Abstract:
A novel system is disclosed for WLAN applications. The inventive system mitigates the problem of interference by overlaying an omni-directional pattern with a plurality of directional beams, where each beam covers only part of the serving area defined by the omni-directional pattern. After an initial communication from the subscriber stations along the omni-directional pattern, the directional beam that provides the best signal quality is determined and the access point thereafter communicates with that subscriber station using only the beam with the best signal quality. The inventive concept can be expanded to encompass MIMO WLAN systems.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to communication in a WLAN (Wireless Local Area Network) system from the access point, more particularly it relates to WLAN communication using multiple beams.  
       BACKGROUND TO THE INVENTION  
       [0002]     WLAN is the name sometimes given to the 802.11 wireless telecommunications standard developed by the IEEE. It was intended to be used for wireless communications between portable devices and a local real network. It enables a person with a WLAN-enabled computer or personal digital assistant (PDA) to connect to the Internet when in proximity to an access point (AP). The geographical region covered by one or several access points is typically referred to as a hotspot. WLAN is also referred to as wi-Fi, is the name of an industry consortium that certifies WLAN systems.  
         [0003]     A typical Wi-Fi hotspot contains one or more Access Points (APs) and one or more clients, also referred to as subscriber stations (SS). An AP broadcasts its Service Set Identifier (SSID) and other system configuration information via packets that are called beacons, which are broadcasted periodically. Based on the received information, the client may decide whether to connect to an AP. The Wi-Fi standard leaves connection criteria and roaming totally open to the client.  
         [0004]     In the current systems, an omni-directional antenna is typically used in both the APs and the clients. The number of active clients that an AP can support is limited by the CSMA/CA access protocol used in the WLAN system. If too many clients try to access the AP, collisions may happen more frequently and thus there is less opportunity to communicate to the AP. The coverage range of the AP is typically determined by the AP&#39;s Equivalent Isotropic Radiated Power (EIRP), the propagation loss and the client&#39;s receive sensitivity.  
         [0005]     For a particular WLAN client, its communication data range is determined by the received signal quality at both the client and the AP ends. The signal quality is affected by both receiver noise and interference from neighbouring systems operating in the same or adjacent frequency channels. This is particularly true for the Wi-Fi standard 802.11b/g systems, due to the very limited number of non-overlapping channels.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention mitigates the interference problem by overlaying the coverage area with multiple directional antenna beams, where each beam covers one part of the serving area. At any given time, only one beam is active between an AP and a SS.  
         [0007]     Tho system could be implemented as an applique system, where the system comprises components that could be added to an existing system in order to improve performance.  
         [0008]     In a preferred embodiment the system consists of a multi-beam antenna and associated intelligent beam selection hardware and software. After an initial broadcast using the omni-directional antenna and handshaking with the subscriber station, which involves determining the directional beam that provides the best signal quality an AP thereafter communicates to each client SS with only the beam with the best signal quality. As a result, the highest communication data rate is achieved between the AP and the desired SS while any interference to and from the AP outside the beam coverage is eliminated or substantially reduced.  
         [0009]     In accordance with a first broad aspect of the present invention there is disclosed a method of communicating data between a subscriber station in a Wi-Fi broadcast area and an access point associated with the broadcast area, comprising the steps of: 
        a. overlapping the broadcast area with a plurality of directional beams and an omni-directional beam;     b. associating the subscriber station with one of the plurality of directional beams from signals received at the omni-directional beam and the plurality of directional beams; and     c. communicating data between the subscriber station and the access point along the associated directional beam.        
 
         [0013]     In accordance with a second broad aspect of the present invention there is disclosed a Wi-Fi access point having an associated broadcast area, comprising:  
         [0014]     a multi-beam antenna for communicating with a subscriber station within the broadcast area, comprising an omni-directional beam and a plurality of directional beams; and  
         [0015]     an access point controller coupled to the multi-beam antenna for selecting a directional antenna beam for communicating with the subscriber station. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a block diagram of an exemplary embodiment of the present invention in integrated form.  
         [0017]      FIG. 2  is an exemplary beam pattern diagram illustrating a beam pattern generated by the embodiment of  FIG. 1 .  
         [0018]      FIG. 3  is a signal flow diagram showing communications between the AP and the SS in accordance with the embodiment of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0019]      FIG. 1  shows a block diagram of an exemplary embodiment of the present invention as a system solution.  
         [0020]     The system comprises a multiple-beam antenna  100 , a plurality of beam switches  120 , a 2:2 switch  130 , an RF filter  142 , a switched attenuator  144 , a low-noise amplifier  146 , an RF circuit  147 , an analog to digital converter (ADC)  148 , a beam controller  110 , a transmit/receive (T/R) switch  171 , an RF Filter  172 , a switched attenuator  174 , a low noise amplifier (LNA)  175 , power amplifier  176 , an RF integrated circuit  178 , and a Wireless Local Area Network (WLAN) processor  170 .  
         [0021]     The multi-beam antenna  100  comprises an omni-directional antenna and a plurality of directional antennas. It is connected through a plurality of signals  114 , to the beam switches  120 . The multi-beam antenna  100  is also connected to the 2:2 switch  130  through an omni-directional beam signal  115 .  
         [0022]     The beam switches  120  are connected to the 2:2 switch  130  through a signal  124 . Furthermore they receive control signals from the beam controller  110 , through a beam selection signal  111 ,  
         [0023]     The 2:2 switch  130  is connected to the RF filter  172  of a communication signal processor  160  by signal  118 . It is also connected to the transmit/receive switch  171  through signal  125 , and it receives a switch control signal  112  from the beam controller  110 .  
         [0024]     The RF filter  172  of the communication signal processor  160  is connected to the switched attenuator  174  through signal  119 .  
         [0025]     The switched attenuator  174  is connected to the low noise amplifier  175  through a signal  121 . It also receives control signals from the WLAN processor  179  through an RF control signal  105 .  
         [0026]     The low-noise amplifier  175  is connected to the RF circuit  178  through a signal  122 .  
         [0027]     The RF circuit  178  is sends information to the WLAN processor  179  through signal  123 , and receives information through signal  104 . It also receives control signals from the WLAN processor  179  through RF control signal  105 . Additionally it is connected to the power amplifier  176  through signal  106 .  
         [0028]     The WLAN processor  179  sends control signals to the beam controller  110  through the antenna control signal  117 , and receives a best bean selection signal  116 , from the beam controller  110 .  
         [0029]     The power amplifier  176  Is connected to the transmit/receive switch  171  through signal  107 .  
         [0030]     The transmit/receive switch  171  is connected to the RF filter  142 , though signal  126 . It furthermore receives the transmit/receive control signal  113  from the beam controller  110 .  
         [0031]     The RF filter  142  is connected to the switched attenuator  144  through signal  127 .  
         [0032]     The switched attenuator  144  is connected to the low-noise amplifier  146  through signal  128 . It also receives control signals from the WLAN processor  179  through RF control signal  105 .  
         [0033]     The low-noise amplifier  146  is connected to the RF circuit  147  through signal  120 .  
         [0034]     The RF circuit  147  is connected to the analog to digital converter (ADC)  148  through signal  102 . It also receives control signals from the WLAN processor  179  through RF control signal  105 .  
         [0035]     The ADC  140  is connected to the beam controller  110  through signal  101 .  
         [0036]     In an exemplary embodiment, the multiple-beam antenna  100  consists of a plurality of antennas, each corresponding to a single beam pattern. One of the antennas included in this multi-beam structure is omni-directional, while the remaining provide directional beam patterns.  
         [0037]     In  FIG. 2 , an exemplary beam pattern diagram of the provided antenna coverage is shown. The multi-beam antenna provides one omni-directional beam  200  and multiple directional beams  210  covering a 360-degree area.  
         [0038]     Those having ordinary skill in the art will readily recognize that the multi-beam antenna  100  could be implemented in a number of ways. For example, an array antenna could be used in combination with beamforming to form the individual directional beams.  
         [0039]     The beam switches  120  are used to select one of the directional beams. In the exemplary embodiment the beam switches  120 , are implemented as a N:1 RF switch.  
         [0040]     The 2:2 switch  130  is used to select between two paths. In the first the omni-directional signal  115  is passed through to the RF filter  172 , while simultaneously the selected directional signal  124  is passed to the T/R switch  171 . In the second path, the omni-directional signal  115  is passed through to the T/R switch  171 , while simultaneously the selected directional signal  124  is passed to the RF filter  172 . In the exemplary embodiment the 2:2 switch  130  is implemented as a 2:2 Double Pole, Double Throw (DPDT) switch.  
         [0041]     The RF filters  172 ,  142 , are designed so that their pass band covers the operational frequency band.  
         [0042]     The switched attenuators  174 ,  144 , are used to allow the system to operate in the full dynamic range defined by the 802.11 standards. More than one attenuator may be used at 2.4 GHZ. The attenuators  174 ,  144  scale down the signal so that the signal would not cause saturation of the system&#39;s circuitry.  
         [0043]     The low noise amplifiers  175 ,  146 , are used to increase the received signal strength.  
         [0044]     The RF circuits  178 ,  147 , are used to down convert the received signal from RF to baseband in-phase and quadrature (I&amp;Q) signals.  
         [0045]     The power amplifier  176 , is used to increase the signal strength of transmitted signals.  
         [0046]     The transmit/receive switch  171 , is used to switch between transmission and reception.  
         [0047]     The analog to digital converter  148  is used to digitize the I&amp;Q signals and then to send the digital signal to the beam controller  110  for further processing. In the exemplary embodiment two analog-to-digital converters (ADC)  148  are used to digitize the I&amp;Q signals.  
         [0048]     The WLAN processor  179  is a slightly modified conventional WLAN processor. The application layer functions are modified to allow the best beam number  116  from the beam controller  110  to be uploaded for each newly received frame, and to update a beam switching table (BST) with each frame. Furthermore for each packet transmitted, the WL processor  179  will examine the beam switching table to determine the best antenna number  117  for the particular Media Access Control (MAC) address, and then add this information to the packet header to be transmitted.  
         [0049]     The beam controller  110  performs a variety of functions. It acts as a relay for control signals coming from the WLAN processor to alter the T/R switch  171 , and beam switches  120 . It provides beam scanning control while processing Request to Send (RTS) signals from a subscriber station (SS). It provides channel filtering and signal quality estimation, selects the best receiver (Rx) beam number  116  based on the signal quality estimation, and then forwards this selection to the WLAN processor  179  before the end of the Rx frame.  
         [0050]     Those having ordinary skill in the art will readily recognize that the beam controller  110  could be implemented in a number of ways. For example, a field programmable gate array (FPGA), digital signal processor (DSF), or a microprocessor could be programmed with the functionality described.  
         [0051]     In operation, the multi-beam antenna  100  receives an RF signal from a subscriber station (SS) through the omni-directional antenna. The signal received is sent  115  to the 2:2 switch  130 . The 2:2 switch  130  is initially configured to transmit this signal through signal  118  to the RF filter  172 .  
         [0052]     The received signal  118  is then filtered and forwarded  119  to the switched attenuator  174 .  
         [0053]     The switched attenuator  179  attenuates the signal and forwards  121  it to the amplifier  175 .  
         [0054]     The low noise amplifier  175  then amplifies the signal and forwards  122  it to the RF circuit  178 .  
         [0055]     The RF circuit  178  brings the signal down to baseband and sends it  123  to the WLAN processor  179 .  
         [0056]     While this is happening with the omni-directional beam  11 S, the directional antennas are also receiving signals  114 .  
         [0057]     The beam controller  110  is in receive mode and recognizes that a signal (such as an RTS) is being received through the directional antennas of the multi-beam antenna  100 .  
         [0058]     The received signals from the directional beams  114  enter the beam switches  120 , and the beam controller selects  111  a signal to pass through to the 2:2 switch  130 ,  
         [0059]     The 2:2 switch  130  sends the selected directional signal  124  to the T/R switch  171  through signal  125 .  
         [0060]     The T/R switch  171  is configured to send the signal  125  to the RF filter  142 .  
         [0061]     The RF filter  142  filters the signal  126  and sends it to the switched attenuator  144 .  
         [0062]     The switched attenuator  144  attenuates the signal  127  and sends it to a low-noise amplifier  146 .  
         [0063]     The amplifier  146  amplifies the signal  128  and sends it to the directional RF circuit  147 .  
         [0064]     The RF circuit  147  brings the signal  129  down to baseband and sends it to the ADC  148 .  
         [0065]     The ADC  148  digitizes the signal  102  and sends it to the beam controller  110 .  
         [0066]     The beam controller  110  receives the digital signal  101 , and processes it to determine the signal strength. This process continues for the other directional beams  114 , until the beam controller  110  can select the best beam number  116 . The beam controller  110  then sends the best beam number  116  to the WLAN processor  179 .  
         [0067]     The WLAN processor  179  processes the received omni-directional signal  123 , and receives the best beam number  116  from the beam controller  110 . The source subscriber&#39;s ID (e.g. Media Access Control (MAC) or Connection Identification (CID)) is identified from the received omni-directional burst  123 . A beam switching table is established and a new entry is added. An example of the beam switching table is shown as Table 1. The subscriber station ID number is correlated with the best beam number  116 , and with a subscriber station&#39;s status value.  
         [0068]     The status in this case is denoted as a “1” for an active station, and a “0” for an inactive station. When a subscriber station (SS) is inactive for a predefined period of time, the corresponding entry in the table is removed.  
                             TABLE 1                           Beam switching table (BST)            Subscriber Station ID   Beam Number   Status               #1   4   1       #2   2   0       . . .                  
 
         [0069]     The WLAN processor  179  then sends the response signal  104  to the RF circuit  178  and sends the antenna control signal  117  to the beam controller  110 .  
         [0070]     The RF circuit  178  converts the signal up to the transmission frequency and Forwards it to the power amplifier  176 .  
         [0071]     The power amplifier receives the signal  106  and amplifies it, and then forwards it to the T/R switch  171 .  
         [0072]     At the same time, the beam controller  110  receives the antenna control signal  117 , and then sends out a transmit/receive signal  113  to the T/R switch  117 , a switch control signal  112  to the 2:2 switch  130  and a beam selection signal  111  to the beam switches  120 .  
         [0073]     The T/R switch  171  has now been configured to transmit through the T/R control signal  113 . The transmit data signal  107  is received and then forwarded to the 2:2 switch  130 .  
         [0074]     The 2:2 switch  130  has been configured by the switch control signal  112  to pass the received signal  125  over to the beam switches  120  through signal  124 .  
         [0075]     The beam switches  110  receive the transmit signal data  124 , and have now been configured to transmit the signal through the selected antenna by the beam selection signal  111 .  
         [0076]     The signal is then transmitted to the subscriber station through the selected best beam. At the next allotted time to receive data from the subscriber station the selected best beam is configured to receive data.  
         [0077]     The system monitors the signal quality during packet reception and selects the beam with the best signal strength. Over time this process builds up the beam switching table and the subscriber station to beam mapping is learned. Before each packet transmission, the best beam is identified by referencing the mapping table and the beam is used for subsequent packet transmission to the subscriber station (SS).  
         [0078]     When the access point (AP) is expecting a packet from a particular subscriber station (SS) during a reception time, the corresponding beam is identified by looking up the subscriber station address in the beam switching table (BST).  
         [0079]     Subscriber stations (SS) may move from one location to anothcr from time to time. The subscriber station (SS) location is tracked using post-processing methods such as correlation of multiple beam selection decisions over time.  
         [0080]     The start of a transmission (Tx) time period is identified by monitoring the T/R switch control signal  113  from the beam controller  110 . The destination subscriber station (SS) of the packet to be transmitted needs to be obtained from the WLAN processor  179  before the start of the transmission. The beam used for the packet transmission is identified by looking up the subscriber station ED number in the beam switching table (BST). If the subscriber station (SS) cannot be found in the table or the packet is a multicast/broadcast packet, an omni-directional beam pattern is used for the transmission and the 2:2 switch  130  is configured for the second path.  
         [0081]     Table 2 is a summary of the mapping between some packet types and the beams used by the access point (AP) to receive and transmit the packets.  
                             TABLE 2                           Beam Assignment                Packet Type   Beam Type                       Request to Send (RTS) (unknown   Omni           SS)           Request to Send (RTS) (known SS)   SS specific beam           Clear to Send (CTS)   SS specific beam           Acknowledge (ACK)   SS specific beam           Power Save Poll (PS-Poll)   SS specific beam           Data   SS specific beam           Beacon   Omni           Association response   SS specific beam           Disassociation   SS specific beam           Re-association response   SS specific beam           Probe Response   SS specific beam           Authentication   SS specific beam           De-authentication   SS specific beam                      
 
         [0082]     Those having ordinary skill in the art will recognize that the RF filter  172 , switched attenuator  174 , low-noise amplifier  175 , and RF circuit  178  could be referred to as an RF front end  140 . Furthermore the person of ordinary skill in the art will recognize that this could be implemented in any number of ways.  
         [0083]     Also those having ordinary skill in the art will recognize that the transmit/receive switch  171 , RF front end  140 , and Wireless Local Area Network (WLAN) processor  179  could be referred to as a communications signal processor  170 .  
         [0084]     Other embodiments consistent with the present invention will become apparent from consideration of the specification and the practice of the invention disclosed therein.  
         [0085]     Accordingly, the specification and the embodiments are to be considered exemplary only, with a true scope and spirit of the invention being disclosed by the following claims.