KR100556890B1 - Method for syncronizing frame of td-scdma - Google Patents

Abstract

The present invention converts a phase used for phase modulation into a symbol consisting of an integer, and determines whether the frame is synchronized using a quadrature phase shift keying (QPSK) characteristic based on the phase of the converted symbol and the sequence of phases detected in the received signal. In addition, the present invention relates to a frame synchronization method of a time division sync code division scheme that can easily obtain frame synchronization without performing a complicated operation. The signal (S2) indicating that there is a broadcast control channel (BCCH) in the next four subframes Converting a phase sequence of an integer into a sequence of integers, and calculating a phase of a received downlink synchronization sequence SYNC_DL based on a phase difference between a phase of the downlink synchronization sequence SYNC_DL sent from a transmitter and a phase change by a channel. And orthogonal phase shifting the phase of the calculated received downlink synchronization sequence (SYNC_DL) and any element of the symbol sequence Calculating using a group QPSK; determining whether a value (phase) calculated using the quadrature phase shift key is in a predetermined decision region; Decoding the broadcast channel (BCH) by synchronizing the frame if the calculated value (phase) for the subframe is in the predetermined decision region, otherwise repeating the above steps, thereby avoiding complicated operation There is an effect that the frame synchronization can be obtained simply.

Description

Frame Synchronization Method using Time Division Synchronization Code Division Method {METHOD FOR SYNCRONIZING FRAME OF TD-SCDMA}

1 is a frame structure diagram of TD-SCDMA.

2 is a flowchart illustrating an embodiment of a frame synchronization method according to the present invention.

3 is an exemplary view showing a determination region by quadrature phase shift keying (QPSK) in the present invention.

4 is a block diagram illustrating a method of frame synchronization matching for the present invention.

The present invention relates to a frame synchronization method of a time division sync code division scheme (TD-SCDMA), and in particular, converts a phase used for phase modulation into a symbol consisting of an integer, and detects the phase of the converted symbol and the received signal. The present invention relates to a frame synchronization method of a time division synchronization code division method, which can obtain frame synchronization simply without performing a complicated operation by determining whether the phase sequence is frame synchronized using a quadrature phase shift keying (QPSK) characteristic.

Phase Modulation of Downlink Pilot Signals is Used for Frame Synchronization in 3G Time Division Synchronous Code Division Multiple Access (TD-SCDMA) do.

In order to decode the phase modulation, four consecutive downlink syncronization sequences (SYNC_DL) are received, the phase distortion caused by the channel is compensated for in each SYNC_DL signal, and then each received phase is detected. The frame synchronization is found by comparing with a given phase sequence.

Then, such a conventional frame synchronization method will be described.

1 shows a frame structure of TD-SCDMA. As shown, one radio frame consists of two subframes, one subframe includes seven normal time slots and three special time slots. ) In the case of the downlink, the mobile station uses phase modulation of the SYNC_DL sequence to match frame synchronization.

The SYNC_DL sequence is phase-modulated based on the midamble sequence of timeslot # 0. This is to know whether a primary common control pilot channel (P-CCPCH) exists. Basically, in a TD-SCDMA system, two radio frames become a basic block of interleaving, and thus, by using phase modulation of SYNC_DL, it is possible to synchronize radio frames.

Table 1 shows the phase modulation used for SYNC_DL of TD-SCDMA.

As shown, the SYNC_DL sequence is transmitted with a constant phase pattern. By using this, synchronization of four subframes, that is, two radio frames is obtained. However, since the signal is distorted by the channel, simply detecting the phase of the transmitted SYNC_DL sequence does not mean that the phase is the phase of the transmitted SYNC_DL.

In order to remove the influence of the phase caused by the channel, the phase of the SYNC_DL sequence is detected by referring to the midamble sequence used in TS # 0. That is, by compensating for the phase of the received SYNC_DL by the phase of the midamble sequence, the influence of the phase caused by the channel can be eliminated.

SYNC_DL is used to obtain subframe synchronization in TD-SCDMA. Subframe synchronization may be obtained through a correlation calculation between a received SYNC_DL sequence and a transmitted SYNC_DL sequence. In this case, the calculated correlation value corr _{SYNC_DL} is represented as a complex value.

When a midamble sequence of the midamble sequence of the received sub-frame m ^R, a transmission sub-frame to be called ^T m, the midamble sequence are represented by equation (1).

The correlation value is calculated using the two midamble sequences. At this time, the position of the midamble sequence is easily obtained since the subframe synchronization is obtained using SYNC_DL. Accordingly, corr _{Mid, which} is a phase of the reception midamble, may be calculated through Equation 2.

The corr _mid may actually be calculated through channel estimation, and N used here does not significantly affect the accuracy even if it is assigned to less than 144 depending on the situation.

In addition, the phase modulation scheme of the SYNC_DL sequence transmitted from the transmitting end is shown in Table 1. Since the receiving end is only interested in decoding the broadcast channel (BCH), only the S2 phase sequence of Table 1 is detected. Just do it. To this end, corr _{SYNC_DL} must compensate for the corr _mid , which is the phase change by the channel. That is, the phase of corr _mid should be subtracted from the phase of corr _{SYNC_DL} .

The phase of the received SYNC_DL may be calculated based on the difference of the phase values, and the above procedure is repeated for four SYNC_DLs to detect a series of phase sequences. If this is the same as the S2 phase sequence of Table 1, the frame synchronization can be known and eventually the BCH can be recovered. This process requires multiple complex multiplications, and sometimes tan ^-1 .

The conventional frame synchronization method as described above requires a large number of complex multiplication operations and operations such as tan-1, resulting in high complexity and high accuracy.

Accordingly, in view of the above problems, the present invention converts a phase used for phase modulation into a symbol composed of integers, and performs a quadrature phase shift keying (QPSK) characteristic on the phase of the converted symbol and the phase sequence detected in the received signal. It is an object of the present invention to provide a frame synchronization method of a time division synchronization code division method that can easily obtain frame synchronization without performing a complicated operation by determining whether the frame is synchronized.

The present invention for achieving the above object comprises the steps of converting the phase sequence of the signal (S2) indicating that the broadcast control channel (BCCH) in the next four subframes to an integer symbol sequence; Calculating a phase of a received downlink synchronization sequence SYNC_DL based on a phase of a downlink synchronization sequence SYNC_DL sent from a transmitting end and a phase change difference by a channel; Calculating any phase of the calculated received downlink synchronization sequence (SYNC_DL) and any element of the symbol sequence using quadrature phase shift keying (QPSK); Determining whether a value (phase) calculated using the quadrature phase shift modulation is in a predetermined decision region; As a result of the determination, if the calculated values (phases) for the four consecutive subframes are in a predetermined determination region, decoding the broadcast channel (BCH) by synchronizing the frames; otherwise repeating the determining Characterized in that consisting of.

The symbol sequence of the integer in which the phase sequence of the signal S2 is converted is (1-j, -1-j, 1-j, 1 + j).

The calculated value using the quadrature phase shift keying (QPSK) is characterized by the following equation.

R is a value calculated using the quadrature phase shift keying (QPSK), P is a phase of the received downlink sync sequence SYNC_DL, and S2 _d is an integer obtained by converting a phase sequence of the signal S2. Arbitrary elements in the symbol sequence of.

The determination as to whether the value (phase) calculated using the quadrature phase shift modulation is in a predetermined determination region is made by the following equation.

Here, R ⁱ and R ^r are imaginary part values and real part values of values calculated using the quadrature phase shift keying (QPSK).

With reference to the accompanying drawings, a preferred embodiment of the frame synchronization method of the time division sync code division method of the present invention having the above characteristics will be described.

2 is a flowchart illustrating a flow of a frame synchronization method according to the time division sync code division method of the present invention. As shown, converting a phase sequence of S2 to an integer symbol sequence indicating the presence of a broadcast control channel (BCCH) in the next four subframes, and the phase of the SYNC_DL sent from the transmitter and the phase by the channel. Calculating a phase of the received SYNC_DL through the change difference, calculating a phase of the calculated received SYNC_DL and any element of the symbol sequence using quadrature phase shift keying (QPSK), and performing the quadrature phase shift keying Determining whether the value (phase) calculated by using the predetermined decision region (-π / 4 <R <π / 4), and as a result of the determination, for the four consecutive subframes Decoding the broadcast channel (BCH) by synchronizing the frame if the calculated value (phase) is in the predetermined decision region, otherwise repeating the above step.

Referring to the operation of the present invention made of these steps are as follows.

First, in order to reduce the amount of complex calculations, the S2 sequence shown in Table 1 is converted into an integer symbol sequence. For example, it may be expressed as Equation 3 below.

S2 _d = (1-j, -1-j, 1-j, 1 + j)

As can be seen from the above, the symbol sequence converted from S2 has a size of 1.414 and the phase is equal to the S2 sequence.

Using an integer symbol like this makes it easier to obtain frame synchronization. Before using the symbol, the phase of the received SYNC_DL is calculated by removing the phase change caused by channel influence. For example, the calculation of the phase of the first received SYNC_DL may be represented by Equation 4 below.

Equation 4 is a correlation value ( corr _{SYNC_DL} ) of the transmitted SYNC_DL sequence and the received SYNC_DL sequence and the transmitted midamble sequence and the received midamble sequence (P ₁ ) of the first received SYNC_DL phase (P ₁ ). corr _Mid ), where P ₁ , corr _{SYNC_DL,} and corr _Mid are complex numbers, and * represents a complex conjugate. Then, the calculation process through Equation 4 is performed for each subframe received.

The phase P ₁ of the received SYNC_DL obtained by the above calculation and an arbitrary element of the sequence shown in Equation 3 are compared using the quadrature phase shift keying (QPSK). For example, if any of the elements shown in equation (3) assumed to be S2d ^1, wherein the phase P ₁ and phase comparison value of S2d _¹ (R ¹⁾ is expressed as Equation (5) below.

As can be seen, the comparison value R ₁ of P ₁ and S2d ¹ phase can be expressed as the product of the complex conjugate of P ₁ and S2d ¹ .

In this case, when the calculated R ₁ exists in the predetermined determination region D as shown in FIG. 3, the two phases P ₁ and S 2d ¹ are determined to be the same, and when the calculated R ₁ is out of the determination region, the two phases ( It is determined that P ₁ and S2d ¹ ) are different.

That is, if R _{1, which} is the difference between the two phases P ₁ and S2d ¹ , is within ± π / 4, the phase is regarded as the same phase, and if it is outside ± π / 4, it is determined as another phase. It is a general method of hard decision of a modulation (QPSK) symbol. Thus, the determination of what the two phase (P ₁ and S2d ¹⁾ is not the same may be represented by the equation (6) below as a real part R and the imaginary part ₁ ^r ₁ R ⁱ of R _1.

I.e., it is smaller than the imaginary part of the value (R ₁ ⁱ⁾ a large amount of real value than the real value of the negative ^{_{(-R 1 r) (R 1}} r) in R ₁ it can be seen that the two phases are the same.

An example of a method of frame synchronization with such a criterion is shown in FIG. 4. As shown, the phase P _i of the received SYNC_DL from the right P _{i + 1} to the left P _{i + 4} is multiplied by the conjugate complex number of the phase sequence of S2 converted into an integer symbol. have. In other words, P _{i + 1} is multiplied by 1 + j, a complex conjugate of 1-j whose phase is converted to an integer symbol of 315 degrees, and the real part value (R _{i + 1} ^r ) and the imaginary part value (R _{i +). 1} ⁱ ) is detected, and the detected values are compared with the received SYNC_DL phase P _{i + 1} for the subframe and the phase 315 degrees of S2 using Equation 6. This process is sequentially performed from left to right, and if one of the four decision blocks does not meet the condition of Equation 6, that is, if no one exists in the decision region shown in Fig. 3, the frame synchronization is not correct. To judge.

On the other hand, if all four decision blocks satisfy the condition of Equation 6, that is, if all are present in the decision region, it is determined that the frame is synchronized and decodes the broadcast channel (BCH). This process updates and compares P _i values each time a subframe is received.

As described in detail above, the present invention converts a phase used for phase modulation into a symbol composed of integers, and uses the quadrature phase shift keying (QPSK) characteristic of the phase of the converted symbol and the sequence of phases detected in the received signal. By determining whether the frame is synchronized, the frame synchronization can be obtained simply without performing a complicated operation.

Claims (4)

Converting a phase sequence of the signal S2 indicating that there is a broadcast control channel BCCH in the next four subframes into an integer symbol sequence; Calculating a phase of a received downlink synchronization sequence SYNC_DL based on a phase of a downlink synchronization sequence SYNC_DL sent from a transmitting end and a phase change difference by a channel; Calculating any phase of the calculated received downlink synchronization sequence (SYNC_DL) and any element of the symbol sequence using quadrature phase shift keying (QPSK); Determining whether a value (phase) calculated using the quadrature phase shift modulation is in a predetermined decision region; As a result of the determination, if the calculated values (phases) for the four consecutive subframes are in a predetermined determination region, decoding the broadcast channel (BCH) by synchronizing the frames; otherwise repeating the determining Frame synchronization method according to the time division sync code division method, characterized in that consisting of. The time division sync code division scheme according to claim 1, wherein the symbol sequence of the integer obtained by converting the phase sequence of the signal S2 is (1-j, -1-j, 1-j, 1 + j). Frame synchronization method. The method of claim 1, wherein the value calculated using the quadrature phase shift keying (QPSK) is expressed by the following equation.

R is a value calculated using the quadrature phase shift keying (QPSK), P is a phase of the received downlink sync sequence SYNC_DL, and S2 _d is an integer obtained by converting a phase sequence of the signal S2. Arbitrary elements in the symbol sequence of. The frame synchronization method according to claim 1, wherein the determination as to whether a value (phase) calculated using the quadrature phase shift modulation is in a predetermined determination region is performed by the following equation. .

Here, R ⁱ and R ^r are imaginary part values and real part values of values calculated using the quadrature phase shift keying (QPSK).

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