KR20040060207A - Hand off Method Using Position Information of Mobile Body - Google Patents

Abstract

PURPOSE: A handoff determining method using position of a mobile is provided to accomplish reliability of wireless communication by controlling handoff with position information of a mobile. CONSTITUTION: If a value of a reception RSS(Received Signal Strength) of a railroad-side system providing a wireless line measured by a mobile becomes smaller than a minimum RSSthresh(dB) required for maintaining communication, the mobile detects failure of the system and requests handover from a different duplex railroad-side system so as to allocate a channel. In a normal state, a network determines the handover, but when such failure occurs, the mobile should determine the handover.

Description

Hand off method using position information of mobile unit {Hand off Method Using Position Information of Mobile Body}

The present invention relates to a handoff determination method using position information of a moving object, and more particularly, to a handoff control method at a cell boundary of a mobile communication terminal mounted on a moving object.

In general, a handoff is a process in which a cellular system transfers an ongoing call to another cell when the user moves from one cell area to another cell area. In handoff, the handoff incidence and handoff delay are important variables. If the incidence of handoff is high, it can increase the load on the network and reduce the available channel of traffic. If the handoff does not occur in a timely manner, the transmission quality is lower than the reference value and the amount of co-channel interference is increased.

In the first and second generation of cellular systems, the received signal strength, averaging magnitude, threshold (usually line quality threshold) and hysteresis margin are used as handoff decision criteria. As a combination of these criteria, a handoff decision algorithm has been proposed and used in a mobile communication network. When the mobile station moves from base station 1 to base station 2 as shown in FIG. 1, the average signal strength of base station 1 decreases as the mobile station moves away from base station 1. On the other hand, the signal strength of base station 2 increases as the mobile station approaches base station 2.

(1) Relative Signal Strength Comparison Method

This method always chooses the strongest signal arriving from the base station. The decision is based on the average of the received signals. In Figure 1 the handoff will occur at position A. Although the signal strength of base station 1 is sufficient, unnecessary handoff occurs.

(2) Signal strength comparison method including threshold

This method results in a handoff when the current signal is weak enough (i.e., less than the threshold) and when the signal from another base station is stronger than the current one. The effect of the thresholds depends on the value compared to their magnitude at the point where the signal strengths of the two base stations are equal. If, when the threshold value is higher than the value when the signal strength of the two base stations are the same, that is, even if the threshold of the first T ₁ day, the above-mentioned (1) the signal strength is the same way as in the comparative method the handoff location A Happens in If the threshold is T _{2 in} Fig. 1, the handoff is delayed until the current signal strength received by the mobile station is less than the signal strength at position B.

If the threshold is T ₃ , the delay is so large that the mobile station goes deep into the new cell while communicating with the channel of cell 1 without performing a handoff. This reduces the communication line quality, as a result of which the signal can be truncated. This will also have greater interference for co-channel users.

(3) Signal strength comparison method including hysteresis

This method allows handoff only when the signal strength of the new base station is stronger than the current signal strength (as strong as the hysteresis margin H in FIG. 1). In this case a handoff will occur at position C. This technique prevents repeated handoff, a so-called ping-pong effect, caused by the signal strength received from two base stations oscillating too quickly.

(4) Comparison of signal strength including hysteresis and threshold

This method allows handoff to the new base station only when the current signal strength falls below the threshold and the signal size of the new base station is greater than the current signal strength by a given hysteresis margin. In FIG. 1, handoff occurs at position C when the threshold is T ₁ or T ₂ . And if the threshold is T ₃ , it will happen at position D. Application fields are currently applied in GSM systems.

In the conventional handoff method as described above, the handoff is always performed correctly when it is in a state suitable for each method, but otherwise, the handoff is not properly performed.

In order to solve this problem, the present invention is to provide a handoff determination method using the position information of the mobile to ensure the reliability of wireless communication by controlling the handoff by using the position information of the mobile.

1 is a graph illustrating a handoff using the received signal strength;

2 is a flowchart illustrating a steady state handoff procedure;

3 is a conventional handoff determination algorithm,

4 is a handoff algorithm according to the present invention,

5 is a flowchart illustrating a handoff procedure when a railroad system breaks down;

6 is an explanatory diagram for explaining a failure detection method and a channel allocation method.

A handoff determination method using the position information of a moving object according to the present invention will be described in detail with reference to the accompanying drawings.

The following description describes the steady state handoff. In most mobile communication systems, the handoff is determined by comparing received signal strengths of neighboring cells to determine a handoff time.

The handoff method of the present invention is based on this.

At this time, the average value of the N sample values (1 to 5 sample values) of each cell is compared according to a specific criterion to select a cell in which RSS is dominant. The central station determines the handoff from the central station rather than the mobile because the central station knows the number and location of the mobiles belonging to each cell.

Since the central station knows the position information of the moving object, it can use this information in the algorithm for determining the handoff time. In mobile communication, hysteresis (H) and threshold (T) are applied together to reduce frequent handoffs, but this results in handoff delay, which in turn degrades the wireless link and co-channel interference. This happens. In order to solve this problem, by using location information together with H and T, handoff delay and frequent handoff are simultaneously reduced.

2 shows a handoff procedure using location information in a normal state. Based on the RSS values reported by the moving object and the criterion of FIG. 3, the central station determines whether to handoff, determines a lineside system to be in charge, and transmits a handoff command to the moving object. The mobile unit sends a completion message to the central station when the handoff is completed, and the existing trackside system retrieves the channel assigned to the mobile unit.

(1) Handoff Decision Algorithm of General Mobile Communication System

In FIG. 3, Pold and BSold represent RSS and line side systems of the current cell, respectively, and Pnew and BSnew represent RSS and line side systems of the cell to be moved. H and T are hysteresis and threshold, respectively. Handoff can occur when Pnew is H larger than Pold, to reduce the pingpong effect that occurs at cell boundaries. However, this has the disadvantage of causing excessive cell overlap by causing a handoff in BSnew rather than a cell boundary.

(2) Proposed Handoff Decision Algorithm

Handoff decision algorithms using T and H can introduce handoff delays and degrade line quality. Here, the location information of the moving object is used to solve this problem. Since the moving object position is detected from the ground (or moving object) and periodically reported to the central station (about 0.5 seconds), the central station can use the location information together with the RSS measured and reported by the moving object when determining the handoff.

When the vehicle position crosses the existing cell boundary (cell boundary in FIG. 4), a handoff to a new cell must occur to eliminate the handoff delay. If a handoff has occurred to the new cell before then, the state remains. In the cell area outside the boundary, the vehicle system continuously reports RSS to the central station in case of failure, and the central station uses the designed H and T to determine the handoff.

In FIG. 4, handoff_state is a criterion for distinguishing a cell to which a cell belongs and a cell in a progress direction.

2) Handoff in case of failure

Shows how to perform a handoff if a failure occurs in a trackside system. First, a method of detecting a failure of a trackside system may be divided into two types according to the presence or absence of a vehicle system in a cell of a specific trackside system.

(1) No moving object

The mobile unit periodically measures the RSS of the cell in the steady state and reports it to the central station. Using the RSS reported by the mobile and the location information of the mobile, the central station can identify the faulty trackside system and have the vehicle system moving to that cell perform a handoff to another redundant railside system.

A simple way to identify a railway station system where the central station has failed is RSS << Mean (RSS) at when the vehicle system is located at αR (α <1, R: cell radius) from the lineside system WS1 of its cell as shown in FIG. If αR is satisfied, it is determined as a failure. Mean (Rss) is determined by the network operator through experiments when designing a cell. The algorithm of the present invention should be included in the handoff decision algorithm of the central station and the handoff procedure is the same as in FIG.

(2) state of moving object

If the incoming RSS value of the trackside system that was providing the wireless line measured by the moving object is less than the minimum RSS _thresh (dB) required to maintain the communication, the moving object detects a failure of the lineside system and duplicates other The system is allocated a channel through a handover request. This procedure is performed in the order as shown in FIG. In the normal state, the handover is determined by the network, but when a failure occurs, the mobile unit must determine the handover.

(3) Channel reservation method for handoff

If there is no empty channel in the cell to be moved, the mobile may have a problem of losing a radio line. In mobile communication, this is called call blocking, and this problem is solved by combining the handoff method and the resource allocation method of the network. The present invention proposes a method associated with a service permission algorithm to remove call blocking. As shown in FIG. 6, the mobile station requests the central station to reserve the channel of WS2 when passing through the reservation point βR using the location information of the mobile station. If there is no free channel, the central station will permit the train to operate only up to the αR position, and if there is a free channel, it will proceed to the cell of WS2.

The present invention as described above can be summarized as follows.

(1) In the steady state of the communication network, the central station performs the handoff at the cell boundary by using the position information of the moving object and the existing method (relative signal, threshold value, hysteresis).

(2) If the mobile body is in a normal state and the communication device installed on the ground has a failure, the mobile body is forced to determine the handover.

(3) If a communication device installed on the ground that is not related to the moving object is damaged, the central station detects it and performs a handoff.

(4) By using the location information of the moving object, the channel reservation is set in advance by the central station to block the radio line loss.

In addition, the operation method of the system is applicable to communication network management because it utilizes the location information of the moving object.

As described above, the present invention utilizes the position information of the moving object to process the software without adding a separate device as compared to the existing handover method.

In particular, since the rate of handoff occurring at the cell boundary is greatly reduced, the available channel of traffic can be increased by reducing the load applied to the network. Since the handoff occurs in a timely manner, the threshold of transmission quality is improved and the amount of co-channel interference is reduced.

In the above, the present invention has been illustrated and described with reference to specific preferred embodiments, but the present invention is not limited to the above-described embodiments and the general knowledge in the technical field to which the present invention pertains without departing from the spirit of the present invention. Various changes and modifications will be made by those who possess.

Claims (5)

In the handoff determination method using the position information of the moving object, (a) identifying position information of the moving object; And and (b) forcibly determining a handoff of the moving body in order to maintain an optimal call state by using the positional information of the moving body. The method of claim 1, wherein the handoff decision in step (b) is performed by the central station for handoff in the cell boundary by using the position information, the relative signal, the threshold value, and the hysteresis of the moving object in a normal state of the communication network. Handoff determination method using the position information of the moving object, characterized in that. The position of the moving object according to claim 1, wherein the handoff determination in step (b) is performed by forcibly determining the handoff in the moving object when the moving object is in a normal state and a failure occurs in a communication device installed on the ground. Information handoff decision method. The method of claim 1, wherein the handoff decision in step (b) is not related to the moving object, and when the communication device installed on the ground has a failure, the central station detects it and forcibly performs the handoff. Handoff determination method using the position information of the moving object. The method of claim 1, wherein the handoff determination in the step (b) uses the position information of the moving object to set the channel reservation in advance in the central station to block the radio line loss. How to determine handoff.