Apparatus and method for canceling inter-modulation products

Abstract

The present disclosure provides an apparatus and a method for canceling inter-modulation (IM) products in a transceiver. The apparatus includes: a pre-distortion circuit configured to estimate a first IM product caused by a transmission signal and pre-distort the transmission signal to cancel the first IM product; an IM product calculator configured to calculate a second IM product caused by the transmission signal in a received signal based on the first IM product; and a subtractor configured to subtract the second IM product from the received signal.

Claims

1. An apparatus for canceling inter-modulation (IM) products in a transceiver, comprising: a pre-distortion circuit configured to estimate a first IM product caused by a transmission signal and pre-distort the transmission signal to cancel the first IM product, wherein the first IM product is produced in a transmission signal path; an IM product calculator configured to calculate a second IM product caused by the transmission signal in a first received signal based on the first IM product, wherein the second IM product is produced in an antenna front end and a reception signal path; and a subtractor configured to subtract the second IM product from the first received signal, wherein the pre-distortion circuit is configured to estimate, during a training period, a reference IM product caused by a reference transmission signal, and the IM product calculator is further configured to: estimate, during the training period, a coefficient characterizing an equivalent transfer function of the antenna front end and the reception signal path based on the reference IM product and a second received signal containing an IM product caused by the reference transmission signal; and calculate the second IM product based on the first IM product and the coefficient.

2. The apparatus of claim 1, wherein the IM product calculator is configured to estimate the coefficient by using a pilot-based estimation algorithm in which the reference IM product is used as a pilot.

3. A method for canceling inter-modulation (IM) products in a transceiver, comprising: estimating a first IM product caused by a transmission signal and pre-distorting the transmission signal to cancel the first IM product, wherein the first IM product is produced in a transmission signal path; calculating a second IM product caused by the transmission signal in a first received signal based on the first IM product, wherein the second IM product is produced in an antenna front end and a reception signal path; subtracting the second IM product from the first received signal; estimating, during a training period, a reference IM product caused by a reference transmission signal, and estimating, during the training period, a coefficient characterizing an equivalent transfer function of the antenna front end and the reception signal path based on the reference IM product and a second received signal containing an IM product caused by the reference transmission signal, wherein the second IM product is calculated based on the first IM product and the coefficient.

4. The method of claim 3, wherein the coefficient is estimated by using a pilot-based estimation algorithm in which the reference IM product is used as a pilot.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features and advantages will be more apparent from the following description of embodiments with reference to the figures, in which:

(2) FIG. 1 shows a structure of a transceiver provided with a DPD circuit according to the prior art;

(3) FIG. 2 is a schematic diagram of signal spectra with and without DPD;

(4) FIG. 3 shows a structure of an antenna front end;

(5) FIG. 4 is a schematic diagram of signal spectra illustrating a PIM product falling into reception frequency band;

(6) FIG. 5 shows a structure of a transceiver including an apparatus for canceling IM products according to an embodiment of the present disclosure;

(7) FIG. 6 is a schematic diagram of signal spectra illustrating the process of canceling IM products from a received signal; and

(8) FIG. 7 is a flowchart illustrating a method for canceling IM products according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

(9) The embodiments of the present disclosure will be detailed below with reference to the drawings. It should be noted that the following embodiments are illustrative only, rather than limiting the scope of the present disclosure.

(10) FIG. 5 shows a structure of a transceiver 500 including an apparatus 510 for canceling IM products according to an embodiment of the present disclosure. The transceiver 500 can be used in a base station. As shown in FIG. 5, the transceiver 500 further includes a transmission signal path 520, an antenna front end 530 and a reception signal path 540. The transmission signal path 520 includes e.g., a Digital-to-Analog Converter (DAC), a modulation and up-conversion circuit and a Power Amplifier (PA). The antenna front end 530 includes e.g., an antenna, a connector connected to the antenna, a connector connected to the transmission filter, a feeder cable connecting the connectors, a transmission filter and a reception filter. The reception signal path 540 includes e.g., a Low Noise Amplifier (LNA), a demodulation and down-conversion circuit and an Analog-to-Digital Converter (ADC). All of the components included in the transmission signal path 520, the antenna front end 530 and the reception signal path 540 are well known in the art and the details thereof will be omitted here.

(11) The apparatus 510 includes a pre-distortion (DPD) circuit 511, an IM product calculator 512 and a subtractor 513.

(12) The pre-distortion circuit 511 estimates an IM product (hereinafter denoted as IM1) caused by a transmission signal and pre-distorts the transmission signal to cancel IM1. Here, IM1 includes IM components produced in the transmission signal path 520, e.g., the 3.sup.rd order and/or the 5.sup.th order IM products. The pre-distortion circuit 511 can estimate IM1 using any known DPD technique.

(13) The IM product calculator 512 calculates an IM product (hereinafter denoted as IM2) caused by the transmission signal in a received signal based on IM1. Here, IM2 includes IM components produced in the antenna front end 530 and the reception signal path 540. The IM product calculator 512 includes a coefficient estimation unit 514 and an IM product calculation unit 515, which will be detailed below.

(14) During a training period, the pre-distortion circuit 511 estimates a reference IM product (hereinafter denoted as x) caused by a reference transmission signal. The coefficient estimation unit 514 estimates a coefficient characterizing an equivalent transfer function (hereinafter denoted as h) of the antenna front end 530 and the reception signal path 540 based on x and a received signal (hereinafter denoted as y) containing an IM product (hereinafter denoted as im) caused by the reference transmission signal.

(15) In particular, the IM product im contains IM components produced in the antenna front end 530 and the reception signal path 540 and possibly a residual IM component leaked from the transmission filter. All these components are caused by the same reference transmission signal. That is, the IM product im and the reference IM product x are caused by the same reference transmission signal and thus have the same characteristics in frequency domain. Therefore, it is possible to calculate im from x:
im=h.Math.x.
where h is an equivalent transfer function of the antenna front end 530 and the reception signal path 540, as described above.

(16) Therefore, the received signal y can be expressed as:
y=im+r=h.Math.x+r.
where r denotes the combination of a wanted signal and a noise but does not include any IM products.

(17) Since both the wanted signal and the noise can be considered as white noises, the coefficient estimation unit 514 can use x as a pilot to estimate h by using any pilot-based channel estimation algorithm (such as Minimum Mean Square Error (MMSE), Least Square (LS), etc.) during the training period.

(18) Since the estimated h can be considered to be quite stable. After the training period, the IM product calculation unit 515 can calculate IM2 based on IM1 and the estimated h:
IM2=h.Math.IM1.

(19) Then, the subtractor 513 subtracts IM2 from the received signal. In this way, the IM product caused by the transmission signal in the received signal can be canceled.

(20) FIG. 6 is a schematic diagram of signal spectra illustrating the process of canceling IM products from a received signal. It can be seen from FIG. 6 that the IM product, including possibly any residual IM components after DPD and filtering at the transmission filter, can be canceled from the received signal.

(21) FIG. 7 is a flowchart illustrating a method 700 for canceling IM products according to an embodiment of the present disclosure. The method 700 can be performed at the transceiver 500. The method 700 includes the following steps.

(22) At step S710, an IM product (IM1) caused by a transmission signal is estimated and the transmission signal is pre-distorted to cancel IM1.

(23) At step S720, an IM product (IM2) caused by the transmission signal in a received signal is calculated based on IM1.

(24) At step S730, IM2 is subtracted from the received signal.

(25) In an embodiment, the method 700 further includes a step of estimating, during a training period, a reference IM product (x) caused by a reference transmission signal, and estimating, during the training period, a coefficient characterizing an equivalent transfer function (h) of the antenna front end and the reception signal path based on x and a received signal (y) containing an IM product (im) caused by the reference transmission signal. IM2 is calculated based on IM1 and h.

(26) It is to be noted that the contents described above in relation to the transceiver 500 of FIG. 5 also apply to the method 700 according to the present disclosure.

(27) With the embodiments of the present disclosure, the IM product estimated by the pre-distortion circuit is reused to calculate the IM product caused by the transmission signal in the received signal and finally cancel the calculated IM product from the received signal. In this way, the IM product caused by the transmission signal, including AIM components and PIM components, can be removed from the received signal.

(28) The present disclosure has been described above with reference to the preferred embodiments thereof. It should be understood that various modifications, alternations and additions can be made by those skilled in the art without departing from the spirits and scope of the present disclosure. Therefore, the scope of the present disclosure is not limited to the above particular embodiments but only defined by the claims as attached.