Patent ID: 8270455
Filing Date: 2012-09-18
Classification: G07C,H04B

Abstract:
1. The wireless communication system comprising: a portable device configured to spread a wireless signal by a first spread code to transmit a first spread wireless signal, an in-vehicle device including a sliding correlator or a matched filter and configured to receive the first spread wireless signal, the in-vehicle device despreading the first spread wireless signal by a second spread code identical to the first spread 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, the portable device changes the first spread code synchronously with the synchronization signal upon reception of the synchronization signal and spreads the wireless signal by the changed first spread code to transmit a second spread wireless signal, the in-vehicle device receives the second spread wireless signal and performs code acquisition for only a portion of the second spread wireless signal by using the sliding correlator or the matched filter, the portion of the second spread wireless signal having a starting point in a search period, the in-vehicle device changes the second spread code synchronously with the second spread wireless signal upon success of the code acquisition and despreads the second spread wireless signal by the changed second spread code, the search period is from a search start point to a search end point and shorter than the reference period, the search start point is identified based on the reference period and a predetermined first correction time that is equal to a time difference between the search start point and a starting point of the reference period, and the search end point is identified based on the reference period and a predetermined second correction time that is equal to a time difference between the search end point and the starting point of the reference period, and wherein the in-vehicle device transmits a first request signal to the portable device together with the synchronization signal, the portable device changes the first spread code synchronously with the synchronization signal and spreads a first response signal having information by the changed first spread code upon reception of the first request signal to transmit a spread first response signal to the in-vehicle device, the in-vehicle device receives the spread first response signal and performs the code acquisition for only a portion of the spread first response signal, the portion of the spread first response signal having a starting point in the search period, the in-vehicle device changes the second spread code synchronously with the spread first response signal upon success of the code acquisition and despreads the spread first response signal by the changed second spread code to generate the first response signal having the information, and the in-vehicle device performs authentication of the portable device based on the information and performs a predetermined control upon success of the authentication.