Digital radio frequency interference canceller

• US 6,456,673 B1
• Filed: 11/30/1999
• Issued: 09/24/2002
• Est. Priority Date: 04/19/1996
• Status: Expired due to Term

• Current Assignee: Amati Communications Corp. (Texas Instruments, Inc.)
• Original Assignee: Amati Communications Corp. (Texas Instruments, Inc.)
• Inventors: Wiese, Brian R., Bingham, John A. C.
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US09/451,472
• Time in Patent Office: 1,029 Days
• Field of Search: 375/284, 375/285, 375/316, 375/346, 375/348, 375/350, 375/219, 375/222, 375/377, 370/210, 455/295, 455/296, 708/400, 708/402, 708/404, 708/405, 329/318, 329/349
• US Class Current: 375/346
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal
• CPC Class Codes: H04B 1/1036 with automatic suppression of narrow band noise or interference, e.g. by using tuneable notch filters H04B1/123 takes precedence; filter circuits H03H
• CPC Class Codes: H04B 1/123 using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H
• CPC Class Codes: H04B 1/126 having multiple inputs, e.g. auxiliary antenna for receiving interfering signal aerials in general H01Q
• CPC Class Codes: H04B 2001/1063 using a notch filter
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04L 5/0062 Avoidance of ingress interference, e.g. ham radio channels

Abstract

Disclosed are radio frequency (RF) interference cancellation techniques that effectively estimate RF interference to the data signals being received using a frequency domain model, and then remove the estimated RF interference from the received data signals. Improved techniques for digitally filtering multicarrier modulation samples to reduce sidelobe interference due to the RF interference are also disclosed.

Claims

1. A receiver for a multicarrier modulation system, comprising:

an analog-to-digital (A/D) converter, said A/D converter receives analog signals that have been transmitted to said receiver over a transmission media and converts the analog signals to digital time domain signals;

a multicarrier demodulator operatively connected to said A/D converter, said multicarrier demodulator receives the digital time domain signals and converts the digital time domain signals into digital frequency domain data;

a digital RF interference canceller operatively coupled to said multicarrier demodulator, said digital RF interference canceller mitigates the effect of RF interference on the digital frequency domain data by modeling the RF interference in accordance with a frequency domain model; and

the digital frequency domain data is provided on a plurality of frequency tones used by the multicarrier modulation system, and

wherein the frequency domain model is produced in accordance with the following equation;

${\mathrm{RFI}}_{n+m}=\left[\underset{k=1}{\overset{\mathrm{MO}+1}{\sum <br><br>}}<br><br>\frac{A_k}{{\left(m-\mathrm{\delta <br><br>}\right)}^k}\right]$

where RFI_n+m is the RF interference at a frequency tone n+m due to a radio interferer at frequency (n+δ

),δ

is an offset amount, MO is a model order for the frequency domain model, and A_k is a complex number.

2. A receiver as recited in claim 1, wherein said digital RF interference canceller mitigates the effect of RF interference on the digital frequency domain data by estimating a frequency of the RF interference, estimating the RF interference in accordance with the frequency domain model for the RF interference and the estimated frequency of the RF interference, and removing the estimated RF interference from the digital frequency domain data.

3. A receiver as recited in claim 1, wherein the digital time domain signals include a plurality of multicarrier modulation symbols carrying data, each of the symbols having a cyclic prefix,

wherein said receiver further comprises:

a cyclic prefix removal and windowing processor operatively connected between said A/D converter and said multicarrier demodulator, said processor performs a time domain windowing operation on the symbols, the time domain windowing includes, for each symbol, adding a portion of the cyclic prefix multiplied by a predetermined coefficient to a rear portion of the symbol.

4. A receiver as recited in claim 3, wherein said receiver further comprises:

an analog RF canceller operatively connected to reduce RF interference from the analog signals prior to their being supplied to said A/D converter.

5. A receiver as recited in claim 3, wherein the time domain windowing is extended windowing, wherein, for each symbol, the window extends beyond the boundaries of the symbol into the cyclic prefix.

6. A method for mitigating radio frequency (RF) interference in a multicarrier modulation system, said method comprising the operations of:

(a) receiving analog signals that have been transmitted over a transmission media;

(b) converting the analog signals to digital time domain signals;

(c) converting the digital time domain signals into digital frequency domain data; and

(d) mitigating the effect of RF interference on the digital frequency domain data by modeling the RF interference in accordance with a frequency domain model, and the digital frequency domain data is provided on a plurality of frequency tones used by the multicarrier modulation system, and wherein the frequency domain model is produced in accordance with the following equation;

${\mathrm{RFI}}_{n+m}=\left[\underset{k=1}{\overset{\mathrm{MO}+1}{\sum <br><br>}}<br><br>\frac{A_k}{{\left(m-\mathrm{\delta <br><br>}\right)}^k}\right]$

where RFI_n+m is the RF interference at a frequency tone n+m due to a radio interferer at frequency (n+δ

), δ

is an offset amount, MO is a model order for the frequency domain model, and A_k is a complex number.