0010] The invention further relates to user equipment which is
adapted to: receive a dedicated control channel transmitted by the
radio network subsystem; receive a dedicated traffic channel of
variable data transmission rate transmitted by the radio network
subsystem; remove the spreading of each channel with a spreading
code. The user equipment is adapted to read from each control
channel frame the spreading code with which the corresponding
traffic channel frame is spread.
[0011] Preferred embodiments of the invention are disclosed in the
dependent claims.
[0012] The invention is based on indicating in each control channel
frame the spreading code with which the corresponding traffic
channel is spread.
[0013] The method and system of the invention provide several
advantages. The data transmission rate can quickly be changed, even
by each frame, by selecting a suitable spreading code. This enables
an efficient utilization of radio resources.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] In the following, the invention will be described in greater
detail in connection with preferred embodiments with reference to
the attached drawings in which:
[0015] FIGS. 1A and 1B show a mobile telephone system,
[0016] FIG. 2A shows a transmitter and receiver of the mobile
telephone system;
[0017] FIG. 2B shows spreading and modulation performed in the
transmitter,
[0018] FIG. 3 shows channels of the mobile telephone system in a
frame,
[0019] FIG. 4A shows a code tree,
[0020] FIG. 4B shows a subcode tree,
[0021] FIG. 5 shows user equipment,
[0022] FIG. 6 shows a flow chart of the operations of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The invention can be used in various mobile telephone
systems that use the code division multiple access method (CDMA).
The examples illustrate the use of the invention in a universal
mobile telephone system using a direct-sequence wideband code
division multiple access method, without limiting the invention to
it, however. The examples are based on the specification of the
WCDMA system, further information on which is available in the ETSI
(European Telecommunications Standards Institute) specification
"The ETSI UMTS Terrestrial Radio Access (UTRA) ITU-R RTT Candidate
Submission (Tdoc SMG2 260/98, May/June 1998), which is incorporated
herein by reference.
[0024] The structure of a universal mobile telephone system is
described with reference to FIGS. 1A and 1B. FIG. 1B includes only
the blocks that are essential for describing the invention, but it
is obvious to those skilled in the art that a common mobile
telephone system also contains other functions and structures which
need not be described in detail herein. The main parts of a mobile
telephone system are a core network CN, a universal mobile
telephone system (UMTS) terrestrial radio access network UTRAN, and
user equipment UE. The interface between CN and UTRAN is referred
to as Iu and the air interface between UTRAN and UE is referred to
as Uu.
[0025] UTRAN comprises radio network subsystems RNS. The interface
between RNSs is referred to as Iur. An RNS comprises a radio
network controller RNC and one or more nodes B. The interface
between RNC and B is referred to as Iub. The service area of node
B, i.e. cell, is indicated with C in FIG. 1B.
[0026] As the presentation in FIG. 1A is very abstract, it is
therefore clarified in FIG. 1 B by setting forth the parts of the
GSM system that approximately correspond to the parts of the UMTS.
It should be noted that the mapping shown is by no means a binding
one but an approximation, since the responsibilities and functions
of the different parts of the UMTS are still being planned.
[0027] FIG. 1B shows a packet transfer through the Internet 102
from a computer 100 connected to a mobile telephone system to a
portable computer 122 connected to user equipment UE. The user
equipment UE can, for instance, be a fixed terminal, a terminal
arranged in a vehicle, or a portable terminal. The infrastructure
of a radio network UTRAN comprises radio network subsystems RNS,
i.e. base transceiver station systems. A radio network subsystem
RNS comprises a radio network controller RNC, i.e. base station
controller, and at least one node B, i.e. base transceiver station,
under its control.
[0028] The base transceiver station B has a multiplexer 114,
transceivers 116 and a control unit 118 which controls the
operation of the transceivers 116 and the multiplexer 114. With the
multiplexer 114, the traffic and control channels used by several
transceivers 116 are placed in the transmission link Iub.
[0029] The transceiver 116 of the base transceiver station B are
connected to an antenna unit 120 with which a bidirectional radio
link Uu is implemented to user equipment UE. The structure of the
frames to be transmitted over the bidirectional radio link Uu is
clearly specified.
[0030] The radio network controller RNC comprises a group switching
field 110 and control unit 112. The group switching field 110 is
used for speech and data connection and to connect signalling
circuits. The base station system formed by the base transceiver
station B and the radio network controller RNC also comprises a
transcoder 108. Work distribution between the radio network
controller RNC and the base transceiver station B as well as their
physical structure can vary depending on implementation. Typically,
the base transceiver station B takes care of the radio path
implementaton as described above. The radio network controller RNC
typically takes care of the following: management of radio
resources, control of handover between cells, power adjustment,
timing and synchronization, paging the user equipment.
[0031] The transcoder 108 is usually located as dose as possible to
a mobile switching centre 106, because speech can then be
transmitted in mobile telephone system format between the
transcoder 108 and the radio network controller RNC saving
transmission capacity. The transcoder 108 converts the different
digital coding formats of speech used between the public switched
telephone network and the mobile telephone network to be compatible
with each other, for instance from the 64 kbits format of a public
network to another (e.g. 13 kbit/s) format of a cellular network
and vice versa. The hardware required is not described in detail
herein, but it can be noted that other data than speech is not
converted in transcoder 122. The control unit 112 takes care of
call control, mobility management, collection of statistics, and
signalling.
[0032] Core network CN comprises an infrastructure belonging to a
mobile telephone system and external to UTRAN. FIG. 1B describes
two of the components in a core network CN, i.e. a mobile switching
centre 106 and a gateway mobile switching centre 104 which handles
the connections of the mobile telephone system to the outside
world, in this case, to the Internet 102.
[0033] FIG. 5 shows an example of the structure of user equipment
UE. The essential parts of the user equipment UE are: an interface
504 to the antenna 502 of the user equipment, a transceiver 506, a
control part 510 of the user equipment, and an interface 512 to a
battery 514. The user interface usually comprises a display 500, a
keyboard 508, a microphone 516, and a loudspeaker 518.
[0034] FIG. 2A describes the operation of a radio
transmitter--radio receiver pair. FIG. 2A describes a case of
downlink where the radio transmitter is located in node B and the
radio receiver in the user equipment UE.
[0035] The upper part of FIG. 2A describes the essential functions
of the radio transmitter. Various services located in the physical
channel include speech, data, moving or still video picture, and
control channels of the system which are processed in the control
part 214 of the radio transmitter. The figure shows the processing
of the control channel and data. Different services require
different source coding means, for instance speech requires a
speech codec. For clarity's sake, source coding means are not,
however, described in FIG. 2A.
[0036] Different channel coding is then performed for different
channels in blocks 202A and 202B. Channel coding includes, for
instance, different block codes, an example of which is cyclic
redundancy check (CRC). In addition, convolution coding and its
various modifications, such as punctured convolution coding or
turbo coding, are typically used.
[0037] When the different channels have been channel-coded, they
are interleaved in an interleaver 204A, 204B. The purpose of
interleaving is to facilitate error correction. In interleaving,
the bits of different services are mixed in a certain manner
together, in which case a momentary fade in the radio path does not
necessarily make the transmitted information unidentifiable. The
interleaved bits are then spread with a spreading code, scrambled
with a scrambling code and modulated in block 206A, 206B, the
operation of which is described in greater detail in FIG. 2B.
Individual signals are combined in block 208 to be transmitted
through one transmitter.
[0038] Finally, the combined signal is forwarded to radio frequency
parts 210 which can comprise different power amplifiers and filters
restricting bandwidth. The analogous radio signal is then
transmitted through an antenna 212 to the radio path Uu.
[0039] The lower part of FIG. 2A describes the essential functions
of the radio receiver. The radio receiver is typically a RAKE
receiver. An analogous radio frequency signal is received from the
radio path Uu with an antenna 234. The signal is forwarded to radio
frequency parts 232 comprising a filter which prevents all
frequencies outside the desired bandwidth. After this, the signal
is converted in a demodulator 230 to an intermediate frequency or
directly to a base band, and the thus converted signal is then
sampled and quantized.
[0040] As the signal in question is a multi-path propagated signal,
the aim is to combine the signal components that propagated via
different paths in block 228 which comprises several RAKE fingers
of prior art. The signal components received at different time
delays by the RAKE fingers are searched for by correlating the
received signal with the spreading codes used and delayed by
predefined time delays. When the time delays of the signal
components have been found, the signal components belonging to the
same signal are combined. At the same time, the spreading of the
signal components is removed by multiplying the signal by the
spreading code of the physical channel. The interleaving of the
received physical channel is then removed in deinterleaving means
226.
[0041] The deinterleaved physical channel is then distributed to
the data streams of various channels in a demultiplexer 224. The
channels are directed each to its own channel decoding block 222A,
222B where the channel coding, for instance block coding or
convolution coding, used in transmission is decoded. Convolution
coding is preferably decoded with a Viterbi decoder. Each
transmitted channel 220A, 220B can then be forwarded to a required
further processing, for instance data 220 is forwarded to a
computer 122 connected to the user equipment UE. The control
channels of the system are forwarded to the control part 236 of the
radio receiver.
[0042] FIG. 2B describes in greater detail the spreading of a
channel with a spreading code and its modulation. In the figure,
the bit stream of the channel arrives from the left to block S/P in
which each two-bit sequence is converted from serial mode to
parallel mode, i.e. one bit is forwarded to the I branch of the
signal and the second bit to the Q branch. Then the I and Q
branches of the signal are multiplied by the same spreading code
C.sub.ch, in which case the relatively narrow-band information is
spread on a wide frequency band. Each link Uu has its own spreading
code by which the receiver identifies transmissions meant for it.
The signal is then scrambled by multiplying it by a scrambling code
C.sub.scramb which is different for each transmitter. The pulse
format of the obtained signal is filtered with a filter p(t).
Finally, the signal is modulated to a radio frequency carrier by
multiplying its different branches offset by 90 degrees from each
other, the thus obtained branches are combined into one carrier
which is ready to be transmitted to the radio path Uu apart from
possible filtering and power amplifications. The described
modulation method is QPSK (Quadrature Phase Shift Keying).
[0043] FIG. 4A describes different spreading codes. Each point 400
represents one possible spreading code. The vertical dashed lines
illustrate different spreading factors SF=1, SF=2, SF=4, SF=8,
SF=16, SF=32, SF=64, SF=128, SF=256. The codes on each vertical
dashed line are mutually orthogonal. It is thus possible to
simultaneously use at most two hundred and fifty six different
mutually orthogonal spreading codes. For instance in UMTS, when
using a 4.096-megachip carrier, a spreading factor of SF=256
corresponds to a transmission rate of thirty two kilobits per
second, and correspondingly the highest practical transmission rate
is achieved with spreading factor SF=4, with which the data
transmission rate is two thousand forty eight kilobits per second.
The transmission rate in the channel varies thus step by step, 32,
64, 128, 256, 512, 1024, and 2048 kbit/s, while the spreading
factor changes correspondingly, 256, 128, 64, 32, 16, 8, and 4. The
data transmission rate available to the user depends on the channel
coding used. For instance, when using 1/3 convolution coding, the
data transmission rate of the user is approximately one third of
the data transmission rate of the channel. The spreading factor
indicates the length of the spreading code. For instance, the
spreading code corresponding to spreading factor SF=1 is (1).
Spreading factor SF=2 has two mutually orthogonal spreading codes
(1,1) and (1,-1). Further, spreading code SF=4 has four mutually
orthogonal spreading codes: under the higher-level spreading code
(1,1), there are spreading codes (1,1,1,1) and (1,1,-1,-1), and
under the second higher-level spreading code (1,-1), there are
spreading codes (1,-1,1,-1) and (1,-1,-1,1). The formation of
spreading codes is thus continued towards the lower levels of the
code tree. The spreading codes of a certain level are always
mutually orthogonal. Similarly, a spreading code of a certain level
is orthogonal with all lower-level spreading codes derived from
another spreading code on the same level.
[0044] With reference to FIG. 3, an example will be described as to
what kind of frame structure can be used in a physical channel.
Frames 340A, 340B, 340C, 340D are numbered sequentially from one to
seventy two and they form a 720-millisecond long super frame. The
length of one frame 340C is 10 milliseconds. Frame 340C is divided
into sixteen slots 330A, 330B, 330C, 330D. The length of one slot
330C is 0.625 milliseconds. One slot 330C typically corresponds to
one power adjustment period during which power is adjusted one
decibel up or down, for instance.
[0045] Physical channels are divided into two different types:
dedicated physical data channels (DPDCH) 310 and dedicated physical
control channels (DPCCH) 312. Dedicated physical data channels 310
are used to transmit data 306 which is generated on the second
layer and above of OSI (Open Systems Interconnection), i.e. the
dedicated control channels and dedicated traffic channels.
Dedicated physical control channels 312 transmit control
information generated on the first layer of OSI. Control
information comprises: pilot bits 300 used in channel estimation,
transmit power control commands (TPC) 302, and optionally a
transport format indicator (TFI) 304. The transport format
indicator 304 indicates to the receiver the transmission rate used
for each dedicated physical data channel of the uplink at a given
time.
[0046] As shown in FIG. 3, the dedicated physical data channels 310
and the dedicated physical control channels 312 on the downlink are
time-multiplexed to the same slot 330C. However, on the uplink, the
channels in question are transmitted parallel so that they are
IQ/code-multiplexed (I=in-phase, Q=quadrature) to each frame 340C
and transmitted using dual-channel QPSK modulation (dual-channel
quadrature phase-shift keying modulation). When additional
dedicated physical data channels 310 need to be transmitted, they
are code-multiplexed to the I or Q branch of the first channel
pair.
[0047] The method of the invention for transmitting data from a
radio network subsystem RNS to user equipment UE can be illustrated
by the flow chart in FIG. 6. The execution of the method for a
single radio frame is started from block 600.
[0048] Next, in block 602, the spreading code used in spreading the
traffic channel is changed according to the required data
transmission rate. The spreading code selected for the traffic
channel is marked X.
[0049] Next, in block 604, each control channel frame indicates the
spreading code with which the corresponding traffic channel frame
is spread when transmitted. In other words, the identification data
of the spreading code X are entered in the control channel
frame.
[0050] In block 606, the radio network subsystem RNS transmits a
dedicated control channel frame to the user equipment UE. During
transmission, the operation in block 608, for instance, is
performed, in which the radio network subsystem RNS spreads each
channel with a spreading code. The spreading code selected here for
the control channel is marked Y.
[0051] In block 610, the radio network subsystem RNS transmits a
dedicated traffic channel of variable data transmission rate to the
user equipment UE. The variable data transmission rate is achieved
by changing the spreading code; as described in connection with
FIG. 4A, each spreading factor has a different data transmission
rate. During transmission, the operation in block 612, for
instance, is performed, in which the radio network subsystem RNS
spreads each channel with a spreading code, i.e. the traffic
channel is spread with the selected spreading code X.
[0052] Thus, in the invention, the transmitter transmits the
traffic channel frame spread with the spreading code X. The
transmitter transmits the control channel frame associated with the
traffic channel in question spread with the spreading code Y. The
control channel frame indicates that the corresponding traffic
channel frame has been spread with the spreading code X. This way,
the receiver can remove the spreading of the traffic channel frame
in question. Thus, the receiver need not know in advance what the
data transmission capacity/spreading code of the traffic channel
frame in question is.
[0053] The association of the control channel frame and the traffic
channel frame with each other must be indicated in some way. The
easiest way to do this is to combine the association with timing,
for instance so that the frames are transmitted at approximately
the same time. The control channel frames and traffic channel
frames associated with each other are preferably transmitted on the
same frequency, spread with different spreading codes, and
substantially simultaneously, i.e. separated by one frame length at
most.
[0054] In a preferred embodiment of the invention, the
identification data of the spreading code X used to spread the
traffic channel is entered into the transport format indicator in
the control channel frame. This provides the advantage that new
fields need not be defined for this function.
[0055] A part of the code tree shown in FIG. 4A must be reserved
for the use of the control channels. The spreading factor can also
be increased to 1024, for instance, by extending the code tree to
lower levels, whereby an adequate data transmission rate of eight
kilobits per seconds could be achieved.
[0056] FIG. 4B shows one preferred embodiment in which the code
tree is divided into sub-code trees, and one branch in a level is a
tree access point to the sub-code tree in question, and the
branches below the tree access point belong to the sub-code tree in
question. In FIG. 4B, one of the eight spreading codes of the
spreading factor SF=8 has been chosen as the tree access point TAP
of the sub-code tree. The size of the sub-code tree has also been
restricted so that the spreading codes of the spreading factor
SF=256 are not meant to be Used, since their data transmission rate
32 kbit/s is relatively low. Data transmission rates of 64 kbit/s,
128 kbit/s, 256 kbit/s, 512 kbit/s, and 1024 kbit/s can thus be
achieved with the selected sub-code tree. The presented sub-code
tree is only one example of several possible sub-code trees, the
specification of sub-code trees in the system depends on the
properties required in the system, such as traffic volume. The data
transmission rate of the traffic channel is changed by changing the
length of its spreading code, i.e. by moving between the levels of
the sub-code tree.
[0057] In one preferred embodiment, each spreading code of a
sub-code tree is numbered in an agreed manner, and the number in
question is entered into the transport format indicator. In the
example of FIG. 4B, the spreading codes are numbered from 1 to 32.
The numbers 1 to 31 each identify one spreading code and the number
32 indicates that no spreading code is used in the frame in
question, i.e. the capacity of the frame in question can be freely
utilized by another link with certain restrictions.
[0058] The restrictions are due to the fact that the spreading
codes used at each instant must be mutually orthogonal. A spreading
code can be used only if no other code on the path to the tree
access point TAP of the sub-tree is being used and none of the
spreading codes on the paths on the levels below the spreading code
in question are being used. For instance, if the spreading code 4
is being used, the spreading codes 8, 9, 16, 17, 18, and 19 on the
levels below it cannot be used. Instead, the spreading codes 5, 6,
7, and all spreading codes on levels below them, i.e. 10 to 15 and
20 to 31, can be used. If spreading code 1 is being used, none of
the spreading codes 2 to 31 of the subcode tree can be used.
[0059] The numbering of the spreading codes in a sub-code tree can
also be implemented in such a way that one number corresponds to
two or more parallel spreading codes. This way, using multi-code
reception in the receiver, the use of too small spreading ratios
can be avoided, for instance in unfavorable propagation conditions
of radio waves or due to the restrictions of the receiver in the
user equipment. When higher transmission rates are needed, the
numbering of the subcode tree can be begun from the lower spreading
code levels.
[0060] A typical situation could be that the system has several
users of a 64 kbit/s link, which means that the spreading codes 16
to 27, for instance, are being used. In such a case, the spreading
codes 1 to 6 and 8 to 13 can, of course, not be used. Instead, the
spreading codes 7, 14, 15, and 28 to 31 are available for use. The
system can thus, in addition to the above users, have one user, for
instance, who uses the spreading code 7 and, with it, the
transmission rate 256 kbits.
[0061] According to the rules described above, it is thus possible
to select from the same sub-code tree a spreading code for one or
more units of user equipment. The radio network subsystem allocates
the spreading codes. When the sub-code tree becomes congested, the
user equipment can be transferred to another sub-code tree. The
described method is good as regards data security, too, because it
does not matter, if a receiver, to which a frame does not belong,
were to detect the frame by accident, since the protection used on
the higher levels, for instance ciphering in a GSM system, makes
sure that the data within the frame cannot be read. Alternatively,
the matter can be taken care of by scrambling, as is done in the
first layer of the CDMA2000 system.
[0062] Processing channels in the radio interface Uu is performed
with a protocol architecture comprising a physical layer, data link
layer and network layer of the ISO (International Standardisation
Organisation) OSI (Open Systems Interconnection) model. The
protocol stacks are located both in the radio network subsystem RNS
and in the user equipment UE. The data link layer is divided into
two sub-layers: the MAC (Medium Access Control) sublayer and the
LAC (Link Access Control) sub-layer. Typically, the services
provided by the physical layer for the higher layers determine the
transmission channel and its properties, such as the spreading code
used. The MAC sub-layer's task is to control access to the physical
layer; the selection of the transport format indicator, for
instance, is performed in this sub-layer. The signalling of the
physical layer, data link layer and network layer is transmitted in
the control channel.
[0063] The user equipment does not send an acknowledgement to the
radio network subsystem after receiving the transport format
indicator, but this signalling is performed as signalling of the
physical layer without acknowledgement. In poor radio conditions,
this may result in that the user equipment cannot read the
spreading code with which the corresponding traffic channel frame
was transmitted. In such a case, the protocols of the higher layers
manage the re-transmission of the packet using the ARQ (Automatic
Repeat Request) method.
[0064] The radio network subsystem signals the tree access point of
the sub-code tree to the user equipment, and the user equipment
sends an acknowledgement to the radio network subsystem. This
signalling is preferably performed between the MAC sub-layers,
because the tree access point of the sub-code tree is not changed
very often, and it is necessary to make sure that, in case of
failure in signalling, a relatively difficult re-signalling need
not be performed.
[0065] In one preferred embodiment, the radio network subsystem
transmits the traffic channel frames in a synchronized manner to
the units of user equipment which belong to the same sub-code tree.
This provides the advantage that the allocation of the sub-code
tree between various links is easier, since the reservations of
different codes are freed and the reservations of new codes are
made always at certain instants, generally at one-frame
intervals.
[0066] In the invention, the required data transmission rate of the
control channel is preferably as low as possible, because the
required signalling does not require a lot of data transmission
capacity; one possible data transmission rate is eight kilobits per
second.
[0067] In one preferred embodiment, the control channel contains
pilot bits for channel estimation. This way, pilot bits are not
necessarily needed in the traffic channel, i.e. the traffic channel
contains only useful load of the user. Channel estimation can be
done by means of the control channel pilot bits only, because the
signal passes through the same channel, only the spreading code is
different.
[0068] In one preferred embodiment, the radio network subsystem
transmits the control channel frames of different user equipment as
non-simultaneously as possible. This procedure facilitates channel
estimation, because the pilot bits overlap as little as possible
during different connections.
[0069] In one preferred embodiment, other than control data, for
instance data or speech, is transmitted in the free capacity of the
control channel frame. The data can even be circuit-switched link
packets, because the control channel capacity is reserved during
the entire link, during which the data transmission rate of the
control channel is fixed.
[0070] The same spreading code is typically always used in
spreading the control channel. Only during handover may the control
channel spreading code need to be changed. The control channel
spreading code in question is selected as described above either
from the part of the code tree reserved for the use of the control
channels or from a code space outside the code tree. However, the
spreading codes must be mutually orthogonal, which is why, for
clarity's sake, all system codes are usually formed by means of a
code tree.
[0071] The invention is preferably implemented by means of
software. The processing required in the radio network subsystem
necessitates changes to the protocol processing software and to the
control of transmitter operation. Correspondingly, in the user
equipment, it is necessary to make changes to the protocol
processing software and to the control of receiver operation.
[0072] Even though the invention has been explained in the above
with reference to examples in accordance with the accompanying
drawings, it is obvious that the invention is not restricted to
them but can be modified in many ways within the scope of the
inventive idea disclosed in the attached claims.
* * * * *