Reverse RFID location system

A system comprising:

• a set of radio frequency identification tags, each tag storing its position in a fixed coordinate system;
• and,
• a radio frequency identification tag reader that estimates its position in the fixed coordinate system based on the positions of tags in the set as reported by the tags to the reader;
• wherein each tag encodes its position in data bits, and data bits representing the position of a tag along a first axis of the coordinate system are interleaved with data bits representing the position of the tag along a second axis of the coordinate system, and,
• the reader solicits replies from tags in progressively smaller volumes of space by:
• (1) requesting that only tags whose first N interleaved bits match a certain bit pattern respond;
• and, (2) increasing N on subsequent queries.