Synchronization-Free Station Locator In Wireless Network

A method of providing synchronization-free station locating in a wireless network, the wireless network including a station having an unknown location and a plurality of access points (APs) having known locations, the method comprising:

• for each set including one of the plurality of APs and the station,
• sending a unicast packet from the AP to the station, the unicast packet having a time of departure TOD(D);
• receiving the unicast packet at the station;
• sending an acknowledgement packet from the station to the AP;
• receiving the acknowledgment packet at the AP, the acknowledgment packet having a time of arrival TOA(D_ACK);
• and
• disassociating with the station, thereby forcing the station to associate with another of the plurality of APs;
• determining a delta distance between the station and two APs;
• and
• using a plurality of computed delta distances to determine a location of the station.

A method of providing synchronization-free station locating in a wireless network, the wireless network including a station having an unknown location and a plurality of access points (APs) having known locations, the method comprising:

• for each set including one of the plurality of APs and the station,
• sending a probe response packet from the AP to the station, the probe response packet having a time of departure TOD(D);
• receiving the probe response packet at the station;
• sending an acknowledgement packet from the station to the AP;
• receiving the acknowledgment packet at the AP, the acknowledgment packet having a time of arrival TOA(D_ACK);
• and
• the AP refusing to associate with the station, thereby forcing the station to try to associate with another of the plurality of APs;
• determining a delta distance between the station and two APs;
• and
• using a plurality of computed delta distances to determine a location of the station.

A method of providing synchronization-free station locating in a wireless network, the wireless network including a station having an unknown location and a plurality of access points (APs) having known locations, the method comprising:

• the plurality of APs switching to a channel used by the station, wherein the plurality of APs other than an associated AP enter a promiscuous mode that allows overhearing an exchange between the associated AP and the station;
• sending a unicast packet from an associated AP to the station, the unicast packet having a time of departure TOD(D);
• receiving the unicast packet at the station;
• sending an acknowledgement packet from the station to the AP;
• and
• receiving the acknowledgment packet at the AP, the acknowledgment packet having a time of arrival TOA(D_ACK);
• determining a distance between the station and each AP of the plurality of APs based on information from the exchange;
• and
• using a plurality of computed distances to determine a location of the station.

A method of providing synchronization-free station locating in a wireless network, the wireless network including a station having an unknown location and a plurality of access points (APs) having known locations, the method comprising:

• for each set including one of the plurality of APs and the station,
• sending a unicast packet from the station to the AP, the unicast packet having a time of departure TOD(D);
• receiving the unicast packet at the AP;
• sending an acknowledgement packet from the AP to the station;
• receiving the acknowledgment packet at the station, the acknowledgment packet having a time of arrival TOA(D_ACK);
• and
• disassociating with the AP and re-associating with another of the plurality of APs;
• determining a delta distance between the station and two APs;
• and
• using a plurality of computed delta distances to determine a location of the station.

A method of providing synchronization-free station locating in a wireless network, the wireless network including a first device having an unknown location and a second device having a known location, the method comprising:

• (a) sending a first packet from the second device to the first device, the first packet being one of a unicast packet and a probe response packet;
• the first packet having a time of departure TOD(D);
• (b) receiving the first packet at the first device, the first packet having a time of arrival TOA(D);
• (c) sending an acknowledgement packet from the first device to the second device, the acknowledgment packet having a time of departure TOD(D_ACK);
• (d) receiving the acknowledgment packet at the second device, the acknowledgment packet having a time of arrival TOA(D_ACK);
• and
• (e) computing a distance between the first device and the second device using a first difference between the TOA(D_ACK) and the TOD(D) and a second difference between the TOD(D_ACK) and the TOA(D);
• (f) moving the second device to another known location and repeating (a)-(e);
• and
• (g) using a plurality of computed distances between the first and second devices to determine a location of the first device.

A method of providing synchronization-free device locating in a wireless network, the wireless network including a first device having an unknown location and a second device having a known location, the method comprising:

• sending a first packet from the second device to the first device, the first packet being one of a unicast packet and a probe response packet;
• the first packet having a time of departure (TOD(D));
• receiving the first packet at the first device, the first packet having a time of arrival TOA(D);
• sending an acknowledgement packet from the first device to the second device, the acknowledgment packet having a time of departure TOD(D_ACK);
• receiving the acknowledgment packet at the second device, the acknowledgment packet having a time of arrival TOA(D_ACK);
• and
• computing a distance between the first device and the second device using a first difference between the TOA(D_ACK) and the TOD(D) and a second difference between the TOD(D_ACK) and the TOA(D);
• receiving at least one constraint regarding an environment of the first device;
• and
• using a computed distance between the first and second devices and the at least one constraint to determine a location of the first device.

A method of correcting a time of arrival of a data symbol at a device in a wireless network, the method comprising:

• performing coarse timing on a short training field of a data packet to generate a coarse symbol boundary of a long training field (LTF);
• performing a cross-correlation between a known LTF sequence and an actual LTF sequence, the actual LTF sequence starting at the coarse symbol boundary;
• identifying a first peak of cross-correlation results as being a first arrival path;
• and
• using the first arrival path to compute the time of arrival of the data symbol.

A method of correcting a time of arrival of a data symbol at a device in a wireless network, the method comprising:

• performing a fine timing estimate on a data packet to locate a guard interval;
• performing a cross-correlation between the guard interval and its corresponding OFDM symbol tail;
• aligning a strongest path of the cross-correlation such that a first predetermined number of samples are provided pre-cursor and a second predetermined number of samples are provided post-cursor;
• and
• using a cursor set between the first and second predetermined number of samples to determine the time of arrival.

A method of correcting a time of arrival of a data symbol at a device in a wireless network, the method comprising:

• obtaining a channel estimate using a long training field (LTF);
• manipulating the channel estimate using an inverse fast Fourier transform (IFFT) to generate a channel delay profile;
• identifying a first signal of the channel delay profile exceeding a predetermined threshold;
• and
• computing the time of arrival based on the first signal.