WO2009116734A1 - Inmarsat communications down-link receiver and data restoration method used in the same - Google Patents

Abstract

An Inmarsat communications down-link receiver is disclosed.  The Inmarsat communications down-link receiver comprises: an analog to digital converter (ADC) that converts an analog received signal to digital and outputs a digital signal r(k); a first interpolater that receives the digital signal r(k) as input and restores the first data; a UW (unique word) detector that multiplies the conjugate complex numbers of r(k-1), which is to say r(k) delayed by 1 sample, and the digital signal r(k) to produce a differential signal, and that uses the correlation of the differential signal to determine whether it is a unique word; a second interpolater that receives the differential signal as input and restores second data; a time difference detector that detects time-related errors in the second data and outputs the time difference; and a controller that outputs a symbol restoration central constant and symbol restoration interval constant according to the time difference; [A1] and the symbol restoration central constant and symbol restoration interval constant are provided in the first and second interpolaters.  Within the communications environment that uses the Inmarsat Mini-m system, data symbols may be sampled with reliability from the received signals that are received.

Description

Data restoration method in downlink receiver and downlink receiver of Inmarsat communication

The present invention relates to a downlink receiver, and more particularly, to a downlink receiver for timing recovery of a signal received in an inmarsat communication.

Inmarsat (International Mobile Satellite) Mini-m system is well known as the system used for relaying the Internet in the Himalayan climbing platform and has been increasing since 1995. Inmarsat-A, B, M, and C services use global satellite beams, but Inmarsat Mini-m services use parabore satellite antennas of about 30 cm because they can be miniaturized using spot beams.

When using the Inmarsat Mini-m system, a frequency offset may occur due to a mismatch of the transceiver oscillator. In this case, there is a problem in that a signal received at a receiver by a frequency offset may change in phase with time. Here, since the phase changes with time, there is a problem in that the receiver cannot accurately sample the data symbols in the received signal.

More specifically, the signal bandwidth of the Inmarsat Mini-m system is 2.4 kHz and has the smallest signal bandwidth of the Inmarsat system. Therefore, the Inmarsat Mini-M system is a relatively large frequency offset system because the frequency tolerance recommended by the Inmarsat specification is 924 Hz. Therefore, even when the parallax with respect to the carrier is corrected, residual frequency offset may occur. There is a problem in that data symbols cannot be sampled reliably in the residual frequency offset environment.

Therefore, since the Inmarsat Mini-m system has a relatively large frequency offset, it is necessary to apply a TED (Timing Error Detector) algorithm that is robust to the frequency offset.

The TED algorithm includes a data added method and a non-data added method.

Basically, data added methods such as ELD, Zero Crossing Detector (ZCD), Muller and Muller Detector (MMD), and the like have a problem in that stable timing synchronization performance cannot be obtained for an environment in which a carrier phase offset exists.

Therefore, the GAD (Gardner Detector) method, which is a non-data added method, has been widely used as an algorithm for minimizing the influence on the presence of the carrier phase offset. However, when considering the influence of the frequency offset that the carrier phase offset changes over time, the GAD method also has a problem that the jitter performance is deteriorated due to the residual carrier phase offset to ensure a stable performance. In addition, the GAD method has a problem that it is impossible to quickly detect the UW signal in the Unique Word (UW) section required by the Inmarsat Mini-m system.

In the conventional communication using the Inmarsat Mini-m system, in consideration of the environment in which the frequency offset occurs, there is no study to correct the parallax to accurately sample data symbols in the received received signal.

An object of the present invention is to propose a downlink receiver for sampling a data symbol so as to be reliable from a received signal in a communication environment using an Inmarsat Mini-m system.

Another object of the present invention, in the communication environment using the Inmarsat Mini-m system, in consideration of the environment where the residual frequency offset may occur, the downlink for correcting the time difference to accurately sample the data symbols in the received signal received It is to propose a receiver.

It is still another object of the present invention to propose a downlink receiver applicable to sampling a data symbol when a preamble exists in a general wireless communication system.

According to an aspect of the invention, the downlink receiver of the INMARSAT communication, Analog to Digital Converter (Analog to Digital Converter) for outputting a digital signal r (k)-where k is A natural number, a first interpolator for receiving the digital signal r (k) and restoring first data, a complex conjugate of r (k-1) with a delay of one sample of r (k), and the A differential signal is generated by multiplying the digital signal r (k), and a UW detector for determining the existence of a unique word using the correlation of the differential signal, and receiving the differential signal to receive the second data. A second interpolator for reconstructing, a parallax detector for detecting a time difference in the second data and outputting a parallax, and a controller for outputting a symbol reconstruction center constant and a symbol reconstruction interval constant according to the parallax, wherein the symbol The circle center and the constant symbol recovery interval constant is provided to the first and second interpolators. Here, when the UW detector determines that the differential signal includes the unique word, the differential signal is input to the second interpolator, and the second interpolator is configured to recover the symbol recovery center constant and the symbol recovery interval. The second data may be restored from the input differential signal using a constant. The symbol recovery center constant and the symbol recovery interval constant are input to the first and second interpolators when the UW detector determines that the unique word is included in the differential signal. Reconstructs the first data from the input digital signal r (k) using the symbol reconstruction center constant and the symbol reconstruction interval constant, and the second interpolator is the symbol reconstruction center constant and the symbol reconstruction interval constant. The second data may be restored from the input differential signal by using. Here, the downlink receiver may further include a loop filter that multiplies the time difference by a predetermined gain. The second interpolator, parallax detector, loop filter, and controller may form a closed loop. Each time the differential signal is input to the second interpolator, the controller updates a symbol recovery center constant and a symbol recovery interval constant provided to the first and second interpolators, and the first interpolator is the closed type. The symbol may be recovered by determining a sampling point of the symbol from the digital data signal r (k) using the symbol recovery center constant and the symbol recovery interval constant updated through a loop.

According to another aspect of the invention, the data recovery method in the downlink receiver of INMARSAT communication, the digital signal r (k) generated by analog-to-digital conversion (Analog to Digital Converting), wherein k is a complex number of r (k-1) with a one-sample delay of natural number and multiplied by the digital signal r (k) to generate a differential signal, and the differential signal includes a unique word. Restoring first data from the input digital signal r (k) by using a symbol restoring center constant and a symbol restoring interval constant in a first interpolator when the first interpolator is determined; If it is determined that the word is included in the second interpolator (interpolater) using the symbol recovery center constant and the symbol recovery interval constant from the second signal from the differential signal A and a step of restoring. The method for restoring data in a downlink receiver of the INMARSAT communication includes detecting a time error in the second data and outputting a time difference, and generating a symbol recovery center constant and a symbol recovery interval constant according to the time difference. The method may further include providing the first and second interpolators.

According to another aspect of the present invention, a method for restoring data in a downlink receiver of a wireless communication includes a digital signal r (k) generated by analog to digital converting an analog received signal, where k is Generating a differential signal by multiplying the complex number of r (k-1) with a delay of one sample by the digital signal r (k), and determining that the differential signal includes a preamble Restoring first data from the input digital signal r (k) by using a symbol restoration center constant and a symbol restoration interval constant in a first interpolator, and the preamble is included in the differential signal. If it is determined that the second interpolator (interpolater) to restore the second data from the differential signal using the symbol recovery center constant and the symbol recovery interval constant It includes the system. The symbol recovery center constant and the symbol recovery interval constant may be updated each time the differential signal is input to the second interpolator and provided to the first and second interpolators. The first interpolator may reconstruct a symbol by determining a sampling point of the symbol from the digital data signal r (k) using the updated symbol reconstruction center constant and symbol reconstruction interval constant.

The data recovery method in the downlink receiver and the downlink receiver according to the embodiments of the present invention has an advantage of sampling data symbols reliably from a received signal in a communication environment using an Inmarsat Mini-m system.

In addition, in a communication environment using the Inmarsat Mini-m system, the parallax may be corrected to accurately sample data symbols in a received signal in consideration of an environment in which residual frequency offset may occur.

In addition, the data recovery method in the downlink receiver and the downlink receiver according to the embodiments of the present invention is applicable to the step of sampling the data symbol when the preamble (preamble) in the conventional wireless communication system.

1 is a view for explaining a data only frame (data only frame) in the Inmarsat Mini-m system.

2 illustrates a downlink receiver of an Inmarsat Mini-m system in accordance with an embodiment of the present invention.

3 is a diagram illustrating a configuration of a UW detector 210 according to an embodiment of the present invention.

4 is a graph illustrating the performance of a UW detector according to an embodiment of the present invention.

5 illustrates the performance of a parallax detector in accordance with one embodiment of the present invention.

6 is a diagram illustrating the structure of a loop filter according to an embodiment of the present invention.

7 and 8 illustrate tracking performance according to gain and jitter performance in a loop filter according to an embodiment of the present invention.

9 is a graph illustrating jitter performance of an interpolator in accordance with an embodiment of the present invention.

10 illustrates a piece interpolater in accordance with an embodiment of the present invention.

11 and 12 are graphs illustrating tracking performance and jitter performance in a steady state of a downlink receiver according to an embodiment of the present invention and a downlink receiver to which a prior art GAD scheme is applied.

<Description of the symbols for the main parts of the drawings>

210: UW detector 211: differential filter

212: matching filter 230: first interpolator

231: second interpolator 240: parallax detector

250: loop filter 260: controller

The present invention may be variously modified and have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all transformations, equivalents, and substitutes included in the spirit and scope of the present invention. In the following description of the present invention, if it is determined that the detailed description of the related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, the same reference numerals will be used for the same means regardless of the reference numerals in order to facilitate the overall understanding.

Hereinafter, in the description of the embodiment of the present invention, the communication environment using the Inmarsat Mini-m system will be described in detail. However, the present invention may be applied when a preamble exists in a general wireless communication system. It is apparent to those skilled in the art in view of the technical spirit of the invention.

1 is a view for explaining a data only frame (data only frame) in the Inmarsat Mini-m system.

In the Inmarsat Mini-m system, a frame includes a frame for transmitting voice and data and a data only frame. Hereinafter, in order to facilitate the understanding and explanation of the present invention, the data will be described using a single frame, but the present invention is not limited thereto, and it will be apparent to those skilled in the art in view of the technical idea of the present invention.

Inmarsat Mini-m system uses Off-Quadrature Phase Shift Key (O-QPSK) as a modulation method, and the data rate is 2.4 kbit / s.

Here, O-QPSK (Offset QPSK) is a modulation method capable of minimizing distortion caused by nonlieanr amplifiers in satellites by reducing the phase change between symbols during QPSK modulation.

The Inmarsat Mini-M system uses convolutional encoding with a code rate of 1/2. That is, when 288 bits of data are encoded at a code rate of 1/2, the data becomes 576 bits.

Referring to FIG. 1, the super frame 104 is composed of two subframes (eg, 102). Here, the subframe 102 is composed of a 84-bit unique word field, a 576-bit data field, and a 12-bit dummy field.

Here, as illustrated in FIG. 1, when 288-bit data 101 and 6-bit dummy 103 perform forward error correction (hereinafter referred to as 'FEC') having a code rate 1/2. The subframe of 672 bits may be generated.

So far, the data single frame in the Inmarsat Mini-m system has been described with reference to FIG. 1. Hereinafter, the receiving end of the Inmarsat Mini-m system will be described.

The received signal received at the receiving end of the Inmarsat Mini-m system may be represented by Equation 1 below.

[Equation 1]

Where {c _i } is an O-QPSK modulated baseband signal,

to be. That is, the average of {c _i } is 1. Here, the baseband signal is a signal filtered by a square root raised cosine (SRRC) filter of a transmitter in a process of including data symbols in a carrier at a transmitter. SRRC filter is required for both the transmitting and receiving end of the Inmarsat Mini-m system, and since it is a known technology, detailed description thereof will be omitted.

Where, g _M (t) is the SRRC filter of the transmitter, g _R (t) is the SRRC filter of the receiver.

Where Δf, T, and τ are residual frequency offsets, symbol periods, and time delays occurring in the wireless channel.

Here, w (t) is Additive White Gaussian Noise (hereinafter referred to as 'AWGN').

When the received signal y (t) passes through the SRRC filter g _R (t) at the receiving end, it becomes r (t) of Equation 2 below.

[Equation 2]

Here, h (t) is a convolution of the SRRC filter g _M (t) of the transmitter and the SRRC filter g _R (t) of the receiver, and is a raised cosine pulse.

Where n (t) is AWGN.

In general, the SRRC filter used in the Inmarsat Mini-m system has a roll-off factor of 0.6, but no tap coefficient.

In the embodiment of the present invention, a 48-tap, 8-oversample TX / RX SRRC filter used in a general wireless communication system such as IS-95 will be described. However, the present invention is not limited thereto. Self-explanatory

Here, the ROF constant defines the excess of the bandwidth, the ROF constant controls the characteristics of the low pass filter (hereinafter referred to as 'low pass filter') in the frequency domain, and in the time domain Control the effect of side lobs.

 The longer the tap coefficient, the longer the SRRC filter becomes the ideal low pass filter in the frequency domain.

In addition, oversampling has an advantage in that the resolution in the sampling time correction of the data symbols increases as the number of oversampling increases.

Hereinafter, a downlink receiver according to an embodiment of the present invention will be described with reference to FIG. 2.

Prior to the detailed description of the drawings, it is intended to clarify that the division of the components in the present specification is only divided by the main function of each component. That is, two or more components to be described below may be combined into one component, or one component may be provided divided into two or more for each function. Each of the components to be described below may additionally perform some or all of the functions of other components in addition to the main functions of the components, and some of the main functions of each of the components are different. Of course, it may be carried out exclusively by. Therefore, the presence or absence of each component described through this specification should be interpreted functionally, and for this reason, the configuration of the components according to the downlink receiver of the present invention is within the limits that can achieve the object of the present invention. Clearly, it may be different from FIG.

2 is a diagram illustrating a downlink receiver of an Inmarsat Mini-m system according to an embodiment of the present invention.

The downlink receiver may include a UW detector 210, first and second interpolators 230 and 231, a parallax detector 240, a loop filter 250, and a controller 260.

Hereinafter, in order to facilitate understanding and explanation of the present invention, the parallax detector 240 is described as an example of a timing error detector (TED) using an Early Late Detector (ELD) as an example, but a data added method It is apparent to those skilled in the art in view of the technical spirit of the present invention that both methods or non-data added methods can be applied.

Hereinafter, it is assumed that an analog-to-digital converter (hereinafter referred to as "ADC") converts the received signal r of Equation 2 to 19.2 KHz, which is eight times the transmission rate of the data symbol.

In this case, r (k) can generate eight sample signals per data symbol.

Subsequently, r (k) may be input to the UW detector 210.

The UW detector 210 may be composed of a differential filter 211 and a matched filter 212.

The differential filter 211 may generate a differential signal by multiplying the complex conjugate of the received signal r (k-1) by delaying the received signal r (k) by one sample to the received signal r (k). The matched filter 212 may determine whether the UW signal is included in the differential signal by using the power of the differential signal, and may turn on / off the first and second switches 281 and 282.

Here, the first switch may control the input of the differential signal to the second interpolater.

Here, the second switch may control the controller 260 to input the symbol recovery center constant and the symbol recovery interval constant to the first and second interpolators 230 and 231.

Here, the first and second interpolators 230 and 231 may restore the first and second data from the r (k) and the differential signals, respectively, by using the received symbol recovery center constant and symbol recovery interval constant. have.

According to an embodiment of the present invention, the differential signal may be sampled by the sampler 222 at twice the data rate before being input to the second interpolator 231.

For example, when the data rate is 2.4KHz, the sampler 222 uses an early delay detector (ELD) using two signals (ie, an early signal and a late signal) as a timing error detector (TED) 240. In this case, we can sample a symbol from a differential signal at 4.8KHz. In this case, two signals may be sampled per one data symbol.

The interpolator recovers a symbol by using a symbol restoration center constant and a symbol restoration interval constant in an input signal. According to an embodiment of the present invention, the signals input to the first and second interpolators 230 and 231 are sampled at twice the data transmission rate. That is, two sample signals per symbol are sampled and input. In this case, the symbol points between the two sample signals may be restored using the sample signals input to the first and second interpolators 230 and 231. This point is described in detail in the following description.

Subsequently, the parallax detector 240 (eg, the ELD in FIG. 2) may output a parallax corresponding to a timing error in the input signal.

The loop filter 250 then adjusts the gain of the parallax to prevent degradation of tracking performance caused by frequency error. Here, the tracking performance is the tracking performance for the sampling point of the symbol. More specifically, it is the time taken to find the exact sampling point of the symbol.

More specifically, the loop filter 250 according to an embodiment of the present invention may be viewed as acting as a low pass filter.

For example, if the gain of the loop filter 250 is small, the bandwidth of the signal passing through the loop filter 250 is small, so that the error applied to the compensation for the symbol sampling point is less reflected, thereby affecting the noise. This can improve jitter performance, but slows down tracking performance. Here, the jitter performance is the variation of the sampling point of the symbol.

On the contrary, when the gain of the loop filter 250 is large, the bandwidth of the signal passing through the loop filter 250 is increased, so that the error applied to the compensation for the symbol sampling point is largely reflected, thereby greatly affecting the noise. This can cause jitter performance degradation. In this case, however, fast tracking is possible.

As described above, the loop filter 250 may adjust tracking gain and jitter performance by adjusting gain.

The controller 260 may generate and output a symbol recovery center point constant and a symbol recovery interval constant 261 using the input signal.

In this case, the first and second interpolators 230 and 231 may restore the symbol from the input signal using the input symbol restoration center constant and the symbol restoration interval constant 261.

For example, the second interpolator 231 receives two sample signals per symbol in the differential signal. More specifically, a half-early sample signal and a half-late sample signal are received per symbol. In this case, the second interpolator 231 uses the input symbol recovery center constant and the symbol recovery interval constant 261 to between the half-early sample signal and the half-late sample signal. It can track the location of the located symbol and restore the symbol.

According to an embodiment of the present invention, the second interpolator 231, the parallax detector 240, the loop filter 250, and the controller 260 may form one closed loop 270. That is, each time the differential signal is input to the second interpolator 231, the controller 260 may update the symbol recovery center constant and the symbol recovery interval constant 261 input to the first and second interpolators. . Accordingly, according to an embodiment of the present invention, the first interpolator 230 receives a received signal input using the symbol recovery center constant and the symbol recovery interval constant 261 updated through the closed loop 270 described above. At r (k), the symbol can be recovered by accurately determining the sampling point of the symbol.

Up to now, a downlink receiver according to an embodiment of the present invention has been described with reference to FIG. 2. Hereinafter, the UW detector 210 will be described with reference to FIG. 3.

3 is a diagram illustrating a configuration of the UW detector 210 according to an embodiment of the present invention, Figure 4 is a graph illustrating the performance of the UW detector according to an embodiment of the present invention.

Referring to FIG. 3, the UW detector includes a differential filter 301, a matched filter 302, and a power calculator 303.

In FIG. 3, the UW detector includes a differential filter 01, a matched filter 302, and a power calculator 303 in order to describe the functions of the UW detector in detail. However, the power calculator 303 is described. It will be apparent to those skilled in the art that may be included in the matched filter 302 can be configured.

The received signal r (k) is a signal digitally converted to 19.2 KHz, which is eight times the symbol transmission rate as described above. R (k) thus contains 8 sample signals per symbol. Here, the k (where k is a natural number) sample and the normalized parallax ε _k may be expressed by Equations 3 and 4 below.

[Equation 3]

 [Equation 4]

Here, T is a sample duration of the sample signal, and τ is an absolute timing error, that is, a timing offset. That is, τ is the time delay occurring in the wireless channel. τ represents absolute parallax, and ε _k represents normalized parallax with respect to the k th sample signal.

here,

Is the time delay for the k th sample signal.

In Equations 3 and 4, assuming normalized parallax ε _{k =} ε _k-1 = ε, the signal r (k) input to the differential filter may be expressed by Equation 5 below.

[Equation 5]

Here, T _s = T / 8, which is a sample duration of the digitally converted sample signal.

Where n (k) is AWGN.

Here, h (t) is as described above,

to be.

The differential signal generated and output by the differential filter 301 may be generated as a product of a complex conjugate of the digitally converted signal r (k) and the r (k-1) signal delayed by one sample, and is represented by Equation 6 below. I can express it.

[Equation 6]

 Here, the reference signal used in the correlation in the matched filter is generated by analog-to-digital conversion (ADC) in the same manner as the received signal r (t) with a known differential UW signal. It can be expressed by Equation 7.

[Equation 7]

In more detail from Equation 6,

Re [Dr (k)] = Re [r (k)] * Re [r (k-1)] + Im [r (k)] * Im [r (k-1)]

Im [Dr (k)] = Re [r (k-1)] * Im [r (k)]-Re [r (k)] * Im [r (k-1)].

here,

ego,

Is an O-QPSK modulated baseband signal at the transmitting end.

Where N (k) is

As AWGN.

Referring to Equation 6, since Δf is independent of time t, it can be seen that the differential signal, which is the output of the differential filter, is a constant value whose frequency offset does not change with time.

Therefore, the output of the UW detector 210 output from the power calculator 303 may be expressed by Equation 8 below.

[Equation 8]

The output Z of the UW detector 210 represents a power value that correlates a received UW differential signal and a known differential UW signal at a transmitting and receiving end when the differential signal includes the UW signal. When the signal does not include a UW signal, the signal has a value smaller than the power value, and is used to determine whether the UW signal is included in the differential signal.

Here, for the convenience of understanding and explanation of the present invention, assume that the power of the r (k) signal is 1,

In this case, N is the number of samples in the UW signal.

In this case, v (k) (ie V _I (k) and V _Q (k))

As AWGN.

According to one embodiment of the present invention, since the UW signal is a signal known to the transmitting and receiving end, the ADC and the received signal and the reference signal in the same manner. Therefore, according to the embodiment of the present invention, no degradation of the timing offset occurs.

Hereinafter, the performance of the UW detector 210 according to the embodiment of the present invention will be described with reference to FIG. 4.

In FIG. 4, the X axis represents the ratio of the change amount of bit energy and noise in dB (decibels), and the Y axis normalizes the probability to 100. In FIG.

Referring to FIG. 4, in the case of the UW detector 210 according to an embodiment of the present invention, the UW detection capability of the AWGN 402 added with the frequency offset 1 KHz and the AWGN 401 not added is substantially different. It can be seen that the same appears without.

So far, the UW detector 201 according to the embodiment of the present invention has been described. Hereinafter, a parallax detector according to an embodiment of the present invention will be described.

 5 is a diagram illustrating the performance of a parallax detector according to an embodiment of the present invention.

As an example of a conventional parallax detector, the GAD (Gardner Detector) algorithm is the on time of the previous symbol (that is, the point at which the symbol is measured / estimated / determined and sampled), the on time of the current symbol, and two on The midpoint of the time is used as the sampling point.

More specifically, the parallax ε _k output from the parallax detector may be expressed by Equation 9 below. Hereinafter, the influence of AWGN will not be considered in order to facilitate the understanding and explanation of the present invention.

[Equation 9]

Where R represents the real component and θ is

As an offset of the fixed carrier phase.

Here, k '= 8k, which is an on-time sample time point (that is, a time point at which a symbol is measured / estimated / determined and sampled) as an over-sampled signal.

Referring to Equation 9, when the conventional GAD scheme is applied, the carrier phase offset is fixed carrier phase offset according to time.

It can be seen that changes to. Also, considering the environment where the relative frequency offset is large, such as an inmarsat system, the carrier phase offset

Increasing the impact of the UAD method, the fast GW detection and stable jitter performance can not be guaranteed in the conventional GAD method. In addition, in the GAD method of the prior art, it can be seen that the jitter performance is further deteriorated by the pattern jitter according to the influence of the data pattern in Equation 6. Here, the pattern jitter is jitter generated by the sidelob of the previous symbol affecting the samples of the current symbol, which is jitter by SRRC filtering.

The parallax detection method according to an embodiment of the present invention uses a differential signal generated and output from the UW detector, thereby minimizing the influence of the fixed carrier phase offset and data pattern, thereby ensuring fast UW detection and stable jitter performance. It will be described below in more detail.

If the differential signal output from the UW detector is r _d (k), it can be expressed by Equation 10 below. Hereinafter, the influence of AWGN is not considered in order to facilitate the understanding and explanation of the present invention.

[Equation 10]

Referring to Equation 10, θ is

As a fixed carrier phase offset.

Referring to Equation 10, the phase offset is affected by the frequency offset of the differential signal r _d (K) output from the UW detector.

It can be seen that the conversion to.

Accordingly, when the parallax detector according to the embodiment of the present invention uses an ELD-based algorithm, the parallax ε _{k '} output from the parallax detector may be expressed by Equation 11 below.

[Equation 11]

Here, k '= 8, which is the on-time sampling time point of the 8 oversampled signal.

Where θ is

As a fixed carrier phase offset.

Where c _{k '} is a known UW symbol pattern.

Referring to Equation 11, the parallax output from the parallax detector according to the embodiment of the present invention is a fixed carrier phase offset

As a fixed carrier phase offset affecting the parallax output of the GAD scheme of the prior art illustrated in Equation 10,

It can be seen that the effect of θ is less than that of.

In addition, according to the embodiment of the present invention, since the known UW signal pattern c _{k '} is used, the influence of pattern jitter caused by the data pattern {c _i } generated in the GAD method can be minimized.

FIG. 5 is a graph comparing open loop jitter performance in a 50 Hz and 100 Hz frequency offset environment with respect to a parallax detector according to an embodiment of the present invention, and a GAD type parallax output.

Referring to FIG. 5, it is confirmed that the parallax detector according to an embodiment of the present invention exhibits better open loop jitter performance than the conventional GAD method by minimizing the influence of the fixed carrier phase offset and the pattern jitter due to the frequency offset. Can be.

So far, the differential detector 240 according to an embodiment of the present invention has been described with reference to FIG. 5. 6 to 8, a loop filter 250 according to an embodiment of the present invention will be described.

The loop filter 250 according to an embodiment of the present invention is used to prevent deterioration of tracking performance caused by frequency error. Here, the gain of the loop filter 250 serves to adjust the tracking performance and the stability in the steady state.

6 is a diagram illustrating a structure of a loop filter according to an embodiment of the present invention.

6, G ₁ 601 and G ₂ 602 are the gains of the loop filter.

The larger the gain of the loop filter, the faster the tracking time, while the less steady-state stability.

The smaller the gain of the loop filter, the slower the tracking time but the higher the stability.

Since the Inmarsat Mini-m system according to an embodiment of the present invention needs to detect the UW signal in the UW interval, fast tracking performance is required, and accordingly, the gain of the loop filter can be largely set by a predetermined method.

7 and 8 illustrate tracking performance and jitter performance according to gain in a loop filter according to an embodiment of the present invention.

In FIG. 7 and FIG. 8, the X axis is a value corresponding to time as a symbol index. The Y-axis is a value at which an error with an accurate sampling time point (on time) changes when sampling a symbol with time. That is, if the Y axis is 0, it can be seen that the timing of sampling the symbol is correctly corrected.

More specifically, the timing jitter is a difference between the current timing error value and the previous timing error value. When the timing jitter value is small, the jitter performance is improved.

Referring to FIGS. 7 and 8, the jitter performance is improved when the loop filter gain is reduced, but the tracking performance is slowed.

6 to 8, the loop filter 250 according to an embodiment of the present invention has been described. Hereinafter, the controller 260 according to an embodiment of the present invention will be described with reference to FIGS. 9 to 10.

According to an embodiment of the present invention, the controller 260 that receives the time difference of which the gain is adjusted in the loop filter 260 may adjust the sampling position by controlling the first and second interpolators 230 and 231. That is, in more detail, the controller 260 receiving the gain-adjusted parallax may output a symbol restoration center constant and a symbol restoration interval constant. The first and second interpolators 230 and 231 adjust the timing of sampling data from the input signal by using the output symbol restoration center constant and the symbol restoration interval constant.

According to an embodiment of the present invention, the second interpolator 231, the parallax detector 240, the loop filter 250, and the controller 260 may form the closed loop 270. In this case, the symbol interval center constant and the symbol interval interval constant may be adjusted by the controller 260 so that the parallax adjustment may be performed more accurately with respect to the sampling time point of the second interpolator by the feedback effect.

9 is a graph illustrating jitter performance of an interpolator according to an embodiment of the present invention.

The interpolator is generally a piecewise interpolater and a cubic interpolater.

Referring to FIG. 9, although the cubic interpolator 902 performs better than the piecewise interpolater 901, the performance difference is not large. Therefore, although the embodiment of the present invention will be described based on the piecewise interpolator, it is obvious to those skilled in the art that the present invention is not limited thereto.

The piecewise interpolator according to the embodiment of the present invention may be represented by Equation 12 below, and the structure diagram may be represented by FIG. 10.

[Equation 12]

Here, μ _k is a symbol reconstruction interval constant, m _k is a symbol reconstruction center constant, and μ _k and m _k may be controlled by the controller 260.

Since the piecewise interpolator which can be represented by Equation 12 can be implemented in FIG.

So far, the controller according to an embodiment of the present invention has been described with reference to FIGS. 9 to 10. Hereinafter, the performance of a downlink receiver according to an embodiment of the present invention will be described with reference to FIGS. 11 to 12.

11 and 12 are graphs illustrating tracking performance and jitter performance in a steady state of a downlink receiver according to an embodiment of the present invention and a downlink receiver applying the GAD scheme of the prior art.

11 and 12, it can be seen that the downlink receiver according to an embodiment of the present invention guarantees UW signal detection and stable performance in the UW signal period.

In the above description, a receiver used in a Mini-m system having an Inmarsat unique word as a preamble has been described. However, when a preamble exists in a general wireless communication system, the data recovery method of the present invention is applied. It may be. In this case, the UW detector of the downlink receiver of the INMARSAT communication of FIG. 2 acts as a preamble detector, generates a differential signal of the current preamble and the previous preamble, and determines that the preamble is included in the differential signal. Provide the differential signal to a second interpolator, the second interpolator recovers a symbol from the input differential signal using a symbol recovery center constant and a symbol recovery interval constant and the first interpolator is the symbol recovery center. The symbol and the symbol recovery interval constant may be used to recover a symbol from the input digital signal r (k).

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art to which the present invention pertains without departing from the spirit and scope of the present invention as set forth in the claims below It will be appreciated that modifications and variations can be made.

Claims (15)

1. In a downlink receiver of INMARSAT communication,

   An analog-to-digital converter for converting an analog received signal into digital to output a digital signal r (k), where k is a natural number;

   A first interpolator for receiving the digital signal r (k) and restoring first data;

   A differential signal is generated by multiplying the complex number of r (k-1) by delaying r (k) by one sample and the digital signal r (k), and using a correlation of the differential signal to generate a unique word. UW detector for determining the presence or absence of Word);

   A second interpolator receiving the differential signal and restoring second data;

   A parallax detector that detects an error in time from the second data and outputs a parallax;

   And a controller for outputting a symbol restoration center constant and a symbol restoration interval constant according to the time difference,

   The symbol recovery center constant and the symbol recovery interval constant are provided to the first and second interpolators.
2. According to claim 1,

   When the UW detector determines that the differential signal includes the unique word, the differential signal is input to the second interpolator,

   And the second interpolator recovers the second data from the input differential signal using the symbol recovery center constant and the symbol recovery interval constant.
3. According to claim 1,

   The symbol recovery center constant and the symbol recovery interval constant are provided to the first and second interpolators when the UW detector determines that the unique signal includes the unique word.

   The first interpolator restores the first data from the input digital signal r (k) using the symbol recovery center constant and the symbol recovery interval constant;

   And the second interpolator recovers the second data from the input differential signal using the symbol recovery center constant and the symbol recovery interval constant.
4. The method of claim 3,

   And a loop filter for multiplying the time difference by a predetermined gain.
5. The method of claim 4, wherein

   And the second interpolator, parallax detector, loop filter, and controller form a closed loop.
6. The method of claim 5,

   Each time the differential signal is input to the second interpolator, the controller updates a symbol recovery center constant and a symbol recovery interval constant provided to the first and second interpolators, and the first interpolator is the closed type. And reconstructing a symbol by determining a sampling point of the symbol from the digital data signal r (k) using a symbol recovery center constant and a symbol recovery interval constant updated through a loop.
7. In the data recovery method in the downlink receiver of the INMARSAT communication,

   Digital signal r (k) generated by analog-to-digital converting an analog received signal, where k is a complex conjugate of r (k-1) with a one-sample delay of natural number and the digital signal r ( multiplying k) to produce a differential signal;

   In the case where it is determined that the differential signal includes a unique word, a first interpolator uses a symbol restoration center constant and a symbol restoration interval constant in a first interpolator to generate a first word from the input digital signal r (k). Restoring data; And

   Restoring second data from the differential signal using the symbol recovery center constant and the symbol recovery interval constant in a second interpolator when it is determined that the unique signal is included in the differential signal. Data recovery method in a downlink receiver of the INMARSAT communication.
8. The method of claim 7, wherein

   Outputting a time difference by detecting an error in time in the second data; And

   Generating and providing the symbol recovery center constant and the symbol recovery interval constant according to the parallax to the first and second interpolators, wherein the data recovery is performed in a downlink receiver of INMARSAT communication. Way.
9. The method of claim 8,

   And multiplying the parallax by a predetermined gain. 10. The method of claim 1, further comprising multiplying the parallax by a predetermined gain.
10. The method of claim 9,

    The symbol recovery center constant and the symbol recovery interval constant are

    And whenever the differential signal is input to the second interpolator, the differential signal is updated and provided to the first and second interpolators.
11. The method of claim 10,

    The first interpolator is configured to determine a sampling point of a symbol from the digital data signal r (k) by using the updated symbol recovery center constant and symbol recovery interval constant to recover a symbol. Method of data recovery at downlink receiver of communication.
12. The method of claim 7, wherein

    The existence of the unique word is determined by the correlation of the differential signal (correlation) characterized in that the data recovery method in the downlink receiver of the INMARSAT communication.
13. In the data recovery method in the downlink receiver of the wireless communication,

    Digital signal r (k) generated by analog-to-digital converting an analog received signal, where k is a complex conjugate of r (k-1) with a one-sample delay of natural number and the digital signal r ( multiplying k) to produce a differential signal;

    When it is determined that the differential signal includes a preamble, first data is obtained from the input digital signal r (k) by using a symbol recovery center constant and a symbol recovery interval constant in a first interpolator. Restoring; And

    Restoring second data from the differential signal using the symbol restoration center constant and the symbol restoration interval constant in a second interpolator when it is determined that the differential signal includes the preamble. A data recovery method in a downlink receiver of a wireless communication.
14. The method of claim 13,

    The symbol recovery center constant and the symbol recovery interval constant are

    And whenever the differential signal is input to the second interpolator, it is updated and provided to the first and second interpolators.
15. The method of claim 13,

    The first interpolator determines a sampling point of a symbol from the digital data signal r (k) by using the updated symbol restoration center constant and the symbol restoration interval constant to restore a symbol. How to restore data at the receiver.

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