JP2008509577A - Receiver for use in wireless communication, and method and terminal using the receiver - Google Patents

Abstract

The input signal path (101) for generating the in-phase component and the quadrature component, the circuit (113), and the amplitude imbalance between the in-phase component and the quadrature component are periodically estimated, and the relative adjustment of the amplitude is performed. A wireless receiver comprising an estimator (204) that compensates for the detected imbalance by performing an estimator (204) comprising: (i) a sample I _{i of the in-} phase component I (t) and a quadrature component Q (t corresponding to the sample Q _i is divided into blocks of), (ii) a block exponentiation value I _n corresponding to the sum of the squares of the samples I _i calculated for each block, (iii) block exponentiation value I _n And a radio reception operable to calculate an amplitude unbalance value An = (Qn / In) ^1/2 from Q _n and (iv) calculate an average value for a set of block amplitude unbalance values Machine.

Description

  The present invention relates to a receiver for use in wireless communication, and a method and a terminal using the receiver. In particular, the present invention relates to a direct conversion receiver capable of demodulating a frequency modulated (FM) RF (radio frequency) signal by utilizing the resolution of the modulated signal and the in-phase (I) and quadrature (Q) components.

  There is a fundamental problem with conventional FM radio constructed using a direct conversion scheme for detecting the I and Q components of the received signal. As will be described later, in such a receiver, errors may occur in the relative phase and amplitude between the I and Q components. This error is sometimes referred to as “orthogonal imbalance” and, as a result, causes distortion of the output audio signal. Users cannot tolerate distortion, especially when the received signal is subject to Rayleigh fading (referred to herein as “attenuation”) and / or has a low signal-to-noise ratio. I will. The prior art does not provide a satisfactory solution to the orthogonal imbalance problem.

The present invention particularly relates to orthogonal unbalanced amplitude unbalanced components.
US Pat. No. 5,705,949 proposed a procedure to remove amplitude or gain errors between the I and Q components. This procedure requires complex processing power and is not satisfactory in a damped environment.

According to a first aspect of the present invention there is provided a radio receiver according to claim 1 of the appended claims.
According to a second aspect of the present invention there is provided a wireless communication method according to claim 12 of the appended claims.

According to a third aspect of the present invention there is provided a wireless communication terminal according to claim 13 of the appended claims.
Embodiments of the invention are described by way of example with reference to the accompanying drawings.

  FIG. 1 shows a known RF direct conversion FM receiver 100 and illustrates the problem addressed by the present invention. The input FM signal x (t) is supplied via the input path 101 and supplied to the mixers 107 and 109 via the branches 103 and 105, respectively. The local oscillator 111 generates a reference signal having the same frequency as the carrier frequency of the input signal x (t). The first component of the reference signal is provided directly to the mixer 107 to multiply the input signal x (t). The second component of the reference signal is provided to the phase shifter 113, and the phase-shifted output from the phase shifter 113 is provided to the mixer 109 to be multiplied by the input signal x (t). The phase shifter 113 combined with the mixers 107 and 109 is intended to give a 90 degree phase shift with a gain of 1 between the components of the reference signal provided to the mixers 107 and 109, but in practice the phase shift is Slightly offset from 90 degrees, gain is given slightly offset from 1. An output signal from the mixer 107 passes through a low-pass filter (LPF) 115 to generate an output in-phase component signal I (t), and an output signal from the mixer 109 passes through a low-pass filter (LPF) 117. Output quadrature component signal Q (t). The amplitude imbalance applied to the output of the mixer 109 is indicated by block 119 as an unbalanced gain A.

A mathematical analysis of the configuration shown in FIG.
The input signal is
x (t) = cos (wt + φ (t) + γ)
It is expressed. Where ω is the RF carrier frequency of the input RF signal x (t), γ is the arbitrary phase of the transmitter, and φ (t) is the frequency modulation of x (t) to be detected.

  In addition, when I (t) and Q (t) are in-phase and quadrature components of x (t), x (t) = I (t) + j * Q (t).

但し、Aは振幅不平衡を表し、aはI(t)及びQ(t)の位相角間の位相不平衡を表す。

However, A represents an amplitude imbalance, and a represents a phase imbalance between the phase angles of I (t) and Q (t).

  In accordance with the described embodiment of the invention, components I (t) and Q (t) are processed in such a way as to estimate and apply adjustments to cancel the amplitude imbalance A. For example, phase imbalance is also estimated and eliminated, as described in UK patent application No. 0411888.1, to which the applicant is co-pending. The results of the adjusted components are combined to form a modulated signal φ (t) and provide an audio signal output.

  FIG. 2 is a block schematic circuit 200 embodying the present invention for use in a direct conversion FM receiver. Components having the same reference numbers as those in FIG. 1 have the same function as such components and will not be described further.

  The output signal I (t) that has passed through the low-pass filter (LPF) 115 is sampled at connection 201 and the output signal Q (t) that has passed through the low-pass filter (LPF) 117 is sampled at connection 203. Each sample signal acquired by connections 201 and 203 is provided as an input to processor 204, which operates an amplitude imbalance algorithm, described in detail below. The output signal from the processor 204 is a signal for correcting the amplitude imbalance indicating the value of 1 / A. This correction signal is provided to the amplitude corrector 205 via connection 202, which corrects the amplitude of Q (t) by a factor 1 / A to eliminate the detected amplitude imbalance A.

  A phase adjustment processing circuit (not shown) using samples of I (t) and Q (t) causes phase imbalance between I (t) and Q (t), for example, the applicant is co-pending. A phase shift control signal is generated that is estimated as described in UK patent application No. 0411888.1 and that corresponds to a value that is the same as or opposite to the value of this estimated phase imbalance. The phase adjustment signal estimated in this way is provided by the phase shifter 207. The signal corresponding to the quadrature component Q (t) is provided to the low pass filter via connection 226 and provided to the phase shifter 207. The phase shifter 207 compensates for the detected phase unbalance angle α by applying phase angle adjustment. The output from phase shifter 200 corresponding to the adjusted value of the phase of Q (t) is provided to processor 209. A signal corresponding to the in-phase component I (t) is also provided as an input to processor 209 via connection 224. The processor 209 calculates the value of the quotient Q (t) / I (t) from each input and supplies a signal representing the result to the processor 221. The processor 211 calculates the value of the arc tangent (arctg) of the quotient parameter represented by the input signal from the processor 209. The output signal 211 from the processor 211 is further provided to the processor 213, and the processor 213 calculates a derivative of the input signal to the processor 213 with respect to time t. Finally, the output signal from the processor 213 is provided to the audio output 215. The audio output 215 includes a transducer (not shown) such as an audio speaker. In the transducer, the electrical signal output from the processor 213 is converted into an audio signal such as audio information.

  The amplitude imbalance algorithm processed by the processor 204 is as follows. Samples of components I (t) and Q (t) are taken at a frequency of 20,000 samples per second. Therefore, the time length of each sample is 1/2000 = 50 μsec. Samples are taken for a sampling interval of 500 milliseconds. Therefore, the total number of samples is 500 milliseconds / 50 microseconds = 10000 samples. Samples are divided into blocks. The block size is selected according to operating conditions, such as received signal strength or S / N (signal to noise ratio). For example, when the received signal strength or the received S / N is greater than or equal to the threshold, the block size is set to the first value, and when the received signal strength or the received S / N is smaller than the threshold, the block size is Set to a larger second value. For example, if the S / N is greater than or equal to the threshold value of 15 dB, each block is 15 samples. Therefore, there are 10,000 / 15 = 666 blocks in the sampling interval. If the S / N is below the 15 dB threshold, each block is 100 samples. Therefore, there are 10,000 / 100 = 100 blocks. The algorithm is better implemented using small block sizes in an attenuation environment.

For each block sample, the power of I (I _n = Σ _{i∈ {block n}} I _i ² ) and the power of Q (Q _n = Σ _{i∈ {block n}} Q _i ² ) is calculated.
For each block, the amplitude imbalance value is calculated from the powers of I and Q using the following calculation, A _n = (Q _n / I _n ) ^1/2 . Therefore, the block value _An is the square root of the value obtained by dividing the value of the power of Q by the power of I.

For example, for each block in a given set of 1000 blocks, the amplitude imbalance values are sorted in order from smallest to largest.
The upper 45% of some block amplitude imbalance values in the sorted set and the lower 45% of some block amplitude imbalance values in the sorted set are discarded, and some of the discarded In the meantime, only some of the 10% block amplitude imbalance values remain. Thus, for example, if a set is 1000 blocks, the 450 upper and 450 lower block amplitude imbalance values are discarded, leaving 100 block amplitude imbalance values, which are further It is processed.

  When K is the number of remaining partial blocks, for example, 10% of the set of blocks estimated in the above example, the geometric mean value from the remaining K unbalanced results is calculated using the following calculation: can get.

但し、A_corrは補正されるべき振幅不平衡である。従って、A_corrは、互いに乗算された、AについてK個のサンプル結果の積のK乗根である。

However, A _corr is an amplitude imbalance to be corrected. Thus, A _corr is the K root of the product of K sample results for A multiplied by each other.

A signal corresponding to 1 / A _corr is provided by the processor 204 and provided to the amplitude corrector 205. During the period in which the signal is received, the algorithm is executed continuously and adaptively on the received FM modulated signal.

  The processor 204 operates when the receiver 200 receives an associated received audio signal in addition to an associated received audio signal. However, if necessary, the algorithm may be selectively processed only when the receiver 200 receives a specific input signal. For example, the receiver may operate with a known analog FM signal that is received by the RF transmitter. This is, for example, a standard FM modulated signal according to the industry standard TIA603.

  As described above, the division of samples processed by processor 204 into blocks is beneficial for processing signals received in an attenuated environment. If the division into blocks is not made, there is no possibility of discarding uncorrected results due to attenuation. In an attenuation environment, there is a fast change in the signal envelope. When the signal is very damped, the result for the quotient Q / I (for the block processed when this is applied) is either very large (I is close to 0) or very small (Q Can be very small). By dividing into blocks, rearranging, and discarding large and small results, it is possible to avoid including inaccurate results due to attenuation in the amplitude imbalance estimation. In fact, wireless terminals tend to always operate in an attenuation environment.

  The block size is also important. In the case of rapid decay, it is optimal to reduce the block size, and in the case where the S / N ratio is small, it is optimal to increase the block size. The received signal power is always measured by the receiver 200 using a known RSSI (Received Signal Strength Display Device). The result is provided to the estimator 204, which operates to automatically adjust the block size using the provided result. It is assumed that there is a relationship between the received signal power and the received S / N ratio so that the S / N ratio becomes higher with respect to the higher received power. For the received power threshold, a small block size should be used when the received power value is equal to or greater than the threshold value, or a large block size should be used when the received power value is less than the threshold value. It is used to determine whether.

  The advantage of significantly reducing the complexity of the algorithm processed by the processor 204 also arises, for example by utilizing selected partial block amplitude imbalance results with only 10% results as in the example above, Thus, the amount of signal required for processing is reduced. Thereby, the power consumption of the battery of the terminal in which the receiver 200 is incorporated is reduced.

  It has been found that taking a geometric mean is more effective than taking an arithmetic mean. This is because the arithmetic mean is known to add a bias to the result and makes the amplitude imbalance estimation inaccurate. The explanation about this is as follows.

  For example, assume that Q1 = 3 and I1 = 2 for block 1 and Q1 = 2 and I1 = 3 and A for block 2 are 1. A1 = 3/2 and A2 = 2/3. Using an arithmetic mean for A, 0.5 (3/2 + 2/3) = 1.0833, which is an incorrect result. However, using the geometric mean for A, sqrt ((3/2) * (2/3)) = 1 (“sqrt” is the square root), which is the correct result.

  Various processors are shown in FIG. As will be apparent to those skilled in the art, these processors may be separate processors as shown, or two or more processor functions may be incorporated into a single processor, such as a digital signal processor programmed with computer software. It may be the one.

(result)
The algorithm operated by the processor 204 was tested with simulation and actual analog FM received signals. The actual signal was recorded utilizing a direct conversion receiver operating as described with reference to FIG. Amplitude imbalance (AmpIM) was measured in%. Amp IM [%] = 100e, where e is given by
Q (t) = Asin (φ (t) + γ + a) = (1 + e) sin (φ (t) + γ + a)
The target performance for the error when applying the algorithm is Amp IM = 0.5% at maximum.

  Amp IM error was measured for various recorded actual 60dbm signals in an attenuation environment at 450MHz, with results ranging from 0.08% up to 0.45%, with an average error of 0.2%. . Similarly, Amp IM errors are estimated for various simulation signals with a signal-to-noise ratio (SNR) ranging from 15 dB to 35 dB, with error ranges from 0.08% (35 dB SNR) to 0.2% (15 dB SNR).

As a control, the amplitude imbalance error using the known calculation A = (ΣQ ² / ΣI ² ) ^1/2 was estimated. In an attenuated signal environment, a 4% Amp IM average error value was obtained using known procedures.
When the present invention is utilized in a radio receiver, the radio memory is written to store a table of initial unbalance values versus RF frequencies after manufacture. During operation of the radio, the unbalance values (amplitude and phase) change over time. Thus, the updated unbalance value is collected during use as in the above embodiment and used to provide appropriate compensation to maintain the proper quality of the audio output signal. The updated unbalance information is also stored in the radio memory and replaced with the original stored information.

(Summary)
In summary, improvements to methods suitable for compensating amplitude imbalance in direct conversion receivers have been provided with receivers operating using this method.

The method provides an important improvement for estimating the necessary unbalance compensation in conditions where the received signal is subject to noise and / or attenuation.
A look-up table of initial amplitude imbalance values versus RF frequencies is written to a memory associated with the receiver, such as the memory of the mobile station where the receiver is utilized. This is, for example, a so-called code plug that stores an operation program and data of a mobile station.

  During receiver utilization, the amplitude imbalance as a function of frequency changes slowly over time. Information collected by processor 204 is used to update information stored in memory.

The present invention improves the voice performance of a wireless terminal having a receiver operating with FM analog signals in direct conversion mode.
In addition, because there were places that could not be expressed in JIS code in the English specification of the international application, alternative notation was used in this translation. Specifically, Σ _{i ∈ {block n}}

のように表現した。

It was expressed as

1 is a schematic block circuit diagram of a known direct conversion RF receiver. 1 is a schematic block circuit diagram of a direct conversion RF receiver embodying the present invention.

Claims (10)

A radio receiver for receiving and demodulating an RF signal after frequency modulation by a direct conversion procedure, and generating an input signal path for supplying an RF input received signal, and an in-phase component and a quadrature component of the received signal And an estimator that periodically estimates an imbalance in amplitude between the in-phase component and the quadrature component and compensates for the detected imbalance by performing relative adjustment of the amplitude; And the estimator is
(i) dividing the sample I _{i of the in-} phase component I (t) and the corresponding sample Q _{i of the} quadrature component Q (t) into blocks;
(ii) for each block, it calculates the said sample I _i block exponentiation value Q _n corresponding to the sum of the squares of the corresponding block exponentiation value I _n to the square sum the sample Q _i of
(iii) Calculate block amplitude imbalance value A _n = Q _n / I _n from block power values I _n and Q _n ,
(iv) calculating an average value for a set of said block amplitude imbalance values;
Receiver that is operable.   The receiver of claim 1, wherein the set of block amplitude imbalance values for which an average value has been calculated by the estimator is a portion selected from a large set of block amplitude imbalance values.   The receiver of claim 2, wherein the estimator is operable to discard at least one other partial block amplitude imbalance value.   The estimator sorts the block amplitude unbalance value by its magnitude, and (i) a block amplitude unbalance value of the first portion whose magnitude exceeds the first threshold, and (ii) does not reach the second threshold. Operable to discard a block amplitude imbalance value of a second portion of magnitude, each of the first and second thresholds corresponding to a portion having a predetermined number of block amplitude imbalance values. The receiver according to claim 3.   The estimator, from the sorted set, a third portion block amplitude unbalance value having a block amplitude unbalance value less than the first portion value and greater than the second portion value. The receiver of claim 4, further operable to select   The receiver of claim 1, wherein the estimator is operable to calculate a geometric mean of the block amplitude imbalance values.   The receiver of claim 1, wherein the receiver is operable to select a predetermined type of received signal to estimate an amplitude imbalance of current between the in-phase component and the quadrature component.   The receiver of claim 1, wherein the estimator is operable to select a size for a block of samples according to at least one detected characteristic of the received signal.   Does the estimator detect that the signal-to-noise ratio or the received signal strength of the received signal is at least one of a) above or below a given threshold and b) above a given threshold Select the magnitude for the block of samples according to whether and select the second magnitude from the top of the block of samples according to whether the signal-to-noise ratio or signal strength is below a given threshold The receiver of claim 8, wherein the receiver is operable.   The receiver of claim 1, comprising means for periodically detecting a phase imbalance between the in-phase component and the quadrature component and adjusting the relative phase to compensate for the detected imbalance.

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