# US 2013/0155833 A1 · Apparatus and method for i/q offset cancellation in sc-fdma system

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- Number: US 2013/0155833 A1
- Document ID: US20130155833A1
- Status: Published application
- Kind: A1
- Application number: 13/820,193
- Filed: 2010-12-30
- Published: 2013-06-20
- Earliest claimed: 2010-09-03
- Assignees: Innowireless Co., Ltd.
- Inventors: Jinsoup Joung; Kyeongmin Ha; Seunghwan Ji; Yonghoon Lim; Byungkwan Jang
- Web page: https://patentgrep.com/patent/US20130155833A1

## CPC

- H04J 1/16: Monitoring arrangements {(for transmission in general H04B17/00; for amplifiers H03F1/52, H03F1/523)}
- H04L 27/2647: {Arrangements specific to the receiver only (equalisation H04L27/01)}
- H04L 27/3854: {using a non - coherent carrier, including systems with baseband correction for phase or frequency offset}
- H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S)
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

The present invention relates to an apparatus and a method for eliminating I/Q offset in a receiver of a SC-FDMA system which improves performance of the system by accurate measurement and cancellation of I/Q offset in a receiver of a SC-FDMA system operating in a 3GPP LTE uplink. An apparatus for eliminating I/Q offset in a receiver of the SC-FDMA system constituting the receiver of the SC-FDMA system includes: a linear interpolation channel estimation unit for estimating channel using demodulation reference symbol (DMRS) that is a training sequence (X) corresponding to the discrete Fourier transformed signal (Y) that has passed through frame sync acquisition, frequency compensation and cyclic prefix elimination; a signal regeneration/cancellation unit for calculating I/Q offset (D=Y−Y′) by subtracting the discrete Fourier transformed signal (Y) from the ideal discrete Fourier transformed signal (Y′=H′X) generated by using channel coefficient (H′), that is an output of the linear interpolation channel estimation unit, and the DMRS that is the training sequence (X); and an I/Q offset measurement/cancellation unit for generating VQ offset-free signal (YNoDC=Y−D′) by subtracting I/Q offset (D′) having corrected phase and power of the VQ offset (D=Y−Y′) from the discrete Fourier transformed signal (Y).

## Claims

### Claim 1

An apparatus constituting a receiver for eliminating I/Q offset in the receiver of a SC-FDMA system comprising:
a linear interpolation channel estimation unit estimating channel using DMRS that is a training sequence (X) corresponding to the discrete Fourier transformed signal (Y) that has passed through frame sync acquisition, frequency compensation and cyclic prefix elimination;
a signal regeneration/cancellation unit calculating I/Q offset (D=Y−Y′) by subtracting the discrete Fourier transformed signal (Y) from the ideal discrete Fourier transformed signal (Y′=H′X) created by using the channel coefficient (H′), that is an output of the linear interpolation channel estimation unit, and the DMRS that is the training sequence (X); and
an I/Q offset measurement/cancellation unit generating I/Q offset-free signal (YNoDC=Y−D′) by subtracting I/Q offset (D′) having corrected phase and power of the I/Q offset (D=Y−Y′) from the discrete Fourier transformed signal (Y).

### Claim 2 (depends on 1)

The apparatus for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 1,
wherein the linear interpolation channel estimation unit estimates channel, to minimize the effect of I/Q offset, approximately ⅓ of left and right sides of the sub-carriers estimate channels using the least square method or MMSE using DMRS that is the training sequence (X) while approximately ⅓ of the remaining sub-carriers estimate channels through linear interpolation using the estimated results from the least square method or MMSE.

### Claim 3 (depends on 2)

The apparatus for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 2, wherein the linear interpolation channel estimation unit comprises;
an I/Q offset power measurement unit for measuring power of the I/Q offset (D) by calculating average value of inverse discrete Fourier transformed I/Q offset (DTime) obtained through inverse discrete Fourier transformed I/Q offset (D) by number of sub-carriers;
an I/Q offset regeneration unit comprising a phase comparator that generates complex sinusoids according to the ideal inverse discrete Fourier transformed I/Q offset (DIdealTime) and adjusts its phase to the complex sinusoid of the inverse discrete Fourier transformed I/Q offset (DTime), and a power comparator that corrects power of the ideal inverse discrete Fourier transformed I/Q offset (DIdealTime) whose phase is corrected through the phase comparator, with the power of the inverse discrete Fourier transformed I/Q offset (DTime); and
an I/Q offset cancellation unit that transforms the inverse discrete Fourier transformed I/Q offset whose phase and power are corrected in the I/Q offset regeneration unit, into the frequency domain by discrete Fourier transform, and generates an I/Q offset (D′) having corrected phase and power, then this I/Q offset (D′) is subtracted from the discrete Fourier transformed signal (Y), that is YNoDC=Y−D′, thereby eliminating the I/Q offset.

### Claim 4 (depends on 3)

The apparatus for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 3, further comprising a linear interpolation channel estimation unit, a signal regeneration/cancellation unit, and an I/Q offset measurement/cancellation unit which perform identical functions corresponding to the above-described linear interpolation channel estimation unit, signal regeneration/cancellation unit, and the I/Q offset measurement/cancellation unit at the back end of the I/Q offset measurement/cancellation unit,
wherein the back-end linear interpolation channel estimation unit among the above-described two linear interpolation channel estimation units estimates channels by selecting a couple of sub-carriers near the DC sub-carrier as a linear interpolation interval.

### Claim 5 (depends on 1)

The apparatus for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 1, wherein the receiver of the SC-FDMA system constitutes a part of the base station in the 3GPP LTE/LTE Advanced uplink.

### Claim 6

A method for eliminating I/Q offset in a receiver of a SC-FDMA system comprising the steps of:
(a) performing discrete Fourier transform of a signal that has been passed through frame sync acquisition, frequency correction, and cyclic prefix elimination;
(b) estimating channel coefficient (H′) of the discrete Fourier transformed signal (Y) using the DMRS that is the training sequence (X);
(c) obtaining an I/Q offset (D=Y−Y′) by subtracting the ideal discrete Fourier transformed signal (Y′=H′X) from the discrete Fourier transformed signal (Y), wherein the ideal discrete Fourier transformed signal (Y′=H′X) is generated using the channel coefficient (H′) that is estimated in step (b), and the DMRS that is the training sequence (X);
(d) generating an I/Q offset (D′) having corrected phase and power of the I/Q offset (D); and
(e) generating a signal (YNoDC=Y−D′) whose I/Q offset is eliminated by subtracting the I/Q offset (D′) having corrected phase and power, from the discrete Fourier transformed signal (Y).

### Claim 7 (depends on 6)

The method for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 6, wherein step (b) is characterized in that approximately ⅓ of right and left sub-carriers estimate channels by the least square method or MMSE using DMRS that is training sequence (X) to minimize the I/Q offset effect, while the remaining ⅓ of the sub-carriers estimate channels by linear interpolation using the results that are estimated by the least square method or MMSE.

### Claim 8 (depends on 7)

The method for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 7, characterized in that step (d) includes the steps of:
(d1) measuring I/Q offset power by calculating average of inverse discrete Fourier transformed I/Q offset (DTime) that is obtained through the inverse discrete Fourier transformed I/Q offset by number of the sub-carriers;
(d2) generating complex sinusoids according to the ideal inverse discrete Fourier transformed I/Q offset (DIdealTime) and adjusting its phase to the complex sinusoid of the inverse discrete Fourier transformed I/Q offset (DTime); and
(d3) correcting power of the ideal inverse discrete Fourier transformed I/Q offset (DIdealTime) whose phase is corrected through the step (d2), with the power of inverse discrete Fourier transformed I/Q offset (DTime) that is measured in the step (d1).

### Claim 9 (depends on 8)

The method for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 8, wherein step (e) is characterized in that an I/Q offset (D′) having corrected phase and power, is generated by discrete Fourier transform and conversion of the inverse discrete Fourier transformed I/Q offset whose phase and power are corrected, into the frequency domain, then this I/Q offset (D′) is subtracted from the discrete Fourier transformed signal (Y), that is YNoDC=Y−D′, thereby eliminating the I/Q offset.

### Claim 10 (depends on 6)

The method for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 6, characterized in that after completion of the above-described step (e), steps starting from the step (b) may be repeated one more time; when repeating step (b), channels can be estimated by selecting a couple of sub-carriers near the DC sub-carrier as a linear interpolation interval.

### Claim 11 (depends on 6)

The method for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 6, characterized in that the receiver of the SC-FDMA system constitutes a part of the base station in the 3GPP LTE/LTE Advanced uplink.

### Claim 12 (depends on 2)

The apparatus for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 2, wherein the receiver of the SC-FDMA system constitutes a part of the base station in the 3GPP LTE/LTE Advanced uplink.

### Claim 13 (depends on 3)

The apparatus for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 3, wherein the receiver of the SC-FDMA system constitutes a part of the base station in the 3GPP LTE/LTE Advanced uplink.

### Claim 14 (depends on 4)

The apparatus for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 4, wherein the receiver of the SC-FDMA system constitutes a part of the base station in the 3GPP LTE/LTE Advanced uplink.

### Claim 15 (depends on 7)

The method for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 7, characterized in that the receiver of the SC-FDMA system constitutes a part of the base station in the 3GPP LTE/LTE Advanced uplink.

### Claim 16 (depends on 8)

The method for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 8, characterized in that the receiver of the SC-FDMA system constitutes a part of the base station in the 3GPP LTE/LTE Advanced uplink.

### Claim 17 (depends on 9)

The method for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 9, characterized in that the receiver of the SC-FDMA system constitutes a part of the base station in the 3GPP LTE/LTE Advanced uplink.

### Claim 18 (depends on 10)

The method for eliminating I/Q offset in a receiver of a SC-FDMA system according to claim 10, characterized in that the receiver of the SC-FDMA system constitutes a part of the base station in the 3GPP LTE/LTE Advanced uplink.