JP2001186117A - Frame timing acquisition method and apparatus, and TDMA demodulation apparatus - Google Patents

Abstract

(57) [Problem] To provide a frame timing capturing method and apparatus capable of capturing frame timing with high accuracy and smoothly capturing frame timing even when timing fluctuations occur rapidly. A frame timing acquisition device samples a burst signal at a sampling period set to be equal to or longer than a symbol period to generate a sample signal. The acquisition device calculates a correlation value based on the sample signal and the reference pattern, and accumulates and adds the correlation value for each sampling cycle. By doing so, the influence of noise or the like can be excluded from the correlation value. Therefore, frame timing can be captured with high accuracy. In addition, since sampling is performed at a sampling period equal to or longer than the symbol period, even when the timing fluctuates rapidly, the frame timing can be captured in units of one symbol or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a TDMA (Time Division Multiple Access) mobile communication system and a satellite TDMA mobile communication system.
TDM received and applied to a DMA wireless communication system
Method and apparatus for capturing frame timing of TDMA radio frame from A burst signal and TD
The present invention relates to a TDMA demodulator for demodulating an MA burst signal.

[0002]

2. Description of the Related Art A TDMA wireless communication system is called TDMA.
Wireless communication is achieved by transmitting and receiving burst signals via a wireless propagation path. More specifically, the transmitting station converts a synchronization word consisting of a bit string and communication data into symbol data having a predetermined symbol period, and creates a TDMA burst signal including the symbol data. Here, the synchronization word is necessary for timing detection, and has a sharp autocorrelation characteristic. The transmitting station transmits the created TDMA burst signal to the receiving station in synchronization with a predetermined time slot of a predetermined TDMA radio frame.

[0003] A receiving station captures frame timing by detecting a synchronizing word from a received TDMA burst signal. This capture of the frame timing is performed by a frame timing capture device. The receiving station demodulates the TDMA burst signal according to the captured frame timing. Thus, the receiving station can restore the original communication data.

As described above, in the TDMA radio communication system, communication is possible by capturing the frame timing and synchronizing it (frame synchronization). In this case, it is desired that the capture of the frame timing be performed as quickly and as accurately as possible. In particular, if the frame timing is erroneously captured and erroneous synchronization occurs, it will be a major obstacle to communication, so it is important to minimize the probability of erroneous synchronization. Therefore, the conventional frame timing acquisition device is configured from such a viewpoint.

That is, the conventional frame timing acquisition device converts the received TDMA burst signal into a digital signal by sampling the symbol every symbol period. Thereafter, the frame timing acquisition device obtains a correlation value between the digital signal and the reference pattern. The reference pattern has the same pattern as the synchronization word. Therefore, the frame timing acquisition device obtains a high correlation value at a position corresponding to the synchronization word in the digital signal. The frame timing capturing device extracts the highest value from the obtained correlation values, and captures the timing corresponding to the highest value as the frame timing.

[0006]

However, in this conventional frame timing capturing device, the detection accuracy of the synchronization word is not yet sufficient, and as a result, there is a risk that the frame timing is erroneously captured.

Further, since the frame timing acquisition unit is a symbol unit, the acquisition unit is coarse, and there is a problem that the frame timing cannot be acquired smoothly depending on the system. More specifically, in a satellite mobile communication system that realizes mobile communication via a communication satellite that travels in a relatively low orbit, timing fluctuation may occur rapidly. In such a case, in order to capture the frame timing smoothly, it is necessary to establish synchronization in units smaller than one symbol. However, as described above, the conventional frame timing acquisition device establishes synchronization in the symbol period, and therefore cannot acquire frame timing smoothly.

[0008] A technique for improving the detection accuracy of the synchronization word is disclosed in, for example, Japanese Patent Application Laid-Open No. 6-296151. The frame timing capturing device disclosed in this publication does not capture the frame timing every time, but accumulates a predetermined number of the captured frame timings, and determines the frame timing having the largest number of the accumulated timings as a regular timing. As a catch.

However, even with the technique disclosed in this publication, the unit of capturing frame timing is a symbol unit, so that the problem that the frame timing cannot be captured smoothly by the system is not solved.

Therefore, an object of the present invention is to solve the above-mentioned technical problems, to obtain a frame timing with high accuracy, and to capture a frame timing smoothly even when timing fluctuations occur rapidly. It is to provide a device.

Another object of the present invention is to provide a TDMA demodulator capable of improving demodulation accuracy.

[0012]

In order to achieve the above object, the present invention provides a TDM having a predetermined symbol period including a synchronization word.
A method for capturing the frame timing of a TDMA radio frame having an A burst signal, comprising:
A sampling step of creating a sample signal by sampling the A burst signal; and a correlation calculating step of finding a correlation value between a reference pattern having the same pattern as the synchronization word and the sample signal created by the sampling step. A cumulative addition step of cumulatively adding the obtained correlation value for each sampling period, and a timing capturing step of capturing a timing corresponding to the maximum value among the cumulative addition values as a frame timing.

As a hardware configuration for realizing this method, for example, a sampling unit for executing the above-mentioned sampling process and a DSP (Digital S / D) for executing the above-described correlation calculation process, cumulative addition process and timing acquisition process are provided.
and a frame timing acquisition device having an I / O processor. In addition, a frame timing acquisition device including a DSP that executes a sampling step, a correlation calculation step, an accumulative addition step, and a timing acquisition step can be considered.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

Embodiment 1 FIG. 1 is a block diagram showing a configuration of a TDMA wireless communication system to which a frame timing acquisition method according to Embodiment 1 of the present invention is applied. This TDMA wireless communication system is a GSM (Global System for Mobile communicat
terrestrial TDMA mobile communication system and satellite T
It corresponds to a DMA mobile communication system or the like. This TDMA
The wireless communication system includes a base station 1 and a mobile station 2.
The base station 1 and the mobile station 2 each include a TDMA communication device 3. TDMA communication device 3 includes a TDMA transmitting device 4 and a TDMA receiving device 5.

The TDMA transmission device 4 creates a TDMA burst signal composed of a data sequence having a predetermined symbol period.
More specifically, TDMA transmitting apparatus 4 creates a bit string by adding a preamble and a synchronization word to communication data, and creates a TDMA burst signal composed of a symbol data string by multiplexing the bits of the bit string. The preamble has information necessary for burst demodulation. The synchronization word is necessary for the TDMA receiver 5 to capture the frame timing, and has a sharp autocorrelation characteristic. The TDMA transmitter 4 transmits the created T
A DMA burst signal is transmitted in synchronization with a predetermined time slot of a TDMA radio frame.

FIG. 2 shows TDM in a TDMA radio frame.
FIG. 3 is a diagram illustrating an A burst signal. In this TDMA wireless communication system, a TDMA wireless frame F having a fixed period is predetermined. The TDMA transmitting apparatus 4 has a function of transmitting a plurality of mobile stations 2 using the same frequency in a time-division manner.
The TDMA burst signal B is intermittently transmitted in synchronization with a predetermined timing (time slot) of the DMA radio frame F. A synchronization word 6 is included at a predetermined position in the TDMA burst signal B.

The TDMA transmitting device 4 provided in the base station 1 constantly transmits a TDMA burst signal called a broadcast burst signal. The broadcast burst signal uses line information necessary for communication as communication data, and all mobile stations 2
Have a common frequency that can be received at The TDMA receiver 5 of the mobile station 2 starts communication when:
The broadcast burst signal is received first, and the frame timing is captured.

The TDMA receiving device 5 receives the TDMA burst signal transmitted from the TDMA transmitting device 4,
The received TDMA burst signal is demodulated to restore the original communication data. In this case, the TDMA receiver 5
Detects the synchronization word from the TDMA burst signal to capture the frame timing, and demodulates the TDMA burst signal according to the frame timing. In other words, the TDMA receiver 5 captures the end timing of the synchronization word as the head timing of the communication data, and performs demodulation of the communication data in synchronization with the captured head timing.

FIG. 3 is a block diagram showing the internal configuration of the TDMA receiver 5. The TDMA receiver 5 includes an antenna 10, a down converter 11, a frame timing acquisition device 12, and a demodulation device 13. Antenna 10
Receives the TDMA burst signal and receives the received TDMA burst signal.
A DMA burst signal is provided to down converter 11.
The down converter 11 converts the given TDMA burst signal into an intermediate frequency band signal,
DMA burst signal is transferred to frame timing acquisition device 12
Give to. The frame timing acquisition device 12 converts the given TDMA burst signal into a digital sample signal. Also, the frame timing acquisition device 1
2 captures the frame timing by detecting the synchronizing word based on the sample signal, and supplies the frame timing signal to the demodulation device 13. The demodulation device 13 includes:
The sample signal is provided in addition to the frame timing signal. The demodulation device 13 demodulates the sample signal according to the frame timing signal provided from the frame timing acquisition device 12, and restores the original communication data.

The frame timing acquisition device 12 will be described in more detail. The frame timing acquisition device 12 includes a sampling unit 20 and a DSP as a hardware configuration.
30. The sampling section 20 creates a sample signal by sampling the TDMA burst signal given from the down converter 11. More specifically, the sampling unit 20 includes two multiplication units 21i and 21q, one oscillation unit 22, and one π
/ 2 phase shifter 23, two low-pass filters (LPF) 2
4i, 24q, two A / D converters 25i, 25q
And one clock generator 26. The TDMA burst signal is provided to two multipliers 21i and 21q.

The carrier wave oscillated from the oscillating unit 22 is directly supplied to one multiplier unit 21i, and the carrier wave via the π / 2 transfer unit 23 is supplied from the oscillating unit 22 to the other multiplier unit 21q. The carrier has a baseband frequency. Therefore, each of the multipliers 21i, 21q
Respectively generate and output a baseband signal related to the in-phase component and a baseband signal related to the quadrature component. Each baseband signal is supplied to a low-pass filter 24i, 24q
After the high-frequency components have been removed from the data, the signals are supplied to A / D converters 25i and 25q, respectively.

The A / D converters 25i and 25q are supplied with a sampling clock from a clock generator 26. The A / D converters 25i and 25q generate sample signals by sampling each baseband signal according to the sampling clock.
Here, the sampling clock has a sampling period set to be equal to or longer than the symbol period of the symbol data string included in the TDMA burst signal. For example, the sampling period is an integral multiple (for example, four times) of the symbol period. Therefore, the sample signal is a signal having a rate equal to or higher than the symbol rate. That is, the sample signal is a signal in which a unit smaller than the symbol unit is one unit. The sampling section 20 supplies the generated sample signal to the DSP 30 and also supplies the signal to the demodulation device 13 as a signal for demodulation as described above.

The DSP 30 implements various functions for capturing frame timing by software. More specifically, the DSP 30 corresponds to a correlation calculation process for obtaining a correlation value between a sample signal and a reference pattern, a cumulative addition process for cumulatively adding a correlation value for each sampling period, and a maximum value among the cumulative added values. A timing capturing process for capturing timing as a frame timing is realized by software.

FIG. 4 is a flowchart for explaining the frame timing acquisition processing in the DSP 30. The DSP 30 obtains a correlation value between the sample signal provided from the sampling unit 20 and the reference pattern (Step S1). The reference pattern has the same pattern as the synchronization word. More specifically, the reference pattern is composed of a unit data sequence of one symbol or less obtained by dividing the same symbol data sequence as the synchronization word for each sampling period. As described above, the synchronization word has sharp autocorrelation characteristics. Therefore, a large correlation value should be obtained only at the timing of the sample signal that matches the reference pattern.

However, since the TDMA burst signal reaches the TDMA receiver 5 via the radio propagation path, it is affected by noise and the like. Therefore, a code error or the like may occur. In this case, the correlation value becomes large at a timing that does not match the reference pattern. Therefore, in the first embodiment, the calculated correlation values are cumulatively added in order to remove the influence of noise and the like.

More specifically, the DSP 30 cumulatively adds the obtained correlation values for each sampling cycle (steps S2 to S3). More specifically, the DSP 30 simply adds the correlation value for each sampling cycle (step S2). Next, the DSP 30 determines whether or not this cumulative addition process has been performed over a predetermined number of frames (step S3). The number of frames in this case is determined according to a request from the system. More specifically, the more the number of frames to be cumulatively added, the more accurate a correlation value can be obtained. Therefore, for example, in the case of data communication, the number of frames is relatively increased, and in the case of voice communication, the number of frames is relatively reduced.

If the simple addition has not been performed for a predetermined number of frames (NO in step S3), the DSP 30 repeatedly executes the simple addition. This makes it possible to absorb the influence of noise and obtain a group of correlation values having a large value at a timing coincident with the synchronization word. When the simple addition is performed over a predetermined number of frames (YES in step S3), the DSP 30 captures a timing corresponding to the maximum value among the obtained cumulative addition values for each sampling period as a frame timing (step S4). ~ S5).

More specifically, the DSP 30 extracts the maximum value among the obtained cumulative addition values for each sampling period (step S4). As described above, the cumulative addition value corresponds to a correlation value from which the influence of noise has been removed. Therefore, the cumulative addition value at the timing coincident with the synchronization word becomes the maximum value. The DSP 30 captures a timing corresponding to the extracted maximum value as a frame timing (Step S
5). The DSP 30 provides the demodulation device 13 with a frame timing signal indicating the captured frame timing.

The demodulation device 13 demodulates the sample signal output from the sampling section 20 according to the frame timing as described above. In this case, the demodulation device 13
Restores a sample signal of a unit smaller than a symbol unit to a sample signal of a symbol unit, and further demodulates the restored sample signal according to the frame timing. More specifically, the demodulation device 13 obtains a sample signal in a symbol unit by integrating a sample signal in a unit smaller than a symbol unit until it becomes one symbol. The demodulation device 13 demodulates the symbol-based sample signal in accordance with the frame timing. By doing so, the original communication data can be restored.

Next, the processing from correlation calculation to frame timing acquisition will be described in more detail. DSP3
A value of 0 quantizes the sample signal with a plurality of bits to create a soft decision signal. For example, the DSP 30 creates a soft decision signal having a resolution of 256 using 8 bits, or creates a soft decision signal having a resolution of 512 using 9 bits based on the sample signal. Next, the DSP
30 classifies the created soft decision signal into positive and negative, and associates it with 0 if positive and 1 if negative to create soft decision data. Further, the DSP 30 obtains a correlation value in the predetermined range by performing convolution addition of the predetermined range and the reference pattern in the soft decision data.

The DSP 30 calculates the correlation value in the predetermined range as
Cumulative addition is performed for each execution range of the convolution addition and for each sampling period. By doing so, it is possible to maximize the correlation value in the range corresponding to the synchronization word regardless of the influence of noise or the like. The DSP 30 captures the frame timing by detecting the range corresponding to the largest cumulative addition value among the cumulative addition values as the insertion position of the synchronization word. In this case, in order to avoid erroneous detection, it is needless to say that a predetermined threshold value may be set, and only when the threshold value is exceeded, the synchronization word may be detected as the insertion position.

FIG. 5 is a diagram for explaining the cumulative addition process of the correlation values. 5A shows a TDMA burst signal B, FIGS. 5B to 5E show correlation values for different TDMA radio frames obtained at the same sampling timing, and FIG. Indicates the value. For example, it is assumed that the synchronization word 6 exists at a position in the burst B shown in FIG.

In this case, as shown in FIGS. 5B to 5E, the correlation value is always relatively high at the position where the synchronization word 6 is inserted. On the other hand, the correlation values other than the insertion position of the synchronization word 6 have a low value or a high value depending on the presence or absence of noise. In some cases, as shown in FIG. Also have a high correlation value. However, by cumulatively adding these correlation values, FIG.
As shown in (f), the correlation value at the insertion position of the synchronization word 6 becomes highest.

As described above, according to the first embodiment, since the correlation values are cumulatively added for each sampling period,
The influence of noise can be eliminated, and an accurate correlation value can be obtained with high accuracy. Therefore, the frame timing can be captured with high accuracy. Therefore, the demodulation accuracy of communication data can be improved. Therefore, the communication quality can be improved.

Further, since the sampling period is set to be equal to or longer than the symbol period, the frame timing can be captured in units smaller than the symbol unit. Therefore, even in a system such as a satellite TDMA mobile communication system in which timing fluctuations occur rapidly, frame timing can be quickly and accurately captured. Therefore, the satellite TDMA
The reliability of the mobile communication system can be improved.

Moreover, since the correlation values are cumulatively added for each sampling period, the number of frames required to obtain sufficient accuracy can be reduced as compared with the case where the correlation values are cumulatively added for each frame. Therefore, as compared with the case where the correlation value is cumulatively added for each frame, the acquisition time of the frame timing with the same accuracy can be shortened. Therefore, the frame timing can be quickly captured.

Other Embodiments Embodiments of the present invention have been described above.
The present invention is not limited to the above embodiment.
For example, in the above embodiment, simple addition is adopted as the cumulative addition processing of the correlation values. However, it goes without saying that, for example, square addition may be employed as the cumulative addition processing of the correlation values. Generally, square addition is an operation used in more signal processing than simple addition. Therefore, many DSPs that implement the square addition can implement the square addition with a very small load. Furthermore,
A DSP that implements square addition generally requires less processing load than a DSP that implements simple addition. Therefore, according to the configuration that employs the square addition, there is an advantage that the processing load can be reduced.

In the above embodiment, the sampling section 20 of the frame timing capturing device 12 is configured as hardware, and the other components are configured as software. However, it goes without saying that, for example, the sampling unit 20 may be a part of the software executed by the DSP. According to this configuration, the frame timing acquisition device 12 can be configured with one DSP. Therefore, the configuration of the TDMA receiver 5 can be simplified, and the size of the TDMA receiver 5 can be reduced.

Further, on the contrary, it goes without saying that each function executed by the DSP 30 may be configured as hardware. FIG. 6 shows a frame timing acquisition device 12 in which each function executed by the DSP 30 according to the first embodiment is configured as hardware.
FIG. 2 is a block diagram showing an internal configuration of the device. That is, the frame timing acquisition device 12
In addition, a correlation calculation unit 31, a reference pattern generation unit 32, a cumulative addition unit 33, and a timing acquisition unit 34 are provided as hardware components.

More specifically, the sample signal output from the sampling section 20 is supplied to a correlation calculating section 31. The correlation calculator 31 calculates a correlation value between the sample signal and the reference pattern generated by the reference pattern generator 32, and provides the correlation value to the accumulator 33 for each sampling period. The accumulator 33 accumulates the correlation value over a predetermined number of frames for each sampling period, and supplies the accumulated value to the timing acquisition unit 34. The timing capturing unit 34 captures the timing corresponding to the maximum value among the accumulated values as the frame timing.

As described above, when the frame timing acquisition device 12 is entirely constituted by hardware, the frame timing acquisition processing can be performed at high speed.

[0043]

As described above, according to the present invention, since the correlation value is cumulatively added for each sampling period, a correlation value from which the influence of noise has been removed can be obtained. Therefore,
Frame timing can be captured with high accuracy. for that reason,
When demodulating the sample signal according to the frame timing, the demodulation accuracy can be improved.

Further, since the sampling period is equal to or longer than the symbol period, it is possible to capture the frame timing in units smaller than the symbol unit. Therefore, even in a system in which timing fluctuations occur rapidly, frame timing can be captured quickly and accurately.

Moreover, since the correlation values are cumulatively added for each sampling period, the number of frames required to obtain sufficient accuracy can be reduced as compared with the case where the correlation values are cumulatively added for each frame. Therefore, the acquisition time of the frame timing with the same accuracy can be short.

When the cumulative addition is performed by simple addition, the cumulative addition can be performed by simple processing.

Further, when the cumulative addition is performed by the square addition, a general-purpose product such as a DSP which can realize complicated processing with a small load although the processing itself is complicated can be used. The processing load can be reduced.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an overall configuration of a TDMA wireless communication system to which a frame timing acquisition device according to a first embodiment of the present invention is applied.

FIG. 2 is a diagram illustrating a configuration of a TDMA radio frame.

FIG. 3 is a block diagram illustrating an internal configuration of a TDMA receiver.

FIG. 4 is a flowchart illustrating a frame timing capture process in a DSP.

FIG. 5 is a diagram for explaining a cumulative addition process of correlation values.

FIG. 6 is a block diagram showing an internal configuration of a frame timing acquisition device according to another embodiment of the present invention.

[Explanation of symbols]

6 synchronization word, 12 frame timing acquisition device, 20
Sampling unit, 30 DSP, 31 correlation calculation unit, 3
2 reference pattern generation unit, 33 accumulative addition unit, 34 timing acquisition unit, BTDMA burst signal, FTDM
A radio frame.

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 5K028 AA01 BB04 BB05 DD02 HH01 KK33 MM17 SS03 SS04 SS14 SS24 5K047 AA04 AA11 BB01 HH01 HH15 HH43 JJ02 MM38 MM44 MM45 5K067 AA14 AA23 AA33 AE21 H0421

Claims (5)

[Claims] 1. A TDM having a predetermined symbol period including a synchronization word.
A method for capturing a frame timing of a TDMA radio frame having an A burst signal, comprising: a sampling step of generating a sample signal by sampling the TDMA burst signal at a sampling period set to be equal to or longer than the symbol period; A correlation calculation step for calculating a correlation value between a reference pattern having the same pattern as the synchronization word and the sample signal generated in the sampling step; and a cumulative addition for cumulatively adding the determined correlation value for each sampling period A frame timing capturing method comprising: a step; and a timing capturing step of capturing, as a frame timing, a timing corresponding to a maximum value of the cumulative addition values. 2. The frame timing acquisition method according to claim 1, wherein the cumulative addition step simply adds the correlation value for each sampling period. 3. The frame timing acquisition method according to claim 1, wherein the accumulative addition step adds a square value of the correlation value for each sampling period. 4. A TDM having a predetermined symbol period including a synchronization word.
An apparatus for capturing a frame timing of a TDMA radio frame having an A burst signal, wherein the sampling unit generates a sample signal by sampling the TDMA burst signal at every sampling period set to be equal to or longer than the symbol period. A reference pattern generation unit for generating a reference pattern having the same pattern as the synchronization word; a correlation calculation for obtaining a correlation value between the sample signal created by the sampling unit and the reference pattern generated by the reference pattern generation unit A cumulative addition section for cumulatively adding the correlation value obtained by the correlation calculation section for each sampling period; and a timing for capturing a timing corresponding to the maximum value among the cumulative addition values of the cumulative addition section as a frame timing. Frame tie including capture section Packaging capture device. 5. A TDM having a predetermined symbol period including a synchronization word.
A TDMA demodulation device for demodulating an A burst signal, comprising: a sampling unit that creates a sample signal by sampling at a sampling period set to be equal to or longer than the symbol period; and a reference pattern having the same pattern as the synchronization word. A reference pattern generator that is generated; a correlation calculator that calculates a correlation value between the sample signal created by the sampling unit and the reference pattern generated by the reference pattern generator; A cumulative addition unit that cumulatively adds the correlation value for each sampling period; a timing capture unit that captures a timing corresponding to a maximum value among the cumulative addition values of the cumulative addition unit as a frame timing; Restoring a sample signal to a symbol-by-symbol signal Moni, TDM of the signal of the symbol unit and a demodulator for demodulating according to the frame timing, which is captured by the timing acquisition unit
A demodulator.