Wireless communication system

• US 20110128995A1
• Filed: 10/26/2010
• Published: 06/02/2011
• Est. Priority Date: 11/27/2009
• Status: Active Grant

• Current Assignee: DENSO Corporation, Nippon Soken, Inc.
• Original Assignee: DENSO Corporation, Nippon Soken, Inc.
• Inventors: Sugiura, Masahiro, Takaoka, Akira, Naitoh, Hiromichi, Sanji, Kenichiro
• Granted Patent: US 8,477,826 B2
• Time in Patent Office: Days
• US Class Current: 375/145
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

In a wireless communication system, a portable device transmits a first signal spread based on a reference period indicated by a synchronization signal transmitted from an in-vehicle device and transmits a second signal spread based on an operation by a user. The in-vehicle device sets a search period based on a variation range in a delay time from when the synchronization signal is transmitted to when the spread first signal is transmitted and sets a residual period that starts at an ending point of the search period and ends at an ending point of the reference period when a starting point of the reference period is set at a starting point of the search period. When the in-vehicle device fails in a synchronous acquisition for the search period, the in-vehicle device performs a synchronous acquisition process for the residual period.

Claims

1. A wireless communication system comprising:

a portable device configured to spread one of a first signal and a second signal by a first spreading code and to transmit a wireless signal that is one of a spread first signal and a spread second signal; and

an in-vehicle device configured to receive the wireless signal and to despread a received wireless signal by a second spreading code identical to the first spreading code to wirelessly communicate with the portable device by a spread spectrum method, wherein;

the in-vehicle device transmits a synchronization signal to the portable device to inform the portable device of a reference period determined by the in-vehicle device;

when the portable device receives the synchronization signal while the portable device is not transmitting the spread second signal, the portable device changes the first spreading code synchronously with the synchronization signal, spreads the first signal by the changed first spreading code, and transmits the spread first signal;

when the portable device receives a predetermined operation by a user, the portable device stops transmitting the spread first signal, spreads the second signal by the first spreading code, and transmits the spread second signal;

when the in-vehicle device receives the wireless signal after transmitting the synchronization signal, the in-vehicle device performs a first synchronous acquisition process of searching for a synchronous acquisition point for a search period;

the synchronous acquisition point is a point where a correlation value in despreading becomes a maximum value;

the search period is determined based on a variation range in a delay time from when the in-vehicle device transmits the synchronization signal to when the portable device transmits the spread first signal;

the search period is from a search starting point to a search ending point and is shorter than the reference period;

when the in-vehicle device fails in the first synchronous acquisition process, the in-vehicle device performs a second synchronous acquisition process of searching for the synchronous acquisition point for a residual period;

the residual period starts at the search ending point and ends at an ending point of the reference period when a starting point of the reference period is set at the search starting point; and

when the in-vehicle device succeeds in one of the first synchronous acquisition process and the second synchronous acquisition process, the in-vehicle device changes the second spreading code synchronously with the received wireless signal, and despreads the received wireless signal by a changed second spreading code.

2. The wireless communication system according to claim 1, wherein

when the in-vehicle device fails in the second synchronous acquisition process, the in-vehicle device searches for the synchronous acquisition point in period that starts after the residual period ends and has a length same as the reference period.

3. The wireless communication system according to claim 1, wherein

when the in-vehicle device detects a failure in despreading after starting despreading, the in-vehicle device searches for the synchronous acquisition point for a period that starts after the in-vehicle device detects the failure and has a length same as the reference period.

4. The wireless communication system according to claim 2, wherein

when the in-vehicle device detects a failure in despreading after starting despreading, the in-vehicle device searches for the synchronous acquisition point for a period that starts after the in-vehicle device detects the failure and has a length same as the reference period.

5. The wireless communication system according to claim 1, wherein

when the in-vehicle device succeeds in the first synchronous acquisition, the in-vehicle device performs a process based on the first signal obtained by despreading, and

when the in-vehicle device receives the wireless signal from the portable device while the in-vehicle device is performing the process based on the first signal, the in-vehicle device searches for the synchronous acquisition point for a period that starts after the in-vehicle device starts receiving the wireless signal and has a length same as the reference period.

6. The wireless communication system according to claim 2, wherein

when the in-vehicle device succeeds in the first synchronous acquisition, the in-vehicle device performs a process based on the first signal obtained by despreading, and

when the in-vehicle device receives the wireless signal from the portable device while the in-vehicle device is performing the process based on the first signal, the in-vehicle device searches for the synchronous acquisition point for a period that starts after the in-vehicle device starts receiving the wireless signal and has a length same as the reference period.

7. The wireless communication system according to claim 3, wherein

when the in-vehicle device succeeds in the first synchronous acquisition, the in-vehicle device performs a process based on the first signal obtained by despreading, and

when the in-vehicle device receives the wireless signal from the portable device while the in-vehicle device is performing the process based on the first signal, the in-vehicle device searches for the synchronous acquisition point for a period that starts after the in-vehicle device starts receiving the wireless signal and has a length same as the reference period.

8. The wireless communication system according to claim 4, wherein

when the in-vehicle device succeeds in the first synchronous acquisition, the in-vehicle device performs a process based on the first signal obtained by despreading, and

when the in-vehicle device receives the wireless signal from the portable device while the in-vehicle device is performing the process based on the first signal, the in-vehicle device searches for the synchronous acquisition point for a period that starts after the in-vehicle device starts receiving the wireless signal and has a length same as the reference period.

9. The wireless communication system according to claim 1, wherein:

the in-vehicle device has a standby mode and a normal mode;

when the in-vehicle device is in the standby mode, the in-vehicle device does not receive the wireless signal from the portable device for reducing electric power consumption;

when the in-vehicle device is in the normal mode, the in-vehicle device receives the wireless signal from the portable device;

a mode of the in-vehicle device changes from the standby mode to the normal mode at intervals of a first predetermined time;

the mode of the in-vehicle device changes from the normal mode to the standby mode at a second predetermined time;

the reference period is determined based on the intervals of the first predetermined time;

the portable device transmits the spread second signal including a preliminary part and a main part;

the preliminary part is transmitted for a period corresponding to a sum of the first predetermined time and a receiving time of the wireless signal for which the synchronous acquisition point is searched in the first synchronous acquisition process and the second synchronous acquisition process; and

the main part includes a transmission data from the portable device to the in-vehicle device and is transmitted following the preliminary part.

10. The wireless communication system according to claim 2, wherein:

the in-vehicle device has a standby mode and a normal mode;

when the in-vehicle device is in the standby mode, the in-vehicle device does not receive the wireless signal from the portable device for reducing electric power consumption;

when the in-vehicle device is in the normal mode, the in-vehicle device receives the wireless signal from the portable device;

a mode of the in-vehicle device changes from the standby mode to the normal mode at intervals of a first predetermined time;

the mode of the in-vehicle device changes from the normal mode to the standby mode at a second predetermined time;

the reference period is determined based on the intervals of the first predetermined time;

the portable device transmits the spread second signal including a preliminary part and a main part;

the preliminary part is transmitted for a period corresponding to a sum of the first predetermined time and a receiving time of the wireless signal for which the synchronous acquisition point is searched in the first synchronous acquisition process and the second synchronous acquisition process; and

the main part includes a transmission data from the portable device to the in-vehicle device and is transmitted following the preliminary part.

11. The wireless communication system according to claim 3, wherein:

the in-vehicle device has a standby mode and a normal mode;

when the in-vehicle device is in the standby mode, the in-vehicle device does not receive the wireless signal from the portable device for reducing electric power consumption;

when the in-vehicle device is in the normal mode, the in-vehicle device receives the wireless signal from the portable device;

a mode of the in-vehicle device changes from the standby mode to the normal mode at intervals of a first predetermined time;

the mode of the in-vehicle device changes from the normal mode to the standby mode at a second predetermined time;

the reference period is determined based on the intervals of the first predetermined time;

the portable device transmits the spread second signal including a preliminary part and a main part;

the preliminary part is transmitted for a period corresponding to a sum of the first predetermined time and a receiving time of the wireless signal for which the synchronous acquisition point is searched in the first synchronous acquisition process and the second synchronous acquisition process; and

the main part includes a transmission data from the portable device to the in-vehicle device and is transmitted following the preliminary part.

12. The wireless communication system according to claim 4, wherein:

the in-vehicle device has a standby mode and a normal mode;

when the in-vehicle device is in the standby mode, the in-vehicle device does not receive the wireless signal from the portable device for reducing electric power consumption;

when the in-vehicle device is in the normal mode, the in-vehicle device receives the wireless signal from the portable device;

a mode of the in-vehicle device changes from the standby mode to the normal mode at intervals of a first predetermined time;

the mode of the in-vehicle device changes from the normal mode to the standby mode at a second predetermined time;

the reference period is determined based on the intervals of the first predetermined time;

the portable device transmits the spread second signal including a preliminary part and a main part;

the preliminary part is transmitted for a period corresponding to a sum of the first predetermined time and a receiving time of the wireless signal for which the synchronous acquisition point is searched in the first synchronous acquisition process and the second synchronous acquisition process; and

the main part includes a transmission data from the portable device to the in-vehicle device and is transmitted following the preliminary part.

13. The wireless communication system according to claim 5, wherein:

the in-vehicle device has a standby mode and a normal mode;

when the in-vehicle device is in the standby mode, the in-vehicle device does not receive the wireless signal from the portable device for reducing electric power consumption;

when the in-vehicle device is in the normal mode, the in-vehicle device receives the wireless signal from the portable device;

a mode of the in-vehicle device changes from the standby mode to the normal mode at intervals of a first predetermined time;

the mode of the in-vehicle device changes from the normal mode to the standby mode at a second predetermined time;

the reference period is determined based on the intervals of the first predetermined time;

the portable device transmits the spread second signal including a preliminary part and a main part;

the preliminary part is transmitted for a period corresponding to a sum of the first predetermined time and a receiving time of the wireless signal for which the synchronous acquisition point is searched in the first synchronous acquisition process and the second synchronous acquisition process; and

the main part includes a transmission data from the portable device to the in-vehicle device and is transmitted following the preliminary part.

14. The wireless communication system according to claim 6, wherein:

the in-vehicle device has a standby mode and a normal mode;

when the in-vehicle device is in the standby mode, the in-vehicle device does not receive the wireless signal from the portable device for reducing electric power consumption;

when the in-vehicle device is in the normal mode, the in-vehicle device receives the wireless signal from the portable device;

a mode of the in-vehicle device changes from the standby mode to the normal mode at intervals of a first predetermined time;

the mode of the in-vehicle device changes from the normal mode to the standby mode at a second predetermined time;

the reference period is determined based on the intervals of the first predetermined time;

the portable device transmits the spread second signal including a preliminary part and a main part;

the preliminary part is transmitted for a period corresponding to a sum of the first predetermined time and a receiving time of the wireless signal for which the synchronous acquisition point is searched in the first synchronous acquisition process and the second synchronous acquisition process; and

the main part includes a transmission data from the portable device to the in-vehicle device and is transmitted following the preliminary part.

15. The wireless communication system according to claim 7, wherein:

the in-vehicle device has a standby mode and a normal mode;

when the in-vehicle device is in the standby mode, the in-vehicle device does not receive the wireless signal from the portable device for reducing electric power consumption;

when the in-vehicle device is in the normal mode, the in-vehicle device receives the wireless signal from the portable device;

a mode of the in-vehicle device changes from the standby mode to the normal mode at intervals of a first predetermined time;

the mode of the in-vehicle device changes from the normal mode to the standby mode at a second predetermined time;

the reference period is determined based on the intervals of the first predetermined time;

the portable device transmits the spread second signal including a preliminary part and a main part;

the preliminary part is transmitted for a period corresponding to a sum of the first predetermined time and a receiving time of the wireless signal for which the synchronous acquisition point is searched in the first synchronous acquisition process and the second synchronous acquisition process; and

the main part includes a transmission data from the portable device to the in-vehicle device and is transmitted following the preliminary part.

16. The wireless communication system according to claim 8, wherein:

the in-vehicle device has a standby mode and a normal mode;

when the in-vehicle device is in the standby mode, the in-vehicle device does not receive the wireless signal from the portable device for reducing electric power consumption;

when the in-vehicle device is in the normal mode, the in-vehicle device receives the wireless signal from the portable device;

a mode of the in-vehicle device changes from the standby mode to the normal mode at intervals of a first predetermined time;

the mode of the in-vehicle device changes from the normal mode to the standby mode at a second predetermined time;

the reference period is determined based on the intervals of the first predetermined time;

the portable device transmits the spread second signal including a preliminary part and a main part;

the preliminary part is transmitted for a period corresponding to a sum of the first predetermined time and a receiving time of the wireless signal for which the synchronous acquisition point is searched in the first synchronous acquisition process and the second synchronous acquisition process; and

the main part includes a transmission data from the portable device to the in-vehicle device and is transmitted following the preliminary part.