JP3096368B2 - Method and circuit for extracting level determination timing in mobile radio using TDM signal transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to TDM (time-division multiplex).
The present invention relates to a method and an apparatus for extracting a level determination timing capable of coping with the occurrence of a multipath propagation path in mobile communication employing a signal transmission method.

[0002]

2. Description of the Related Art As a transmission method for mobile communication, TDM is used.
The adoption of is being considered. This is because the TDM signal transmission system has various advantages such as effective use of frequency and facilitation of reproduction, and is considered to be effective for mobile communication.

[0003]

SUMMARY OF THE INVENTION In mobile communications, TD
When the M signal transmission method is adopted, timing synchronization at the time of occurrence of a multipath propagation path becomes a problem. The multipath propagation path means that the path of the radio wave from the transmission point becomes multi at the reception point. The radio wave to the receiving point includes a direct wave transmitted directly from the transmitting point, a reflected wave which rebounds to reach a mountain or a building, and a ground wave which propagates and reaches the ground. The radio waves of these nuclides each make a path, and collectively form a multipath propagation path. In the following, for simplicity of description, it is limited to two examples of a path of a direct wave and one path of a reflected wave. Here, the reflected wave arrives at the receiving point later than the direct wave, and is also called a delayed wave. Further, when the reception electric fields of the direct wave and the delayed wave are weak, it is preferable to select and receive the stronger reception electric field, but the selection timing is determined by the level determination timing. Normally, the electric field of the direct wave increases, but if there is a radio wave shield in the path of the direct wave, the electric field of the direct wave may be smaller than the electric field of the delayed wave or may not be sent . In these cases,
It is preferable to sort out delayed waves. However, it is difficult to directly determine which is a direct wave and which is a delayed wave, so it is necessary to extract the level determination timing and select the electric field at that time based on this timing. It is.

An object of the present invention is to enable a wave having a high electric field strength to be selected and taken in even when the strength of an electric field is generated between a direct wave and a delayed wave due to the generation of a multipath propagation path. An object of the present invention is to provide a method and apparatus for extracting a level determination timing in mobile communication employing a TDM signal transmission method.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for extracting a level judgment timing which can prevent the error rate characteristic from being deteriorated in a situation where a multipath propagation path occurs under a TDM signal transmission system. Here, (a), the presence of a delayed wave due to a multipath propagation path is detected from the correlation peak value of the preamble signal of the received signal, and (b), the correlation peak value and the level determination timing generated by the PLL circuit of the receiver. And compare the timing with, to determine the delay time of the delayed wave,
(C) According to the determined amount of delay time, the PLL
Input to the circuit. The exchange point signal of the delayed wave is pre-shifted, and (d) the level determination timing is post-shifted in accordance with the determined delay time, and the level determination timing for the delayed wave is changed to the TDM corresponding to the delayed wave. Only the period of the signal is changed (claim 1).

Further, the present invention relates to a level judgment timing extraction circuit which can prevent the deterioration of the error rate characteristic under the situation where a multipath propagation path occurs under the TDM signal transmission system. A conversion point detection circuit for detecting an exchange point of a signal; and (b) a PLL circuit for extracting and outputting a level determination timing from the detected conversion point signal;
A correlation detection circuit for detecting the correlation value of the preamble signal of the received signal, (d) a peak detection circuit for detecting the peak of the detected correlation value, and (e) a timing of the detected peak value and the PLL circuit. And (f) when the difference is larger than a prescribed value, the timing of the detected conversion point signal is shifted forward according to the magnitude of the difference. Means for inputting the shifted conversion point signal to the PLL circuit in place of the non-shifted conversion point signal; and (g) when the difference is larger than a specified value, a level determination timing signal which is an output of the PLL circuit. Means for shifting afterward according to the magnitude of the difference, and outputting the shifted level determination timing signal thereafter.

[0007]

When a multipath propagation path occurs in a TDM system, if the level of the delayed wave is higher than that of the direct wave, the optimum sampling point of the received signal when the TDM signal is received is the case where the direct wave is received. It is conceivable that it is shifted compared to. The shift of the sample point becomes a time difference between the delayed wave and the direct wave. Generally, in TDM transmission, a transmission signal is continuously transmitted, and timing synchronization extraction is established by a PLL circuit. However, when the multipath propagation path as described above occurs, the PL of the timing synchronization circuit
The L circuit is controlled and works so as to follow the delayed wave, and adjusts the sampling points. In this case, in order for the PLL circuit to follow the delayed wave, it is necessary to widen the bandwidth of the PLL circuit. However, if the bandwidth of the PLL circuit of the timing synchronization circuit is widened, the timing jitter increases, and the sampling point is also the same, so that the error rate characteristics deteriorate. The present invention provides such a TD
This is to improve the condition of M transmission by using the format of a TDM signal. That is, according to the present invention, the timing for determining the delayed wave can be set to the point where the aperture of the eye pattern of the delayed wave is maximized, and the deterioration of the error rate is prevented.

[0008]

FIG. 3 shows the form of a TDM transmission signal. Figure 1
Slot indicates a channel CH in one slot.
1, CH2, CH3,... Are allocated by time division multiplexing. Such a signal form is called slot data. Here, the preamble signal [11] is a predetermined bit sequence necessary for stabilization and synchronization of the channel itself, a signal sequence known to the receiving station, and information data [12].
Is data transmitted from the transmitting side which has meaning as information only after demodulation by the receiving station.

Next, such a TDM signal is transmitted,
FIG. 4 shows a situation where a multipath propagation path occurs. This figure comprises a transmitting station [21], a receiving station [22], a reflector [23], and a shield [24]. First path (path of radio wave; this is path of delayed wave) (A → C →
B) and the second path (this is the direct wave path) (A →
Compared with B), the former is longer, and the difference between the signal that the radio wave emitted from the transmission point [21] reaches the reception point [22] following the former path and the signal that the latter reaches the reception point is different. It arrives later by the time divided by the radio wave propagation speed. Also, if the shield [24] is present in the latter path, the direct wave (A → B) is attenuated, and the reception level is lower than that of the delayed wave (A → C → B).

FIG. 5 shows a received signal in the above situation. FIG. 5A shows an eye pattern [31] of a received signal in the case of a direct wave (a signal propagating through a path from A to B) (where the abscissa represents time and the ordinate represents amplitude). , A level determination timing signal [32], and a correlation output [33] of the preamble signal.

FIG. 5B shows the path signal waveform of the delayed wave (A → C → B) on the same time axis. The fact that the correlation output indicating the delayed wave eye pattern [34], the level determination timing signal [35], and the correlation output [36] of the delayed wave preamble signal are obtained in this manner can be obtained, for example, by a "spread spectrum communication system" ( RC Dixon
Author, Toshiya Tateno et al .: Jatec Publishing Co., Ltd.) Due to the relationship between these waveforms, the time difference Td is a value expressing the radio wave path difference in time.

It is assumed that these signals are independently input to the receiver. If there is no multipath, a signal of a direct wave eye pattern [31] is input, and a level determination timing signal [32] is extracted by a timing extraction PLL circuit. At this timing, the eye pattern is determined and the data is restored. Next, when the shield [24] is inserted into the path (A → B), this radio wave does not reach the receiver, and a delayed wave (A → C → B) is input to the receiver. At this time, the timing extraction PLL circuit signal [32] gradually changes to [34] based on the reception eye pattern [34]. Therefore, while the timing shifts, the reception eye pattern [3
4] is determined at the level determination timing [32]. In this case, the determination position is determined not at the point a where the eye pattern is maximally open, but at a portion other than a where the amplitude is small, and the error rate deteriorates. Therefore, in order to prevent the error rate from deteriorating, it is necessary to immediately change the level determination timing when the delayed wave becomes stronger than the direct wave. To change the judgment timing,
A method of shortening the time constant (widening the bandwidth) of the timing extraction PLL circuit to speed up the tracking characteristic can be considered. In this case, however, the error rate characteristic deteriorates because the timing jitter increases.

Therefore, in this embodiment, the level determination timing is manipulated without changing such a timing extraction PLL circuit. That is, when the correlation value [36] of the preamble signal included in the delay wave at the receiver is viewed, the peak point of the correlation value of the delay wave and the ideal level determination timing [35] for the delay wave eye pattern [34] are the same. This is a method that utilizes the fact that there is a positional relationship. Therefore, if the level determination timing signal in the absence of a delayed wave is delayed by the time difference Td of the multipath signal, the eye pattern [34] of the delayed wave can be accurately determined. Td is the timing signal [32] and the preamble output of the delayed wave [36].
Can be obtained by taking the difference from the peak value.

It is considered that the occurrence of multipath is temporary depending on the terrain, and is different for each slot data. Direct waves occupy the majority of communications and their timing can be averaged. For this reason, a specific number of PLL circuits for extracting the timing of the direct wave is increased to suppress the jitter. When a multipath occurs, the correlation peak point a of the preamble signal of the delayed wave and before the multipath occurs The level extraction timing is changed for each burst by the time difference Td from the level extraction timing of the direct wave output from the timing extraction PLL circuit.
Whether a direct wave or a delayed wave is identified may be determined by identifying a time difference between the extracted determination timing and the peak point of the preamble signal.

FIG. 6 shows an example of this case. The level determination timing [41] of the direct wave does not change. On the other hand, when the reception eye pattern [42] has a delayed wave and becomes stronger than the direct wave, the eye pattern changes from [423] to [42].
4] Further, it shifts while changing to [425].
26], a delayed wave is received. In this situation, the corrected level determination timing [43] corresponds to the direct wave level determination timing [41] since the peak point b of the correlation signal [44] of the preamble signal is not detected until the eye pattern [421 to 426]. It is the same timing. When the peak point b of the correlation signal of the preamble is detected, the time difference T between the timing signal [426] and the peak point [446] is obtained.
As for the determination timing corresponding to the eye pattern [427] when d is determined, a new level determination timing is created by delaying the time by Td. Hereinafter, this timing is continued until the end of the slot data. In this manner, the determination timing of the eye pattern after [427] is determined at an appropriate point, that is, at the point b where the eye of the eye pattern is maximally opened, and is shifted from the center point where the eye pattern is maximally opened. The error rate is smaller than the old timing (the timing indicated by a dotted line with an arrow) determined based on the point.

FIG. 1 is a diagram showing an embodiment of a synchronous circuit according to the present invention, and FIG. 2 is a time chart thereof. The synchronization circuit of FIG.
Conversion point detection circuit 51, switching circuit 52, timing extraction P
LL circuit 53, correlation detection circuit 54, peak extraction circuit 5
5, timing comparison circuit 56, timing shift determination circuit 57, timing shift circuits 58 and 59, switching circuit 51
Consists of zero.

Based on the received eye pattern [61], the conversion detection circuit 51 generates a conversion point signal [62] which is a timing acquisition signal. This signal is generated from the conversion point or the envelope component of the eye pattern, but any method may be used. Here, a description will be given assuming that the eye pattern is generated at the conversion point of the eye pattern. The conversion point signal [621] is a signal generated from a direct wave. When only a direct wave is received, this signal is input to a timing extraction PLL circuit [53] to generate a level determination timing signal [63]. In this case, the switching circuit [52] passes the conversion point signal [62] (the signal on the upper path). The correlation circuit [54] outputs a correlation signal [64] of the preamble signal. The peak point d is detected from the correlation waveform by the peak extraction circuit [55]. This peak point d is determined by the timing comparison circuit [56].
The other input signal is a level determination timing signal [63] based on a direct wave which is an output signal from the timing extraction circuit [53]. This circuit [56] outputs the time difference Td between the direct wave and the delayed wave [65]. Td is a timing deviation judging circuit [57]
And the circuit instructs to change the timing when the value of Td becomes larger than a prescribed value. In the specified value, Td is set to 10 to 20% of the symbol length. This is because if the level determination timing is shifted more than this, the error becomes worse.

The timing shift judgment output [66] becomes a timing change execution command when the level becomes high, and the timing shift circuit [58, 59] and the switching circuit [52, 51].
0]. The timing shift circuit [58] changes the conversion point signal [62] to T
The conversion point signal [67] is obtained by shifting (advancing, that is, pre-shifting) by d. Note that, among the signals [67] in FIG. 2, [671 to 674] are conversion point signals output as they are without being shifted by the shift circuit 58. These conversion point signals are not selected by the switching circuit 52, and thus are discarded as they are.
The conversion point signal after the shift is [675]. The conversion point signals [675, 676-] are selected by the switching circuit [52] and input to the timing extraction PLL circuit [53]. The signal [67] after being selected by the switching circuit [52]
5,676,677,678,679] is input to the timing extracting PLL circuit [53] at the same time intervals T ₀ and the conversion point signal of the direct wave. All of these operations are executed by the output [66] of the timing deviation judging circuit [57]. As a result, the output of the timing extraction PLL circuit [53] continues to output the determination timing signal [63] at the direct wave timing without being affected by the delayed wave. The conversion point signal [672, 673, 674] indicates a case where the delayed wave and the direct wave are input to the receiver with almost the same strength. Takes another value, but its duration is short, so the timing extraction PLL
By making the time constant of the circuit [53] sufficiently large, the effect can be ignored.

The output of the timing extraction PLL circuit [53] is added with a time delay of Td (that is, post-shift) by the timing shift circuit [59] by the output [66] of the timing deviation determination circuit [57], and the level determination timing is obtained. It is output as a signal and is further selected by the switching circuit [510] to become the final output signal [68] of the timing circuit. The eye pattern [69] of the direct wave when there is no delayed wave is indicated by a broken line for reference.

The present timing synchronization circuit system can be applied not only to TDM communication but also to TDMA (time-division multiple access) communication. This is the same as that in the TDMA communication that the slot data of the TDM communication described above has become a burst, and it can be easily understood from the fact that the same discussion holds when the delayed waves are considered as those burst signals.

Finally, the position of this circuit in wireless communication will be briefly described with reference to FIG. The data to be transmitted is input to a modulator [71], and the carrier is modulated by an appropriate modulation method.
The carrier output is amplified by a transmitter [72], radiated from a transmission antenna [73] to an electric line [74] after being received by a reception antenna [75], and then amplified by a receiver to an appropriate level and demodulated by a demodulator. It is converted to a demodulated signal. The converted signal is a so-called eye pattern, and based on the signal, a determination circuit [78] determines a signal to be an eye pattern at a determination timing to become reception data. The circuit for generating the judgment timing used here, that is, the judgment timing generating circuit [79] is the circuit of the present invention.

[0022]

As described above, in the TDM type wireless transmission system, a delayed wave is generated, and the delayed wave becomes stronger than the direct wave.
In the timing extraction in the case of detecting data by demodulating a delayed wave, by using the present invention, the timing for determining the delayed wave can be set to the point where the aperture of the eye pattern of the delayed wave is maximized. Thereby, the deterioration of the error rate can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a synchronization timing extraction circuit according to the present invention.

FIG. 2 is a time chart thereof.

FIG. 3 is a diagram illustrating a TDM signal form in a TDM transmission system.

FIG. 4 is a diagram showing a propagation model.

FIG. 5 is a time chart based on a received signal model.

FIG. 6 is a time chart of an operation principle based on a received signal model of the present invention.

FIG. 7 is a diagram showing a mobile radio system to which the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Preamble signal 12 Information 21 Transmitting station 22 Receiving station 23 Reflector 24 Shielding object 31, 42, 61 Eye pattern 32, 41, 43, 63 Level determination timing signal 33, 36, 44, 64 Correlation output 51 Conversion point detection circuit 52 , 510 switching circuit 54 correlation detection circuit 55 peak extraction circuit 56 timing comparison circuit 57 timing deviation determination circuit 58, 59 timing shift circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B ^7/ 24-7/26 102 H04Q ^7/ 00-7/38

Claims (2)

(57) [Claims] 1. A level determination timing extraction method which can prevent deterioration of error rate characteristics under a situation where a multipath propagation path occurs under a TDM signal transmission method. The presence of a delayed wave due to a multipath propagation path is detected from the correlation peak value of the signal preamble signal, and (b) timing comparison between the correlation peak value and the level determination timing generated by the PLL circuit of the receiver is performed. (C) determining the delay time of the delayed wave;
Input to the circuit. (D) shifting the level determination timing backward according to the determined amount of delay time, and changing the level determination timing for the delayed wave to the TDM equivalent to the delayed wave. A method for extracting a level determination timing in mobile communication using a TDM signal transmission method, wherein the level determination timing is changed only during a signal period. 2. A level determination timing extraction circuit capable of preventing deterioration of an error rate characteristic under a situation where a multipath propagation path occurs under a TDM signal transmission system. A conversion point detection circuit for detecting a point; (b) a PLL circuit for extracting and outputting a level determination timing from the detected conversion point signal; and (c) a correlation detection circuit for detecting a correlation value of a preamble signal of a received signal. (D) a peak detection circuit for detecting a peak of the detected correlation value; (e) a comparison circuit for calculating a timing difference between the timing of the detected peak value and the level determination timing obtained by the PLL circuit; F) When the difference is larger than a specified value, the timing of the detected conversion point signal is shifted forward according to the magnitude of the difference, and the previously shifted conversion signal is not shifted. Means for inputting to the PLL circuit in place of the conversion point pulse; (g) when the difference is larger than a specified value,
Means for shifting the level judgment timing signal output from the LL circuit in accordance with the magnitude of the difference, and for outputting the shifted level judgment timing signal thereafter. Level determination timing extraction circuit for mobile communication.