U.S. patent application number 11/704920 was filed with the patent office on 2007-06-21 for communication system.
This patent application is currently assigned to Nokia Corporation. Invention is credited to Pekka T. Kohonen, David Soldani.
Application Number | 20070142070 11/704920 |
Document ID | / |
Family ID | 32467971 |
Filed Date | 2007-06-21 |
United States Patent
Application |
20070142070 |
Kind Code |
A1 |
Soldani; David ; et
al. |
June 21, 2007 |
Communication system
Abstract
Common channel resources can be controlled in the uplink of a
communication system. The control of the common channel resources
can be dependent upon the quality requirements associated with a
radio access for use on the up-link common channel relative to a
predetermined quality threshold.
Inventors: |
Soldani; David; (Espoo,
FI) ; Kohonen; Pekka T.; (Espoo, FI) |
Correspondence
Address: |
SQUIRE, SANDERS & DEMPSEY L.L.P.
14TH FLOOR
8000 TOWERS CRESCENT
TYSONS CORNER
VA
22182
US
|
Assignee: |
Nokia Corporation
|
Family ID: |
32467971 |
Appl. No.: |
11/704920 |
Filed: |
February 12, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10310129 |
Dec 5, 2002 |
7197314 |
|
|
11704920 |
Feb 12, 2007 |
|
|
|
Current U.S.
Class: |
455/515 ;
455/509 |
Current CPC
Class: |
H04W 52/50 20130101;
H04W 52/26 20130101; H04L 1/18 20130101; H04L 1/203 20130101 |
Class at
Publication: |
455/515 ;
455/509 |
International
Class: |
H04Q 7/20 20060101
H04Q007/20; H04B 7/00 20060101 H04B007/00 |
Claims
1. A method, comprising: controlling common channel resources in
the uplink of a communication system; and making control of the
common channel resources dependent upon quality requirements
associated with a radio access for use on an up-link common channel
relative to a predetermined quality threshold.
2. The method of claim 1, wherein the controlling the common
channel resources comprises selectively allocating the common
channel to the radio access.
3. The method of claim 2, wherein the selectively allocating the
common channel to the radio access is performed in dependence upon
a quality threshold.
4. The method of claim 3, further comprising: configuring the
quality threshold to be uplink measured quality information.
5. The method of claim 3, further comprising: allocating a
dedicated channel to the radio access when the common channel is
not allocated to the radio access.
6. The method of claim 5, further comprising: determining whether
to allocate the dedicated channel based upon the quality
characteristics required for the radio access.
7. A method, comprising: controlling common channel resources in
the uplink of a mobile communication system; and making control of
the common channel resources dependent upon quality requirements of
a radio access for use on an up-link common channel being within a
predetermined threshold.
8. An element, comprising: a controller configured to control
common channel resources in an uplink of a communication system,
wherein the controller is configured to control the common channel
resources in dependence upon quality requirements associated with a
radio access for use on an up-link common channel relative to a
predetermined quality threshold.
9. The element of claim 8, wherein the controller is configured to
selectively allocate the common channel to the radio access.
10. The element of claim 9, wherein the controller is configured to
selectively allocate the radio access in dependence upon a quality
threshold.
11. The element of claim 10, wherein the quality threshold is
uplink measured quality information.
12. The element of claim 10, wherein a dedicated channel is
allocated to the radio access when the common channel is not
allocated to the radio access.
13. The element of claim 12, wherein the controller is configured
to determine whether to allocate a dedicate channel to the radio
access based upon the quality characteristics required for the
radio access.
14. The element of claim 10, wherein the common channel is a random
access channel.
15. The element of claim 10, wherein the common channel is a common
packet channel.
16. A radio network controller, comprising: a control unit
configured to control common channel resources in an uplink of a
mobile communication system, wherein the control unit is configured
to control the common channel resources in dependence upon quality
requirements of a radio access for use on an up-link common channel
being within a predetermined threshold.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/310,129, filed Dec. 5, 2002. The entire content of the prior
application is hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to establishing uplink
connections in a radio telecommunications network.
BACKGROUND TO THE INVENTION
[0003] UTRA-FDD is an example of a third generation mobile
communication system, in which a communication network
infrastructure establishes communication with various mobile
entities in a radio access network.
[0004] In the radio access network, communication takes place from
the network to user equipment (UE) in the downlink, and from the UE
to the network in the up-link.
[0005] For the purpose of communicating, there are provided two
types of transport channels--dedicated channels and common
channels. A common channel is a resource divided between all or a
group of users in a cell, whereas a dedicated channel is by
definition reserved for a single user.
[0006] In a typical UTRA-FDD system, there are two common channels
for the uplink communication: the random access channel (RACH)
which is mapped to the physical random access channel; and the
common packet channel (CPCH), which is mapped to the physical
common packet channel.
[0007] In current techniques radio access bearers are allocated to
the common channels in the UTRA-FDD system on the basis of
resources determination, such as network capacity.
[0008] It is an object of the present invention to provide an
improved technique for optimizing the use of common channels in the
uplink of a communication system.
SUMMARY OF THE INVENTION
[0009] According to a first aspect of the present invention there
is provided a method of controlling common channel resources in the
uplink of a communication system, wherein the control of the common
channel resources is dependent upon the quality requirements
associated with a radio access for use on the up-link common
channel relative to a predetermined quality threshold.
[0010] The control of common channel resources may comprise
selectively allocating the common channel to the radio access. The
common channel may be selectively allocated to the radio access in
dependence upon a quality threshold. The quality threshold may be
uplink measured quality information. A dedicated channel may be
allocated to the radio access if the common channel is not
allocated to the radio access. Said determination may be based upon
the quality characteristics required for the radio access.
[0011] The control of common channel resources may comprise
dynamically controlling the power difference between an
initialization transmission in the common channel and a message in
the common channel. The power difference may be initially set to a
predetermined value.
[0012] The power difference may be set to a value determined on the
basis of the power difference required for at least one previous
radio access having the same quality profile as the current radio
access.
[0013] The power difference may be increased if the up-link
measured quality is below a threshold value. The power difference
may be decreased if the up-link measured quality is above a
threshold value.
[0014] The common channel may be a random access channel. The
common channel may be a common packet channel.
[0015] According to a further aspect of the present invention there
is provided a method of controlling common channel resources in the
uplink of a mobile communication system, wherein the control of the
common channel resources is dependent upon the quality requirements
of a radio access for use on the up-link common channel being
within a predetermined threshold.
[0016] In a further aspect, the present invention provides an
element for controlling common channel resources in the uplink of a
communication system, comprising means for controlling the common
channel resources in dependence upon the quality requirements
associated with a radio access for use on the up-link common
channel relative to a predetermined quality threshold.
[0017] The control means may be adapted to selectively allocate the
common channel to the radio access. The control means may be
adapted to selectively allocate the radio access in dependence upon
a quality threshold. The quality threshold may be uplink measured
quality information.
[0018] A dedicated channel may be allocated to the radio access if
the common channel is not allocated to the radio access. Said
determination is based upon the quality characteristics required
for the radio access.
[0019] The control means may comprise means for dynamically
controlling the power difference between an initialization
transmission in the common channel and a message in the common
channel. The power difference may be initially set to a
predetermined value.
[0020] The power difference may be set to a value determined on the
basis of the power difference required for at least one previous
radio access having the same quality profile as the current radio
access. The power difference may be increased if the up-link
measured quality is below a threshold value. The power difference
may be decreased if the up-link measured quality is above a
threshold value.
[0021] The common channel may be a random access channel. The
common channel may be a common packet channel.
[0022] The present invention still further discloses a radio
network controller for controlling common channel resources in the
uplink of a mobile communication system, comprising control means
for controlling the common channel resources in dependence upon the
quality requirements of a radio access for use on the up-link
common channel being within a predetermined threshold.
BRIEF DESCRIPTION OF THE FIGURES
[0023] The invention is now described by way of example with
reference to the accompanying drawings, in which:
[0024] FIG. 1 illustrates an example of a UMTS radio access
network;
[0025] FIG. 2 illustrates the structure of a random access message
part radio frame;
[0026] FIG. 3 illustrates the physical random access channel power
ramping and message transmission; and
[0027] FIGS. 4(a) and 4(b) illustrate a method incorporating
embodiments of the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0028] Referring to FIG. 1, there is illustrated schematically an
example of a UMTS (Universal Mobile Telecommunication System) with
respect to which embodiments of the present invention may be
utilized.
[0029] In FIG. 1, the UMTS radio access network (RAN) 100 includes
a plurality of Node B's, such as node B's 106,108,110. Each Node B
is connected to a radio network controller (RNC). Node B's 106 and
108 are connected to an RNC 102, and Node B 110 is connected to RNC
104. Various mobile terminals are in the radio access network, as
represented by user equipment (UE) 112 connected to Node B 106.
Each RNC is connected to a core network (CN) 114. The core network
may further be connected to external networks, such as an ISDN
network 116 or a Packet Data network 118.
[0030] The present invention is described herein with reference to
the example of a UTRA-FDD communication system. The invention is
not limited, however, to such a system. The invention is more
broadly applicable to the allocation of channels in the up-link of
a communication system, which will become apparent from the
following description.
[0031] In UTRA-FDD two common transport channels have been
specified: (i) the Random Access Channel (RACH) and (ii) the Common
Packet Channel (CPCH).
[0032] The RACH is mapped onto the Physical Random Access Channel
(PRACH). It carries uplink common control information, i.e. Common
Control Channel (CCCH), such as requests to set up radio resource
control (RRC) connections. It may further carry dedicated control
information, i.e. the Dedicated Control Channel (DCCH), between the
UE and the network, established through the RRC connection setup
procedure. The RACH is further used for sending dedicated user
information, i.e. the Dedicated Traffic Channel (DTCH), such as
small amounts of uplink packet data.
[0033] The uplink CPCH carries dedicated packet-based user data
(DTCH) or dedicated control information (DCCH). It supports uplink
inner loop Power Control (PC), with the aid of a downlink Dedicated
Physical Control Channel (DPCCH). Its transmission may span several
radio frames and it is mapped onto the Physical Common Packet
Channel (PCPCH).
[0034] Embodiments of the present invention are described
hereinbelow with particular reference to the random access channel.
However this is for illustrative purposes only, and the present
invention is not limited in its applicability to the RACH.
[0035] The slot structure of the PRACH message is illustrated in
FIG. 2. It consists of two parts: a data part 200 where the RACH
transport channel is mapped, and a control part 202 where the Layer
1 control information is carried. The data 200 and control 202
parts are transmitted in parallel. The spreading factors of the
data part are 256, 128, 64, and 32. The control part consists of a
set of pilot bits 204 and a set of transport format combination
indicator (TFCI) bits 206, and has a spreading factor of 256. The
TFCI (Transport Format Combination Indicator) field indicates the
TF (Transport Format) of the RACH mapped to the data part of the
radio frame and it is repeated in the second radio frame if the
message part lasts for 20 ms. The TF defines the bit rate, channel
coding, TTI etc. These concepts are described in 3GPP TS
25.302.
[0036] Each cell of the radio access network is configured by radio
network planning (RNP). A cell is associated with a Node B. A
"cell" is defined by a cell identification (C-ID), Configuration
Generation ID, Timing delay (T_Cell), UTRA Absolute Radio Frequency
Channel Number (UARFCN), Maximum transmission power, Closed Loop
Timing Adjustment Mode and Primary scrambling code. For each cell,
the RNP sets: [0037] (i) the preamble scrambling code; [0038] (ii)
the message length in time (either 10 or 20 ms); [0039] (iii) the
AICH (acquisition indicator channel) transmission timing parameter
(0 or 1, for setting the preamble-to-acquisition indicator
distance); [0040] (iv) the set of available signatures; and [0041]
(v) the set of available RACH sub-channels for each Access Service
Class (ASC).
[0042] Other essential parameters that need to be set by the RNP
are: [0043] (vi) the power-ramping factor (Power ramp step); [0044]
(vii) the maximum number of preamble retransmission (Preamble
Retrans Max); [0045] (viii) the power offset between the power of
the last transmitted preamble and the control part of the PRACH
message (Power offset Pp-m=P.sub.message-control-P.sub.preamble);
and [0046] (ix) the set of transport format (TF) and transport
format combination (TFC) parameters (this includes the gain factors
between the data and control part of the random-access message for
each TFC). Certain ones of these parameters may be automatically
produced by the radio network controller (RNC).
[0047] The user equipment (UE) receives these parameters from the
system information broadcast on the broadcast control channel
(BCCH). The BCCH may be updated by the RNC before any physical
random access procedure is initiated.
[0048] In summary, the physical random-access procedure is
illustrated in FIG. 3. The UE derives the available uplink access
slots (in the next full access slot set) from the set of available
RACH sub-channels within the given ASC. It randomly selects one of
the available access slots and a signature from the set of
available signatures within the given ASC. The random function is
such that each of the possible selections is chosen with equal
probability. In FIG. 3, the time line 304 represents uplink
transmission and the time line 306 represents downlink
transmission.
[0049] The UE transmits the first preamble 302 using the selected
uplink access slot, signature, and preamble transmission power,
calculated as: Preamble_Initial_Power=Primary CPICH DL Tx
power-CPICH_RSCP+UL interference+UL_required_CI The Primary CPICH
DL Tx power and the UL required Carrier to Interference ratio (a
constant value in 3GPP) are set by the RNP. The UL interference
(receiver total wideband power in 3GPP) is measured at the base
station. All are broadcast on the BCCH. The same procedure is
followed by the UE when setting up the power level of the first
PCPCH access preamble. The CPICH RSCP is the Received Signal Code
Power, i.e. the received power on one code measured on the Primary
CPICH. This is a quantity that the UE measures, in accordance with
known techniques.
[0050] If no positive or negative Acquisition Indicator
(AI.noteq.+1 or -1) corresponding to the selected signature is
detected in the downlink access slot 308 corresponding to the
selected uplink access slot, then the terminal selects the next
available access slot in the set of available RACH sub-channels
within the given ASC, randomly selects a new signature from the set
of available signatures within the given ASC, and increases the
preamble power by .DELTA.P.sub.0, which represents the power ramp
in dB. The second preamble transmission is represented by block 310
in FIG. 3.
[0051] Responsive to the second preamble 310 in the uplink, the UE
receives a positive acquisition indicator 312. Thereafter, the UE
transmits the random access message 314 three or four uplink access
slots after the uplink access slot of the last transmitted
preamble, depending on the AICH transmission timing parameter. The
transmission power of the control part of the random access message
is Pp-m dB higher than the power of the last transmitted preamble.
The transmission power of the data part of the random access
message is set according to a corresponding gain factor, such gain
factor being set between the control and data parts.
[0052] The message part of the RACH is transmitted at a higher
power level than the preamble part, due to their differing
processing gains.
[0053] For the CPCH, there is a power offset between the transmit
power of the collision detect preamble and the initial transmit
power of the CPCH power control preamble.
[0054] If the number of retransmissions exceeds the maximum number
of retransmissions available (the Preamble Retrans Max value), or
if a negative AI corresponding to the selected signature is
detected, meaning that the up-link transmission cannot be received
for some reason, then the UE exits the physical random access
procedure.
[0055] In accordance with the present invention, and as discussed
in further detail hereinbelow, the use of the random access
channel, and the power control of the random access channel, is
further controlled in dependence on the quality of service (QoS)
requirements of the different UMTS bearer services that may be
carried by the random access channel at the radio interface. As
stated hereinabove, embodiments of the present invention are
described herein with reference to the RACH channel, but the
invention is not limited in its applicability to the RACH
channel.
[0056] For different communications, the layer 2 block error rate
(BLER) target is derived from the UMTS QoS bearer profile. The
retransmission parameters, i.e. the number of RLC retransmissions
allowed, are also derived from the UMTS bearer QoS profile. However
none of the above-stated physical layer management parameters, used
for controlling the power of the physical random access channel,
have been defined on the basis of the distinct quality requirements
of the service. The quality requirements may be set on the
different logical channels mapped on the RACH.
[0057] As a result, the usage of these common resources may be
ineffective. For example, when the RACH is employed in the uplink
transmission, the quality of the communication may be set too low
or too high, resulting in excessive power increases in most
situations.
[0058] In accordance with the present invention, it is proposed to
adapt the usage and power control of the random access channel in
dependence on the quality requirements of the service. As described
hereinafter, this is preferably achieved by the implementation of
one of three described embodiments.
[0059] However, alternative arrangements to the described
embodiments may achieve the same result.
[0060] Referring to FIGS. 4(a) and 4(b), an example implementation
of uplink bearer service transmission incorporating three
embodiments of the present invention is described. Although the
embodiments are described in combination, they may in fact operate
individually.
[0061] In accordance with the first embodiment of the present
invention, before initiation of the RACH transmission begins, the
RNC derives the BLER (block error rate) target for the bearer
services. In a step 404 of FIG. 4(a), the RNC assesses the BLER
target for the bearer services. The BLER defines the ratio of the
incorrectly received transport blocks to the total number of
received transport blocks. The BLER target--which preferably also
defines the value of Pp-m of the parameters (i)-(ix)--may be
directly set by RNP or indirectly calculated by the RNC from the
UMTS QoS bearer profile, provided by the core network when the
radio access bearer is set up or reconfigured. The RNC keeps a
track of the measured BLER (i.e. Pp-m), and whether the measured
BLER meets the BLER target, and whether the BLER target meets the
RACH requirements.
[0062] In accordance with this first embodiment of the invention,
in a step 406 of FIG. 4(a) the uplink transport channel is selected
based on the BLER target. In step 406, the RNC determines whether
the BLER target is within the predetermined BLER targets for the
RACH. For example, this may be determined by the maximum number of
RLC retransmissions allowed in the RACH. The definition of a target
BLER will be understood by one skilled in the art. The significance
of the use of the BLER in the preferred embodiments of the
invention, is that the higher the BLER target the less transmission
power is needed.
[0063] If the BLER target is not within the RACH requirements, then
in a step 407 the bearer services are allocated to another channel.
If the BLER target is within the RACH requirements, then the RACH
channel control moves onto a step 408.
[0064] Thus, the UE may be allocated a dedicated channel when the
target BLER and RLC re-transmission setting can be defined more
specifically than on the RACH (or CPCH). There are thus two
parameters which are significant, in the embodiments of the
invention, for determining use of the RACH. These are the BLER
target and the number of RLC retransmissions . The higher the
numbers of RLC retransmission, and the lower the BLER target, the
greater the interference and the RACH blocking. If a radio access
bearer has a very strict QoS requirement then it can be allocated a
dedicated channel immediately.
[0065] In accordance with the second embodiment of the present
invention, further before initiation of the RACH transmission
begins, the RNC assesses the uplink measured quality on the RACH.
In a step 408, the RNC determines the uplink measured quality
information for the RACH, measured at the network side.
[0066] In step 410 of FIG. 4(a), the RNC then determines whether
the quality of the RACH in the up-link is within a threshold value.
The threshold value may be predetermined. If it is determined that
the quality is outside the threshold, then in a step 411 of FIG.
4(a) the bearer services are allocated to a different channel. If
it is determined that the quality is within the threshold value,
then the process proceeds to step 412.
[0067] The allocation of the RACH channel for bearer services is
represented by step 419 in FIG. 4(a).
[0068] Thereafter, as illustrated by step 402 of FIG. 4(b), in
accordance with standard techniques, the UE receives from the
network the RNP parameters for the bearer services intended to be
transmitted in the uplink random access channel. These parameters
include the parameters stated in (i) to (ix) above. In the prior
art, these parameters are used in order to initiates a RACH
transmission for the bearer services.
[0069] Step 412 of FIG. 4(b) represents the initialisation of the
RACH in the UE in accordance with conventional techniques.
Referring to FIG. 3, the UE determines the power level for the
first preamble, based on the parameters received in step 402 and in
accordance with the formula stated hereinabove, and transmits the
first preamble in the RACH as represented by block 302 in FIG.
3.
[0070] In a step 414 of FIG. 4(b), it is determined whether the
first pre-amble is acknowledged. If it is not acknowledged, then in
a step 416 of FIG. 4(b) it is determined whether the maximum number
of retransmissions permissible has been exceeded. This parameter is
provided by the RNP. If the maximum number of retransmissions is
exceeded, then the routine exits. If the maximum number of
retransmissions is not exceeded, then the process returns to step
412 for transmission of a second preamble.
[0071] For the second preamble, and as discussed hereinabove, the
power level of the preamble is increased by .DELTA.Po. The
transmission of the second preamble is represented by block 310 in
FIG. 3.
[0072] Again, in step 414, it is determined whether an
acknowledgement is received. In practice, two types of
acknowledgement may be received: a negative acknowledgement or a
positive acknowledgement. A negative acknowledgement indicates that
the message cannot be transmitted, as is known in the art. In the
present example, it is assumed that the positive acknowledgement
312 of FIG. 3 is received in the downlink. As such, the process
moves on to step 418 of FIG. (b).
[0073] In step 418 the message (318 in FIG. 3) is transmitted using
the increased power level, over the last preamble, Pp-m.
[0074] In accordance with the third preferred embodiment of the
present invention, the RNC monitors the uplink measured quality
information in a step 420 of FIG. 4(a) after RACH transmissions
have taken place. In this embodiment, for each bearer service there
is preferably set a threshold level for the uplink quality, i.e. an
uplink quality target. The RNC then compares, in a step 422 of FIG.
4(b), the uplink measured quality to the threshold level for that
bearer service. If the uplink measured quality deteriates or
improves, then a corresponding change in the value Pp-m is made,
and communicated to the UE, before the next physical random access
procedure for that bearer service is initiated.
[0075] Thus, in dependence on the comparison of the quality with
the threshold level, the process moves on to one of steps 424, 426
or 428 of FIG. 4(b). If the quality level is within the current
threshold value, then in a step 426 the power level is maintained.
If the quality deteriates below an acceptable threshold level, then
in a step 428 the power level is increased. If the quality improves
above an acceptable threshold level, then in a step 424 the power
level is decreased. The RNC communicates the adjusted power level
to the UE, for use in uplink transmission.
[0076] Thus, if it appears that the measured BLER is below the BLER
target then too high power is being used in the PRACH, and the
value of Pp-m is decreased by a step. If it appears that the BLER
is over the BLER target then too low power is being used in the
PRACH, and the value of Pp-m is increased by a step. The new Pp-m
value is included in the system information that is broadcast in
the cell. In further refined embodiments, both the threshold
determination in step 410 and the threshold determination in step
422 may be based on the BLER measurements. The uplink quality, and
in particular the BLER, can be can be measured for each bearer
service carried by the RACH considering its in-band identification
and the information reported to the RNC by the Node B, i.e. NBAP C:
Averaged number of successfully decoded RACH messages per radio
frame during the reporting period per PRACH.
[0077] The invention thus allows for, in a described embodiment,
the efficient usage of the random access channel for carrying UMTS
bearer services with different quality requirements (i.e. different
QoS profiles). The invention avoids any unnecessary uplink power
rise due to the very different quality requirements of the bearer
services carried by the RACH at the radio interface.
[0078] In particular, the invention allows the RACH to be used for
bearer services with QoS attributes for which a particular BLER
target with a particular number of RLC retransmissions is
sufficient. Other bearer services with more strict QoS requirements
are allocated to alternative resources, e.g. dedicated
resources.
[0079] The present invention enables the power levels for different
radio access bearers in the RACH to be adjusted. Without the
present invention, the power level for all radio access bearers in
the RACH is the same, and the number of RLC retransmissions needed
will vary according to the QOS parameters.
[0080] The invention takes into account the fact that the PRACH
parameters for all radio access bearers are the same, but different
RAB's may have different quality requirements.
[0081] Based on statistics, the RNC learns what Pp-m can be used
when a radio bearer with certain QoS profile (BLER target) is set
up. This statistical value improves the convergence of this outer
loop PC.
[0082] The invention has particular advantages for use in Third
Generation (3G) UMTS (Universal Mobile Telecommunication System)
Terrestrial Radio Access (UTRA-FDD) mobile telecommunications
networks, and is therefore described herein with reference to such
an implementation. However, it will be appreciated by those skilled
in the art that the invention may be applied to other protocols and
standards.
* * * * *