Signal decoding systems

• US 20100034323A1
• Filed: 08/04/2009
• Published: 02/11/2010
• Est. Priority Date: 08/05/2008
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Artimi Ltd. (Veebeam Corporation)
• Inventors: Stoye, William
• Granted Patent: US 8,953,696 B2
• Time in Patent Office: Days
• US Class Current: 375/341
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• 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 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

We describe an ultra wideband (UWB) orthogonal frequency division multiplexed (OFDM) modified dual carrier modulation (MDCM) decoder comprising: first and second inputs to input first and second signals for first and second OFDM carriers; third and fourth inputs for respective third and fourth signals comprising channel quality estimates for the OFDM carriers; a set of integer arithmetic units coupled to said first, second, third and fourth inputs to form a set of intermediate terms; a first set of adders to form first and second sets of combinations of said intermediate terms, one for each MDCM coded bit value; a compare-select stage to select a first and second minimum valued said combination of said intermediate terms from said first and second set; and a subtracter to determine a log likelihood ratio (LLR) value for said bit from said first and second minimum valued combinations.

Claims

1. A modified dual carrier modulation (MDCM) decoder for MDCM decoding of an orthogonal frequency division multiplexed (OFDM) signal, the decoder comprising:

first and second inputs to input first and second signals dependent on signals from respective first and second carriers of said OFDM signal;

third and fourth inputs for respective third and fourth signals responsive to respective first and second channel quality estimates for said first and second carriers;

a set of arithmetic units coupled to said first, second, third and fourth inputs to form a set of intermediate terms comprising integer multiples of signals derived from said first, second, third and fourth signals;

a first set of adders coupled to said set of arithmetic units to form first and second sets of combinations of said intermediate terms, one set for each binary value of a bit of MDCM coded data encoded on said first and second carriers;

at least one compare-select stage coupled to said set of adders to select a first minimum valued said combination of said intermediate terms from said first set and to select a second minimum valued said combination of said intermediate terms from said second set; and

a subtractor to determine a log likelihood ratio (LLR) value for said bit from said first and second minimum valued combinations.

2. An MDCM decoder as claimed in claim 1 wherein said first and second sets of combinations of said intermediate terms each define a set of distances from a set of constellation points in which said bit has a respective first and second said binary value.

3. An MDCM decoder as claimed in claim 1 wherein said first and second signals are dependent on a product of signals from said respective first and second carriers and said respective first and second channel quality estimates.

4. An MDCM decoder as claimed in claim 1 wherein each said arithmetic unit comprises a second set of adders each said set coupled to a respective one of said first, second, third and fourth inputs, and wherein each set of said second set of adders is configured to provide on a set of outputs a set of said intermediate terms comprising a set of odd integer multiples or a set of squared odd integer multiples of signals derived from said first, second, third and fourth signals.

5. An MDCM decoder as claimed in claim 1 configured to decode LLR values for a plurality of said bits in parallel, and wherein said first set of adders is configured to form a plurality of pairs of said sets of combinations of said intermediate terms, one said pair of said sets for each said decoded bit LLR value.

6. An MDCM decoder as claimed in claim 5 wherein a said combination of intermediate terms comprises a combination of first and second channel intermediate terms and first and second signal intermediate terms, and wherein said first and second channel intermediate terms are dependent on said first and second channel quality estimates respectively, and wherein said first and second signal intermediate terms are dependent on a product of signals from said respective first and second carriers and said respective first and second channel quality estimates.

7. An MDCM decoder as claimed in claim 6 wherein said first set of adders includes a third set of adders to form said first and second channel intermediate terms and said first and second signal intermediate terms and a fourth set of adders coupled to said third set of adders to combine pairs of said channel intermediate terms and said signal intermediate terms to provide said combinations of intermediate terms.

8. An MDCM decoder as claimed in claim 2 further comprising a multiply unit to rotate said first and second signals by a factor, and wherein said constellation points comprise points rotated by substantially the same factor.

9. An MDCM decoder as claimed in claim 8 wherein said first and second signals are dependent on a product of signals from said respective first and second carriers and squared said respective first and second channel quality estimates, and wherein said third and fourth signals are derived from squared said respective first and second channel quality estimates.

10. An MDCM decoder as claimed in claim 1, wherein the MDCM decoder is part of an ultrawideband (UWB) receiver or transceiver.

11. An OFDM MDCM decoder for decoding at least one bit value from a DCM OFDM signal, the decoder comprising:

a first input to receive a first signal dependent on a product of a received signal from a first carrier of said MDCM OFDM signal and a channel quality estimate for said first carrier;

a second input to receive a second signal dependent on a product of a received signal from a second carrier of said MDCM OFDM signal and a channel quality estimate for said second carrier;

an arithmetic unit coupled to said first and second inputs and configured to form a plurality of joint distance metric terms including a first pair of joint distance metric terms derived from both said first and second signals and a second pair of joint distance metric terms derived from both said first and second signals, said first pair of joint distance metric terms corresponding to a first binary value of said bit value for decoding, said second pair of joint distance metric terms corresponding to a second binary value of said bit value for decoding;

at least one selector coupled to receive said first pair of joint distance metric terms as inputs and to select one of said first pair of joint distance metric terms having a minimum value, and coupled to receive said second pair of joint distance metric terms as inputs and to select one of said second pair of joint distance metric terms having a minimum value; and

an output coupled to said at least one selector and configured to output a likelihood value. Is defining a likelihood of said at least one bit value having either said first or said second binary value responsive to a difference between said selected one of said first pair of joint distance metric terms and said selected one of said second pair of joint distance metric terms.

12. An OFDM MDCM decoder as claimed in claim 11, wherein the OFDM MDCM decoder is part of an ultrawideband (UWB) receiver or transceiver.

13. A method of decoding an MCDM OFDM signal, the method comprising:

inputting first and second signals dependent on signals from respective first and second carriers of said OFDM signal;

inputting third and fourth signals responsive to respective first and second channel quality estimates for said first and second carriers;

generating a set of intermediate terms comprising integer multiples of signals derived from said first, second, third and fourth signals;

generating first and second sets of combinations of said intermediate terms, one set for each binary value of a bit of MDCM coded data encoded on said first and second carriers;

selecting a first and second minimum valued said combination of said intermediate terms respectively from each of said first and second sets; and

determining a log likelihood ratio (LLR) value for said bit from said first and second minimum valued combinations.

14. A method as claimed in claim 13 wherein said MDCM modulated OFDM signal is a UWB signal.

15. A method of determining a bit log likelihood ratio, LLR for an MDCM (modified dual carrier modulation) modulated OFDM signal, the method comprising calculating a value for

$L$



L 



R 

( b n ) = min x j ∈

S 



0 

( ρ

1 



r 1 - x j 1 

2 + ρ

2 



r 2 - x j 2 

2 ) - min x i ∈

S 



1 

( ρ

1 



r 1 - x i 1 

2 + ρ

2 



r 2 - x i 2 

2 )

where x_j ε

S0 represents a set of MDCM constellation points for which b_n has a first binary value and x_i ε

S1 represents a set of MDCM constellation points for which b_n has a second, different binary value;

x_j¹ and x_j² and x_i¹ and x_i² represent constellation points for x_j and x_i in different first and second constellations of said MDCM modulation respectively, the superscripts Is labelling constellations;

ρ

₁ and ρ

₂ representing signal levels or signal-to-noise ratios of first and second OFDM carriers modulated using said first and second constellations respectively;

r₁ and r₂ representing equalised received signal values from said first and second OFDM carriers respectively;

min ( ) representing determining a minimum value; and

∥

·

∥

representing a distance metric.

16. A method as claimed in claim 15 wherein said MDCM modulated OFDM signal is a UWB signal.

17. A method of decoding an MDCM (modified dual carrier modulation) modulated OFDM signal, the method comprising:

inputting first received signal data representing modulation of a multibit data symbol onto a first carrier of said OFDM signal using a first constellation;

inputting second received signal data representing modulation of said multibit data symbol onto a second, different carrier of said OFDM signal using a second, different constellation;

determining a combined representation of said first and second received signal data, said combined representation representing a combination of a distance of a point representing a bit value of said multibit data from a constellation point in each of said different constellations; and

determining a decoded value of a data bit of said multibit data using said combined representation;

wherein said determining of a decoded value comprises determining a log likelihood ratio (LLR) for said data bit, wherein said determining of said combined representation comprises determining combined distance data representing a sum of distances of a point representing a first binary value of said bit from corresponding constellation points in said first and second constellations at which said bit has said first binary value, said corresponding constellation points representing the same symbol in said different constellations, further comprising performing said determining for a plurality of said corresponding constellation points and selecting minimum combined distance data representing a minimum sum of said distances, performing said determining of said combined distance data for said plurality of corresponding constellation points for a second binary value of said bit and selecting minimum combined distance data representing a minimum sum of said distances, and determining a difference between said minimum combined distance data for said first and second binary values of said bit to determine said LLR.

18. A method as claimed in claim 17 wherein said MDCM modulated OFDM signal is a UWB signal.