TRANSMIT SIGNAL CANCELATION APPARATUS AND METHODS

• US 20130294295A1
• Filed: 04/27/2013
• Published: 11/07/2013
• Est. Priority Date: 05/02/2012
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Viswanathan, Nagarajan, Pentakota, Visvesvaraya, Dantoni, Francesco, Keller, Robert Clair, Neu, Thomas
• Granted Patent: US 9,001,712 B2
• Time in Patent Office: Days
• US Class Current: 370/278
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver
• CPC Class Codes: H04L 5/1461 Suppression of signals in the return path, i.e. bidirectional control circuits

Abstract

Apparatus and methods disclosed herein implement an RF receive-band filter at a receive chain input of a wireless base station with a co-located transmitter and receiver. The RF receive-band filter includes an adaptive filter component to perform filtering operations on samples of a digital baseband or intermediate frequency signal x(n) from a transmit chain associated with the wireless base station. An adaptive filter transfer function is determined in real time such that samples of the baseband transmit signal x(n) are transformed into a cancellation baseband signal z(n). The digital cancelation baseband signal z(n) is then digital-to-analog converted and the resulting analog baseband signal z(t) is up-converted to obtain a subtractive RF cancelation signal c(t). C(t) is summed with a desirable received signal RF component r(t) and an undesirable transmitter leakage RF signal component l(t) appearing at the input to the base station receiver. C(t) cancels l(t), leaving r(t) to be processed by the receiver section of the base station.

Claims

1. A radio frequency (RF) receive-band filter in a wireless base station, comprising:

an observation chain in a receive path to receive a composite RF signal sum including a received signal component r(t), a transmitter leakage signal component l(t) and a subtractive correction signal component c(t) and to amplify and convert the time domain sum of [r(t)+l(t)−

c(t)] to a digital domain data set f(n);

an adaptation chain communicatively coupled to the observation chain to receive a digital baseband data set x(n) from a transmitter generating the transmitter leakage component l(t), to digitally down-convert and filter f(n) to a baseband frequency associated with x(n) to obtain y(n), to generate a set of adaptive cancelation filter coefficients H_C, and to filter x(n) using H_C to obtain a cancelation data set z(n); and

a correction chain communicatively coupled to the adaptation chain to perform digital-to-analog conversion and filtering operations on z(n) to obtain z(t) and to up-convert z(t) to obtain the subtractive correction RF signal component c(t).

2. The RF receive-band filter of claim 1, further comprising:

an RF signal summing module communicatively coupled to a base station duplexer, to the correction chain, and to the observation chain to filter a received RF sum [r(t)+l(t)] by summing the subtractive correction signal component c(t) with l(t) in order to cancel at least a portion of l(t) and to thereby reduce noise produced in a receive frequency band.

3. The RF receive-band filter of claim 2, the observation chain further comprising:

a low noise amplifier (LNA) communicatively coupled to the RF summing module to amplify the RF signal sum [r(t)+l(t)−

c(t)]; and

a wideband analog-to-digital converter (ADC) communicatively coupled to the LNA to convert the amplified RF signal sum [r(t)+l(t)−

c(t)] to the digital domain data set f(n).

4. The RF receive-band filter of claim 1, the adaptation logic chain further comprising:

an adaptation logic module communicatively coupled to the observation chain to receive the digital baseband data set x(n) from the transmit chain generating the transmitter leakage component l(t), to digitally down-convert and filter f(n) to a baseband frequency associated with x(n) to obtain y(n), and to generate the set of adaptive cancelation filter coefficients H_C; and

an adaptive filter communicatively coupled to the adaptation logic module to filter x(n) using H_C to obtain the cancelation data set z(n).

5. The RF receive-band filter of claim 1, the adaptation logic chain further comprising:

a storage register communicatively coupled to the adaptation logic module to store the adaptive cancelation filter coefficients H_C.

6. The RF receive-band filter of claim 1, the correction chain further comprising:

a digital-to-analog converter (DAC) and filter communicatively coupled to the adaptation chain 222 to perform the digital-to-analog conversion and filtering operations on z(n) to obtain z(t);

an RF modulator and up-converter communicatively coupled to the DAC and filter to up-convert z(t); and

a saw filter communicatively coupled to the RF modulator and up-converter to filter noise created in the DAC and filter and/or noise created in the RF modulator and up-converter and to obtain the subtractive correction RF signal component c(t).

7. The RF receive-band filter of claim 1, further comprising:

a transmit chain to create the digital baseband data set x(n), to convert x(n) to an analog signal, and to filter, up-convert, and amplify the analog signal to create an analog transmit signal, the transmitter leakage component l(t) being a portion of the analog transmit signal; and

a saw filter in the transmit chain at a power amplifier input to reduce wideband noise capable of being coupled into the receive chain.

8. The RF receive-band filter of claim 1, further comprising:

a duplexer to provide a transmit chain to antenna path and an antenna to receive chain path and to provide filtering to help isolate the transmit signal from the receive signal path.

9. An adaptive filtering apparatus, comprising:

a down-conversion module to receive a digitized radio frequency (RF) signal f(n) and to down-convert and filter f(n) to produce a baseband received signal y(n), f(n) to include a digitized received signal component r(t), a digitized transmitter leakage signal component l(t), and a subtractive RF correction signal component c(t);

a pseudorandom bit sequence (PRBS) module to generate a first PRBS P_A and a second PRBS P_B, P_A to inject into a transmit chain for summing with a digital baseband transmit signal x(n) and P_B to sum with a digital baseband cancelation signal z(n);

a correction chain transfer function estimation module H_CORR communicatively coupled to the down-conversion module and to the PRBS module to initiate a P_B operation and to generate a set of estimated correction chain transfer function coefficients H_CORR(k) as 1/N*Σ

[y(n) P_B(n−

k)], H_CORR corresponding to digital-to-analog conversion and up-conversion of z(n) to obtain the RF correction signal component c(t);

a cancelation chain transfer function adaptation module H_C communicatively coupled to the down-conversion module to iteratively generate a set of adaptive filter coefficients using an adaptation sequence; and

an adaptive filter communicatively coupled to the cancelation chain transfer function adaptation module H_C to load the set of adaptive filter coefficients and to filter x(n) to obtain the digital baseband cancelation signal z(n).

10. The adaptive filtering apparatus of claim 9, the adaptation sequence being:

H_—

C(k)^T+1=H_—

C(k)^T−

μ

[Y(n−

k).H_CORR].

11. The adaptive filtering apparatus of claim 9, further comprising:

a first set of transfer function coefficient registers to store H_CORR; and

a second set of transfer function coefficient registers to store H_C.

12. A method of transmitter leakage signal cancelation, comprising:

receiving a radio frequency (RF) signal sum including a desirable received signal component r(t), a transmitter leakage signal component l(t), and a subtractive correction signal component c(t) at a base station receive chain;

amplifying and digitizing the RF signal sum to obtain a digital domain data set f(n);

at an adaptation chain, receiving a digital baseband data set x(n) from a transmit chain generating the transmitter leakage component l(t);

down-converting and filtering f(n) to a baseband frequency associated with x(n) to obtain y(n);

generating a set of adaptive cancellation filter coefficients H_C using an adaptation sequence operating on y(n);

filtering x(n) using H_C to obtain a cancellation data set z(n);

performing digital-to-analog conversion and filtering operations on z(n) to obtain z(t); and

up-converting z(t) to obtain the subtractive correction RF signal component c(t).

13. The method of noise cancelation of claim 12, the adaptation sequence being:

H_—

C(k)^T+1=H_—

C(k)^T−

μ

[Y(n−

k).H_CORR].

14. The method of noise cancelation of claim 12, further comprising:

algebraically summing r(t), l(t), and c(t) as [r(t)+l(t)−

c(t)] to obtain the RF signal sum.

15. The method of transmitter leakage signal cancelation of claim 12, transmit chain operations further comprising:

creating the digital baseband data set x(n);

converting x(n) to an analog signal; and

filtering, up-converting, and amplifying the analog signal to create an analog transmit signal, the transmitter leakage component l(t) including energy associated with the analog transmit signal.

16. The method of transmitter leakage signal cancelation of claim 12, further comprising:

generating a first pseudorandom bit sequence (PRBS) P_A and a second PRBS P_B;

injecting P_A into the transmit chain by summing with the digital baseband transmit signal x(n); and

summing P_B with correction chain input signal z(n).

17. The method of transmitter leakage signal cancelation of claim 16, further comprising:

receiving a calibration RF signal sum including a received signal component r(t), a transmitter leakage signal component l(t), and a subtractive correction signal component c(t) at a base station receive chain input, c(t) to include a PRBS component; and

amplifying and digitizing the calibration RF signal sum to obtain a digital domain calibration data set f(n)_CALIBRATE.

18. The method of transmitter leakage signal cancelation of claim 17, further comprising:

at an adaptation chain, receiving a digital baseband data set x(n) from a transmit chain generating the transmitter leakage component l(t); and

down-converting and filtering f(n) to a baseband frequency associated with x(n) to obtain y(n)_CALIBRATE.

19. The method of transmitter leakage signal cancelation of claim 18, further comprising:

estimating a correction chain transfer function H_CORR as 1/N*Σ

[y(n)_CALIBRATE*P_B(n−

k)]; and

storing H_CORR coefficients H_CORR(k).

20. The method of transmitter leakage signal cancelation of claim 19, further comprising:

determining whether the estimation of H_CORR is complete; and

performing additional H_CORR estimation operations on additional blocks of f(n) if the estimation of H_CORR is not complete.