Pico Cell Wireless Local Area Network (Wlan)

Abstract

A pico cell wireless LAN and pre-emptive roaming algorithm is provided to allow mobile devices in the WLAN to hand-off to another different access point quickly and efficiently. Once associated with an access point (AP), the mobile device receives information about neighboring APs that may be available for hand-off during roaming (or insufficient signal strength). Signal strength of the associated AP is continuously monitored and if signal strength from the associated AP falls below a threshold, the mobile device measures signal strength of the neighboring APs in the list, ranks them, and selects an AP for hand-off. AP load and other information may be used to rank the neighboring APs. The mobile device hands-off to (or associates with) one of the neighboring APs, if appropriate. Hand-offs are attempted in order or rank. Cell sizes in the pico cell WLAN are relatively small, on the order of 1000 square feet or less.

1 . A method of hand-off for a mobile terminal from a first access point to a second access point in a wireless local area network (WLAN), the method comprising: 
 measuring in a mobile terminal signal to noise ratio (SNR) of first RF signals received from the first access point;    if the measured SNR of the first RF signals exceeds a first threshold, measuring SNR of RF signals received from a plurality of candidate access points in a roaming candidate list stored on the mobile terminal;    determining from measured SNRs of the candidate access points whether any of the measured SNR exceed a second threshold, and if so, identifying those candidate access points in a new association list;    selecting one of the candidate access points in the new association list; and    attempting to associate the mobile terminal to the selected candidate access point.    
   
   
       2 . The method in accordance with  claim 1  further comprising: 
 associating the mobile terminal to the first access point in the WLAN; and    receiving from the first access point the roaming candidate list identifying the plurality of candidate access points in the WLAN.    
   
   
       3 . A mobile terminal operable for wireless connection to one or more access points in a wireless local area network (WLAN), the device comprising: 
 means for measuring signal to noise ratio (SNR) of first RF signals received from the first access point;    if the measured SNR of the first RF signals exceeds a first threshold, means for measuring SNR of RF signals received from each of a plurality of candidate access points in a roaming candidate list;    means for determining from measured SNRs of the candidate access points whether any of the measured SNR exceed a second threshold, and if so, identifying those candidate access points in a new association list;    means for selecting one of the candidate access points in the new association list; and    means for attempting to associate the mobile device to the selected candidate access point.    
   
   
       4 . The method in accordance with  claim 3  further comprising: 
 means for associating the mobile terminal to a first access point in the WLAN; and    means for receiving from the first access point the roaming candidate list identifying the plurality of candidate access points in the WLAN.    
   
   
       5 . A state machine for use by a mobile terminal in a wireless area network, the state machine comprising: 
 a first state in which the mobile terminal is associated with a first access point in the network and signal to noise ratio (SNR) of first RF signals received from the first access point are measured;    a second state in which SNR of RF signals received from a plurality of candidate access points in a roaming candidate list are measured and it is determined from measured SNRs of the candidate access points whether any of the measured SNRs exceeds a second threshold, and if so, identifying those candidate access points in a new association list, the state machine transitioning from the first state to the second if the measured SNR of the first RF signals exceeds a first threshold;    a third state in which one of the candidate access points in the new association list is selected and an attempt is made to associate the mobile terminal to the selected candidate access point, the state machine transitioning from the second state to the third state if there is at least one candidate access point in the new association list.    
   
   
       6 . The state machine in accordance with  claim 5  further comprising: 
 a fourth state in which a plurality of channels associated with a plurality of access points are scanned to determine SNRs for each of the plurality of access points, one of the plurality of access points is selected and the mobile terminal attempts to associate to the selected access point, the state machine transitioning from the fourth state to the first state when the mobile terminal associates with the selected access point.    
   
   
       7 . A mobile terminal for communicating with one or more access points in a wireless local area network (WLAN), the device comprising: 
 a processor;    a transceiver coupled to the processor;    an antenna coupled to the transceiver for receiving and transmitting RF signals from and to the one or more access points in the WLAN; and    wherein the processor is operable for: 
 measuring signal to noise ratio (SNR) of first RF signals received from the first access point,  
 if the measured SNR of the first RF signals exceeds a first threshold, measuring SNR of RF signals received from each of a plurality of candidate access points in a roaming candidate list stored in the mobile terminal,  
 determining from measured SNRs of the candidate access points whether any of the measured SNR exceed a second threshold, and if so, identifying those candidate access points in a new association list,  
 selecting one of the candidate access points in the new association list, and  
 attempting to associate the mobile device to the selected candidate access point.  
   
   
   
       8 . The mobile terminal in accordance with  claim 7  wherein the processor is further operable to: 
 associate the mobile terminal to a first access point in the WLAN; and    receive from the first access point the roaming candidate list identifying the plurality of candidate access points in the WLAN.    
   
   
       9 . A wireless local area network (WLAN), the WLAN comprising: 
 a plurality of sets of access points operable for communicating wirelessly with one or more remote client devices, each set of access points defines a cell having a predefined communication coverage area within the WLAN;    a plurality of switches communicatively coupled to access points; and    wherein the communication coverage area of each defined cell is less than about 1000 hundred square feet and the access points in a first cell are operable for transmitting a roaming candidate list to a mobile device associated with one of the access points in the first cell, the list identifying one or more neighborhood access points.