Method and system for determining a location of a client device, a client device apparatus and a network device apparatus

A location determination method for determining a location of a client device in a wireless network including the client device and at least three network devices, each of the three network devices having a known location, the method comprising:

• receiving messages exchanged in a pairwise message exchange between at least three different pairs of network devices of said at least three network devices and recording time of reception of said messages, wherein
• in the pairwise message exchange,
• a first network device transmits a first message and a second network device receives the first message transmitted from the first network device and transmits the second message to the first network device,
• the first network device receives the second message transmitted from the second network device and transmits a third message to the second network device,
• the second network device transmits a fourth message and the first network device receives the fourth message transmitted from the second network device,
• the first network device calculates either:
• (1) a first time difference between transmission of the first message and subsequent reception of the second message, or (2) a second time difference between reception of the second message and subsequent transmission of the third message,
• the first network device includes, in the third message, first time difference information indicating either the calculated first time difference or the calculated second time difference,
• the second network device calculates either:
• (3) a third time difference between reception of the first message and subsequent transmission of the second message, or (4) a fourth time difference between transmission of the second message and subsequent reception of the third message, and
• the second network device includes either second time difference information indicating the calculated third time difference in the second message, or third time difference information indicating the calculated fourth time difference in the fourth message.

A second network device for use in a wireless network including a client device and at least three network devices, each of the three network devices having a known location, the second network device comprising:

• a receiver configured to receive a first message transmitted from a first network device, with which a pairwise message exchange is performed;
• and
• a transmitter configured to transmit a second message to the first network device, wherein
• the receiver is further configured to receive a third message from the first network device,
• the transmitter is further configured to transmit a fourth message to the first network device,
• the first network device calculates either:
• (1) a first time difference between transmission of the first message and subsequent reception of the second message, or (2) a second time difference between reception of the second message and subsequent transmission of the third message,
• the first network device includes, in the third message, first time difference information indicating either the calculated first time difference or the calculated second time difference,
• the second network device calculates either:
• (3) a third time difference between reception of the first message and subsequent transmission of the second message, or (4) a fourth time difference between transmission of the second message and subsequent reception of the third message, and
• the second network device includes either second time difference information indicating the calculated third time difference in the second message, or third time difference information indicating the calculated fourth time difference in the fourth message.

A method of operating a second network device in a wireless network including a client device and at least three network devices, each of the three network devices having a known location, the method comprising:

• receiving a first message transmitted from a first network device, with which a pairwise message exchange is performed by the second network device;
• transmitting a second message to the first network device;
• receiving a third message transmitted from the first network device;
• and
• transmitting a fourth message to the first network device, wherein
• the first network device calculates either:
• (1) a first time difference between transmission of the first message and subsequent reception of the second message, or (2) a second time difference between reception of the second message and subsequent transmission of the third message,
• the first network device includes, in the third message, first time difference information indicating either the calculated first time difference or the calculated second time difference,
• the second network device calculates either:
• (3) a third time difference between reception of the first message and subsequent transmission of the second message, or (4) a fourth time difference between transmission of the second message and subsequent reception of the third message, and
• the second network device includes either second time difference information indicating the calculated third time difference in the second message, or third time difference information indicating the calculated fourth time difference in the fourth message.