JPH11164351A - Timing adjustment circuit for clock signal and its adjustment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve communication quality by reducing radio wave interference between adjacent cabinets. SOLUTION: The timing adjustment circuit 1 is provided with a delay time adjustment section 4 that delays a master clock signal sent through plural distribution paths and is placed on the way of the distribution paths. Thus, the delay time adjustment section 4 is used to adjust a timing of clock signals which are distributed through plural the distribution paths.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a timing control circuit for a wireless transmission / reception timing clock signal used in a cordless system for business use.

[0002]

2. Description of the Related Art In an office cordless system, a cordless telephone (hereinafter referred to as a mobile terminal) is used as an extension telephone. In such a system, a private branch exchange (PB)
X) connects an existing communication network outside the office and the mobile terminal, and controls the entire system in the office. This P
The BX has a plurality of base stations (hereinafter, referred to as CSs) under its control. This CS has a plurality of mobile terminals (hereinafter referred to as MS) under its control.
And communicates with this MS via radio according to a standard.

As this standard, for example, the standard of the second generation cordless telephone system (hereinafter referred to as RCR-STD)
-28). This RCR-STD-
28, a multi-carrier TDMA-
The TDD system is adopted. Therefore, the transmitted and received signals are
It is framed and is timing synchronized throughout the system. In order to synchronize the timing, the PBX creates a timing clock and distributes it to CS, MS, and the like.

[0004]

However, the above-mentioned conventional techniques have the following problems to be solved. A certain amount of delay time occurs while the clock signal passes through the timing distribution path from the PBX to the terminal MS. The cause of this delay time is the propagation time of the clock signal through the cable in the distribution path, P
Response time of a circuit in a device such as a BX. Therefore, between a plurality of paths through which the timing clock passes,
A delay time difference may occur. This delay time difference is
It appears as a phase difference between the transmitted signals. When the signals having the phase difference overlap each other at the boundary between adjacent CSs, communication quality deteriorates due to mutual radio interference.

[0005]

The present invention adopts the following constitution in order to solve the above points. <Configuration 1> A plurality of base stations, each of which communicates with a mobile station moving within a predetermined area, and an exchange which distributes a master clock serving as a time reference of the entire system to these base stations are provided. In the system, a delay time adjusting unit that delays the master clock by a predetermined time is inserted into a distribution path that distributes the master clock from the exchange to each of the base stations, and each of the delay time adjusting units includes: A cordless system wherein a delay time for delaying the master clock by a predetermined time is set so that each of the base stations receives the master clock from the distribution path at the same timing.

<Structure 2> In the system described in Structure 1, when T is the delay time of the distribution path having the largest delay with respect to the master clock among the distribution paths for allocating the master clock to each base station, this delay A predetermined delay time equal to or longer than the time T is defined as the maximum allowable delay time of the master clock, and inserted into each distribution path so that the input timing of the master clock input to each base station matches the maximum allowable delay time. A cordless system, wherein a delay time is set by a delay time adjusting unit.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 is a block diagram of a CS connection unit. The clock signal timing adjustment circuit according to the present invention is one component of the CS connection unit shown in FIG. Before describing the timing adjustment circuit of the clock signal, the flow of the clock signal in the office cordless system will be described.

FIG. 2 is an explanatory diagram showing the flow of a clock signal. As shown in the figure, the office cordless system includes an integrated unit 22, N cabinets P1 to PN, a plurality of CS connection units F11 to F1n branching from each cabinet, and a plurality of branching units from each connection unit. The mobile station includes a plurality of base stations CS11 to CS1n and m mobile terminals MS1 to MSm.

Here, the control unit 22 and N from P1 to PN
The cabinets and the CS connection units F1 to Fn are arranged inside the private branch exchange (PBX) 1. The supervising unit 22 is a unit that generates a master clock that serves as a time reference for the entire system, and is also a unit that links a system under its control with another existing communication network 21. Furthermore,
It is also the part that controls the entire system.

The cabinets P1 to PN are connected in a daisy chain with the control section 22 interposed therebetween (shown by solid lines and dotted lines in the figure).
This is a section that is connected and regenerates a clock signal in synchronization with the reference clock received from the control section 22. Each of the cabinets P1 to PN is also a part that supplies a clock signal regenerated by itself to a plurality of CS connection units F11 to F1n that are branched and connected to the cabinets P1 to PN, respectively. The CS connectors F11 to F1n are interfaces between the cabinet and the base station. This is a part that receives a clock signal from the cabinet P1 to which it is connected and distributes it to a plurality of base stations CS11 to CS1M that are branched and connected to itself.

The base stations CS11 to CS1M receive a clock signal from the CS connection unit F11 to which they are connected, and
It is a part that converts to electromagnetic waves. It is also a part that supplies the clock signal converted into the electromagnetic wave to mobile terminals MS1 to MSm located in a wireless service area formed around itself. The mobile terminals MS1 to MSm are connected to the base station C.
The clock signals converted into the electromagnetic waves are received from S11 to CS1M. The overall flow of the clock signal has been described above. Next, the background in which the present invention is required in the entire flow of the clock signal will be described.

FIG. 3 is a layout diagram of the system. From the cabinet P1 to a plurality of CS connection units F11 to F1n,
Further, a plurality of base stations CS1 are transmitted from the one CS connection unit F1.
The system for dendritic expansion from 1 to CS1M is limited to one branch for simplicity. Further, in the figure, areas E1 to E1
The area EN represents an area under the control of the clock signal regenerated by each of the cabinets P1 to PN. Therefore, the timing of the transmission signal that flies in the area coincides with the clock signal regenerated by the cabinets P1 to PN that govern the area. In this one area, a plurality of base stations CS11 to CS1M
However, although it includes a plurality of wireless service areas, each of which operates at the same timing.

Assume that the office cordless system operates in accordance with RCR-STD-28. R
The CR-STD-28 employs a multicarrier TDMA-TDD system as a communication system. here,
In the TDMA-TDD system, a plurality of carriers each having a different frequency constitute a separate channel. The base station and the mobile terminal are communicating alternately on the same channel. Further, the same channel is divided on the time axis, and other base stations and mobile terminals are simultaneously communicating.

[0014] In RCR-STD-28, the frame length is specified as 5 msec. Here, a frame is a unit of data for transmitting and receiving a certain amount of data collectively. The roles of a plurality of slot signals constituting this frame are determined in order with reference to the leading end of the frame.

Therefore, it is assumed that the mobile terminal MS1 located at the boundary between the area E1 and the area EN simultaneously receives a signal from the area E1 and a signal from the area EN having a delay time difference. At this time, since the two signals do not have the same timing, they interfere with each other and deteriorate the communication quality.
Therefore, it is necessary to accurately match the timing as well as the frame length and 5 msec. To this end, all transmission signals are required to be frequency and phase synchronized throughout the system.

In order to achieve this requirement, the control unit 22
Creates a frame clock with a pulse repetition period of 5 msec and distributes it to each component such as a cabinet, a CS connection unit, a base station, and a mobile terminal. However, a delay time occurs due to a propagation time in a coaxial cable constituting the distribution path, a response time in a circuit in the device, and the like. For example, there is a difference in the number of cabinets in the distribution path between the signal from the area E1 and the signal from the area EN. Furthermore, there is a difference in the length of the coaxial cable. Therefore, a delay time difference occurs.

As a configuration for minimizing the delay time difference, a star connection (indicated by a dashed line in the figure) in which the cabinets P1 to PN are connected in a star shape around the control unit 22 can be considered. In this star connection, it is also possible to make the number of private branch exchanges for each distribution path the same and to adjust the length of the coaxial cable to such an extent that the difference in delay time does not matter. However, this construction requires a lot of man-hours. As a means for absorbing a delay time difference between distribution paths without increasing the number of steps, a timing adjustment circuit according to the present invention is newly provided. The necessity of timing adjustment and the positioning of the timing adjustment circuit in the office cordless system system have been described above, and therefore, returning to FIG. 1 again, a specific example of the timing adjustment circuit according to the present invention will be described.

<Configuration of Specific Example> As shown in FIG. 1, the timing adjustment circuit 1 according to the specific example includes a control unit 2, a storage unit 3, and a delay time adjustment unit 4. The timing adjustment circuit 1 includes C, an interface portion between the cabinet and the base station.
It is a part of the internal configuration of the S connection parts F11 to F31 (FIG. 3). The control unit 2 is a unit that receives timing information sent from a CPU (hereinafter, referred to as an upper CPU) inside the control unit 22 (FIG. 3) and stores the timing information in the storage unit 3.

Also, based on the control of the upper CPU, this section is also a section for taking out the information stored in the storage section 3 and converting it into delay time information. Further, based on the converted delay time information, the delay time adjustment unit 4 is controlled to control the cabinet P
1 (FIG. 3) is a portion for adjusting the timing of the clock signal transferred from FIG. The storage unit 3 is a memory that stores timing information sent from the host CPU based on the control of the control unit 2.

The delay time adjusting section 4 is based on the delay time information transferred from the control section 2 and controls the cabinet P1.
This is a part for adjusting the timing of the clock signal received from FIG. Further, it is a part for transferring a clock signal adjusted in timing to the CS interface circuit.
The timing adjustment circuit having the above configuration operates as follows.

<Operation of Specific Example> FIG. 4 is an explanatory diagram of the timing of a clock signal. (A) shows the timing of the frame clock (repetition cycle 5 msec) generated by the control unit 22. Hereinafter, this clock is referred to as a master clock. (B) shows the timing of the clock signal regenerated by the cabinet P1 receiving the master clock and synchronizing with the master clock. (C) similarly shows the timing of the clock signal that the cabinet P2 has received the master clock and regenerated in synchronization with the master clock. In all of the above figures, the horizontal axis represents time, and the vertical axis represents signal level. Furthermore, all figures are drawn with the time axis coincident.

For convenience of explanation, the clock distribution path is limited to a path passing through the cabinet P1 and a path passing through the cabinet P2. As shown in FIGS. (A) and (b),
The timing of the clock signal regenerated by the cabinet P1 has a delay time T compared to the timing of the master clock.
Assume that it is d1 behind. Similarly, it is assumed that the timing of the clock signal regenerated by the cabinet P2 is delayed by the delay time Td2 as compared with the timing of the master clock, as shown in FIGS. Hereinafter, the operation of the timing adjustment will be limited to the distribution path passing only through the cabinet P1, and will be disassembled into operation steps.

S-1. The maximum delay time Td0 that can occur between the master clock and the clock signal regenerated by all cabinets in the system is set. This maximum delay time T
In setting d0, the maximum delay time that can be assumed is set in consideration of the future line expansion. S-2. The delay time Td1 between the master clock and the clock signal regenerated by the cabinet P1 is measured.
For this measurement, there is a method of accurately measuring both clocks at the time of line installation work. Further, after the line is installed, the same signal transmitted through a different route to a specific mobile terminal is received by the specific mobile terminal, whereby the delay time difference can be measured. S-3. The control unit 2 temporarily stores the Td0 and Td1 as timing information in the storage unit 3 based on the upper CPU control.

S-4. The control unit 2 stores Td1 in the storage unit 3
And Td1 are read, and the difference Td0−Td0−Td1 between Td0 and Td1 is read.
Td1 (hereinafter referred to as delay time information) is calculated. S-5. The control unit 2 calculates the calculated delay time information (Td0−
Td1) is transferred to the delay time adjusting unit 4. S-6. The delay time adjustment unit 4 receives the clock signal transferred from the cabinet P1, delays the clock signal by delay time information (Td0-Td1), and transfers the clock signal to the CS interface circuit 6. Therefore, the delay time adjustment unit 4 receives the clock signal delayed by Td1 with respect to the master clock, and transmits a clock signal delayed by Td0 with respect to the master clock ((b), lower figure).

The same operation is performed for all clock distribution paths. As a result, in all the paths, the clock signal received by the CS interface circuit 6 is delayed by Td0 from the master clock, and the timings match. When a plurality of cabinets are cascade-connected to the clock distribution path, a similar result can be obtained by adjusting the delay time at the subordinate delay time adjustment unit 4. For example, when the cabinet P1 and the cabinet P2 are cascade-connected, the delay time information is set to (Td0− (Td1 + Td).
d2)), the delay time adjustment unit 4 of the cabinet P2 sends a clock signal delayed by Td0 with respect to the master clock.

Although the master clock is limited to the frame clock only for convenience of explanation, it operates in exactly the same manner with other clock signals. Further, by providing a plurality of inputs and outputs of the delay time adjustment unit 4, it is possible to simultaneously adjust the timings of a plurality of clock signals. In the above description, the cordless system for offices has been described as an example. However, the present invention can be applied to various cordless systems in which a plurality of base stations are controlled by an exchange to communicate with a mobile unit. is there.

[0027]

By providing the delay time adjusting unit 4 in the clock distribution path, the timing adjustment of the clock signal in the system becomes easy and accurate, and the following effects are obtained. 1. Radio interference between adjacent cabinets is reduced,
This has led to improved communication quality. 2. Eliminates the need for inefficient star connections
This has led to a reduction in man-hours for laying the system. 3. Since cabinets can be connected in a subordinate manner, system expansion work has been simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram of a CS connection unit.

FIG. 2 is an explanatory diagram showing a flow of a clock signal.

FIG. 3 is a layout diagram of a system.

FIG. 4 is an explanatory diagram of a timing of a clock signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Timing adjustment circuit 2 Control part 3 Storage part 4 Delay time adjustment part 5 CPU interface circuit 6 CS interface circuit

Claims (2)

[Claims] 1. A system comprising: a plurality of base stations each communicating with a mobile station moving within a predetermined area; and a switching station for distributing a master clock serving as a time reference of the entire system to these base stations. In the system, a delay time adjusting unit that delays the master clock by a predetermined time is inserted in a distribution path that distributes the master clock from the exchange to each of the base stations. And a delay time for delaying the master clock by a predetermined time so that each of the base stations receives the master clock from the distribution path at the same timing. 2. The system according to claim 1, wherein T is a delay time of a distribution path having the largest delay amount with respect to the master clock among distribution paths for distributing the master clock to each base station. The predetermined delay time of T or more is defined as the maximum allowable delay time of the master clock, and inserted into each distribution path so that the input timing of the master clock to be input to each of the base stations matches the maximum allowable delay time. A cordless system, wherein a delay time is set by a delay time adjusting unit.