Apparatus and method for supporting frequency overlay in broadband wireless communication system

BACKGROUND OF THE INVENTION

1. Field of the Invention

0001The present invention relates generally to a broadband wireless communication system, and in particular, to an apparatus and a method for communicating using a multi-Frequency Allocation (FA) access scheme in a broadband wireless communication system.

2. Description of the Related Art

0002A great number of wireless communication techniques has been suggested for a high-speed mobile communication. Among them, an Orthogonal Frequency Division Multiplexing (OFDM) scheme is considered as the most dominant next-generation wireless communication technique. It is anticipated that the OFDM will be applied to most of the wireless communication techniques in 2010. A Wireless Metropolitan Area Network (WMAN) of the Institute of Electrical and Electronics Engineers 802.16 called the 3.5^th-Generation technology also adopts OFDM as the standard specification.

0003Meanwhile, wireless communication systems have advanced to serve high-speed data or address various issues in the implementation. In the process of the development, various systems can coexist in the same region according to their compatibility with the existing systems. For example, a new advanced system can be installed in the region of an IEEE 802. 16e system. In this case, the new system should be able to support the service to both of the existing terminal and the new terminal.

0004Through a single Frequency Allocation (FA), the current OFDM broadband wireless communication system supports only a terminal which uses a single bandwidth. Hence, to support a new terminal to be developed to use a wider bandwidth, the FA of the system needs to be changed to a new FA of the corresponding bandwidth. However, the system of the changed FA cannot serve the terminal, which uses the existing narrow bandwidth. In other words, when the FA of the system is changed, it is necessary to change the existing terminals at the same time. In this respect, in the development of the broadband wireless communication system, a method for supporting both the existing terminal using the narrow bandwidth and the new terminal using the wide bandwidth is needed.

0005<patcit id="pcit0001" dnum="WO2006138288A2"><text>WO 2006/138288 A2</text></patcit> refers to a flexible bandwidth communication system and method using a common physical layer technology platform. A method includes selecting one of a plurality of transmitter systems used to transmit data. Each transmitter system corresponds to one of a plurality of subbands. Each subband has a bandwidth and at least two of the subbands have different bandwidths. A physical layer technology is common to and used by each transmitter system to transmit on a respective subband. The selected transmitter system transmits the data. An apparatus includes a plurality of transmitter systems, each corresponding to one of a plurality of subbands. Each subband has a bandwidth and at least two of the subbands have different bandwidths. A physical layer technology is common to and used by each transmitter system to transmit on a respective subband. A controller is operable to select one of the transmitter systems to use to transmit data, and is operable to cause the selected transmitter system to transmit the data.

0006<patcit id="pcit0002" dnum="WO2006073225A2"><text>WO 2006/073225 A2</text></patcit> refers to a method for handover between frequency allocation in broadband wireless access system. A handover control method in a broadband wireless access system is disclosed. In a broadband wireless access system supporting multiple frequency allocations, in which a serving base station controls a handover, the disclosed technique includes the steps of receiving from a mobile subscriber station a handover request message including an identifier of the mobile subscriber station, transmitting a handover request notification message including the identifier of the mobile subscriber station to a handover target base station, receiving a handover request notification response message including information for frequency allocation supportable by the target base station, and transmitting a handover response message including the information for the frequency allocation to the mobile subscriber station.; Accordingly, in the broadband wireless access system supporting the multiple FA, the disclosed technique enables the handover between FAs within one cell or between FAs in different cells.

SUMMARY OF THE INVENTION

0007An aspect of the present invention is to solve at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below.

0008It is the object of the present invention to provide an improved apparatus and method for concurrently supporting terminals, which use different bandwidths in a broadband wireless communication system.

0009This object is solved by the subject matter of the independent claims.

0010Preferred embodiments are defined by the dependent claims.

0011Another aspect of the present invention is to provide an apparatus and a method for a pair of a sender and a receiver to communicate using a multiple Frequency Allocations (FAs) at the same time in a broadband wireless communication system.

0012The above aspects are achieved by providing a sending apparatus in a broadband wireless communication system. The sending apparatus includes a controller for distributing packets to a plurality of processors to transmit the packets in a multi-Frequency Allocation (FA) access mode; the plurality of the processors for processing the packet provided from the controller in a Media Access Control (MAC) layer; and a plurality of senders for encoding the packets provided from the corresponding processors in a physical layer and transmitting a signal generated through the physical layer encoding.

0013In accordance with an aspect of the present invention, a receiving apparatus in a broadband wireless communication system includes a plurality of receivers for performing a physical layer decoding on a signal received through a corresponding FA among a plurality of signals concurrently received through multiple FAs from a sending end in multi-FA access communications; a plurality of processors for performing a MAC layer processing on packets recovered through the physical layer decoding of the corresponding receiver of the plurality of the receivers; and a controller for aggregating and processing packets processed by the processors.

0014In accordance with another aspect of the present invention, a communication method of a sending end in a broadband wireless communication system includes distributing packets on a FA basis to transmit the packets in a multi-FA access mode; performing a MAC layer processing on the packets for each FA; and performing a physical layer encoding on the packets which are completely MAC layer processed, on the FA basis and transmitting signals generated through the physical layer encoding.

0015In accordance with yet another aspect of the present invention, a communication method of a receiving end in a broadband wireless communication system includes performing a physical layer decoding on a plurality of signals concurrently received through multiple FAs from a sending end in multi-FA access communications; performing a MAC layer processing on packets recovered through the physical layer decoding; and aggregating and processing packets processed by the processors.

BRIEF DESCRIPTION OF THE DRAWINGS

0016The above and other aspects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG. 1A</figref> illustrates a bandwidth change in a broadband wireless communication system;</li><li>FIG. IB illustrates a bandwidth change in a broadband wireless communication system;</li><li><figref idref="f0003">FIG. 2</figref> illustrates a frequency band usage in a broadband wireless communication system according to the present invention;</li><li><figref idref="f0004">FIG. 3</figref> illustrates a protocol stack in the broadband wireless communication system according to the present invention;</li><li><figref idref="f0005">FIG. 4</figref> illustrates a sending end in the broadband wireless communication system according to the present invention;</li><li><figref idref="f0006">FIG. 5</figref> illustrates a receiving end in the broadband wireless communication system according to the present invention;</li><li><figref idref="f0007">FIG. 6</figref> illustrates a communication process of the sending end in the broadband wireless communication system according to the present invention;</li><li><figref idref="f0008">FIG. 7</figref> illustrates a communication process of the receiving end in the broadband wireless communication system according to the present invention;</li><li><figref idref="f0009">FIG. 8</figref> illustrates signal exchanges for a mode transition in the broadband wireless communication system according to the present invention; and</li><li><figref idref="f0010">FIG. 9</figref> illustrates signal exchanges for a handover in the broadband wireless communication system according to the present invention.</li></ul>

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

0017The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the present invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

0018The present invention provides a technique for supporting terminals, which use different bandwidths at the same time in a broadband wireless communication system. An Orthogonal Frequency Division Multiplexing (OFDM) wireless communication system is illustrated by way of example, but the present invention is applicable to any other wireless communication systems.

0019<figref idref="f0001">FIGs. 1A</figref> and <figref idref="f0002">1B</figref> illustrate two expected bandwidth change processes. In <figref idref="f0001">FIGs. 1A</figref> and <figref idref="f0002">1B</figref>, a Mobile Station (MS) A is an existing terminal using a narrow bandwidth and MS B and MS C are new terminals using wide bandwidths.

0020In the first case, (a) of <figref idref="f0001">FIG. 1A</figref> depicts the bandwidth usage of legacy system. Since the MS A supports 10MHz, the system divides the total 40MHz bandwidth by 10MHz. Accordingly, the MS A can communicate using one of four 10MHz bandwidths. (b) of <figref idref="f0001">FIG. 1A</figref> depicts the bandwidth usage of a transitional system. To serve both of the MS A supporting 10MHz and the MS B supporting the 20MHz at the same time, the system divides the total 40MHz bandwidth to two 10MHz bandwidths and one 20MHz bandwidth. Hence, the MS A can communicate using one of the two 10MHz bandwidths and the MS B can communicate using the 20MHz bandwidth. (c) of <figref idref="f0001">FIG. 1A</figref> depicts the bandwidth usage of a future system. Since the MSs will support only 20MHz in the future, the future system divides the total 40MHz bandwidth by 20MHz. Hence, the MSs B and C can communicate using one of the two 20MHz bandwidths.

0021In the second case, (a) of FIG. IB depicts the bandwidth usage of the legacy system. Since the MS A supports 10MHz, the system divides the total 20MHz bandwidth by 10MHz. Hence, the MS A can communicate using one of the two 10MHz bandwidths. (b) of FIG. IB depicts the bandwidth usage of the transitional system. To serve both of the MS A supporting 10MHz and the MS B supporting 20MHz, the system divides the total 20MHz bandwidth by 10MHz. The system frequency-overlays two 10MHz Frequency Allocations (FAs) with 20MHz bandwidth. Accordingly, the MS A can use one of the two FAs for communications, and the MS B can use both of the two FAs for communications. (c) of FIG. IB depicts the bandwidth usage of the future system. Since the MSs will support only 20MHz in the future, the future system utilizes the total 20MHz bandwidth for the MS C. That is, the MS C uses the 20MHz bandwidth for communications.

0022In <figref idref="f0001">FIGS. 1A</figref> and <figref idref="f0002">1B</figref>, the MS B of the transitional system and the MS C of the future system are separately provided because they can comply with different standards while supporting the same bandwidth.

0023The present invention pertains to the transitional system in (b) of FIG. IB. When the system supports both of the legacy MS and the transitional MS using the frequency overlay as shown in <figref idref="f0002">FIG. 1B</figref>, the legacy MS and the new MS can be supported using the narrower bandwidth at the same time. Thus, it is more effective than the system of <figref idref="f0001">FIG. 1A</figref> in terms of the frequency utilization.

0024<figref idref="f0003">FIG. 2</figref> illustrates a frequency band usage in a broadband wireless communication system according to the present invention. It is assumed that there are two FAs in <figref idref="f0003">FIG. 2</figref> for the understanding. Note that the system can use three or more FAs.

0025A Base Station (BS) 210 uses two FAs of 10MHz bandwidth. Legacy MS A-1 220-1 and MS A-2 220-2 communicate using only one FA of 10MHz bandwidth. A new MS B 230 uses two FAs of 10MHz bandwidth at the same time for communications. Herein, the connection between the BS 210 and the MS B 230 is established per FA in <figref idref="f0003">FIG. 2</figref>. The MS B 230 holds two connections through two FAs of 10MHz bandwidth and uses 20MHz bandwidth in total for communications. As such, using the frequency overlay, the BS 210 can support both of the new MS and the legacy MS. Since the two FAs are independent of each other, similar to the legacy MS, the MS B 230 can use only one FA for communications if necessary.

0026To independently operate two FAs, the BS and the MS need to have an independent Media Access Control (MAC) address for each FA, and to manage and operate a network entry, a context (e.g., CID, AK ID, and SA ID), and a handover signaling on the FA basis using the separate MAC addresses. With the independent MAC addresses on the FA basis, the change of the legacy standard is minimized. Even with the independent MAC addresses on the FA basis, an upper layer should recognize as a single MS. For doing so, it is required to map the plurality of the MAC addresses of one MS to a single Internet Protocol (IP) address.

0027<figref idref="f0004">FIG. 3</figref> illustrates a protocol stack in the broadband wireless communication system according to the present invention.

0028The protocol stack for supporting the multi-FA in <figref idref="f0004">FIG. 3</figref> largely includes a PHYsical (PHY) layer and a Media Access Control (MAC) layer. The MAC layer includes a Security Sublayer (SS), a MAC Common Part Sublayer (CPS), and a Convergence Sublayer (CS). To support two FAs, two PHY layers and two MAC layers are provided. To coordinate the two FAs, the CS includes a Multi FA Supporting Entity (MFSE). Herein, the position of the MFSE is a mere example. The MFSE can be placed in other upper layer (e.g., IP layer) of the MAC layer, and in a separate layer or in a separate sublayer.

0029The CS converts a service protocol such as digital audio/video multicast protocol, digital telephony protocol, and Internet access protocol, in conformity to the MAC protocol. The CS converts an IP packet to a MAC Service Data Unit (SDU) having the corresponding Connection ID (CID) and provides the MAC SDU to the MAC CPS. Conversely, the CS converts a MAC SDU received from the MAC CPS to an IP packet and provides the IP packet to the upper layer.

0030The MAC CPS controls the access to the shared radio medium, and controls the flow of data and control signal according to a prescribed MAC protocol. Also, the MAC CPS generates a MAC Protocol Data Unit (PDU) and a burst with MAC SDUs received from the CS and provides the MAC PDU and the burst to the lower layer, and extracts MAC SDUs from data received from the lower layer and provides the extracted MAC SDUs to the CS.

0031The SS performs security related functions such as authentication, encryption, and key management. The PHY layer converts the burst generated at the MAC CPS to a transmittable signal. The PHY layer converts a signal received in a radio link to data and provides the data to the upper layer.

0032The MFSE controls a multi-FA capability negotiation to check if the multi-FA is supported between the MS and the BS. The MFSE distributes packets received from the upper layer to the FAs and aggregates packets from the lower layer to one IP. When the MFSE is present in the MAC CPS, the packets can be distributed using an IP fragmentation function. In the handover, the MFSE controls to hand the multiple FAs connected to the same MS over to the same target BS.

0033<figref idref="f0005">FIG. 4</figref> is a block diagram of the sending end in the broadband wireless communication system according to the present invention. In <figref idref="f0005">FIG. 4</figref>, it is assumed that the sending end uses two FAs.

0034The sending end of <figref idref="f0005">FIG. 4</figref> includes a multi-FA controller 410, a first MAC processor 420-1, a second MAC processor 420-2, a first sender 430-1, and a second sender 430-2.

0035The multi-FA controller 410 distributes transmit packets provided from the upper layer to the first MAC processor 420-1 and the second MAC processor 420-2 for the communications through the multiple FAs. More specifically, the multi-FA controller 410 fragmentizes the MAC SDU provided from the upper layer and distributes the fragments to the first MAC processor 420-1 and the second MAC processor 420-2 according to a predefined rule. The multi-FA controller 410 controls the first MAC processor 420-1 and the second MAC processor 420-2 not to use the same band. Also, in the initial connection to the receiving end, the multi-FA controller 410 checks if the communications using the multiple FAs are feasible by controlling the multi-FA capability negotiation.

0036When the sending end is a mobile terminal, the multi-FA controller 410 selects the FA to use for the communications and determines the number of the FAs to be used. When the sending end is the mobile terminal and the handover is conducted during the communications using the multiple FAs, the multi-FA controller 410 controls the first MAC processor 420-1 and the second MAC processor 420-2 to hand over to different FAs of the same target BS with respect to the currently used FAs.

0037The first MAC processor 420-1 performs the function of the MAC layer to transmit the packet using one of the multiple FAs. The first MAC processor 420-1 generates the MAC PDU by inserting a MAC header and an error check (e.g., Cyclic Redundancy Check (CRC)) code to the packet distributed by the multi-FA controller 410, and generates control information for using the radio resource for the corresponding FA. The first MAC processor 420-1 constitutes a frame by arranging the packet and the control information. In doing so, the CID mapped to the MAC PDU is different from the CID mapped by the second MAC processor 420-2. Also, the first MAC processor 420-1 performs a control signaling (e.g., handover signaling and access signaling) on the corresponding FA. The second MAC processor 420-2 performs the same function as the first MAC processor 420-1 with respect to one of the multiple FAs. Note that the second MAC processor 420-2 has the MAC address different from the first MAC processor 420-1. In other words, the first MAC processor 420-1 and the second MAC processor 420-2 perform the function of the MAC layer using the independent MAC addresses.

0038The first sender 430-1 encodes the bit stream provided from the first MAC processor 420-1 in the PHY layer and transmits the signal generated through the PHY layer encoding over an antenna. For example, the first sender 430-1 channel-codes and modulates the fed bit stream, and generates OFDM symbols through an Inverse Fast Fourier Transform (IFFT) operation. The first sender 430-1 up-converts the OFDM symbols to the frequency band corresponding to the FA managed by the first MAC processor 420-1 and transmits the converted symbols over the antenna.

0039The second sender 430-2 receives the bit stream from the second MAC processor 420-2 and performs the same function as the first sender 430-1. Note that the second sender 430-2 up-converts the signal to the different frequency band from the first sender 430-1 and then transmits the converted signal. The second sender 430-2 up-converts the bit stream to the frequency band corresponding to the FA managed by the second MAC processor 420-2 and then transmits the converted signal.

0040<figref idref="f0006">FIG. 5</figref> is a block diagram of the receiving end in the broadband wireless communication system according to the present invention. In <figref idref="f0006">FIG. 5</figref>, it is assumed that the receiving end uses two FAs.

0041The BS of <figref idref="f0006">FIG. 5</figref> includes a first receiver 510-1, a second receiver 510-2, a first MAC processor 520-1, a second MAC processor 520-2, and a multi-FA controller 530.

0042The first receiver 510-1 converts the received signal to an information bit stream by decoding the received signal in the PHY layer. In other words, the first receiver 510-1 recovers the control information and the packet from the received signal. For instance, the first receiver 510-1 acquires the frequency-domain signal of the corresponding FA by filtering the signal received on an antenna. The first receiver 510-1 converts the acquired signal to sample data, OFDM-demodulates the sample data through a FFT operation, recovers the information bit stream by demodulating and decoding the signal, and provides the information bit stream to the first MAC processor 520-1. The second receiver 510-2 acquires the frequency-domain signal corresponding to the FA managed by the second MAC processor 520-2 from the received signal and converts the received signal to the information bit stream in the same process as in the first receiver 510-1. The second receiver 510-2 provides the converted bit stream to the second MAC processor 520-2.

0043The first MAC processor 520-1 and the second MAC processor 520-2 perform the MAC layer processing on the packet received through one of the multiple FAs. Specifically, the first MAC processor 520-1 conducts several examinations such as error code check and packet header check. The first MAC processor 520-1 performs the control signaling (e.g., handover signaling and initial access signaling) on the corresponding FA. The second MAC processor 520-2 carries out the same function as the first MAC processor 520-1 with respect to one of the multiple FAs. Note that the second MAC processor 520-2 has the different MAC address from the first MAC processor 520-1. That is, the first MAC processor 520-1 and the second MAC processor 520-2 perform the MAC layer function using the independent MAC addresses.

0044The multi-FA controller 530 maps the receive packets provided from the first MAC processor 420-1 and the second MAC processor 420-2 to one IP address and provides the packets to the upper layer. The multi-FA controller 530 controls the first MAC processor 520-1 and the second MAC processor 520-2 not to use the same band. In the initial connection to the sending end, the multi-FA controller 530 checks if the communications using the multiple FAs are feasible by conducting the multi-FA capability negotiation. When the receiving end is a terminal, in the handover, the multi-FA controller 530 controls the first MAC processor 520-1 and the second MAC processor 520-2 to hand the FAs over to different FAs of the same target BS.

0045<figref idref="f0007">FIG. 6</figref> illustrates a communication process of the sending end in the broadband wireless communication system according to the present invention.

0046In step 601, the sending end distributes the transmit packets on an FA basis. The sending end distributes the transmit packets generated in the IP layer according to the prescribed rule to transmit the packets through the multiple FAs.

0047In step 603, the sending end performs the MAC layer processing on the FA basis to send the distributed packets. For example, the sending end inserts the MAC header and the error check code for each FA. In doing so, the MAC layer processing utilizes the independent MAC address and the independent CID for each FA.

0048In step 605, the sending end generates the control information for using the radio resource for each FA. For example, the sending end generates the message according to the signaling (e.g., handover signaling and initial access signaling) to control the communications.

0049In step 607, the sending end generates the transmit signal including the transmit packet and the control information for each FA. More specifically, the sending end converts the bit stream to the complex symbol through the channel coding and the modulation, and generates the OFDM symbols through the IFFT operation.

0050In step 609, the sending end up-converts the signal generated for each FA to the frequency band corresponding to the relevant FA, and then transmits the signal.

0051<figref idref="f0008">FIG. 7</figref> illustrates a communication process of the receiving end in the broadband wireless communication system according to the present invention.

0052In step 701, the receiving end acquires the signal of the frequency band corresponding to each FA from the received signal. The receiving end splits the received signal on an FA basis by filtering the received signal with the corresponding frequency band on the FA basis.

0053In step 703, the receiving end converts the FA signal to the information bit stream by decoding the FA signal in the PHY layer. That is, the receiving end recovers the control information and the packet. Specifically, the receiving end acquires the bit stream of each FA by Fast Fourier Transform (FFT)-processing, demodulating, and decoding the signal by the OFDM symbol.

0054In step 705, the receiving end confirms the control information for using the radio resource for each FA. For example, the receiving end confirms the message according to the communication control signaling (e.g., handover signaling and initial access signaling).

0055In step 707, the receiving end performs the MAC layer processing on the received packet on the FA basis. For example, the receiving end performs the MAC layer processing such as encryption key description.

0056In step 709, the receiving end aggregates and processes the received packets processed on the FA basis as a single packet.

0057<figref idref="f0009">FIG. 8</figref> illustrates signal exchanges for a mode transition in the broadband wireless communication system according to the present invention. In particular, <figref idref="f0009">FIG. 8</figref> illustrates the signal exchange in the transition from the communications where the MS and the BS use one FA to the communications where the MS and the BS use the multiple FAs. Herein, the mode of the single FA is referred to as a single FA mode, and the mode of the multiple FAs is referred to as a multi-FA mode.

0058To access in the single FA mode, the multi-FA controller 812 of the MS 810 grants the connection of the first MAC processor 814 in step 801.

0059Upon receiving the connection grant, the first MAC processor 814 of the MS 810 performs the connection process including the capability negotiation with the first MAC processor 824 of the BS 820, and establishes the connection. In the capability negotiation, the MS 810 and the BS 820 confirm that the multi-FA connection is possible between them through the multi-FA capability negotiation in step 803.

0060In step 805, the first MAC processor 824 of the BS 820 informs the multi-FA controller 822 of the connection to the MS 810.

0061In step 807, the MS 810 and the BS 820 exchange the traffic through their respective first MAC processors 814 and 824 and communicate in the single FA mode.

0062Communicating in the single FA mode, the multi-FA controller 812 of the MS 810 determines whether to switch to the multi-FA mode in step 809. The multi-FA controller 822 of the BS 820 may determine whether to switch to the multi-FA mode.

0063In step 811, upon determining to switch to the multi-FA mode, the multi-FA controller 812 of the MS 810 grants the connection of the second MAC processor 816. In doing so, the multi-FA controller 812 directs the frequency band to be used by the second MAC processor 816. Since the frequency band can collide with the frequency band of the first MAC processor 814, the multi-FA controller 812 directs the second MAC processor 816 to use the frequency band not used by the first MAC processor 814.

0064Upon receiving the connection grant, the second MAC processor 816 of the MS 810 establishes the connection to the second MAC processor 826 of the BS 820 through the connection process in step 813.

0065In step 815, the second MAC processor 826 of the BS 820 informs the multi-FA controller 822 of the connection to the MS 810.

0066In step 817, the MS 810 and the BS 820 exchange the traffic through the first MAC processors 814 and 824 and the second MAC processors 816 and 826 and communicate in the multi-FA mode.

0067In step 819, as communicating in the multi-FA mode, the multi-FA controller 812 of the MS 810 determines whether to switch to the single FA mode. The multi-FA controller 822 of the BS 820 can determine whether to switch to the single FA mode.

0068Upon determining to transit to the single FA mode, the multi-FA controller 812 of the MS 810 requests the connection release to the second MAC processor 816 in step 821.

0069In step 823, receiving the connection release request, the second MAC processor 816 of the MS 810 releases the connection by performing the release process with the second MAC processor 826 of the BS 820.

0070In step 825, the second MAC processor 826 of the BS 820 informs the multi-FA controller 822 of the connection release from the MS 810.

0071In step 827, the MS 810 and the BS 820 exchange the traffic through their respective first MAC processors 814 and 824 and communicate in the single FA mode.

0072<figref idref="f0010">FIG. 9</figref> illustrates signal exchanges for the handover in the broadband wireless communication system according to the present invention. In particular, <figref idref="f0010">FIG. 9</figref> illustrates the signal exchanges in the handover when the MS enters the multi-FA mode.

0073In step 901, the MS 910 and the serving BS 920 exchange the traffic through their respective first MAC processors 914 and 924 and second MAC processors 916 and 926 and communicate with each other in the multi-FA mode.

0074Communicating in the multi-FA mode, the MS 910 scans for the handover. Measuring the signal strength from neighbor BSs as the signal strength from the serving BS 920 weakens in step 903.

0075In step 905, the multi-FA controller 912 of the MS 910 determines the handover and sets the target BS 930.

0076For the handover, the multi-FA controller 912 of the MS 910 requests the connection release to the second MAC processor 916 in step 907.

0077In step 909, the second MAC processor 916 of the MS 910, upon receiving the connection release request, releases the connection through the connection release process with the second MAC processor 926 of the serving BS 920.

0078In step 911, the multi-FA controller 912 of the MS 910 requests the handover to the target BS 930, to the first MAC processor 914.

0079In step 913, receiving the handover request, the first MAC processor 914 of the MS 910 establishes the connection by performing the handover process with the first MAC processor 934 of the target BS 930.

0080After the handover of the first MAC processor 914 is complete, the multi-FA controller 912 of the MS 910 grants the connection to the second MAC processor 916 in step 915. In doing so, the multi-FA controller 912 of the MS 910 directs the target BS 930 and the frequency band to use to the second MAC processor 916.

0081In step 917, the second MAC processor 916 of the MS 910 establishes the connection through the connection process to the second MAC processor 936 of the target BS 930.

0082In step 919, the MS 910 and the target BS 930 exchange the traffic through their respective first MAC processors 914 and 934 arid second MAC processors 916 and 936, and communicate with each other in the multi-FA mode.

0083As set forth above, the broadband wireless communication system supports the terminal which uses the wide bandwidth by means of the frequency overlay. Therefore, the compatibility for various terminals can be maintained in the process of the system bandwidth conversion.

0084While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the present invention as defined by the appended claims.