System and method for performing handover operation in broadband wireless access communication system

System and method for performing cross-zone handover operation in broadband wireless access communication system

Technical field

The present invention relates to a broadband wireless access communication system, and in particular, to a method used in a BWA (Broadband Wireless Access) communication system using an OFDM (Orthogonal Frequency Division Multiplexing) scheme, when receiving System and method for performing cross-area handover operation after SS (subscriber station) request.

Background technique

Intensive research is being directed to 4G (fourth generation) communication systems, which is one of the next-generation communication systems for providing specific services with various QoS (Quality of Service) to multiple users at a transmission rate of about 100 Mbps. At present, the 3G (third generation) communication system provides a transmission rate of about 384kbps in an outdoor channel environment with a relatively poor channel environment, and provides a maximum transmission rate of about 2Mbps in an indoor channel environment with a relatively good channel environment. A wireless local area network (LAN) system and a wireless metropolitan area network (MAN) system have been designed to provide a transmission rate of 20-50 Mbps. The 4G communication system provides wireless LAN and MAN systems with relatively high transmission rates, mobility and QoS, and many secondary developers are conducting intensive research on the high-speed services provided by the 4G communication system.

However, the wireless MAN system is suitable for high-speed communication services because it has a wide coverage area and supports high-speed transmission rates. However, it does not consider the mobility of the subscriber station (SS) at all. Therefore, it does not consider the movement caused by the SS. Handover operation (ie, cell selection operation). The communication system currently considered in the IEEE (Institute of Electrical and Electronics Engineers) 802.16a specification is used as a specific communication system that performs a ranging operation between an SS and a base station (BS). The communication system considered in the IEEE 802.16a specification will be described below with reference to FIG. 1.

Fig. 1 is a block diagram showing a BWA communication system using an OFDM/OFDMA (Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiple Access) scheme. In more detail, Figure 1 describes the IEEE 802.16a communication system.

Compared with wireless LAN, the wireless MAN system used as a BWA communication system has a much wider coverage area and a much higher transmission rate. In the case of applying the OFDM scheme and the OFDMA scheme to the physical channel of the wireless MAN system to provide the wireless MAN system with a broadband transmission network, the application system is called an IEEE 802.16a communication system. The IEEE 802.16a communication system applies the OFDM/FODMA scheme to the wireless MAN system so that it uses multiple subcarriers to transmit physical channel signals, resulting in high-speed data transmission. The IEEE 802.16e communication system has been designed to take the mobility of SS into account in the IEEE 802.16a communication system. There is no detailed specification for the IEEE 802.16e communication system.

Referring to FIG. 1, the IEEE 802.16a communication system has a single-cell structure and is composed of a BS 100 and a plurality of SSs 110, 120, and 130 managed by the BS 100. The signal transmission/reception between the BS 100 and the SS 110, 120, and 130 can be established using an OFDM/OFDMA scheme. The downlink frame structure used in IEEE 802.16a will be described below in conjunction with FIG. 2.

Fig. 2 is a conceptual diagram showing a downlink frame structure used in a BWA communication system using an OFDM/OFDMA scheme. In more detail, FIG. 2 describes the downlink frame structure used in the IEEE 802.16a communication system.

Referring to FIG. 2, the downlink frame includes a preamble field 200, a broadcast control field 210, and a plurality of TDM (Time Division Multiplexing) fields 220 and 230. A synchronization signal (ie, a preamble sequence) for obtaining synchronization between the BS and the SS is transmitted through the preamble field 200. The broadcast control field 210 is composed of a DL (downlink)_MAP field 211 and a UL (uplink)_MAP field 213. The DL_MAP field 211 is used to send a DL_MAP message. Table 1 below shows multiple IEs (information elements) included in the DL_MAP message: Table 1:

Referring to Table 1 above, the DL_MAP message includes: a Management Message Type (Management Message Type) field representing a plurality of IEs (ie, sending message type information); PHY(s) established in response to the modulation or demodulation scheme applied to the physical channel Physical Synchronization Field (PhysicalSynchronization Field), used to perform synchronization acquisition; DCD Count (DCD Count) field, which indicates the response to the DCD (Downlink Channel Descriptor) containing the downlink burst profile (burst profile) Message configuration change count information; Base Station ID (Base Station ID) field indicates the base station identifier; and Number of DL_MAP Element n (Number of DL_MAP Element n), which indicates the number of elements found after the base station ID. In particular, the DL_MAP message (not shown in Table 1) includes information related to adjustment codes assigned to each adjustment process (described later).

The UL_MAP field 213 is used to send the UL_MAP message. The multiple IEs included in the UL_MAP message are shown in Table 2: Table 2:

Referring to Table 2, the UL_MAP message includes a management message type (ManagementMessage Type) field (that is, sending message type information) representing multiple IEs; an Uplike Channel ID (Uplike Channel ID) field representing the uplink channel ID used; UCD Count (UCD Count) field, which indicates the count information in response to the change of the UCD (Uplink Channel Descriptor) message configuration containing the uplink burst profile; and the number of UL_MAP elements n (Number of UL_MAP Element n) field, which represents the number of elements found after the UCD count field. In this case, the uplink channel ID can only be allocated to the medium access control (MAC) sublayer.

The UIUC (Uplink Interval Usage Code) area record indicates the usage of the offset recorded in the offset area. For example, if 2 is recorded in the UIUC area, then the start offset used in the initial adjustment process is recorded in the offset area. If 3 is recorded in the UIUC area, then the start offset used in bandwidth request adjustment or maintenance adjustment processing is recorded in the offset area. The offset area records the start offset value used in the initial adjustment process or the maintenance adjustment process based on the information recorded in the UIUC area. The physical channel characteristic information to be transmitted from the UIUC area is recorded in the UCD.

If the SS causes the adjustment to fail, a predetermined back-off value is set to increase the probability of success in the next attempt, and the adjustment process is re-executed after the predetermined time corresponding to the back-off time has passed. In this case, the information required to determine the yield value is included in the UCD message. The aforementioned UCD message configuration is shown in Table 3 below:

Referring to Table 3, the UCD message includes: a management message type (ManagementMessage Type) field representing multiple IEs (ie, sending message type information); and an uplink channel ID (Uplink channel ID) field representing the uplink channel identifier used ; Configuration Change Count (Configuration Change Count) field counted by the BS; Mini-slot size (Mini-slot size) field representing the number of mini-slots of the uplink physical channel; The Range Backoff Start field of the initial backoff window size of the initial adjustment process; the Range Backoff End field that represents the backoff end point for the initial adjustment process (that is, the size of the last backoff window); The Request Backoff Start field that establishes the contention data and the request backoff start point (ie the initial backoff window size); and represents the backoff end point (ie the final backoff window size) used to establish the contention data and the request Request Backoff Start) field. In this case, the backoff value indicates the type of waiting time, which is the duration between the start of the access failure of the SS and the re-access time of the SS. If the SS fails to perform the initial adjustment, the BS must send a backoff value indicating the waiting time information, and the SS must wait for this period of time to arrive at the next adjustment process for the SS. For example, assuming that the "Ranging BackoffStart" and "Ranging Backoff End" fields shown in Table 3 are determined to be a specific number of 10, then the SS must cross 210 executable access opportunities (ie, 1024 executable access opportunities), and then Perform the next adjustment process according to the Truncated Binary Exponential Backoff Algorithm.

The TDM fields 220 and 230 indicate fields corresponding to time slots allocated using the TDM/TDMA (Time Division Multiplexing/Time Division Multiple Access) scheme. The BS uses a predetermined center carrier to transmit the broadcast information to be broadcast on the DL_MAP field 211 to the SS managed by the BS. After receiving the power-on signal, the SS monitors all the frequency bands previously allocated to each SS so that they detect the pilot channel signal with the highest signal strength, that is, the highest pilot CINR (Carrier to Interference and Noise Ratio). It is determined that the SS belongs to a specific BS that has transmitted a pilot channel signal with the highest pilot CINR. The SS checks the DL_MAP field 211 and UL_MAP field 213 of the downlink frame transmitted from the BS so that they recognize their own uplink and downlink control information and specific information indicating the actual data transmission/reception position.

With reference to FIG. 2, the downlink frame structure used in the IEEE 802.16a communication system is disclosed. The uplink frame structure used in the IEEE 802.16a communication system will be described below in conjunction with FIG. 3.

FIG. 3 is a conceptual diagram showing the structure of an uplink frame used in a BWA communication system using an OFDM/FODMA scheme. In more detail, FIG. 3 describes the structure of an uplink frame used in the IEEE 802.16a communication system.

Before describing the uplink frame structure shown in Figure 3, the following describes in detail the three adjustment processing used in the IEEE 802.16a communication system, namely: initial adjustment processing, maintenance adjustment processing (also called period adjustment processing) and bandwidth Request adjustment processing.

First, the initial adjustment process will be described in detail.

The initial adjustment process used to establish synchronization acquisition between the BS and the SS establishes the correct time offset between the SS and the BS, and is used to control the transmission power (also referred to as the transmission power). In more detail, the SS is powered on, and receives the DL_MAP message, the UL_MAP message, and the UCD message to establish synchronization with the BS, thereby performing initial adjustment processing to control the transmission power between the BS and the time offset. In this case, the IEEE 802.16a communication system uses the OFDM/OFDMA scheme, so that the adjustment process requires multiple adjustment sub-channels and multiple ranging codes. The BS allocates available adjustment codes to the SS according to the target of the adjustment processing (ie, adjustment processing type information). This operation will be explained in detail below.

The adjustment code is established by segmenting a PN (pseudorandom noise) sequence with a length of 215-1 bits into a plurality of predetermined units. Typically, an adjustment channel is composed of two adjustment sub-channels, each of which has a length of 53 bits. The PN code segmentation is performed on the adjustment channel with a length of 106 bits to establish an adjustment code. Up to 48 adjustment codes RC#1~RC#48 can be assigned to SS. More than two adjustment codes for each SS are applied as default values to three adjustment processes with different targets, namely, initial adjustment processing, period adjustment processing, and bandwidth request adjustment processing. In this way, the adjustment code is assigned to the SS differently according to the respective targets of the three adjustment processes. For example, as indicated by the prescribed item "N RC (Ranging Codes) for Initial Ranging" (N adjustment codes for initial adjustment), N adjustment codes are assigned to the SS used for initial adjustment processing; As indicated by "M RCs for maintenanceranging" (M RCs for maintenance adjustment), M adjustment codes are assigned to the SS used for periodic adjustment processing; and as in the specified item "L RCs for BW-request rangin (L RCs used for bandwidth request adjustment), L adjustment codes are assigned to the SS used for bandwidth request adjustment processing. The DL_MAP message is used to send the specified adjustment codes to the SS, and the SS uses The adjustment code contained in the DL_MAP message performs necessary adjustment processing.

Next, the cycle adjustment processing will be described in detail.

The bandwidth request adjustment process is performed periodically so that the SS that has controlled the time offset and the transmission power between the SS and the BS in the initial adjustment process can control the channel state associated with the BS. The SS uses the adjustment code assigned to the period adjustment process to perform the period adjustment process.

Third, the bandwidth request adjustment processing will be explained in detail.

The bandwidth request adjustment process is used to enable the SS, which has controlled the time offset and transmission power between the SS and the BS in the initial adjustment process, to request bandwidth allocation from the BS, so that the SS can communicate with the BS.

3, the uplink frame includes an initial maintenance opportunity (initial maintenance opportunity field) field 300 using initial and periodic adjustment processing, a request contention opportunity field 310 using bandwidth request adjustment processing, and a multiple An SS scheduled data (SS scheduled data) field 320 composed of uplink data of the SS. The initial maintenance opportunity field 300 includes a plurality of access burst fields each of which has actual initial and periodic adjustment processing, and a collision in which there is a conflict between the access burst fields. ) Field. The request contention opportunity field 310 includes a plurality of bandwidth request fields each of which has a real bandwidth request adjustment process, and a contention field in which there is contention between the bandwidth request adjustment fields. Each of the SS scheduling data fields 320 is composed of multiple SS scheduling data fields (ie, SS 1 scheduling data field to SS N scheduling data field). The SS transition gap (transition gap) is located between the SS scheduling data field (that is, the SS 1 scheduling data field to the SS N scheduling data field).

Figure 3 discloses the structure of an uplink frame used in the IEEE 802.16a communication system. The adjustment process of the IEEE 802.16a communication system using the OFDM scheme will be described below with reference to FIG. 4.

The flowchart of FIG. 4 shows an adjustment process between the SS and the BS in the BWA communication system using the OFDM scheme.

Referring to FIG. 4, the SS 400 monitors all its own predetermined frequencies after receiving the power-on signal so that it detects the pilot channel signal with the highest signal strength (ie, the highest pilot CINR (Carrier to Interference and Noise Ratio)). It is determined that the SS 400 belongs to the specific BS 420 that has transmitted the highest pilot CINR. The SS 400 receives the preamble of the downlink frame from the BS 420, thereby acquiring system synchronization with the BS 420.

After synchronization is established between the SS 400 and the BS 420, the BS 420 sends a DL_MAP message and a UL_MAP message to the SS 400 in steps 411 and 413, respectively. As shown in the previous Table 1, the DL_MAP message includes various information, for example, necessary information for establishing synchronization between SS 400 and BS 420 in the downlink direction and establishing the ability to be received and sent on the downlink channel. Configuration information of the physical channels of various messages of multiple SS 400. As shown in Table 2, the UL_MAP message notifies the SS 400 of SS scheduling interval information and physical channel configuration information.

The DL_MAP message is periodically broadcast from the BS to all SSs. In the case where the SS 400 can continuously receive periodically broadcast DL_MAP messages, it is assumed that the SS is synchronized with the BS. The SS receiving the DL_MAP message can receive all messages sent via the downlink channel.

As shown in the foregoing Table 3, if the SS causes an access failure, the BS sends a UCD message containing indication information of the available backoff value to the SS.

In the case of performing the above-mentioned adjustment process, the SS 400 transmits an RNG_REQ (Adjustment Request) message to the BS 420 in step 415. The BS 420 that has received the RNG_REQ message transmits an RNG_RSP (Adjustment Response) message containing information for controlling various factors (for example, frequency, time, and transmission power) to the SS 400 in step 417.

The configuration of the RNG_REQ message is shown in Table 4: Table 4:

Referring to Table 4, the Downlink Channel ID (Downlink Channel ID) field indicates the downlink channel ID included in the RNG_REQ message received via UCD in the SS. The Pending Until Complete field indicates the priority information for sending the adjustment response. Specifically, if the Suspend Until Completion field is set to "0", the preceding adjustment response has priority. Conversely, if the Suspend Until Completion field is not set to "0", the current sending adjustment response has priority.

Table 5 shows the detailed configuration of the RNG_RSP message of the RNG_REQ message shown in Table 4.

table 5:

Referring to Table 5, the Uplink Channel ID (Uplink Channel ID) field indicates the uplink channel ID included in the RNG_REQ message.

Fig. 4 discloses the adjustment process when the IEEE 802.16a communication system uses the OFDM scheme. The adjustment processing of the IEEE 802.16a communication system using the OFDMA scheme will be explained below with reference to FIG. 5. In this case, the IEEE 802.16a communication system includes a dedicated adjustment interval so that the IEEE 802.16a communication system can perform adjustment processing using the OFDMA scheme more efficiently, so that it can transmit according to the adjustment code transmission scheme in the dedicated adjustment interval. Ranging-Code (adjustment code) instead of RNG_REQ message.

Referring to FIG. 5, BS 520 sends a DL-MAP message and a UL_MAP message to SS 500 in steps 511 and 513, respectively. The specific operations of steps 511 and 513 are the same as steps 411 and 413. The communication system using the OFDMA scheme shown in FIG. 5 transmits an adjustment code instead of the RNG_REQ message described in FIG. 4 in step 515. The BS 520 that has received the adjustment code sends an RNG_RSP message to the SS 500 in step 517.

New information must be added to the RNG_RSP message so that the information corresponding to the adjustment code sent to the BS can be recorded in the RNG_RSP message. The aforementioned new information to be added to the RNG_RSP message consists of the adjustment code (i.e., the received adjusted CDMA code), the adjustment symbol (i.e., the OFDM symbol in the received adjusted CDMA code), and the arrangement of sub-channels (i.e., The permutation subchannel in the received permutation CDMA code) and the adjustment frame number (ie, the frame number in the received adjustment CDMA code).

As described above, the IEEE 802.16a communication system works on the basis of the current SS's fixed state (that is, the mobility of the SS is not considered) and the single-cell structure. However, the IEEE 802.16e communication system has been defined as a system that considers the mobility of the SS in the IEEE 802.16a communication system. Therefore, the IEEE 802.16e communication system must consider the mobility of the SS in a multi-cell environment. In order to provide the mobility of the SS in a multi-cell environment, it is necessary to switch the respective operation modes of the SS and BS. However, the IEEE805.16e communication system has not yet proposed a new method for the mobility of the SS in a multi-cell environment. In short, it is necessary to develop a handover system that takes into account the idle state and the communication service execution mode to provide mobility to the SS of the IEEE 802.16e communication system.

Summary of the invention

Therefore, the present invention has been made from the perspective of the above-mentioned problems, and an object of the present invention is to provide a system and method for performing a handover operation in a BWA communication system.

Another object of the present invention is to provide a system and method for performing a handover operation after receiving an SS request signal in a BWA communication system.

According to one aspect of the present invention, the above-mentioned and other objects are adopted for a broadband wireless access (BWA) communication system composed of a serving base station (BS) and a plurality of neighbor base stations adjacent to the serving BS, The SS handover method is implemented after receiving a handover request from a subscriber station (SS). The method includes the following steps: a) receiving information related to multiple neighbor BSs from a serving BS; b) receiving After the information related to the neighbor BS, measure the carrier-to-interference and noise ratio (CINR) of the pilot signal sent from the neighbor BS; c) combine the handover request signal with the pilot signal CINR of the neighbor BS The information is sent to the serving BS together; d) receiving information from the target BS among the neighbor BSs from the serving BS; and e) performing a handover function from the serving BS to the target BS.

According to another aspect of the present invention, there is provided a broadband wireless access (BWA) communication system composed of a serving BS and a plurality of neighbor BSs adjacent to the serving BS. The serving BS handover method after a handover request includes the following steps: a) sending information related to the neighbor BS to the SS; b) receiving a pilot signal containing the neighbor BS from the SS The handover request signal of the carrier-to-interference and noise ratio (CINR) information of the signal; c) Determine whether the neighbor BS included in the handover request signal can support the function of handover for the SS, and from Among the neighbor BSs capable of supporting the handover function of the SS, select a target BS as the handover target of the SS; and d) send the response signal related to the handover request signal of the SS and all The target BS information, and notify the target BS of the handover ready status of the SS.

According to another aspect of the present invention, there is provided a broadband wireless access (BWA) communication system composed of a serving base station (BS) and a plurality of neighbor BSs adjacent to the serving BS. ) The SS handover method after receiving the handover request includes the following steps: a) receiving information related to multiple neighbor BSs and handover condition information from the serving BS; b) after receiving neighbor BS information Measure the carrier-to-interference and noise ratio (CINR) of the pilot signal transmitted from the neighbor BS; c) Select multiple candidate BSs corresponding to the handover condition information from the neighbor BS, and request the handover The signal is sent to the serving BS together with the pilot signal CINR information of the candidate BS; d) after receiving the handover request signal, the information from the target BS among the candidate BSs is received from the serving BS ; And e) Perform a handover function from the serving BS to the target BS.

According to still another aspect of the present invention, there is provided a broadband wireless access (BWA) communication system composed of a serving base station (BS) and a plurality of base stations adjacent to the serving BS, in a slave subscriber station ( SS) a handover method after receiving a handover request, the method includes the following steps: a) controlling the serving BS to send neighbor BS information and handover condition information to the SS; b) according to the Neighbor BS information, controlling the SS to measure the carrier-to-interference and noise ratio (CINR) of the pilot signal transmitted from the neighbor BS; c) controlling the SS to determine multiple information corresponding to the handover condition from the neighbor BS Candidate BS, and send the handover request signal together with the pilot CINR information of the candidate BS to the serving BS; d) if the serving BS receives the handover request information from the SS, it is determined to be included in the cross-area Whether the neighbor BS in the handover request signal can support the handover function for the SS, and select the target BS from the candidate BSs that can support the handover function for the SS as the handover target of the SS; e) Control the serving BS to send the response signal related to the handover request signal to the SS together with the target BS information, and notify the target BS of the handover ready state of the SS; and f) according to the inclusion The target BS information in the handover request response signal controls the SS to perform a handover operation from the serving BS to the target BS.

According to another aspect of the present invention, there is provided a broadband wireless access (BWA) communication system composed of a serving base station (BS) and a plurality of neighbor BSs adjacent to the serving BS. ) The handover device after receiving the handover request includes: a serving BS that sends neighbor BS information and handover condition information to the SS, and after receiving a handover request signal from the SS Then, it is determined whether the neighbor BS included in the handover request signal can support the handover function for the SS, and the target BS is selected as the candidate BS that can support the handover function for the SS. The handover target of the SS, the response signal related to the handover request signal is sent to the SS together with the information of the target BS, and the handover ready status of the SS is notified to the target BS; and SS, the SS measures the carrier-to-interference and noise ratio (CINR) of the pilot signal transmitted from the neighbor BS according to the information of the neighbor BS, and selects multiple candidates corresponding to the handover condition information from the neighbor BS The BS sends the handover request signal together with the pilot signal CINR information of the candidate BS to the serving BS, and executes from the serving BS to the target BS according to the target BS information contained in the handover request response signal Handover operation of BS.

Description of the drawings

Through the following detailed description in conjunction with the accompanying drawings, the above and other objectives, features and advantages of the present invention will become easier to understand. Among them: The block diagram of Figure 1 shows a conventional BWA (Broadband Wireless) using the OFDM/OFDMA scheme. Access) communication system; Fig. 2 is a conceptual diagram showing a conventional downlink frame structure used in a BWA communication system using an OFDM/OFDMA scheme; Fig. 3 is a conceptual diagram showing an OFDM/OFDMA scheme The conventional uplink frame structure used in the BWA communication system; the flowchart of FIG. 4 shows the conventional adjustment process between the SS and the BS in the BWA communication system using the OFDM scheme; the flowchart of FIG. 5 shows The conventional adjustment process between the SS and the BS in the BWA communication system using the OFDMA scheme; the block diagram of FIG. 6 shows a BWA that performs various functions using the OFDM/OFDMA scheme according to a preferred embodiment of the present invention Communication system; FIG. 7 is a flowchart showing a handover process after receiving a handover request from an SS in a BWA communication system using an OFDM scheme according to a preferred embodiment of the present invention; the flowchart of FIG. 8 Shows a handover process based on receiving a handover request from an SS in a BWA communication system using an OFDMA scheme according to a preferred embodiment of the present invention; the block diagram of FIG. 9 shows a block diagram according to the present invention The internal configuration of the SS for performing the inventive function of a preferred embodiment; the flowchart of FIG. 10 shows the operation of the SS according to a preferred embodiment of the present invention; and the flowchart of FIG. 11 shows the operation of the SS according to the present invention. Invented a preferred embodiment of the operation of the serving BS.

detailed description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same or similar elements are denoted by the same reference numerals, even if they are described in different drawings. In the following description, when the description of known functions and configurations introduced here makes the subject of the present invention obscure, the description thereof will be omitted.

Fig. 6 is a block diagram showing a BWA communication system using an OFDM/OFDMA scheme to perform various functions according to a preferred embodiment of the present invention.

Before describing the BWA communication system shown in FIG. 6, it should be noted that the present invention adopts an IEEE 802.16e communication system using an OFDM/OFDMA scheme as a representative example. It should also be noted that the IEEE 802.16e communication system, which is a communication system in which SS mobility is considered in the IEEE 802.16a communication system, has not yet been developed. Assuming that the mobility of the SS is considered in the IEEE 802.16a communication system, the multi-cell structure and the handover operation of the SS between multiple cells (ie, the cell selection operation) can be considered. Therefore, the present invention provides the IEEE 802.16e communication system shown in FIG. 6.

Referring to FIG. 6, the IEEE 802.16e communication system includes a multi-cell structure, that is, multiple cells 600 and 650. More specifically, the IEEE 802.16e communication system includes a first BS 610 for the management unit 600, a second BS 640 for the management unit 650, and a plurality of SSs 611, 613, 630, 651, and 653. The OFDM/OFDMA scheme is used to establish signal transmission/reception between BS 610 and 640 and SS 611, 613, 630, 651, and 653. Among the user stations 611, 613, 630, 651, and 653, the user station 630 is located in the boundary area or the handover area between the cell 600 and the cell 650. Therefore, the cross-zone handover of the user station 630 must be supported in order to support the mobility of the user station 630.

Generally and according to an embodiment of the present invention, the SS used in the BWA communication system receives multiple signals from multiple BSs. The SS detects each CINR (Carrier to Interference and Noise Ratio) of the received pilot signal. The SS selects a specific BS that has transmitted the pilot channel with the highest CINR among the CINRs of the pilot signals, and determines the selected BS as the serving BS (that is, the active BS) to which the SS belongs. In more detail, the SS selects a BS with the best receiving state from a plurality of BSs that transmit pilot signals, and recognizes the selected BS as its own serving BS. For ease of description, the term "active BS" or "serving BS" may be used in the present invention for illustrative purposes.

The SS that has selected the active BS receives downlink frames and uplink frames from the active BS. The detailed structure of the downlink frame and the uplink frame received from the active BS has been disclosed in the prior art, and therefore, for the convenience of description, their description is omitted here. The present invention must add a new IE (information element) to the DL_MAP message provided by the IEEE802.16a/IEEE 802.16e communication system, so as to support the handover operation after receiving the request from the SS. Table 6 below shows the detailed configuration of the DL_MAP message used to support the handover operation after receiving the request of the SS: Table 6:

Referring to Table 6 above, the number of neighbor BSs (represented by "Neighbor list BS Num") represents the number of neighbor BSs included in the neighbor list. The neighbor list field refers to a list of neighbor BSs where the BS appears. "Neighbor list Info" means neighbor BSs included in the neighbor list, that is, multiple neighbor BSs from the first neighbor BS to the last neighbor BS. The neighbor list information represented by "Neighbor listInfo" includes a neighbor list BS ID (Neighbor list BS ID) field, a neighbor frequency (Neighbor Frequency) field, a neighbor frequency offset (NeighborFrequency Offset) field, and a neighbor frame offset (Neighbor Frame Offset) Field. The Neighbor list BS ID field indicates the ID of each BS included in the neighbor list. The NeighborFrequency field indicates the center frequency of the corresponding neighbor BS. The Neighbor Frequency Offset field indicates the frequency offset of the corresponding neighbor BS. The Neighbor Frame Offset field indicates the frame offset of the corresponding neighbor BS. The Measurement Info field includes the minimum pilot CINR (Pilotmin CINR) field, maximum time (MAX_T) field, and minimum time (MIN_T) field. The Pilot minCINR field is used as a reference for selecting neighbor BSs that can be included in the Neighbor list Info field from multiple BSs in the IEEE 802.16e communication system. In more detail, only BSs that transmit pilot signals each higher than Pilot min CINR can be used as neighbor BSs included in the neighbor list. The MAX_T field indicates the maximum time that each neighbor BS is allowed to have a pilot signal lower than Pilot min CINR. In more detail, the neighbor BS must send a pilot signal higher than the Pilot min CINR. If a pilot signal lower than Piolot min CINR is sent during the MAX_T time period, the corresponding neighbor BS is deleted from the neighbor list. In this way, if it can be sent within the MAX_T time period with Pilot min The neighbor BS of the pilot signal of the CINR has been deleted from the neighbor list, so the SS does not need to measure the unnecessary pilot CINR. The MIN_T time represents the minimum time during which the highest pilot CINR among the multiple pilot CINRs from the neighbor BS must be higher than the pilot CINR of the active BS. In more detail, in order to control the handover of the SS from the active BS to a specific neighbor BS (ie, the target BS), the CINR of the pilot signal sent from the target BS must be high for more than MIN_T time. To avoid the ping-pong (ping_pong) phenomenon in the CINR of other pilot signals sent from the current BS, the user station will send a notification to the CINR whenever the CINR of the received pilot channel is higher than the CINR of the active base station. The base station sends a handover request. In this case, it should be noted that the MAX_T time and MIN_T time can be determined differently according to the status and channel condition information of each BS in the IEEE 802.16e communication system.

The SS that has received the DL_MAP message and the UL_MAP message requests an adjustment request step for the adjustment process from the current BS and the adjustment response step for sending a response signal to the adjustment correction request to the SS that has already sent the adjustment request is the same as these steps in the prior art. Therefore, for the convenience of description, the related description is omitted here. Successfully established wireless communication between the adjusted SS and the current BS. The handover process in response to the SS request signal during the wireless access communication time period between the SS and the active BS will be described below with reference to FIG. 7.

Fig. 7 is a flowchart showing a handover process after a handover request is received from an SS in an IEEE 802.16e communication system using an OFDM scheme according to a preferred embodiment of the present invention.

Referring to FIG. 7, after the system synchronization is established between the SS 701 and the serving BS (also referred to as the active BS) 702, the serving BS 702 sends a DL_MAP message and a UL_MAP message to the SS 701 in steps 711 and 712, respectively. The DL_MAP message format and the UL_MAP message format are disclosed in Table 6 and Table 2, respectively, so detailed descriptions thereof will be omitted here. The SS 701 receives the DL_MAP message to detect the information of the neighbor BS of the SS 701, thereby enabling the SS 701 to measure the CINR of the pilot signal received from the neighbor BS in step 731.

The SS 701 suspends receiving the transmission data of the serving BS 702. In detail, the SS 701 measures the CINR of the pilot signal received from the neighbor BS during the interruption of the reception of data transmitted by the serving BS 702. In this case, the SS 701 does not measure the CINR of each pilot signal received from all neighbor BSs included in the neighbor list of the DL_MAP message, and is only used to measure the pilot signal received by the neighbor BS that exceeds the MIN_T time. CINR of the frequency channel signal. The method of measuring the CINR of the pilot signal received from the neighbor BS will be described in detail below.

The SS 701 uses various information of neighbor BSs included in the neighbor list of the DL_MAP message to establish synchronization with each neighbor BS. After establishing synchronization with the neighbor BS, the SS 701 measures the CINR of the pilot signal received from the neighbor BS.

The SS 701, which has measured the CINR of the pilot signal received from the neighbor BS, determines whether it needs to handover to another BS instead of handover to the serving BS 702. The handover steps of the SS 701 will be described in detail below. At least one of the CINRs of the pilot signals received from the neighbor BS must satisfy the MAX_T condition. Assuming that in a period longer than MAX_T, the CINR of the pilot signal received from the neighbor BS included in the neighbor list is less than the minimum pilot CINR indicated by "Pilot min CINR", then the corresponding pilot signal will be Delete from the neighbor list, so that the MAX_T condition must be met. In this case, each neighbor BS that has satisfied the MAX_T condition is called a candidate BS (ie, target BS). If the MAX_T condition has been met, the SS 701 determines whether the CINR of the pilot signal transmitted from the neighbor BS is greater than the CINR of the pilot signal received from the serving BS 702. If it is determined that the CINR of the pilot signal received from the serving BS 702 is greater than the respective CINRs of the pilot signals received from the neighbor BS, the SS702 does not request the serving BS 702 for the handover operation. Conversely, if it is determined that the CINR of the pilot signal received from the serving BS is less than the CINR of the pilot signal received from the neighbor BS, then the SS 701 requests the serving BS 702 for the handover operation. Needless to say, SS 701 requests the serving BS 702 for the handover operation only when a neighbor BS meeting the MIN_T condition is found. The reason why the SS 701 requests a handover operation from the serving BS 702 only when the MIN_T time condition is met is to avoid the aforementioned ping-pong phenomenon.

If the handover operation is determined, the SS 701 sends a handover request (HO_REQ) message to the serving BS 702 in step 713. Table 7 shows the format of the HO_REQ message: Table 7:

Before describing Table 7, it should be noted that after receiving the handover request from the SS 701, the neighbor BS acts as the target BS. Therefore, after the SS has generated the handover request, they are the same as the target BS. Referring to FIG. 7, the Neighbor list BS carrier frequency field indicates the carrier frequency of the neighbor BS (ie, the target BS) that has received the handover request from the SS 701. The CNIR (CNIR of Neighbor list BS) field of the neighbor list BS indicates the CINR of the pilot signal transmitted from the neighbor BS. The QoS field indicates the quality of service (QoS) expected by the SS 701. The BW request (BW request) field indicates the requested bandwidth in response to the QoS expected by the SS 701. In this case, QoS consists of various service levels, namely, Unsoliciated Grant Sercice (UGS), real-time polling service (rtPS), non-real-time polling service (nrtPS) and best effort service (Best Effort). Service, BE). The serving BS 702 that has received the handover request message from the SS 701 arranges the neighbor BSs included in the handover request message. There are various possible ways to arrange neighbor BSs. As mentioned above, stop using SS 701 The CINR of the neighbor BS that measures the CINR of the pilot signal is set to "0". The serving BS 702 may configure the information of the arranged neighbor BSs in the form of a list, and may store the information in the list format.

The serving BS 702 that arranges the neighbor BSs sequentially sends HO_CONNECTION_REQ (Handover Connection Request) messages to the corresponding neighbor BS (ie, the target BS) in steps 714 and 716 according to the order of the neighbor BSs. The format of the HO_CONNECTION_REQ message is shown in Table 8 below: Table 8:

Referring to Table 8, Target BS ID (Target BS ID) represents ID information of the target BS. CID (Connection ID) is a connection ID assigned from the serving BS 702 to the SS 701. The QoS field indicates the quality of service (QoS) expected by the SS 701. The BW request field indicates the requested bandwidth in response to the QoS expected by the SS 701. The reason why the serving BS 702 sends the HO_CONNECTION_REQ message to the target BS (ie, the target BS1 703 and the target BS2704) is to determine whether the QOS and bandwidth associated with the service expected by the SS 701 can be satisfied.

If the target BSs 703 and 704 receive the HO_CONNECTION_REQ message, they send the HO_CONNECTION_RSP (Handover Connection Response) message to the serving BS702 in steps 715 and 717. Table 9 below shows an example of the HO_CONNECTION_RSP message format: Table 9:

Referring to Table 9, the Target BS ID (Target BS ID) field indicates the ID information of the target BS sending the HO_CONNECTION_RSP, and the CID is the connection ID of the serving BS 702 for the SS 701. The ACK/NACK field indicates HO (Handover) approval or disapproval information of SS 701. In more detail, in the case where the ACK message is included in the HO_CONNECTION_RSP message, the corresponding target BS can provide the SS 701 with the handover function. In the case where the NACK message is included in the HO_CONNECTION_RSP message, the corresponding target BS cannot provide the SS 701 handover function. As shown in FIG. 7, the target BS 703 sends a HO_CONNECTION_RSP message including a NACK field indicating that the handover to the SS 701 cannot be supported. Assume that the target BS2 704 sends a HO_CONNECTION_RSP message including an ACK field indicating that the handover to the SS 701 can support the state.

The HO_CONNECTION_REQ message and the HO_CONNECTION_RSP message are sent sequentially as shown in FIG. 7, but they can also be sent at the same time when needed.

After receiving the HO_CONNECTION_RSP message from the target BS, the serving BS 702 detects the ACK/NACK field included in the received HO_CONNECTION_RSP message, thereby setting the target BS (ie, target BS2 704) that sent the HO_CONNECTION_RSP message containing the ACK field It is the last target BS that the SS 701 will be handed over to. Thereafter, the serving BS 702 sends a HO_RSP (Handover Response) message containing the information of the last target BS to the SS 701 in step 718. The HO_RSP message includes the information of the last target BS to which the SS 701 will be handed over. Table 10 shows an example of the HO_RSP message:

Table 10:

Referring to Table 10, the target BS ID (Target BS ID) field indicates the ID information of the last target BS to which the SS 701 will handover. Target BS carrier frequency (Target BS carrier frequency) represents the carrier frequency of the last target BS. The serving BS 702 that has sent the HO_RSP message sends a HO_CONNECTION_CFM (Handover Connection Confirmation) message to the last target BS (ie, target BS 2704) in step 719. In this case, a HO_CONNECTION_CFM message indicating that SS 701 will be handed over to the last target BS704 is sent. Table 11 shows an example of the HO_CONNECTION_CFM message: Table 11:

Referring to Table 11, the target BS ID (Target BS ID) field indicates the ID information of the neighbor BS (that is, the last target BS) that receives the HO_CONNECTION_CFM message. The CID represents the connection ID allocated from the serving BS 702 to the SS 701. The serving BS 702 that has sent the HO_CONNECTION_CFM message to the target BS 2704 releases the link connected to the SS 701 in step 734.

The target BS2 704 sends the DL_MAP message and the UL_MAP message to the SS 701 in steps 720 and 721, respectively. The DL_MAP message and the UL_MAP message contain the update message of the SS 701. The SS 701 that has received the DL_MAP message and the UL_MAP message sends an RNG_REQ (Adjustment Request) message to the target BS 2704 in step 722. The target BS2 704 that has received the RNG_REQ message transmits the RNG_RSP message as a response message related to the RNG_REQ message to the SS 701 in step 723. The detailed processing performed in steps 720 to 723 is the same as steps 411 to 417 shown in FIG. 4. Therefore, a detailed description of these steps will not be given here.

FIG. 7 discloses the handover process performed after receiving a handover request from the SS in the IEEE 802.16e communication system using the OFDM scheme. The flowchart of FIG. 8 shows the handover process performed after receiving the handover request from the SS in the IEEE 802.16e communication system using the OFDMA scheme according to a preferred embodiment of the present invention.

Before describing FIG. 8 in detail, it should be noted that steps 811 to 821 and steps 831 to 834 shown in FIG. 8 are respectively the same as steps 711 to 721 and steps 731 to 734 shown in FIG. The description will be omitted. Since the OFDMA scheme is applied to FIG. 8, the SS 801 transmits an adjustment code instead of the RNG_REQ message to the last target BS (ie, target BS2 804) in step 822. The target BS2 804 that has received the adjustment code sends an RNG_RSP message as a response related to the adjustment code to the SS 801 in step 823. More specifically, the handover process of FIG. 7 is basically the same as the handover process of FIG. 8. However, the IEEE 802.16e communication system transmits the RNG_REQ message according to the OFDM scheme of FIG. 7, and the adjustment is transmitted according to the OFDMA scheme of FIG. 8. code. FIG. 8 discloses the handover process performed after receiving a handover request from the SS in the IEEE 802.16e communication system using the OFDMA scheme. The internal configuration of the SS for implementing the present invention will be described below with reference to FIG. 9.

Fig. 9 is a block diagram showing the internal configuration of an SS for performing the functions of the present invention according to a preferred embodiment of the present invention. 9, the internal configuration of the SS includes a matched filter 900, a received power measurement unit 910, a received power comparator 920, a controller 930, and a transmitter 940. The matched filter 900 determines whether the PN (pseudo-noise) code used for synchronization detection is synchronized, and outputs a predetermined energy value according to the determined result. In this case, the correlator may be used as the matched filter 900. The matched filter 900 compares the received synchronization detection PN code with the unique PN code of the SS, and outputs the energy value associated with the same PN code. Specifically, the matched filter 900 sequentially puts the received signals of the SS in a predetermined window, and performs a predetermined bit operation in parallel with the unique PN code value, thereby generating a sum of bit operation values. Therefore, if the received signal of the SS is equal to the value of the unique PN code stored in the SS, this state is called an auto-correlation state, resulting in the maximum energy value. If the SS received signal is different from the value of the unique PN code, this state is called an inconsistent synchronization state, resulting in a relatively low energy value. Generally, the output energy value is compared with a predetermined threshold value in order to determine whether an autocorrelation state is established. In short, the output value of the matched filter 900 is compared with the predetermined threshold value, so that the presence or absence of the autocorrelation state can be determined.

If the received power measurement unit 910 is synchronized with the pilot signal received from the neighbor BS through the matched filter, the received power measurement unit 910 measures the received power of the received pilot signal. The received power measurement unit 910 measures the CINR of the received pilot signal, and sends the measured CINR of the pilot signal to the received power comparator 920. After receiving the CINR of the pilot signal from the received power measurement unit 910, the received power comparator 920 compares the received CINR of the pilot signal of the neighbor BS with a predetermined threshold (ie, Pilot min CINR). If at least one pilot signal CINR among the pilot signals CINR transmitted from the neighbor BS is greater than the threshold, then the received power comparator 920 proceeds to the next step. More specifically, it is determined whether the CINR of at least one pilot signal among the CINRs of the pilot signals of the neighbor BS is greater than the CINR of the pilot signal of the serving BS. If it is determined that the neighbor BS whose pilot signal CINR is greater than the CINR of the serving BS's pilot signal is determined, then the information of the neighbor BS whose pilot signal's CINR is greater than the CINR of the serving BS's pilot signal will be sent to the controller 930. The controller 930 determines whether the SS sends its own handover request to the serving BS according to the information received from the received power comparator 920.

More specifically, if the CINR of the pilot signal transmitted from the neighbor BS is greater than the CINR of other pilot signals transmitted from the serving BS, the controller 930 generates the handover request signal of the SS. In this case, although it is not described in the drawings, it should be noted that in the handover process, the MAX_T and MIN_T conditions must be satisfied. The controller 930 generates a handover request (HO_REQ) message by controlling the transmitter 940, and sends the generated handover request message to the serving BS. The transmitter 940 generates a HO_REQ message after receiving the control command from the controller 930, and sends the HO_REQ message to the serving BS.

Figure 9 discloses the internal configuration of the SS according to the present invention. The operation of the SS will be described below with reference to FIG. 10. Fig. 10 is a flowchart showing the operation of the SS according to a preferred embodiment of the present invention. 10, the SS reads the DL_MAP message received from the serving BS in step 1000, reads the UL_MAP message received from the serving BS in step 1002, and reads the neighbor BS list information contained in the DL_MAP message in step 1004. If so The SS reads the information of the neighbor BS in step 1004, then it sets the ID "i" indicating the number of neighbor BSs to "0" (i.e., i=0) in step 1004.

The SS adds the number 1 to the variable "i" (i.e., i=i+1), measures the CINR of the pilot signal sent from the i-th neighbor BS in step 1006, and proceeds to step 1008. In this case, it is assumed that the number of neighbor BSs transmitted from the serving BS is in the range from "BS_1" to "MAX_BS_NUM", therefore, the SS measures the CINR of the pilot signal of the "BS_1" neighbor BS in step 1006, And it is determined in step 1008 whether the number of neighbor BSs whose pilot signal CINR has been measured is equal to or greater than "MAX_BS_NUM". If it is determined in step 1008 that the number of measured neighbor BSs is equal to or greater than "MAX_BS_NUM", the SS proceeds to step 1010. Conversely, if it is determined in step 1008 that the number of neighbor BSs to be measured is less than "MAX_BS_NUM", the SS returns to step 1006.

If it is determined that the value of MAX_Neighbor BS CINR is equal to or less than the CINR of the pilot signal of the serving BS, the SS returns to step 1000. Conversely, if it is determined that the value of MAX_Neighbor BS CINR is greater than the CINR of the pilot signal of the serving BS, the SS determines its own handover request, and proceeds to step 1012.

The SS sends the HO_REQ message to the serving BS in step 1012. The detailed configuration of the HO_REQ message is disclosed in the foregoing Table 7. The SS receives the HO_RSP message related to the HO_REQ message from the serving BS in step 1014, and proceeds to step 1016. The detailed configuration of the HO_RSP message is disclosed in the foregoing Table 10. The SS reads the ID and carrier frequency information of the last target BS from the HO_RSP message in step 1016, and then proceeds to step 1018. In this case, the last target BS serves as the specific BS to which the SS is handed over.

The SS converts the SS frequency to the target BS frequency, and proceeds to step 1020, thereby interrupting the data transmission/reception between the SS and the serving BS, and the SS can communicate with the last target BS. The SS reads the DL_MAP message received from the last target BS in step 1020, and proceeds to step 1022. The SS reads the UL_MAP message received from the last target BS and proceeds to step 1024. In step 1024, the SS communicates with the last target BS and ends its handover operation.

Figure 10 discloses the operation of the SS according to the present invention. The operation of the serving BS will be described below with reference to FIG. 11. FIG. 11 is a flowchart showing the operation of a serving BS according to a preferred embodiment of the present invention. The serving BS sends a DL_MAP message to the SS in step 1100, and sends a UL_MAP message to the SS in step 1102.

The serving BS receives the HO_REQ message from the SS in step 1104, and proceeds to step 1106. The detailed configuration of the HO_REQ message is disclosed in the foregoing Table 7. The serving BS arranges the CINRs of the pilot signals of the neighbor BSs in order of decreasing amplitude, and proceeds to step 1108. In this case, the CINR of the pilot signal of the neighbor BS is included in the HO_REQ message. As described above, the neighbor BS used to order the SS to measure the pilot signal CINR acts as a candidate BS that satisfies the MAX_T and MIN_T conditions. Therefore, each candidate BS has a signal greater than the Pilot min CINR (ie, the minimum pilot signal CINR) . As previously described in FIG. 10, it is assumed that the number of neighbor BSs of the SS is within the range from BS_1 to MAX_BS_NUM. In addition, in step 1106, ID "i" indicating the number of neighbor BSs is set to "0" (i.e., i=0). The ID representing the number "i" of neighbor BSs is determined in the order of the pilot CINR.

The serving BS transmits the HO_CONNECTION_REQ message to the neighbor BS having the largest pilot CINR among the arranged neighbor BSs in step 1108. The detailed configuration of the HO_CONNECTION_REQ message is shown in the foregoing Table 8.

The serving BS receives the HO_CONNECTION_RSP message indicating the response to the HO_CONNECTION_REQ message from the neighbor BS that has sent the HO_CONNECTION_REQ message in step 1110, and proceeds to step 1112. The foregoing Table 9 discloses the detailed configuration of the HO_CONNECTION_RSP message. The serving BS determines whether any neighbor BS among the neighbor BSs that send the SS handover request signal can support the handover function of the SS. More specifically, the serving BS determines whether the ACK message is included in the HO_CONNECTION_RSP message. If it is determined that a specific neighbor BS among the neighbor BSs can support the handover service of the SS, the serving BS proceeds to step 1116. Conversely, if it determines that no neighbor BS can support the handover service of the SS, then the serving BS proceeds to step 1114. The serving BS selects the neighbor BS with the second largest pilot CINR among the neighbor BSs in step 1114 and adds 1 to the variable "i" (ie, i=i+1), and returns to step 1108.

The serving BS sends the HO_RSP message to the SS in step 1116 and proceeds to step 1118. The foregoing Table 10 has disclosed the detailed configuration of the HO_RSP message. The serving BS sends the HO_CONNECTION_CFM message to the neighbor BS capable of supporting the handover function (ie, the final target BS) in step 1118, and returns to step 1120. The foregoing Table 11 has disclosed the detailed configuration of the HO_CONNECTION_CFM message. Needless to say, the serving BS may first send the HO_CONNECTION_CFM message to the last target BS, or may send the HO_RSP message to the SS. The serving BS releases the link connected to the SS in step 1120 and ends its handover operation.

It can be clearly seen from the above description that the present invention enables an SS based on a multi-cell structure to perform a handover operation, thereby ensuring the mobility of the SS. More specifically, the traditional SS performs communication functions in a single cell, so when the SS moves to another cell, it must abandon the link connected to the BS currently communicating with the SS. In addition, the traditional SS must re-establish the communication mode with the new BS, and therefore, it must re-execute the initial adjustment process. However, for the aforementioned problems of the traditional SS, the present invention performs handover processing without having to perform initial adjustments on the new BS, thereby reducing the interruption time of data communication.

Although the preferred embodiments of the present invention have been described for illustrative purposes, it is clear to those skilled in the art that various modifications and additions can be made without departing from the scope and spirit of the present invention as defined by the appended claims. And replacement is possible.