Micron Technology Incorporated

Omnipoint Corporation

Eugene P Hoyt

John R Tuttle

James C Springett

Randolph L Durrant

Mark T Burbach

A method for RF communication between transceivers in a radio frequency identification system that improves range, decreases multipath errors and reduces the effect of outside RF source interference by employing spread spectrum techniques. By pulse amplitude modulating a spread spectrum carrier before transmission, the receiver can be designed for simple AM detection, suppressing the spread spectrum carrier and recovering the original data pulse code waveform. The data pulse code waveform has been further encrypted by a direct sequence pseudo-random pulse code. This additional conditioning prevents the original carrier frequency components from appearing in the broadcast power spectra and provides the basis for the clock and transmit carrier of the transceiver aboard an RFID tag. Other advantages include high resolution ranging, hiding transmissions from eavesdroppers, and selective addressing.

Modulated spread spectrum in RF identification systems method

An apparatus and method for receiving spread spectrum signals, and, further, for decoding phase encoded information from such signals, requires correlation of input signals into real and imaginary components and determination of the phase angles of the received signal. A transmitter can divide an input signal into a plurality of data streams, independently modulate these streams, and then superpose the plurality of resultants for transmission. A receiver can receive the superposed signal and separate it into real and imaginary parts. In one embodiment, the receiver uses a plurality of spread spectrum codes to generate a plurality of real correlation signals and a plurality of imaginary correlation signals. A transmitter may also generate a differentially phase encoded signal. Phase encoding of a signal generally involves the imposition of known phase changes in the transmitted signal at selected intervals. Decoding of the phase changes at the receiver allows recognition of the phase encoded information. Differential phase encoding, specifically, involves the imposition of a selected phase upon the signal to be transmitted, giving consideration to a prior phase of the signal. In other embodiments, a receiver uses the generated real and imaginary correlation signals to determine a sector of a phase angle of a received signal. This sector can be compared with a previously generated sector, the resultant being an indication of the differential phase encoding performed at the transmitter.

Method and apparatus for decoding a phase encoded signal

A method and apparatus for phase encoding and decoding a CPM spread spectrum signal. A transmitter divides a data stream into a data symbol portion and an associated phase information portion. The data symbol portion is used to select one of a plurality of spread spectrum codes for transmission from a symbol table. The phase information portion is used to differentially phase encode the data symbol prior to transmission. The transmitter divides the phase encoded spread spectrum codes into a plurality of data streams (such as I and Q data streams), independently modulates the I and Q data streams using CPM or a related technique, and superposes the plurality of resultants for transmission. A receiver receives the superposed spread spectrum signal and simultaneously attempts to correlate for a plurality of chip sequences (such as I and Q chip sequences), and derives a real correlation signal and an imaginary correlation signal. For each received symbol, the receiver determines which of a plurality of phase sectors the phase angle lies in, and compares the difference between the present phase sector and the immediately preceding phase sector. For biphase encoding, if the difference in closer to 0.degree., then the receiver outputs a first bit, and if the difference is closer to 180.degree., the receiver outputs a second bit. In a particular embodiment, a plurality of correlators operate in parallel to carry out phase decoding of the received signal.

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Colorado Springs, CO, United States of America

Eugene P Hoyt