JPH0568002A - Split-window time matching - Google Patents

Abstract

PURPOSE: To make a communication via a TDMA channel by holding synchronism between an area radio transmitter receiver and a remote transmitter receiver. CONSTITUTION: A time mismatch of a communication from the remote transmitter receiver to the area radio transmitter receiver is detected, and the transmission timing is adjusted until the remote transmitter receiver finishes adjusting the transmission timing completely; while one of two discontinuous time intervals is centered on the generation time of a synchronizing pattern before a command step and the other is centered on a prediction time generated by synchronism patterning in response to the command pattern, a synchronizing pattern attached to transmission by the remote transmitter receiver is searched for.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to communication synchronization, and more particularly to a method and apparatus for time alignment of mobile station transmissions in relation to a base station time reference in a mobile radiotelephone system.

[0002]

BACKGROUND OF THE INVENTION Currently, much interest and development effort is focused on digital mobile radiotelephone systems. Typically, the mobile station and each base station in such a system communicate over a TDMA channel whereby multiple mobile stations share the same transmit and receive frequencies, but within different times within these frequencies. -A slot is assigned. Each mobile station must fit its transmission exactly within the allocated time slot. Otherwise, transmissions from different mobile stations will "collide" when received at the base station.
However, they will interfere with each other.

Accurate time alignment becomes especially important as the cell size of cellular systems increases. This is because the maximum time variance of transmissions from mobile stations at the base station increases as well. Time dispersion refers to different propagation delays of different transmitting mobile stations located at different distances from the base station. As the mobile station moves, the effects of different propagation delays at the base station are compensated for by the base station instructing the mobile stations to adjust their transmission timing. Therefore, the time slots occur in a regular order with no apparent effect on the base station from different propagation delays.

Techniques have been developed to keep the transmissions of each mobile station in proper time alignment. Typically, while communication is established between the mobile station and the base station, the mobile station synchronizes its transmission with the transmission it receives from the base station according to a "standard offset criterion". For example, in one proposed system, the mobile station synchronizes its transmission so that the next expected communication runs out of transmit power at the end of the transmission 42 symbol periods before bursting from the base station. The mobile station transmits a shorter burst than usual to minimize the possibility of collision with other transmissions until the base station assigns the mobile station a specific transmission timing.

When a time slot is assigned to a mobile station, the time alignment of transmissions by the mobile station is continuously checked by the base station, noting the arrival time of the synchronization pattern transmitted by the mobile station during each burst. It The time drift of the transmission at the mobile station with respect to the base station clock occurs due to the time dispersion. When this time variance exceeds a predetermined threshold, the base station sends a time alignment command to the mobile station, instructing the mobile station to either advance or delay its transmission at certain times.

Further, the synchronization pattern transmitted by the mobile station in each burst may occur randomly in normal voice data. Therefore, in order not to excessively detect an apparent sync pattern (“false sync”), the base station ignores sync patterns that do not occur within a certain time interval, ie the “window” that is expected to occur. ..

[0007]

When the base station issues a time adjustment command to the mobile station, the mobile station cannot respond to the command and accurately notify when the transmission starts according to the adjusted time. Occurs. Therefore, in the case of a short time, the synchronization pattern occurs at the old timing or the commanded new timing. In the prior art, to provide both possibilities, the time alignment window that identifies the synchronization pattern was stretched or widened to include the old and new timing positions. Widening the time alignment window increases the likelihood of detecting false syncs and proportionally reduces voice quality.

[0008]

SUMMARY OF THE INVENTION In accordance with the present invention, a remote transmitter / receiver is adapted to detect a time mismatch in communication from a remote transmitter / receiver to a local wireless transmitter / receiver and adjust the transmit timing.
Two discontinuity intervals, one of which is centered around the time of occurrence of the sync pattern before the command, until the receiver commands and the remote transmitter / receiver adjusts its transmit timing. A local wireless transmitter / receiver and a remote transmitter by searching for a sync pattern associated with transmission by the remote transmitter / receiver during an interval of discontinuity centered around the predicted occurrence time of the sync pattern in response to a command by another. / Keeps synchronization with the receiver and allows communication via the TDMA channel. Therefore, the unsuitably wide time window of the prior art is divided into two appropriate narrow time windows so that false syncs are not detected. False syncs are less detected and voice quality is improved.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The communication synchronization portion of a base station and a mobile station in a mobile radiotelephone system will now be described with reference to FIG. For simplicity, elements that are not important to an understanding of the invention have been omitted. The base station has a transmitter unit, a receiver unit, and a control unit, and the control unit is realized by a CPU. Among other functions, the CPU realizes the control function (BS-control) of the base station and the logic function (TA-logic) of time alignment, among other functions. The receiver includes, among other elements that are not essential for understanding the invention,
Includes a correlator. The correlator has BS-control and TA
Generate an output signal for both logic and
Receive output signals from each. The correlator holds a reference time base and synchronizes the generation of incoming sync signals in relation to the time alignment window. The measurement result is sent to the CPU. The CPU subsequently supplies new parameters for the time matching window.

To explain the CPU in more detail, its BS
The control unit predicts and determines the expected synchronization time. In addition, the BS-control receives the time measurements from the correlator and informs the TA-logic and the correlator of the expected synchronization time. The TA-logic part of the CPU is the correlator and B
Make the necessary calculations to adjust the required time alignment according to the information collected from the S-Control. The time adjustment is sent to the transmitter to form the time alignment message and to the correlator to adjust the time alignment window. TA
-The time-aligned window adjustment message generated by the logic is
It is inserted in the physical layer control message by the transmitter and transmitted to the mobile station. Therefore, at the mobile station, the corresponding TA-logic receives the time alignment message from the transmitter and adjusts the mobile station's time base.

Referring to FIG. 2a, the format of the time slot for communication from the mobile station to the base station or land station is shown to include a 28 bit sync field SYNCH in the preferred embodiment. Each mobile station communicating with a specific frequency is assigned a different sync word. The sync word is preferably selected to have good autocorrelation properties to facilitate correlator synchronization and training. The remaining fields of the slot format are not particularly relevant to the invention, so
Description of this is omitted.

Adjustment of the time alignment may optionally be directed by the base station using the fields of the physical layer control message shown in FIG. 2b. The physical layer control message is
Periodically issued on the "Fast Access Control Channel" (FACCH) and / or the "Slow Access Control Channel" (SACCH) defined between the base station and the mobile station.
In one embodiment, the time alignment field of the physical layer control message contains 9 bits. The first 4 bits represent time alignment because the parameters are affected,
The remaining 5 bits specify the amount of time adjustment in terms of half symbol time. According to the preferred embodiment, the mobile station timing can be advanced or delayed from the standard offset reference by up to 30 half symbol times, except by returning to the standard offset reference.
In other words, the mobile station is instructed to transmit a certain amount of time before the standard offset criterion. The symbol is π / 4
Represents 2 bits of digital information according to DQPSK.

The principles of the present invention will now be described with reference to FIGS. 3a-3c. In the prior art, as shown in Figures 3a and 3b, the sync pattern from the mobile station is typically detected in a narrow time window centered around the expected time of occurrence of the sync pattern. Time shall increase from left to right. When the mobile station is in the correct time alignment, the synchronization pattern and the expected time of the actual occurrence time t _sync are substantially coincident. The window starts, or "opens," at time t _open , which precedes t _sync , and ends or "closes," at time t _close that follows t _sync . Therefore, the actual synchronization pattern occurring in the time matching window is correctly detected. On the other hand, spurious synchronization patterns that occur naturally in the voice data before the closing of the time alignment are ignored.

When the base station commands the mobile station to adjust its timing, the base station widens the time alignment window to release all of the old and expected sync patterns before the old and expected sync patterns. Close the rear part of the rear part. Therefore, intervening false sync patterns are detected, resulting in sync errors and degraded voice quality. The probability of detecting false syncs is particularly high when commanding maximum time adjustment.

According to the present invention, as shown in FIG.
Two standing synchronization windows are defined. One is old sync
Time t centered on the time of the pattern₀₁Open at the time
t_c1Closed in. The other is expected to generate a new sync pattern
Time t centered on raw time ₀₂Opened at t_c2Closed in
To be done. Time matching window is the maximum time for mobile radio telephone system
It is preferable to make it as narrow as possible according to the dispersion. Preferred
In another embodiment, the windows are time aligned with a total width of 80 μs.
The window is spread 40 μs on either side of the nominal synchronization time.
Therefore, the total time for detecting the sync pattern is
Remain constant independent of
The turn detection risk remains constant. Therefore, the intervention
Fake sync pattern is still undetected,
It reduces synchronization errors and improves voice quality.

The operation of the prior art system and the operation of the present invention are contrasted with reference to FIGS. 4a, 4b, 5a and 5b. First, referring to FIGS. 4a and 4b, in the prior art, the synchronization detection routine is executed by waiting for the start of the time slot at the reference time _{tr = 0} in step S1 and then waiting for the synchronization detection signal in step S2. Was done. In step S3, when the sync detection signal is received at the sync detection time t _s , the corresponding reference time _tr is recorded. In step S4, it is determined whether the synchronization detection time t _s is within the time matching window. If no, the sync signal is determined to be false sync and the routine returns to step S2 to await the next detection signal.

When it is determined that the synchronization detection time t _s is inside the time alignment window, it is determined in step S5 whether or not the time alignment window has been widened in response to the time alignment command. If the window is not open,
In step S6, whether the synchronization detection time t _s is within a predetermined adjustment threshold value for the predicted synchronization position,
That is, it is confirmed that the adjustment has not been commanded. If the sync detection time t _s is within the appropriate threshold, the mobile station is in the correct time alignment and the routine returns to wait for the start of the next time slot. If the synchronization detection time t _s is not within the appropriate threshold, the mobile station is instructed in step S7 to adjust its timing according to the calculated deviation. Following the adjustment command, in step S8, the time alignment window is widened by adjusting the opening or closing of the window according to the amount of deviation. The routine then returns and waits for the start of the next time slot.

Step S in the next iteration of the routine
At 5, the window will be determined to be extended, so that in step S9 the sync detection time t _s is within the established threshold for the expected sync position, ie in response to the time alignment command. It will be determined whether or not. If no, the window remains open, the routine returns to wait for the start of the next time slot. When the sync detection time t _s is within the established threshold, the time alignment window is narrowed by adjusting the open or close times to surround the new sync position.

The above processing should be contrasted with that of the present invention shown in FIGS. 5a and 5b. 5a and 5b, the first three steps S11, S
It will be appreciated that 12 and S13 are correspondingly the same as steps S1, S2 and S3 in the prior art routine described above. However, in steps S14 and S15, the synchronization detection time t _s is within two individual windows (one of which is a window for predicted sync position (without adjustment) and another window for predicted sync position (with adjustment)). Or not. As the terms "predict" and "predict" mean, the sync position before issuing the adjustment command is somewhat less certain than the sync position followed by the adjustment command due to the drift of the time base of the mobile station. I know. Although the exact time at which the mobile station responds to the adjustment command is uncertain,
When the mobile station responds, the resulting sync position is fairly well established. If the sync detection time t _s is not in any window, a false sync is displayed and the routine proceeds to step S
It returns to 12 and waits for the next synchronization detection signal.

In step S14, the synchronization detection time t
_When it is determined that _s is within the window of the predicted synchronization time, it is determined in step S17 whether the synchronization detection time t _s satisfies the establishment threshold for the predicted synchronization time. If yes, the routine returns. If no, step S1
At 8, a sync adjustment command is issued as in the routine described above. However, in step S19, instead of simply widening the old time-aligned window, a new window is formed with the opening and closing times surrounding the expected synchronization position.

In step S15, ie, following the time alignment adjustment command, if it is determined that the sync detection time t _s is within the window for the expected sync position, the old window for the expected sync time is discarded and the The window for the sync position is replaced with a new window for the expected sync position. When no adjustments have been performed, the windows for predicted and predicted sync positions appear to be the same.

[0022]

According to the present invention, a small time matching window is set in the time matching procedure.
Dividing into two windows reduces the risk of detecting spurious sync patterns. As a result, synchronization errors are reduced and average voice quality is improved.

Those skilled in the art will appreciate that the invention can be practiced in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore,
It should be considered that the embodiments disclosed herein are illustrative and non-limiting in all respects. The scope of the present invention is indicated by the appended claims rather than the above description, and all modifications that come within the meaning and range of equivalents thereof are intended to be included in the present invention.

[Brief description of drawings]

FIG. 1 is a block diagram of a communication synchronization part of a base station and a mobile station in a mobile radio telephone system.

FIG. 2a is a format diagram of communication exchanged between a base station and a mobile station. b is a conventional format diagram of communication exchanged between a base station and a mobile station.

FIG. 3A is a timing diagram showing the operating principle of the conventional technique.
b is a timing chart showing the operating principle of the prior art. c is a timing chart showing the operating principle of the present invention.

FIG. 4A is a flowchart of a time matching process according to a conventional technique. b is a flowchart of the time matching process according to the conventional technique.

FIG. 5A is a flowchart of a time matching process according to the present invention. b is a flowchart of the time matching process according to the present invention.

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[Procedure amendment]

[Submission date] May 28, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

[Figure 4]

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 5

[Correction method] Change

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[Figure 5]

 ─────────────────────────────────────────────────── —————————————————————————————————————————————————————————————————————— Inventor Peter Warstroam, Swingen Country, Burlingby, Urangergatan 19

Claims (2)

[Claims] 1. A synchronization maintaining method for maintaining synchronization between a local wireless transmitter / receiver and a remote transmitter / receiver and communicating via a TDMA channel, the remote transmitter / receiver to the local wireless transmitter / receiver. Detecting a time inconsistency in the communication of the communication, a command step of instructing the remote transmitter / receiver to adjust its transmission timing, and 2 until the remote transmitter / receiver adjusts its transmission timing. One discontinuous time interval, one of which is a time interval centered on the generation time of the synchronization pattern before the command step,
And the other searching for a sync pattern associated with a transmission by the remote transmitter / receiver during a time interval centered on an expected time for the sync pattern to occur in response to the command step. How to keep synchronization. 2. A synchronization maintaining method for maintaining synchronization between a local wireless transmitter / receiver and a remote transmitter / receiver and communicating via a TDMA channel, the remote transmitter / receiver to the local wireless transmitter / receiver. Means for detecting a time inconsistency in communication to the remote transmitter / receiver, means for instructing the remote transmitter / receiver to adjust its transmission timing, and 2 until the remote transmitter / receiver adjusts its transmission timing. Means for searching a synchronization pattern associated with the transmission by the remote transmitter / receiver during one discontinuous time interval, one of the discontinuous times being adjusted by the remote transmitter / receiver. As fingers Is a time interval centered on the time of occurrence of the synchronization pattern before the instruction, and the other of the discontinuous times is the occurrence of the synchronization pattern of the previous period after the remote transmitter / receiver has instructed to adjust its transmission timing. A synchronization holding device, characterized in that it is an interval of the discontinuous time centered on an estimated time.