KR20070118807A - Appaturus and method for handoff using diversity gain in mobile communication system - Google Patents

Abstract

A handoff device using a diversity gain in a mobile communication system and a method thereof are provided to use 2 antennas with a serving base station during handoff, so as to move a handoff start point to a target base station from the serving base station, thereby lowering generation frequency of ping-pong as reducing delay time. Signal strength of a signal with a serving base station is measured(410). It is checked whether a value of the measured signal strength is less than a reference value(420,430). If so, a user terminal starts handoff to a target base station(440). The preset reference value is a minimum signal strength value capable of transceiving the signal between the user terminal and the serving base station.

Description

APPARATUS AND METHOD FOR HANDOFF USING DIVERSITY GAIN IN MOBILE COMMUNICATION SYSTEM}

1 is a view schematically showing the structure of a mobile communication system using a general IEEE 802.16e system,

2 is a diagram illustrating a change point of a handoff execution point according to an exemplary embodiment of the present invention.

3 is a block diagram of a user terminal performing a handoff according to an embodiment of the present invention; and

4 is a flowchart illustrating a handoff process according to an exemplary embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system, and more particularly, to an apparatus and a method for reducing the frequency and delay of occurrence of handoff using reception diversity gain.

In the 4th Generation (hereinafter, referred to as '4G') communication system, providing users with services having various quality of service (QoS) with a transmission rate of about 100 Mbps. Active research is in progress. In particular, in the current 4G communication system, broadband wireless access such as a wireless local area network (LAN) system and a wireless urban area network (MAN) system Access: Research is being actively conducted to support high-speed services in the form of guaranteeing mobility and quality of service (QoS) in a BWA communication system. Further, the representative communication system is a broadband wireless access communication system, and the broadband wireless access communication system is one kind of mobile communication system. The Institute of Electrical and Electronics Engineers (IEEE) 802.16a communication system and the IEEE 802.16e communication system are representatively used.

The IEEE 802.16a communication system and the IEEE 802.16e communication system are orthogonal frequency division multiplexing (OFDM) for supporting a broadband transmission network on a physical channel of the wireless MAN system. (Orthogonal Frequency Division Multiple Access (hereinafter referred to as 'OFDMA')).

The IEEE 802.16a communication system is a system currently considering only a single cell structure and a state in which a subscriber station (hereinafter referred to as SS) is fixed, that is, no mobility of the SS is considered.

In contrast, the IEEE 802.16e communication system is a system considering mobility of the SS in the IEEE 802.16a communication system, and the SS having the mobility is called a mobile station. Hereinafter, the mobile terminal and the subscriber terminal will be referred to as a user terminal. The structure of a general IEEE 802.16e communication system is as follows.

1 is a diagram schematically illustrating a structure of a mobile communication system using a general IEEE 802.16e system.

Referring to FIG. 1, the mobile communication system has a multi-cell structure, that is, a specific base station 110 that has a cell 150 different from a specific cell 100 and manages the specific cell 100. ), Another base station 140 that manages the other cell 150, and a plurality of user terminals 111, 113, 130, 151, and 153. Here, signal transmission and reception between the base stations 110 and 140 and the user terminals 111, 113, 130, 151, and 153 is performed using the OFDM / OFDMA scheme.

When the specific user terminal 130 of the user terminals 111, 113, 130, 151, and 153 exists in a boundary area between the specific cell 100 and the other cell 150, the moving direction or other reasons Therefore, handoff may be performed. That is, when the specific user terminal 130 moves to another cell 150 managed by the other base station 140 while transmitting and receiving a signal with the specific base station 110, a handover occurs. A serving BS of a specific user terminal 130 is changed from the specific base station 110 to the other base station 140.

In the mobile communication system using the IEEE 802.16e system, the receiving end is composed of two antennas to improve downlink performance, and when the handoff is not performed, the traffic flowing through the two antennas is combined. In order to improve the performance, a diversity gain method may be used.

However, the handoff is currently designed to use only one antenna instead of two antennas. When two antennas are used, the handoff is not necessary in terms of reception performance. Off may occur. That is, there is a problem that the probability that unnecessary "Ping Pong", which is an unnecessary handoff between base stations, may increase, and a traffic path change phenomenon due to handoff may occur frequently, thereby reducing performance.

Accordingly, there is a need for a technique capable of using two antennas even when performing handoff.

An object of the present invention is to provide a handoff apparatus and method using diversity gain in a mobile communication system.

Another object of the present invention is to provide a device and method for reducing the frequency of handoff in a mobile communication system.

Another object of the present invention is to provide an apparatus and method for reducing handoff delay time in a mobile communication system.

It is still another object of the present invention to provide an apparatus and method for using two antennas during handoff in a mobile communication system.

According to a first aspect of the present invention for achieving the above object, a handoff using diversity gain of a user terminal communicating with a serving BS using a plurality of antennas in a mobile communication system In the Off) method, measuring the signal strength of the serving base station and the signal (Signal), checking whether the value of the measured signal strength is less than a predetermined reference value, and the value of the measured signal strength If the reference value is less than the user terminal, characterized in that it comprises the step of starting the handoff to the target base station (Target BS).

According to a second aspect of the present invention for achieving the above object, a handoff apparatus using diversity gain of a user terminal communicating with a serving base station using a plurality of antennas in a mobile communication system, which is required for handoff processing A control unit for providing information and an indication of a handoff decision to a handoff processing unit and receiving a result and starting a handoff process; and measuring signal strength with a serving base station based on the information and instructions provided from the control unit. And a handoff processing unit which determines to start a handoff when the reference value is less than a reference value and provides the determination information to the control unit.

.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, an apparatus and method for handoff using diversity gain in a mobile communication system will be described.

The handoff technique of the present invention is described by using a carrier to interference and noise ratio (CINR) in which a user terminal measures a signal strength from a base station. same.

2 illustrates a change point of a handoff execution point according to an exemplary embodiment of the present invention. In the present invention, the user terminal measures the CINR combining the signals received through the two antennas with the serving base station at the time of handoff, and measures the CINR from the signal received through one antenna with the target base station do.

Referring to the case of 1) of FIG. 2, first, portions (a, b) indicated by solid lines indicate CINRs of the user terminal and the serving base station, and portions (c, d) indicated by dashed lines indicate a user terminal and a target. CINR with a base station is shown.

A) denotes a data channel, that is, CINR at the time of traffic transmission, when diversity gain is reflected using two antennas, and b) denotes a CINR of a signal, and one antenna The result in the case of using is shown.

In the present invention, when the user terminal measures the CINR obtained by merging the signals received through the two antennas with the serving base station at the time of handoff, the reason shown in the case of using one antenna as shown in b) Is to compare the use of one conventional antenna and the use of two antennas of the present invention.

When performing handoff, when considering the diversity gain using two antennas when transmitting and receiving traffic, the same path gain is maintained even after moving from the serving base station to the target base station more distantly than when using one antenna. Can be. That is, even after moving further toward the target base station in distance, the same CINR as in the conventional method can be maintained.

Therefore, when the user terminal is handed off, the handoff start point can be moved in the target base station direction (f)-> (g). Of course, the signal CINR value between the serving base station and the user terminal is within a range capable of transmitting and receiving signals with each other.

Referring to the case of 2) of FIG. 2, first, portions (a, b) indicated by solid lines indicate CINRs of the user terminal and the target base station, and portions (c, d) indicated by dotted lines indicate the user terminal and the serving. CINR with a base station is shown.

C) represents the CINR of the data channel, that is, the traffic transmission, diversity gain is reflected using two antennas, and d) represents the CINR of the signal, and one antenna. The result in the case of using is shown.

In the present invention, when the user terminal measures the CINR obtained by merging the signals received through the two antennas with the serving base station at the time of handoff, the result of the case of using one antenna as shown in d) Is to compare the use of one conventional antenna and the use of two antennas of the present invention.

When performing handoff, when considering the diversity gain using two antennas when transmitting and receiving traffic, the same path gain is maintained even after moving from the serving base station to the target base station more distantly than when using one antenna. Can be. That is, even after moving further toward the target base station in distance, the same CINR as in the conventional method can be maintained.

Therefore, when the user terminal is handed off, the handoff start point can be moved in the target base station direction ((f)-> (e)). Of course, the signal CINR value between the serving base station and the user terminal is within a range capable of transmitting and receiving signals with each other.

According to the present invention, the CINR between the user terminal and the serving base station is measured and the handoff start point is moved by lowering the reference value of the CINR required for performing the existing handoff function.

Table 1 below shows a gain difference between using one antenna and using two antennas.

User terminal 1 One 2 3 4 Average 1 antenna 0.4 -2 -0.04 -0.35 -0.4975 2 antennas 6.788 4.6 6.115 5 5.62575 Difference 6.388 6.6 6.155 5.35 6.12325

Referring to Table 1 above, in the average value, the gain difference between one antenna and two antennas is 6.123 dB on average. This indicates that when the handoff start point is moved toward the target base station, the signal strength with the serving base station can be moved to about 6 dB lower.

In fact, if the handoff is started where the signal strength with the serving base station is 1.5 dB, it indicates that the handoff can be started at about 6 dB lower, that is, -4.5 dB.

In addition, the handoff start point can be moved toward the serving base station and the target base station, as compared with the case where the midpoint of the overlapping area of the existing jurisdiction of the two base stations is the handoff start point. Similar to the split towards base station.

Thus, the difference in CINR between the user terminal and the serving and target base station in the divided region is relatively clear, so the possibility of ping pong is lowered.

Although the present invention has been described with the CINR as an embodiment, any value may be used as long as it represents a signal strength between the user terminal and the serving base station.

3 is a block diagram of a user terminal performing a handoff according to an embodiment of the present invention.

First, referring to FIG. 3, the controller 301 controls the overall operation of the user terminal. For example, it performs processing and control for voice call and data communication, and provides the handoff processing unit 307 with information necessary for handoff, such as CINR with a serving base station, in addition to the usual functions according to the present invention. Processing for off (eg, measuring CINR value, determining whether to perform handoff) is instructed and handoff is performed according to the result. The control unit 301 provides a control message received from the base station to the message processing unit 303 and receives a message to be transmitted to the base station from the message generating unit 305 to the interface module 311.

The handoff processing unit 307 measures the CINR with the serving base station based on the instruction and the provision data of the control unit 301 to determine whether the current position or the current state is when the handoff starts. Give results.

For example, when the CINR value between the serving base station and the user terminal is measured and the CINR value becomes a reference value that can be handed off, the handoff is determined.

The reference value represents a minimum signal strength value at which a user terminal can transmit and receive the signal with a serving base station, and may be changed for reasons such as cell planning, surrounding environment, implementation characteristics, and the like.

The message processing unit 303 decomposes a control message received from the base station and provides the result to the control unit 301.

The message generator 305 generates a message to be transmitted to the base station under the control of the controller 301. The message generator 305 may generate a handoff related message. The message generated by the message generator 305 is transferred to the interface module 311 through the controller 301.

The storage unit 309 stores a program for controlling the overall operation of the user terminal and temporary data generated during program execution. That is, the storage unit 309 may generally store data and control information to be transmitted from the user terminal to the base station.

The interface module 311 is a module for communicating with the base station, and includes an RF processor and a baseband processor. The RF processor converts a signal received through an antenna into a baseband signal and provides the baseband signal to the baseband processor, and transmits a baseband signal from the baseband processor on an actual air. Transmit to and transmit through the antenna.

For example, when the broadband wireless access method is used, the baseband processor transfers the FFT (Fast Fourier Transform) operation and channel decodes the signal from the RF processor to transfer the original information data to the controller 301. Conversely, channel encoding and inverse fast fourier transform (IFFT) operations are performed on the data from the controller 301 and provided to the RF processor.

In the above block configuration, the controller 301 controls the message processor 303, the message generator 305, and the handoff processor 307. That is, the controller 301 may perform the functions of the message processor 303, the message generator 305, and the handoff processor 307.

In the present invention, it is shown to configure them separately to explain each function separately. Therefore, in the case of actually implementing a product, all of them may be configured to be processed by the controller 301, and only some of them may be configured to be processed by the controller 301.

Now, the handoff process will be described.

4 is a flowchart illustrating a handoff process according to an exemplary embodiment of the present invention. In the present invention, the user terminal measures the CINR combining the signals received through the two antennas with the serving base station at the time of handoff, and measures the CINR from the signal received through one antenna with the target base station do.

Referring to FIG. 4, when the user terminal performs handoff in step 410, a signal signal strength reference value (CINR) for determining a handoff start point is set. The reference value may be set differently for reasons such as cell planning, surrounding environment, implementation characteristics, and the like, and may be input by the producer or service provider during implementation. The user then uses the user terminal.

In operation 420, the user terminal performs general communication.

Thereafter, in step 430, while the user terminal performs communication while moving, the signal strength (CINR) between the serving base station and the serving base station is determined in the overlapping region of the serving base station and the target base station, and the input signal signal strength value is input in step 410. Check if it is below.

The process of step 430 is to allow the user terminal to start the handoff process closer to the target base station closer to the target base station in the overlapping area where the signal can be transmitted and received with the serving base station.

If the signal strength (CINR) with the serving base station is less than or equal to the signal signal strength reference value in step 410, the mobile station proceeds to step 440 to perform a handoff to the target base station.

The process of step 440 indicates that the user terminal moves closer to a target base station closer to the target base station in a distance from the overlapping area where signals can be transmitted and received with the serving base station, and then performs a handoff. Proceed with general communication.

The algorithm of the present invention is then terminated.

Performance according to the experimental results of the present invention are as follows.

Table 2 below shows the results of experiments in specific region 1 (Sinchon region).

HO Th (dB) HO count Re-entry HO-IND Pingpong HO latency DE RER (max) User terminal 1 1.5 25 One 35 3 279.8 5 0 -One 22 2 23 2 204.54 3.02 0 User terminal 2 1.5 25 3 34 3 335 5.23 0 -One 26 2 30 4 350.19 5.72 0 -4.5 20 0 20 0 207.25 6.18 0

In Table 2, "HO Th" represents a reference value of the CINR with the serving base station from which the portable terminal starts handoff. "Re-entry" indicates a case in which the portable terminal reenters the network after failing handoff, and "HO-IND" indicates the number of transmission of the "HO-IND" message which is a handoff related signal message. A large number indicates that a message transmission error has occurred.

 "Pingpong" indicates the number of times ping-pong has occurred during the handoff, and "HO Latency" indicates the delay time during the handoff. "DE" (DL-MAP Error) indicates the number of reception errors of "DL-MAP Error" at handoff. "PER" represents the maximum error rate (%).

When the technique of the present invention is used in the specific region 1, the number of handoffs is reduced to 80% compared to the conventional method, and the delay time during the handoff is also reduced by about 30%.

Table 3 below shows the results of experiments in specific region 2 (Gangnam region 1).

HO Th (dB) HO count Re-entry HO-IND Pingpong HO latency DE RER (max) User terminal 1 1.5 23 5 33 One 533.69 12.43 0.92 -4.5 12 One 14 One 210.41 7.93 One

When the technique of the present invention is used in the specific region 2, the number of handoffs is reduced to 50% compared to the conventional method, and the delay time at the time of handoff is also reduced by 60%.

Table 4 below shows the results of experiments in specific region 3 (Gangnam region 2).

HO Th (dB) HO count Re-entry HO-IND Pingpong HO latency DE RER (max) User terminal 1 1.5 21 2 39 3 380.71 5.33 0 -4 20 0 20 3 220.25 5.56 0 -4.5 18 0 18 One 190 5.49 0

When the technique of the present invention is used in the specific region 3, the number of handoffs is reduced to 85% compared to the conventional method, and the delay time at the time of handoff is also reduced by about 50%.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, in the present invention, by using two antennas with the serving base station during handoff, the handoff start point can be moved from the serving base station to the target base station, thereby reducing the number of occurrences of ping-pong and reducing the delay time.

Claims (9)

In a handoff method using diversity gain of a user terminal communicating with a serving BS using a plurality of antennas in a mobile communication system, Measuring a signal strength of the serving base station and a signal; Checking whether the value of the measured signal strength is equal to or less than a preset reference value; And when the value of the measured signal strength is less than or equal to a reference value, starting the handoff by the user terminal to a target BS. The method of claim 1, The preset reference value is a minimum signal strength value that the user terminal can transmit and receive the signal with the serving base station. The method of claim 1, And the user terminal communicates with the target base station using one antenna. The method of claim 1, The signal strength is characterized in that the carrier to interference noise ratio (CINR). A handoff apparatus using diversity gain of a user terminal communicating with a serving base station using a plurality of antennas in a mobile communication system,  A control unit which provides the handoff processing unit with information necessary for handoff processing and an instruction for handoff determination, receives the result, and starts the handoff process; And a handoff processing unit for measuring a signal strength with a serving base station according to the provision information and instructions from the control unit to determine the start of the handoff when the reference value is less than a preset reference value and to provide the determination information to the control unit. Characterized in that the device. The method of claim 5, The device, And an interface module for converting the information from the control unit according to a prescribed radio standard and transmitting the information through the antenna, and converting the information received from the serving base station into a baseband signal and providing the information to the handoff processing unit. Device. The method of claim 5, The predetermined reference value is a device, characterized in that the minimum signal strength value that the user terminal can transmit and receive the signal with the serving base station. The method of claim 5, And the user terminal communicates with the target base station using one antenna. The method of claim 5, The signal strength is characterized in that the carrier to interference noise ratio (CINR).

Images