System and method for mitigating co-channel interference in white space modems

• US 10,014,904 B1
• Filed: 09/11/2017
• Issued: 07/03/2018
• Est. Priority Date: 07/27/2017
• Status: Active Grant

• Current Assignee: Saankhya Labs Pvt Ltd.
• Original Assignee: Saankhya Labs Pvt Ltd.
• Inventors: Anand, Sudeep Mirpadi, Bhat, Shrinivas Subramania, Saha, Anindya
• Primary Examiner(s): Gonzales, April G
• Application Number:
  US15/700,342
• Time in Patent Office: 295 Days
• Field of Search: 455 6713
• 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 1/525 with means for reducing leakage of transmitter signal into the receiver
• CPC Class Codes: H04B 2001/1045 Adjacent-channel interference
• CPC Class Codes: H04B 2001/1063 using a notch filter
• CPC Class Codes: H04L 1/0006 by adapting the transmission format
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0054 Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/143 for modulated signals H04L5/1469 takes precedence
• CPC Class Codes: H04L 5/1461 Suppression of signals in the return path, i.e. bidirectional control circuits

Abstract

Disclosed is a system for mitigating co-channel interference (CCI) caused due to narrow multiband signal in white space (WS) modems. The system includes a base-station that includes a base-station transmitter and a base-station receiver. The base-station receiver receives an orthogonal frequency division multiplexing signal (OFDM) from one or more customer premises equipment (CPE) transmitters. An interference detection module detects a presence of co-channel interference in carriers of the OFDM signal and determines co-channel interference affected carriers. A dynamic notch filter module receives the central interference carriers from interference detection module and mitigates the co-channel interference of co-channel interference affected carriers without affecting frame detection capability of the system. The base-station transmitter includes an interference aware frequency interleaver that spreads co-channel interference affected carriers based on interference specific interleaving parameters and frequency de-interleaving is performed corresponding to frequency interleaving in the base-station receiver.

Claims

1. A system for mitigating co-channel interference (CCI) caused due to narrow multiband signal in white space (WS) modems, comprising:

a base-station that comprises;

a base-station receiver that receives an orthogonal frequency division multiplexing signal (OFDM) from one or more customer premises equipment (CPE) transmitters, wherein said base-station receiver comprises;

an interference detection module that detects a presence of said co-channel interference (CCI) in carriers of said OFDM signal and determines co-channel interference affected carriers by identifying central interference carriers corresponding to said co-channel interference affected carriers, wherein said co-channel interference is represented in said carriers using at least one of (i) a position, (ii) a spread or (iii) an interference power, of said co-channel interference affected carriers; and

a dynamic notch filter module that (i) receives said central interference carriers from said interference detection module and (ii) mitigates said co-channel interference of said co-channel interference affected carriers without affecting frame detection capability by suppressing said interference power of said co-channel interference affected carriers;

a base-station transmitter that comprises an interference aware frequency interleaver that spreads said co-channel interference affected carriers based on interference specific interleaving parameters and frequency de-interleaving is performed corresponding to a frequency interleaving in said base station receiver.

2. The system of claim 1, wherein said dynamic notch filter module

converts said position of said co-channel interference affected carriers into baseband frequency values to calculate notch frequencies;

calculates notch filter co-efficient based on said notch frequencies; and

filters said co-channel interference of said co-channel interference affected carriers from an output of an analog to digital (A/D) converter based on said notch filter co-efficient.

3. The system of claim 1, wherein said interference aware frequency interleaver

pre-determines said interference specific interleaving parameters that control said spread of said frequency interleaving;

and

stores said interference specific interleaving parameters in a lookup table,

wherein said interference aware frequency interleaver comprises an interference aware interleaver selection module that determines an interference profile based on central interfering carrier indices of said narrow multiband signal to select an appropriate interference specific interleaving parameters based on said lookup table, wherein said interference aware interleaver selection module selects said appropriate interference specific interleaving parameters from said lookup table using said central interference carriers based on (a) said position of said co-channel interference affected carriers and (b) said interference profile,

wherein said selected interference specific interleaving parameters are added into said WS modems when an interference flag associated with said OFDM signal is high.

4. The system of claim 3, wherein default frequency interleaving parameters are added into said WS modems when said interference flag associated with said OFDM signal is low.

5. The system of claim 1, wherein said co-channel interference in said OFDM signal is suppressed to provide entire dynamic range of fast fourier transform (FFT) to be available for said OFDM signal.

6. The system of claim 1, wherein said interference detection module detects said presence of said co-channel interference (CCI) in said carriers of said OFDM signal by performing the steps of:

obtaining 2^N fast fourier transform (FFT) samples where 2^N represents FFT block size in said interference detection module;

multiplying said 2^N FFT samples with a complex conjugate of a previous block of said 2^N fast fourier transform (FFT) samples;

normalizing output samples by dividing absolute value of said 2^N FFT samples using a norm of a vector;

accumulating and adding said vector across M blocks of said 2^N fast fourier transform (FFT) samples using a first equation

7. The system of claim 6, wherein said co-channel interference is detected in said carriers when said interference_carrier_positions is not a null set and said interference flag is set to 1, wherein said threshold1 is determined based on simulations in different channel conditions and is selected such that probability of false detection of said co-channel interference is minimal.

8. The system of claim 1, wherein said WS modem utilizes a turbo-like interleaving (TLI) algorithm for said frequency interleaving to generate a permutation rule L(x) using parameters, wherein said parameters comprises (a) interleaving block size K, (b) integers p and q and (c) number of iterative calculations j in said TLI algorithm, wherein an output sequence is generated at each step of iteration, wherein a value of said permutation rule L(x) in an input sequence corresponds to x in said output sequence, wherein an index pattern is calculated at an output of iteration m using an equation

I_p,q,K^(m)(x)=[K−

p+x+q·

p·

[−

x−

p·

I_p,q,K^(m-1)(x)] mod K] mod K,

wherein said index pattern is utilized as said permutation rule after j iterations using an equation L(x)=I_p,q,K^(j)(x), wherein a performance of said TLI algorithm is characterized by an interleaving spread depth Δ

L(Δ

x) that is calculated for indices x and x+Δ

x in said output sequence using an equation

9. The system of claim 3, wherein said pre-determining said interference specific interleaving parameters comprises the steps of:

(a) setting a value for said integer q to determine combinations of values for said integer p and number of said iterative calculations j for which said interleaving spread depth Δ

L(Δ

x) is greater than 60% of maximum possible interleaving spread depth;

(b) tracing said position of said co-channel interference affected carriers into each forward error correction (FEC) block to determine number of data positions of said co-channel interference affected carriers in each of said FEC block;

(c) determining maximum number of said co-channel interference affected carriers present in said FEC block;

(d) selecting said appropriate interference specific interleaving parameters which minimize said maximum number of said co-channel interference affected carriers present in said FEC block to spread interference affected data across all FEC modules to recover an error prone data;

(e) repeating said steps (a) to (d) for each value of said integer q, wherein said combination of said interference specific interleaving parameters spread said co-channel interference affected carriers effectively across a spectrum of said narrow multiband signal;

(f) running simulations with said interference specific interleaving parameters for different channel conditions and determining said interference specific interleaving parameters that provide best performance for all modulations and code-rates for at least one interference profile; and

(g) repeating said steps (a) to (f) for different possible interference profiles, wherein said lookup table is generated to store said best performing one or more interference specific interleaving parameters for each interference profile after determining said interference specific interleaving parameters.

10. The system of claim 1, wherein said co-channel interference is detected at said base-station that receives data from said one or more CPE, wherein said co-channel interference detected at said base-station affects said data of said one or more CPE simultaneously.

11. The system of claim 10, wherein said base-station

transmits said interference flag and said central interference carriers to said one or more CPE;

receives interference specific interleaving parameters from said one or more CPE, wherein said one or more CPE utilize said same central interference carriers for selecting said interference specific interleaving parameters, wherein said interference corresponding to said one or more CPE are same so said one or more CPE utilize said same central interference carriers for selecting said interference specific interleaving parameters.

12. The system of claim 1, wherein said dynamic notch filter module comprises an infinite impulse response (IIR) dynamic notch filter module.

13. The system of claim 1, wherein said system further detects and mitigates said co-channel interference of said narrow multiband signal in at least one of (i) frequency division duplex modems or (ii) time division duplex modems.

14. A system for mitigating co-channel interference (CCI) caused due to narrow multiband signal in white space (WS) modems, comprising:

a customer premises equipment (CPE) that comprises;

one or more CPE receivers that receive an orthogonal frequency division multiplexing signal (OFDM) from a base-station transmitter, wherein said one or more CPE receivers comprise;

an interference detection module that detects a presence of said co-channel interference (CCI) in carriers of said OFDM signal and determines co-channel interference affected carriers by identifying central interference carriers corresponding to said co-channel interference affected carriers, wherein said co-channel interference is represented in said carriers using at least one of (i) a position, (ii) a spread, or (iii) an interference power, of said co-channel interference affected carriers; and

a dynamic notch filter module that (i) receives said central interference carriers from said interference detection module and (ii) mitigates said co-channel interference of said co-channel interference affected carriers without affecting frame detection capability by suppressing said interference power of said co-channel interference affected carriers;

one or more CPE transmitters that comprise an interference aware frequency interleaver that spreads said co-channel interference affected carriers based on interference specific interleaving parameters and frequency de-interleaving is performed corresponding to a frequency interleaving in said one or more CPE receivers.

15. The system of claim 14, wherein said dynamic notch filter module

converts said position of said co-channel interference affected carriers into baseband frequency values to calculate notch frequencies;

calculates notch filter co-efficient based on said notch frequencies; and

filters said co-channel interference of said co-channel interference affected carriers from an output of analog to digital (A/D) converter based on said notch filter co-efficient.

16. The system of claim 14, wherein said interference aware frequency interleaver

pre-determines said interference specific interleaving parameters that control said spread of said frequency de-interleaving;

and

stores said interference specific interleaving parameters in a lookup table,

wherein said interference aware frequency interleaver comprises an interference aware interleaver selection module that determines an interference profile based on central interfering carrier indices of said narrow multiband signal to select an appropriate interference specific interleaving parameters based on said lookup table, wherein said interference aware interleaver selection module selects said appropriate interference specific interleaving parameters from said lookup table using said central interference carriers based on (a) said position of said co-channel interference affected carriers and (b) said interference profile,

wherein said selected interference specific interleaving parameters are added into said WS modems when an interference flag associated with said OFDM signal is high.

17. The system of claim 14, wherein said WS modem utilizes a turbo-like interleaving (TLI) algorithm for said frequency interleaving to generate a permutation rule L(x) using parameters, wherein said parameters comprise (a) interleaving block size K, (b) integers p and q and (c) number of iterative calculations j in said TLI algorithm, wherein an output sequence is generated at each step of iteration, wherein a value of said permutation rule L(x) in an input sequence corresponds to x in said output sequence, wherein an index pattern is calculated at an output of iteration m using an equation

I_p,q,K^(m)(x)=[K−

p+x+q·

p·

[−

x−

p·

I_p,q,K^(m-1)(x)] mod K] mod K,

wherein said index pattern is utilized as said permutation rule after j iterations using an equation L(x)=I_p,q,K^(j)(x), wherein a performance of said TLI algorithm is characterized by an interleaving spread depth Δ

L(Δ

x) that is calculated for indices x and x+Δ

x in said output sequence using an equation

18. The system of claim 16, wherein said pre-determining said interference specific interleaving parameters comprises the steps of:

(a) setting a value for said integer q to determine combinations of values for said integer p and number of said iterative calculations j for which said interleaving spread depth Δ

L(Δ

x) is greater than 60% of maximum possible interleaving spread depth;

(b) tracing said position of said co-channel interference affected carriers into each forward error correction (FEC) block to determine number of data positions of said co-channel interference affected carriers in each said FEC block;

(c) determining maximum number of said co-channel interference affected carriers present in said FEC block;

(d) selecting said appropriate interference specific interleaving parameters which minimize said maximum number of said co-channel interference affected carriers present in said FEC block to spread interference affected data across all FEC modules to recover an error prone data;

(e) repeating said steps (a) to (d) for each value of said integer q, wherein said combination of said interference specific interleaving parameters spread said co-channel interference affected carriers effectively across a spectrum of said narrow multiband signal;

(f) running simulations with said interference specific interleaving parameters for different channel conditions and determine said interference specific interleaving parameters that provide best performance for all modulations and code-rates for at least one interference profile; and

(g) repeating said steps (a) to (f) for different possible interference profiles, wherein said lookup table is generated to store said best performing of said interference specific interleaving parameters for each interference profile after determining said interference specific interleaving parameters.

19. The system of claim 14, wherein said co-channel interference in said OFDM signal is suppressed to provide entire dynamic range of fast fourier transform (FFT) to be available for said OFDM signal.

20. The system of claim 14, wherein said interference detection module detects said presence of said co-channel interference (CCI) in said carriers of said OFDM signal by performing the steps of:

obtaining 2^N fast fourier transform (FFT) samples where 2^N represents FFT block size in said interference detection module;

multiplying said 2^N FFT samples with a complex conjugate of a previous block of said 2^N fast fourier transform (FFT) samples;

normalizing output samples by dividing absolute value of said 2^N FFT samples using a norm of a vector;

accumulating and adding said vector across M blocks of said 2^N fast fourier transform (FFT) samples using a first equation

21. The system of claim 20, wherein said co-channel interference is detected in said carriers when said interference_carrier_positions is not a null set and said interference flag is set to 1, wherein said threshold1 is determined based on simulations in different channel conditions and is selected such that probability of false detection of said co-channel interference is minimal.

22. The system of claim 14, wherein said system identifies said one or more CPE that are affected by said co-channel interference and changes frequency interleaving parameters related to said one or more CPE affected by said co-channel interference, wherein said one or more CPE need different set of said frequency interleaving parameters as said one or more CPE are situated at different independent locations.

23. The system of claim 22, wherein said one or more CPE

transmit said interference flag and said central interference carriers to said base-station, wherein said base-station runs said interference aware interleaver selection module separately for each CPE to select said appropriate interference specific interleaving parameters for each of said CPE,

wherein said OFDM signals comprise a generic control structure data that are interleaved using said default frequency interleaving parameters as said generic control structure data is shared across said one or more CPE, wherein said OFDM signals specific to each of said CPE are interleaved with CPE specific set of frequency interleaving parameters.

24. A method for mitigating co-channel interference (CCI) caused due to narrow multiband signal in white space (WS) modems, comprising:

receiving an orthogonal frequency division multiplexing signal (OFDM) from at least one of (a) one or more customer premises equipment (CPE) uplink transmitters or (b) a base-station downlink transmitter;

detecting, using an interference detection module, a presence of said co-channel interference (CCI) in carriers of said OFDM signal and determining co-channel interference affected carriers, comprising;

identifying central interference carriers corresponding to said co-channel interference affected carriers, wherein said co-channel interference is represented in said carriers using at least one of (i) a position, (ii) a spread, or (iii) an interference power, of said co-channel interference affected carriers;

receiving, using a dynamic notch filter module, said central interference carriers from said interference detection module;

mitigating, using said dynamic notch filter module, said co-channel interference of said co-channel interference affected carriers without affecting frame detection capability of a system, wherein said mitigating comprises suppressing said interference power of said co-channel interference affected carriers; and

spreading, using an interference aware frequency interleaver, said co-channel interference affected carriers based on interference specific interleaving parameters and performing frequency de-interleaving corresponding to a frequency interleaving in at least one of (a) a base-station uplink receiver or (b) one or more CPE downlink receivers.