RFID receiver

• US 8,400,271 B2
• Filed: 10/21/2009
• Issued: 03/19/2013
• Est. Priority Date: 10/28/2005
• Status: Expired due to Fees

• Current Assignee: Mojix Inc
• Original Assignee: Mojix Inc
• Inventors: Sadr, Ramin
• Primary Examiner(s): Zimmerman, Brian
• Assistant Examiner(s): Khan, Omer S
• Application Number:
  US12/603,027
• Publication Number:
  US 20100310019A1
• Time in Patent Office: 1,245 Days
• Field of Search: 340/10.1, 375/343, 375/341
• US Class Current: 340/10.1
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/01 Details
• CPC Class Codes: G06K 7/10009 sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
• CPC Class Codes: H03M 13/098 using single parity bit
• CPC Class Codes: H03M 13/2957 Turbo codes and decoding
• CPC Class Codes: H03M 13/3905 Maximum a posteriori probability [MAP] decoding or approximations thereof based on trellis or lattice decoding, e.g. forward-backward algorithm, log-MAP decoding, max-log-MAP decoding
• CPC Class Codes: H03M 13/6331 Error control coding in combination with equalisation
• CPC Class Codes: H04L 1/0041 Arrangements at the transmitter end
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/006 Trellis-coded modulation
• CPC Class Codes: H04L 1/0065 Serial concatenated codes
• CPC Class Codes: H04L 1/08 by repeating transmission, e.g. Verdan system H04L1/1858 and H04L1/189 take precedence
• CPC Class Codes: H04L 25/0242 using matrix methods
• CPC Class Codes: H04L 25/03012 operating in the time domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 25/03114 non-adaptive, i.e. not adjustable, manually adjustable, or adjustable only during the reception of special signals
• CPC Class Codes: H04L 25/03222 using the T-algorithm
• CPC Class Codes: H04L 25/067 providing soft decisions, i.e. decisions together with an estimate of reliability H04L25/068 and H04L25/069 take precedence; sequence estimation techniques H04L25/03178
• CPC Class Codes: H04L 27/02 Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation H04L27/32 takes precedence
• CPC Class Codes: H04L 27/10 Frequency-modulated carrier systems, i.e. using frequency-shift keying H04L27/32 takes precedence

Abstract

RFID data signals from RFID tags may be recovered by determining the probabilities of transitions between data states between a series of a pairs of signal samples using a set of predetermined probabilities related to data, timing, baud rate and/or phase variables affecting the received signal and processing those determined probabilities to determine the sequence of such transitions that has the highest probability of occurrence. A second set of predetermined probabilities related to transitions in the opposite direction may be used to sequence in a reverse direction. The determination of the sequence representing the RFID tag data may be iterated in both directions until further iterations do not change the determined probabilities.

Claims

1. A method for detecting a data sequence from a sequence of symbols backscattered by an RFID tag, comprising:

receiving the sequence of backscattered symbols at a receiving antenna, where each backscattered symbol has a random symbol duration, and a random phase resulting from random variations introduced by instability in the RFID backscatter process;

using a receiver to;

over sample the received symbols to produce a set of samples;

estimate data values for short sequences of consecutive symbols that are most likely to have occurred based upon the set of samples, where the duration of each symbol and the phase of each symbol are assumed fixed during each short sequence and are assumed randomly varying between the short sequences due to the instability in the RFID backscatter process, by;

determining a chosen fixed number of samples per symbol;

selecting a first sample from the set of samples corresponding to the start of a first symbol in the short sequence of consecutive symbols;

selecting a sample from the set of samples that is half the chosen fixed number of samples from the first sample in the short sequence of consecutive symbols, where the selected sample is chosen to be the first sample within the second half of the first symbol in the short sequence of consecutive symbols;

selecting the chosen fixed number of samples starting from the first sample within the second half of the first symbol in the short sequence of consecutive symbols;

selecting a first sample and a first sample within the second half of each symbol within the short sequence of consecutive symbols based on the selected first sample of the first symbol and the chosen fixed number of samples;

applying a matched filter with a length determined based upon the chosen fixed number of samples per symbol to the selected chosen fixed number of samples starting from the first sample within the second half of the first symbol in the short sequence of consecutive symbols; and

determining the following;

2. The method of claim 1, wherein using the receiver to estimate data values for short sequences of consecutive symbols that are most likely to have occurred based upon the set of samples, where the duration of each symbol and the phase of each symbol are assumed fixed during each short sequence and are assumed randomly varying between the short sequences due to the instability in the RFID backscatter process further comprises estimating each short sequence of consecutive symbols by:

determining data values for a first short sequence of symbols that are most likely to have occurred based upon samples selected from the set of samples, where the determination includes choosing a fixed number of samples per symbol;

using the data value determined for the last symbol in the first short sequence of symbols as the first symbol of a next short sequence of symbols; and

using the chosen fixed number of samples per symbol to determine the starting point for the estimation of the data values of the next short sequence of symbols.

3. The method of claim 1, wherein the matched filter is implemented using an integrate and dump circuit.

4. The method of claim 1, wherein the real parts of the matched filter outputs are used as the values of the matched filter outputs in the equation: