08231506 is referenced by 87 patents and cites 73 patents.

Systems, apparatuses, and methods estimate the distance between a player and a ball by transmitting a chirp (sweep signal) to a radio tag located on the ball. During the chirp, the frequency of the transmitted signal is changed in a predetermined fashion. The radio tag doubles the transmitted frequency and returns the processed signal to a transceiver typically located on the player. The currently transmitted frequency is then compared with the received frequency to obtain a difference frequency from which an apparatus may estimate the distance. The apparatus may simultaneously receive the processed signal from the radio tag while transmitting the sweep signal.

Title
Athletic performance monitoring systems and methods in a team sports environment
Application Number
12/980800
Publication Number
8231506 (B2)
Application Date
December 29, 2010
Publication Date
July 31, 2012
Inventor
Edward S Lowe
Seattle
WA, US
Bert B Buxton
Issaquah
WA, US
Jordan M Rice
Portland
OR, US
Clayton J Lindsay
Portland
OR, US
Scott R Berggren
Portland
OR, US
Brandon S Burroughs
Portland
OR, US
Aaron B Weast
Portland
OR, US
James Molyneux
Portland
OR, US
Agent
Banner & Witcoff
Assignee
NIKE
OR, US
IPC
A63B 71/00
View Original Source