Description
Title of Invention: COMMUNICATION CONTROL METHOD,
COMMUNICATION SYSTEM, AND MANAGEMENT SERVER
Technical Field
[0001] The present invention relates to a communication control method, a communication
system, and a management server.
Background Art
[0002] In recent years, a heterogeneous network has been proposed as a next-generation
communication network. The heterogeneous network is a network in which a plurality
of kinds of small-to-medium-sized base stations coexist in a macro cell by performing
underlay transmission or spectrum sharing. The small-to-medium-sized base stations
involve a RRH (Remote RadioHead) cell base station, a hotzone base station
(Pico/micro cell eNB), a femtocell base station (Home eNB), a relay node (relay base
station) and the like.
[0003] In such a heterogeneous network, there is a concern that, when different base
stations, such as a macro cell base station and a femtocell base station, for example,
use the same frequency, improvement of an area capacity is hindered due to the oc
currence of interference. Regarding such a concern, Patent Literature 1 and Patent
Literature 2, for example, disclose techniques to overcome the interference issue
between different transmitting devices.
Citation List
Patent Literature
[0004] PTL 1: Japanese Patent Laid-open No. 2009- 159452
PTL 2: Published Japanese Translation No. 2009-542043 of PCT International Pub
lication
Summary of Invention
[0005] According to one exemplary embodiment, the disclosure is directed to a management
server in a network including a first transmitting device configured to communicate
with a first receiving device and a second transmitting device configured to com
municate with a second receiving device, the management server comprising: a
network interface configured to receive a parameter corresponding to a level of im
provement of communication quality at the second receiving device; a processor
configured to calculate an allowable interference amount at the first receiving device
based on the parameter, wherein the network communication unit is configured to
output the calculated allowable interference amount.
[0006] The second transmitting device and the second receiving device may communicate
using a frequency that overlaps with a frequency used for communication between the
first transmitting device and the first receiving device.
[0007] The network interface may be configured to receive management information in
dicating a state of a cell formed by the first transmitting device.
[0008] The processor may be configured to control communication in the cell formed by the
first transmitting device based on the received management information.
[0009] The network communication unit may be configured to output the calculated
allowable interference amount to a second management server that controls commu
nications between the second transmitting device and the second receiving device.
[0010] The processor may be configured to calculate a maximum allowable interference
amount based on the parameter, and the allowable interference amount may be
calculated to be less than the maximum allowable interference amount.
[001 1] The processor may be configured to set at least one of a transmitting power of the
first transmitting device and a transmission rate of the first transmitting device based
on the allowable interference amount.
[0012] The processor may be configured to calculate the allowable interference amount
based on at least one or more of a reception power at the first receiving device, a
reception power at the second receiving device, interference from the first transmitting
device at the second receiving device, interference from the second transmitting device
at the first transmitting device, a power of the first receiving device and a power of the
second receiving device.
[0013] According to another exemplary embodiment, the disclosure is directed to
management server in a network including a first transmitting device configured to
communicate with a first receiving device and a second transmitting device configured
to communicate with a second receiving device, the management server comprising: a
processor configured to calculate a parameter corresponding to a level of improvement
of communication quality at the second receiving device; a network interface
configured to transmit the calculated parameter to a another management server, and
receive an allowable interference amount at the first receiving device from the another
management server, wherein the processor is configured to control communications
between the second transmitting device and the second receiving device based on the
allowable interference amount.
[0014] The second transmitting device and the second receiving device may communicate
using a frequency that overlaps with a frequency used for communication between the
first transmitting device and the first receiving device.
[0015] The network interface may be configured to receive management information in
dicating a state of a cell formed by the second transmitting device.
[0016] The processor may be configured to control communication in the cell formed by the
second transmitting device based on the received management information.
[0017] The processor may be configured to determine whether to improve the receiving
communication quality based on a comparison between a current communication
quality and a desired communication quality.
[0018] The processor may be configured to calculate the parameter based on a relationship
between the current communication quality and the desired communication quality.
[0019] The relationship between the current communication quality and the desired commu
nication quality may be a ratio between the desired communication quality and the
current communication quality.
[0020] The processor may be configured to control communications between the second
transmitting device and the second receiving device so that an amount of interference
caused by the second transmitting device at the first receiving device is less than the
allowable interference amount.
[0021] According to another exemplary embodiment, the disclosure is directed to network
comprising: a first management server configured to control communications between
a first transmitting device and a first receiving device; a second management server
configured to control communications between a second transmitting device and a
second receiving device; a first processor, at the second management server,
configured to calculate a parameter corresponding to a level of improvement of com
munication quality at the second receiving device; a first network interface, at the
second management server, configured to transmit the calculated parameter to the first
management server; a second processor, at the first management server, configured to
calculate an allowable interference amount at the first receiving device based on the
parameter; a second network interface, at the first management server, configured to
transmit the calculated allowable interference amount to the second management
server, wherein the processor of the second management server is configured to control
communications between the second transmitting device and the second receiving
device based on the allowable interference amount.
[0022] According to another exemplary embodiment, the disclosure is directed to method of
controlling communications in a network including a first management server
configured to control communications between a first transmitting device and a first
receiving device and a second management server configured to control commu
nications between a second transmitting device and a second receiving device, the
method comprising: calculating, at the second management server, a parameter corre
sponding to a level of improvement of communication quality at the second receiving
device; transmitting the calculated parameter from the second management server to
the first management server; calculating, by the first management server, an allowable
interference amount at the first receiving device based on the parameter; transmitting
the calculated allowable interference amount from the first management server to the
second management server; and controlling communications between the second
transmitting device and the second receiving device based on the allowable in
terference amount.
Technical Problem
[0023] Assume the case where there are a first network composed of a receiving device and
a transmitting device and a second network, and the first network suffers interference
from the second network. In this case, the receiving quality in the receiving device of
the first network can be improved by increasing the transmission power of the
transmitting device of the first network, for example.
[0024] However, with the increase in the transmission power of the transmitting device of
the first network, the amount of interference from the first network to the second
network increases accordingly. Therefore, it has been difficult to increase the total
capacity of the entire network merely by unilaterally increasing the transmission power
in one local network.
[0025] In light of the foregoing, it is desirable to provide novel and improved commu
nication control method, communication system, and management server capable of
increasing the total capacity of the entire network by controlling a transmission
parameter of each transmitting device of different networks in cooperation between the
networks.
Brief Description of Drawings
[0026] [fig. 1]Fig. 1 is an explanatory view showing an exemplary architecture of a het
erogeneous network;
[fig.2]Fig. 2 is an explanatory view showing an overview of each smallto-
medium-sized base station;
[fig.3]Fig. 3 is an explanatory view showing an exemplary configuration of a commu
nication system according to an embodiment of the present invention;
[fig.4]Fig. 4 is a functional block diagram showing a configuration of a management
server;
[fig.5]Fig. 5 is a sequence chart showing an overall operation in a communication
system;
[fig.6]Fig. 6 is an explanatory view showing a relationship between a receiving quality
improvement level Mreq desired for a second reviving device 20 and an allowable in
terference amount in a first receiving device 20A;
[fig.7]Fig. 7 is an explanatory view showing a relationship between an allowable in
terference amount M' and an average communication capacity in the case of obtaining
the allowable interference amount M' by transmission power control; and
[fig.8]Fig. 8 is an explanatory view showing a relationship between an allowable in
terference amount M' and an average communication capacity in the case of obtaining
the allowable interference amount M' by transmission rate control.
Description of Embodiments
[0027] Hereinafter, preferred embodiments of the present invention will be described in
detail with reference to the appended drawings. Note that, in this specification and the
appended drawings, structural elements that have substantially the same function and
structure are denoted with the same reference numerals, and repeated explanation of
these structural elements is omitted.
[0028] Further, in this specification and the drawings, each of a plurality of structural
elements having substantially the same function is distinguished by affixing a different
alphabetical letter to the same reference numeral in some cases. For example, a
plurality of structural elements having substantially the same function are distinguished
like user equipments 20A, 20B and 20C where necessary. However, when there is no
particular need to distinguish between a plurality of structural elements having sub
stantially the same function, they are denoted by the same reference numeral. For
example, when there is no particular need to distinguish between the user equipments
20A, 20B and 20C, they are referred to simply as the user equipment 20.
[0029] A preferred embodiment of the present invention will be described hereinafter in the
following order.
1. Exemplary Architecture of Heterogeneous Network
2. Overview of Embodiment of Present Invention
3. Detailed Description of Operation by Embodiment of Present Invention
3-1. Determination of Necessity of Receiving Quality Improvement (Step 1)
3-2. Calculation of Receiving Quality Improvement Level Expected Value Mreq
(Step 2)
3-3. Calculation of Allowable interference amount M (Step 3)
3-4. Control of Transmission Power Based on Allowable interference amount M
(Step 4)
4. Advantageous Effects of Embodiment of Present Invention Indicated by
Numerical Analysis Results
5. Supplementary Description
6. Summary
[0030] <1. Exemplary Architecture of Heterogeneous Network>
An embodiment of the present invention is applicable to communication systems in
which a plurality of local networks using the same frequency coexist, for example. An
example of such communication systems is a heterogeneous network.
[003 1] A heterogeneous network is a network in which a plurality of kinds of smallto-
medium-sized base stations coexist in a macro cell by performing underlay
transmission or spectrum sharing. The small-to-medium-sized base stations may be a
RRH (Remote RadioHead) cell base station, a hotzone base station (Pico/micro cell
eNB), a femtocell base station (Home eNB), a relay node (relay base station) and the
like. Note that the underlay transmission is a transmission mode in which a transmitter
and a receiver existing in the range that interferes with each other's communication
link perform communication using the same frequency channel. It is necessary for the
transmitter on the side of making secondary usage of the frequency by the underlay
transmission to adjust the interfering level so that it does not act as critical interference
for the communication link of the one making the primary usage. The architecture of
the heterogeneous network is specifically described below.
[0032] Fig. 1 is an explanatory view showing an exemplary architecture of a heterogeneous
network. Referring to Fig. 1, the heterogeneous network includes a macro cell base
station 10 (which is synonymous with a base station 10), a relay node 30, a hotzone
base station 31, a femtocell base station 32, an RRH cell base station 33 and
management servers 16A and 16B.
[0033] The management server 16A receives management information indicating the state
of a cell formed by the macro cell base station 10 from the macro cell base station 10
and controls communication in the cell formed by the macro cell base station 10 based
on the management information. Likewise, the management server 16B receives
management information indicating the state of a cell formed by the femtocell base
station 32 from the femtocell base station 32 and controls communication in the cell
formed by the femtocell base station 32 based on the management information.
Further, the management servers 16A and 16B have functions for the macro cell base
station 10 and the small-to-medium-sized base stations to operate in cooperation with
each other. Note that the functions of the management server 16 may be incorporated
into the macro cell base station 10 or any one of the small-to-medium-sized base
stations.
[0034] The macro cell base station 10 manages scheduling information of the smallto-
medium-sized base station 30 and the user equipment 20 located inside the macro
cell and can communicate with the small-to-medium-sized base station 30 and the user
equipment 20 according to the scheduling information.
[0035] The hotzone base station 3 1 (a pico cell base station, a micro cell base station) has
the smaller maximum transmission power than the macro cell base station 10 and com
municates with the macro cell base station 10 with use of an interface such as X2 or SI
of a core network. Note that the hotzone base station 31 creates OSG (Open Subscriber
Group) which is accessible from any user equipment 20.
[0036] The femtocell base station 32 has the smaller maximum transmission power than the
macro cell base station 10 and communicates with the macro cell base station 10 with
use of a packet exchange network such as ADSL. Alternatively, the femtocell base
station 32 may communicate with the macro cell base station 10 by a radio link. Note
that the femtocell base station 32 creates CSG (Closed Subscriber Group) which is ac
cessible only from the limited user equipments 20.
[0037] The RRH cell base station 33 is connected with the macro cell base station 10 by an
optical fiber. Thus, the macro cell base station 10 transmits signals to the RRH cell
base stations 33A and 33B installed in geographically different places through the
optical fiber and allows the RRH cell base stations 33A and 33B to transmit signals by
radio. For example, only the RRH cell base stations 33 close to the position of the user
equipment 20 may be used. Note that functions related to a control system are in
corporated into the macro cell base station 10, and optimum transmission mode is
selected according to the distribution of the user equipments 20. [0031]
Fig. 2 shows the overview of the respective small-to-medium-sized base stations
described above. The small-to-medium-sized base stations such as the hotzone base
station 31 and the femtocell base station 32 can increase the total capacity by making
secondary usage of the frequency used by the macro cell base station 10.
[0038] If the transmission power of the femtocell base station 32 increases, the receiving
quality in the user equipment 20D can be improved. However, with the increase in the
transmission power of the femtocell base station 32, the amount of interference from
the femtocell base station 32 to other communication in the macro cell increases ac
cordingly. Therefore, it has been difficult to increase the total capacity of the entire
macro cell merely by unilaterally increasing the transmission power of the femtocell
base station 32.
[0039] Given such circumstances, an embodiment of the present invention has been
invented. According to the embodiment of the present invention, it is possible to
increase the total capacity of the entire network by controlling a transmission
parameter of each transmitting device (e.g. the macro cell base station 10 and the
femtocell base station 32) of different networks in cooperation between the networks.
Such an embodiment of the present invention is described hereinafter in detail.
[0040] <2. Overview of Embodiment of Present Invention>
Firstly, a configuration of a communication system 1 according to the embodiment of
the present invention which is applicable to the above-described heterogeneous
network, for example, is described with reference to Fig. 3.
[0041] Fig. 3 is an explanatory view showing an exemplary configuration of the commu
nication system 1 according to the embodiment of the present invention. Referring to
Fig. 3, the communication system 1 according to the embodiment of the present
invention includes a management server 16A (first management server), a management
server 16B (second management server), a receiving device 20A (first receiving
device), a receiving device 20B (second receiving device), a transmitting device 40A
(first transmitting device), and a transmitting device 40B (second transmitting device).
Note that the receiving device 20A and the receiving device 20B correspond to each
receiving device 20 shown in Fig. 1, the transmitting device 40A corresponds to the
macro cell base station 10 shown in Fig. 1, for example, and the transmitting device
40B corresponds to the femtocell base station 32 shown in Fig. 1, for example.
[0042] The management server 16A controls communication by the transmitting device 40A
and the receiving device 20A, and the management server 16B controls commu
nication by the transmitting device 40B, which makes secondary usage of the same
frequency as the transmitting device 40A, and the receiving device 20B.
[0043] In the communication system 1, as shown in Fig. 3, a radio signal transmitted from
the transmitting device 40A acts as an interference wave in the receiving device 20B,
and a radio signal transmitted from the transmitting device 40B acts as an interference
wave in the receiving device 20A. Therefore, it is important to appropriately control
transmission parameters by the transmitting devices 40A and 40B for optimization of
SINR in the receiving devices 20A and 20B. Hereinafter, after the overall operation in
the communication system 1 is schematically described with reference to Figs. 4 and 5,
each operation is described in detail in "3. Detailed Description of Operation by Em
bodiment of Present Invention".
[0044] Fig. 4 is a functional block diagram showing a configuration of the management
servers 16A and 16B. Referring to Fig. 4, the management server 16A includes a
network communication unit 110, an allowable interference amount calculation unit
120, a transmission parameter setting unit 130, and a communication control unit 140.
Further, the management server 16B includes a network communication unit 210, an
expected value calculation unit 220 (improvement level calculation unit), a
transmission power setting unit 230, and a communication control unit 240. The
network communication unit 110 of the management server 16A is an interface for
communication with the management server 16B and the transmitting device 40A, and
the network communication unit 210 of the management server 16B is an interface for
communication with the management server 16A and the transmitting device 40B. The
other components are described in conjunction with the overall operation in the com
munication system 1, which is described below with reference to Figs. 4 and 5.
[0045] Fig. 5 is a sequence chart showing the overall operation in the communication system
1. Referring to Fig. 5, the overall operation in the communication system 1 includes
the following step 1 to step 4.
[0046] Step 1:
The expected value calculation unit 220 of the management server 16B determines
whether it is necessary to improve the receiving quality of the receiving device 20B. If
it is necessary to improve the receiving quality of the receiving device 20B, the
operation after the step 2 is performed.
[0047] Step 2:
The expected value calculation unit 220 of the management server 16B calculates an
improvement level Mreq of the receiving quality desired for the receiving device 20B.
Then, the calculated Mreq is notified to the management server 16A. Note that the
processing may be performed by a co-operation manager for the management servers
16A and 16B to operate in cooperation with each other. The same applies to the
processing after the step 3.
[0048] Step 3:
The allowable interference amount calculation unit 120 of the management server
16A calculates an ideal allowable interference amount M' in the receiving device 20A
which is necessary for achieving Mreq, and determines an allowable interference
amount M (or an increment M of an allowable interference amount) to be actually
applied from the allowable interference amount M'. Then, the transmission parameter
setting unit 130 sets a transmission parameter (a transmission power or a transmission
rate) of the transmitting device 40A in such a way that the allowable interference
amount M is obtained in the receiving device 20A. Further, the allowable interference
amount M in the receiving device 20A is notified to the management server 16B.
[0049] Step 4:
The transmission power setting unit 230 of the management server 16B sets the
transmission power of the transmitting device 40B according to the allowable in
terference amount M determined by the management server 16A.
[0050] It should be noted that the entity of performing each of the above-described steps is
not particularly limited. For example, the entity of performing each of the above steps
may involve the transmitting device 40A, the transmitting device 40B or the like, and
may not involve the management server 16A or the management server 16B. In more
detail, the transmitting device 40B may perform the first step, the second step and the
four step, and the transmitting device 40A may perform the third step. Further, any one
of the management server 16A, the management server 16B, the transmitting device
40A and the transmitting device 40B may perform all of the above steps.
[0051] <3. Detailed Description of Operation by Embodiment of Present Invention>
Each of the step 1 to the step 4 described above is described in detail hereinbelow.
[0052] (3-1. Determination of Necessity of Receiving Quality Improvement (Step 1))
The expected value calculation unit 220 of the management server 16B determines
that it is necessary to improve the receiving quality of the receiving device 20B in the
following cases, for example.
[0053] Case A:
Case where an actual receiving quality SINR (SINR_secondary) of the receiving
device 20B is lower than a required SINR (SINR_required,secondary) required for the
receiving device 20B. Specifically, case where the following expression 1 is satisfied.
[0054] Expression (1)
[0055] Case B:
Case where a plurality of receiving devices 20B exist under management of the
management server 16B, and the receiving quality SINR (SINR_secondary) of each of
the receiving devices 20B is lower than the required SINR (SINR_required,secondary)
required for each receiving device 20B. Specifically, case where the following ex
pression 2 is satisfied. Note that the suffix i in the expression 2 indicates a commu
nication link of the i-th receiving device 20B managed by the management server 16B.
[0056] Expression (2)
K onda y , i) r q ir d,secondary,(f)
[0057] Case C:
Case where an average SINR of a certain level or higher is necessary (for example,
communication of a particular application such as video transmission in need of QoS
guarantee is expected) in a given communication range, and a capacity (C_secondary)
of a network managed by the management server 16B is insufficient, and improvement
(M times) of the capacity is expected as represented in the following expression 3.
[0058] Expression (3)
[0059] (3-2. Calculation of Receiving Quality Improvement Level Expected Value Mreq
(Step 2))
The expected value calculation unit 220 of the management server 16B calculates the
improvement level Mreq of the receiving quality desired for the receiving device 20B
by the following method, for example. Then, the network communication unit 210 of
the management server 16B notifies the Mreq calculated by the expected value cal
culation unit 220 to the management server 16A.
[0060] Case A: The expected value calculation unit 220 calculates the ratio of
SINR_secondary and SINR_required,secondary as Mreq as represented in the
following expression 4.
[0061] Expression (4)
q = equired ,secondary / se da y
[0062] Case B: The expected value calculation unit 220 calculates the receiving quality im
provement level Mreq for each communication link as represented in the following ex
pression 5.
[0063] Expression (5)
eq i) = N R required,s ondary,(>) / ' N s ondary ,
[0064] Case C: Because the relationship between the capacity C and SINR is generally rep
resented as the following expression 6, the required SINR_required,secondary can be
calculated according to the expression 7. The expected value calculation unit 220 can
calculate Mreq according to the expression 4 or 5 by using the required
SINR_required,secondary.
[0065] Expression (6)
C = log2(\ +SINR)
[0066] Expression (7)
= 2 - 1
[0067] (3-3. Calculation of Allowable interference amount M (Step 3))
The allowable interference amount calculation unit 120 of the management server
16A first calculates the allowable interference amount M' in the receiving device 20A
by the follwing method so as to achieve the Mreq notified from the management server
16B.
[0068] -Case A: When a calculation target of the allowable interference amount is a single
link
Method A-l: Calculation of the allowable interference amount M' by transmission
power control
In the case of obtaining the allowable interference amount corresponding to Mreq by
increasing the transmission power of the transmitting device 40A, the allowable in
terference amount calculation unit 120 of the management server 16A calculates the
allowable interference amount M' according to the following expression 8, for
example. Note that a method of deriving the expression 8 is described later in "5. Sup
plementary Description".
[0069] Expression (8)
Rprimary {P o d ry primary + req n r o dar -pri y onda y )
P rx,primaryKx,secondary ~ req p ima y zondary o da y - p rimar rimar nd ry
where
p rx primary ' Receiving power of the receiving device 20A (before start of power
control according to the embodiment),
P e onda y : Receiving power of the receiving device 20B (before start of
power control according to the embodiment),
primarysecondary
: Interference from the transmitting device 40A to the
receiving device 20B,
I
secondaryprimary
: Interference from the transmitting device 40B to the
receiving device 20A,
N ' ri mar ' (Interference + noise) power of the receiving device 20A, and
ary ' (Interference + noise) power of the receiving device 20B.
[0070] Note that the parameters in the expression 8 can be acquired through sensing by the
receiving device 20A, the receiving device 20B, the transmitting device 40A and the
transmitting device 40B, and transmitted and received via the management server 16A
or the management server 16B.
[0071] Method A-2: Calculation of the allowable interference amount M' by transmission
rate control
In the case of obtaining the allowable interference amount corresponding to Mreq by
decreasing the transmission rate of the transmitting device 40A, the allowable in
terference amount calculation unit 120 of the management server 16A calculates the
allowable interference amount M' according to the following expression 9, for
example. Note that a method of deriving the expression 9 is described later in "5. Sup
plementary Description".
[0072] Expression (9)
SINR rjm y Pr onda p' rim + sea ndar secondary , primary primary -^secondary + secondary ) = P P
rx,primary rx,secondary
[0073] -Case B: When a calculation target of the allowable interference amount is a
multilink
Method B-l: Calculation of the allowable interference amount M' by transmission
power control
In the case of obtaining the allowable interference amount by increasing the
transmission power of the transmitting device 40A, the allowable interference amount
calculation unit 120 of the management server 16A calculates the total allowable in
terference amount M' for communication links of a plurality of receiving devices 20A
according to the following expression 10, for example.
[0074] Expression (10)
[0075] Method B-2: Calculation of the allowable interference amount M' by transmission
rate control
In the case of obtaining the allowable interference amount by decreasing the
transmission rate of the transmitting device 40A, the allowable interference amount
calculation unit 120 of the management server 16A calculates the total allowable in
terference amount M' for communication links of a plurality of receiving devices 20A
according to the following expression 11, for example.
[0076] Expression (11)
t ,primary rxsecondary,( )
[0077] After the allowable interference amount calculation unit 120 of the management
server 16A calculates the ideal allowable interference amount M' in the receiving
device 20A for achieving Mreq by the above method, it determines an allowable interference
amount M to be actually applied, with the ideal allowable interference
amount M' as an upper limit. This is because the case where it is difficult to obtain the
ideal allowable interference amount M' is assumed according to circumstances.
[0078] For example, when the transmitting device 40A already transmits a radio signal with
the maximum transmission power or with a power close to the maximum transmission
power, it is unable to sufficiently increase the transmission power and obtain the ideal
allowable interference amount M'. An alternative case is when certain QoS guarantee
is expected for the communication link of the receiving device 20A, and the lower
limit of a rate or latency is restricted.
[0079] In such cases, the allowable interference amount calculation unit 120 of the
management server 16A determines the allowable interference amount M to be
actually applied in a best effort manner, with the ideal allowable interference amount
M' as the upper limit. Note that the allowable interference amount calculation unit 120
may determine the allowable interference amount M which is closer to the ideal
allowable interference amount M' by combining the increase in transmission power
and the decrease in transmission rate. For example, when the allowable interference
amount obtained by the increase in transmission power is Ml, and the allowable in
terference amount obtained by the decrease in transmission rate is M2, the allowable
interference amount M = Ml * M2 can be obtained by combining the increase in
transmission power and the decrease in transmission rate.
[0080] Then, the transmission parameter setting unit 130 of the management server 16A
changes the transmission parameter of the transmitting device 40A in order to obtain
the allowable interference amount M determined by the allowable interference amount
calculation unit 120. For example, the transmission parameter setting unit 130 may
change the transmission power of the transmitting device 40A to M times. Alter
natively, the transmission parameter setting unit 130 may change the transmission rate
of the transmitting device 40A so that the current transmission power of the
transmitting device 40A becomes M times the transmission power necessary to satisfy
the required SINR of the transmission rate after change. Further, the transmission
parameter setting unit 130 may increase the transmission power and decrease the
transmission rate so that the product of multiplying the allowable interference amount
Ml obtained by the increase in transmission power by the allowable interference
amount M2 obtained by the decrease in transmission rate becomes M.
[0081] Further, the network communication unit 110 of the management server 16A notifies
the allowable interference amount M determined by the allowable interference amount
calculation unit 120 to the management server 16B.
[0082] (3-4. Control of Transmission Power Based on Allowable interference amount M
(Step 4))
The transmission power setting unit 230 of the management server 16B increases the
transmission power of the transmitting device 40B within the range that the amount of
interference from the transmitting device 40B to the transmitting device 40A is the
allowable interference amount M or less, based on the allowable interference amount
M notified from the management server 16A.
[0083] (Setting of Transmission Power for Single Link)
Specifically, the transmission power setting unit 230 calculates a transmission power
P'tx,secondary after update of the transmitting device 40B as follows.
[0084] Expression (12)
P tx
',secondary ' req^tx, secondary
, r m r - SINRp r mar y 'primary ) ^ix, secondary
primary 1 secondary primary
where
^rx, p rim ry - SINR'primar y primary
'primary secondary-* primary
[0085] (Setting of Transmission Power for Multilink)
Further, when the allowable interference amount M is given, the transmission power
setting unit 230 can calculate the transmission power of each communication link
evenly as represented in the following expression 13.
[0086] Expression (13)
{^rx, imary - p rim ry primary ) ^tx.secondary 1
tx, secondary, (i) ~ J R J N
3 primary secondary -^primary B
[0087] Alternatively, the transmission power setting unit 230 may calculate the transmission
power of each communication link by assigning weights according to the required
allowable interference amount (Mreq(i)) of each communication link as represented in
the following expression 14.
[0088] Expression (14)
[0089] <4. Advantageous Effects of Embodiment of Present Invention Indicated by
Numerical Analysis Results>
Since numerical analysis of the increasing amount of the average communication
capacity between the transmitting device 40A and the receiving device 20A and
between the transmitting device 40B and the receiving device 20B which is obtained
by the embodiment of the present invention is performed, results of the numerical
analysis are described hereinbelow. In the numerical analysis, it is assumed that the
distance between the transmitting device 40A and the transmitting device 40B is 300m,
the receiving devices 20A and 20B are located within the range of 50m from the
transmitting device 40B, and M=M'.
[0090] Fig. 6 is an explanatory view showing a relationship between the receiving quality
improvement level Mreq desired for the second reviving device 20B and the allowable
interference amount M' in the receiving device 20A. Referring to Fig. 6, it is verified
that M' increases exponentially with respect to Mreq with use of any of transmission
power control (TPC) and transmission rate control (RC). Particularly, because M'
increases abruptly when Mreq is 40dB or higher, it is considered that the control of M'
in this region is effective.
[0091] Further, it is found that the increasing amount of M' with respect to the same Mreq is
greater when performing the transmission power control than when performing the
transmission rate control. This is because, when performing the transmission power
control, both of the amount of interference from the transmitting device 40A to the
receiving device 20B and the amount of interference from the transmitting device 40B
to the receiving device 20A increase, and it is thus necessary to further increase the
transmission power of the transmitting device 40A. In actual operation, there is the
upper limit of the transmission power of each transmitting device 40, and the
management server 16A controls the value of M within the range not exceeding the
upper limit.
[0092] Fig. 7 is an explanatory view showing a relationship between the allowable in
terference amount M' and the average communication capacity in the case of obtaining
the allowable interference amount M' by transmission power control. Referring to Fig.
7, in the case of obtaining the allowable interference amount M' by transmission power
control, the communication capacity (TPC, PS) between the transmitting device 40A
and the receiving device 20A is controlled to be constant with respect to M'. Therefore,
it is shown that the increment of the communication capacity (TPC, SS) between the
transmitting device 40B and the receiving device 20B serves as the increment of the
total communication capacity.
[0093] Further, referring to Fig. 7, the communication capacity between the transmitting
device 40B and the receiving device 20B tends to be saturated when M' reaches ap
proximately 5dB. Specifically, it is considered that an unlimited increase in M' does
not contribute to the increase in the total communication capacity. Thus, the allowable
interference amount calculation unit 120 of the management server 16A may
determine the value of the allowable interference amount M within the range that does
not exceed a predetermined upper limit (e.g. 5dB).
[0094] Fig. 8 is an explanatory view showing a relationship between the allowable in
terference amount M' and the average communication capacity in the case of obtaining
the allowable interference amount M' by transmission rate control. Referring to Fig. 8,
in the case of obtaining the allowable interference amount M' by transmission rate
control, the transmission power of the transmitting device 40A is kept constant, and
therefore the communication capacity between the transmitting device 40A and the
receiving device 20A tends to decrease with an increase in M'. However, because the
increment of the communication capacity between the transmitting device 40B and the
receiving device 20B is greater than the decrement of the communication capacity
between the transmitting device 40A and the receiving device 20A, the total commu
nication capacity increases.
[0095] Further, just like the case of transmission power control, the communication capacity
between the transmitting device 40B and the receiving device 20B tends to be
saturated when M' reaches approximately 5dB. Specifically, it is considered that an
unlimited increase in M' does not contribute to the increase in the total communication
capacity. Thus, the allowable interference amount calculation unit 120 of the
management server 16A may determine the value of the allowable interference amount
M within the range that does not exceed a predetermined upper limit (e.g. 5dB) in the
case of obtaining the allowable interference amount by transmission rate control as
well.
[0096] <5. Supplementary Description>
Hereinafter, processes of deriving the expression 8 and the expression 9 for cal
culating the allowable interference amount M' on the basis of Mreq are described.
[0097] - Derivation of Expression 8
One example of a method of calculating an allowable interference amount M' of the
receiving device 20A and an actual transmission power increasing amount M'req of the
transmitting device 40B from Mreq required by the management server 16B is to solve
the system of linear equations with two unknowns by SINR condition of the receiving
device 20A and SINR condition of the receiving device 20B.
[0098] First, as the SINR condition of the receiving device 20A, the following expression 15
can be used.
[0099] Expression (15)
M'P
SINRprimary - 'pnmary
req secondaryprimary primary
[0100] Further, as the SINR condition of the receiving device 20B, the following expression
16 can be used.
[0101] Expression (16)
[0102] Summarizing the expression 15 and the expression 16 yields the simultaneous
equations with respect to M' and M'req.
[0103] Expression (17)
[0104] Solving the above expression 17 with respect to M' yields the expression 8, and
solving the expression 17 with respect to M'req after M is determined in the abovedescribed
step 3 yields the expression 12.
[0105] Note that the parameters in the expressions 15 to 17, the expression 8 and the ex
pression 12 can be also represented as follows.
[0106] Expression (18)
Prx,primary = L primaryprimaryP tx,primary
P rx,secondary = L secondary-tsecondary P tx,secondary
Jprimarysecondary = T primary-secondary Ptx,primary
Jsecondary-*primary = Tsecondary-*primary Ptx,secondary
p
SINR - - " y _ _
primary j + 
secondary-*primary primary
p
SINR ~ rx,secondary
secondary
primarysecondary secondary
where
prima rypri ar -'
a l s s of a communication link between the transmitting
device 40A and the receiving device 20A,
e n arye dary ' am s s a communication link between the transmitting
device 40B and the receiving device 20B,
p r ryary ' a S interference link between the transmitting device
40A and the receiving device 20B,
e ndaryp mary ' a S interference link between the transmitting device
40B and the receiving device 20A,
tx,s d ry '• Transmission power before change of the transmitting device 40A,
and
P n a / : Transmission power before change of the transmitting device 40B.
[0107] By substituting the respective parameters represented in the above expression 18 into
the expression 8 and the expression 12, M' can be represented by the following ex
pression 19, and M'req can be represented by the following expression 20.
[0108] Expression (19)
[0109] Expression (20)
secondaryprimary tx,secondary
[0110] - Derivation of Expression 9
In the case of obtaining the allowable interference amount M' of the receiving device
20A and the actual transmission power increasing amount M'req of the transmitting
device 40B by controlling the transmission rate also, M' and M'req can be obtained by
solving the system of linear equations with two unknowns by SINR condition of the
receiving device 20A and SINR condition of the receiving device 20B.
[0111] First, as the SINR condition of the receiving device 20A, the following expression 2 1
can be used.
[0112] Expression (21)
l . primary SINR^primary, req =— SINRprrimary T'
j l req 1 secondaryprimary primary
[0113] Further, as the SINR condition of the receiving device 20B, the following expression
22 can be used.
[0114] Expression (22)
D — \ — req^rx, secondary
ary q ~ '1 req secondary ~ 
primarysecondary secondary
[0115] Summarizing the expression 2 1 and the expression 22 yields the following system of
linear equations with two unknowns shown below.
[0116] Expression (23)
[01 17] Solving the above expression 23 with respect to M' yields the expression 9, and
solving the expression 23 with respect to M'req after M is determined in the abovedescribed
step 3 yields the expression 12.
[0118] Further, by substituting the respective parameters represented in the above expression
18 into the expression 9 and the expression 12, M' can be represented by the following
expression 24, and M'req can be represented by the following expression 25.
[0119] Expression (24)
' eq 'se ondary primary^ tx, secondary p i y
1secondary primary
P
tx, secondary
+ N
p
'rimary
[0120] Expression (25)
, secondary-* primary tx,secondary primary ) primary
~
secondary primary tx,secondary
[0121] <6. Summary>
As described above, according to the embodiment of the present invention, the
allowable interference amount M in the receiving device 20A is obtained by increasing
the transmission power of the transmitting device 40A or decreasing the transmission
rate of the transmitting device 40A. Then, the transmitting device 40B sets the
transmission power in the range that interference on the receiving device 20A does not
exceed the allowable interference amount M. In such a configuration, as described
above with reference to Figs. 7 and 8, it is possible to effectively increase the commu
nication capacity of the entire network.
[0122] Although a preferred embodiment of the present invention is described in detail
above with reference to the appended drawings, the present invention is not limited
thereto. It should be understood by those skilled in the art that various modifications,
combinations, sub-combinations and alterations may occur depending on design re
quirements and other factors insofar as they are within the scope of the appended
claims or the equivalents thereof.
[0123] Further, it is possible to create a computer program that causes hardware such as a
CPU, ROM and RAM incorporated in the management server 16 to function equally to
the respective elements of the management server 16 described above. Further, a
memory medium that stores such a computer program may be provided.
[0124] It should be noted that the term "secondary usage" in this specification typically
means utilization of an additional or alternative communication service (a second com
munication service) using a part or whole of a spectrum assigned to a first commu
nication service. In this context about the meaning of the term "secondary usage", the
first communication service and the second communication service may be services of
different types or the same type. The services of different types may be selected from
services such as digital TV broadcasting service, satellite communication service,
mobile communication service, wireless LAN access service, P2P (Peer To Peer)
connection service and the like.
[0125] On the other hand, services of the same type may contain, for example, a relationship
between a service using the macro cell provided by a communication carrier and a
service using the femtocell operated by users or MVNO (Mobile Virtual Network
Operator) in a mobile communication service. Additionally, services of the same type
may contain, for example, a relationship between a service provided by a macro cell
base station and a service provided by a relay station (relay node) to cover a spectrum
hole in a communication service conforming to LTE-A (Long Term Evolution-
Advanced).
[0126] The disclosed concept is applicable in various different types of communication
systems. For example, in LTE-A, a control area (PDCCH: Physical Downlink Control
Channel) and data area (PDSCH: Physical Downlink Shared Channel) are separately
assigned in a communication area. In this configuration, there are generally two ways
to solve the problem of interference between different types of communication nodes.
[0127] A first solution is to reduce interference in both of the control area (PDCCH) and the
data area (PDSCH). This is a basic way to reduce interference occurring between
different types of communication nodes.
[0128] A second solution is to reduce interference only in the control area (PDCCH). This
solution is based on the fact that the scheduler in the node assigns data resources for a
particular data area. Here, the scheduler, which is normally implemented in a MAC
function of a base station, is the component that assigns the data resources. In other
words, with regard to the resource that interference between different types of nodes is
estimated to occur, interference can be avoided by assigning resources only to one of
the nodes. This can be realized by collaboration of schedulers running on the different
types of nodes. On the other hand, with regard to the control area (PDCCH), since the
scheduler can not change the resource allocation, it is important to reduce interference
in the control area from the beginning.
[0129] The configuration disclosed herein can be applied to both of the control area and the
data area as well as only to the control area.
[0130] Further, the second communication service may be a service utilizing a plurality of
fragmentary frequency bands aggregated using spectrum aggregation technology. Fur
thermore, the second communication service may be a supplementary communication
service provided by femtocells, relay stations or small-to-medium-sized base stations
providing smaller service areas than a macro cell base station, which are located within
the service area provided by the macro cell base station. The subject matter of each
embodiment of the present invention described in this specification is widely ap
plicable to every type of mode of such secondary usages.
Reference Signs List
16, 16A, 16B Management server
20, 20A, 20B Receiving device
40, 40A, 40B Transmitting device
110, 210 Network communication unit
120 Allowable interference amount calculation unit
130 Transmission parameter setting unit
140 Communication control unit
220 Expected value calculation unit
230 Transmission power setting unit
240 Communication control unit
PCT/JP2011/001507
Claims
A management server in a network including a first transmitting device
configured to communicate with a first receiving device and a second
transmitting device configured to communicate with a second receiving
device, the management server comprising:
a network interface configured to receive a parameter corresponding to
a level of improvement of communication quality at the second
receiving device;
a processor configured to calculate an allowable interference amount at
the first receiving device based on the parameter,
wherein the network communication unit is configured to output the
calculated allowable interference amount.
The management server of claim 1, wherein the second transmitting
device and the second receiving device communicate using a frequency
that overlaps with a frequency used for communication between the
first transmitting device and the first receiving device.
The management server of claim 1, wherein the network interface is
configured to receive management information indicating a state of a
cell formed by the first transmitting device.
The management server of claim 3, wherein the processor is configured
to control communication in the cell formed by the first transmitting
device based on the received management information.
The management server of claim 1, wherein the network commu
nication unit is configured to output the calculated allowable in
terference amount to a second management server configured to control
communications between the second transmitting device and the
second receiving device.
The management server of claim 1, wherein the processor is configured
to calculate a maximum allowable interference amount based on the
parameter, and the allowable interference amount is calculated to be
less than the maximum allowable interference amount.
The management server of claim 1, wherein the processor is configured
to set at least one of a transmission power of the first transmitting
device and a transmission rate of the first transmitting device based on
the allowable interference amount.
The management server of claim 1, wherein the processor is configured
to calculate the allowable interference amount based on a reception
PCT/JP2011/001507
power at the first receiving device, a reception power at the second
receiving device, interference from the first transmitting device at the
second receiving device, interference from the second transmitting
device at the first transmitting device, a power of the first receiving
device and a power of the second receiving device.
A management server in a network including a first transmitting device
configured to communicate with a first receiving device and a second
transmitting device configured to communicate with a second receiving
device, the management server comprising:
a processor configured to calculate a parameter corresponding to a level
of improvement of communication quality at the second receiving
device;
a network interface configured to transmit the calculated parameter to a
another management server, and receive an allowable interference
amount at the first receiving device from the another management
server,
wherein the processor is configured to control communications
between the second transmitting device and the second receiving device
based on the allowable interference amount.
The management server of claim 9, wherein the second transmitting
device and the second receiving device communicate using a frequency
that overlaps with a frequency used for communication between the
first transmitting device and the first receiving device.
The management server of claim 9, wherein the network interface is
configured to receive management information indicating a state of a
cell formed by the second transmitting device.
The management server of claim 11, wherein the processor is
configured to control communication in the cell formed by the second
transmitting device based on the received management information.
The management server of claim 9, wherein the processor is configured
to determine whether to improve the receiving communication quality
based on a comparison between a current communication quality and a
desired communication quality.
The management server of claim 13, wherein the processor is
configured to calculate the parameter based on a relationship between
the current communication quality and the desired communication
quality.
The management server of claim 14, wherein the relationship between
WO 2011/121914 PCT/JP2011/001507
the current communication quality and the desired communication
quality is a ratio between the desired communication quality and the
current communication quality.
[Claim 16] The management server of claim 9, wherein the processor is configured
to control communications between the second transmitting device and
the second receiving device such that an amount of interference caused
by the second transmitting device at the first receiving device is less
than the allowable interference amount.
[Claim 17] A network comprising:
a first management server configured to control communications
between a first transmitting device and a first receiving device;
a second management server configured to control communications
between a second transmitting device and a second receiving device;
a first processor, at the second management server, configured to
calculate a parameter corresponding to a level of improvement of com
munication quality at the second receiving device;
a first network interface, at the second management server, configured
to transmit the calculated parameter to the first management server;
a second processor, at the first management server, configured to
calculate an allowable interference amount at the first receiving device
based on the parameter;
a second network interface, at the first management server, configured
to transmit the calculated allowable interference amount to the second
management server,
wherein the processor of the second management server is configured
to control communications between the second transmitting device and
the second receiving device based on the allowable interference
amount.
[Claim 18] A method of controlling communications in a network including a first
management server configured to control communications between a
first transmitting device and a first receiving device and a second
management server configured to control communications between a
second transmitting device and a second receiving device, the method
comprising:
calculating, at the second management server, a parameter corre
sponding to a level of improvement of communication quality at the
second receiving device;
transmitting the calculated parameter from the second management
PCT/JP2011/001507
server to the first management server;
calculating, by the first management server, an allowable interference
amount at the first receiving device based on the parameter;
transmitting the calculated allowable interference amount from the first
management server to the second management server; and
controlling communications between the second transmitting device
and the second receiving device based on the allowable interference
amount.