Abstract:
A method of implementing packet corruption to halt propagation in an optical wireless communication link in a manner that simultaneously minimizes network overhead and maintains a high bandwidth loop sufficient to control the motion of the mirror.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to optical wireless communication links, and more particularly, to a method of packet corruption to halt propagation in an optical wireless link.  
           [0003]    2. Description of the Prior Art  
           [0004]    An optical wireless link system consists of two stations or optical wireless links (OWLs): Each of which contains an optical transmitter and an optical receiver. The transmitter is able to change the direction of its transmitted beam by known amounts of angular displacement. The receiver sees this motion and sends position correction information back to the transmitter. This feedback is used by a servo control loop to position the transmitted beam on the receiver of the remote station.  
           [0005]    Status packets and link control packets associated with the two OWLs can have detrimental effects on the system since they both require processing power; and if implemented as standard protocol packets, can also be transmitted on to the rest of the network, using up bandwidth.  
           [0006]    When a packet arrives at the receiver, the receiver has to look at the data contained in the packet, decide if the packet is a servo packet, and if so, pull data out of the packet for control use. This processing uses computational resources of the processor that could be used for other purposes. FIG. 3 is a timing diagram illustrating one embodiment of periodic servo timing, including an exploded view detailing tasks performed during one servo period.  
           [0007]    Servo packets can also be passed on to the rest of the network, as stated above. This can be problematic since this increases system overhead by undesirably reducing the available system bandwidth, especially if there are many OWLs operating in the network. Further, control packets from one link may undesirably reach another OWL in another link, and be misinterpreted as data from its linked unit with an unpredictable result.  
           [0008]    In view of the foregoing, it would be desirable and advantageous in the optical wireless communication art to provide a technique for processing link control or status packets in an optical wireless communication link in a manner that simultaneously minimizes network overhead and maintains a high bandwidth loop sufficient to control the motion of the mirror.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention is directed to a method of implementing packet corruption to halt propagation in an optical wireless communication link in a manner that simultaneously minimizes network overhead and maintains a high bandwidth loop sufficient to control the motion of the mirror.  
           [0010]    The data stream is passed through “packet pillaging” hardware which recognizes link control or status packets. If the packet is a regular data packet, the pillager passes the data packet with no modification(s). If however, the packet is recognized as a link control or servo packet, the pillager hardware pulls the control information out of the packet and then corrupts the data as it is passed. This corruption will cause the receiver to reject the packets since, due to the corruption, they are no longer valid packets.  
           [0011]    In one aspect of the invention, a method of packet corruption to halt propagation in an optical wireless communication link is implemented in a manner that frees up the resources that would have been needed to process the packet.  
           [0012]    In another aspect of the invention, a method of packet corruption to halt propagation in an optical wireless communication link is implemented in a manner that does not flood the network with control packets which have no use outside of the link.  
           [0013]    In still another aspect of the invention, a method of packet corruption to halt propagation in an optical wireless communication link is implemented in a manner that permits use of the same data protocol for servo packets and data packets.  
           [0014]    According to one embodiment, an optical wireless link (OWL) comprises a packet pillager and a receiver, wherein the packet pillager is operational to extract control data from an incoming communication packet containing servo data, and then corrupt the communication packet data subsequent to the data extraction such that the receiver will reject the communication packet as an invalid packet, and further such that the receiver will process only the extracted servo data.  
           [0015]    According to another embodiment, an optical wireless link (OWL) comprises means for extracting control data from an incoming data packet containing servo data, and for corrupting the data packet subsequent to extracting the control data; and means for rejecting the corrupted data packet as an invalid packet, and for processing only the extracted control data.  
           [0016]    According to yet another embodiment, an optical wireless link (OWL) comprises a packet pillager configured to extract control data from an incoming data packet containing servo data, and then corrupt the packet data subsequent to the data extraction such that the data packet will be rejected by the OWL as an invalid packet, and further such that the OWL will process only the extracted servo data.  
           [0017]    According to still another embodiment, a method of optical wireless communication comprises the steps of providing an optical wireless link (OWL) having a receiver and a packet pillager; extracting control data via the packet pillager from an incoming data packet only if the incoming data packet is a servo packet; and corrupting the incoming data packet subsequent to extracting the control data such that the receiver will reject the incoming data packet as an invalid data packet.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    Other aspects, features and advantages of the present invention will be readily appreciated, as the invention becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing figures wherein:  
         [0019]    [0019]FIG. 1 is a block diagram illustrating a pair of OWLs communicating with one another in which each OWL includes a transmitter, receiver and a processor/controller;  
         [0020]    [0020]FIG. 2 is a block diagram illustrating one embodiment of a control loop suitable for use in an optical wireless link;  
         [0021]    [0021]FIG. 3 is a timing diagram illustrating one embodiment of periodic servo timing, including an exploded view detailing tasks performed during one servo period; and  
         [0022]    [0022]FIG. 4 is a block diagram illustrating a pair of OWLs communicating with one another in which each OWL includes a “packet pillager” according to one embodiment of the present invention. 
     
    
       [0023]    While the above-identified drawing figures set forth particular embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    [0024]FIG. 1 is a block diagram illustrating an OWL system  100  having a pair of OWLs  102 ,  103  communicating with one another in which each OWL includes a transmitter  104 , a receiver  106  and a processor  112 . The transmitter  104  is able to change the direction of its transmitted beam by known amounts of angular displacement. The receiver  106  sees this motion as a linear displacement, and sends position correction information back to the transmitter  104 . This feedback is used by a servo control loop algorithm to position the transmitted beam on the receiver  106  of the remote station.  
         [0025]    [0025]FIG. 3 shows one embodiment of a timing diagram illustrating periodic servo timing, including an exploded view detailing tasks performed during one servo period. U.S. patent application Ser. No. 10/060,549, entitled Calibration Method For Station Orientation, filed by Oettinger et al. on Jan. 30, 2002, discloses a method of calibrating station orientation in an OWL. The &#39;549 patent application is assigned to the assignee of the present invention, and is hereby incorporated by reference in its entirety herein.  
         [0026]    [0026]FIG. 2 is a block diagram illustrating one embodiment of a control loop  200  suitable for use in an optical wireless link such as OWL  102 ,  103  depicted in FIG. 1. Operational details of control loop  200  are set forth in U.S. patent application entitled Method Of Sampling Local And Remote Feedback In An Optical Wireless Link, docket no. TI-33553, filed by Oettinger et al., on Apr. 29, 2002, and which is incorporated by reference in its entirety herein.  
         [0027]    [0027]FIG. 4 is a block diagram illustrating an OWL system  300  having a pair of OWLs  302 ,  304  communicating with one another in which each OWL includes a transmitter  104 , a receiver  106 , a packet pillager  306 , and a processor  112 . OWL system  300  functions in a similar fashion to OWL system  100  discussed herein before with reference to FIG. 1; wherein the transmitter  104  is able to change the direction of its transmitted beam by known amounts of angular displacement; and the receiver  106  sees this motion as a linear displacement, and sends position correction information back to the transmitter  104 . This feedback is likewise used by a servo control loop algorithm to position the transmitted beam on the receiver  106  of the remote station.  
         [0028]    OWL system  300  differs from OWL system  100  however, in that OWL system  300  can also be seen to include a “packet pillager”  306 . Further structural details regarding packet pillager  306  are not set forth herein to preserve brevity and clarity, and since those skilled in the art of “wireless communication” will be aware of a multiplicity of techniques that can be employed to receive and corrupt a data stream. With continued reference now to FIG. 4, the data stream is passed through hardware (packet pillager  306 ) that is configured to recognize link packets. If the packet is a regular data packet, the packet pillager  306  simply passes the data packet on to the receiver  106  with no modification. If however, the packet is recognized as a servo packet, then the packet pillager  306  extracts the control information out of the packet and proceeds to corrupt the remaining packet data as it is passed to the receiver  106 . This corruption will cause the receiver  106  to reject the packet data, since this packet data will not be recognized as a valid data packet due to the corrupted packet data. This process then frees up the processing resources that would have been necessary to process the remaining packet data, such that this remaining packet data is prevented from flooding the network with control packets which have no use outside of the associated communication link  350 .  
         [0029]    Those skilled in the art will appreciate that defining a unique transfer protocol for link to link communication could also be implemented to providing similar results. This approach however, would require additional work to transmit packets that are not required with the solution described above with reference to FIG. 4. The method described herein with reference to FIG. 4 advantageously permits use of the identical data protocol for servo packets.  
         [0030]    In view of the above, it can be seen the present invention presents a significant advancement in the art of optical wireless communication techniques. Further, this invention has been described in considerable detail in order to provide those skilled in the optical wireless communication art with the information needed to apply the novel principles and to construct and use such specialized components as are required. In view of the foregoing descriptions, it should be apparent that the present invention represents a significant departure from the prior art in construction and operation. However, while particular embodiments of the present invention have been described herein in detail, it is to be understood that various alterations, modifications and substitutions can be made therein without departing in any way from the spirit and scope of the present invention, as defined in the claims which follow.