KR101148410B1 - Apparatus and method for deciding vertical handoff - Google Patents

Abstract

An apparatus and method for determining handoff between heterogeneous networks in a terminal capable of communicating with a WLAN network and a broadband wireless communication network, the apparatus comprising: a MAC (Medium Access Control) for providing information on transmission rate of signals transmitted and received with the WLAN to a handoff determination module between heterogeneous networks; A layer and a heterogeneous network handoff determination module for determining whether to make a handoff between the heterogeneous networks by using the transmission rate information provided from the MAC layer, and considering performance of other nodes connected to the WLAN. Prevents Performance Anomaly In addition, there is an advantage of more reliably guaranteeing seamless connectivity of the node by using the amount of change in transmission rate according to the distance between the AP and the node of the WLAN.

Heterogeneous Handoff, Beacon Message, Broadband Wireless Communication System, Wireless LAN

Description

Apparatus and method for determining heterogeneous manganese handoff {APPARATUS AND METHOD FOR DECIDING VERTICAL HANDOFF}

1 is a diagram illustrating a typical Hormonal / Vertical handoff;

FIG. 2 is a diagram illustrating a MAC protocol enabling efficient sharing of multiple nodes in a typical WLAN.

3 is a view showing a change in throughput according to the number of nodes in a typical wireless LAN,

4 is a view illustrating a change in transmission speed according to a distance between a conventional WLAN and a node;

5 is a diagram illustrating a throughput release phenomenon occurring in a conventional wireless LAN.

6 is a diagram illustrating a hierarchical structure of nodes for performing heterogeneous network handoff according to the present invention;

7 is a view showing a multiple transmission rate according to the distance of a wireless LAN according to the present invention;

8 is a diagram illustrating a physical layer format of a transmission / reception call of a wireless LAN according to the present invention;

9 is a diagram showing a service range of an IEEE 802.16 system and a WLAN according to an embodiment of the present invention;

10 is a diagram illustrating a ping pong phenomenon between a WLAN and an IEEE 802.16 system according to a first embodiment of the present invention;

11 is a diagram illustrating a ping pong phenomenon between a WLAN and an IEEE 802.16 system according to a second embodiment of the present invention;

12 is a diagram illustrating an operation procedure of a node for determining handoff from an WLAN to an IEEE 802.16 system according to a first embodiment of the present invention;

13 is a diagram illustrating an operation procedure of a node for determining handoff from an WLAN to an IEEE 802.16 system according to a second embodiment of the present invention;

14 is a diagram illustrating an operation procedure of a node for determining handoff to a WLAN in an IEEE 802.16 system according to a first embodiment of the present invention;

15 is a diagram illustrating an operation procedure of a node for determining handoff to a WLAN in an IEEE 802.16 system according to a second embodiment of the present invention; and

16 is a graph for receiving a beacon message in accordance with the IEEE 802.11 standard.

The present invention relates to an apparatus and a method for determining handoff between heterogeneous networks, and in particular, to solve resource imbalance between networks in a heterogeneous network environment (e.g., IEEE 802.16 broadband wireless communication, WLAN). An apparatus and method for determining a network to perform handoff between heterogeneous networks in a terminal in consideration of load of a system.

Recently, as the interest in the wireless multimedia era and ubiquitous has increased, the necessity of transmitting large amounts of data at high speed using a wireless channel is rapidly increasing, and thus, a wireless and high-speed data transmission system for supporting Internet services through a mobile channel and a wireless channel. Is being actively studied around the world.

As part of the research on the wireless high-speed data transmission system, mobility in wireless local area network (LAN) and IEEE of Institute of Electrical and Electronics Engineers (IEEE) 802.16 system guaranteeing a relatively high transmission speed at a transmission rate of 20Mbps to 50Mbps. ) And new communication systems are being developed to ensure QoS.

Here, the WLAN was developed in 1999 for short-range communication for stationary users in limited areas such as indoors, crowded urban centers, and university libraries to expand the conventional wired LAN based on IEEE 802.11. The WLAN provides Internet access at a high data rate of up to 11-54 Mbps in accordance with technical standards within a hot spot.

In addition, the cost of the access point (hereinafter referred to as "AP") for establishing the hot spot is not only low in cost, but also has an advantage of easy installation.

However, as the radius of the wireless LAN is about 100m and a service area is narrow, a very large number of APs are required to widen the area. In addition, handoff (horizontal handoff) is not supported during the movement between the wireless LAN, and also has a disadvantage in that it is difficult to provide a service during the movement in the hot spot.

Next, the IEEE 802.16 system is a service that enables wireless Internet access at any time and anywhere without interruption, walking, and moving at medium speed (up to 60 km / h). In particular, the IEEE 802.16 system provides a transmission speed of 1Mbps or more that can smoothly provide various ultra-high speed wireless multimedia services, and can support various multimedia terminals such as notebooks, PDAs, or smart phones.

Moreover, the cell radius is around 10km, and nationwide wide area service is possible through network configuration. The IEEE 802.16 system supports handoff to provide a seamless service even during high-speed movement. However, due to the low transmission rate of hundreds of kbps, which is much lower than the high transmission rate of the wireless LAN, there is a limit to serving a large amount of multimedia content that meets the needs of consumers. Accordingly, the IEEE 802.16 system is a wireless Internet technology suitable for providing a service such as the Internet to a user in a high speed mobile state at a medium / low speed transmission speed.

As described above, since the WLAN and the IEEE 802.16 system have opposite characteristics, by utilizing the advantages of each network, it is possible to construct a new type of communication system having high performance more efficiently. That is, when a user belongs to the service area of the WLAN and the IEEE 802.16 system at the same time, a heterogeneous handset for efficiently using the system by adaptively selecting the WLAN and the IEEE 802.16 system according to the situation of the user. The research on the off is emerging.

FIG. 1 illustrates a typical Horizontal / Vertical handoff.

Referring to FIG. 1, handoffs (steps 115, 117, and 119) performed in the homogeneous network in each layer (101, 103, and 105) mean horizontal handoff, and are performed between heterogeneous networks. The handoffs (steps 107, 109, 111, and 113) are referred to as vertical handoffs.

As shown in FIG. 1, the horizontal handoff is made between the same networks, whereas the network service area is the same, whereas the vertical handoff is handoff (steps 107 and 109) from a small service area to a large area. Then, handoff (steps 111 and 113) is performed from the large area to the small area.

As described above, the heterogeneous network handoff between networks having different characteristics (for example, WLAN and IEEE 802.16 system) has higher performance according to the characteristics of each of the networks and efficiently distributes resources to efficiently utilize resources. It should be maximized. In addition, it is very important to support seamless connectivity between networks performing the heterogeneous network handoff.

For example, the WLAN and the IEEE 802.16 system have a hierarchical structure in which the service area of the IEEE 802.16 system includes the service area of the WLAN. Handoff between the two systems (IEEE 802. 16 system and WLAN) does not cause problems for the users to perform handoff to the IEEE 802. 16 system.

However, if only the high transmission rate is pursued without considering the efficient distribution of resources of the two systems, the access is attempted only to the wireless LAN having a higher transmission rate than the IEEE 802.16 system. As a result, the wireless LAN increases in number of users, resulting in deterioration in performance due to performance deformity and packet collisions. In addition, there is a problem of resource imbalance that wastes resources of the IEEE 802.16 system.

Looking at the problem caused by the user access to the WLAN in detail as follows.

First, performance degradation due to packet collision in the WLAN will be described. The WLAN is a Point Coordination Function (PCF) that enables efficient sharing of the limited wireless channel of the IEEE 802.11 standard by multiple nodes (Nodes, " Stations ", " Terminals "). Two types of medium access control (MAC) protocols are specified: and Distributed Coordination Function (DCF).

2 illustrates a MAC protocol that enables efficient sharing of multiple nodes in a typical WLAN.

As shown in FIG. 2, the PCF 203 is used on the DCF 201 base. First, the DCF 201 is a protocol based on carrier-sense multiple access with collision avoidance (CSMA / CA). That is, the DCF 201 does not control channel access by an infrastructure such as an access point (AP) of the WLAN, but allows each node to form a network by contention. Meanwhile, the PCF 203 controls channel access by specific stations such as the AP on the base of the DCF 201.

In other words, the DCF 201 performs a service in the form of best effort, and the PCF 203 performs a time-bound service to guarantee QoS. However, the PCF 203 has not been used commercially yet due to its complexity and various problems. Currently, only the DCF 201 is implemented and used as a wireless LAN card. Therefore, in the present invention, it is assumed that the IEEE 802.11 DCF protocol is used.

The IEEE 802.11 DCF protocol is used as an operation method of most WLAN cards because of its simplicity and flexibility. However, since the DCF is distributed based on the CSMA / CA method for each node, when a large number of nodes are connected to a single AP for service, the probability of packet collision between the nodes is increased. As illustrated in the graph illustrating a change in throughput according to the number of nodes of the WLAN, the throughput of the WLAN is reduced.

Next, the performance heterogeneity of the WLAN occurs as follows. Another notable feature of the IEEE 802.11 protocol related to the throughput of the WLAN is that it supports multi-rate at the physical layer. This means that each node can not only use a fixed transmission rate, but also change the transmission rate according to the channel state.

Table 1 below shows various modulation techniques used in a wireless LAN such as IEEE 802.11a / h.

Mode Modulation Code rate Data rate BpS One BPSK 1/2 6 Mbps 3 2 BPSK 3/4 9 Mbps 4.5 3 QPSK 1/2 12 Mbps 6 4 QPSK 3/4 18 Mbps 9 5 16-QAM 1/2 24 Mbps 12 6 16-QAM 3/4 36 Mbps 18 7 64-QAM 2/3 48 Mbps 24 8 64-QAM 3/4 54 Mbps 27

As shown in Table 1, data rates can be performed at various rates from 6Mbps to 54Mbps through various modulation techniques and different code rates used in the WLAN.

The reason why the various transmission rates are used through the other modulation schemes is that the state of each channel is different depending on the distance between the AP and the corresponding node or the peripheral interference. That is, a node with good channel condition has a high modulation order such as 64-QAM (Quadrature Amplitude Modulation) and 16-QAM, but does not have a high bit error rate (BER). Can be used. However, a node with poor channel condition cannot transmit due to BER being too high when using modulation schemes such as 64-QAM and 16-QAM. Therefore, a modulation scheme such as Binary Phase Shift Keying (BPSK) or Quadrature Phase Shift Keying (QPSK), which is a robust modulation technique against errors such as noise and interference, has a low data rate.

In addition, the communication range varies depending on the signal-to-interference noise ratio (hereinafter referred to as SINR) of the communication channel. Table 2 below shows that the SINR required for communication differs according to a modulation scheme.

Table 2 below shows the SINR according to the modulation scheme according to IEEE 802.11a.

Rate (Mbps) Modulation Coding rate SINR (dB) 54 64-QAM 3/4 54.56 48 64-QAM 2/3 24.05 36 16-QAM 3/4 18.80 24 16-QAM 1/2 17.04 18 QPSK 3/4 10.79 12 QPSK 1/2 9.03 9 BPSK 3/4 7.78 6 BPSK 1/2 6.02

Table 2 shows the change of SINR according to modulation scheme and code rate. For example, to decode a 54 Mbps signal even at the same distance as the sender, more than 48.54 dB (54.56-6.02) of intensity is required than when decoding a 6 Mbps signal. Thus, modulation schemes with high data rates require strong signals for decoding. That is, the distance to the sender should be close.

4 shows usable transmission rates according to distance in the IEEE 802.11 a / b / g standard. In the following description, FIG. 4A shows a graph of available transmission rates according to distance in the IEEE 802.11 a / b / g standard, and FIG. 4B shows changes in transmission rates with distance in IEEE 802.11a. In addition, the horizontal axis represents the distance between the sender and the receiver, and the vertical axis represents the transmission speed.

As shown in FIG. 4A, the available transmission rates for distances of 802.11a (401), 802.11b (403), and 802.11g (405) may be used as the distance between the transceivers increases. It can be seen that the speed is lowered. For example, looking at the amount of change in the transmission rate of the IEEE 802.11a (401), when the distance between the transmitter and the receiver is more than 125 feet 407, communication is possible only at the minimum speed of 6 Mbps and farther than about 150 feet. (409) Communication becomes impossible. In other words, as the distance between the transmitters and receivers increases, noise or interference becomes more severe. Therefore, a transmission rate must be lowered because communication is possible by using a robust modulation technique for noise and interferences.

5 illustrates a throughput release phenomenon occurring in a conventional wireless LAN. In the following description, it is assumed that only two nodes exist on the WLAN based on the IEEE 802.11b.

5A illustrates a case in which the two nodes 501 and 503 both have a transmission rate of 11 Mbps. In FIG. 5A, when the Node A 501 and the Node B 503 alternately transmit data according to the DCF protocol, the wireless LAN overall throughput takes into consideration a protocol overhead. In this case, each node has a throughput of about 3.3Mbps.

FIG. 5B shows a case in which the node C 505 has a transmission rate of 1 Mbps and the node D 507 has a transmission rate of 11 Mbps among the two nodes 505 and 507. In FIG. 5B, when the Node C 505 and the Node D 507 alternately transmit data according to the DCF protocol, the wireless LAN overall throughput takes into consideration a protocol overhead. Each node has a throughput of about 0.76Mbps.

In other words, as described above, the phenomenon of affecting other nodes having a high transmission rate due to the participation of a node having a low transmission rate and causing a decrease in throughput is referred to as the throughput release phenomenon.

Meanwhile, the IEEE 802.16 service requires a transmission delay condition (QoS), such as video streaming, audio streaming, and interactive games, and provides a real-time service that guarantees resources during the service, and a non-real-time service (eg, file transmission, Multimedia mail, chat, e-commerce), and web services and e-commerce.

Table 3 below shows the main schemes and requirements to be used for wireless access of a 2.3 GHz IEEE 802.16 system.

Item Method or value Multiplexing TDD Multiplexed Connection OFDMA Channel bandwidth 10 MHz Transmission rate per subscriber Upward minimum / maximum transfer rate: 128Kbps / 1Mbps
Downward minimum / maximum transfer rate: 512Kbps / 3Mbps Frequency reuse factor One Frequency efficiency Maximum Frequency Efficiency: Downlink / Uplink (6/2)
Average Frequency Efficiency: Downlink / Uplink (2/1) Handoff Inter-cell handoff, inter-base handoff
Inter-frequency handoff: 150 ms or less Mobility Up to 60 km / h
Service coverage Picocell 100m
Microcell: 400m
Macrocell: 1 km

As shown in Table 2, the IEEE 802.16 system can allocate resources to nodes using TDD and OFDMA. Therefore, there is no degradation in throughput such as the performance anomaly phenomenon mentioned in the aforementioned WLAN. As a result, when the number of users increases, the throughput of the IEEE 802.16 system is divided / allocated according to the number of users according to the number of users without degrading the overall throughput.

As described above, the WLAN and the IEEE 802.16 systems show different types of throughput changes as the number of users increases. In particular, in the case of the wireless LAN, when a low-transmission node is newly added due to a throughput heterogeneity phenomenon, a sudden throughput degradation may be caused. If the WLAN and the IEEE 802.16 system ignore heterogeneous characteristics of each user and perform only the high transmission speed and perform the inter-network handoff, the nodes tend to move to the WLAN. As a result, the throughput of the WLAN is lowered, and a problem arises that resources of the IEEE 802.16 system are wasted.

Therefore, a method should be presented that allows the overall resource efficiency to be pursued without incurring load imbalance between systems.

Accordingly, an object of the present invention is to provide an apparatus and method for determining handoff between heterogeneous networks in a heterogeneous network environment.

Another object of the present invention is to provide an apparatus and method for determining a handoff between heterogeneous networks in a terminal using transmission speed and modulation / demodulation characteristics of each network in a heterogeneous network environment.

Another object of the present invention is to provide an apparatus and method for determining a handoff between heterogeneous networks using a transmission rate and a modulation / demodulation characteristic of a WLAN.

According to a first aspect of the present invention for achieving the above objects, a heterogeneous network handoff determination device in a terminal capable of communicating with a WLAN network and a broadband wireless communication network, handoff between heterogeneous network handoff rate information of the signals transmitted and received with the WLAN And a medium access control (MAC) layer provided to a determination module, and the heterogeneous network handoff determination module for determining whether to perform handoff between the heterogeneous networks using the transmission rate information provided from the MAC layer. .

According to a second aspect of the present invention, a method for determining a handoff between heterogeneous networks in a terminal capable of communicating with a WLAN and a broadband wireless communication network includes: determining a transmission rate of a signal to be transmitted to the WLAN; Retransmitting the transmission signal at the transmission rate of the second threshold when the transmission rate of the signal is less than or equal to the first threshold for a predetermined time and the transmission rate of the transmission signal is less than or equal to the first threshold for the predetermined time. And if the retransmission of the signal is not successful, determining a handoff to the broadband wireless communication network.

According to a third aspect of the present invention, a method for determining a handoff between heterogeneous networks in a terminal capable of communicating with a WLAN and a broadband wireless communication network, when receiving the signal of the WLAN by discovering the WLAN, the received signal. Checking a payload transmission rate of the payload and comparing the payload with a first threshold; and if the payload is greater than or equal to the first threshold, attempting to decode the payload; If the decoding succeeds more than a predetermined number of times, characterized in that it comprises the step of determining the handoff to the WLAN.

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

Hereinafter, a description will be given of a technique for determining and performing a handoff between heterogeneous networks in a heterogeneous network environment. In other words, a technique for discovering a system for performing a handoff between heterogeneous networks in the node (System Discovery) and a handoff decision will be described. In the following description, a wireless local area network (WLAN) and an IEEE 802.16 system will be described as an example. In addition, it is assumed that each of the nodes has multiple network adapters (Multi Network Adapters) that can use the WLAN and the IEEE 802.16 system, respectively.

Heterogeneous handoff can be divided into three major operations. First, a process of discovering a system to find out which networks are currently available to mobile nodes, and then a handoff decision to decide whether to move to another network or keep the network currently in use. to be. Lastly, when handoff is determined to another network through the handoff decision process, the determined handoff is performed (HandOff Execution).

As described above, among the three steps for performing the inter-network handoff, the present invention focuses on the algorithm for determining the system discovery and the handoff.

6 illustrates a hierarchical structure of nodes for performing heterogeneous network handoff according to the present invention.

As shown in FIG. 6, in the IEEE network layer model, a link layer (601) and a lower layer of a medium access control (MAC) layer exist. Furthermore, according to the present invention, in case of having multiple networks of a wireless LAN and an IEEE 802.16 system, a plurality of MAC layers (wireless LAN 605 and IEEE 802.16 system 607) are owned. In addition, there are 2.5 layers 603 for connecting the multiple MAC layers with the link layer 601. The 2.5 layers are packets of each network from the MAC layers 605 and 607 of the WLAN and IEEE 802.16 system. It performs the function of performing handoff between heterogeneous networks by receiving performance change information according to transmission speed of.

In addition, the link layer 601, the MAC layer 605, 607, and the 2.5 layer 603 communicate with each other through a service access point (SAP) interface 609 to 613.

A method for determining handoff between the WLAN and the IEEE 802.16 system in the hierarchical structure as shown in FIG. 6 will be described below.

First, in order for a node using the IEEE 802.11 system to discover the WLAN, it is necessary to periodically check whether there is a WLAN AP around by repeatedly turning on / off the WLAN card of the node. Always turning on the network interface and checking the discovery of the WLAN is a waste of energy, typically checking the reception of the beacon message of the WLAN while turning on periodically. In this case, the beacon message is a management packet containing information corresponding to various types of operation / management of the WLAN, with the purpose of informing its existence to the nodes to be located around the AP in the WLAN. packet).

It is important how well to find a new network in the heterogeneous network environment, but it is also very important to recognize when the current network will be disconnected. In other words, it is possible to perform continuous communication without disconnection by moving to another network before the current network is disconnected.

The continuous communication without disconnection is not a problem since the service area of the IEEE 802.16 system includes the service area of the WLAN when handing off from the IEEE 802.16 system to the WLAN.

However, since the wireless LAN has a small service area of about 100 to 150 m, the node is easily disconnected from the wireless LAN service area, and thus a problem occurs when the wireless LAN is handed off to the IEEE 802.16 system. .

Therefore, before a node is disconnected from a WLAN, another network (eg, an IEEE 802.16 system) is discovered and a handoff is performed to provide a method of guaranteeing seamless connectivity.

7 shows multiple transmission rates according to the distance of a wireless LAN according to the present invention. The following description takes IEEE 802.11b as an example.

As shown in FIG. 7, the AP (Access Point) 701 of the WLAN is close to the node 703 to communicate at a transmission rate of 11 Mbps. The node 705 within the node checks the sender address and the recipient address of the medium access control (MAC) header contained in the payload (805 of FIG. 8) of the transmission signal of the AP 701, thereby checking the sender address and the recipient address. Recognize that 703 is communicating. However, when the nodes 707, 709, and 711 that exist outside the 11 Mbps transmission range decode the payload 805 of the transmission signal to determine which node the communication signal is for communicating with, Because the BER (Bit Error Rate) is too far from the AP 701, decoding cannot be performed. In this case, nodes that fail to decode the payload 805 of the transmission signal recognize that the distance from the AP 701 is far.

Here, the nodes 707, 709, and 711 that are far from the AP 701 do not decode the payload 805, so that the nodes that receive the transmission signal are subject to a modulation scheme of the sender. Decode accordingly. Therefore, the information on the modulation scheme is included in the header of the transmission signal. Even though the nodes recognize the modulation scheme, the supported modulation scheme is different according to the distance between the AP 701 and the nodes. The nodes 707, 709, and 711, which are far from each other, cannot decode the payload 805. In addition, since the header uses the most robust modulation technique for noise at the lowest transmission rate in the WLAN, decoding is possible in all sections of the WLAN.

If a specific node is capable of decoding only the 1 Mbps packet of FIG. 7, and an error occurs when decoding a packet having a transmission rate of 2 Mbps or more, the specific node is connected to the AP 701 through an ARF (Auto Rate Fallback) algorithm. ) At 1Mbps. That is, it is recognized that the specific node exists at a location far from the AP 701. The ARF algorithm is an algorithm for selecting a transmission rate based on an average packet error rate.

That is, the specific node is outside the service area of the WLAN (R _M0 to R _M1 area (eg, 802.11b (M0: 1Mbps, M1: 2Mbps), 802.11a (M0: 6Mbps, M1: 9Mbps))) Since it is highly likely to leave the service area of the WLAN, it is determined to handoff from the WLAN to the IEEE 802.11 system in order to maintain seamless connectivity.

In addition, due to the low transmission speed of the specific node, performance anomaly may occur, so it is decided to handoff from the WLAN to the IEEE 802.11 system.

8 illustrates a physical layer format of a transmission / reception signal of a WLAN according to the present invention.

Referring to FIG. 8, the physical layer format is largely divided into a physical layer convergence procedure (PLCP) preamble 801, a PLCP header 803, and a payload 805.

First of all, the PLCP preamble 801 includes a synchronization unit and an SFD in order to synchronize transmission / reception. The PLCP header 803 contains information necessary for physical layer transmission, and the signal field of the PLCP header 803 is the payload 805 according to the modulation scheme and coding rate shown in Table 1 and Table 2. Indicates the baud rate. In addition, HEC (PLCP Header Error Check) determines whether the PLCP header 803 has an error.

The payload 805 is a part containing information of the MAC layer and is divided into a MAC header and a data part. By using the address field of the MAC header portion, it is possible to determine which packet is transmitted from which node to which node. Therefore, if the payload 805 cannot be decoded, it is impossible to know to which node the packet is transmitted.

As described above, the determination of the handoff from the WLAN to the IEEE 802.16 system is performed when the ARF algorithm shows a transmission rate of M0 for a predetermined time (T1) or more and attempts to retransmit at the transmission rate of M1, but fails to retransmit. If decoding of the payload of the received signal from the WLAN is impossible during the time T2, the handoff is determined by the IEEE 802.16 system.

12 illustrates an operation procedure of a node for determining handoff from the WLAN to the IEEE 802.16 system according to the first embodiment of the present invention. In the following description, M0 denotes the lowest transmission rate of the WLAN, and M1 denotes the next higher transmission rate than the M0. Here, M0 and M1 vary depending on the type of protocol of the wireless LAN (eg, 802.11b (M0: 1Mbps, M1: 2Mbps), 802.11a (M0: 6Mbps, M1: 9Mbps)).

Referring to FIG. 12, first, in step 1201, a node determines a current transmission rate R to be transmitted to a WLAN using an ARF (Auto Rate Fallback) algorithm.

Thereafter, the node proceeds to step 1203 in which the node compares R with M0 and if R is greater than M0 (R> M0), the node ends the present algorithm. That is, it maintains communication with the WLAN.

If R is less than or equal to M0 (R <= M0), the node proceeds to step 1205 to increase the variable T _M0 indicating the number of times R is continuously less than or equal to _M0 , and then In operation 1207, the node compares the T _M0 with a predetermined reference value T1. That is, it is checked whether the node transmits the packet for a predetermined time or more at the transmission rate of the M0. Here, T _M0 has an initial value of 0.

If the T _M0 is less than or equal to the reference value (T _M0 <= reference value), the node returns to step 1201.

If the T _M0 is greater than the reference value (T _M0 > reference value), the node proceeds to step 1209 and attempts to transmit a packet by setting the transmission rate of the node to M1.

Thereafter, the node proceeds to step 1211 and checks whether the packet is successfully transmitted at the transmission rate of M1. If the transmission of the packet succeeds at the transmission rate of M1, the node terminates the present algorithm. That is, it maintains communication with the WLAN.

If the transmission of the packet fails at the transmission rate of M1, the node proceeds to step 1213 and determines the handoff to the IEEE 802.16 system, and then the node terminates the algorithm.

FIG. 13 illustrates an operation procedure of a node for determining handoff from an WLAN to an IEEE 802.16 system according to a second embodiment of the present invention. In the following description, M0 represents the lowest transmission rate of the WLAN, and M1 represents the next higher transmission rate than the M0. Here, M0 and M1 vary depending on the type of protocol of the wireless LAN (eg, 802.11b (M0: 1Mbps, M1: 2Mbps), 802.11a (M0: 6Mbps, M1: 9Mbps)).

Referring to FIG. 13, when a node receives a signal from a WLAN in step 1301, the node proceeds to step 1303, and the node decodes a PLCP header of the received signal to transmit a payload (R) of the received signal. Check it.

Thereafter, the node proceeds to step 1305 to compare the R with the M1. If R is smaller than M1 (R < M1), that is, if the transmission rate of the received signal is smaller than M1, the node terminates this algorithm. That is, it maintains communication with the WLAN.

If R is greater than or equal to M1 (R> = M1), that is, if the transmission rate of the received signal is greater than or equal to M1, the node proceeds to step 1307 and the payload of the received signal is decoded. Check if If the payload is decoded, the node terminates this algorithm. That is, it maintains communication with the WLAN.

If the payload is not decoded, the node proceeds to step 1309 and increases the variable (T _ERR ) indicating the number of failures to decode the payload. Then, the node proceeds to step 1311 to determine the T _ERR and a predetermined value. Compare the reference value T2. In other words, it is checked whether the decoding of the payload fails a predetermined number of times. Here, the T _ERR has an initial value of 0. The payload decoding may be determined by checking a cyclic redundancy check (CRC) of the received signal.

If the T _ERR is less than or equal to the reference value (T _ERR <= reference value), the node returns to step 1301. If the T _ERR is greater than the reference value (T _ERR > reference value), the node proceeds to step 1313 and determines the handoff to the IEEE 802.16 system, and then the node terminates this algorithm.

Next, the handoff from the IEEE 802.16 system to the WLAN is determined as follows.

9 illustrates a service range of an IEEE 802.16 system and a WLAN according to an embodiment of the present invention. In the following description, it is assumed that a node communicates with the IEEE 802.16 system.

Referring to FIG. 9, the cell area 902 of the BS (Base Station) 901 of the IEEE 802.16 system and the cell station 904 of the AP (Access Point) # 1 903 of the WLAN or the AP of the WLAN A cell region 906 of # 2 905 exists as shown in FIG. 9 above.

In this case, only the node 913 included in both the cell area 906 of the AP # 2 905 of the WLAN and the cell area 902 of the IEEE 802.16 system and the cell area 902 of the IEEE 802.16 system are included. Depending on the node 911, the WLAN may or may not be recognized.

The node 913 that is included in the cell area 902 of the IEEE 802.16 system can recognize the wireless LAN and perform handoff to the wireless LAN unconditionally when the communication with the wireless LAN is good. none.

That is, when the node 913 accesses the WLAN, it is determined whether the node 913 is handoff in consideration of performance anomaly. Therefore, when the node 913 exists in the area of R _M0 to R _M1 capable of communicating with the AP at only the lowest transmission rate (M0) of the WLAN, another node connected to the WLAN due to performance heterogeneity. Since performance of the WLAN is higher than that of the IEEE 802.16 system, the handoff between heterogeneous networks cannot be performed.

In addition, as shown in FIG. 10, the R _M0 to R _M1 regions of the WLAN have a high probability of the node leaving the WLAN region (1001), and thus do not perform a handoff to prevent unnecessary ping pong. . On the other hand, as shown in FIG. 11, when the node is included in the R _M1 region, when the node exits to the R _M0 to R _M1 region, a ping pong phenomenon occurs, but the R _M0 to R _M1 region buffers the The likelihood of a node being disconnected is reduced.

Accordingly, in order to perform a handoff from the IEEE 802.16 system to the WLAN, first, when decoding of a packet of M1 or more in the PLCP header of a packet transmitted by the AP of the WLAN succeeds more than a predetermined number of times, When the WLAN is very idle and there is no traffic without sampling data such as 1, the signal-to-interference noise ratio (SINR) of the signal received from the WLAN is obtained by M1 of Table 2. If greater than or equal to SINR, determine to perform a handoff.

14 illustrates an operation procedure of a node for determining handoff to a WLAN in an IEEE 802.16 system according to a first embodiment of the present invention. In the following description, M0 represents the lowest transmission rate of the WLAN, and M1 represents the next higher transmission rate than the M0. Here, M0 and M1 vary depending on the type of protocol of the wireless LAN (eg, 802.11b (M0: 1Mbps, M1: 2Mbps), 802.11a (M0: 6Mbps, M1: 9Mbps)).

Referring to FIG. 14, first, when a node receives a signal from a WLAN in step 1401, the node proceeds to step 1403 to decode a PLCP header of the received signal to transmit a payload (R) of the payload of the received signal. Check it.

In step 1405, the node compares the R with the M1. If R is less than M1 (R < M1), that is, if the transmission rate of the received signal is less than M1, the node proceeds to step 1415.

If R is greater than or equal to M1 (R> = M1), that is, if the transmission rate of the received signal is greater than or equal to M1, the node proceeds to step 1407 and the payload of the received signal is decoded. Check if If the payload is not decoded, the node proceeds to step 1415 and is included in the cell area of the WLAN to recognize the WLAN. Then, the node terminates the algorithm. That is, it maintains communication with the WLAN.

When the payload is decoded, the node proceeds to step 1409 to increase the variable T _S indicating the number of successful payload decoding operations, and then the node proceeds to step 1411 to determine the T _S and a predetermined reference value K. ). That is, it is checked whether the decoding of the payload succeeds more than a predetermined number of times. Here, T _S has an initial value of 0. The payload decoding may be determined by checking a cyclic redundancy check (CRC) of the received signal.

If the T _S is less than or equal to the reference value (T _S <= reference value), the node returns to step 1401. If the T _S is larger than the reference value (T _S > reference value), the node proceeds to step 1413 and determines the handoff to the WLAN, and the node ends the present algorithm.

FIG. 15 illustrates an operation procedure of a node for determining handoff to a WLAN in an IEEE 802.16 system according to a second embodiment of the present invention. In the following description, M0 represents the lowest transmission rate of the WLAN, and M1 represents the next higher transmission rate than the M0. Here, M0 and M1 vary depending on the type of protocol of the wireless LAN (eg, 802.11b (M0: 1Mbps, M1: 2Mbps), 802.11a (M0: 6Mbps, M1: 9Mbps)).

Referring to FIG. 15, when a node receives a signal from the WLAN in step 1501, the node proceeds to step 1503 and measures the SINR of the received signal.

In step 1505, the node compares the SINR of the received signal with the SINR _M1 value at the transmission rate of M1 of the WLAN. Here, the SINR _M1 refers to Table 2.

If the SINR is less than SINE _M1 (SINR <SINE _M1 ), the node terminates this algorithm. That is, it maintains communication with the IEEE 802.16 system.

If the SINR is greater than or equal to SINE _M1 (SINR> = SINE _M1 ), the node proceeds to step 1507 to increase the variable T _SINR indicating the number of times the SINR is continuously greater than or equal to the SINR _M1. In operation 1509, the node compares the T _SINR with a predetermined reference value K. That is, it is checked whether the SINR _M1 beam is greater than or equal to a certain number of times. Herein, the T _SINR has an initial value of 0.

If the T _SINR is less than or equal to a reference value (T _SINR <= reference value), the node returns to step 1501. If the T _SINR is greater than the reference value (T _SINR > reference value), the node proceeds to step 1511 and determines the handoff to the WLAN, and the node ends the present algorithm.

In the IEEE 802.16 system, when performing a handoff between heterogeneous networks to the WLAN, a technique for discovering the WLAN is important. In order for the node communicating with the IEEE 802.16 system to detect the WLAN, the WLAN module periodically performs ON / OFF. If the period is assumed to be T _M , the node turns off again after checking whether a beacon message is received by turning on power every T _M period.

Here, the beacon message is transmitted at the lowest transmission rate periodically (1601, 1603) as shown in FIG. That is, since the beacon message is transmitted at the lowest transmission rate, all nodes in the R _M0 region may also receive the beacon message.

Furthermore, according to the present invention, since the beacon message is aimed for discovery in the R _M1 region, the period of the beacon message may be longer than the T _M. That is, it is also possible to use a period of time by T _M + α.

Equation 1 below is a formula for calculating the period of the beacon message.

Here, R _M0 and R _M1 represent the width of the transmission region, and r _M0 and r _M1 represent the radius of the transmission region.

It is checked whether the beacon message is received every cycle calculated by Equation 1.

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

As described above, the present invention is a method for determining a handoff between heterogeneous networks in a heterogeneous network environment, such as an IEEE 802.16 system and a wireless LAN, in consideration of the performance of other nodes connected to the WLAN during handoff between heterogeneous networks. To prevent performance anomaly. In addition, there is an advantage of more reliably guaranteeing seamless connectivity of the node by using the amount of change in transmission rate according to the distance between the AP and the node of the WLAN.

Claims (29)

An apparatus for determining handoff between heterogeneous networks in a terminal capable of communicating with a WLAN network and a broadband wireless communication network, A medium access control (MAC) layer for providing information on transmission speeds of signals transmitted and received through the WLAN network to a handoff determination module between heterogeneous networks during communication through the WLAN network; And a heterogeneous network handoff determination module configured to determine whether the heterogeneous network is handoff by using the transmission rate information provided from the MAC layer. The heterogeneous handoff determination module, If the transmission rate of the signal transmitted through the wireless LAN network is continuously equal to or less than the first threshold value for more than a predetermined time, set the transmission rate of the signal to the second threshold value, If transmission of the signal transmitted at the transmission rate of the second threshold fails, handoff to the broadband wireless communication network is determined, The second threshold value, characterized in that the transmission rate is one step faster than the lowest transmission rate of the wireless LAN network. delete The method of claim 1, And the first threshold is the lowest transmission rate of the wireless LAN. delete An apparatus for determining handoff between heterogeneous networks in a terminal capable of communicating with a WLAN network and a broadband wireless communication network, A medium access control (MAC) layer for providing information on transmission speeds of signals transmitted and received through the WLAN network to a handoff determination module between heterogeneous networks during communication through the WLAN network; And a heterogeneous network handoff determination module configured to determine whether the heterogeneous network is handoff by using the transmission rate information provided from the MAC layer. The heterogeneous handoff determination module, The payload transmission rate of the signal received through the WLAN network is checked, and if the payload transmission rate is greater than or equal to a second threshold, the payload is decoded and the payload decoding may fail. And if the payload decryption failure count is greater than or equal to the reference count, determining a handoff to the broadband wireless communication network. The method of claim 5, The second threshold value, characterized in that the transmission rate is one step faster than the lowest transmission rate of the wireless LAN network. The method of claim 5, Failure of the payload decoding, And checking the received signal using a cyclic redundancy check (CRC). 1. A method for determining handoff between heterogeneous networks in a terminal capable of communicating with a WLAN and a broadband wireless communication network. Determining a transmission rate of a signal to be transmitted through the WLAN network during communication through the WLAN network; Checking whether a transmission rate of the transmission signal is less than or equal to a first threshold value for a predetermined time; When the transmission speed of the transmission signal is less than or equal to the first threshold value for a predetermined time, transmitting the signal by setting the transmission speed of the signal to the second threshold value; Determining a handoff to the broadband wireless communication network when the transmission of the transmitted signal by setting the transmission speed to the second threshold is not successful. The second threshold value, characterized in that the transmission rate is one step faster than the lowest transmission rate of the WLAN. 9. The method of claim 8, The transmission rate of the transmission signal, characterized in that determined using the ARF (Auto Rate Fallback) algorithm. 9. The method of claim 8, The transmission rate of the transmission signal is not less than or equal to the first threshold value for a predetermined time, And if the retransmission of the signal is successful, maintaining the communication with the WLAN network. 9. The method of claim 8, The first threshold value is characterized in that the lowest transmission rate of the wireless LAN network. delete 1. A method for determining handoff between heterogeneous networks in a terminal capable of communicating with a WLAN and a broadband wireless communication network. Checking the payload transmission rate of a signal received through the WLAN network and comparing it with the first threshold while performing communication through the WLAN network; Decoding the payload when the payload transmission rate is greater than or equal to the first threshold; When the decoding of the payload fails, comparing the payload decoding failure times with a reference number of times; And determining the handoff to the broadband wireless communication network when the number of payload decoding failures is equal to or greater than a reference number. The method of claim 13, The transmission rate of the payload is And decoding and confirming a physical layer convergence procedure (PLCP) header of the received signal. The method of claim 13, The transmission rate of the payload is less than the first threshold value, If decoding of the payload is successful, further comprising maintaining communication with the WLAN network. The method of claim 13, The first threshold value, characterized in that the transmission rate is one step faster than the lowest transmission rate of the wireless LAN network. The method of claim 13, Failure of the payload decoding, And checking the received signal using a cyclic redundancy check (CRC). 1. A method for determining handoff between heterogeneous networks in a terminal capable of communicating with a WLAN and a broadband wireless communication network. Checking a payload transmission rate of a signal received through the wireless LAN network when the wireless LAN network is detected and the signal is received through the wireless network during communication through a broadband wireless communication network; Comparing the payload transmission rate of the signal with a first threshold; If the payload transmission rate of the signal is greater than or equal to the first threshold, decoding the payload; When the decoding of the payload fails, comparing the payload decoding failure times with a reference number of times; And determining a handoff to the WLAN when the payload decoding failure count is equal to or greater than a reference number. The method of claim 18, The process of discovering the WLAN network, And detecting a beacon message through a WLAN network by turning on / off a WLAN module at a predetermined cycle and discovering the WLAN network. The method of claim 19, The constant period is characterized by calculating using the following equation (2)

Here, R _M0 and R _M1 represent the width of the transmission area of the WLAN, and r _M0 and r _M1 represent the radius of the transmission area of the WLAN. The method of claim 18, Checking the payload transmission rate of the signal, And decoding and verifying a physical layer convergence procedure (PLCP) header of the signal received through the WLAN network. The method of claim 18, If the payload transmission rate of the signal is less than the first threshold value, or the decoding of the payload is successful, the method further includes the step of recognizing the discovery of the WLAN and maintaining communication with the broadband wireless communication network. How to feature. The method of claim 18, The first threshold value, characterized in that the transmission rate is one step faster than the lowest transmission rate of the wireless LAN network. The method of claim 18, Failure of the payload decoding, And checking the received signal using a cyclic redundancy check (CRC). 1. A method for determining handoff between heterogeneous networks in a terminal capable of communicating with a WLAN and a broadband wireless communication network. Detecting a signal to the interference noise ratio (SINR) of a signal received through the wireless LAN network when the wireless LAN network is detected and the wireless LAN network is received during communication through a broadband wireless communication network; , Comparing the SINR of the signal received through the WLAN network with the SINR of the first threshold; And if the SINR of the signal received through the WLAN network is equal to or greater than the SINR of the first threshold more than a predetermined number of times in a row, determining to handoff to the WLAN network. 26. The method of claim 25, The process of discovering the WLAN network, And detecting a beacon message through the WLAN network by turning on / off a WLAN module at regular intervals and discovering the WLAN network. The method of claim 26, The constant period is calculated using the following equation (3)

Here, R _M0 and R _M1 represent the width of the transmission area of the WLAN, and r _M0 and r _M1 represent the radius of the transmission area of the WLAN. 26. The method of claim 25, And if the SINR of the received signal is smaller than the SINR of the first threshold, maintaining the communication with the broadband wireless communication network. 26. The method of claim 25, The first threshold value, characterized in that the transmission rate is one step faster than the lowest transmission rate of the WLAN network.

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