KR20000061351A - Method for controlling of transmittion clock in mobile communication system - Google Patents

Abstract

PURPOSE: A method for controlling transmission clocks of a mobile station on a mobile communication system is provided to perform calls in areas having restricted round trip delay(RTD) processes, by differently controlling the transmission clocks according to a distance between a base station and the mobile station operated with a normal mode and an extend mode. CONSTITUTION: A round trip delay(RTD) is received from a base station in a state of operating in a normal mode. The received RTD is compared with a reference RTD(RTD_ref). If the received RTD is less than or same with the reference RTD, the present normal mode is maintained to perform a determined next process. If the received RTD is more than the reference RTD, an operation mode of a mobile station is converted into an extend mode. Transmission clocks of the mobile station are controlled according to the received RTD in the extend mode. Controlled values of the transmission clocks are transmitted to the base station.

Description

Method for controlling of transmittion clock in mobile communication system

The present invention relates to a mobile station transmission clock control in a code division multiple access (CDMA) mobile communication system. In particular, the present invention relates to a mobile station transmission clock depending on a distance from a base station in a mobile station operating in a normal mode and an extended mode. The present invention relates to a method for controlling a mobile station transmission clock in a mobile communication system in which a call can be made even when there is a restriction of a round trip propagation delay (RTD) by controlling the differential.

In the normal mode, the normal mode refers to a mobile station operating mode when the distance between the mobile station and the base station is located within the default set talkable distance, and the extended mode refers to a mobile station operating mode when the distance between the mobile station and the base station falls outside the set default talking distance. Say. The operating mode (normal mode and extended mode) of such a mobile station is not a well-known standardized term but is a term for the description of a specific mobile station intended to realize a call by extending coverage by adjusting a transmission clock.

In general, all base stations of a digital mobile communication system (digital cellular mobile communication system, personal digital communication system) using the CDMA system are time-synchronized based on the CDMA system time. The mobile station also synchronizes the time with the CDMA system reference time using the time information provided by the base station. Here, the base station obtains the system reference time using the GPS time, but the mobile station synchronizes time with the base station using the time information transmitted from the base station.

Therefore, the reference time of the mobile station is a point in time delayed by the propagation delay time until the time information transmitted from the base station reaches the mobile station. The degree of delay here depends on the relative distance between the mobile station and the base station and the surrounding environment.

The mobile station uses an access channel to access a base station system in the coverage area. The access channel is a channel used when a mobile station registers or requests a call as a reverse channel from a mobile station to a base station, and is configured in a unit called an access channel slot. Therefore, the access channel message is allocated to one access channel slot. The access channel message is composed of a minimum of 4 frames (frames: 20ms) and a maximum of 26 frames depending on the size, and uses an appropriate value according to the system. The access channel message transmits a message frame at the time when the slot starts, and the next message waits until the start of the slot, and then transmits the message frame. Thus, the boundary of the access channel slot coincides with the frame boundary.

On the other hand, when the mobile station attempts to access the base station system in the coverage area, it transmits an origination message using an access channel. In this case, one access channel slot is used to transmit one outgoing message. The outgoing message includes information such as mobile station information (terminal number, mode indicating whether the mobile station is in CDMA-only mode or dual mode, class indicating whether it is PCS or cellular phone, etc.) and called number. If the mobile receives an acknowledgment from the system (base station) within a certain time for an outgoing message sent through the access channel, the system access attempt is successfully terminated. However, if the mobile station does not receive an acknowledgment from the system (base station) within a certain time, it resends the outgoing message and waits for an acknowledgment. If it does not receive an acknowledgment again, it retries. The number of retransmissions is defined (determined by the sum of Num_Step and Max_Req_Seq in the access parameter message sent from the base station to the mobile station), and the system does not receive an acknowledgment from the system after retransmitting the prescribed number of times. The connection attempt terminates with a failure.

Therefore, the base station does not know when the mobile station attempts to connect. Therefore, the base station continuously monitors the access channel. Here, it is meaningless for the mobile station to search for the access signal for the entire time by transmitting a message using the access channel slot, and access the mobile station within a certain range that the access signal of the mobile station can reach based on a frame boundary every 20 ms. Searching for signals is most advantageous for mobile station acquisition. The time range in which the base station searches to capture the access signal of the mobile station is called a search window.

The search window is determined by considering the propagation delay and the basic processing delay according to the service radius of the base station, and the service radius of the base station is determined at the base station design and optimization stage. The service radius of each base station can be appropriately adjusted according to the surrounding environment, neighboring base stations, and population density. Base stations installed in densely populated and heavily populated areas reduce the service radius (for example, 1 to 3 km), while areas with few buildings and low population density tend to increase the service radius (for example, For example, 20 to 30 km).

Next, calculating the time range in which the access signal of the mobile station can reach the base station is as follows. The minimum time that the access signal of the mobile station can reach the base station is when the mobile station is right next to it (there is no propagation delay in the air). The arrival time at this time is the sum of the transmission delay of the base station, the processing delay of the mobile station, and the reception delay time of the base station. The maximum time that the access signal of the mobile station can reach the base station is when the mobile station is in the outermost part of the base station service area. The arrival time at this time is the sum of the minimum time and the propagation delay * 2 in the air. The propagation delay in the air is added twice because the mobile station sends the signal to the base station based on the time information of the base station, and the actual time obtained by the mobile station is the time delayed by the delay from the base station to the mobile station. Therefore, the time that the signal arrives at the base station when attempting to access the mobile station should add up the original delayed time (delay time until the time information is transmitted from the base station to the mobile station) until the signal arrives at the base station from the mobile station. . For this reason, the propagation delay in the air is also called a round trip delay (RTD).

On the other hand, when the mobile station transmits, the number of preambles specified by the operator is transmitted first, and the base station channel element starts demodulation using this preamble. Therefore, the maximum allowable delay of the mobile station signal reaching the base station is determined according to the size of the window set in the base station.

Preamble-Window-Length + Preamble_PN by starting the search from the preamble-PN-offset (Preamble_PN_offset) away from the system time (access channel slot) in response to the half PN chip during the preamble search of the access channel access probe. _ Search up to offset. Accordingly, the base station adjusts the PN offset to the largest correlation value among (preamble_window_length) / 4 correlation results.

However, such a conventional mobile communication system has a disadvantage in that it cannot process a signal having a delay of more than a Walsh symbol due to RTD constraints. In other words, when the signal transmitted from the mobile station arrives, the base station cannot capture the mobile station access signal when a delay of two or more Walsh symbols occurs.

Accordingly, the present invention has been proposed to solve all the problems occurring in the prior art as described above,

SUMMARY OF THE INVENTION An object of the present invention is a mobile station operating in a normal mode and an extended mode, where a restriction of round trip propagation delay (RTD) is caused by differentially controlling the mobile station transmission clock according to the distance from the base station. The present invention also provides a method for controlling a mobile station transmission clock in a mobile communication system capable of making a call.

Mobile station transmission clock control method according to the present invention for achieving the above object,

Receiving a round trip propagation delay (RTD) value transmitted from a base station in normal mode;

Comparing the received round trip propagation delay value with a set round trip propagation delay value;

Switching an operation mode to an extended mode when the received round trip propagation delay value is greater than the round trip propagation delay value set as the reference;

Adjusting a mobile station transmit clock in accordance with a round trip propagation delay value received after switching to the extended mode;

And transmitting the adjusted transmission clock adjustment value to the base station.

In the above, the mobile station transmits the transmission clock adjustment value through the access channel if the connection channel with the current base station is the access channel every predetermined time after the transmission clock adjustment, and transmits the transmission clock adjustment value through the traffic channel if the connection channel is the traffic channel. It features.

Further, the base station transmits the RTD value to the mobile station at regular intervals through the access channel or the traffic channel, and when the transmission clock adjustment value is received from the mobile station, corrects the RTD value according to the received transmission clock adjustment value to the access channel or traffic channel. It is characterized in that for transmitting to the mobile station through.

1 is a block diagram of a mobile station in a mobile communication system to which the present invention is applied;

2 is a flowchart illustrating a method for controlling a mobile station transmission clock in a mobile communication system according to the present invention;

3 is a transmission and reception diagram of a clock adjustment value and a round trip propagation delay (RTD) between a base station and a mobile station in the present invention;

4 is an explanatory diagram for explaining a mobile station transmission clock adjustment value in the present invention;

5 is a flowchart illustrating a process of changing an RTD value of a base station in the present invention.

<Description of the code | symbol about the principal part of drawing>

10: clock generator

20: base station signal receiving unit

30: clock adjustment unit

40: mobile station signal transmitter

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail.

1 is a block diagram of a mobile station in a mobile communication system to which the present invention is applied.

As shown, the clock generation unit 10 for generating a clock required by the mobile station from the time information transmitted from the base station, the base station signal receiving unit 20 for receiving a signal transmitted from the base station, and the base station signal receiving unit ( According to the round trip propagation delay (RTD) value received at 20), the clock obtained by the clock generator 10 is transmitted to the mobile station signal transmitter 40 of the next stage as it is, or the clock obtained by the clock generator 10 is adjusted. And a clock adjusting unit 30 for transmitting to the mobile station signal transmitting unit 40, and a mobile station signal transmitting unit 40 for transmitting a mobile station signal synchronized with a clock obtained from the clock adjusting unit 30.

2 is a flowchart illustrating a mobile station transmission clock control method in a mobile communication system according to the present invention.

As shown, receiving the RTD transmitted from the base station in the normal mode (S101 ~ S102), comparing the received RTD and the reference RTD (RTD_ref) set as a reference (S103), the received Maintaining the current normal mode and performing a predetermined next operation when the RTD is less than or equal to the reference RTD (S104 to S105); and switching the mobile station operation mode to the extended mode when the received RTD is larger than the reference RTD. Step S106, adjusting the transmission clock according to the reception RTD in the extended mode (S107), and transmitting the transmission clock adjustment value to the base station after the transmission clock adjustment (S108).

Hereinafter, with reference to the drawings 1 to 5 attached to the operation of the present invention configured and made as described above in detail as follows.

First, the clock generator 10 generates a clock required by the mobile station with time information transmitted from the base station and inputs the clock to the base station signal receiver 20 and the clock adjuster 30, respectively.

In such a state, the clock adjusting unit 30 compares the round trip propagation delay (RTD) value obtained from the base station signal receiving unit 20 with the reference RTD (RTD_ref), and generates the clock generator 10 according to the magnitude of the case. The clock is adjusted and transmitted to the mobile station signal transmitter 40.

In this case, when the mobile station operates in the normal mode or the extended mode, the base station transmits the current RTD value to the mobile station every predetermined period (T_step1) because the distance between the mobile station and the base station changes according to the movement of the mobile station. . In this case, the base station transmits the RTD calculated by the base station to the mobile station through a paging channel when the mobile station is in the idle state (Idle state), otherwise, when the mobile station is busy, the traffic is transmitted at the predetermined period (T_step1). The RTD calculated by the base station is transmitted to the mobile station through a traffic channel.

Then, as shown in Fig. 2, the mobile station receives the RTD transmitted from the base station in the ultra-high operating state (operating in the normal mode) (S101) (S102). The received RTD is compared with the reference RTD (RTD_ref) (S103). When the received RTD is equal to or smaller than the reference RTD, the normal mode, which is the current operation mode, is maintained (S104). In the normal mode as described above, an existing predetermined operation is performed (S105).

On the other hand, when the received RTD is larger than the reference RTD (RTD_ref), the clock adjusting unit 30 of the mobile station switches the operation mode to the extended mode (S106) and adjusts the transmission clock according to the received RTD (S107). ). 4 shows a transmission clock adjustment value when the mobile station adjusts a transmission clock according to a reception RTD. This transmission clock adjustment is actually advanced in time for the transmission clock in proportion to the distance between the mobile station and the base station. Here, when the mobile station moves at high speed, the RTD value of the base station fluctuates rapidly. Therefore, since the change in the clock adjustment value of the mobile station is faster accordingly, the time interval for transmitting the RTD to the mobile station should be changed to be smaller.

The mobile station signal transmitter 40 transmits the mobile station signal to the base station based on the adjusted transmission clock, and transmits a transmission clock adjustment value to the base station through a channel connected to the current base station (S108). That is, if the connection channel with the current base station is an access channel, the transmission clock adjustment value is transmitted to the base station through the access channel every predetermined period (T_step2). If the connection channel is a traffic channel (during a call), the transmission channel is fixed through the traffic channel. The transmission clock adjustment value is transmitted through the traffic channel every period (T_step2). Here, the reporting time interval of the transmission clock adjustment value reported by the mobile station to the base station is changed according to the speed of the mobile station. That is, if the mobile station is moving fast, the transmission clock adjustment value transmission interval transmitted to the base station should be relatively fast.

The reason why the mobile station adjusts the transmit clock and then transmits the adjusted transmit clock adjustment value to the base station is that the RTD transmitted from the base station does not adjust the clock of the clock adjuster 30 of the mobile station when the mobile station operates in the normal mode. Because it is not, the exact value is. However, when the mobile station operates in the extended mode, since the transmission clock of the mobile station is changed, the RTD value calculated by the base station is not accurate. Therefore, the base station must know exactly which mode the mobile station is operating in to accurately calculate the RTD. For this reason, when the transmission clock is adjusted by the mobile station, the adjusted transmission clock adjustment value is transmitted to the base station at regular intervals.

On the other hand, when the base station receives the transmission clock adjustment value from the mobile station as shown in Fig. 5 (S112), the base station corrects the RTD value according to the received transmission clock adjustment value (S114). On the other hand, when the transmission clock adjustment value is not transmitted from the mobile station, the current RTD value is kept as it is (S113).

3 shows an RTD and a mobile clock transmission clock adjustment value transmission / reception relation channel between a base station and a mobile station.

As shown, the base station transmits the RTD to the mobile station through the paging channel when the mobile station is idle, and transmits the RTD to the mobile station via the traffic channel when the mobile station is busy.

Similarly, the mobile station transmits the mobile station transmit clock adjustment to the base station through the access channel if the current idle state, and transmits the mobile station transmit clock adjustment to the base station through the traffic channel when the current connection channel is a traffic channel.

As described above, the present invention adjusts the mobile station transmission clock based on the RTD which changes according to the distance between the base station and the mobile station, so that the call can be made even when the distance between the mobile station and the base station is out of the basic callable distance. Extension is possible.

In addition, by extending the service radius as described above, there is an advantage that the number of unnecessary base stations can be reduced in the area where the number of service subscribers is small, and in particular, by extending the service radius in the coastal area, it is possible to increase the range of on-line mobile communication area in the coast There is an advantage to that.

Claims (5)

A mobile station of a CDMA mobile communication system, Receiving a round trip propagation delay (RTD) value transmitted from a base station in normal mode; Comparing the received round trip propagation delay value with a set round trip propagation delay value; Switching an operation mode to an extended mode when the received round trip propagation delay value is greater than the round trip propagation delay value set as the reference; Adjusting a mobile station transmit clock in accordance with a round trip propagation delay value received after switching to the extended mode; And transmitting the adjusted transmission clock adjustment value to the base station. 2. The method of claim 1, wherein the mobile station transmits a transmission clock adjustment value through a connection channel if the connection channel with the current base station is an access channel every predetermined time after the transmission clock adjustment, and if the connection channel is a traffic channel, the transmission clock adjustment through the traffic channel. And a mobile station transmission clock control method in a mobile communication system. The mobile station transmission clock control in a mobile communication system according to claim 1 or 2, wherein the mobile station varies transmission time intervals of transmission clock adjustment values transmitted to the base station according to a current movement speed after transmission clock adjustment. Way. The method of claim 1, wherein the base station transmits the RTD value to the mobile station at regular intervals through an access channel or a traffic channel, and corrects the RTD value according to the received transmission clock adjustment value when the transmission clock adjustment value is received from the mobile station. A mobile station transmission clock control method in a mobile communication system. The method according to claim 1 or 4, wherein the base station varies a transmission time interval of an RTD transmitted to the mobile station in response to the moving speed of the mobile station.