Method and device for selecting access point in wireless network

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to wireless communication, and more particularly to a technique for selecting an access point in a wireless network.

【0002】

[Conventional technology]

Broadband access networks such as DSL (Digital Subscriber Line), Broadband Networks, All Fiber Networks, ISDN (Integrated Services Digital Network), and Fixed Wireless Networks, due to consumer demand for high-speed access to the Internet and intranet-related services and applications. There are several options.

【0003】

Fixed radios provide a viable alternative to classic wire-based access, especially in geographic areas where the cost of upgrading and maintaining wireline connections is high. In essence, a fixed wireless network is a cellular network that relies on a short-range transmitter / receiver (transmitter / receiver) base station to serve subscribers in a small area (cell) of a large service area. is there. By dividing the service area into cells with a limited range of transmitters and receivers, the same frequency can be reused in different areas of the service area, and for communication with the base station providing the service. , A subscriber terminal that consumes relatively little power can be used.

【0004】

Figure 1 shows a traditional wireless Internet access system (WIAS), which has four main components: (1) wireless connectivity and radio coverage for subscriber units 102 (a)-(d) (eg). , Multiple data base stations (BS) 100 (a) and 100 (b) provided to (residential and corporate terminal equipment shown in Fig. 1), and (2) subscriber units 102 (a) to (d) in the forward direction. A radio that enables communication with BS100 (a) or 100 (b) via air interface links 115 (a)-(c) in the opposite direction (from base station to subscriber) and in the opposite direction (from subscriber to base station). A data exchange center that routes modems (WM) 170 (a) to (c) and (3) data packets from BS100 (a) and 100 (b) or from BS100 (a) and 100 (b). It is a specific implementation of a fixed radio technology having (DSC) 125 and (4) a backbone transmission network 135 such as a public IP (Internet Protocol) network connected to the DSC 125.

【0005】

The subscriber unit can be connected to the backbone transmission network 135 in various ways, examples of which are shown in Figure 1. Corporate terminals 102 (c) and 102 (d) are connected to backbone transmission network 135 via local area network (LAN), wireless router and / or firewall (not shown), and shared WM170 (c). , Subscriber units 102 (a) and 102 (b) are equipped with their own WM170 (a) and 170 (b), respectively. BS100 (a) and 100 (b) may connect directly to the DSC125 or may communicate with the DSC125 via the service provider's private IP network 127.

【0006】

FIG. 2 shows an exemplary cell pattern suitable for performing fixed wireless access. As shown in FIG. 2, each BS100 (a) and 100 (b) transmits a signal via an air interface at a specified frequency block (eg, a 5 MHz wide transmit frequency block and a 5 MHz wide receive frequency block). By transmitting and receiving, 360-degree RF service coverage is provided to the subscriber terminals in cells 150 (a) and 150 (b), respectively. Normally, cell coverage is such that the frequency blocks specified in a given cell are distributed among multiple sectors (eg, 1 MHz block for transmission and 1 MHz block for reception, respectively, per cell structure 5). One cell), sectorized. Therefore, each BS100 (a) and (b) contains a plurality of access points (AP, not shown in FIG. 1), one for each sector.

【0007】

Depending on the location of the subscriber WM relative to the cell / sector boundary and the radio frequency (RF) propagation characteristics of the surrounding area, the subscriber may have multiple APs, i.e. multiple APs for a single cell, and / or It is possible to communicate with APs from different cells. For example, the subscriber's WM may be on or near the boundaries of two or more sectors and / or two or more cells. In this implementation of fixed wireless access, the subscriber's WM installer selects a single AP during setup based on the forward link signal strength, and the assignment of APs to send and receive to the subscriber's WM does not change.

【0008】

However, due to changes in the FR propagation characteristics of the surrounding area, the AP that provides the best performance during installation is not always the best or even the best AP that guarantees the right service quality or data throughput rate. There are many. For example, changes in temperature and weather, especially humidity that changes the reflectance coefficient, can significantly affect RF propagation between the AP and the subscriber's WM. In addition, service degradation can result if the AP assigned to the user temporarily fails or the sectors served by the AP are overloaded. Furthermore, service providers can continue to deploy better APs (eg, as a result of growth and "cell splitting").

【0009】

[Problems to be Solved by the Invention]

Therefore, there is a need for high-speed AP selection and allocation technology that allows the subscriber's WM to select and switch which APs to serve in response to network conditions.

【0010】

[Means for solving problems]

The present invention is a method and apparatus for selecting an access point in a wireless communication network that can maintain an appropriate service quality and throughput rate under dynamic network conditions. In one embodiment, the present invention is a technique for selecting and assigning access points in a fixed wireless network, monitoring signals transmitted by a plurality of adjacent access points, signal strength at a user location, signal quality at a user location, and the like. Communication link quality measurements such as signal strength at the access point, signal quality at the access point, packet error rate (PER) at the wireless model, PER at the access point, or a combination of two or more of these measurements, and relatives. It is a technology to select the best access point as a function of various sector load levels.

【0011】

By dynamically selecting the access point that provides the best service as a function of communication link quality measurements and relative load levels, the subscriber's wireless modem adapts to the changing RF propagation characteristics of the surrounding area and is high. Service quality and throughput rates can be maintained, and service outages can be avoided by orienting the traffic away from the failed or overloaded access point.

【0012】

In one exemplary embodiment, a wireless modem in a fixed wireless network provides service when the wireless model is first powered up, when service quality deteriorates below a threshold level, when a sector load exceeds a threshold, or when. Performs an AP search / select sequence and (re) selects the access point in response to a trigger event, such as when the AP instructing it to do so. When a trigger event occurs, the subscriber's wireless modem detects an access control signal, commonly referred to as a "beacon," transmitted by multiple adjacent access points. The access point beacon contains an adjacency list for identifying the access point and identifying the adjacency access point and the frequency channel that the adjacency access point is transmitting, as well as a field indicating the load level of the access point. .. After detecting the beacon and obtaining the communication link quality measurement for each adjacent access point, the wireless modem selects the best access point based on the communication link quality measurement and the relative load level.

【0013】

By considering the relative load level, it is possible to maintain a reasonable throughput rate by distributing the service across a larger number of access points (ie, load balancing) when possible. In addition, when the service quality deteriorates below the threshold level, or when the sector load exceeds the threshold, by initiating an access point re-search, the subscriber's wireless modem can affect the temperature and communication quality. It can react to changes in RF propagation conditions in the surrounding area, such as other weather changes.

【0014】

The present invention will be more fully understood from the detailed description and accompanying drawings given below. In the accompanying drawings, similar elements are represented by similar reference numbers. The accompanying drawings are provided only as explanations and are not intended to limit the present invention.

【0015】

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is a method and apparatus for (re) selecting an AP in a wireless communication environment such as a fixed wireless access network. In one embodiment, the invention dynamically selects the AP as a function of relative communication link quality and load level, changes the RF propagation characteristics of the service area, and / or causes the AP to fail or overload. Even if this is the case, it is implemented as a search algorithm performed by the subscriber's WM in order to maintain proper performance and data throughput. An embodiment of the present invention will be described with reference to FIGS. 3A, 3B, and 4 to 6. First, an exemplary base station and subscriber terminal architecture will be described. Specific base station and subscriber terminal configurations will be described below, but it should be recognized that such details are for illustration purposes and the present invention can be implemented in various wireless network configurations.

【0016】

FIG. 3A schematically shows an exemplary base station suitable for use according to one embodiment of the present invention. In FIG. 3A, base station 200 includes a radio hub 205 and at least one AP 210. Preferably, base station 200 includes five AP210s (1-5), each serving five sectors with 72 degree coverage. Each base station in the network service area is assigned the same 5MHz wide spectral block for transmission and reception, and each of the five AP210s (1-5) has a different 1MHz channel for transmission and a separate 1MHz channel for reception. Is assigned.

【0017】

The wireless hub 205 shall be a power source that supplies voltage and data (eg, 48V DC and standard 10Base-T LAN data) to each AP210 through a signal router and cable 211 (1-5) such as a 10Base-T cable. Is preferable. All radio and signal processing functions (ie, transmission and reception with respect to BS200) are performed by AP210 (1-5). In addition, the wireless hub 205 provides connections 213 (1-4) to the DSC (not shown).

【0018】

FIG. 3B schematically illustrates an exemplary subscriber terminal configuration 202 suitable for use according to one embodiment of the present invention. The subscriber terminal 202 includes a WM270, an interface adapter box 275, and a power supply 280 (eg, a 24V DC power supply). The WM270 is preferably mounted near the roof of the subscriber's home or office to communicate with the selected AP210. The PC290 is connected to the interface adapter box 275 to send and receive data using the WM270 via an Ethernet® hub 295 and a 10Base-T cable 296, for example in a LAN environment. ..

【0019】

Both the WM270 and AP210 include a radio unit having a receiver circuit and a transmitter circuit, which provide a receiving function and a transmitting function, respectively. The reverse link (subscriber to base station) signal transmitted from the WM270 to the AP210 preferably operates on a 1MHz RF channel between approximately 3450 and 3500MHz, while the forward link (base) transmitted from the AP210 to the WM270. The signal (from station to subscriber) preferably occupies a 1MHz RF channel between approximately 3550 and 3600MHz. In addition, both radio units allow automatic gain control (AGC) capability to provide linear demodulation over a wide dynamic range and digital control of AGC, and receive signal strength for use in AP search algorithms described below. With indicator (RSSI) functionality, both radio units perform modulation and demodulation using, for example, quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM) techniques.

【0020】

FIG. 4 is a block diagram showing an exemplary architecture of the WM270. In the exemplary configuration of FIG. 4, the WM270 includes (1) WM antenna 281, (2) radio board 251 and (3) digital board 261 and (4) power supply 271 and (5) interface 264. To be equipped with. The radio board 251 converts the RF signal received from the AP 210 via the WM antenna 281 into a digital signal, and converts the digital transmission signal into an analog RF signal. The analog RF signal is then transmitted by the WM antenna 281. The radio board 251 includes an analog RF / IF processing unit 252 that performs such analog / digital conversion and downconverts the signal received from the WM antenna 281 into an intermediate frequency (IF) signal. The radio board 251 also includes a digital signal processor (DSP) 253 that demodulates the IF signal output by the analog RF / IF processing unit 252. The DSP 253 also modulates the signal received from the digital board 261 for transmission, and the modulated signal is then up-converted to an RF signal by the analog RF / IF processing unit 252.

【0021】

The digital board 261 includes a control processor 262 that provides intermediate access control (MAC) and protocol functions such as data transmission timing. As will be described in more detail below, the control processor 262 also executes the AP search / selection algorithm according to one embodiment of the present invention. The digital board 261 also converts the MAC format data output by the control processor 262 into a data stream such as a standard 10Base-T data stream for output to the subscriber's PC290 (not shown) via interface 264. It also has a format converter 263. The power supply 271 supplies power to the power radio board 251 and the digital board 261.

【0022】

FIG. 5 is a block diagram of an exemplary architecture of AP210 suitable for use according to the present invention. In the exemplary configuration of FIG. 5, the AP210 has (1) a horizontally polarized antenna 282, (2) a vertically polarized antenna 281, (3) a matrix board 241 and (4) an RX / TX board pair 221. , (5) TX board pair 231 and (6) power supply / hub board 212.

【0023】

Like the WM270 in FIG. 4, the AP210 includes a radio board and a digital board that perform the functions described above, respectively. The AP210 comprises both transmit / receive (TX / RX) board vs. 221 and transmit (TX) board vs. 231 having radio boards 222 and 232 and digital boards 223 and 233, respectively. The radio boards 222 and 232 include analog RF / IF processing units 224 and 234 and DSP 226 and 236, respectively, and the digital boards 223 and 233 include control processors 225 and 235 and format converters 227 and 237, respectively.

【0024】

The RX / TX board pair 221 transmits and receives when the AP210 is used in half-duplex mode (ie, the transmit and receive functions are performed sequentially using a board with only one AP), and the radio board 251 and the above WM270 radio board 251 and Works like a digital board 261. The TX board pair 231 is used for transmission when the AP210 is used in full-duplex mode (ie, when the APs transmit and receive at the same time).

【0025】

The matrix board 241 selects the desired board pair for transmission and / or reception and the best antenna for reception (vertically polarized antenna 281 or horizontally polarized antenna 282) via switches 242 and 244. The transmission / reception switch 243 separates the transmission / reception function on the vertically polarized antenna 281 while the reception separation filter (not shown) filters the signal received from the horizontally polarized antenna 282. The signal is always transmitted by the vertically polarized antenna 281 while the reception of the signal is done by both antennas and which of the two signals the RX / TX board vs. 221 chooses based on performance. To determine. The power supply / hub board 212 is an Ethernet hub for transmitting and receiving data streams to and from the power supply 214 that powers the radio boards 222, 232, the digital boards 223, 233, and the matrix board 241 and the digital boards 223, 233. 213 and.

【0026】

Next, the operation of the AP search / selection technique according to the embodiment of the present invention will be described with reference to the flow chart l of FIG. The AP search / selection described below with reference to FIG. 6 can be performed by the WM270 control processor 262.

【0027】

The WM270 performs an AP search / selection sequence after it is determined that a trigger event has occurred. A number of different occurrences may constitute a trigger event. For example, the WM270 is when a deterioration in service quality or an increase in load level is detected at a predetermined time interval each time the subscriber's terminal is powered on, or when commanded by a previously selected AP. AP search / selection can be performed on.

【0028】

When the AP search / selection is initiated (step 402), the subscriber WM270 selects the initial RF channel for the AP search (step 404). Since the same frequency is used throughout the wireless network area, only a limited number of channels are available. The WM270 may select any possible frequency channel within the search range (eg, lowest frequency channel or highest frequency channel) as the initial RF channel.

【0029】

Each frame transmitted by the AP contains access control information, commonly referred to as a "beacon." According to the present invention, each beacon identifies an AP transmitting, indicates the load level of the AP, and displays an adjacency list to identify the number of adjacent APs and the channel transmitted by each adjacent AP. Including. The beacon may further include control information such as data packet authorization (ACK). The WM270 attempts to detect the beacon transmitted by the AP in the initial RF channel (step 406). When a beacon is found on the selected channel (step 408), the WM270 extracts the adjacency list from the detected beacons to identify the adjacency APs and the channels assigned to them (step 410). Using the extracted adjacency list information, the WM270 detects a beacon from each adjacency AP (step 412).

【0030】

If the WM270 does not detect a beacon on the assigned RF channel within a given time period, eg, 10 seconds (step 418), a new RF channel is selected (step 420). If the newly selected RF channel is within the channel search range (step 422), the WM270 attempts to detect the beacon on the newly selected channel (step 406). If the newly selected RF channel is not in the channel search range (ie, higher / lower than the highest / lowest channel in the search range), the WM270 reselects the initial FR channel (step 404) and performs beacon detection. Try (step 406).

【0031】

After extracting the adjacency list from the beacon detected in step 410 and detecting the beacon from the adjacent AP (step 412), the WM270 has at least one acceptable AP based on the communication link quality measurement. (Step 413) and, if there is at least one acceptable AP, select one AP based on the communication link quality measurement and AP relative load level (step 414). A communication link quality measurement is one of a signal strength in WM270 (eg, RSSI), a signal quality in WM270, a signal strength in AP210, and a signal quality in AP210, or a combination of two or more of these measurements. sell. Signal quality can be represented by any number of measurements, including signal-to-noise ratio, bit error rate, frame error rate, packet approval percentage (ie, percentage of approved transmitted packets), and the like.

【0032】

The signal strength / quality in the WM270 indicates the quality of the forward link, while the signal strength / quality in the AP210 indicates the quality of the reverse link. Combining one or more measurements that indicate forward link quality and one or more measurements that indicate reverse link quality, both forward and reverse communication link quality (ie, bidirectional link quality). It is possible to obtain a communication link quality measurement value representing. If the AP does not have an acceptable communication link quality measurement (step 413), the WM270 initiates an AP search / selection again (step 402).

【0033】

The AP relative load level is also considered in step 414 for the best AP selection. For example, if the AP with the highest communication link quality measurement also has a load level below the threshold, that AP is selected. If each AP with an acceptable communication link quality measurement also has a load level above the threshold, the AP with the best communication link quality measurement is selected. If some APs with acceptable communication link quality have a load level above the threshold, but at least one of such APs has a load level below the threshold, the AP with the lowest load level is selected. .. The load level can be represented by any number of measurements. For example, the AP210 can calculate the average data throughput per user multiplied by the number of users. Other measurements, such as the average number of bits transmitted by the AP210 per second, "CPU uptime" at the hub, and / or data buffer overflow status, may be monitored to indicate the load.

【0034】

If the WM270 assigns the best AP in step 414 followed by changes in service quality and / or load level, the WM270 can be re-entered with the AP search / selection sequence described above. For example, degraded forward link quality can cause the WM270 to perform AP search / selection (step 426). Also, for example, if the reverse link quality drops below the threshold, the previously selected AP may explicitly instruct the WM270 to perform an AP search / selection. In addition, the WM270 can continuously or periodically monitor the load level of the servicing AP and perform AP search / selection if the load level exceeds the threshold (step 428). .. If the WM270 makes an AP search / selection based on degraded service quality or excessive load level for the AP selected earlier (or if the AP instructs it to do so), the WM270 selects first. The adjacency list received in the beacon of the adjacent AP can be used to detect the beacon of the adjacent AP (step 412) and select the best AP (step 414).

【0035】

By performing the AP search / selection sequence above, the WM can switch APs based on variable local performance as a result of RF propagation status, signal level, load level, and network redesign. In addition, the subscriber's WM can select a new AP and orient the traffic away from the failed or overloaded AP to avoid temporary service degradation.

【0036】

Those skilled in the art should understand that various modifications and uses of the present invention can be realized without departing from the spirit and scope of the present invention. As an example, the subscriber terminal may include a mechanical control mechanism for positioning the WM antenna 281. In this method, when a new AP is selected, the WM antenna 281 can be reoriented to improve the communication link quality for the newly selected AP. In addition, during AP search / selection, the WM antenna 281 may be controlled to scan beacons to improve selection accuracy when determining communication link quality measurements for each AP in the adjacency list. Further, in the above embodiment, the control processor of the WM270 specifies that the AP search / selection is performed, but the AP search / selection sequence and its parts are subjected to an arbitrary number of software-driven processing circuits and application-specific integrated circuits. It should be understood that it can be implemented in, or in other configurations. Further, although the above embodiment specifies that the wireless modem obtains the adjacency list from the detected beacon, the wireless modem may obtain the adjacency list independently of the beacon.

[Simple explanation of drawings]

[Figure 1]

It is a figure which shows the exemplary wireless Internet access configuration system which is the environment suitable for the embodiment of the present invention.

[Figure 2]

It is a figure which shows an exemplary cell pattern layout for a fixed radio access network.

[Fig. 3A]

It is a figure which shows typically the exemplary base station configuration suitable for the embodiment of the embodiment of this invention.

[Fig. 3B]

It is a figure which shows typically the exemplary subscriber terminal configuration suitable for the embodiment of the embodiment of this invention.

[Fig. 4]

It is a block diagram which shows the component selection of the wireless modem by embodiment of this invention.

[Fig. 5]

It is a block diagram which shows the component selection of the access point by a preferable embodiment.

[Fig. 6]

It is a flow chart of the access point search / selection sequence according to one Embodiment of this invention.