Technical Field
[0001] The present invention relates to mobile communications devices and networks, p ar
ticularly but not exclusively those operating according to the 3rd Generation
Partnership Project (3GPP) standards or equivalents or derivatives thereof. The
invention has particular although not exclusive relevance to the Long Term Evolution
(LTE) of UTRAN (called Evolved Universal Terrestrial Radio Access Network
(E-UTRAN)), including LTE- Advanced.
Background Art
[0002] In a mobile (cellular) communications network, (user) communication devices (also
known as user equipment (UE), for example mobile telephones) communicate with
remote servers or with other communication devices via base stations. In their commu
nication with each other, communication devices and base stations use licensed radio
frequencies, which are typically divided into frequency bands and/or time blocks.
[0003] In recent times there has been an increasing demand for indoor high-speed mobile
communication and the increasing deployment of small- sized, localised, cells, often
referred to as 'femtocells' or 'pico-cells', operated by base stations that use a low
transmission power is seen one of the inevitable consequences of this trend. Very
small-sized cells, such as femtocells, are generally deployed in a home or small office/
home office (SOHO) environment with the intention of enhancing capacity of the
wider cellular system (e.g. in the manner of a 'hotspot') and/or of compensating for a
coverage hole in a larger conventional cell or 'macro' cell (e.g. at the cell edge).
[0004] In long-term evolution (LTE) or LTE-Advanced, a base station that operates a small
cell such as a femtocell or the like is often referred to as a 'home' base station, home
eNodeB (HeNB), low power node (LPN), pico base station, or femto base station. A
base station that operates a larger conventional cell is often referred to, in LTE, as a
macro base station or Macro eNodeB (MeNB). For the purposes of this document the
terms 'macro base station' and 'home base station' will generally be used.
[0005] Where there is an overlap of coverage between them interference between a small
cell and the larger macro cell (or between a small cell other small cells) can be a major
problem, especially where there is a dense deployment of small cells. This is because
small cells are often closed cells and the home base station operating the small cell
often shares a common channel with the base stations, such as the macro base station,
operating other cells. The uplink (UL) interference from a small cell to a large cell can
be a significant contributor to such interference. Thus, communication throughput in a
macro cell can be reduced undesirably.
[0006] To help mitigate UL interference, it is known for the home base stations that operate
small cells to employ UL power control in which the UL transmit power of mobile
terminals and/or other UEs communicating via the small cells (home UEs / 'HUEs') is
controlled adaptively (e.g. in UL data and control channels such as the Physical Uplink
Shared Channel, 'PUSCH' and Physical Uplink Control Channel, 'PUCCH').
[0007] In many cases, the parameters of UL power control such as the maximum allowed
UE transmit power and/or the target received power (user or cell specific) are
optimized on the basis of the path loss from the home base station or from a commu
nication device in the small cell ('small cell UE') to the macro base station. The path
loss is estimated by the difference between the transmit power of the macro base
station and the received power at the home base station or UE. However, in this path
loss based method, the UL interference from only a single small cell can be considered.
Therefore, as the number of small cells increases, the UL interference is also increased
resulting ultimately in a significant degradation of the UL throughput in the macro cell.
[0008] More recently, a proposal was made for a 'centralised' UL power control method in
which the target received power for home base stations is adaptively set based on an
aggregated resource usage for all small cells in a macro cell. In this more recent
proposal a centralised UL power control algorithm (using a Home eNodeB
Management System, 'HeMS') an algorithm was defined that used the aggregated UL
resource usage (physical resource block, 'PRB', usage) of all home base stations in a
particular macro cell to reduce interference of the home base stations to a macro base
station. Where aggregate resource usage was large, the target received power of all
home base stations was reduced by reducing the transmit power of all user equipment
within the small cell of the home base stations with the intention of reducing overall
interference towards the macro base station. Where aggregate resource usage was
small, the target received power of all home base stations was increased by increasing
transmit power of all user equipment within the small cell of the home base stations
with the intention of improving throughput of home base station users.
[0009] In this way, therefore, it was expected that UL interference between the small cells,
and the larger macro cell, could effectively be suppressed, regardless of the traffic load
in the small cell, while the UL transmit power for the small cells could be maximized.
Summary of Invention
Technical Problem
[0010] There are, however, a number of potential issues associated with the centralised UL
power control method. Firstly, for example, the method has the potential for sig
nificantly high signalling traffic between the home base stations and the HeMS
because the home base stations have to report their UL PRB usage to the HeMS and
because the HeMS has to report the aggregate UL PRB usage to all home base stations
to allow each home base station to determine what their target received power should
be and to control the transmit power of all user equipment within the small cell of that
home base station.
[001 1] Further, the centralised UL power control method requires complex synchronisation
between the home base stations and the HeMS: firstly because all the home base
stations have to synchronise their measurement periods (e.g. using a synchronised
global system time maintained on an "internal timing clock" at each home base
station); and secondly because the HeMS has to synchronise the process of aggregate
UL PRB usage calculation with the UL PRB measurements of the home base stations
and the UL PRB reporting timers.
[0012] Moreover, the centralised UL power control method requires support for extended
signalling and new vendor specific parameters under appropriate broadband network
specifications (e.g. under Technical Report 069, 'TR-069') of the Broadband Forum
(also known as the DSL Forum). Such support may not always be guaranteed, e s
pecially if the HeMS is provided by a third party.
[0013] Still further, the centralised UL power control method can result in an inherent un
fairness between different home base stations because all home base stations are
affected equally regardless of the respective level of interference that each home base
station causes to the macro base station.
[0014] The invention therefore aims to provide a mobile communication system, a mobile
communication device, a communication node and associated methods which
overcome or at least mitigates the above issues.
Solution to Problem
[0015] According to one aspect there is provided a home base station for a communication
system in which a macro base station operates a macro cell, the home base station
comprising: means for operating a cell located at least partially within the macro cell;
means for obtaining information identifying a quantity of home base stations that each
operate at least one respective cell that is located at least partially within the macro
cell; means for determining resource usage via said home base station; means for
setting a target power for said home base station based on said information identifying
a quantity of home base stations and said determined resource usage; and means for
communicating said target power set for said home base station to at least one user
communication device.
[0016] According to one aspect there is provided a base station for a communication system,
the base station comprising: means for operating a cell in which at least one cell
operated by at least one home base station is located at least partially; and means for
providing, to said at least one home base station, information identifying a quantity of
home base stations that each operate at least one respective cell that is located at least
partially within the macro cell to facilitate setting of a target power by said at least one
home base station based on said information identifying a quantity of home base
stations and a resource usage via said at least one home base station.
[0017] According to one aspect there is provided a communication device for a commu
nication system in which a macro base station operates a macro cell in which at least
one cell operated by at least one home base station is located at least partially, the com
munication device comprising: means for communicating with other communication
devices via said at least one cell, operated by said at least one home base station; and
means for setting a transmission power of said communication device, responsive to
receipt from said at least one home base station of information identifying a target
power, whereby to meet said received target power, wherein said information
identifying a target power received from said at least one home base station identifies a
target power that is based on information identifying a quantity of home base stations
operating a cell that is located at least partially in said macro cell and on resource
usage via said at least one home base station from which said target power is received.
[0018] According to one aspect there is provided a method performed by a home base
station in a communication system in which a macro base station operates a macro cell,
the method comprising: operating a cell located at least partially within the macro cell;
obtaining information identifying a quantity of home base stations that each operate at
least one respective cell that is located at least partially within the macro cell; de
termining resource usage via said home base station; setting a target power for said
home base station based on said information identifying a quantity of home base
stations and said determined resource usage; and communicating said target power set
for said home base station to at least one user communication device.
[0019] According to one aspect there is provided a method performed by a base station in a
communication system, the method comprising: operating a cell in which at least one
cell operated by at least one home base station is located at least partially; and
providing, to said at least one home base station, information identifying a quantity of
home base stations that each operate at least one respective cell that is located at least
partially within the macro cell to facilitate setting of a target power by said at least one
home base station based on said information identifying a quantity of home base
stations and a resource usage via said at least one home base station.
[0020] According to one aspect there is provided a method performed by a communication
device of a communication system in which a macro base station operates a macro cell
in which at least one cell operated by at least one home base station is located at least
partially, the method comprising: communicating with other communication devices
via said at least one cell, operated by said at least one home base station; and setting a
transmission power of said communication device, responsive to receipt from said at
least one home base station of information identifying a target power, whereby to meet
said received target power, wherein said information identifying a target power
received from said at least one home base station identifies a target power that is based
on information identifying a quantity of home base stations operating a cell that is
located at least partially in said macro cell and on resource usage via said at least one
home base station from which said target power is received.
[0021] Aspects of the invention extend to corresponding systems, methods, and computer
program products such as computer readable storage media having instructions stored
thereon which are operable to program a programmable processor to carry out a
method as described in the aspects and possibilities set out above or recited in the
claims and/or to program a suitably adapted computer to provide the apparatus recited
in any of the claims.
[0022] Each feature disclosed in this specification (which term includes the claims) and/or
shown in the drawings may be incorporated in the invention independently (or in com
bination with) any other disclosed and/or illustrated features. In particular but without
limitation the features of any of the claims dependent from a particular independent
claim may be introduced into that independent claim in any combination or indi
vidually.
Brief Description of Drawings
[0023] Embodiments of the invention will now be described by way of example only with
reference to the attached figures in which:
[fig.l]Figure 1 schematically illustrates a telecommunication system;
[fig.2]Figure 2 shows a simplified block diagram of a macro base station for the
telecommunication system of Figure 1;
[fig.3]Figure 3 shows a simplified block diagram of a small cell base station for the
telecommunication system of Figure 1;
[fig.4]Figure 4 shows a simplified block diagram of a mobile communication device
for the telecommunication system of Figure 1;
[fig.5]Figure 5 shows a simplified timing diagram illustrating a procedure for im
plementing distributed power management;
[fig.6]Figure 6 shows a simplified timing diagram illustrating a procedure for obtaining
information for use in the distributed power management procedure of Figure 5;
[fig.7]Figure 7 shows a simplified timing diagram illustrating a procedure for obtaining
information for use in the distributed power management procedure of Figure 5; and
[fig.8]Figure 8 shows a simplified timing diagram illustrating a procedure for obtaining
information for use in the distributed power management procedure of Figure 5.
Description of Embodiments
[0024]
Figure 1 schematically illustrates a mobile (cellular) telecommunication system 1 in
which a user of any of a plurality of user communication devices 3-1 to 3-4 can com
municate with other users via one or more of a plurality of base stations 5, 7 including,
in this example, a large cell base station 5 and a plurality of small cell base stations
7-1, 7-2 and 7-3. In the system illustrated in Figure 1, each base station 5, 7 shown is
an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) base station
capable of operating in a multi-carrier environment.
[0025] In Figure 1, the large cell base station 5 comprises a so called 'macro' base station
operating a relatively geographically large 'macro' cell 8. The other, small cell, base
stations 7-1 to 7-3 shown in Figure 1 each comprises a so called 'home' (or 'pico', or
'femto') base station operating a respective small (or 'pico', or 'femto') cell 9-1 to 9-3.
It will be appreciated that each base station 5, 7 may operate a respective plurality of
cells, especially where carrier aggregation is used (e.g. so called primary cells,
'PCells', and/or secondary cells, 'SCells').
[0026] The power used to provide small cells 9 is low relative to the power used for the
macro cell 8 and the small cells 9 are therefore small relative to the macro cell 8. As
shown in Figure 1, in this example the geographical coverage of each of the small cells
9 falls completely within the geographical coverage of the macro cell 8 although it will
be appreciated that they may overlap partially with the geographical coverage of the
macro cell 8.
[0027] The base stations 5, 7, are interconnected with one another by a so-called 'X2'
interface via which the base stations 5, 7 can communicate directly with one another.
[0028] One of the user communication devices 3-4 is operating, as 'macro user equipment
(MUE)', in the macro cell 8 and is served by the macro base station 5. The other com
munication devices 3-1 to 3-3 are each operating, as 'home user equipment (HUE)' in
a respective small cell 9-1 to 9-3, and are each served by a respective home base
station 7-1 to 7-3.
[0029] In the example illustrated in Figure 1, uplink communication from the HUEs 3-1 to
3-3 to their respective home base stations 7-1 to 7-3 causes interference with the uplink
communication of the MUE 3-4 and the uplink communication from the MUE 3-4
causes interference with the uplink communication of one of the HUEs 3-2.
[0030] Advantageously, the mobile (cellular) telecommunication system 1 employs a di s
tributed uplink power control algorithm in which each home base station 7 is able to
individually set a respective uplink target received power based on a calculation r e
flecting their own likely contribution to overall interference. Specifically, respective
uplink target received power is respectively set, at each base station 7, adaptively
based on the location of that home base station 7 and that home base station's own in
dividual uplink physical resource block usage contribution to the overall resource
block usage.
[0031] More specifically, in the calculations used in this example, the respective uplink
target received power (P0_H, d f r each home base station, i, is set in dependence on:
(i) the target received power (Po M) at the macro base station 5, Po M a cell
specific parameter that is broadcasted by a base station as a part of the system in
formation;
(ii) an internal signal to interference plus noise ratio (SINR) parameter (G ) for
that home base station 7;
(iii) a measure of the path loss (LM, between a 'home' user communication
device (HUE) 3-1 to 3-3 of that home base station 7 and the macro base station 5
(modified appropriately by a path loss compensation factor ( M) for the macro base
station 5);
(iv) a measure of the path loss (LH 0 between the 'home' user communication
device (HUE) 3-1 to 3-3 and that home base station 7 (modified appropriately by a
path loss compensation factor (a H) for the home base station 7);
(v) a measure of the home base station's own individual uplink physical resource
block usage (UH i); and
(vi) the number of home base stations 7 in the cell 8 of the macro base station 5
that have active HUEs 3-1 to 3-3.
[0032] The user communication device (HUE) served by the home base station reports the
measured values of Reference Signal Received Power (RSRP) for both the home base
station and the master base station. The home base station calculates LH , by sub
tracting the RSRP from its reference signal power, and LM by subtracting the RSRP
from the reference signal power broadcasted by master base station. The path loss
compensation factor is a cell specific parameter that is provided by higher layers.
[0033] It will be appreciated that, whilst the above set of parameters are particularly useful,
the respective uplink target received power (P0_H, d f r each home base station may be
set based on a different, augmented, or simplified set of parameters and still reflect that
home base station's own likely contribution to overall interference sufficiently. For
example, instead of the number of home base stations 7 in the cell 8 of the macro base
station 5 that have active HUEs, the calculation may be based on the number of home
base stations 7 in the cell 8 of the macro base station 5 regardless of whether they have
active users or not.
[0034] Beneficially, to support implementation of the distributed uplink power control
algorithm the macro base station and home base stations 5, 7 of the communication
system 1, are configured to exchange the number (N) of home base stations having
active home user communication devices (HUEs) 3-1 to 3-3, in the macro cell, via the
X2 interfaces. Advantageously, such an exchange can occur between the macro base
station 5 and each home base station 7 (e.g. via a respective macro base station to
home base station X2 interface). Such an exchange can also occur between the macro
base station 5 and one or more of a subset of the home base stations 7, and between a
home base station 7 that receives the number (N) of home base stations having active
HUEs 3-1 to 3-3 and another home base station 7 (e.g. via a home base station to home
base station X2 interface).
[0035] It can be seen, therefore, that the distributed uplink power control algorithm, helps to
ensure fairer treatment of home base stations in dependence on their own individual
contribution to overall interference in the macro cell.
[0036] This provides a number of advantages over currently proposed systems including, but
not limited to: eliminating (or at least reducing) the need for a home base station
management system (HeMS) for the purposes of UL power control for interference
management; significantly reducing signalling traffic load between the home base
stations and any home base station management system; and eliminating, or at least
mitigating, the need for synchronisation between the home base stations and any home
base station management system.
[0037]
Figure 2 is a block diagram illustrating the main components of the macro base
station 5 shown in Figure 1. The macro base station 5 comprises an E-UTRAN base
station comprising a transceiver circuit 231 which is operable to transmit signals to,
and to receive signals from, the mobile communication devices 3 via a plurality of
antennas 233. The base station 5 is also operable to transmit signals to and to receive
signals from a core network via a network interface 235 and with other macro or home
base stations via an X2 interface 236.
[0038] The operation of the transceiver circuit 231 is controlled by a controller 237 in ac
cordance with software stored in memory 239.
[0039] The software includes, among other things, an operating system 241, a commu
nication control module 242, an X2 communication module 243, and a broadcast com
munication module 245.
[0040] The communication control module 242 is operable to control communication with
the mobile communication devices 3-4 in the macro cell 8 and with the core network
and other base stations via the associated interfaces 235 and 236.
[0041] The X2 communication module 243 forms part of the communication control module
242 and manages the communication with other macro or home base stations via the
X2 interface 236, and the broadcast communication module 245 manages broadcast
communications via the antenna, for example of system information in the form of
system information blocks (SIBs).
[0042]
Figure 3 is a block diagram illustrating the main components of a home base station
7 of shown in Figure 1. Each home base station 7 comprises an E-UTRAN home base
station comprising a transceiver circuit 331 which is operable to transmit signals to,
and to receive signals from, the communication device, 3-1 to 3-3, operating in the cell
9 of that base station via at least one antenna 333. The base station 7 is also operable to
transmit signals to and to receive signals from a core network via a core network via a
network interface 335 and with macro or home base stations via an X2 interface 336.
[0043] The operation of the transceiver circuit 331 is controlled by a controller 337 in ac
cordance with software stored in memory 339.
[0044] The software includes, among other things, an operating system 341, a commu
nication control module 342, an X2 communication module 343, an NMM module
345, HeNB number obtaining module 347, PRB usage determination module 349, path
loss determination module 351, a parameter storage module 353, and a target received
power setting module 355.
[0045] The communication control module 342 is operable to control communication with
the communication devices 3-1 to 3-3 in the cell 9 operated by the home base station 7,
and with the core network and other base stations via the associated interfaces 335 and
336.
[0046] The X2 communication module 343 forms part of the communication control module
342 and manages the communication with other base stations via the X2 interface 336.
[0047] The NMM module 345 handles network monitor mode (NMM) functions such as the
monitoring of system information broadcast in system information blocks (SIBs). The
HeNB number obtaining module 347 obtains the total number of home base stations in
the macro cell 8 and/or the total number of home base stations in the macro cell 8,
having active users. The PRB usage determination module 349 determines uplink PRB
usage (UH i) (and other PRB usage) by the home base station 7. The path loss deter
mination module 351 measures or otherwise determines a path loss measure (LM ) for
communication between a home user communication device (HUE) 3-1 to 3-3 of that
home base station 7 and the macro base station 5 and a measure of the path loss (LH 0
between the home user communication device (HUE) 3-1 to 3-3 and that home base
station 7.
[0048] The parameter storage module 353 stores the other parameters required for the cal
culation of an appropriate target received power including: the target received power
(P0_M) at the macro base station 5; an internal signal to interference plus noise ratio
(SINR) parameter (G ) for that home base station 7; path loss compensation factors ( M,
a H) for the macro base station 5 and home base station 7.
[0049] The target received power setting module 355 sets the target received power based
on: the target received power (POM) t the macro base station 5; the internal signal to
interference plus noise ratio (SINR) parameter (G ) for that home base station 7; the
measure of the path loss (LM ) between a 'home' user communication device (HUE)
3-1 to 3-3 of that home base station 7 and the macro base station 5 (modified appro
priately by a path loss compensation factor (aM) for the macro base station 5); the
measure of the path loss (LH ) between the 'home' user communication device (HUE)
3-1 to 3-3 and that home base station 7 (modified appropriately by a path loss com
pensation factor (a H) for the home base station 7); a measure of the home base station's
own individual uplink physical resource block usage (UH i); and the number of home
base stations 7 in the cell 8 of the macro base station 5 (e.g. that have active HUEs 3-1
to 3-3).
[0050] The target received power setting module 355 also manages the communication
between the home base station 7 and the HUEs 3-1 to 3-3 in its cell 9 to adjust the
transmission power of those HUEs to meet the target received power set by the target
received power setting module 355.
[0051]
Figure 4 is a block diagram illustrating the main components of the user commu
nication devices 3 shown in Figure 1. Each user communication device 3 comprises a
mobile (or 'cell') telephone. The user communication device 3 comprises a transceiver
circuit 451 which is operable to transmit signals to, and to receive signals from, the
base stations 5, 7 via at least one antenna 453 and a user interface 452 for receiving
inputs from and providing outputs to a user.
[0052] The operation of the transceiver circuit 451 is controlled by a controller 457 in ac
cordance with software stored in memory 459.
[0053] The software includes, among other things, an operating system 451, a commu
nication control module 462, and a transmitter power setting module 465.
[0054] The communication control module 442 is operable to control communication with
the base stations 5, 7 and the transmitter power setting module manages commu
nication with the base stations 5, 7 to set the transmitter power of the user commu
nication device 3 in order to fulfil any target received power requirements at the base
stations 5, 7.
[0055]
The operation to apply the distributed uplink power control mechanism will now be
described in more detail, by way of example only, with reference to Figure 5 which is a
simplified timing diagram illustrating the procedure followed by a single home base
station 7-1 implementing the distributed uplink power control mechanism.
[0056] As seen in Figure 5, the home base station 7-1 calculates the path loss at S500, prior
to obtaining, at S501, the number, N, of home base stations 7, in the macro cell 8,
having active users.
[0057] In this example the number, N, of home base stations 7 is obtained from the macro
base station 5 although it will be appreciated that it may be obtained from another
home base station 7. Further it will be appreciated that, instead of the number of home
base stations 7 having active users, the total number of home base stations 7
(regardless of whether or not they have active users) may be obtained and used in the
subsequent calculation of target received power.
[0058] The home base station 7-1 calculates its UL PRB usage at S503 and sets its target UL
received power accordingly at S505. In this example, the target UL received power (P
_H, i) for each home base station, i, is set using the following equation:
[Math.l]
o _ H i = P o _ - i + < M L , - L , i 1 0 H , t 'N ) _
where,
• Po M is the target received power at the macro base station 5;
G is an internal signal to interference plus noise ratio (SINR) parameter for that
home base station i, representing the SINR of a macro served user communication
device (MUE) at the macro base station taking account of the usage of home base
station, i;
• LM is a measure of the path loss between a 'home' user communication device
(HUE) of that home base station, i, and the macro base station 5;
Mis a path loss compensation factor for the macro base station 5;
• LH is a measure of the path loss between the 'home' user communication
device (HUE) and that home base station, i ;
H is a path loss compensation factor for the home base station 7;
• UH i is the measure of the home base station's own individual uplink physical
resource block usage; and
• N is the obtained number of home base stations 7 in the cell 8 of the macro
base station 5 that have active HUEs.
[0059] Once target UL received power has been set at S505 the home base station 7-1 com
municates with the HUE(s) 3-1 in the cell 9-1 of that base station to adjust their
transmission power appropriately whereby to alleviate interference. Typically, the
home base station 7-1 broadcasts the target received power P0_H, I value to all user communication
devices within range, when the target received power is reduced, and the
affected user communication devices reduce their transmission power by a corre
sponding amount thereby reducing interference to the macro base station. Specifically,
based on the P H , each user communication device (HUE) will calculate its transmit
power as follows:
[Math.2]
Ptx = n {P x ,10 log 1 ( ) + P + a ·PL + A + f c }
where Ptx [dBm] is the transmit power of the physical uplink shared channel
(PUSCH), PM x [dBm] is the configured maximum UE transmit power, M is the
bandwidth of the PUSCH resource assignment expressed in the number of physical
resource blocks (PRB) scheduled for a user and a subframe, P [dBm] is target received
power (user or cell specific), a is a cell-specific path loss compensation factor, PL [dB]
is a downlink path loss estimate calculated in the UE, AT [dB] is a user-specific
parameter that depends on the Modulation and Coding Scheme (MCS), and fc [dB] is a
user-specific correction. As a whole, the power control equation consists of open loop
(P + a.PL) and closed loop (fc) components. The open loop component decides the
target received power for all users and is compensated by the slow change of the path
loss including shadowing, while the closed loop is used for user-specific adjustments.
[0060] It will be appreciated that whilst the procedure has been described in a sequential
order some of the steps may occur in parallel or in a different order. For example the
determination of path loss (S500) and UL PRB usage (S505) may occur at any ap
propriate time prior to setting the uplink target received power (S507).
[0061]
A derivation of the target UL received power equation (1) will now be provided to
assist the skilled reader.
[0062] The derivation starts with an equation for desired UL received power, SM,i, at the
macro base station 5 for a macro served user device, and an equation for UL in
terference power, IH ,received at the macro base station 5 from a home user commu
nication device 3-1 to 3-3 as follows:
[Math.3]
Where equations (2) and (3) are written below using linear quantities, rather than of dB
quantities, with tildes denoting the linear quantities. As explained above: , P0_H, I the
target UL received power for each home base station, i ; POMis the target received
power at the macro base station 5; LM is a measure of the path loss between a 'home'
user communication device of that home base station, i, and the macro base station 5; a
M is a path loss compensation factor for the macro base station 5; LH is a measure of
the path loss between the 'home' user communication device and that home base
station, i; and His a path loss compensation factor for the home base station 7.
[0063] The (linear) SINR of the macro served user communication device (MUE) 3-1 at the
macro base station 5, taking into account a usage factor of each home base station 7, is:
[Math.4]
Where, as explained above: N is the number of home base stations 7 in the macro
cell (typically, but not essentially, comprising the number having active users); and UH.
is a measure of the individual uplink physical resource block usage of the home base
station, i.
[Math.5]
Substituting for SM i and I J and re-arranging gives
N p n p T
[0065] A constraint is then applied in the form of an operator configurable parameter, b, that
is constant for all home base stations and lies in the range not smaller than 0 and not
greater than 1 such that:
[Math.6]
[0066] Thus if b = 0 then this implies that the (linear) UL interference power, IH ,received at
the macro base station 5 is constant for all home base stations. If, on the other hand, b
> 0, it implies that the received power target of each home base station can be reduced
in proportion to (U H,i)p (and hence that home base stations with lower PRB usage can
be allowed to use a higher received power target).
[0067] The SINR condition of equation (5) may thus be rewritten as:
[Math.7]
p Ja l
T (7)
i=l
[0068] Taking log10 of each side and re-arranging gives:
[Math. 8]
101og (c )= P0_M + MLM - T - LM -lOlo. 8)
[0069] And then substituting for C gives:
[Math.9]
f N
- p
M - Ti + MLM - L -101og ¾ ¾ (9)
v = 1 J
[0070] As expected, if b=0 then this results in the same target received power being applied
at all home base stations based on a summation (aggregation) of UL PRB usage for all
home base stations. However, setting b= 1 results in equation (1) as repeated below:
[Math. 10
[0071] Thus, instead of a target received power that is the same for all home base stations,
based on a summation (aggregation) of UL PRB usage, the target received power
varies in dependence on the individual PRB usage at a particular home base station -
(i.e. UH
iN is used instead of
[
[0072]
As explained above, in order for a home base stations 7 to do the calculation for
setting the target received power it is necessary for them to obtain an estimated or
actual number, N, of home base stations in the macro cell 8. There are a number of
ways in which this can be achieved.
[0073] Re-use of Current Information Elements (IEs) of X2 Setup Request Message
In one example, as illustrated in Figure 6, the information on the number, N, of home
base stations (either home base stations having active users or all home base stations)
in the macro cell 8 is provided in an appropriate X2 message from the macro base
station 5 to the home base station 7 doing a calculation for setting the target received
power, or from another home base station 7 to that home base station 7. Specifically, in
this example, the distributed UL power control technique beneficially makes use of an
existing X2 message - the X2 Setup Request - to inform the home base station 7 doing
the calculation. The X2 Setup Request Message is defined in section 9.1.2.3 of the 3rd
Generation Partnership Project (3GPP) Technical Standard (TS) 36.423.
[0074] As defined in 3GPP TS 36.423, the X2 Setup Request Message message is sent by an
eNB to a neighbouring eNB to transfer the initialisation information for a Transport
Network Layer 'TNL' association. The contents of the current version of the X2 Setup
Request Message are summarised below in Tables 1(a) and 1(b) below.
[0075] Unlike the current X2 Setup Request Message, however, the number, N, of home
base stations in the macro cell 8 is provided by using the 'maxnoofNeighbours' as part
of the Neighbour-Information information element (i.e. instead of the current
maximum value of 512). The E-UTRAN Cell Global Identifier (ECGI) is sent to the
home base station 7 in the X2 Setup Request Message in order to allow the home base
station 7 to identify the macro base station 5 operating the cell 8 in which the home
base stations 7, in the list of neighbouring cells in the X2 Setup Request Message, are
located thereby allowing the home base station 7 setting the target received power to
determine how many home base stations 7 there are in the cell 8 of that macro base
station 5.
[0076] Specifically, as set out in section 9.2. 14 of 3GPP TS36.423 (repeated in Table 2
below) the leftmost bits of the E-UTRAN Cell Identifier, on which the ECGI referred
to in Table 1(a) is based, correspond to the value of the eNB ID IE contained in the
Global eNB ID IE defined in and 9.2.22 of 3GPP TS36.423 (repeated in Table 3
below). The Macro eNB ID it is equal to the 20 leftmost bits of the value of the EUTRAN
Cell Identifier IE contained in the ECGI IE while the Home eNB ID is equal
to the full value (all 28 bits) of the E-UTRAN Cell Identifier IE contained in the ECGI
IE.
[0077]
[Table 1(a)]
Table 1(a)
[0078] [Table 1(b)]
Table 1(b)
[0079]
[Table 2]
Table 2
[0080] [Table 3]
Table 3
[0081] New IE in current X2 Setup Request Message
In a variation of the above example, as illustrated in Figure 7, a new dedicated in
formation element is provided in the X2 Setup Request message to carry the value of
the number, N, of home base stations in the macro cell 8 (either home base stations
having active users or all home base stations). The name of such a new dedicated in
formation element is, of course, somewhat arbitrary but it is envisaged that it would be
called 'NumofHeNBinMacro' or the like as set out in Table 4 below which is a
modified extract of Table 1(a). It will be appreciated that it may be mandatory for the
macro base station 5 to include such an IE in the X2 Setup Request message with an
optional requirement for the home base stations to include it in the X2 Setup Request
message for exchange between home base stations 7.
[0082] [Table 4]
Table 4
[0083] Using Network Monitoring Mode (NMM
In another variation, as illustrated in Figure 8, the home base stations 7 could advan
tageously make use of the so called 'Network Monitoring Mode' (NMM) to obtain the
number, N, of home base stations in the macro cell 8. It will be appreciated that this
could be provided in addition to or as an alternative to one or more of the other
methods for obtaining the number, N, of home base stations7 in the macro cell 8.
[0084] In this case the home base stations 7 would use the Network Monitoring Mode
(NMM) to acquire the information on neighbouring intra-frequency cells that is
broadcast by a macro base station 5, using the fourth type of system information block
(SIB4 - IE 'SystemInformationBlockType4'), as illustrated in Tables 5(a) to 5(c)
below, for the purposes of intra-frequency cell re-selection, as set out in section 6.3.1
of 3GPP TS 36.331. The IE SystemInformationBlockType4 contains neighbouring cell
related information relevant for intra-frequency cell re-selection. The IE includes cells
with specific re- selection parameters as well as blacklisted cells and is illustrated in
Tables 5(a) to 5(c) below
[0085] However, because SIB4 information only provides a physical cell ID ('physCellld')
list, the home base station 7 beneficially differentiates between the PCI list of macro
base stations 5 and the PCI list of home base stations 7. Specifically, before starting the
NMM procedure, a network management system splits the PCI resources, based on the
cell type information, so that macro base stations 5 will be assigned a different PCI
range compared to the PCI range allocated to home base stations 7. In this way,
therefore, when listening to the SIB4 information of neighbouring cells 9, a home base
station can differentiate between the PCI ranges of the macro base stations and home
base stations in order to identify home base stations and thus obtain the number of
neighbouring home base stations in the cell 8 of the serving macro base station 5.
[0086]
[Table 5(a)]
SystemlnformationBlockType4 information element
- ASM START
SystemlnformationBlockType4 ::= SEQUENCE {
intraFreqNeighCellList IntraFreqNeighCellList
OPTIONAL, - Need OR
intraFreqBlackCellList IntraFreqBlackCellList
OPTIONAL, - Need OR
csg-PhysCellldRange PhysCellldRange
OPTIONAL, - Cond CSG
lateNonCriticalExtension OCTET STRING
OPTIONAL - Need OP
}
IntraFreqNeighCellList ::= SEQUENCE (SIZE (1 ..maxCelllntra)) OF IntraFreqNeighCelllnfo
IntraFreqNeighCelllnfo ::= SEQUENCE {
physCellld PhysCellld,
q-OffsetCell Q-OffsetRange,
}
IntraFreqBlackCellList ::= SEQUENCE (SIZE ( 1 ..maxCellBlack)) OF PhysCellldRange
—ASN1 STOP
Table 5(a)
[0087] [Table 5(b)]
SystemInformationBlockType4field descriptions
csg-PhysCellldRange
Set of physical cell identities reserved for CSG cells on the frequency on which this field was received.
The received csg-PhysCellldRange applies if less than 24 hours has elapsed since it was received and
the UE is camped on a cell of the same primary PLMN where this field was received. The 3 hour validity
restriction (section 5.2.1 .3} does not apply to this field. The UE shall not apply any stored csg-
PhysCel!ldRange when it is in any cell selection state defined in TS 36.304 [4].
intraFreqBlackCellList
List of blacklisted intra-frequency neighbouring cells.
intraFreqNeighbCellList
List of intra-frequency neighbouring cells with specific ceil re-selection parameters.
q-OffsetCell
Parameter "Qoffsets,-" in TS 36.304 [4],
Table 5(b)
[0088] [Table 5(c)]
Table 5(c)
[0089]
Detailed embodiments have been described above. As those skilled in the art will ap
preciate, a number of modifications and alternatives can be made to the above em
bodiments and variations whilst still benefiting from the inventions embodied therein.
[0090] In the above embodiments, an essentially mobile telephone based telecommunications
system was described. As those skilled in the art will appreciate, the
signalling techniques described in the present application can be employed in other
communications system. Other communications nodes or devices may include user
devices such as, for example, personal digital assistants, laptop computers, web
browsers, etc. As those skilled in the art will appreciate, the system can be used to
provide coverage in a network having one or more fixed computing devices as well as
or instead of the mobile communicating devices.
[0091] In the embodiments described above, the base stations 5, 7 and mobile commu
nication devices 3 each include transceiver circuitry. Typically, this circuitry will be
formed by dedicated hardware circuits. However, in some embodiments, part of the
transceiver circuitry may be implemented as software run by the corresponding
controller.
[0092] In the above embodiments, a number of software modules were described. As those
skilled in the art will appreciate, the software modules may be provided in compiled or
un-compiled form and may be supplied to the base stations or the user communications
devices as a signal over a computer network, or on a recording medium. Further, the
functionality performed by part or all of this software may be performed using one or
more dedicated hardware circuits.
[0093] In each embodiment described above, processing of the embodiment may be
executed by a program, software, or a computer-readable storage medium that is coded
with a computer-executable command. The storage medium includes not only portable
recording media such as optical discs, floppy (a trademark) disks, and hard disks, but
also networks and other transmission media that record and keep data temporarily.
[0094] This invention has been described above by way of the embodiment, but this
invention is not limited to the embodiment described above. Various changes that can
be understood by a person skilled in the art can be made to the configuration and
details of this invention within the scope of this invention. Various other modifications
will be apparent to those skilled in the art and will not be described in further detail
here.
[0095] This application is based upon and claims the benefit of priority from United
Kingdom patent application No. 1417245.6, filed on September 30, 2014, the
disclosure of which is incorporated herein in its entirety by reference.
PCT/JP2015/004765

Claims
1.A home base station for a communication system in which a macro
base station operates a macro cell, the home base station comprising:
means for operating a cell located at least partially within the macro
cell;
means for obtaining information identifying a quantity of home base
stations that each operate at least one respective cell that is located at
least partially within the macro cell;
means for determining resource usage via said home base station;
means for setting a target power for said home base station based on
said information identifying a quantity of home base stations and said
determined resource usage; and
means for communicating said target power set for said home base
station to at least one user communication device.
A home base station as claimed in claim 1 wherein said obtaining
means is operable to obtain said information from said macro base
station that operates said macro cell.
A home base station as claimed in claim 2 wherein said obtaining
means is operable to obtain said information over an X2 interface with
said macro base station.
A home base station as claimed in claim 3 wherein said obtaining
means is operable to obtain said information from an X2 Setup Request
message received over an X2 interface.
A home base station as claimed in claim 4 wherein said obtaining
means is operable to obtain said information from at least one
Neighbour Information information element (IE) in said X2 Setup
Request message.
A home base station as claimed in claim 5 wherein said obtaining
means is operable to obtain said information by determining said
quantity from respective Neighbour Information for each of a plurality
of different base station reported in said X2 Setup Request message.
A home base station as claimed in claim 6 wherein said obtaining
means is operable to distinguish between Neighbour Information for a
home base station, and Neighbour Information for a macro base station,
in said X2 Setup Request message by reference to a respective global
identifier (e.g. a E-UTRAN Cell Global Identifier (ECGI)) provided in
the Neighbour Information for each base station whereby to determine
PCT/JP2015/004765
said quantity.
A home base station as claimed in claim 4 or 5 wherein said obtaining
means is operable to obtain said information from at least one in
formation element (IE) dedicated to reporting said quantity of home
base stations.
A home base station as claimed in any of claims 2 to 8 wherein said
obtaining means is operable to obtain said information from system in
formation broadcast by said macro base station.
A home base station as claimed in claim 9 wherein said obtaining
means is operable to obtain said system information provided is
provided in a system information block (SIB).
A home base station as claimed in claim 10 wherein said obtaining
means is operable to obtain said SIB is a SIB type (e.g. SIB type 4
under the 3GPP standards) dedicated to providing neighbouring cell
related information (e.g. neighbouring cell related information relevant
for intra-frequency cell re-selection).
A home base station as claimed in any of claims 1 to 11 wherein said
means for determining means is operable to determine uplink resource
usage via said home base station.
A home base station as claimed in any of claims 1 to 12 wherein said
means for determining means is operable to determine physical
resource block usage via said home base station.
A home base station as claimed in any of claims 1 to 13 wherein said
means for setting a target power is operable to set said target power for
said base station further based on at least one of the following:
a target received power at the macro base station;
an internal signal to interference plus noise ratio (SINR) parameter
for the home base station;
a measure of the path loss between a user communication device
served by the home base station and the macro base station;
a path loss compensation factor for the macro base station;
a measure of the path loss between a user communication device
served by the home base station and the home base station; and
a path loss compensation factor for the home base station.
A home base station as claimed in any of claims 1 to 14 wherein said
target power set for said base station is an uplink received target power.
A home base station as claimed in any of claims 1 to 15 wherein said
means for setting a target power is operable to set said target power for
WO 2016/051712 PCT/JP2015/004765
said base station based on an equation.
[Claim 17] A home base station as claimed in claim 16 wherein said means for
setting a target power is operable to set said target power for said base
station based on an equation.
[Claim 18] A home base station as claimed in claim 17 wherein said means for
setting a target power is operable to set said target power for said base
station based on the followin equation:
where Po H is the target received power at the home base station; P _M
is the target received power at the macro base station; G is an internal
signal to interference plus noise ratio (SINR) parameter for the home
base station i ; LM is a measure of the path loss between a user commu
nication device served by that home base station, i, and the macro base
station; Mis a path loss compensation factor for the macro base
station; LH i is a measure of the path loss between the user commu
nication device served by the home base station and the home base
station; H is a path loss compensation factor for the home base station;
UH, i is the measure of the home base station's own individual uplink
physical resource block usage; and N is the obtained quantity of home
base stations.
[Claim 19] A home base station as claimed in any of claims 1 to 18 wherein said
quantity of home base stations obtained that said obtaining means is
operable to obtain is a quantity of home base stations that each operate
at least one respective cell that is located at least partially within the
macro cell, and that is serving at least one active communication
device.
[Claim 20] A base station for a communication system, the base station
comprising:
means for operating a cell in which at least one cell operated by at least
one home base station is located at least partially; and
means for providing, to said at least one home base station, information
identifying a quantity of home base stations that each operate at least
one respective cell that is located at least partially within the macro cell
to facilitate setting of a target power by said at least one home base
station based on said information identifying a quantity of home base
stations and a resource usage via said at least one home base station.
[Claim 21] A communication device for a communication system in which a
WO 2016/051712 PCT/JP2015/004765
macro base station operates a macro cell in which at least one cell
operated by at least one home base station is located at least partially,
the communication device comprising:
means for communicating with other communication devices via said at
least one cell, operated by said at least one home base station; and
means for setting a transmission power of said communication device,
responsive to receipt from said at least one home base station of in
formation identifying a target power, whereby to meet said received
target power, wherein said information identifying a target power
received from said at least one home base station identifies a target
power that is based on information identifying a quantity of home base
stations operating a cell that is located at least partially in said macro
cell and on resource usage via said at least one home base station from
which said target power is received.
[Claim 22] A communication system comprising a home base station according to
any of claims 1 to 19, a macro base station comprising a base station
according to claim 20, and a communication device according to claim
21.
[Claim 23] A method performed by a home base station in a communication
system in which a macro base station operates a macro cell, the method
comprising:
operating a cell located at least partially within the macro cell;
obtaining information identifying a quantity of home base stations that
each operate at least one respective cell that is located at least partially
within the macro cell;
determining resource usage via said home base station;
setting a target power for said home base station based on said in
formation identifying a quantity of home base stations and said de
termined resource usage; and
communicating said target power set for said home base station to at
least one user communication device.
[Claim 24] A method performed by a base station in a communication system, the
method comprising:
operating a cell in which at least one cell operated by at least one home
base station is located at least partially; and
providing, to said at least one home base station, information
identifying a quantity of home base stations that each operate at least
one respective cell that is located at least partially within the macro cell
WO 2016/051712 PCT/JP2015/004765
to facilitate setting of a target power by said at least one home base
station based on said information identifying a quantity of home base
stations and a resource usage via said at least one home base station.
[Claim 25] A method performed by a communication device of a communication
system in which a macro base station operates a macro cell in which at
least one cell operated by at least one home base station is located at
least partially, the method comprising:
communicating with other communication devices via said at least one
cell, operated by said at least one home base station; and
setting a transmission power of said communication device, responsive
to receipt from said at least one home base station of information
identifying a target power, whereby to meet said received target power,
wherein said information identifying a target power received from said
at least one home base station identifies a target power that is based on
information identifying a quantity of home base stations operating a
cell that is located at least partially in said macro cell and on resource
usage via said at least one home base station from which said target
power is received.
[Claim 26] A computer program product comprising computer implementable in
structions for causing programmable processing apparatus to perform a
method according to any of claims 23 to 25.