KR20070061250A - Apparatus and method for phase tracking in the wireless pico cell communication systems - Google Patents

Abstract

An apparatus and a method for tracking a phase of a wireless pico cell communication system of a direct sequence band diffusion scheme are provided to improve the system performance and lower complexity of the system by compensating a phase error. An apparatus for tracking a phase of a wireless pico cell communication system of a direct sequence band diffusion scheme includes a phase error detection unit(21), a loop filtering unit(22), a level adjustment unit(23), and a phase error compensation unit(24). The phase error detection unit applies a phase shift value to a symbol and detects a phase error of a receiving signal. The loop filtering unit adjusts a previous loop output and the phase error detected in the phase error detection unit with a loop gain, and obtains a loop output for a next symbol. The level adjustment unit adjusts the output of the loop filtering unit to be matched with a range of a phase level. The phase error compensation unit compensates the phase error by reflecting an addition value of the loop output adjusted in the level adjustment unit and the loop output in the previous compensation process to the next receiving signal.

Description

Apparatus and Method for Phase Tracking in the Wireless Pico Cell Communication Systems}

1 is a configuration diagram of an embodiment of a wireless picocell communication system of a direct sequence spread spectrum method to which the present invention is applied;

2 is a configuration diagram of a phase tracking apparatus in a wireless picocell communication system of a direct sequence spread spectrum method according to the present invention;

3 is an exemplary view illustrating a performance analysis result of a phase tracking device according to the present invention;

4 is another exemplary view showing a performance analysis result of the phase tracking device according to the present invention;

5 is a flowchart illustrating a phase tracking method in the phase tracking apparatus according to the present invention.

* Explanation of symbols for the main parts of the drawings

20: equalizer 21: phase error detector

22 loop filter 23 level control

24: phase error compensator

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a phase tracking device and a method thereof in a direct sequence spread spectrum wireless picocell communication system. More particularly, the present invention relates to a phase shift to a symbol extracted using a despreading code value and a cross-correlation function value of a received signal. Detects the phase error of the received signal by applying a value, adjusts the detected phase error and the previous loop output with a loop gain to obtain a loop output for the next symbol and then adjusts it to a range of phase levels. The present invention relates to a phase tracking apparatus and a method thereof in a wireless picocell communication system of a direct sequence spread spectrum scheme for reducing a phase error by reducing an excess frequency offset of a loop output.

In general, the Direct Sequence Spread Spectrum (DSSS) method refers to a method of communicating by spreading one signal symbol in a predetermined sequence.

That is, when a transmitter inputs a signal to be transmitted to a pseudo-random noise sequence, acquires a spread spectrum signal having a low power density per frequency, and transmits the same to the receiver, the receiver receives the same pseudo noise sequence. To reproduce the original signal.

The direct sequence spread spectrum method has the advantages of good modulation efficiency, fast signal synchronization, and low in-band interference due to low power density, which has been used in the code division multiple access (CDMA) technique. It is also used for (Zigbee) communication.

The wireless picocell system to which the direct sequence spreading scheme is applied causes performance degradation due to the phase change at the receiver as in the case of other wireless communication systems. That is, the change in phase at the receiver causes a decrease in signal-to-noise ratio (SNR), thereby degrading the performance of the wireless picocell system.

In addition, an error in sampling timing caused by a difference in sampling frequency at the receiving end also degrades the performance of the direct sequence spread spectrum wireless picocell system.

At this time, although the transmitter and the receiver of the direct sequence spread spectrum wireless picocell system use an oscillator generating the same frequency, a phase offset occurs in the actual reception process.

In addition, phase shift can also occur due to the Doppler shift in the fading channel, which degrades performance in the correct signal demodulation process at the receiver.

Even if the frequency error of the received signal is minimized by using the frequency offset estimation algorithm, the error still occurs in the demodulation process of the received signal unless the accurate frequency error compensation is performed.

As a result, the phenomenon that the phase of the symbol is shifted due to the excess frequency error, which makes it difficult to demodulate the correct signal.

Therefore, there is a need for a method of eliminating errors that may occur due to such a phase error and maintaining the minimized frequency error so as not to increase any more.

The present invention has been proposed to meet the above-mentioned requirements, and detects a phase error of a received signal by applying a phase shift value to a symbol extracted by using a cross-correlation function value of a despreading code value and a received signal, and detecting the phase error of the received signal. Higher performance by adjusting error and previous loop output with loop gain to obtain a loop output for the next symbol and then adjusting it to a range of phase levels, and compensating for phase error by reducing the excess frequency offset of the adjusted loop output. An object of the present invention is to provide a phase tracking apparatus and method in a wireless picocell communication system of a direct sequence spread spectrum method having a low complexity.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

A device of the present invention for achieving the above object is a phase tracking device in a wireless picocell communication system of the direct sequence spread spectrum method, a phase error for detecting a phase error of a received signal by applying a phase shift value to a symbol Detection means; Loop filtering means for adjusting a phase error detected by the phase error detecting means and a previous loop output with a loop gain to obtain a loop output for a next symbol; Level adjusting means for adjusting the output of the loop filtering means to match a range of phase levels; And phase error compensating means for compensating for phase error by reducing an excess frequency offset of the loop output adjusted by the level adjusting means.

On the other hand, the method of the present invention, a phase tracking method in a phase tracking device, comprising: detecting a phase error of a received signal by applying a phase shift value to a symbol; Adjusting the detected phase error and a previous loop output with a loop gain to obtain a loop output for a next symbol; Adjusting the obtained loop output according to a range of phase levels; And compensating for the phase error by reducing the excess frequency offset of the adjusted loop output.

에 따라 정상 상태(Steady-state)로 도달하는 응답 시간과 지터 변동(jitter variance)을 조절한 다. In addition, the present invention removes the phase error due to the excess frequency offset in the process of demodulating the symbol through a closed-loop compensation mechanism to move to the correct symbol position, two parameters

Adjust the response time and jitter variance to reach steady-state.

In addition, the present invention tracks the residual phase due to the error of the carrier frequency and the sampling frequency at the receiving end and performs the compensation operation accordingly.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a configuration diagram of an embodiment of a wireless picocell communication system of a direct sequence spread spectrum method to which the present invention is applied.

First, the phase tracking apparatus 11 performs a function of removing an error that may occur due to excess frequency error and maintaining a minimized frequency error through a channel coefficient estimation algorithm.

That is, the phase estimator 11 detects a phase error of the received signal by applying a phase shift value to a symbol extracted by using the despreading code value and the cross-correlation function value of the received signal, and detects the phase error of the received signal. The output is adjusted to a loop gain to obtain a loop output for the next symbol and then adjusted to a range of phase levels, to compensate for the phase error by reducing the excess frequency offset of the adjusted loop output.

In addition, an equalizer (DFE: Decision Feedback Equalizer) 12 despreads the received signal and extracts a symbol.

In addition, the Channel Matched Filter (CMF) 13 minimizes the influence of signal interference by the channel.

2 is a configuration diagram of a phase tracking apparatus in a wireless picocell communication system of a direct sequence spread spectrum method according to the present invention.

As shown in FIG. 2, a phase tracking device in a direct sequence spread spectrum wireless picocell communication system according to an embodiment of the present invention applies a phase shift value to a symbol to detect a phase error of a received signal. (Phase Error Detector) 21, a loop filter 22 for obtaining a loop output for the next symbol by adjusting the phase error detected by the phase error detector 21 and the previous loop output with a loop gain. A level controller 23 for adjusting the output of the loop filter 22 according to a range of phase levels, and a loop output adjusted in the previous compensation process to a loop output adjusted by the level controller 23. And a phase error compensator 24 for compensating for the phase error in reflection of the received signal.

In addition, the equalizer (DFE) 25 extracts a symbol using a despreading code value and a cross-correlation function value of the received signal r (n) through a despreader.

Hereinafter, a phase tracking method of a phase tracking device in a wireless picocell communication system using a direct sequence spread spectrum method will be described.

First, the phase error detector 21 is multiplied for despreading in the equalizer DFE (data multiplied when spreading), for example, a code value corresponding to "11-chip Barker code" or "complementary code" ( A symbol R (n) is extracted using a crossword function value of a codeword and a received signal. In this case, when the packet received by the phase error compensator 24 is r (n), the extracted symbol R (n) is expressed by Equation 1 below.

Where M is the symbol period corresponding to "11-chip (11 bits multiplied for despreading)" or codeword length, and C (i) is the "11-chip Barker code (multiplied for despreading). One bit of 11 bits) "or a code value.

,

,

) 천이 값을 이용하여, 하기의 [수학식 2]와 같은 위상 에러를 검출한다.Then, four phases (0,) for the extracted current symbol R (n)

,

,

) Using the transition value, a phase error as shown in Equation 2 below is detected.

의 범위 내에 존재한다.At this time, since the symbol is modulated using DQPSK (Differential Quardrature Phase Shift Keying), the phase error of the current symbol indicated by the surplus frequency offset due to the modulation characteristic is within the DQPSK category.

It exists in the range of.

Then, in order to remove noise from the phase error as shown in Equation 2, second-order loop filtering is performed as shown in Equation 3 below.

는 루프 이득(Loop Gain)을 의미하는 파라미터(parameter)이다. here,

Is a parameter representing a loop gain.

Then, the previous filter output value and the current detected phase error are adjusted with the loop gains to obtain a loop output for the next symbol. This is shown in Equation 4 below. In addition, it is desirable to perform a weighting process (some sort of filtering process) on the loop output to adapt to the range of phase levels to be compensated.

Then, the phase error is compensated for the next symbol as shown in Equation 5 below using the phase error of the current symbol obtained through Equation 4.

에 현재(n) 시점의 위상 에러(수학식 4) 검출 값으로 다음 심벌 데이터인 r(n+1)의 위상 에러를 보상하여, 최종적으로 수신 신호에 남아 있는 잉여 주파수 옵셋(offset)을 점차 감소시킨다. That is, the phase error reflected in the previous (n-1) compensation process

Compensate for the phase error of the next symbol data, r (n + 1), with the phase error (Equation 4) detection value at the current (n) point in time, and gradually reduce the excess frequency offset remaining in the received signal. Let's do it.

FIG. 3 is an exemplary view illustrating a performance analysis result of a phase tracking device according to the present invention. In a steady-state according to a loop gain when a frequency offset of 1 KHz is provided under an AWGN channel (Additive White Gaussian Noise), FIG. This is an example of measuring "RMS jitter".

를 0.95, 0.97, 0.99로 부여하고, 웨이팅(weighting) 값은 0.1로 고정하였다. 이때, 그래프는 신호대잡음비(SNR)가 변화함에 따라 정상상태에서의 "RMS jitter"를 나타낸다.First, the loop gain

Was given as 0.95, 0.97, 0.99, and the weighting value was fixed at 0.1. At this time, the graph shows the "RMS jitter" in the steady state as the signal-to-noise ratio (SNR) changes.

As shown in FIG. 3, it can be seen that the larger the loop gain, the smaller the "jitter" fluctuations in the steady state, so that the demodulator performance deteriorates less. As the SNR changes, the "RMS jitter" value gradually decreases. Able to know.

4 is another exemplary diagram illustrating a performance analysis result of a phase tracking device according to the present invention. When an 1 KHz frequency offset is given in an AWGN channel having an SNR of 10 dB or less, transient compensation is performed. The response is measured over time by loop gain.

As shown in FIG. 4, 100 times of packet repetitions are performed for each time index, and the average phase tracking result is converted into frequency and displayed.

In other words, the smaller the loop gain, the higher the fluctuation in the steady state and the larger the "jitter" fluctuations, while the higher the loop gain causes the little of the steady wave and the "jitter" fluctuation is maintained at the low level. You can see the tendency to become.

5 is a flowchart illustrating a phase tracking method in the phase tracking apparatus according to the present invention.

First, a phase error of a received signal is detected by applying a phase shift value to a symbol (501).

Thereafter, the detected phase error and the previous loop output are adjusted to the loop gain to obtain a loop output for the next symbol (502).

Thereafter, the obtained loop output is adjusted to match the range of the phase level (503).

Thereafter, the residual frequency offset of the adjusted loop output is reduced to compensate for the phase error (504).

As described above, the method of the present invention may be implemented as a program and stored in a recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.) in a computer-readable form. Since this process can be easily implemented by those skilled in the art will not be described in more detail.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

As described above, the present invention detects a phase error of a received signal by applying a phase shift value to a symbol extracted by using a despreading code value and a cross-correlation function value of the received signal, and detects the detected phase error and the previous loop output. By adjusting the loop gain to obtain the loop output for the next symbol and then adjusting it to a range of phase levels, reducing the excess frequency offset of the regulated loop output to compensate for phase errors, improving system performance and reducing low complexity. Has the effect of enabling a system to be implemented.

Claims (6)

A phase tracking apparatus in a wireless picocell communication system of a direct sequence spread spectrum method, Phase error detecting means for detecting a phase error of a received signal by applying a phase shift value to a symbol; Loop filtering means for adjusting a phase error detected by the phase error detecting means and a previous loop output with a loop gain to obtain a loop output for a next symbol; Level adjusting means for adjusting the output of the loop filtering means to match a range of phase levels; And Phase error compensation means for compensating for phase error by reflecting the loop output adjusted by the level adjusting means plus the loop output reflected in the previous compensation process to the next received signal. Phase tracking apparatus in a wireless picocell communication system of the direct sequence spread spectrum method comprising a. The method of claim 1, The phase error detection means, (0,

,

,

A phase tracking device in a wireless picocell communication system of a direct sequence spread spectrum method, characterized by detecting a phase error of a received signal using a phase shift value. The method of claim 2, The detected phase error is A phase tracking device in a wireless picocell communication system of a direct sequence spread spectrum method, which is expressed as in Equation A. Equation A

Here, R (n) means a symbol. The method according to claim 1 or 2, The loop filtering means, Phase tracking apparatus in a wireless picocell communication system of the direct sequence spread spectrum method characterized in that the loop filtering using the following [Equation B]. Equation B

here,

Is a parameter representing a loop gain. The method of claim 4, wherein The phase error compensation means, Phase error reflected in previous (n-1) compensation process

Compensating for the phase error of the next symbol data r (n + 1) with the phase error detection value at the current (n) time point at, finally reducing the excess frequency offset remaining in the received signal. Phase Tracking Device in Wireless Picocell Communication System of Direct Sequence Spread Spectrum. In the phase tracking method in the phase tracking device, Detecting a phase error of a received signal by applying a phase shift value to a symbol; Adjusting the detected phase error and a previous loop output with a loop gain to obtain a loop output for a next symbol; Adjusting the obtained loop output according to a range of phase levels; And Compensating for phase error by reducing the excess frequency offset of the adjusted loop output Phase tracking method in a phase tracking device comprising a.

Images