Method and apparatus for full duplex sideband communication

DETAILED DESCRIPTION While the present invention retains utility within a wide variety of communication devices and may be embodied in several different forms, it is advantageously employed in connection with communication devices having strict power limitations.
Examples of such devices are passive devices that obtain power from a RF carrier or active devices that operate on batteries or require high bandwidth such that a standard RF channel is not practical.
Though these are the forms of the preferred embodiments and will be described as such, these embodiments should be considered illustrative and not restrictive.
FIG.
1 shows a communication system 10 wherein an interrogator 12 transmits an interrogator signal 14 to a transponder 16.
In this embodiment, the transponder 16 is a passive device disposed on a package 18.
The transponder 16 identifies the package 18 thereby providing inventory control.
As is described more particularly in commonly assigned U.
S.
patent application Ser.
No.
08/616,261 entitled "Vehicle Data Acquisition System" filed on Mar.
15, 1996, and incorporated herein by reference, the interrogator signal is used to provide power to the transponder 16.
One skilled in the art will realize however, that though the preferred embodiment draws energy from the carrier wave, solar cells, thermopiles, or other devices can be used to power the transponder in the passive embodiment.
The transponder 16 then encodes onto the interrogator signal 14 or copies the interrogator signal 14 and retransmits the copied signal with additional encoding.
The transponder 16 encodes a code that provides information relative to the transponder 16.
That is, if the transponder 16 is attached to a package 18, as is the case in this embodiment, the code would be indicative of the contents of the package 18.
The encoded signal 20 is then transmitted back to the interrogator 12 where it is decoded.
This embodiment then allows for the reading of transponders located within a predetermined distance of the interrogator 12