Interference mitigation in mobile units having location transmitters
A mobile device for data communications has a radio circuit for data communications with a wireless network access point and a radio tag for transmitting location-identifying radio signals. The radio circuit and the radio tag are co-located on a circuit board or are commonly powered. The operation of the radio circuit and the radio tag are segregated in time to avoid interference. Standard wireless network interface protocol functions are exploited to identify time intervals in which the radio circuit is inactive for data communications. These time intervals are used to operate the radio tag to transmit the location-identifying radio signals.
1. A method for wireless data communications between a network of wireless access points and a mobile device, wherein the mobile device comprises a first radio circuit for bidirectional wireless communication with an associated access point and a second radio circuit for transmitting identification signals for the purpose of revealing at least one of mobile unit's identification and location, the method comprising the steps of:
identifying a time interval during which the first radio circuit is inactive in wireless communication with the associated access point by:
sending a request-to-send frame from the mobile device to the associated access point;
receiving a clear-to-send duration value from the associated access point; and
reserving a time interval within the duration value exclusively for transmitting identification signals from the mobile device;
activating a power save mode in the mobile device to indicate that no data transmissions are intended by the first radio circuit during the time interval, wherein the power save mode shuts down power to the first radio circuit;
buffering data intended for the mobile unit in the associated access point while power to the first radio circuit is shut down;
operating the second radio circuit to transmit the location and identification signals during the time interval of the identifying step while power to the first radio circuit is shut down; and
periodically re-activating the first radio circuit to receive beacon transmissions from the access point according to a regular polling schedule and scheduling operation of the second radio circuit according to the polling schedule.
2. The method of claim 1 wherein the wireless network access points and the mobile device interface through a protocol layer having functions for managing flow of wireless communications between the wireless network access points and the mobile device, and wherein the identifying step further comprises using a function of protocol layer to identify a time interval during which the first circuit is inactive in wireless communication with the associated access point.
3. The method of claim 2 wherein the protocol layer is a medium access control layer selected from the group of IEEE 802.11, IEEE 802.16, IEEE 802.20, and industry Standard wireless medium access control layers.
4. An arrangement for data communications between a network of wireless access points and a mobile device, wherein the mobile device comprises a first radio circuit for bidirectional wireless communication with an associated access point and a second radio circuit for transmitting identification signals for the purpose of revealing the mobile device's location, wherein the arrangement comprises:
a provision for identifying a time interval during which the first radio circuit is inactive in wireless communication with the associated access point by:
sending a request-to-send frame from the mobile device to the associated access point;
receiving a clear-to-send duration value from the associated access point; and
reserving a time interval within the duration value exclusively for transmitting identification signals from the mobile device;
a provision for activating a power save mode in the mobile device to indicate that no data transmissions are intended by the first radio circuit during the time interval, wherein the power save mode shuts down power to the first radio circuit;
a provision for buffering data intended for the mobile unit in the associated access point while power to the first radio circuit is shut down;
a provision for operating the second radio circuit to transmit the location and identification signals during the time interval from the provision for identifying while power to the first radio circuit is shut down; and
a provision for periodically re-activating the first radio circuit to receive beacon transmissions from the access point according to a regular polling schedule and scheduling operation of the second radio circuit according to the polling schedule.
5. The arrangement of claim 4 wherein the wireless network access points and the mobile device interface through a protocol layer having functions for managing flow of wireless communications between the wireless network access points and the mobile device, and wherein the provision for identifying comprises use of a function of protocol layer to identify the time interval during which the first radio circuit is inactive in wireless communication with the associated access point.
6. The arrangement of claim 5 wherein the protocol layer is a medium access control layer selected from the group of IEEE 802.11, IEEE 802.16, IEEE 802.20, and industry Standard wireless medium access control layers.