U.S. patent application number 13/026724 was filed with the patent office on 2011-06-09 for dynamic allocation of radio resources.
This patent application is currently assigned to Telefonaktiebolaget LM Ericsson (publ). Invention is credited to Pal Frenger, Goran KLANG, Johan Nystrom, Stefan Parkvall.
Application Number | 20110136496 13/026724 |
Document ID | / |
Family ID | 34928974 |
Filed Date | 2011-06-09 |
United States Patent
Application |
20110136496 |
Kind Code |
A1 |
KLANG; Goran ; et
al. |
June 9, 2011 |
DYNAMIC ALLOCATION OF RADIO RESOURCES
Abstract
Radio resources are allocated to communication between a mobile
station and a base station. The available set of radio resources
may comprise radio resources primarily assigned to a neighboring
cell if the 5 mobile station experience an instantaneous low level
of co-channel interference from such neighboring cells. The
existence of interference is preferably deduced from signal quality
measurements of pilot signals. The allocation may concern uplink
and/or downlink communication. Devices for performing the
measurements are located in the mobile station, while devices for
performing the evaluation, selection and actual allocation can be
placed in different parts of the communications system-in the
mobile station, in a base station or in a core network node, or as
a distributed means.
Inventors: |
KLANG; Goran; (Enskede,
SE) ; Frenger; Pal; (Vallingby, SE) ;
Parkvall; Stefan; (Stockholm, SE) ; Nystrom;
Johan; (Stockholm, SE) |
Assignee: |
Telefonaktiebolaget LM Ericsson
(publ)
Stockholm
SE
|
Family ID: |
34928974 |
Appl. No.: |
13/026724 |
Filed: |
February 14, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11578515 |
Oct 16, 2006 |
7912475 |
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PCT/EP2005/051408 |
Mar 29, 2005 |
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13026724 |
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Current U.S.
Class: |
455/452.1 |
Current CPC
Class: |
H04W 72/08 20130101;
H04W 16/10 20130101 |
Class at
Publication: |
455/452.1 |
International
Class: |
H04W 72/08 20090101
H04W072/08; H04W 24/00 20090101 H04W024/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 19, 2004 |
EP |
04101597.5 |
Claims
1-18. (canceled)
19. A base station of a radio communications system, comprising:
evaluation means arranged to determine a radio resource reuse area
occupied by a mobile terminal (occupied reuse area) based on a
quality report from said mobile terminal, the quality report
including a report of quality measures of signals transmitted from
a plurality of base stations measured at said mobile terminal;
selection means arranged to select a set of one or more radio
resources allowed to be used (allowed resource set) based on the
occupied reuse area; and allocation means arranged to allocate one
or more radio resources from the allowed resource set for use in
actual communication (actual radio resource(s)) between said mobile
terminal and said base station, wherein the occupied reuse area is
one of a plurality of radio resource reuse areas of said base
station, the plurality of radio resource use areas including at
least an inner part that encloses said base station, an
intermediate part that encloses the inner part, and an outer part
that encloses the intermediate part and bounded by a cell of said
base station, and a reuse factor of radio resources is highest for
the outer part and lowest for the inner part.
20. The base station according to claim 19, wherein the reuse
factor for the inner part is substantially one.
21. The base station according to claim 19, wherein said radio
communication system includes one or more neighbor base stations
such that the cell of said base station is directly adjacent to
each cell of said one or more neighbor base stations, a primary set
of radio resources is assigned to each base station including said
base station (main primary set) and said neighbor base station(s)
(neighbor primary set(s)) such that the main primary set has no
radio resources in common with any of the neighbor primary set(s),
when the occupied reuse area is the outer part, the allowed
resource set includes at most the main primary set, when the
occupied reuse area is the intermediate part, the allowed resource
set includes the main primary set and one or more radio resources
of the neighbor primary set of at least one neighbor base station,
and when the occupied reuse area is the in part, the allowed
resource set includes substantially all radio resources available
to the radio communication system.
22. The base station according to claim 21, wherein when the
allowed resource set includes radio resource(s) other than the main
primary set, said allocation means is arranged to prioritize
allocating the radio resources not in the main primary set over the
radio resources in the primary set.
23. The base station according to claim 21, wherein, said
evaluation means is arranged to determine which of said neighbor
base station(s) would contribute to a co-channel interference (CCI)
experienced by said mobile terminal being at or above a
predetermined unacceptable CCI level based on the quality report,
and said selection means is arranged to exclude, from the allowed
resource set, the neighbor primary set(s) of said neighbor base
station(s) contributing to the unacceptable CCI level, and include,
in the allowed resource set, the neighbor primary set(s) of said
neighbor base station(s) not contributing to the unacceptable CCI
level.
24. The base station according to claim 21, wherein said evaluation
means is arranged to send information on relative emission powers
between data and pilot signals transmitted by said plurality of
base stations to said mobile terminal, and receive a determination
of which of said neighbor base station(s) would contribute to being
at or above a predetermined unacceptable co-channel interference
(CCI) level from said mobile terminal, and said selection means is
arranged to exclude, from the allowed resource set, the neighbor
primary set of said neighbor base station(s) contributing to the
unacceptable CCI level, and include, in the allowed resource set,
the neighbor primary set of said neighbor base station(s) not
contributing to the unacceptable CCI level.
25. The base station according to claim 21, wherein said selection
means is arranged to send information on relative emission powers
between data and pilot signals transmitted by said plurality of
base stations and information on the main primary set and the
neighbor primary set(s) to said mobile terminal, and the allowed
resource set from said mobile terminal.
26. The base station according to claim 21, wherein said evaluation
means is arranged to relay the quality report to a core network
node, and receive a determination of which of said neighbor base
station(s) would contribute to being at or above a predetermined
unacceptable co-channel interference (CCI) level from said core
network node, and said selection means is arranged to exclude, from
the allowed resource set, the neighbor primary set of said neighbor
base station(s) contributing to the unacceptable CCI level, and
include, in the allowed resource set, the neighbor primary set of
said neighbor base station(s) not contributing to the unacceptable
CCI level.
27. The base station according to claim 21, wherein said evaluation
means is arranged to relay the quality report to a core network
node, and said selection means is arranged to receive the allowed
resource set from said core network node.
28. The base station according to claim 19, wherein said selection
means and said allocation means operate independently of other base
stations in said radio communication.
Description
TECHNICAL FIELD
[0001] The present invention relates in general to allocation of
radio resources in mobile communications systems.
BACKGROUND
[0002] The radio spectrum assigned to a mobile communications
system must in general be reused within different geographical
sub-areas, so called cells, in order to provide both coverage and
capacity. Depending on technology choices and factors such as what
multiple access techniques that is employed and how robust to
interference the mobile and base station receivers are, the so
called reuse distance between different cells using the same
portion of spectrum may however vary. This variation appears, not
only between different types of systems, but also within the same
system. The latter is due to e.g. the topology of the service
area.
[0003] In practice, to model the cellular layout of a mobile
communications system a heterogeneous grid of regular hexagons is
often used. Although not providing a true description of the real
cell and its coverage area, as an approximation, hexagons have
proven useful for cell planning purposes as they provide a
convenient framework in which a wide range of tessellating
cell-reuse clusters can be defined to describe the distribution of
the available spectrum/channel resources over the total service
area of a given system.
[0004] It is known that tessellating clusters of size N can be
constructed if
N=i.sup.2+ij+j.sup.2,
where i and j are non-negative integers and i.gtoreq.j. From the
relation above, it follows that the allowable cluster sizes are
N=1, 3, 4, 7, 9, 12, . . . .
[0005] Clearly, to optimise the spectrum efficiency of a given
system, it is desirable to use an as small cluster reuse factor as
possible. However, unless spread spectrum or space division
multiplexing techniques are used, employing small reuse factors may
not be possible since the impact of co-channel interference from
neighbouring cells may become too severe. That is, the impact of
co-channel interference may potentially wreck the ability of the
receivers in the different cells to demodulate and recover their
intended data meeting quality of service expectations. To
circumvent this problem and to gain control over the emission and
impact of co-channel interference reuse factors larger than one are
typically used in many systems in real life.
[0006] Employing a fixed reuse factor larger than one automatically
implies that only a portion of the available system bandwidth is
offered to any mobile station in a given cell. This is clearly,
both from a network point-of-view as well as from a user
perspective, non-advantageous for many reasons. A small selection
of such reasons are: [0007] The maximum peak throughput rate is
reduced. [0008] The mobile station exposure to co-channel
interference increases as the transmission time increases. Hence,
the probability that base stations in nearby cells simultaneously
transmits packets to different users using the same channel
resources increases. [0009] Base station emission period of
interference into neighbouring cells increases. [0010] The
accessibility of the channel resource is reduced. Serving many
mobile stations, the delay in the base station may become
substantial. This will be due to both the actual transmission time
but also to the time required for retransmissions. [0011] Linked to
the reduced peak data rate and the deteriorated channel
accessibility is also the risk that the user perception of the
air-interface as being slow may increase.
[0012] One example of frequency planning is disclosed in the U.S.
Pat. No. 6,498,934. Enhanced path-loss estimates are here used for
assigning channels to different base stations. The path-loss
estimates are obtained by instructing mobile stations being
connected to the system to measure certain neighbouring cell
signals and to lock the mobile stations power to enable
synchronized measurements in neighbouring base stations. From these
measurements, statistics on path-loss estimates are calculated,
which in turn are used for improving the frequency planning.
[0013] In the published US patent application 2003/0013451 A1, a
method is disclosed, where the reuse plan for the cells of a
communications system is dynamically redefined. Based on a number
of factors, such as the observed interference levels, loading
conditions, system requirements etc, the reuse plan for the
division of resources to the different cells can be adapted. The
publication also discloses methods for efficient allocation of
resources within the available set of resources for each cell.
[0014] A problem with the reuse plan adaptation presented in US
2003/0013451 A1 is that the entire communications system has to
involved in the adaptation. Resources that are influenced by the
adaptation have to be unused and system configuration data has to
be updated throughout the entire system before the new reuse plan
can be utilised. This problem makes it less advantageous to use the
adaptation ideas, at least for adapting to short-term changes in
the communications system.
SUMMARY
[0015] A general problem with prior-art resource allocation is that
the radio resources can not be efficiently utilised in the view of
the actual interference situation as experienced by a mobile
station at a specific location and at a specific time.
[0016] A general object of the present invention is thus to provide
resource allocation devices and methods improving the radio
resource utilisation efficiency. A further object with the present
invention is to utilise local and present signal quality to improve
the radio resource utilisation efficiency. Another further object
with the present invention is to allow for allocation adaptation on
very short terms.
[0017] The above objects are achieved by methods and arrangements
according to the enclosed claims. In general, radio resources are
allocated to communication between a mobile station and a base
station. The available set of radio resources may comprise radio
resources primarily assigned to a neighbouring cell if the mobile
station experience an instantaneous low level of co-channel
interference from such neighbouring cells. The presence of
co-channel interference is preferably deduced from signal quality
measurements of pilot signals. The allocation may concern uplink
and/or downlink communication. Devices for performing the
measurements are located in the mobile station, while devices for
performing the evaluation, selection and actual allocation can be
placed in different parts of the communications system--in the
mobile station, in a base station or in a core network node, or as
distributed means.
[0018] An advantage of the present invention is that the overall
radio resource utilisation may be increased. Furthermore,
fluctuations of resource demands on short-term time-scales can be
handled efficiently.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The invention, together with further objects and advantages
thereof, may best be understood by making reference to the
following description taken together with the accompanying
drawings, in which:
[0020] FIG. 1 is a schematic illustration of a cellular
communications system;
[0021] FIG. 2A is a schematic illustration of reuse of radio
resources in a cellular communications system;
[0022] FIG. 2B is a diagram illustrating division of radio resource
space into subsets;
[0023] FIG. 3 is a schematic illustration of an embodiment of a
cellular communications system operating according to the present
invention;
[0024] FIG. 4A is a block diagram of embodiments of a base station
and a mobile station according to the present invention;
[0025] FIG. 4B is a block diagram of other embodiments of a base
station and a mobile station according to the present
invention;
[0026] FIG. 4C is a block diagram of embodiments of a core network,
a base station and a mobile station according to the present
invention;
[0027] FIG. 4D is a block diagram of other embodiments of a core
network, a base station and a mobile station according to the
present invention;
[0028] FIG. 5 is an illustration trying to visualise the
disintegration of the conventional reuse concept as a result of the
present invention; and
[0029] FIG. 6 is a flow diagram of basic steps of an embodiment of
a method according to the present invention.
DETAILED DESCRIPTION
[0030] A fundamental reason for considering reuse larger than one
is that it provides means for controlling the impact of co-channel
interference (CCI). Since mobile stations at the rim of cells are
the ones theoretically most likely to be exposed to CCI, the idea
of using a reuse factor larger than one is thus to, at least to
some degree, guarantee throughput in all positions of all cells.
This is of course highly desirable from a network point-of-view
since most mobile stations can be served. However, the approach is
conservative. In some positions of a cell, for example, in the area
close to the base station but potentially also in other sub-areas,
the interference situation may be such that a larger portion of the
spectrum could be used without causing strong co-channel
interference in other neighbouring cells. That is, if only mobile
stations were present in such areas, a smaller reuse factor could
be used. This observation fowls the basis on which the invention
described in the present disclosure takes advantage of. The actual
interference situation in the part of the cell where a mobile
station is present may permit traffic to be conducted using a
larger portion of the system bandwidth than was originally granted
by the reuse scheme primarily applied.
[0031] In order to illustrate this basic idea, a general mobile
communications network will first be discussed. In FIG. 1, a mobile
communications network 1 comprises a core network 10. The core
network 10 is in turn connected 12 to external networks. A number
of base stations 20:1-20:5 are connected to the core network 10.
Each base station 20:1-20:5 is responsible for covering a certain
respective geographical area or cell 30:1-30:5. In the present
disclosure, the cells 30:1-30:5 are, as a matter of illustrative
convenience, represented by hexagons. A mobile station being
situated within a certain, cell will typically be connected to the
communications network via a radio link to the corresponding base
station 20:1-20:5.
[0032] A mobile station being situated at the outer part of a cell
will experience signals having relatively high powers also from
t-adjacent cells. In order to counteract interference between the
different cells, only a part of the totally the available radio
resources is in a typical case used in each cell. In a commonly
used manner, the available resources are divided into a number of
groups, and each cell has the opportunity to use radio resources
within one such group. This is the basic idea of resource reuse.
One typical example is illustrated in FIG. 2A. Here, the radio
resources are divided into three parts, R1, R2, R3, and each cell
is allowed to use one of these sets of radio resources. In the
illustrated example, the so-called reuse factor is 3. One can
immediately notice that the same radio resources are not used in
any adjacent cells, but are used in cells further away.
[0033] FIG. 2B illustrates a volume of the radio resource space. In
this illustration, the radio resource space is spanned by the
quantities time, frequency and code. Depending on the actual radio
techniques used, the totally available radio resource space is
divided into smaller volumes, which are allocated for
communication, uplink or downlink, between a base station and a
mobile station. When a reuse plan is applied, the totally available
radio resource space is divided in a number of part volumes. In
FIG. 2B, the totally available radio resource space is divided into
three parts, R1, R2 and R3, which e.g. could be used as illustrated
in FIG. 2A. The division in FIG. 2B is made in the frequency
dimension, i.e. the radio resources assigned to each cell is
defined by a number of frequencies. However, the definition of the
part resource spaces can be made in any manner, in time dimension,
in code dimension or in any combination thereof. The resource space
can also be extended into more dimensions, such as the spatial
domain.
[0034] FIG. 3 illustrates an embodiment of a mobile communications
system according to the present invention. A number of base
stations 20:1-3 of which only three have reference numbers, are
associated with a respective cell 30:1-3. A set of radio resources
R4 is primarily assigned to base station 20:1, a set of radio
resources R5 is primarily assigned to base station 20:2, and a set
of radio resources R6 is primarily assigned to base station 20:3.
R4, R5 and R6 are typically exclusive in relation to each other
within expected interference distance, i.e. comprise no common
resources if they are likely to give rise to co-channel
interference. However, sets of radio resources further away from
each other may comprise common resources, i.e. the sets are
typically non-exclusive when seen on a larger scale. The sets of
radio resources are typically assigned according to a reuse plan,
but may also be decided in other ways.
[0035] Three mobile stations 40:1-3 are illustrated to be present
within the coverage of cells 30:1 and 30:2. The mobile station 40:1
is situated close to its own base station 20:1 and communicates
with the base station 20:1 by radio resources 50. The mobile
station 40:2 is situated within cell 30:1, but relatively close to
the border to cell 30:2 and communicates with the base station 20:1
by radio resources 51. The mobile station 40:3 is situated within
cell 30:2, but relatively close to cell 30:3, and communicates with
the base station 20:2 by radio resources 52.
[0036] The mobile station 40:1 experiences in general a lot of
radio signals 60 from different base stations within the
communications system. The strongest signals are probably the ones
from the own base station 20:1, but normally, also signals from the
closest other base stations are possible to detect. For the mobile
station 40:1, being situated close to its own base station 20:1,
the signals from the own base station 20:1 are probably much
stronger than the second strongest signals, in this example
probably the signals from base station 20:3. However, for the
mobile station 40:2, the signal strengths from the base stations
20:1 and 20:2 will probably not differ very much. It is obvious for
anyone skilled in the art, that the mobile station 40:2 typically
is more exposed to co-channel interference than the mobile station
40:1. The assignment of radio resources is therefore typically made
considering the worst case, e.g. the mobile station 40:2. However,
for the mobile station 40:1, a higher utilisation of the radio
resources could be of interest.
[0037] According to an embodiment of the present invention, a base
station is allowed to allocate also radio resources that are not
primarily assigned to the base station for use in the entire cell.
In certain cases, i.e. for certain mobile stations situated at
certain locations or having certain interference situations, radio
resources assigned to neighbouring cells can also be utilised. In
other words, with variable resource allocation according to the
present invention, mobile stations can in some situations "borrow"
spectrum from other cells. The condition for this is that the
co-channel interference situation allows so. This is valid in both
uplink and downlink situations.
[0038] In the uplink scenario, and with reference to FIG. 3, mobile
stations are in general allowed to utilise the radio resources
R4-R6 assigned to a certain cell. Mobile station 40:1 and 40:2 can
e.g. communicate with base station 20:1 using radio resources
within R4, while mobile station 40:3 communicates with base station
20:2 using radio resources from R5. However, mobile station 40:1,
which is located close to base station 20:1 and far from e.g. base
station 20:2 (in the radio sense) may also transmit using radio
resources from R5. The reason for this is that the co-channel
interference created at base station 20:2 is quite small due to the
large distance and the fact that mobile station 40:1 probably sends
at low power. The mobile station 40:2, on the other hand, cannot
use radio resources from R5, as this may result in significant
interference at base station 20:2 and corrupt the possibility for
terminals in the corresponding cell 30:2 to transmit to base
station 20:2.
[0039] In the downlink scenario, the situation is similar. To
ensure good performance for mobile station 40:2, downlink
transmission from base station 20:1 to mobile station 40:2 is only
using the resources of R4. However, for the mobile station 40:1,
the situation is somewhat different as it is located far from other
base stations than base station 20:1. Hence, transmission to mobile
station 40:1 from base station 20:1 may use also resources from R5
and R6 (provided that the mobile station 40:1 reports a
sufficiently low interference level on frequencies other than
within R4).
[0040] In order for the base station to decide whether a higher
utilisation of radio resources than primarily assigned may be
considered or not when serving a specific mobile station, the base
station needs to know the interference situation at the mobile
station location when the packet is to actually be transmitted. In
a general case, the mobile station measures quality measures of
signals transmitted from a multitude of base stations. From these
quality measures, an evaluation is made concluding which base
stations of the multitude of base stations that do not risk causing
any significant co-channel interference. In other words, base
stations outside and inside, respectively, a co-channel
interference distance or area relative to the first mobile station
are determined. Radio resources only used by non-interfering base
stations can then be candidates for allocation of communications to
and/or from the mobile station in question.
[0041] It is here important to notice that the set of allowed or
available radio resources to select between is unique for each
mobile terminal and for each situation. The assignments of radio
resources for general use by the different base stations are not
altered. Instead, the rules for allowing utilisation of resources
outside the primarily assigned resources are changed and allows for
using resources primarily assigned to neighbouring cells at certain
interference situations. In this way, there is no need for a
general adaptation of the entire division of the resource space
over the entire communications system coverage area. The use or
"borrowing" of spectrum is made on a temporary basis, connected to
a specific mobile station at a specific situation. The time-scale
of the adaptation can be very fast and may even vary between one
burst and the next. Furthermore, no notifications have to be spread
over the rest of the communications system.
[0042] In most communications systems, packed data transmissions
are typically by nature bursty. This poses a potential problem,
since the mobile station may not be able to establish an accurate
interference situation estimate based on the actual interference
seen at a certain time instant or period in data signals, that is
valid at the time of the base station's actual transmission. In a
preferred embodiment of the present invention, typically in an
Orthogonal Frequency Division Multiplexing (OFDM) based system, the
individual mobile stations measure observed pilot powers. Pilot
tones or more general pilot signals are transmitted on different
sub-carriers or sub-carrier groups from different cells with
different reuse cluster identification numbers. The measured pilot
signal powers for the different reuse cluster groups are preferably
reported prior to that a package is to be sent from the base
station to the mobile station. That is, the spectrum allocation is
decided based on the received pilot powers and not the actual data
traffic. This approach is advantageous since, in contrast to packet
data traffic, the transmission of pilot information from the
different cells is continuous in time.
[0043] If the power of the pilot carriers transmitted in all cells
defines the cells, i.e. no other carrier in a given cell is
transmitted with a higher power than the pilot carriers, the pilot
power measurement report from a mobile station will provide its
serving base station with two important pieces of information.
Worst-case estimates of the interference levels that can be
expected in the neighbouring radio resource spaces, i.e. in all
other resources than the ones primarily assigned by the reuse
scheme. Note that the actual interference situation most likely is
better. Furthermore, it also provides a means for estimating the
absolute path loss from the base station to the mobile station by
comparing the report received signal power in the allocated
frequency band with the known transmitted power. Since the
transmission of pilots in all cells is continuous, the obtained
interference estimates will be conservative. However, of the same
reason making them conservative, they will also be quasi-stationary
thus making them valid at the transmission time of the packet if
the measurement is requested by the base station sufficiently close
in time to the actual transmission time.
[0044] Thus, given a measurement report from a mobile station, the
base station can based on the estimated path loss and some
predefined signal-to-interference ratio (SIR) target calculate what
transmission powers that are needed in each sub-band in order to
convey data to the mobile station with some predefined
quality-of-service. If these calculated power levels can be
accepted, i.e. they are lower than some maximum values ultimately
determined by some network control algorithm or set to some fixed
levels proportional to the maximum allowed power in the primarily
allocated resources, the base station can decide whether the
individual resources can be used or not for data transfer. Finally,
depending on the size of the packet to be conveyed and the number
of resources that can theoretically be allocated for a given mobile
station, the base station can inform the mobile station using for
example some logical control channel what resources to consider in
the next packet transmission.
[0045] The interference estimates transmitted from the mobiles to
the network can also be used to determine the allowed radio
resources for a specific mobile in the uplink. If the mobile
reports a low power level on downlink frequencies other than its
own, e.g. with reference to FIG. 3, mobile station 40:1 is
reporting a low interference level on downlink resources of R5, it
is likely that the mobile is close to its own base station and the
network can decide to let the mobile communicate on multiple
resources in the uplink, i.e. borrow resources from neighbouring
cells. The mobile could also autonomously decide on the bandwidth
to use in the uplink transmission based on downlink measurements,
although it is preferable to involve the network in the decision
process. Activity indicators transmitted from the base stations to
the terminals could also be used to decide on the instantaneous
uplink radio resource use. If base stations in the neighbourhood
all report low traffic intensity in their resources, terminals in
neighbouring cells could borrow these resources for uplink
transmission.
[0046] Although the present disclosure basically involves the
context for frequency reuse and OFDM systems, the use of the
invention is not limited to this case. Other transmission
technologies, e.g. CDMA, and reuse in other dimensions than
frequency is possible.
[0047] FIG. 4A illustrates an embodiment of a communications system
according to the present invention having a mobile station 40 and a
base station 20 operating together according to the ideas of the
present invention. The base station 20 is further connected to a
core network 10 and nodes 70 therein. The mobile station 40
receives a number of signals 60 from surrounding base stations. As
mentioned above, the signals 60 are preferably pilot signals, but
other signals, e.g. containing user data, can also be utilised. The
mobile station 40 comprises means 41 for measuring a quality
measure of the signals 54, 60. This quality measure may be based on
the signal powers, resulting in e.g. a path loss measure, a channel
gain measure or different kinds of interference measures. The
measurements are compiled and transmitted 53 to the base station 20
in a measurement report.
[0048] The base station 20 receives the measurement report. The
base station 20 comprises in this embodiment evaluation means 22
for evaluating the quality measures associated with the different
base stations. More precisely, the evaluation means 22 determines
which of the base stations that pose potential co-channel
interference problems. In other words, it is determined if the
different base stations are inside or outside co-channel
interference distance relative to the mobile station 40. The
co-channel interference distance being defined e.g. by a C/I
threshold ratio. The base station 20 of the present embodiment
further comprises selection means 23 for obtaining a set of radio
resources that the mobile station 40 could be allowed to use. This
available set of resources does of course comprise the radio
resources primarily assigned to the base station 20. Furthermore,
if there are other radio resources that are primarily assigned only
to base stations outside co-channel interference distance, these
radio resources are included in the available set of resources for
the specific mobile station 40. The risk for co-channel
interference is low even if these resources not primarily assigned
to the own base station 20 are used.
[0049] The base station 20 further comprises allocation means 24,
which is responsible for the actual allocation of radio resources
for communication between the mobile station 40 and the base
station 20. In this embodiment, radio resources selected from the
available set of radio resources are allocated for downlink
communication 54. The allocation is performed to give the mobile
station 40 an appropriate quality-of-service in competition with
other mobile stations connected to the same base station 40. Each
of the connected mobile stations may then have their own available
set of resources. By utilising allowed resources that are not
primarily assigned to the base station 20 to mobile stations having
a favourable interference situation, the resources primarily
assigned to the base station 20 can be saved for any mobile
stations being more exposed to co-channel interference. A higher
utilisation degree of the total radio resource can thus be
achieved.
[0050] FIG. 4B illustrates another embodiment of a communications
system according to the present invention. Similar parts as in FIG.
4A are denoted by the same reference numbers and are not in general
discussed any further. In the present embodiment, the mobile
station 40 comprises the measuring means 41. However, in this
embodiment, the mobile station 40 also comprises an evaluation
means 42, which by its functionality resembles the corresponding
means of the base station in previous embodiment. The base station
20 can provide the mobile station 40 with information about
relative emission powers between data and pilot signals. Such
information can be provided not only for the own base station, but
also for base stations that are believed to be within hearing
(radio) distance. A message 55 is sent from the mobile station 40
to the base station 20, which message 55 now comprises information
about which neighbouring base stations that are experienced as
interfering. This information is used in the selection means 23 for
obtaining the available set of radio resources for the mobile
station 40.
[0051] If the mobile station 40 also is provided with information
about the primary assignment of radio resources, also the
functionalities performed by the selection means 23 can be
performed at the mobile station 40 instead, and in such a case, the
mobile station 40 may even suggest which radio resources to use for
the subsequent communication.
[0052] The different functionalities of the method according to the
present invention can be performed at different parts of the
communications system. This means that a device for performing a
procedure according to the present invention typically is a
distributed means. The measurement of the base station signals has
to be performed at the mobile station. However, the remaining steps
can be performed where it is appropriate for each
implementation.
[0053] FIG. 4C illustrates another embodiment of a communications
system according to the present invention. In this embodiment, the
measurements are performed at the mobile station 40 and a
measurement report 53 is provided to the base station 20. However,
in this embodiment, the base station 20 forwards the information to
a node 70 in the core network 10. The node 70 then comprises
evaluation means 72 and selection means 73 in analogy with earlier
embodiments. The available set of radio resources is then
communicated back to the base station 20 as a basis for the final
allocation of the downlink traffic.
[0054] FIG. 4D is to most parts identical to FIG. 4C, but the
available set of radio resources now comprises resources intended
for uplink communication 56. The mobile station 40 measures the
signals from the neighbouring base stations as before and sends a
measurement report to the base stations 20, which forwards the
information to a node 70 in the core network 10. The basic idea
when allocating uplink traffic is that a mobile station that does
not experience interference from other base stations is less likely
to create interference with the same base stations. The node 70 may
e.g. perform an actual C/I estimation and using C/I measures over a
certain threshold as indications of presumed co-channel
interference. The node 70 may preferably also use additional
geographical knowledge about the communications system to refine
the evaluation of the interference situation. Other complementary
information may be activity indicators from neighbouring cells.
[0055] When selecting the available set of radio resources, the
node 70 may also set a maximum emission power that is allowed to be
used for each resource. Such power limitations can then be taken
into account when allocating resources for the uplink communication
56.
[0056] As anyone skilled in the art understands, allocation of
uplink resources and downlink resources can preferably be
combined.
[0057] In a conventional cellular communications system, the
concept of "reuse" is often used. The reuse is then defined with a
cell basis, i.e. each cell is assigned a certain part of the radio
resources. The present invention will, however, disintegrate of the
conventional reuse concept, since each individual mobile station
may have its own set of allowable radio resources. FIG. 5 tries to
illustrate this condition. The figure illustrates a number of cells
30 as hexagons. In the outer part 31, in a radio sense, of each
cell 30, a certain portion of radio resources can be utilised.
Since the risk for interference from neighbouring cells is large, a
"reuse" factor larger than 1 is typically used. In an inner part
33, in a radio sense, of each cell 30, the interference risk is
much lower, and basically all radio resources can be utilised. This
corresponds to a reuse factor of 1. In an intermediate part 32, in
a radio sense, of each cell 30, the risk for interference with
certain base stations is large, while it still is small for other
base stations. This means that some additional resources are
available, as compared with the outer part 31. However, compared
with the inner part 33, there is a restriction in the allowed radio
resources. As anyone skilled in the art understands, there is of
course a smooth transition between these different stages, and the
locations may vary from one cell to another or for one mobile
station to another.
[0058] FIG. 6 illustrates a flow diagram of the basic steps of an
embodiment of a method according to the present invention. This
embodiment corresponds basically to the system illustrated in FIG.
4A. The procedure starts in step 200. In step 202, quality measures
of signals from all base stations within bearable distance are
measured at a mobile station. In step 204, the measurements are
reported to a base station. In step 206, it is evaluated which base
stations are within or outside interfering radio distance with the
mobile station. Based on the result of step 206, an available set
of resources is selected in step 208. This selection comprises
resources primarily assigned to the own base stations as well as
resources assigned only to non-interfering base stations. In step
210, resources from the available set of resources are allocated
for communication between the mobile station and the base stations.
The data is then sent using the allocated resources in step 212.
The procedure ends in step 214.
[0059] The embodiments described above are to be understood as a
few illustrative examples of the present invention. It will be
understood by those skilled in the art that various modifications,
combinations and changes may be made to the embodiments without
departing from the scope of the present invention. In particular,
different part solutions in the different embodiments can be
combined in other configurations, where technically possible. The
scope of the present invention is, however, defined by the appended
claims.
REFERENCES
[0060] U.S. Pat. No. 6,498,934 [0061] US 2003/0013451 A1
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