KR101884228B1 - Oqpsk receving system - Google Patents

Abstract

An offset quadrature phase shift keying (OQPSK) receiving system is disclosed. The receiving system of the present invention estimates a channel to remove intersymbol interference (ISI), outputs an estimation error for the channel, and estimates a phase offset in an estimation error for the channel. According to the present invention, the channel estimation error in the equalizer is fed back to the phase offset estimation of the carrier recovery unit to enable the broadband transmission.

Description

[0001] OQPSK RECEIVING SYSTEM [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving system, and more particularly, to a receiving system of an OQPSK scheme.

Generally, in a digital communication system, a carrier is recovered (carrier recovery) to remove an error component in order to recover an offset of a phase and a frequency on a channel.

In the conventional broadband transmission system, an equalizer is used to remove inter-symbol interference (ISI) due to channel fading.

If the phase / frequency offset and the ISI are present at the same time, severe performance deterioration occurs, so that the signal is not received well, and the carrier recovery unit and the equalizer are used at the same time.

1 is an exemplary diagram schematically illustrating a conventional receiving system.

As shown in the drawing, a conventional receiving system includes a carrier recovery unit 100 and an equalizer 200 to remove a phase / frequency offset and an ISI of a received signal Rx at the same time, send.

However, when the above conventional reception system is applied to Offset Quadrature Phase-Shift Keying (hereinafter referred to as 'OQPSK') scheme, it is difficult to estimate a phase error component by the ISI, 100 is difficult to recover a carrier wave and causes a carrier recovery error. Such a carrier recovery error makes channel estimation of the equalizer 200 more difficult, so that the OQPSK scheme has a problem of low utilization as a broadband transmission.

It is an object of the present invention to provide an OQPSK receiving system for predicting a phase / frequency offset in a channel estimation error of an equalizer and adjusting a gain of a feedback signal of a carrier recovery unit .

According to an aspect of the present invention, there is provided an offset orthogonal phase shift keying (OQPSK) receiving system comprising: an equalizer for estimating a channel to remove inter-symbol interference (ISI) and outputting an estimation error for a channel; And a carrier recovery unit estimating a frequency offset and estimating a phase offset at an estimation error of the channel of the equalizer.

In one embodiment of the present invention, an automatic gain controller (AGC) for normalizing the power level of a received signal; A symbol timing recovery unit (STR) for converting a signal input from the AGC into a symbol; And a direct digital waveform synthesizer (DDS) for removing the phase and frequency offset received from the carrier recovery unit.

In one embodiment of the present invention, the equalizer preferably performs a decision feedback equalization.

In one embodiment of the present invention, the equalizer includes: a plurality of delay units each delaying an output of the STR; A minimum mean square multiplier (LMS) for performing channel estimation of a signal delayed in phase by the plurality of delay units; A determiner for determining an OQPSK signal in a signal estimated by the LMS; And an operation unit for calculating a difference between an input and an output of the determination unit and outputting an estimation error for the channel.

In one embodiment of the present invention, the carrier recovery unit includes a first loop filter for separating a frequency error and outputting a frequency offset; A second loop filter for separating the phase error and outputting a phase offset; And a multiplier for multiplying the estimation error by an output of the second loop filter.

The present invention as described above has an effect that the channel estimation error in the equalizer is fed back to the phase offset estimation of the carrier recovery unit to enable the broadband transmission.

1 is an exemplary diagram schematically illustrating a conventional receiving system.
2 is a block diagram schematically illustrating a receiving system according to an embodiment of the present invention.
3 is a detailed configuration diagram of a conventional OQPSK receiving system.
4 is a detailed configuration diagram of an OQPSK receiving system according to an embodiment of the present invention.
5 is a detailed structural diagram of an OQPSK receiving system according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Terms including ordinals such as first, second, etc. may be used to describe various elements, but the elements are not limited by such terms. These terms are used only to distinguish one component from another.

When an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but other elements may be present in between . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, the terms "comprises", "having", and the like are used to specify that a feature, a number, a step, an operation, an element, a component, or a combination thereof, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

The receiving system of the present invention proposes a reception algorithm that is robust to fading channels as well as broadband transmission by applying shrinkage carrier recovery.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram schematically illustrating a receiving system according to an embodiment of the present invention. As shown in the figure, a receiving system according to an embodiment of the present invention includes a carrier recovery unit 10, an equalizer 20, and an amplification unit 40.

The carrier recovery unit 10 of the present invention predicts the phase / frequency offset in the channel estimation error of the equalizer 20 and adjusts the gain of the feedback signal of the carrier recovery unit 10.

That is, the gain of the feedback signal increases or decreases the weight of the carrier phase error component as the phase component of the channel estimation error.

The present invention can more dynamically cope with a wideband transmission in a manner that a weight is lowered (constrictive) and an estimation error is avoided when an estimation is not accurate by the carrier reconstruction unit 10.

Hereinafter, a conventional OQPSK receiving system will be described in detail, and then an OQPSK receiving system according to an embodiment of the present invention will be described focusing on differences from a conventional OQPSK receiving system.

3 is a detailed configuration diagram of a conventional OQPSK receiving system.

As shown in the figure, in a conventional OQPSK receiving system, a baseband signal is input from a front end, and an analog-to-digital converter (ADC) 110) converts it to a digital sample.

A direct digital synthesis (hereinafter referred to as 'DDS') 170 combines a received sample and a phase / frequency error component to remove an offset.

An automatic gain controller (AGC) 120 compensates a power level of a received signal and normalizes the received signal.

A Square Root Raised Cosine (SRRC) 130 is a matched filter that estimates a transmission signal and removes channel noise.

The delay 140 delays the Q channel of the input signal for a half symbol period.

A symbol timing recovery (hereinafter referred to as 'STR') 160 finds timing from a received sample and converts the timing into symbols.

The carrier recovery unit 100 estimates the phase / frequency offset using the phase information of the symbol and compensates for the error.

The equalizer 200 estimates a channel and removes the ISI signal.

As described above, in the conventional reception system, since the carrier recovery unit 100 and the equalizer 200 operate independently, reception is difficult when the phase / frequency offset and the ISI are present at the same time.

4 is a block diagram of an OQPSK receiving system according to an embodiment of the present invention.

As shown in the figure, the receiving system of the present invention includes an ADC 31, an AGC 32, an SRRC 33, a delay unit 34, a downsampling unit 35, an STR 36, a DDS 37 ), A carrier recovery unit (10), and an equalization unit (20).

The baseband signal is input from the front end, the ADC 31 converts the signal into a digital sample, and the DDS 37 synthesizes the received sample and the phase / frequency error component to remove the offset.

The AGC 32 compensates and normalizes the power level of the received signal, and the SRRC 33 estimates the transmission signal and removes the channel noise. The delay unit 34 delays the Q channel of the input signal for half a symbol period, and the STR 36 finds the timing from the sample received from the delay unit 34 and converts the timing into a symbol. The downsampling unit 35 performs downsampling on the samples received from the delay unit 34. The above general reception system is the same as the above-described function of FIG. 3, and is well known in the technical field to which the present invention belongs, so that detailed description thereof will be omitted.

The carrier recovery unit 10 estimates the phase / frequency offset using the phase information of the symbol and compensates for the error. The equalizer 20 estimates the channel and removes the ISI signal.

In an embodiment of the present invention, an estimation error due to the phase / frequency offset of the equalizer 20 is fed back to the carrier recovery unit 10.

Therefore, the carrier recovery unit 10 that has received such an estimation error adjusts the weight for the phase component in the estimation error of the equalizer 20 to a gain.

In practice, the carrier recovery unit 10 is difficult to estimate the phase / frequency error by the ISI, and in the case of the equalizer 20, it is difficult to estimate the channel by the phase / frequency offset, It is possible to efficiently remove the phase / frequency offset and remove the ISI by an interdependent method of feeding back the estimation error due to the phase / frequency offset of the equalizer 20 to the carrier recovery unit 10. [

FIG. 5 is a detailed structural diagram of an embodiment of an OQPSK receiving system according to an embodiment of the present invention. In FIG. 5, only a part of the system of FIG. 4, which emphasizes the function of an embodiment of the present invention, is shown in more detail. In Fig. 5, the constituent elements of Fig. 4 that are not related to the present invention are shown and deleted.

For the input digital signal, it is already described that the AGC 32 normalizes the power level and the STR 37 finds the timing in the received sample and converts it into a symbol. The output of the STR 37 is input to the carrier recovery unit 10 and the equalizer 20.

The carrier recovery unit 10 includes loop filters 11 and 13 and a multiplier 12. In the present invention, in order to illustrate multiplying the filtering error of the phase error by the carrier recovery unit 10, there are two loop filters for indicating that the phase error and the frequency error are separated and filtered. But the present invention is not limited thereto.

Although the DDS 37 includes two DDSs 37 for the sake of convenience of description, it is assumed that only one DDS 37 is provided. It is also possible to simultaneously receive both signals.

The equalizer 20 includes a plurality of phase delay units 21 and 24 and a plurality of minimum mean square (LMS) units 22 and 25 and a determination unit 23 do. The equalizer 20 according to an embodiment of the present invention is an equalizer of a decision feedback equalizer method, but is not limited thereto.

The plurality of phase delay units 21 and 24 delays the phase of the output of the STR 36 and the plurality of LMSs 22 respectively perform channel estimation of the phase delayed signal.

The decision unit 23 determines an OQPSK signal in the thus estimated signal, and the difference between the input and the output of the decision unit 23 is an estimation error fed back to the carrier reconstruction unit 10. [

The frequency error of the symbol outputted from the STR 36 is subjected to the filtering by the loop filter 13 and the phase error of the symbol is subjected to the filtering by the loop filter 11 to compensate the frequency error and the phase error. At this time, it is possible to calculate an estimation error with respect to the output passed through the loop filter 11, and to apply the estimation error based on the ISI estimated by the equalizer 20 to the carrier reconstruction unit 10.

In the meantime, embodiments of the present invention can be implemented by recording computer-readable program codes on a computer-readable recording medium. When embodiments of the present invention are implemented using software, the constituent means of the present invention are code segments that perform the necessary tasks. The program or code segments may also be stored in a medium readable by a processor of the computer or transmitted in a computer data signal coupled with a carrier wave via a transmission medium or a communication network.

The computer-readable recording medium may include any type of recording device that stores data that can be read by a computer system. For example, the computer-readable recording medium may include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage, and the like. In addition, the computer readable recording medium may be distributed to the networked computer system so that the computer readable code is stored and executed in a distributed manner.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Accordingly, the true scope of the present invention should be determined by the following claims.

10: Carrier wave restoration unit 20:
31: ADC 32: AGC
33: SRRC 34: delay unit
35: down-sampling unit 36: STR
37: DDS 40: amplification unit

Claims (10)

A converter for receiving a baseband signal and converting the baseband signal to a digital sample signal;
A symbol timing recovery unit (STR) for converting the digital sample signal into a symbol;
An equalizer for estimating a channel to remove inter-symbol interference (ISI) and outputting an estimation error for the channel;
A carrier recovery unit that generates a feedback signal including a phase offset and a frequency offset using the phase information of the symbol and adjusts a gain of the phase offset using the estimation error; And
And a direct digital waveform synthesizer (DDS) for synthesizing the feedback signal with the digital sample signal,
An output of the STR is input to the equalizer and the carrier recovery unit,
The equalization unit delays the phase of the output of the STR, performs channel estimation of the phase-delayed signal, determines the OQPSK signal in the estimated signal, and outputs the difference between the input and the output to the carrier recovery unit Lt; / RTI >
Wherein the carrier recovery unit multiplies the feedback error estimate by the filtered phase error of the output of the STR.
The method according to claim 1,
And an automatic gain controller (AGC) for normalizing the power level of the digital sample signal.
The method according to claim 1,
Wherein the equalizer comprises:
OQPSK receiving system performing decision feedback equalization.
3. The method of claim 2,
Wherein the equalizer comprises:
A plurality of delay units respectively delaying outputs of the STRs;
A minimum mean square multiplier (LMS) for performing channel estimation of a signal delayed in phase by the plurality of delay units;
A determiner for determining an OQPSK signal in a signal estimated by the LMS; And
And an operation unit for calculating a difference between an input and an output of the determination unit and outputting an estimation error for the channel.
5. The method of claim 4,
The carrier-
A first loop filter for separating a frequency error and outputting a frequency offset;
A second loop filter for separating the phase error and outputting a phase offset; And
And a multiplier for multiplying the estimation error by an output of the second loop filter.
Receiving a baseband signal and converting the baseband signal into a digital sample signal;
Converting the digital sample signal to a symbol;
Estimating a channel to remove inter-symbol interference (ISI), and outputting an estimation error for the channel;
Generating a feedback signal including a phase offset and a frequency offset using the phase information of the symbol, and adjusting a gain of the phase offset using the estimation error; And
And combining the feedback signal with the digital sample signal,
The converted symbols are input to the equalizer and the carrier recovery unit, respectively,
Wherein outputting an estimation error for the channel comprises:
Delaying phases of the symbols;
Performing channel estimation of a signal delayed in phase;
Determining an OQPSK signal in the estimated signal; And
And feedback the difference between the input and the output to the carrier recovery unit as an estimation error,
Wherein adjusting the gain of the phase offset multiplies the filtered phase error of the input symbol by the estimation error fed back from the equalizer.
The method according to claim 6,
And normalizing the power level of the digital sample signal.
The method according to claim 6,
In outputting the estimation error for the channel,
OQPSK receiving method for performing decision feedback equalization.
delete The method according to claim 6,
Wherein the step of generating the feedback signal and adjusting the gain of the phase offset comprises:
Separating the frequency error and outputting a frequency offset;
Separating the phase error and outputting a phase offset; And
And multiplying the estimation error by the phase offset.

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