Technical Field
[000l]
The present disclosure relatcs to a communicatioil control device, a
10 communication control mcthod, a program, and a communication control system.
Background Art
[OOO2]
As indicated by the Federal Communications Commission (FCC), the main
cause of depletion or frequency resources for wireless communication is an
ineflicient frequency allocation policy (see Non-Patent Literature 1 below). Most
of the frequency resources are allocatcd to a particular service provider with an
exclusive license, and a strict constraint is imposed on the transmission power on the
lirequency resources in order to prevent a mutual interference. Under such
conditions, a cognitive radio that is a wireless communication device capable oi
adaptively changing an operation parameter has been developed. With the advent
or the cognitive radio, a new policy has been developed in many countries in order to
open frequency resources within the range of not causing harmful interference with
an unlicensed user.
[OOO3]
A system of a service provider that has a license for a certain frequency
channel is referred to as a primary system (PS). On the other hand, a system that
secondarily uscs the frequency channel protected for the sake of the primary system
is referred to as a secondary system (SS). Approaches to the secondary use of the
frequcncy channel are classified into two groups. The first approach is an
opportunistic spectmm access that monitors the frequency resource of the primary
system to detect the absence of a PS user and allows an SS user to use a so-called
spectrum hole that has been detected (see Non-Patent Literature 2 below). Thc
second approach is spcctruln sharing that recognizes the coexistence of a PS uscr and
an SS user and controls parameters such as the transmission power of the secondary
5 system in order to prevent the SS user from giving interference exceeding an
allowable level to the PS uscr (see Non-Patent Literature 3 below). Every approach
is important in terms of the efficient use of frequency resources.
Citation List
10 Non-Patent Literature
[0004]
Non-Patent Literature 1 : Federal Com~nunications Commission,
"Spectrum policy taslc force" ET Docket No. 02-1 35, Nov. 2002, Technical Report
Non-Patent Literature 2: J. Mitola and G. Q. Maguire, "Cognitive radio:
15 Malcing software radios more personal" IEEE Personal Con~munications,v o1.6, no.4,
pp.13-18, August 1999
Non-Patent Literature 3: S. Haykin, "Cognitive radio: Brain-empowered
wireless communications" lEEE Journal on Selected Areas in Communication,
vo1.23, no.2, pp.201-220, February 2005
20
Summary of Invention
'Technical Problem
[0005]
In the above-described second approach, that is, the spectrum sharing,
25 interfcrcnce given to the PS user is often estimated by subtracting a path loss (from
the SS user to the PS user) from the transmission power of the SS user. The path
loss depends on not only the distance between the users but also fading and varies
temporally. Therefore, in an existing method, interference is estimated based on the
average value or the minimum value of a path loss estimated within a predetermined
30 period of time, to dctermine the transmission power of the SS uscr. However,
according to the existing method, even when the path loss increases within a short
time, the SS user cannot efficiently use a margin of a power increase caused by the
increase in the path loss. Therefore, the communication capacity of the sccondary
systcin is not optimized. On the other hand, close signaling between a transmitting
side and a receiving side is necessary to estimate a varying path loss with high
5 accuracy. Therefore, when interfcrence is estimated based on the path loss in a
short cycle, a signaling overhead increases.
[0006]
Thereforc, it is desirable to implement a mechanism that makes it possible
for the secondary system to use the frequency resources more efficiently than the
10 existing method, without excessively increasing the signaling overhead.
Solution to Problem
[0007]
According to the prescnt disclosure, there is provided a communication
15 control device including a power control unit configured to determine a transmission
power of a wireless signal, which is transmitted from an interfering device, by using
a fading index that is estimated based on a change in a relative distance between the
interfering device and an interfered device.
20 Further, according to the present disclosure, there is provided a
co~nmunication control method, which is executed by a communication control
device that controls a transmission power of an interfering device, the
communication control method including determining a transmission power of a
wircless signal, which is transmitted from the interfering device, by using a fading
25 index that is estimated based on a change in a relative distance between the
interfering device and an interfered device.
Further, according to the present disclosure, there is provided a program for
causing a computer, which controls a communication control device, to function as a
30 power control unit configured to determinc a transmission power of a wireless signal,
which is transmitted from an interfering device, by using a fading index that is
estimated based on a change in a relativc distance between the interfering device and
an interfered device.
[00 1 01
Furthel; according to the present disclosure, there is provided a
5 cornmunication control system including a wireless communication device of a
second wireless communication system located in a cell of a first wireless
co~nmunications ystem, and a cornmunication control device configured to determine
a transmission power of a wireless signal, which is transmitted from thc wireless
communication device, not to give harmful interference to the first wireless
1.0 communication system, by using a fading index that is estimated bascd or1 a change
in a relative position of the wireless communication device.
Advantageous Effects of Invention
[OOI 11
15 According to the technology of the present disclosure, the communication
capacity of the secondary system may be increascd in comparison with the existing
method without excessively increasing the signaling overhead.
Brief Description of Drawings
20 [OO12]
[FIG. 11 FIG. 1 is an illustrative diagram for illustrating a scheme of speclrum sharing.
[FIG. 21 FIG. 2 is an illustrative diagram for illustrating an example of an existing
method for controlling the transmission power of a secondary system.
[FIG 31 FIG. 3 is an illustrative diagram for conceptually illustrating a new
25 interference model.
[FIG. 41 FIG. 4 is an illustrative diagram illustrating an example of a configuration or
a comn~unicationc ontrol system according to an cnibodiment.
[FIG 51 FIG. 5 is an illustrative diagram illustrating an example of a configuration of
a communication control device.
30 [FIG. 61 FIG. 6 is a flow chart illustrating an example of an overall flow of a
communication control process.
(FIG. 71 FIG. 7 is a flow chart illustrating an example of a detailed flow of a process
for constructing a power calculation formula.
[FIG. 81 PIG. 8 is a flow chart illustrating another example of a detailed flow of a
process for constructing a power calculation formula.
6
Description of Embodiments
[OO13]
Hereinafter, preferred embodiments of the present disclosure will be
described in detail with reference to the appended drawings. Note that, in this
10 specification and thc drawings, elements that have substantially the same function
and structure are denotcd with the same reference signs, and repeated explanation is
omitted.
[00 141
In addition, description will be provided in the following order.
15 1. Overview
1 - 1. Spectrum sharing
1-2. Technical problem
1-3. New interference model
2. Example of configuration of communication control system
2-1. Summary of systenl
2-2. Example of configuration of communication control device
2-3. Flow of process
3. Conclusion
[00 151
25
[1 - 1. Spectrum sharing]
FIG. 1 is an illustrative diagram for illustrating a scheme of spectrum
sharing rclated to the technology of the present disclosure. Referring to FIG. 1, a
base station (hereinafter refcrrcd to as a PS base station) 10 of a primary system is
30 illustrated. The primary system is a wireless communication system of a service
provider having a license for a certain frequency channel. The PS base station 10
provides a wireless communication service to one or more terminals (hereinaftcr
refeli-ed to as PS tenninals) 14 of the primary system that are located in a cell 12 on a
licensed frequency channel. Hcrein, when the number of active PS terminals
located in the ceil 12 is small, a surplus (an unused resource) is generated in a
5 frequency resource of the priillary system. When an unlicensed service provider
cannot at all use a frequency channel protected for the saltc of the primary system,
the use efficiency of frequency resources is degraded. On the other hand, when the
unlicensed service provider can freely operate its own wireless communication
service, harmful interference may be generated in the wirelcss communication
10 service of the primary system that should be naturally protected. Thus, from thc
viewpoint of the improvcmcnt of the use efficiency of frequency resources, it is
approved that the unlicensed service provider secondarily uses a surplus frequency
resourcc of the primary system within the range of not causing harmful interference.
[00 1 61
15 In the example of FIG. 1, a base station (hereinafter referred to as an SS base
station) 20 that is a master node of the primary system and one or more terminals
(hereinafter referred to as SS terminals) 24 of the secondary system are located in the
cell 12 of the primary system. The SS base station 20 is a communication control
device that operates the secondary system by secondarily using a frequency channel
20 that is protected for thc sake of the primary system. The SS base station 20 may be,
for example, a wireless access point, a femto cell base station, a hot zone base station,
a remote radio head (RRH), or a device having other types of cognitive radio
functions. Iierein, for example, when a wireless signal 26 is transmitted from the
SS terminal 24 at the same timing as the transmission of a downlink signal 16 from
25 the PS base station 10, the wireless signal 26 may interfere with the downlink signal
16 in the PS terminal 14. Thus, the SS base station 20 controls the transmission
power of the SS terminal 24 so that an interference level observed in the PS terminal
14 does not exceed an allowable level. Also, the SS base station 20 controls the
transmission power of the SS base station 20 in the same manner.' Accordingly, safe
30 spectrum sharing between the primary system and the secondary system is realized.
Also, when the secondary -system transmits a wireless signal at the timing of uplink
transmission (not downlink transmission), the PS base station 10 is a protection
target in spcctrurn sharing.
[0017]
11-2. Technics1 problem]
5 In general, interference given to the primary system is cstimatcd by
subtracting a path loss between an interfering dcvice (for example, the SS terminal
24 of FIG. 1) of the secondary system and an interfered device (for example, the PS
terminal 14 of FIG. 1) oC the primary system from the transmission power of the
interfering device. However, the path loss depends on not only the position or a
10 terminal but also fading factors such as multipath fading and shadow rading and
varies tcmporally. Thereforc, it is difficult to accurately estimate the path loss in a
short cycle. Thus, in the existing method, the average value or the minimum value
of a path loss estimation value is calculated for each period having a predetermined
time length, and the transmission power of the secondary system is controlled based
15 on an indicator thereof.
LOO1 81
FIG. 2 is an illustrative diagram for illustrating an examplc of an existing
method for controlling the transmission power of a secondary system. In FIG. 2, a
horizontal axis represents time and a vertical axis represents a path loss estimation
20 value, and a temporally-varying path loss estimation value is graphed. In the
existing method, for example, an average value L,, or a minimum valuc of the
path loss estimation value over a period TLo is calculated. Then, by using the
average value La,, or the minimum value LWrstt,h e transmission power of the
secondary systcm is determined within the range of not giving interference exceeding
25 an allowable level to the primary system.
100 191
Here, for example, in periods of a time Toot o a time Tol, a time TOZto, a time
To3, and a time Tgq to a time Tos, the path loss cstilnation value exceeds the average
value L,,. Thus, when the transmission power of the secondary system is
30 determined by using the average value L,,,, the transmission power corresponding to
an area R01 hatched in the drawing is not used while being able to be naturally used.
Also, when the transmission power of the secondary system is determined by using
thc minimum value L,,,, the transmission power corresponding to both the area R01
and an area R02 shaded with dots in the drawing is not uscd while being able to be
naturally used. This inefficiency may bc solved by shortening the period TLo.
5 However, this solution may cause the demerit of an increase in the signaling
overhead for estimating and feeding back a path loss in a short cycle.
[0020]
[I-3. New interference model]
(1) Basic principle
10 Therefore, the technology of the present disclosure introduccs a new
interference model for controlling transmission power by using a fading index
instead of a path loss, which may be estimated more easily than the path loss. FIG.
3 is an illustrative diagram for conceptually illustrating the new interference model.
In the example of FIG. 3, a dashed graph represents a deviation of a path loss
15 estimation value. In general, when a contribution of fading changes, a variation of a
path loss changes together with the path loss. Thus, the path loss estimation value
and the deviation thereof correlate with each other. Therefore, in the new
interference model, a parameter referred to as a fading index about a deviation of the
path loss estimation value is employed to construct a power calculation formula as a
20 function of thc fading index. The power calculation formula is constructed to
express a so-called water filling principle. Then, an instantaneous valuc of the
fading index is estimated by a simple method, and the estimated instantaneous value
is substituted into the power calculation formula to determine the transmission power
of the secondary system. Therefore, the transmission power of the secondary
25 system may be increased by the amount corresponding to the areas R01 and R02
illustrated in FIG. 2. Consequently, the use efficiency of frequency resources may
be improved.
[0021]
(2) Construction of power calculation formula
30 The new interrerence model has thc following assumption. That is,
referring to FIG. I, it is assumed that thc PS terminal 14 is probabilistically
uniformly distributed in the cell 12 of the primary system. Also, it is assumed that
the SS terminal 24 is probabilistically unifor~i~ldyi stributed in a circular region
having a radius r,, around the SS base station 20. Here, a radius of the cell 12 is &,
a distance between the PS base station 10 and the PS terminal 14 is r,,, a distance
5 between the PS base station 10 and the SS base station 20 is r,,, a distance between
the SS base station 20 and the SS terminal 24 is I.,,, a distance between the SS
terminal 24 and the PS terminal 14 is r,,, an angle between a path of the PS base
station 10 to the PS terminal 14 and a path of the PS base station 10 to the SS base
station 20 is 0, and an angle between a path of thc SS base station 20 to the PS base
10 station 10 and a path of the SS base station 20 to the SS terminal 24 is (1). Also, a
fading index ola n interfcrence signal from the SS te~lllinal2 4 to the I'S terminal 14
is ESP. A distance between the nodes and a joint probability density function ol the
angle are expressed as Formula (1) below.
[0022]
15 [Math. 11
[0023]
When the transmission power of a transmitter station (hereinafter referred to
as an SS transmittev station; for exanlple, the SS terminal 24) of thc secondary
20 system, which is separated fro111 the SS base station 20 by the distance r,,, is
represented by P5 (r,,, 5 s ~ ) as a function of thc fading index Esp, since r and 6 are
independent, an average signal to interference and noise ratio (SINR) loss of a
receiver station (hereinafter referred to as a PS recciver station; for example, the PS
terminal 14) of the primary system may be expressed as Formula (2) below.
25 [0024]
[Math. 21
where
100251
In Formula (2), fg,, (5) represents a zero mean Gaussian distribution in a
standard deviation 0 [dB] of the fading index. In Formula (3), GUF represents an
5 antenna gain of the terminal, N, represents a noise power ol: the interfc~ed device.
En {GpathUL, , UF (rSp)} is an expectation value of a path loss that is calculated over a
joint probability density function of an internode distance expressed by Formula (1).
[0026]
Here, an average signal to noise ratio (SIR) of a receiver station (hereinafter
10 referred to as an SS receiver station) of the secondary system is a function of the
fading index tspa nd the distance rss as expressed in the following formulas.
I
I
I
I
~00271
, I [Math. 31
where
15 [0028]
In Formula (5), I'p represents the transmission power of the PS base station
10, Gus represents an antenna gain of the PS base station 10, and Gpath, UL, ,,I. (rs~)
represents a path loss between the SS transmitter station and the SS receiver station.
En {l/G,,tl,, ur, UF (rp~)}is an expectation value of a reciprocal of the path loss that is
calculated over the joint probability density function of the internode distance as in
Formula (1).
[0029]
5 From the Jensen's inequality, an upper bound of an ergodic capacity may be
expressed as the following formula. In addition, the unit of the ergodic capacity is
bps/Hz.
[0030]
[Math. 41
1003 11
In the following description, suffixes are omitted for conciseness. A
constrained optimization problcm as in the following formulas is constructed in order
to maximize the upper bound of the capacity of the secondary system.
15 [0032]
[Math. 51
where
[0033]
In Formula (S), SrNlt~,,,,,,,I is an allowance of an SJNR loss of the prima~y
20 system. K is an intcrference model parameter that is calculated according to
Formula (3). A lagrangian for solution of the constrained optimization problem of
Formula (7) is expressed as the following formula
[0034]
[Math. 61
[0035]
5 When the lagrangian is differentiated with Ps (k), the following rolmula is
derived.
[003 61
[Math. 7]
10 [0037]
When Ps ({) is solved with a constraint of Ps (5) 2 0, a solution of the water
filling principle that has a cutoff threshold value 50 is derived as in the following
formula.
[003S]
15 [Math. 81
[0039]
Formula (1 1) indicates that the transmission power Ps (rss, 5~pi)s zero in a
period of time whcn the fading index between an SS transmitter station (an
interfering device) and a PS terminal (an interfered device) exceeds the cutoff
threshold value to [dB]. Accordingly, the constraint that an SINR loss observed in
the PS terminal is less than the allowance SINRI,,,, is satisfied. The cutoff
5 threshold valuc 50 is calculated by solving the following relation formula that is
described in a closed form.
[0040]
[Math. 91
10 [0041]
Also, when the zero mean Gaussian distribution (normal distribution) is
assumed, Formula (12) may bc equivalently substituted as in the following formula
by using the given standard deviation G [dB] of the fading index (sp.
[0042]
15 [Math. 101
100431
In Formula (13), Q(.) is a Q function of the tail probability of a standard
normal distribution.
20 100441
In the new interference model, the cutoff threshold value 50 may be
calculated by calculating the parameters I< (rss), x (rss), and y and solving Formula
(12) or Formula (13). Then, the power calculation formula (Formula (11)) for
calculation of the transmission power Ps (rsr, typ) may be constructed by using the
calculated cutoff threshold value t o . The argument of the power calculation
formula (1 1) is the fading index 5sp alone. Since the positional relation between the
primary system and the secondary system is probabilistically assumed, an actual
measured value of the path loss between the SS transmitter station and the PS
5 terminal may not be used in constructing the power calculation formula.
[0045]
In the technology of the present disclosure, after the power calculation
formula of the interference model is constructcd, the transmission power of ihe SS
transmitter station is dctermined by using the fading index Esp that is estimated based
10 on the relative movement of the interfering device.
[0046]
(3) Estimation of fading index
The instantaneous value of the fading index may be estimated, for cxample,
by using a least square-based fading estimation technique that will be described
15 below. The least square-based fading estimation technique has been described, for
example, in literatures such as "Experimental analysis of the joint statistical
properties of azimuth spread, delay spread, and shadow fading" (A. Algans, I<. I.
Pedersen, and P. E. Mogensen, IEEE Journal on Sclectcd Areas in Communication,
vol. 20, no. 3, pp. 523-531, April 2002) and "inter- and intrasite correlations of large-
20 scale parameters from macrocellular measurements at 1800 mhz" O\i. Jalden, P.
Zetterberg, B. Otlcrsten, and L. Garcia, EUMSIP Journal 011 Wireless
Communications and Networking, 2007).
[0047]
When the distance between the interfering device and the interfered device
25 is d, a relation between a fading index hsl, and a distance-dependent path loss h,~, (d)
in the least square-based fading estimation technique is expresscd as the following
formula.
[0048]
[Math. 111
[0049]
It is assumed that the distance d is the sum of a reference distance do and a
change d, of a relative distance from the reference distance do (d = do + d,). Then,
5 Formula (14) is rewritten as follows.
[00S0l
[Math. 121
[005 11
i 10 Here, a Taylor expansion as in the following formula is established for x in
!
I therangeol-l < x S 1.
!
[0052]
[Math. 131
15 [0053]
Accordingly, when a Taylor expansion is performed on loglo (1 + d,/do) in
the range of -1 < d,/do 5 1 while focusing on the third term of Porn~ula (1 5), the
following approximation formula is established. Also, the third and subsequent
terms of the Taylor expansion are neglected.
20 [0054]
[Math. 141
where
[0055]
When Formula (17) is further gcneralized, the approximation formula is
expressed as follows
[0056]
[Math. 151
100571
Here, m sets of the change d, of thc relative distance from the reference
distance do and the reception power P, measured at thc distance d = do + d, are
prepared (i = 1, 2, ..., m), the following simultaneous equation is constructed. Also,
it is assumed that /di/ < do and m is sufficicntly greater than n.
[0058]
[Math. 161
100591
A coefficient vector a = (ao,al, ..., a,) is given as a least square solution of
Fornlula (19) as expressed in the following formula.
[0060]
[Math. 171
[0061]
As a result, when the coefficient vector a = (ao,al, ..., a,) may be obtained in
advance by solving the simultaneous equation of Formula (19), the instantaneous
5 value of thc fading index may be estimated from a vel-tical distance between the
average reception power and the distance-dependent path loss estimation value
estimated from the polynomial (18) with respect to the given relative distance d,.
Then, the transmission power of the SS transmitter station may be dctcrmined by
substituting the estimated instantaneous value of the fading index into the powcr
10 calculation formula (1 1).
100621
Also, the instantaneous value of the fading index is not limited to the
example described herein and may be estimated according to other methods.
[0063]
15 12. Example of configuration of communication control system>
In this section, an exemplary embodiment of a communication control
system that controls the transmission power of a secondary system by using the
above-described interference model will be described.
[0064]
20 12-1. Overview of system]
FIG. 4 is an illustrative diagram illustrating an example of a configuration or
a communication control systcm 1 according to an embodiment. Referring to FIG.
4, the communication control system 1 includes a PS basc station 10, a PS terminal
14, an SS basc station 20, an SS terminal 24, and a data server 30.
25 [0065]
The data server 30 is a server device that has a database that is equipped to
manage the secondary usc of a frequency channel by the sccondary system. The
data server 30 collccts system information of the primary system from the PS basc
station 10. The system information collected from the PS base station 10 may
include, for example, a position of the PS base station 10, a cell radius, an antenna
gain, a noise powcr, a transmission power of the PS base station 10, an SlNR loss
allowance, and thc like. Then, when the sccondary system starts to operate, the data
server 30 provides the system information of the primary system to the SS base
5 station 20 in response to the request of the SS base station 20. The data server 30
may provide the SS base station 20 with information such as a spectrum mask and a
frequency channel to bc used by the secondary system. The communication
between the SS base station 20 and the data servcr 30 may be perlbrmzd, for
cxamplc, through any nctworlc such as the internet. Also, the SS base station 20
10 may directly receive the system information of the primary system lrorn the PS base
station 10.
[0066]
In the present embodiment, the SS base station 20 functions as a
communication control device that controls the transmission power of the SS base
15 station 20 and the transmission power of the SS terminal 24. The SS base station 20
determines the transmission power of an SS transmitter station (for example, the SS
base station 20 or the SS terminal 24) by using an instantaneous value of a fading
index according to thc above-described interference model. When a power
calculation formula expressing a water filling principle is once constructed, only a
20 fading index substituted into the constructed power calculation formula may be
periodically updated in a short cycle. The power calculation formula may be
reconstructed when interference exceeding an allowance (that is, an allowance
violation) is observed in the primary system. The 1's terminal 14 (or the PS base
station 10) transmits an observation report on an interference amount periodically or
25 when interference exceeding an allowance is observed. The SS base station 20
receives the observation rcport and may reconstruct (that is, modify) the power
calculation formula when necessary. Accordingly, the protection of the primary
system is reinforced.
[0067]
30 Also, instead of the SS base station 20, the data server 30 or anothcr node
may opelate as a con~municationc ontrol device that controls the transmission power
of the secondary system.
[0068]
[2-2. Example of configuration of com~nunicationc ontrol device]
FIG. 5 is an illustrative diagram illustrating an example of a configuration of
5 a communication control dcvice 20. Referring to FIG 5, the communication control
device 20 includes a network communication unit 110, a wireless communication
unit 120, a storage unit 130, and a control unit 140. The control unit 140 includes a
data acquisition unit 150 and a power control unit 160.
[0069]
10 The network communication unit 110 is a communication interface for
communication between the communic'ation control device 20 and the data server 30.
The communication between the commullication control device 20 and the data
server 30 may be implemented by wired communication, wireless comn~unicationo, r
a combination thereof.
15 [0070]
The wireless communication unit 120 is a wireless communication interface
for thc communication control device 20 to provide a wireless communication
service to one or more SS terminals 24. The wireless communication unit 120
transmits a wireless signal on a frcqnency channel that is protected for the sake of the
20 primary systcm, by using the transmission power that may be determined according
to the above-described interference model.
[0071]
The storage unit 130 stores a program and data for operation of the
communication control device 20 by using a storage medium such as a hard disk or a
25 semiconductor memory. For example, the storage unit 130 stores the system
information of the primary system that is received kom the data servcr 30. Also,
the storage unit 130 stores a paramcter that is prepared or calculated to the
transmission power of the secondary system.
[0072]
30 The control unit 140 corresponds to a proccssor such as a central processing
unit (CPIJ) or a digital signal processor (DSP). Thc control unit 140 activates
various functions of the communication control device 20 by executing a program
that is stored in the storage unit 130 or other storage media.
[0073]
The data acquisition unit 150 acquires data that are necessary Sor the control
5 of transmission power by the power control unit 160. For example, when the
secondary system starts to operate, the data acquisition unit 150 acquires the system
information of the primary system from the data server 30. Also, the data
acquisition unit 150 acquires information such as the position, the antenna garn, and
the maximum transmission power of the SS terminal 24 that joins in the secondary
10 system.
[0074]
The power control unit 160 determines the transmission power of a wireless
signal that is transmitted fiom an interfering device of the secondary system, in order
not to give interference exceeding an allowable level to an interfered device of the
15 primary system. In addition, when a wireless signal is transmitted from the SS
terminal 24 at the downlink transmission timing of the primary system, the SS
terminal 24 is an interfering device and the PS terminal 14 is an interfered device.
On the other hand, when a wireless signal is transmitted from the SS terminal 24 at
thc uplink transmission timing of the primary system, the PS base station 10 is an
20 interfered device. When a wireless signal is transmitted fiom the SS base station 20,
the SS base station 20 is an interfering device.
100751
More specifically, the power control unit 160 determines the transmission
power of the interfering device by using an instantaneous value of a fading index that
25 is estimated based on a change in a relative distance between the interfering device
and the interfered device according to the above-described interference model. The
instantaneous value of the fading index is periodically cstimated in a short cycle, and
the transmission power is dynamically updated by using thc estimated instantaneous
value. The transmission power is determined by substituting the instantaneous
30 value of the fading index into the above-described power calculation fornlula (11)
expressing the water filling principle, for example. The cutofl'threshold value 50 of
thc power calculation formula is dependent on the deviation of fading and is
calculated through the interference model parameters K, X, and y.
[0076]
The instantaneous value of thc fading index may be estimated in the
5 communication control device 20. Alternatively, the instantaneous value of the
fading indcx may be estimated in other devices (for example, the individual SS
terminal 24). In the former case, the power control unit 160 periodically estimates
the instantaneous value of the fading index about each interfering device based on a
change in the relative distance of the interlering device, that is, the relative
10 movement amount (from the reference point) corrcsponding to the abovc-described
paramctcr d,. In the latter case, the instantaneous valuc of the fading index is
estimated by a device, and the estimated instantaneous value is transmitted from the
device and is received by the network comnlunication unit 110.
COO771
15 The power control unit 160 instructs each interfering device to use the
dynamically-updated transmission power (or less transmission power). In the result,
the communication capacity of the secondary system is optimized within such a
range that the SlNR loss expressed by Formula (2) does not exceed the SlNR loss
allowance of the primary system. However, the above-described interference model
20 is based on a probabilistic method and does not zcro out the risk of harmful
interference. Therehe, the power control unit 160 reconstructs a power calculation
formula when the dynamically-updated transmission power causes interference
exceeding an allowance in the interfered device. The occurrence of the interference
exceeding the allowance may be detected by receiving an observation report from the
25 interfered device (for example, the PS terminal 14).
100781
For example, the storage unit 130 prestores a mapping table that maps a
quality indicator measured in the interfered device and a parameter constituting the
power calculation lormula. Herein, the quality indicator may be any indicator that
30 is dependent on an interference amount. For example, the quality indicator may be
an absolute interference amount, a relative interference amount about an allowable
level, an absolute SWR loss, a relative SWR loss about an SlNlI loss allowance, or
the like. The parameter constituting the power calculation formula may include, for
example, one or more of the above-described interference model parameters K, X,
and y and the cutoff threshold value 50. Then, when receiving the observation
5 report from the interfered device, the power control unit 160 reconstructs a power
calculation formula according to the quality indicator included in the observation
report by reference to the mapping table stored in the storage unit 130. For example,
when harmful interference exceeding the allowable level by A1 is observed, the
cutoff threshold value (0 may be reduced by AI.
10 [0079]
[2-3. Flow of process]
(I) Overall flow
FIG. 6 is a flow chart illustrating an example of an overall flow of a
comn~unicationc ontrol process according to the present embodiment.
15 [0080]
Referring to FIG 6, first, when the secondary system starts to operate, thc
data acquisition unit 150 acquires system information of the primary system from the
data server 30 (step S110). Also, the data acquisition unit 150 acquires system
information of the secondary system, such as the antenna gain and the position of the
20 interlering device (stcp S120).
[0081]
Next, the power control unit 160 acquires a coefficient vector h r estimation
of a fading index (step S130). The coel'ficient vector may be precalculated as a
least square solution of the above-described simultaneous equation (19) in a control
25 initialization phase (or before it) based on a plurality of sets of measured reception
power P, and a change d, in the relative distance of the interfering device.
[0082]
Next, the power control unit 160 constructs a power calculation formula of
the above-dcscribed interference model by using the inlormation acquired in stcps
30 SllO and S120 (step S140). A detailed flow thereof will be further described later.
[0083]
Next, the power control unit 160 estimates an instantaneous value
20 Up to here, the embodiments of the technology of the present disclosure
have been described in detail with reference to FIGS. 1 to 8. According to the
above-described embodiments, the transmission powcr of the wireless signal
transmitted from the interfering device is determined by using the fading index that is
estimated based on thc change in the relative distance between the interfering device
25 and the interfered dcvice. Therefore, a margin of a power increase generated by a
path loss variation caused by fading may be efficiently uscd in the interfering device
without accurately estimating a path loss between the systems by close signaling.
Accordingly, the communication capacity of the secondary system using the
frequency channel protected for the sake of the primary system may be optimized
30 while suppressing an increase in thc signaling overhead.
100991
Also, according to the above-dcscribed embodiments, the transmission
power is determined by substituting the instantaneous value of the fading index into
the power calculation formula expressing the water filling principle. The
instantaneous value or the fading index may be updated in a shorter cycle than the
5 existing method. Thus, for example, the communication capacity may be increased
by dynamically increasing the transmission power of the interfering device at the
timing of the generation of a path loss exceeding an average value during a period of
time. Also, the powcr calculation Sorm~tlai s derived by using the cutoff thleshold
value that is dependent on a deviation of Fading. Therefore, harmful interference
10 may be prevented from occurring in the intcrfcred dcvicc, by ~eroing out the
transmission power of the interfering device at the timing when a path loss varying
due to fading is small.
[OlOO]
Also, according to the above-described embodiments, the power calculation
15 formula is updated when the dynamically-updated transmission powcr causes
interference exceeding an allowance. Thus, since the r~sk of harmful interference
caused by an error in the interference model is reduced by a feedback loop from the
interfered device, robuster interference control may be implemented. The power
calculation formula may be updated by reference to the mapping table between the
20 observed quality indicator and the interference model parameter. Therefore, the
amount of data signaled for the sake of the feedback loop may be suppressed.
[OlOl]
In terms of "secondary use", the wireless communication service of the
primary system and the wireless communication service of the secondary system
25 may be different types of services or may be the same type of services. The
different types of wireless communication services may be, for example, two or more
different types of wireless communication services selected Srom any services such
as a digital TV broadcasting service, a satellite communication service, a mobile
communication service, a wireless LAN access service, and a peer to peer (1'21')
30 connection service. On the other hand, the same types of wireless communication
services may include, for example, a relation between a macro cell service, which is
provided by a communication service provider, and a femto cell service, which is
operated by a user or a mobile virtual network operator (MVNO), in a mobile
communication service. Also, the same type of communication services may
include a relation between a service, which is providcd by a base station, and a
5 service, which is providcd by a relay station (a relay node) to covcr a spectrum hole,
in a communication service based on WiMAX, UTE (Long Tcrm Evolution), LTE-A
(LTE-Advanced), or the like. In addition, the secondary system may use a plurality
of fragmentary frequency bands that are aggregated by using a spectrum aggregation
technology. In addition, thc secondary system may be a fenlto cell group existing in
10 a service area provided by a base station, a relay station group, or a small and
medium-sized base station group that provides a smaller service area than a basc
station. The interlerence model described in this specification may be widely
applied to all these types of secondary use modes.
10 1021
15 Also, the interference model described in this specification is not limited to
thc purpose of secondary use of a frequency channel but may be applied to the
purpose of various interference controls.
[0 1031
The calculation process described in this specification may be implemented
20 by using software, hardware, or a combination of software and hardware. Programs
constituting the soflware are prestored, for example, in a storage mecliurn that is
provided inside or outside the dcvicc. Then, for example, each program is loaded
into a randoin access memory (RAM) and executed by a processor such as a CPU.
[0 1041
25 The preferred embodiinerits of the present disclosure have been described
abovc with relerence to the accompanying drawings, whilst the present disclosure is
not limited to the above examples, of course. A person sltillcd in the art may find
various alterations and modifications within the scope of the appended claims, and it
should be understood that they will naturally come under the technical scope of the
30 present disclosure.
[0105]
Additionally, the present technology may also be configured as below.
(1)
A communication control device including:
a power control unit configured to determine a transmission power of a
5 wireless signal, which is transmitted fiom an interfering device, by using a fading
index that is estimated based on a change in a relative distance between the
interfering device and an interfered device.
(2)
The communication control device according to (I),
10 wherein the power control unit dctcrmines the transmission power by
substituting the fading index into a calculation formula that expresses a water filling
principle.
(3)
The communication control device according to (2),,
15 wherein the calculation formula is derived by using a cutoff threshold value
that is dependent on a deviation of fading.
(4)
The communication control device according to (2) or (3),
wherein the power control unit dynamically updates the transmission power
20 by using an instantaneous value of the fading index.
(5)
The communication control device according to (41,
wherein the power control unit updatcs the calculation formula when the
dynamically-updated transmission power causes interference exceeding an allowance
25 in the intcrfered device.
(6)
The communication control device according to (5),
wherein the powcr control unit updates the calculation formula by using a
quality indicator that is observed in the interfered device and by reference to a
30 mapping table that maps the quality indicator and a parameter constituting the
calculation formula.
(7)
The communication control device according to any one of (1) to (6),
wherein the fading index is estimated by substituting the change in the
relative distance into an estimation formula that has coefficients that are
precalculated based on a plurality of relative distances and a plurality of reception
powers that arc measured at the plurality olrelative distances, respectively.
(8)
The communication control devicc according to any one of (1) to (7),
wherein the interfered device is a receiver station of a primary system, and
wherein thc interfering device is a transmitter station of a scconclary system
that secondarily uses a frequency channel that is protected for the sake of the primary
systcm.
(9)
The communication control device according to (8),
wherein the communication control device is the transmitter station of the
secondary system.
(10)
The communication control device according to (8),
wherein the communication control device is a scrvcr device that manages
the secondary use of the frequency channcl.
(11)
The con~municationc ontrol device according to any one of (1) to (lo),
wherein the power control unit estimates the fading index based on the
change in the relative distance.
(12)
The communication control devicc according to any one ol (1) to (lo),
further including:
a communication unit configured to receive the estimated fading index from
a device that has estimated the fading index bascd on the change in the relative
distance.
(13)
A communication control method, which is executed by a communication
control device that controls a transmission power of an interfering device, the
communication control method including:
determining a transmission power of a wireless signal, which is transmitted
5 from the interfering devicc, by using a fading index that is estimated based on a
changc in a relative distance between the interfering device and an interfered device.
(14)
A program for causing a computer, which controls a communication control
device, to function as:
10 a power control unit configured to determine a tra~~smissiopno wer of a
wireless signal, which is transmitted from an interfering device, by using a fading
index that is estimated based on a change in a relative distance between the
interfering device and an interfered device.
(15)
15 A communication control system including:
a wireless communication device of a second wirelcss communication
system located in a cell of a first wireless communication system; and
a comlnunication control dcvice configured to determine a transmission
power of a wireless signal, which is transmitted from the wireless communication
20 device, not to give harmful interference to the first wireless communication system,
by using a fading index that is estimated based on a change in a rclativc position of
the wireless communication device.
IZefercnce Signs List
25 [0106]
20 communication control device
110 network communication unit
120 wireless communication unit
130 storage unit
30 140 control unit
150 data acquisition unit
160 powcr control unit

WE CLAIMS:-
A communication control device comprising:
a power control unit configured to determine a transmission power of a
5 wireless signal, which is transmitted from an interfering device, by using a fading
index that is estimated based on a change in a relative distance between the
interfering device and an interfered device.
Claim 2
10 The communication control device according to claim 1,
wherein the power control unit determines the transmission power by
substituting the fading index into a calculation formula that expresses a water filling
principle.
?,
>,
15 Claim 3
,! The communication control device according to claim 2,
wherein the calculation fornlula is derived by using a cutoff threshold valuc
that is dcpcndent on a deviation of fading.
20 Claim 4
Thc commurlication control device according to claim 2,
wherein the power control unit dynamically updates the transmission power
by using an instantaneous value of the fading index.
25 Claim 5
Thc communication control device according to claim 4,
wherein the power control unit updates the calculation formula when the
dynamically-updated transmission power causes interference exceeding an allowance
in the interfered device.
30
I
Claim 6
The communication control device according to claim 5,
wherein the power control unit updates the calculation formula by using a
quality indicator that is observcd in the interfered device and by reference to a
mapping table that maps the quality indicator and a parameter constituting the
5 calculation formula.
Claim 7
The communication control device according to claim 1,
wherein thc fading index is estimated by substituting the change in the
10 rclative distance into an estimation fornlula that has cocfficienls that are
precalculated based on a plurality of relative distances and a plurality of reception
powers that are measured at the plurality of relative distances, respectively.
Claim 8
15 The communication control device according to claim 1,
wherein the interfered device is a receiver station of a primary system, and
wherein the interfering device is a transmitter station of a secondary system
that secondarily uses a frequency channel that is protccted for the sake of the primary
system.
20
Claim 9
The communication control device according to claim 8,
wherein the communication control device is the transmitter station of the
secondary system.
25
Claim 10
The communication control device according to claim 8,
wherein the communication control dcvice is a server device that managcs
the secondary usc ofthe frequency channel.
30
Claim 11
The communication control device according to claim 1,
wherein the power control unit estimates the fading index based on the
change in the relative distance.
5 Claim 12
The communication control device according to claim 1, further comprising:
a communication unit configured to receive the estimated fading index from
a device that has estimated the fading index based on the change in the relative
distance.
10
Claim 13
A communication control method, which is executed by a communication
control device that controls a transmission power of an interfering device, the
communication control method comprising:
15 determining a transmission power of a wireless signal, which is transmitted
from the interfering device, by using a fading index that is estimated based on a
change in a relative distance between the interfering dcvicc and an interfered device.
Claim 14
20 A program for causing a computer, which controls a communication control
device, to function as:
a powcr control unit configured to dctermine a transmission power of a
wireless signal, which is transmitted from an interfering device, by using a fading
index that is estimated based on a change in a relative distance between the
25 interfering dcvice and an interfered device.
Claim 15
A communicatiocnon trol system comprising:
a wireless communicatio~l device of a second wireless communication
30 system located in a cell of a first wireless communication system; and
a communication control dcvice conegured to determine a transmission
power of a wireless signal, which is transmitted from the wireless communication
device, not to give harmful interference to the first wireless communication system,
by r fading index that is estimated based on a change in a relative position of
the wireless comn~unicationd evice.