U.S. patent application number 10/371199 was filed with the patent office on 2003-11-13 for radio resource management for a high speed shared channel.
Invention is credited to Amirijoo, Sharokh, Beming, Per, Englund, Eva, Karlsson, Patrik, Parkvall, Stefan, van Lieshout, Gert-Jan, Wiberg, Niclas.
Application Number | 20030210660 10/371199 |
Document ID | / |
Family ID | 26655702 |
Filed Date | 2003-11-13 |
United States Patent
Application |
20030210660 |
Kind Code |
A1 |
Wiberg, Niclas ; et
al. |
November 13, 2003 |
Radio resource management for a high speed shared channel
Abstract
Radio resources like spreading codes and transmission power are
optimally allocated to various different types of radio channels
supported in the cell including a specialized channel like a
high-speed shared channel. One or more measurements made at the
base station are provided to the radio resource manager. Such
measurements include other-channel power, high speed shared channel
code usage, high speed shared channel transport format usage,
average active load on the high speed shared channel, empty buffer,
excess power, and similar parameters that relate to a high speed
shared channel. One or more of these reported measurements may then
be used to access, allocate, and/or regulate resources associated
with the base station's cell.
Inventors: |
Wiberg, Niclas; (Linkoping,
SE) ; Englund, Eva; (Linkoping, SE) ;
Amirijoo, Sharokh; (Sollentuna, SE) ; van Lieshout,
Gert-Jan; (Apeldoorn, NL) ; Beming, Per;
(Stockholm, SE) ; Parkvall, Stefan; (Stockholm,
SE) ; Karlsson, Patrik; (Alta, SE) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
1100 N GLEBE ROAD
8TH FLOOR
ARLINGTON
VA
22201-4714
US
|
Family ID: |
26655702 |
Appl. No.: |
10/371199 |
Filed: |
February 24, 2003 |
Current U.S.
Class: |
370/320 |
Current CPC
Class: |
H04J 13/16 20130101;
H04W 4/24 20130101; Y02D 70/1244 20180101; H04W 52/08 20130101;
Y02D 30/70 20200801; H04W 24/00 20130101; H04W 52/281 20130101;
H04W 52/0206 20130101; H04B 17/382 20150115; H04W 72/085 20130101;
H04W 52/286 20130101; H04W 52/367 20130101; H04W 28/18 20130101;
H04W 72/08 20130101; H04W 52/228 20130101; H04W 52/343 20130101;
H04W 24/08 20130101; H04W 52/346 20130101; H04W 52/143 20130101;
H04W 72/0473 20130101; H04W 52/246 20130101; Y02D 70/1242 20180101;
H04W 52/16 20130101 |
Class at
Publication: |
370/320 |
International
Class: |
H04B 007/216 |
Foreign Application Data
Date |
Code |
Application Number |
May 13, 2002 |
SE |
0201467-8 |
Sep 23, 2002 |
SE |
0202845-4 |
Claims
What is claimed is:
1. A method for a mobile communications network supporting mobile
radio communication using plural radio channels associated with a
radio base station including first radio channels and a high speed
shared radio channel, comprising: the radio base station measuring
one or more parameters that affect management of the high speed
shared radio channel; the radio base station reporting one or more
of the measured parameters to a radio resource controller; and the
radio resource controller using the measured parameters to
efficiently use radio resources associated with the high speed
shared radio channel.
2. The method in claim 1, wherein the base station measures an
other transmission power for signals transmitted over the first
radio channels that do not include a measurement of a transmission
power for signals transmitted over the high speed shared radio
channel, and wherein the radio resource controller uses the other
transmission power measurement to regulate a power level associated
with one of the first radio channels or the high speed shared radio
channel.
3. The method in claim 2, further comprising: the radio resource
controller allocating a power to the high speed shared radio
channel based on the measured transmission power so that when the
allocated power is combined with the other power measured for the
first radio channels, the combined power does not exceed a
predetermined maximum power associated with the base station.
4. The method in claim 1, wherein the communications are code
division multiple access (CDMA) based, wherein the base station
measures a CDMA code usage for the high speed shared radio channel
during a predetermined time period, and wherein the radio resource
controller uses the CDMA code usage to regulate CDMA code
allocation to one or both of the first radio channels and the high
speed shared radio channel.
5. The method in claim 4, wherein the predetermined time period
includes plural transmission time intervals (TTIs), the method
further comprising: measuring a number of TTIs a CDMA code is used
for the high speed shared radio channel during the predetermined
time period or a number of TTIs a set of the CDMA codes is used for
the high speed shared radio channel during the predetermined time
period.
6. The method in claim 5, wherein the CDMA code usage is reported
by the base station as a histogram.
7. The method in claim 1, wherein the communications are code
division multiple access (CDMA) based, wherein the base station
measures a transport format usage for the high speed shared radio
channel during a predetermined time period, and wherein the radio
resource controller uses the transport format usage to regulate
CDMA code allocation to one or both of the first radio channels and
the high speed shared radio channel.
8. The method in claim 1, wherein the base station measures a
number of mobile radio users currently having data to transmit over
the high speed shared channel in a base station buffer at a data
transmission scheduling time for the high speed shared channel and
provides the number as an active load measurement for the high
speed shared channel to the radio network controller, and wherein
the radio resource controller uses the active load measurement in
controlling the base station.
9. The method in claim 1, wherein the base station measures an
amount of data being buffered per high speed shared channel user,
determines a number of high speed shared channel transmission time
intervals (TTIs) over a measurement period when the measured amount
of data does not keep its corresponding buffer loaded with data,
and provides the number of TTIs to the radio network controller,
and wherein the radio resource controller uses the number of TTIs
in performing one or more radio resource operations.
10. The method in claim 1, wherein the base station measures a
first power level actually used for transmission to a mobile radio
user over the high speed shared channel, determines a second power
level for reliable transmission to the mobile radio user over the
high speed shared channel, determines the difference between the
first and second power levels, and provides the difference to the
radio network controller, and wherein the radio resource controller
uses the difference in performing one or more radio resource
operations.
11. The method in claim 1, wherein the first radio channels and the
high speed shared channel are downlink radio channels from the
mobile communications network to one or more of the mobile radios,
wherein the first radio channels include one or more of the
following: one or more dedicated channels dedicated to a connection
between the mobile communications network and one of the mobile
radios, one or more common channels shared by the mobile radios,
one or more control channels, and one or more broadcast
channels.
12. The method in claim 1, further comprising: the radio resource
controller using the measured parameters to perform one or both of
congestion control and admission control.
13. A radio base station for use in a mobile communications network
that supports radio communications with plural mobile radios,
wherein first radio channels and a high speed shared radio channel
are associated with the radio base station, comprising: one or more
detectors for measuring one or more parameters that affect
management of the high speed shared radio channel, the radio base
station being configured to report one or more of the measured
parameters to a radio resource controller, and a high speed shared
channel controller for using information from the radio resource
controller based on the measured one or more parameters to
efficiently use radio resources associated with the high speed
shared radio channel.
14. The radio base station in claim 13, wherein the one or more
detectors includes an other power detector for measuring an other
transmission power for signals transmitted over first radio
channels that do not include a measurement of a transmission power
for signals transmitted over the high speed shared radio
channel.
15. The radio base station in claim 14, wherein the high speed
shared channel controller is configured to allocate a power level
for the high speed shared radio channel so that when the allocated
power level is combined with the other power measured for the first
radio channels, the combined power level does not exceed a
predetermined maximum power level associated with the base
station.
16. The radio base station in claim 13, wherein the communications
are code division multiple access (CDMA) based, wherein the one or
more detectors includes a CDMA code usage detector for measuring
CDMA code usage for the high speed shared radio channel during a
predetermined time period.
17. The radio base station in claim 16, wherein the predetermined
time period includes plural transmission time intervals (TTIs), the
CDMA code usage detector being configured to measure a number of
TTIs a CDMA code is used for the high speed shared radio channel
during the predetermined time period or a number of TTIs a set of
the CDMA codes is used for the high speed shared radio channel
during the predetermined time period.
18. The radio base station in claim 16, wherein the base station is
configured to send the CDMA code usage as a histogram to a radio
network controller.
19. The radio base station in claim 13, wherein the one or more
detectors includes a transport format usage detector for measuring
transport format usage for the high speed shared radio channel
during a predetermined time period.
20. The radio base station in claim 13, wherein the one or more
detectors includes an active load monitor for measuring a number of
mobile radio users currently having data to transmit over the high
speed shared channel in a base station buffer at a data
transmission scheduling time for the high speed shared channel.
21. The radio base station in claim 13, wherein the one or more
detectors includes a buffer monitor for measuring an amount of data
being buffered per high speed shared channel user and determining a
number of high speed shared channel transmission time intervals
(TTIs) over a measurement period when the measured amount of
buffered data reaches zero or is below a threshold.
22. The radio base station in claim 13, wherein the one or more
detectors includes an excess power monitor for measuring a first
power level actually used for transmission to a mobile radio user
over the high speed shared channel, determining a second power
level required for reliable transmission to the mobile radio user
over the high speed shared channel, and determining the difference
between the first and second power levels.
23. The radio base station in claim 13, wherein the first channels
and the high speed shared channel are downlink radio channels from
the mobile communications network to one or more of the mobile
radios, wherein the first radio channels include one or more of the
following: one or more dedicated channels dedicated to a connection
between the mobile communications network and one of the mobile
radios, one or more common channels shared by the mobile radios,
one or more control channels, and one or more broadcast
channels.
24. A radio base station mobile communications network that
supports radio communications with plural mobile radios,
comprising: a detector for measuring a transmission power for
signals transmitted over plural first radio channels that does not
include a measurement of a transmission power for signals
transmitted over a second radio channel, and a power controller for
receiving a power level for transmitting signals over the second
radio channel determined based on the measured transmission power
and for transmitting over the second radio channel at the
determined power.
25. The radio base station in claim 24, wherein the first and
second channels are downlink radio channels from the mobile
communications network to one or more of the mobile radios, wherein
the first radio channels include: one or more dedicated channels
dedicated to a connection between the mobile communications network
and one of the mobile radios, one or more common channels shared by
the mobile radios, one or more control channels, one or more
broadcast channels, and wherein the second channel is a high speed
downlink shared channel.
26. The radio base station in claim 24, wherein the power allocated
to the second radio channel combined with the power measured for
the first radio channels does not exceed a predetermined maximum
power associated with the base station.
27. Apparatus for use in a code division multiple access (CDMA)
mobile communications network including one or more radio base
stations that support radio communications with plural mobile
radios, comprising: a detector for measuring a CDMA code usage for
the second radio channel during a predetermined time period; a
controller for determining whether CDMA codes currently allocated
to the second radio channel are being efficiently used based on the
measured CDMA code usage and for changing a current CDMA code
allocation for the second radio channel if the CDMA codes currently
allocated to the second radio channel are not being efficiently
used.
28. The apparatus in claim 27, wherein the predetermined time
period includes plural transmission time intervals (TTIs), the
further configured to measure a number of TTIs a CDMA code is used
for the second radio channel during the predetermined time period
or a number of TTIs a set of the CDMA codes is used for the second
radio channel during the predetermined time period.
29. The apparatus in claim 28, wherein the CDMA code usage is
reported as a histogram.
30. The apparatus in claim 28, wherein the detector is in a radio
base station and the controller is in a radio network controller
coupled to the radio base station.
31. Apparatus for use in a code division multiple access (CDMA)
mobile communications network including one or more radio base
stations that support radio communications with plural mobile
radios, comprising: a detector for measuring a transport format
usage for the second radio channel during a predetermined time
period; a controller for determining whether a transport format
currently allocated to the second radio channel is inefficient
based on the measured transport format usage and for changing a
current transport format for the second radio channel if the
current transport format for the second radio channel is
inefficient.
32. A radio base station for use in a mobile communications network
that supports radio communications with plural mobile radios,
wherein first radio channels and a high speed shared radio channel
are associated with the radio base station, comprising: an active
load monitor for measuring a number of mobile radio users currently
having data to transmit over the high speed shared channel in a
base station buffer at a data transmission scheduling time for the
high speed shared channel, and a controller for providing the
measured number to a radio resource controller for use in managing
a load on the high speed shared channel.
33. The radio base station in claim 32, wherein the active load
monitor is configured to average the measured number over a
predetermined time interval.
34. A radio base station for use in a mobile communications network
that supports radio communications with plural mobile radios,
wherein first radio channels and a high speed shared radio channel
are associated with the radio base station, comprising: a buffer
monitor for measuring an amount of data being buffered per high
speed shared channel user and determining a number of high speed
shared channel transmission time intervals (TTIs) over a
measurement period when the measured amount of buffered data
reaches zero or is below a threshold, and a controller for
providing the measured number to a radio resource controller for
use in configuring the high speed shared channel.
35. A radio base station for use in a mobile communications network
that supports radio communications with plural mobile radios,
wherein first radio channels and a high speed shared radio channel
are associated with the radio base station, comprising: an excess
power monitor for measuring a first power level actually used for
transmission to a mobile radio user over the high speed shared
channel, determining a second power level required for reliable
transmission to the mobile radio user over the high speed shared
channel, and determining the difference between the first and
second power levels, and a controller for providing the difference
to a radio resource controller for use in allocating resources
associated with the high speed shared channel.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to radio communications, and
more particularly, to radio resource management for a high speed
shared channel.
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] Third generation (3G) Universal Mobile Telephone
communications Systems (UMTS), based on Wideband Code Divisional
Multiple Access (WCDMA) radio access, provide wireless access at
high data rates and support enhanced bearer services not
realistically attainable with first and second generation mobile
communication systems. A WCDMA radio access network, like the UMTS
Terrestrial Radio Access Network (UTRAN), also enhances quality of
service by providing robust operation in fading environments and
transparent (soft/softer) handover between base station/base
station sectors. For example, deleterious multipath fading is used
to improve received signal quality with RAKE receivers and improved
signal processing techniques.
[0003] Demand continues for improved multimedia communications in
the UTRAN including higher peak data rates, lower radio interface
delay, and greater throughput. A High Speed-Downlink Shared Channel
(HS-DSCH) has been proposed for use in WCDMA UTRAN networks to
support higher peak rates on the order of 8-10 megabits per second.
One of the ways the HS-DSCH achieves higher data speeds is by
shifting some of the radio resource coordination and management
responsibilities to the base station from the radio network
controller, including one or more of the following briefly
described below: shared channel transmission, higher order
modulation, link adaptation, radio channel dependent scheduling,
and hybrid-ARQ with soft combining.
[0004] Shared channel transmission and higher order modulation: In
shared channel transmission, radio resources, like spreading code
space and transmission power in the case of CDMA-based
transmission, are shared between users using time multiplexing. A
high speed-downlink shared channel is one example of shared channel
transmission. One significant benefit of shared channel
transmission is more efficient utilization of available code
resources as compared to dedicated channels. Higher data rates may
be also be attained using higher order modulation, which is more
bandwidth efficient than lower order modulation, when channel
conditions are favorable.
[0005] Link Adaptation and Rate Control: Radio channel conditions
experienced on different communication links typically vary quite
significantly, both in time and between different positions in the
cell. In traditional CDMA systems, power control compensates for
differences in variations in instantaneous radio channel
conditions. Unfortunately, a larger part of the total available
cell power is allocated to communication links with bad channel
conditions to ensure similar quality of service to all
communication links. But radio resources are more efficiently
utilized when allocated to communication links with good channel
conditions. For services that do not require a specific data rate,
such as many best effort services, rate control or adjustment can
be used to ensure there is sufficient energy received per
information bit for all communication links as an alternative to
power control. By adjusting the channel coding rate and/or
adjusting the modulation scheme, the data rate can be adjusted to
compensate for variations and differences in instantaneous channel
conditions.
[0006] Channel Dependent Scheduling and Hybrid ARQ: For maximum
cell throughput, radio resources may be scheduled to the
communication link having the best instantaneous channel condition.
Rapid channel dependent scheduling performed at the bases station
allows for very high data rates at each scheduling instance and
thus maximizes overall system throughput. Hybrid ARQ with soft
combining increases the effective received signal-to-interference
ratio for each transmission and thus increases the probability for
correct decoding of retransmissions compared to conventional ARQ.
Greater efficiency in ARQ increases the effective throughput over a
shared channel.
[0007] FIG. 1 illustrates a high speed shared channel concept where
multiple users 1, 2, and 3 provide data to a high speed channel
(HSC) controller that functions as a high speed scheduler by
multiplexing user information for transmission over the entire
HS-DSCH bandwidth in time-multiplexed intervals. For example,
during the first time interval shown in FIG. 1, user 3 transmits
over the HS-DSCH and may use all of the bandwidth allotted to the
HS-DSCH. During the next time interval, user 1 transmits over the
HS-DSCH, the next time interval user 2 transmits, the next time
interval user 1 transmits, etc.
[0008] High-speed data transmission is achieved by allocating a
significant number of spreading codes (i.e., radio resources in
CDMA systems) to the HS-DSCH. FIG. 2 illustrates an example code
tree with a fixed Spreading Factor (SF) of sixteen. A subset those
sixteen codes, e.g., twelve, is allocated to the high-speed shared
channel. The remaining spreading codes, e.g., four are shown in the
figure, are used for other radio channels like dedicated, common,
and broadcast channels.
[0009] Although not necessarily preferred, it is also possible to
use code multiplexing along with time multiplexing. Code
multiplexing may be useful, for example, in low volume transmission
situations. FIG. 3 illustrates allocating multiple spreading codes
to users 1, 2, and 3 in code and time multiplexed fashion. During
transmission time interval (TTI) 1, user 1 employs twelve codes.
During transmission time interval 2, user 2 employs twelve
spreading codes. However, in transmission time interval 3, user 1
uses two of the codes, and user 3 uses the remaining ten codes. The
same code distribution occurs in TTI=4. In TIT=5, user 3 uses two
of the codes while user 2 uses the remaining codes.
[0010] To achieve higher throughput and high peak data rates, a
high speed shared channel may not use closed loop power control,
(as dedicated channels do), but instead simply uses the remaining
power in the base station cell up to a preset maximum. Because the
high-speed shared channel is used along with other channels, radio
resources must be allocated to the different channels efficiently
and without overloading the cell with too high of a power level.
The power level for channels other than the high-speed shared
channel must be managed to leave sufficient power for the shared
channel to have the desired, high throughput.
[0011] The code assignment affects the throughput on the high-speed
shared channel as well as the available code space for other
channels. An optimal code assignment depends on several factors,
such as traffic load, the type of traffic, and current radio
conditions. If too many CDMA codes are assigned to the high-speed
shared channel, some of those codes maybe underutilized, which is a
waste of radio resources. If too few codes are assigned, the
channel throughput over the high-speed shared channel is too
low.
[0012] The radio network controller (RNC) performs radio resource
management. Radio resources like spreading codes are allocated
using one or more resource management algorithms. Other examples of
such resource management include power/interference control,
admission control, congestion control, etc. The radio network
controller can better perform its resource management tasks if it
knows the current resource status or use in the cell. One
measurement useful to the radio network controller is how often the
codes currently allocated to the high-speed shared channel are
being used. The present invention provides measurements from the
base station to the radio network controller about the usage of the
set of codes currently allocated to a particular channel, like a
high speed shared channel. Based on those measurements, the RNC can
adjust (if necessary) the code allocation to the high speed shared
channel.
[0013] Another managed radio resource that needs judicious
allocation to different radio channels in a base station cell is
radio transmission power level. FIG. 4 shows a graph of base
station cell power against time. The radio transmission power for
one or more common channels, shown in the bottom graph, takes up a
first portion of the allowed or maximum cell power. On top of the
common channel power is the combined radio transmission power
currently allocated to the dedicated channels. The hatched portion
shows the radio transmission power that can be used by the
high-speed shared channel. At time t.sub.m, the combined common and
dedicated channel power equals the maximum cell power. As a result,
the high speed shared channel has no available power, and therefore
no throughput, assuming the maximum cell power level is observed.
On the other hand, if the high speed shared channel uses more than
the maximum cell power, signals may be distorted leading to
degraded quality of service.
[0014] Some base stations already provide measurements to the RNC,
e.g., channel quality estimates for link adaptation. But such base
station measurements do not take into account the special nature of
a high-speed downlink shared channel (HS-DSCH). Indeed, one typical
base station measurement provided to the RNC is total transmitted
carrier power for all downlink channels. That measurement would
include the transmission power for the high-speed shared channel.
Including the high-speed downlink shared channel in the total
transmitted carrier power measurement presents a problem. First,
the HS-DSCH, by design, uses all of the remaining transmission
power up to the cell maximum. Second, the RNC uses the total
transmission power measurement to decide whether to set up new
dedicated radio channels. Consequently, the RNC will always
conclude that the cell is operating at full capacity as long as
there is a moderate traffic demand on the high-speed downlink
shared channel. For the same reason, channel requests will be
denied as soon as there is even moderate traffic demand on the
high-speed downlink shared channel. Nor is it possible in this
situation to determine an accurate congestion level in the cell.
Because the high speed shared channel uses the remaining cell
power, the total carrier power measurement will always be equal or
close to the cell maximum erroneously suggesting that the cell is
always fully loaded.
[0015] The present invention provides a cell transmission power
measurement to a radio resource manager that specifically takes
into account a high-speed shared channel even where that channel is
designed to use the remaining transmission power in a cell up to a
cell maximum. The radio network controller is informed when a high
speed shared channel has little or no power available because of
increasing power demands required by channels other than the high
speed shared channel. Other parameters may also be measured at the
base station that may be useful to a radio resource controller.
[0016] One or more base station measurements provided to a radio
resource manager allows it to optimally access, allocate, and/or
regulate radio resources, like spreading codes and transmission
power, to different types of radio channels supported in the cell,
including a specialized channel like a high-speed shared channel.
Such measurements include one or more of the following:
other-channel power, HS-DSCH code usage, transport format usage,
average active load, empty buffer, excess power, and/or similar
parameters.
[0017] In one example embodiment, transmission power is measured
for signals transmitted over first radio channels that do not
include measurement of a transmission power for signals transmitted
over a second radio channel, e.g., a high speed shared channel.
CDMA code usage may also be measured for the second channel during
a predetermined time period. One or both of the measured
transmission power and the measured CDMA code usage are reported to
a radio resource controller which may take appropriate resource
management action(s). In a preferred example, the first and second
channels are downlink radio channels from the CDMA mobile
communications network to one or more of the mobile radios. The
first radio channels include one or more of the following: one or
more dedicated channels, one or more common channels, one or more
control channels, and one or more broadcast channels. The second
channel is a high speed downlink shared channel.
[0018] The measured transmission power maybe used to perform radio
resource control such as power allocation to the second radio
channel and/or the first radio channels, code allocation to the
second radio channel and/or first radio channel, congestion
control, and admission control. The measurement also alerts the
radio resource controller to situations where the power being used
by the other channels leaves insufficient or rapidly decreasing
power for the HS-DSCH. The radio resource controller may take
appropriate action to reallocate power resources to ensure there is
sufficient power for the HS-DSCH to function.
[0019] Using the measured CDMA code usage information, a
determination may be made whether CDMA codes currently allocated to
the second radio channel are being efficiently used. If not, the
current CDMA code allocation for the second radio channel is
changed. In one implementation, the predetermined time period
includes plural transmission time intervals (TTIs). The number of
TTIs that a CDMA code is used for the second radio channel during
the determined time period is measured. Alternatively, a number of
TTIs that a set of the CDMA codes is used for the second radio
channel during the predetermined time period may be measured. The
CDMA code usage measurement maybe reported in any number of
fashions. In one example, the code usage is reported to the
resource manager as a histogram.
[0020] Other example base station measurements may be used alone or
in combination with each other and/or those measurements described
above. For example, a number of mobile radio users may be measured
that currently have data to transmit over the high speed shared
channel in a base station buffer at a data transmission scheduling
time for the high speed shared channel. The measured number
corresponds to an active load and is provided to a radio network
controller for use in managing a load on the high speed shared
channel. A buffer monitor may be used to measure an amount of data
being buffered per high speed shared channel user. A number of high
speed shared channel transmission time intervals (TTIs) is
determined over a measurement period when the measured amount of
buffered data reaches zero or is below a threshold. The measured
number can be used to (re)configure the high speed shared channel.
An excess power monitor maybe used to measure a first power level
actually used for transmission to a mobile radio user over the high
speed shared channel and determine a second power level required
for reliable transmission to the mobile radio user over the high
speed shared channel. The difference between the first and second
power levels is calculated and used in allocating resources
associated with the high speed shared channel.
[0021] The present invention enables efficient radio resource
management without excessive signaling. By accounting for the
specific characteristics of a particular type of channel, like a
high-speed shared channel, one or more measurements in accordance
with the present invention permits an accurate estimate of current
cell conditions. As a result, a radio resource manager can better
control cell congestion, admit new users to the cell, block new
users, or even drop existing users, if necessary. Actions can be
taken to ensure that maximum power limitations are not exceeded
before the maximum power is reached which would otherwise result in
unpredictable signaling distortion and poor signal quality.
Moreover, the invention allows the radio resource controller to
ensure the high-speed shared channel has enough resources to
fulfill its job as a high-speed shared channel. Since spreading
codes are a limited resource in a CDMA system, an optimal code
allocation is assured to various channels, which is particularly
advantageous for a high-speed shared channel. Proper code
allocation to a high-speed shared channel ensures optimal
performance of that channel without under-utilizing or otherwise
wasting radio resources.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The foregoing and other objects, features, and advantages of
the present invention may be more readily understood with reference
to the following description taken in conjunction with the
accompanying drawings.
[0023] FIG. 1 illustrates conceptually a high speed downlink shared
channel;
[0024] FIG. 2 illustrates a code tree;
[0025] FIG. 3 illustrates a time division code division multiplex
diagram in conjunction with the high speed downlink shared
channel;
[0026] FIG. 4 is a cell power diagram;
[0027] FIG. 5 is a function block diagram illustrating one example
embodiment of the present invention in the context of a mobile
radio communications system;
[0028] FIG. 6 is a flowchart diagram illustrating radio resource
management procedures for a high-speed shared channel in accordance
with one example embodiment of the present invention;
[0029] FIG. 7 is flowchart illustrating example other channel power
measurement procedures;
[0030] FIG. 8 is a block diagram illustrating one way to perform
other channel power measurement;
[0031] FIG. 9 is a flowchart illustrating example code resource
measurement procedures;
[0032] FIG. 10 illustrates a code usage/transport format usage
measurement;
[0033] FIG. 11 is a graph illustrating certain base station
measurements;
[0034] FIG. 12 is a flowchart illustrating example average active
load measurement procedures;
[0035] FIG. 13 is a flowchart illustrating example empty buffer
measurement procedures; and
[0036] FIG. 14 is a flowchart illustrating example excess power
measurement procedures.
DETAILED DESCRIPTION
[0037] In the following description, for purposes of explanation
and not limitation, specific details are set forth, such as
particular embodiments, procedures, techniques, etc. in order to
provide a thorough understanding of the present invention. However,
it will be apparent to one skilled in the art that the present
invention may be practiced in other embodiments that depart from
these specific details. For example, while the present invention is
described in an example application to a CDMA-based cellular system
that uses a high-speed downlink shared channel, the present
invention maybe employed in any cellular system having different
types of channels.
[0038] In some instances, detailed descriptions of well-known
methods, interfaces, devices, and signaling techniques are omitted
so as not to obscure the description of the present invention with
unnecessary detail. Moreover, individual function blocks are shown
in some of the figures. Those skilled in the art will appreciate
that the functions may be implemented using individual hardware
circuits, using software functioning in conjunction with a suitably
programmed digital microprocessor or general purpose computer,
using an application specific integrated circuit (ASIC), and/or
using one or more digital signal processors (DSPs).
[0039] The present invention finds advantageous, but still example,
application to a CDMA mobile communications network such as that
shown at reference numeral 10 in FIG. 5. Plural external networks
12 are coupled to a CDMA-based radio access network 14 which, for
example, may be a UMTS Terrestrial Radio Access Network (UTRAN).
Network 14. The UTRAN 14 includes one or more radio network
controllers (RNC) 16 which communicate over a suitable interface.
Each RNC 16 may include, among other things, an admissions
controller 18, a cell load controller 20, and radio resource
controller 22. Each of the controller entities maybe implemented in
hardware, software, or a combination of both. Each RNC 16 is
coupled to plural radio base stations (BS) 24. Each radio base
station 24 includes, among other things, radio transceiving
circuitry 26, one or more transmit power monitors 27, a high speed
channel code usage monitor 28, a transport format usage monitor 29,
average active load monitor 30, empty buffer monitor 31, excess
power monitor 32, and a high speed channel controller 33. The radio
base station 24 communicates over a radio interface with various
mobile stations identified as user equipments (UE) 34.
Communications over the radio interface are made using spreading
codes, i.e., one or more spreading codes corresponds to a radio
channel.
[0040] System 10 includes different types of radio channels: one or
more dedicated channels, one or more common channels, one or more
broadcast channels, and a high speed shared channel such as a high
speed downlink shared channel (HS-DSC. Although an HS-DSCH is used
in the examples below, the invention is not limited to HS-DSCHs.
Base station 24 has a particular number of spreading codes
available for use. See the example code tree with a spreading
factor of 16 shown in FIG. 2. A certain number of the available
spreading codes will be allocated to the high speed downlink shared
channel, and the remaining codes are allocated to the other
channels. The present invention strives to allocate the optimal
number of spreading codes to the high speed downlink shared channel
and to the other channels. The optimal allocation ensures that a
desired data rate, throughput, and/or quality of service is/are
provided over the high speed downlink shared channel while
efficiently using all of the codes allocated to the high speed
downlink shared channel. The high speed channel code usage monitor
28 provides the RNC 16 with actual spreading code usage for the
high speed downlink shared channel over a predetermined period of
time.
[0041] Similarly, each base station cell is assigned a maximum
downlink radio transmission power level. Transmission power is
distributed amongst the various channels in the cell. In the power
distribution shown in FIG. 4, the common channels use a certain
transmission power, the dedicated channels are allocated
transmission power on top of the common channel power, and the high
speed channel uses whatever transmission power remains up to the
maximum power established for that cell.
[0042] The high speed channel controller 32 may perform the various
functions described above for a the high speed downlink shared
channel such as shared channel transmission, higher order
modulation, link adaptation, radio channel dependent scheduling,
and hybrid-ARQ with soft combining. Particularly, the high speed
channel controller 32 controls fast scheduling of transmissions
(and retransmissions) over the high speed downlink shared channel
in each transmission time interval (TTI). The high speed controller
32 preferably allocates all of the codes allocated to the high
speed downlink channel, e.g., twelve codes in the code tree of FIG.
4, to a single mobile radio UE connection in one TTI. But if the
payload is insufficient for a single UE connection, or if the UEs
are low-end UEs, code division multiplexing may also be employed by
the radio resource controller 22 as explained above with regard to
FIG. 3. For the admissions controller 18 to perform admissions
control, the load controller 20 to perform load control, and the
radio resource controller 22 to optimally manage radio resources in
each cell, the RNC 16 must receive relevant and accurate
measurement information from the base station 24.
[0043] In a first general example embodiment, one or more
measurements are made and reported by the base station and used by
a resource controller, which in this non-limiting example, is
located the RNC. Refer to the Radio Resource Management for a High
Speed Downlink Shared Channel procedures shown in flowchart form in
FIG. 6. In the first step (block 40), the base station measures one
or more of the following parameters: "other" channel power (other
than HS-DSCH channel power), a HS-DSCH code usage, transport format
usage, average active load, empty buffer, and excess power. Each of
these example base station measurements is described below.
However, it should be understood that these measurements are only
examples, and that the present invention is not limited to any one
or combination of these specific measurements.
[0044] The base station sends to the RNC one or more of the base
station measurements, and the resource controller 22 in the RNC
uses that measurement information to perform power allocation and
perhaps power control on the dedicated channels based upon the
reported measurements. It also adjusts spreading code allocation
adjustments based upon the reported measurements. The admissions
controller 18 uses these measurements as a factor in determining
whether to admit new call requests. The load controller 20, with
this same information, determines whether congestion/load control
is required in this cell (block 42).
[0045] Other Channel Power: Other channel power is transmission
power attributable to transmissions made over one or more channels
other than the high speed downlink shared channel. In this example,
it includes the power of all channels but the high speed downlink
shared channel. These channels may include, for example, one or
more dedicated channels dedicated to a connection between the UTRAN
14 and the UEs 34, one or more common channels shared by the mobile
radios, one or more control channels, and one or more broadcast
channels. Other channel power may be measured by the power monitor
27 in the example manner described in conjunction with FIG. 8.
[0046] Example Other Channel Power Measurement procedures are
illustrated in flowchart form in FIG. 7. The total power of all (or
only some) downlink channels from the base station is measured with
the exception of the transmission power of the high speed downlink
shared channel (block 50). The total power measurement(s) is(are)
forwarded to the RNC and used by one or more resource controllers
like the radio resource controller 22, the load controller 20, and
the admission controller 18 (block 52). Based on the measurements,
the RNC (or the base station) determines the total power for the
downlink channels except the high-speed downlink shared channel
(block 54).
[0047] The power allocated to the high speed downlink shared
channel is controlled so that the remaining power in the base
station cell is used without exceeding (at least not significantly)
the maximum power designed for that cell (block 56). Other power
control operations such as power control for one or more of the
dedicated channels, congestion control, and/or admission control
maybe performed using the total power measurement. In addition, the
base station preferably notifies the RNC when there is little or no
transmission power available for the high speed downlink shared
channel.
[0048] The transmitted signal is the sum of the signals from all
individual physical channels, including common physical channels,
dedicated physical channels, and shared physical channels (in
particular the high-speed shared physical channel). The preferred,
example implementation is to sum all signals except from the shared
physical channel(s). The other channel power is measured by taking
the average of the squared chip magnitudes of the signal sum. The
signal to be transmitted is formed by adding the HS-DSCH signal to
that signal sum.
[0049] Alternatively, the power measurement can be formed as a sum
of several individual power measurements made on individual channel
signals, or on sums of subsets of non-shared channel signals. This
can be advantageous if the summing of the signals in an
implementation must be done in a certain order different from the
one described above. Individual power measurements are made by
averaging the squared chip magnitudes of the individual channel
signals or of the subsets.
[0050] If the individual power measurements are performed on
individual channel signals (and not on subsets), the power
measurements may be generated more easily based on knowledge of the
configured transmission power and the current usage of each
channel. The measured power value of an individual channel signal
is then formed as the product of the squared gain factor for that
signal and the activity factor for that channel. The activity
factor is the ratio of the number of actually transmitted symbols
to the total number of symbols.
[0051] FIG. 8 shows one example way in which other channel power
may be measured at the base station. In this case, the other
channels include dedicated physical channels (DPCH) 1, 2, . . . , N
and a common channel (CC). Each other channel signal is multiplied
in a corresponding multiplier 60, 62, 64, and 66 by an appropriate
gain or power control value determined. The power control (PC)
signals are summed together in summer 68, and the total power is
determined in power detector 70 by taking the average of the
squared chip magnitudes of the signal sum. Each chip in a spreading
code has an I and a Q component so that its power={square
root}{square root over (I.sup.2+Q.sup.2)}. The measured power of an
individual channel signal may be determined as the product of the
squared gain or power control (PC) factor for that signal and an
activity factor for that channel, defined above. As an alternative
mentioned above, subsets of the non-shared channel signals can be
summed.
[0052] The total other channel power is provided to the RNC as
indicated. The total other channel power is also summed in a summer
74 with the power of the high speed downlink shared channel.
Although the HS-DSCH is not power controlled in the same manner as
dedicated channels, the power must be set according to the power
needed for other channels. Because the HS-DSCH uses the remaining
power, which varies over time, the HS-DSCH power also vanes. Thus,
the PC factor for the HS-DSCH depends on the measured, non-HS-DSCH
power. The sum of all downlink channels including the HS-DSCH is
processed in the signal and radio processing block 76 and
transmitted via antenna 78.
[0053] HS-DSCH Code Usage/Transport Format Usage: The high speed
channel code usage monitor 28 measures the HS-DSCH code usage over
a predetermined time period. A code resource/transport format usage
measurement procedure is illustrated in flowchart form in FIG. 9.
For each high speed downlink shared channel transmission time
interval (TTI), e.g., two milliseconds, a transport format is
selected by the high speed channel controller 33. The transport
format specifies a particular number of spreading codes up to the
allocated number of codes for use by the high speed downlink shared
channel (block 80). The high speed channel controller 33 may also
decide not to transmit over the high speed downlink shared channel
during a TTI which would correspond to using zero spreading codes.
Over a predetermined time period, such as 100 milliseconds, the
high speed channel code usage monitor 28 measures a number of
transmission time intervals (TTIs) that each spreading code is used
by the high speed downlink shared channel. Alternatively, the
monitor 28 may measure a number of TTIs that each particular set of
codes is used by the high speed downlink shared channel (block 82).
An example of the latter might be that a set of codes including
codes 1 through 6 is used in only two TTIs. A set of codes
including just codes 1 and 2 is used in twenty-five TTIs. A
transport format usage monitor 29 may additionally or alternatively
measure a number TTI's that each transport format is used.
[0054] The code usage data detected by the monitor 28 and/or the
transport format usage data detected by the monitor 29 for the
predetermined time period is provided to the RNC. In one
non-limiting example, the code usage information and/or the
transport format usage data may be delivered in the form of a usage
histogram. The radio resource controller (RRC) 22 in the RNC 16
determines whether to change the code allocation for the high speed
downlink shared channel based on that code usage data or the
transport format based on that transport format usage data (block
84).
[0055] FIG. 10 gives an example histogram mapping spreading codes 1
through 12 allocated for each two millisecond TTI for the high
speed downlink shared channel, the high speed channel controller 32
selects a transport format. Of course, the entire histogram need
not be sent over the radio interface but some abbreviated form of
the histogram information could be transmitted instead. The code
usage measurement need not include all possible number of codes.
Alternatively, the number of times any subset of codes is used, for
example 0-3, 4-7, 8-11, 12-15, etc., maybe measured. As another
alternative, the proportion of HS-DSCH TTI's for each code subset
may be measured, or the time or proportion of time that each code
subset is used.
[0056] The HS-DSCH code usage measurement may be generalized and
expressed statistically as a function of the transport formats
used. Based on certain available information, such as buffer
status, channel conditions, available power resources, etc., the
high speed channel controller 33 selects one of the transport
formats. During a defined time interval, the base station transport
format usage monitor 29 counts the number of times each transport
format is used for the HS-DSCH. The result is a two-dimensional
histogram describing for each transport format the number of times
this transport format is used. The measurement can either be the
two-dimensional histogram or a function thereof.
[0057] FIG. 11 illustrates an example of forming statistics over
the set of possible transport formats. The numbers shown in the
graph represent the transport block size (payload). The x-axis is
the number of spreading codes used for the HS-DSCH. The y-axis
represents the signal-to-noise ratio required for transmission
expressed as a carrier-to-interference (C/I) ratio. The dotted line
exemplifies a group of transport formats and is described in the
text.
[0058] In a preferred, example embodiment, groups of transport
formats are defined and only the number of times any transport
format within this group is used is reported. In FIG. 11, a dotted
line illustrates an example of such a group of transport formats
including for each number of spreading codes, the transport format
with the largest payload. Frequent use of transport formats in this
group indicate the HS-DSCH is limited in the number of spreading
codes rather than in the available energy. If possible, the RNC
should assign more spreading codes to the HS-DSCH in order to
increase its capacity.
[0059] As an alternative to reporting the number of times each
group is used, the fraction of TTIs in each transport format group
can be measured or the proportion of time that each transport
format group is used. A relative measurement, e.g., the number of
times one transport format group is used in relation to another
transport format group, may be used. Furthermore, the statistics
may be collected and reported individually for several data streams
with different priorities. Individual statistics for each priority
level used for packet data streams for the HS-DSCH are reported. In
this situation, the RNC may be configured to act only on
measurements for streams for which it wants to guarantee a certain
quality of service.
[0060] Average Active Load: The active load for the HS-DSCH at a
certain time instant is the number of users the high speed channel
controller 33 can select between at that time instant. As indicated
in the average active load measurement flowchart shown in FIG. 12,
the average active load monitor 30 detects a number of users
currently having data to transmit over the HS-DSCH at the time of
the scheduling decision (block 90). For example, if 20 users have
data to transmit over the HS-DSCH in the base station buffers at
the time when the high speed channel controller 33 makes a
scheduling decision, i.e., selects to which user(s) to transmit to,
the active load at this time is 20. There could be more users than
the active load actually assigned to the HS-DSCH, but it is only
those users currently having data in the base station buffers that
are included in the active load. The detected numbers collected
over a preset time interval are averaged (block 92) and provided to
the RNC (block 94). The average active load can be used for
admission control, for example, to block users requesting an
HS-DSCH if the average active load exceeds a certain limit.
Admitting them in this situation would excessively degrade the
overall performance of the HS-DSCH. As the transport format
measurements described above, the average active load can be
defined per priority level.
[0061] EmptyBuffer: At each scheduling instant, the high speed
channel controller 33 selects a suitable transport format,
including the payload size, for the user(s) assigned to the HS-DSCH
for the upcoming TTI. The payload size depends on the radio channel
quality, i.e., a higher (lower) channel quality supports a larger
(smaller) payload, and on the amount of data available in the base
station buffers. Referring to the flowchart of FIG. 12, the buffer
monitor 31 detects an amount of data being buffered per DS-DSCH
user for transmission (block 100). The amount of buffered data
awaiting transmission for a certain UE forms an upper limit for the
payload size, and thus, for the transport format selected. If the
transport format is dictated by the data in the buffers rather than
by the radio channel conditions, the HS-DSCH is underutilized, and
the system is traffic-limited rather than limited by the radio
environment. This situation may also indicate a need for more code
multiplexing, (e.g., configuration of additional HS-shared control
channels), especially if the transport format statistics described
above indicate that transport formats with small payloads are used
frequently. The buffer monitor 31 determines the empty buffer
measurement as the number of TTIs in a defined measurement interval
where less data-was transmitted than would have been transmitted if
the user's data buffer had not been emptied of if the amount
buffered is less than a threshold amount (block 102). The empty
buffer measurement can either be defined for all traffic regardless
of priority, or it can be defined individually per priority level.
The empty buffer measurement is provided to the RNC for use, for
example, in reconfiguring transport format, code allocation, etc.,
for the HS-DSCH (block 104).
[0062] Excess Power: Excess power is the difference between the
power actually used for a transmission to a user and the power
required for sufficiently reliable transmission that user with the
selected transport format. As shown in the flowchart in FIG. 14,
the excess power monitor 32 detects power actually used for
transmission to a user over the HS-DSCH (block 110). The excess
power monitor 32 detects the power required for reliable
transmission to that user over the HS-DSCH (block 112) and
determines the difference (block 114). If the difference is
positive, the excess power monitor 32 sends the excess power to the
RNC for possible allocation of more radio resources, e.g.,
spreading codes, to the HS-DSCH.
[0063] An excess power example is illustrated in the graph shown in
FIG. 11. The lower circle represents the transport format selected
at a certain scheduling instant, and the upper circle represents
the power actually used for the transmission with the selected
transport format. In the example, the excess power is 4 dB.
Preferably, the excess power measurement is the average excess
power used during a defined measurement time interval, e.g., 100
ms. A high excess power measurement indicates that the HS-DSCH is
not operating in the power-limited region. Power can be used more
efficiently by assigning more HS-DSCH codes to other channels.
[0064] As an alternative to specifying a single excess power
measurement for the HS-DSCH, the excess power measurement may be
defined per transport format or per transport format group. The
transport format statistics described above can be used to generate
"transport format and resource usage" statistics. So in addition to
counting the number of times a certain transport format is used,
the average excess power for this transport format is also
recorded.
[0065] While the present invention has been described with respect
to particular embodiments, those skilled in the art will recognize
that the present invention is not limited to these specific
exemplary embodiments. Different formats, embodiments, and
adaptations besides those shown and described as well as many
variations, modifications, and equivalent arrangements may also be
used to implement the invention. Therefore, while the present
invention has been described in relation to its preferred
embodiments, it is to be understood that this disclosure is only
illustrative and exemplary of the present invention. Accordingly,
it is intended that the invention be limited only by the scope of
the claims appended hereto.
* * * * *