Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-08-20
2002-07-02
Le, Amanda T. (Department: 2634)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S145000, C375S356000, C370S328000, C370S441000, C455S426100, C455S517000
Reexamination Certificate
active
06414986
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio communication method and a radio communication system, and more particularly, is suitably applied to a wireless local area network (LAN) system having plural communication terminals connected to each other by radio, for example.
2. Description of the Related Art
There is a cable LAN system having a LAN constructed by connecting plural computers to each other by cables. In this cable LAN system, the plural computers can share files or data, and also can forward electronic mails or data to each other.
However, in construction of such LAN system, a complicated construction to mutually connect the plural computers is necessary, and a system configuration is complicated because various cables are needed for connecting. Recently, then, the system is turning from a cable LAN system to a wireless LAN system.
For this wireless LAN system, a system has been proposed, in which terminals send/receive data to/from each other using a transmission signal generated by performing spectrum diffusion on transmission data in the form of a diffusion code being a pseudonoise code (e.g., a pseudo random noise (PN) code)) (hereinafter, this system is referred to as a spectrum diffusion system).
Such the wireless LAN system using the spectrum diffusion system multiplies a PN code by the transmission signal to diffuse over a wide band, and transmits the transmission signal by a radio wave having a low power density. Since the transmission is performed by a radio wave with a small power density, the spectrum diffusion system has characteristics in which the transmission has little influence on terminals which do not communicate and also the transmission is hard to be influenced by other terminals because of performing diffusion and inverse-diffusion using a PN code.
Moreover, in the spectrum diffusion system, a receiving end can demodulate a transmission signal only by multiplying a diffusion code having the same sequence pattern and the same phase as one used by a transmitting end by a reception signal for the inverse-diffusion processing. Therefore, it is superior in a secret story and has a great effect of security against wiretapping.
By the way, as shown in
FIG. 1
, a wireless LAN system
1
of the spectrum diffusion system having the above configuration is composed of plural communication terminals
2
and
3
and a communication terminal controller
4
for controlling the communication terminals
2
and
3
. The communication terminal controller
4
is prescribed distances L
1
and L
2
away from the communication terminals
2
and
3
respectively.
To synchronize with the communication terminals
2
and
3
, as shown in
FIG. 2
, the communication terminal controller
4
transmits a PN code PN
1
having a prescribed code sequence pattern to the communication terminals
2
and
3
, which are different in distance from the controller
4
, at the timing of the head of frames. The communication terminals
2
and
3
receive the PN code PN
1
after delay times &Dgr;t
1
and &Dgr;t
2
that correspond to the distances L
1
and L
2
from the communication terminal controller
4
.
For instance, as shown in
FIG. 3
, when the communication terminal controller
4
transmits the PN code PN
1
to the communication terminal
2
at the timing of the head of frame, the communication terminal
2
receives the PN code PN
1
after the delay time &Dgr;t
1
(=approximately 33 nsec). Then, the communication terminal
2
transmits packet data PD
1
including desired information data to the communication terminal controller
4
a time assigned to transmit T
X1
after reception.
In this case, the communication terminal controller
4
receives the packet data PD
1
, sent from the communication terminal
2
being the distance L
1
away therefrom, after a delay time T
TX1′
that is obtained by adding a delay times for transmitting and receiving 2×&Dgr;t
1
to the time assigned to transmit T
TX1
, since it takes the delay time &Dgr;t
1
to transmit data with the communication terminal
2
.
Also, it is not shown but, the communication terminal controller
4
receives packet data PD
2
, sent from the communication terminal
3
, after a delay time T
TX2′
that is calculated by adding delay times for transmitting and receiving 2×&Dgr;t
2
to the time assigned to transmit T
TX2
.
Accordingly, the communication terminal controller
4
receives the packet data PD
1
and PD
2
from the communication terminals
2
and
3
at separate timings. As a result, in the case of expecting that the packet data PD
1
and PD
2
will be received at fixed timings, if the packet data PD
1
and PD
2
are demodulated at the expected timing, the controller
4
had a problem in that the error of receiving timing would cause a demodulation error.
With respect to an error of receiving timing 2×&Dgr;ti (i=1 or 2), for instance, if a transmission rate in transmitting is approximately 30 Mbps, an error 2×&Dgr;ti (2×33 nsec) to the bit length of transmission data becomes an extremely high value; a demodulation error will occur definitely.
Furthermore, data communication between the communication terminal
2
and
3
also had a problem that an error of receiving timing would cause a similar demodulation error.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of this invention is to provide a radio communication method and a radio communication system capable of always accurately demodulating data.
The foregoing object and other objects of the invention have been achieved by the provision of a method for radio communication for exchanging a transmission signal modulated by a prescribed method based on information data between plural communication terminals and for controlling the plural communication terminals by a control terminal. In this method, the control terminal generates and transmits a first code sequence used for making the control terminal synchronize with the plural communication terminals, to the plural communication terminals, the communication terminal synchronizes with the control terminal based on a reference timing obtained by receiving the first code sequence, generates and transmits a second code sequence that represents a demodulation timing of a transmission signal, to another communication terminal out of the plural communication terminals, and then, transmits the transmission signal to the other communication terminal after the second code sequence, and the other communication terminal demodulates the transmission signal received following the second code sequence based on the demodulation timing of receiving the second code sequence.
The communication terminal synchronizes with the control terminal based on the first code sequence sent from the control terminal, transmits the second code sequence representing the demodulation timing of the transmission signal to the other communication terminal, and then transmits the transmission signal to the other communication terminal after the above second code sequence, so that the other communication terminal can accurately demodulate the received transmission signal, provided that it starts demodulation processing based on the demodulation timing of receiving the second code sequence.
In a radio communication system composed of plural communication terminals which exchange a transmission signal modulated by a prescribed method based on information data with each other and a control terminal for controlling the plural communication terminals, the control terminal comprises a first code sequence generating means for generating a first code sequence used to make the control terminal synchronize with the plural communication terminals, and a first transmission means for transmitting the first code sequence to the plural communication terminals, and each communication terminal comprises a second code sequence generating means for generating a second code sequence that represents a demodulation timing of the transmission signal, a modul
Le Amanda T.
Maioli Jay H.
Sony Corporation
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