DESCRIPTION
COMMUNICATION APPARATUS AND TRANSMISSION LINE ESTIMATION METHOD
TECHNICAL FIELD
The present invention relates to a communication apparatus
and a transmission line estimation method. More specifically,
the present invention relates to a communication apparatus sending
and receiving data based on the characteristics of a transmission
line between apparatuses without lowering the throughput, and a
transmission line estimation method (channel estimation)
performed by the communication apparatus, by which the
characteristics of the transmission line are estimated and
evaluated with a high precision.
BACKGROUND ART
In a communication method by which communication parameters
such as a subcarrier and a modulation method used for transmission
and reception are determined based on estimation on the
characteristics of a transmission line, it is important to
precisely determine the communication parameters that are suitable
for the characteristics of the transmission line in transmission.
In particular, in a communication system having attenuation
characteristics that deeply depend on the frequency (power line
carrier communications having a power line as a communication

medium, for example) , it is effective to use a multi-carrier
transmission line method using a subcarrier and a modulation method
that are suitable for the characteristics of the transmission line .
In a transmission line estimation method used in conventional
communication systems, a transmission line is estimated
periodically or when the number of retransmissions due to
communication errors exceeds a specified value (considering that
the characteristics of the transmission line are deteriorated).
Then, based on the result of this estimation on the transmission
line, new parameters are selected, and data is sent or received.
This technique has been disclosed in, for example, JP2002-158675A.
However, in an environment in which the characteristics of
the transmission line vary periodically, the communication
parameters selected when estimating the transmission line often
do not suit for the characteristics of the transmission line when
sending data if a timing of sending data is not synchronized with
the periodical variation of the characteristics of the transmission
line. Thus, in the above-described conventional method, the
maximum communication efficiency is not always obtained even when
the transmission line is estimated
Thus, as a countermeasure for this problem, a following
method has been conventionally proposed
First, the variation cycle of the characteristics of a
transmission line is synchronized with the frame period of a
communication system, and this variation cycle is divided into

a plurality of sections. Next, within one frame period, the
plurality of divided sections of the transmission line are
continuously estimated section by section. Then, as a result of
the transmission line estimation, communication parameters
obtained in a section with the highest communication efficiency
are selected and then communications are performed. FIG 12 is
a process sequence of this conventional method for estimating a
transmission line
However, in the conventional method shown in FIG. 12, there
is the problem that the transmission line is estimated continuously,
and thus requests to estimate the transmission line and their
response messages occupy the transmission line and disturb
communications of stream data, audio data, or other data that is
supposed to be sent Furthermore, in this conventional method,
a time from the starting point of the frame period of the
communication system to the starting time of a transmission line
estimation section is different for each frame period. As a result,
when the band is guaranteed, for example, with time sharing, not
only is scheduling for transmission line estimation complicated,
but also arises a case in which a scheduling condition cannot be
satisfied.
DISCLOSURE OF THE INVENTION
Therefore, an object of the present invention is to provide
a communication apparatus in which a transmission line is estimated

xn a distributed manner by a simple scheduling, so that the
characteristics of the transmission line are estimated and
evaluated with a high precision and thus data can be sent and received
at a high throughput without affecting other streams, and a
transmission line estimation method performed by the communication
apparatus.
The present invention is directed to a communication
apparatus performing periodical communications with another
communication apparatus via a transmission line. In order to
achieve the above-described object, the communication apparatus
of the present invention is provided with a communication control
portion, a transmission line estimation portion, and a
communication parameter determination portion.
The communication control portion sets the communication
period to (Lxm/n) (L is the variation cycle of the characteristics
of a transmission line, n is an integer that is 2 or larger, and
in is an integer that is n or larger and whose greatest common measure
with n is 1) to perform communications. The transmission line
estimation portion estimates the characteristics of the
transmission line within a time (L/n) after a certain offset time
(Lxk/n) (k is a real number that is 0 or larger) has passed since
the communication period started. The communication parameter
determination portion determines a communication parameter to be
used by the communication control portion, based on a result of
estimation by the transmission line estimation portion.

It is preferable that the transmission line estimation
portion estimates the characteristics of the transmission line
at least n times Furthermore, the communication apparatus may
estimate the characteristics of the transmission line at the
initial starting up or upon detecting a change in a state of the
transmission line A typical communication period is the period
of beacons sent from a communication apparatus serving as a base
unit. When there is a request to estimate the characteristics
of the transmission line, the communication apparatus sends a
request to allocate a time for estimating the characteristics of
the transmission line to the communication apparatus serving as
the base unit, and the characteristics of the transmission line
are estimated only when permission is given. This request may
be notified using the beacon frame or the polling frame to another
communication apparatus. A typical variation cycle L of the
characteristics of the transmission line is the half cycle of the
commercial power supply cycle.
Each of the processes performed by each of the components
of the communication apparatus described above can be regarded
as a transmission line estimation method that gives a series of
procedures This method is provided in the form of a program for
letting a computer execute the series of procedures. This program
may be introduced in a computer in the form stored in a
computer-readable storage medium Furthermore, a part of the
functional blocks described above that constitute the

communication apparatus may be realized as an LSI, which is an
integrated circuit.
As described above, according to the present invention, a
transmission line is estimated in a distributed manner by a simple
scheduling, so that the characteristics of the transmission line
are estimated and evaluated with a high precision and thus data
can be sent and received at a high throughput without affecting
other streams.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing a configuration example of a
communication network system using communication apparatuses
according to a first embodiment of the present invention.
FIG. 2 is a diagram showing an example of timings at which
a transmission line is estimated by the communication apparatuses
according to the first embodiment of the present invention
FIG. 3 is a diagram showing another example of timings at
which a transmission line is estimated by the communication
apparatuses according to the first embodiment of the present
invention
FIG. 4 is a diagram showing another example of timings at
which a transmission line is estimated by the communication
apparatuses according to the first embodiment of the present
invention.
FIG 5 is a communication sequence showing the procedure

following which a transmission line is estimated by the
communication apparatuses according to the first embodiment of
the present invention.
FIG. 6 is a diagram showing an example of a tonemap.
FIG. 7 is a diagram explaining the relationship between a
noise and transmission line estimation sections.
FIG. 8 is another communication sequence showing the
procedure following which a transmission line is estimated by the
communication apparatuses according to the first embodiment of
the present invention.
FIG. 9 is a diagram explaining a method by which a beacon
period is determined by the communication apparatuses according
to the first embodiment of the present invention.
FIG. 10 is a diagram explaining a method by which a beacon
period is determined by the communication apparatuses according
to the first embodiment of the present invention.
FIG. 11 is a diagram showing an example of a communication
network system in which the communication apparatuses of the
present invention are applied to high-speed power line
transmission.
FIG. 12 is a communication sequence showing the procedure
following which a transmission line is estimated by a conventional
communication apparatus
BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be
described with reference to the drawings
First Embodiment
FIG 1 is a diagram showing a configuration example of a
communication network system using a communication apparatus 1
according to a first embodiment of the present invention. In FIG 1,
in the communication network system of the present invention, a
plurality of communication apparatuses 1 are connected to each
other via a transmission line 2. The transmission line 2 may be
either wired or wireless. This embodiment will be described using,
as an example, the communication network system in which one of
the plurality of communication apparatuses 1 is a master unit,
and this master unit periodically transmits a beacon so as to control
the communications of the other communication apparatuses 1 (slave
units).
The communication apparatus 1 is provided with a
communication control portion 11, a transmission line estimation
portion 12, and a communication parameter determination
portion 13. The communication control portion 11 deals with most
of the communication processes performed by the communication
apparatus 1. Basically, this communication control portion 11
performs communications with another communication apparatus 1
using communication parameters determined by the communication
parameter determination portion 13. The transmission line
estimation portion 12 measures the characteristics of the

transmission line 2 at predetermined periodical timings and
estimates a state of the transmission line 2. The communication
parameter determination portion 13 sets or updates communication
parameters based on the result obtained when transmission line
estimation portion 12 estimates the transmission line 2.
Hereinafter, a method by which the thus configured
communication apparatus 1 estimates the characteristics of a
transmission line will be described. FIGS. 2 to 4 are diagrams
each showing an example of timings at which a transmission line
is estimated by the communication apparatus 1 according to the
first embodiment of the present invention. FIG. 5 is a
communication sequence showing the procedure following which a
transmission line is estimated by the communication apparatus 1
according to the first embodiment of the present invention.
In this embodiment, a case will be described in which in
the transmission line 2 in the communication network system, a
noise with a certain pattern (the mark X in FIG. 2) is generated
with certain intervals as shown in FIG. 2, that is, the variation
cycle of the characteristics of the transmission line corresponds
to these certain intervals. In this case, the communication
control portion 11 in each of the communication apparatuses 1 that
constitute the communication network system sets the beacon period,
which will be the communication period, in the following manner
Herein, the beacon period refers to a time interval between when
a beacon is transmitted by the master unit and when its next beacon

is transmitted.
There is a case in which due to an influence of a power circuit
of, for example, a household electrical appliance that is connected
to a power line, the cycle of a noise pattern on the power line
is the same as the half cycle of a commercial power supply (50 Hz
or 60 Hz). Accordingly, when assuming a communication network
system using a power line, it is necessary to consider the
characteristics of a transmission line that has been synchronized
with the half cycle of the commercial power supply described above
(see sine waves in FIG. 2) .
A point of the setting is that a variation cycle L of the
characteristics of the transmission line is divided into n sets
of sections (n sections), a procedure is repeated in which
transmission line estimation is performed for only one section
among n sections in one beacon period, and thus transmission line
estimation is performed for all of the n sections. A beacon
period T for realizing this point is set based on "T=Lxm/n", where
n is an integer that is 2 or larger, and in is an integer that is
n or larger and whose greatest common measure with n is 1
Furthermore an offset time is set based on "Lxk/n", where k is
a real number that satisfies 0^k