KR20080043924A - Apparatus and method for excuting partial handover in broadband wireless communication system - Google Patents

Abstract

An apparatus and a method for performing partial handover in a broadband wireless communication system are provided to improve the communication quality of a terminal located in a cell boundary and increase the flexibility of resource utilization. An active set management unit(527) manages resource situation of adjacent base stations and reception signal strength threshold value information of each service. If a reception signal strength received from a serving base station is lower than a certain threshold value, a message generator(531) generates a connection request message for connecting the first service corresponding to the certain threshold value via an adjacent base station. A service connection controller(529) controls to connect the first service via the adjacent base station and connect the second service via the serving base station. The active set management unit updates the resource situation and the reception signal strength threshold value information of each service according to a message broadcast from the adjacent base station.

Description

Apparatus and method for performing partial handover in broadband wireless communication system {APPARATUS AND METHOD FOR EXCUTING PARTIAL HANDOVER IN BROADBAND WIRELESS COMMUNICATION SYSTEM}

1 is a view schematically showing a connection of a terminal and a base station during handover in a broadband wireless communication system according to the prior art;

2 is a diagram schematically illustrating a connection between a terminal and a base station during handover in a broadband wireless communication system according to the present invention;

3 is a diagram illustrating a handover time point in a broadband wireless communication system according to an embodiment of the present invention;

4 is a diagram illustrating resource usage during handover in a broadband wireless communication system according to an embodiment of the present invention;

5 is a block diagram of a terminal in a broadband wireless communication system according to the present invention;

6 is a block diagram of a base station in a broadband wireless communication system according to the present invention;

7 is a diagram illustrating a procedure of performing a handover by a terminal in a broadband wireless communication system according to an embodiment of the present invention;

8 is a diagram illustrating a procedure for a handover by a base station in a broadband wireless communication system according to an embodiment of the present invention;

9 is a diagram illustrating signal exchange between a terminal and a base station during handover in a broadband wireless communication system according to an embodiment of the present invention;

10 illustrates frame use in a broadband wireless communication system according to an embodiment of the present invention; and

11 is a diagram illustrating the performance when performing a handover according to the present invention and the prior art.

The present invention relates to a handover in a broadband wireless communication system, and more particularly, to an apparatus and a method for efficiently performing a handover of a terminal connecting a plurality of services simultaneously in a broadband wireless communication system.

In the 4th Generation (hereinafter referred to as 4G) communication system, which is the next generation communication system, active researches are being conducted to provide users with services having various Quality of Service (Qos) having a transmission rate of about 100 Mbps. have. Particularly, in 4G communication systems, studies are being actively conducted to support high-speed services in a form of ensuring mobility and quality of service in broadband wireless access communication systems such as wireless local area network systems and wireless urban area network systems. In addition, the representative communication system is the Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system.

The IEEE 802.16 communication system includes orthogonal frequency division multiplexing (hereinafter, referred to as OFDM) / orthogonal frequency division multiple access to support a broadband transmission network on a physical channel of the wireless communication system. A communication system employing the following OFDMA) scheme. Accordingly, the next generation 4G communication system can simultaneously use various kinds of services due to the broadband and high speed of the OFDMA / OFDM scheme. For example, you can transfer files using a file transfer protocol (FTP) service while making a voice call.

1 schematically illustrates a connection between a terminal and a base station during handover in a broadband wireless communication system according to the prior art.

1A illustrates a situation in which the base station A 110 and the terminal 130 maintain two service connections. In this case, when the terminal 130 moves to the base station B 120, the signal strength between the terminal 130 and the base station A 110 is weakened. Accordingly, the terminal 130 performs a handover to the base station B 120. That is, as shown in (b) of FIG. 1, the terminal 130 terminates two connections with the base station A 110 and connects the base station B 120 with the two services.

As described above, in a broadband wireless communication system, a terminal connecting a plurality of services terminates all connections with a serving base station during handover and connects the plurality of services to a target base station. That is, although there is no probability that the connected multiple services must be connected through the same path, and although the channel state required for each service is different, all connected services are received due to low received signal strength from the serving base station. The service route is redirected to the target base station. For this reason, there is a problem that the load ratio of the target base station increases rapidly and acts as a burden on the system.

Accordingly, an object of the present invention is to provide an apparatus and method for reducing the burden on a target base station during handover in a broadband wireless communication system.

Another object of the present invention is to provide an apparatus and method for connecting only a part of services being connected to a target base station during handover in a broadband wireless communication system.

According to a first aspect of the present invention for achieving the above object, a terminal device of a broadband wireless communication system, the active set management unit for managing the resource status and the received signal strength threshold information for each of the neighbor base stations and from the serving base station; A message generator for generating a connection request message for connecting a first service corresponding to the predetermined threshold through an adjacent base station if the received signal strength is lower than a predetermined threshold; and connecting the first service through the neighboring base station; And a service connection control unit controlling to connect a second service through the serving base station.

According to a second aspect of the present invention for achieving the above object, in a base station apparatus of a broadband wireless communication system, a message generator for generating a broadcast message including acceptable service information and received signal strength threshold information for each service; And a message processor for checking a connection request message of the terminal for the acceptable service, and a service connection processor for connecting the service requested by the terminal.

According to a third aspect of the present invention for achieving the above object, a method for a terminal to communicate with an adjacent base station in a broadband wireless communication system, the process of checking whether the received signal strength from the serving base station is lower than a predetermined threshold And requesting connection of a first service corresponding to the predetermined threshold to a neighboring base station, connecting the first service through the neighboring base station, and connecting a second service through the serving base station. Characterized in that it comprises a.

According to a fourth aspect of the present invention for achieving the above object, a method for a base station to connect with a terminal in a broadband wireless communication system, transmitting a broadcast message including available resources and received signal strength threshold information for each service; And checking whether a connection request message for a predetermined service is received from the terminal, and connecting the service requested by the terminal.

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, the present invention will be described for a technique for performing partial handover for each service connection during handover of a terminal receiving a plurality of services simultaneously in a broadband wireless communication system. In the following description, the wireless communication system is described using orthogonal frequency division multiplexing (OFDM) based wireless communication system as an example, and may be equally applicable to a cellular based wireless communication system. have.

2 schematically illustrates a connection between a terminal and a base station during handover in a broadband wireless communication system according to the present invention.

Referring to FIG. 2, as shown in FIG. 2A, the terminal 210 connects two services through the base station A 250. At this time, when the terminal 210 moves in the direction of the base station B 260, the received signal strength from the base station A 250 is lowered below the threshold of the connection 2 301 as shown in FIG. 3.

At this time, as shown in (b) of FIG. 2, one of two service connections is connected through the base station B 260. Then, when the terminal 210 approaches the base station B 260 further, the received signal strength is lowered below the threshold of the connection 1 303 as shown in FIG.

That is, when the received signal strength from the base station A 250 is lowered to maintain all connections, the terminal 210 provides all services to the base station B 260 as shown in FIG. ) To complete the handover.

In other words, the terminal sequentially connects one of a plurality of services in use through the target base station according to the threshold value of the received signal strength for each service and performs handover. Here, a handover in which only some services are connected through a target base station is called a partial handover.

Here, a problem of resource collision may occur in performing the partial handover. For example, in a situation in which the first service is connected through the base station A 450 and the second service is connected through the base station B 460, as shown in FIG. 4, the base station A 450 and the base station B 460. ) Does not know the resources allocated to each other terminal, so that a resource conflict may occur by transmitting data to the same resource to the terminal. Therefore, the terminal should inform the target base station of the available resource area when performing the partial handover.

The following description will be described in detail with reference to the drawings the configuration and operation of the base station and the terminal for performing the partial handover described above.

5 is a block diagram of a terminal in a broadband wireless communication system according to the present invention.

As shown in FIG. 5, the terminal includes a wireless communication unit 501, a channel estimator 523, a message processor 525, an active set management unit 527, a service connection control unit 529, and a message generator. 531 is configured.

The wireless communication unit 501 performs signal processing for transmitting and receiving data through a wireless channel, RF (Radio Frequency) receiver 503, analog to digital converter (hereinafter referred to as ADC) 505, OFDM Demodulator 507, resource demapper 509, demodulator and decoder 511, encoding and modulator 513, resource mapper 515, OFDM modulator 517, digital to analog converter, Hereinafter referred to as DAC) and an RF transmitter 521.

The RF receiver 503 converts an RF signal received through an antenna into a baseband analog signal. The ADC 505 converts an analog signal provided from the RF receiver 503 into a digital signal and outputs the digital signal. The OFDM demodulator 507 outputs a frequency domain signal by performing Fast Fourier Transform (FFT) on the time domain signal provided from the ADC 505. The resource demapper 509 reconstructs the signal mapped to the frequency domain provided from the OFDM demodulator 507 to a form before being mapped. In addition, a pilot signal is extracted and output to the channel estimator 523, and an information signal is output to the demodulator and decoder 511. The demodulator and decoder 511 demodulates and decodes a signal provided from the resource demapper 509 in a corresponding manner to output an information bit string.

The encoder and modulator 513 encodes and modulates an information bit string provided from an upper end in a corresponding manner to output a complex symbol signal. The resource mapper 515 maps a signal provided from the encoder and modulator 513 to a corresponding subcarrier. The OFDM modulator 517 outputs a time domain signal by performing an inverse fast Fourier transform (IFFT) on the signals provided from the resource mapper 515. The DAC 519 converts the digital signal from the OFDM modulator 517 into an analog signal and outputs the analog signal. The RF transmitter 521 converts the baseband signal from the DAC 519 into an RF band signal and transmits it through an antenna.

The channel estimator 523 receives a pilot signal from the resource demapper 509 to estimate a channel with a base station. For example, a signal to noise ratio (SNR), a received signal strength, and the like are estimated.

The message processor 525 checks the contents of the message received from the base station among the information bit strings provided from the demodulator and decoder 511. In particular, according to the present invention, a broadcast message received from neighboring base stations is identified and output to the active set manager 527. Here, the broadcast message includes resource margin information of the neighboring base station, acceptable service information according to the resource margin, and received signal strength threshold information for requesting connection of the acceptable service.

The active set manager 527 receives broadcast message information of neighbor base stations from the message processor 525 and manages acceptable service information of the neighbor base stations and threshold value information of received signal strength for each service.

The service connection controller 529 receives the received signal strength information of the serving base station from the channel estimator 523 and performs a partial handover according to the received signal strength. In other words, the mobile station performs partial handover of the corresponding service according to the received signal strength with reference to the information managed by the active set manager 527, and controls to maintain both the connection with the serving base station and the neighboring base station.

The message generator 531 generates a message to be transmitted to the serving base station and the neighbor base station. In particular, according to the present invention, a resource allocation request message for a specific service connection is generated to the neighboring base station to perform the partial handover. Here, the resource allocation request message for the partial handover includes the items shown in Table 1 below.

 Item  Contents   AllocatedInfo  TimeFreqRegion Resource zone information assigned to connections on other paths  AllocationType The periodicity of resources allocated to connections in other paths  AllocationInterval Allocation cycle of resources allocated for connections in other paths  CorrelatedFlag  Association between services connected by different paths

Items shown in Table 1 above are information for informing available resources to the target base station in order to prevent resource conflicts as shown in FIG. In Table 1, 'AllocatedInfo' is an item including information of a resource being used by a serving base station, 'TimeFreqRegion' is time and frequency domain information of a resource being used, and 'AllocationType' is a value of the resource being used. Periodic presence or absence (for a real-time service such as Voice over IP (VoIP)), the 'AllocationInterval' indicates the allocation period of the resource if the active resource is periodic. In addition, the 'CorrelatedFlag' indicates whether a service connected through a serving base station and a service connected through a target base station are related (in the case of a video service and a voice service in a video service).

6 is a block diagram of a base station in a broadband wireless communication system according to the present invention.

As shown in FIG. 6, the terminal includes a wireless communication unit 601, a message processor 623, a service connection processor 625, and a message generator 627.

The wireless communication unit 601 performs signal processing for transmitting and receiving data through a wireless channel, and includes a radio frequency (RF) receiver 603, an ADC 605, an OFDM demodulator 607, and a resource demapper 609. And a demodulator and decoder 611, an encoder and modulator 613, a resource mapper 615, an OFDM modulator 617, a DAC 619, and an RF transmitter 621.

The RF receiver 603 converts an RF signal received through an antenna into a baseband analog signal. The ADC 605 converts an analog signal provided from the RF receiver 603 into a digital signal and outputs the digital signal. The OFDM demodulator 607 outputs a frequency domain signal by performing fast Fourier transform on the time domain signal provided from the ADC 605. The resource demapper 609 reconstructs the signal mapped to the frequency domain provided from the OFDM demodulator 607 in the form before it is mapped. In addition, a pilot signal is extracted and output to the channel estimator 623, and an information signal is output to the demodulator and decoder 611. The demodulator and decoder 611 demodulates and decodes a signal provided from the resource demapper 609 in a corresponding manner to output an information bit string.

The encoder and modulator 613 encodes and modulates an information bit string provided from an upper end in a corresponding manner to output a complex symbol signal. The resource mapper 615 maps a signal provided from the encoder and modulator 613 to a corresponding subcarrier. The OFDM modulator 617 outputs a time domain signal by performing inverse fast Fourier transform on the signals provided from the resource mapper 615. The DAC 619 converts the digital signal from the OFDM modulator 617 into an analog signal and outputs the analog signal. The RF transmitter 621 converts the baseband signal from the DAC 619 into an RF band signal and transmits it through an antenna.

The message processor 623 checks the contents of the message received from the terminal among the information bit strings provided from the demodulator and decoder 611. In particular, according to the present invention, the contents of the resource allocation request message for partial handover from the terminal are checked and output to the service connection processor 625. In addition, the terminal checks a message requesting connection of a specific service from the terminal and outputs the message to the service connection processing unit 625.

The service connection processor 625 receives the resource allocation request message information of the terminal from the message processor 623 and connects the service requested by the terminal. In other words, when the resource allocation is possible to the terminal by comparing the available resource region information of the terminal and the assignable resource region as shown in Table 1, included in the resource allocation request message, the service is connected. In this case, if the association with the service connected through the serving base station is confirmed through the 'CorrelatedFlag' item of the information shown in Table 1, that is, when the synchronization of the two services is required, the serving for uplink data Forwarding to the base station to ensure synchronization.

The message generator 627 generates a message to be sent to the terminal. In particular, according to the present invention, a broadcast message including resource status and received signal strength threshold information for each service and a response message for a resource allocation request message for partial handover of the terminal are generated.

7 is a flowchart illustrating a handover procedure performed by a terminal in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 7, the terminal first maintains two or more service connections in step 701.

In step 703, the terminal determines whether the received signal strength from the serving base station is lower than a threshold. Here, the threshold is a received signal strength threshold for a specific service.

If the received signal strength is lower than the reference value, the terminal proceeds to step 705 to check the resource status of the neighboring base station, and selects the neighboring base station that can connect the specific service as a target base station. Here, the resource situation of the neighboring base station is confirmed through a message broadcast from the neighboring base station.

After selecting the target base station, the terminal proceeds to step 707 and transmits a resource allocation request message to the target base station. Here, the resource allocation request message includes resource information used from the serving base station as shown in Table 1 above.

In step 709, the terminal determines whether a resource allocation request is granted from the target base station. That is, it is checked whether a resource allocation grant message is received from the target base station.

If the resource allocation request is granted, the terminal proceeds to step 711 and connects the service for which the resource allocation request is permitted, that is, the service for which the connection is allowed through the target base station, and then the received signal strength of the serving base station gradually decreases. Handover is performed sequentially accordingly.

8 is a flowchart illustrating a handover process performed by a base station in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 8, the base station first checks whether the resource status broadcast cycle is performed in step 801.

If the resource status broadcast period, the base station proceeds to step 803 and transmits a broadcast message including the resource status, that is, resource information that can be allocated, and connectable received signal strength threshold information for each service.

On the other hand, if it is not the resource status broadcast period, the base station proceeds to step 805 and checks whether a resource allocation request message is received from the terminal.

When the resource allocation request message is received, the base station proceeds to step 807 and checks the information on the resource request of the terminal included in the resource allocation request message. That is, it checks the available resource area of the terminal and the minimum resource requirement of the corresponding service.

After checking the resource request information of the terminal, the base station proceeds to step 809 and compares the resource allocation information and the resource request information of the terminal to determine whether the resource allocation is possible.

If the resource allocation is not possible, the base station proceeds to step 811 and transmits a resource allocation response message indicating that the resource allocation is not allowed to the terminal.

On the other hand, if the resource allocation is possible, the base station proceeds to step 813 and transmits a resource allocation response message indicating that the resource allocation is allowed to the terminal.

Thereafter, the base station proceeds to step 815 to perform a process for connecting the service requested by the terminal, and subsequently performs handover according to the request of the terminal.

9 illustrates signal exchange between a terminal and a base station during handover in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 9, the target base station 930 transmits a broadcast message informing of a resource situation and a service connection threshold in step 901.

Upon receiving the broadcast message, the terminal 910 confirms that the received signal strength from the serving base station 920 is lower than the threshold (step 903).

After checking the received signal strength, the terminal 910 transmits a resource allocation request message to a target base station 930 to request resource allocation for a service corresponding to the threshold (step 905). At this time, the resource allocation request message includes the items shown in Table 1 above.

Upon receiving the resource allocation request message, the target base station 930 compares the available resource information of the terminal 910 with the assignable resources and determines whether the resource allocation is possible to the terminal 910 (step 907).

The target base station 930 confirming whether the resource allocation is possible transmits a resource allocation response message to the terminal 910 to inform that the resource allocation is possible (step 909).

Upon receiving the resource allocation response message, the terminal 910 transmits a partial handover indication message 911 to the serving base station 920 (step 911).

Subsequently, the terminal 910 transmits a connection request message 913 to the target base station 930 (step 913).

The above-described embodiment has described a technique in which the terminal performs partial handover with a separate threshold for each service connection during handover. In this case, the base station does not consider a separate scheduling for a terminal requiring handover, that is, a terminal located at a cell boundary.

However, as another embodiment, as shown in FIG. 10, resources allocated to terminals located at cell boundaries between adjacent base stations may be used. Referring to FIG. 10, the base station A 1010 and the base station B 1020 allocate resources to terminals located at the boundary of each cell in areas separated from each other on the time axis. That is, the base station A 1010 allocates resources to the terminal 1030 only in the slot i 1050, and the base station B 1020 allocates resources to the terminal 1030 only in the slot j 1060. As a result, since the base station A 1010 and the base station B 1020 can communicate with the terminal 1030 at high power, the base station A 1010 and the base station B 1020 can ensure a high transmission rate to the terminal 1030 located at a cell boundary. .

11 illustrates performance when performing handover according to the present invention and the prior art. 11 is a graph showing the handover failure rate according to the number of users according to the present invention and the prior art. That is, the horizontal axis represents the number of users (load rate), and the vertical axis represents the handover failure rate.

11 (a) assumes that the handover fails when not receiving a data rate of 40 kbps for 50 msec, and FIG. 11 (b) assumes that handover fails when not receiving a rate of 60 kbps for 50 msec. It was.

Referring to FIG. 11, in the case of (a) and (b), the improvement effect does not appear significantly in a situation where the number of users (load rate) of the base station is small, but the handover failure rate is large in a situation where the number of users (load rate) is large. You can see the decrease.

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, by using the received signal strength threshold differently according to the type of service during handover in the broadband wireless communication system, the burden on the target base station due to the handover can be reduced. In addition, it is possible to improve the communication quality of the terminal located at the cell boundary and increase the resource utilization flexibility of the system.

Claims (12)

A terminal device of a broadband wireless communication system, An active set management unit for managing resource status and received signal strength threshold information of each neighboring base station; A message generator for generating a connection request message for connecting a first service corresponding to the predetermined threshold value through an adjacent base station if the received signal strength from the serving base station is lower than the predetermined threshold value; And a service connection control unit for connecting the first service through the neighbor base station and controlling to connect the second service through the serving base station. The method of claim 1, The active set management unit, And updating the resource status and received signal strength threshold information for each service through a message broadcast from the neighbor base station. The method of claim 1, The message generator, And generate a resource allocation request message including resource region information allocated from the serving base station. The method of claim 3, wherein The service connection control unit, And when the permission response message for the resource allocation request message is received, control to connect the first service through the neighbor base station. A base station apparatus of a broadband wireless communication system, A message generator for generating a broadcast message including acceptable service information and received signal strength threshold information for each service; A message processor for checking a connection request message of the terminal for the acceptable service; And a service connection processing unit for connecting the service requested by the terminal. The method of claim 5, The message handler, And identifying an available resource area of the terminal through a resource allocation request message received from the terminal. The method of claim 6, The service connection processing unit, And comparing the available resource area of the terminal with the assignable resource area and connecting the service requested by the terminal when at least the amount of resources required for the service requested by the terminal is matched. A method for a terminal to communicate with an adjacent base station in a broadband wireless communication system, Checking whether the received signal strength from the serving base station is lower than a predetermined threshold value; Requesting connection of a first service corresponding to the predetermined threshold value to an adjacent base station; Connecting the first service through the adjacent base station; Connecting a second service through the serving base station. The method of claim 8, And receiving a broadcast message including resource status information and received signal strength threshold information for each service from the neighboring base station. The method of claim 8, When the received signal strength of the serving base station is lower than a predetermined threshold, transmitting a resource allocation request message including resource area information allocated from the serving base station to the neighboring base station; And confirming whether an authorization response message for the resource allocation request message is received. In the broadband wireless communication system, a base station for connecting with a terminal, Transmitting a broadcast message including available resources and received signal strength threshold information for each service; Checking whether a connection request message for a predetermined service is received from the terminal; Connecting the service requested by the terminal. The method of claim 11, After transmitting the broadcast message, checking whether a resource allocation request message including available resource area information of the terminal is received from the terminal; Comparing the available resource area and the assignable resource area of the terminal to identify a matching resource area; And transmitting a resource allocation permission response message to the terminal when the matching resource region is at least as large as the amount of resources required for the service requested by the terminal.

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