Method and apparatus for fast acquisition and synchronization of transmission frames

Abstract

A method and apparatus for providing frame acquisition and synchronization for ATM transmissions in terrestrial wireless and satellite systems. During acquisition ( 1020 ), the transmitter ( 15 ) fills the entire payload of a frame with a pattern that is used by the receiver ( 18 ) to determine the location of the frame boundary. As to synchronization ( 1020 ), a procedure is utilized for using frame sequence number field in the header and Reed-Solomon decoding result ( 1012 ) for correction and maintaining frame synchronization.

What is claimed is:  
     
         1  A communication system for transmitting cell/packet-formatted signals comprising at least two local area networks that are connected by a wireless communication link, each network comprising: 
 (a) a switch for switching cell/packets for providing a plurality of cell/packets, each cell/packet comprising a header portion and a payload portion; and  
 (b) an interconnect apparatus which provides a means of interconnecting said switch over the communication link, said interconnect apparatus comprising: 
 (i) means for processing, in whole or in part, each cell/packet in said plurality of cell/packets to at least separate said header portion from said payload portion and filter said cell/packets on the basis of predetermined criteria;  
 (ii) means for compressing at least said payload portion;  
 (iii) first queue means for receiving at least said compressed payload portion and assembling said compressed portions into high and low priority queues;  
 (iv) means for assembling the content of said queues into fixed sized frames on a predetermined basis, said frames comprising a frame header, a data payload and a code, wherein said frame header comprises a plurality of parameters including parameters relating to cell/packet count per frame, size of partial cell/packet space, frame number and coding; and  
 
 (c) means for transmitting said assembled frame,  
  wherein, said interface further comprises means for filling an entire payload in a frame with a sequence of predetermined numbers useable for acquisition.  
 
     
     
         2 . A communication system as set forth in  claim 1  wherein at least one network further comprises encoding means for encoding said assembled frame and at least the other network comprises decoding means for decoding said assembled frame.  
     
     
         3 . A communication system as set forth in  claim 1  wherein at least one network further comprising an interleaver for interleaving a plurality of said assembled frames and at least said other network comprises deinterleaving means for deinterleaving interleaved frames.  
     
     
         4 . A communication system as set forth in  claim 1  wherein at least one network further comprises an interface to the wireless communication link.  
     
     
         5 . A communication system as set forth in  claim 1  wherein each network further comprises: 
 (d) means for receiving transmitted frames from said wireless communication link;  
 (e) a frame disassembler for disassembling said frames into a plurality of cell/packets; and  
 (f) a second queue means for holding said cell/packets for transmission to a cell/packet switch, and  
 wherein said means for receiving further comprises a means for detecting said sequence of predetermined numbers and for enabling acquisition.  
 
     
     
         6 . A communication system as set forth in  claim 5 , wherein said means for receiving is further operative to locate a frame boundary for synchronization on the basis of at least said detected sequence of numbers.  
     
     
         7 . A communication system as set forth in  claim 5 , wherein said interconnect apparatus further comprises: 
 means for encoding transmitted frames and decoding received frames.    
     
     
         8 . A communication system as set forth in  claim 1 , wherein said payload frame has no complete or partial cell/packets when used for acquisition.  
     
     
         9 . The communication system as set forth in  claim 1 , wherein said cell/packets comprise at least one of ATM cells, Internet packets and frame relay packets.  
     
     
         10 . An assembly of signals into a transmission frame useable in a communication system for transmitting cell/packet-formatted signals, said system comprising at least two local area networks that are connected by a wireless communication link, said signals comprising at least one of data, acquisition and synchronization information comprising: 
 a header portion comprising at least a frame number identifier;    a coding portion; and    a payload portion, said payload portion when containing data comprising at least one of cell/packets and partial cell/packets, and when containing acquisition data comprising solely a predetermined sequence without any data.    
     
     
         11 . The assembly of signals into a transmission frame as set forth in  claim 10 , further comprising, when said payload contains synchronization information, both data in the form of cell! packets, in whole or in part, and a fill pattern comprising a number sequence.  
     
     
         12 . The assembly of signals into a transmission frame as set forth in  claim 10  wherein said payload size is fixed and unrelated to cell or packet size.  
     
     
         13 . The assembly of signals into a transmission frame as set forth in  claim 10  wherein the frame has a fixed size and the size of said coding portion is variable inversely with the size of said payload portion.  
     
     
         14 . An interconnection apparatus between a local area network and a communication system operative to transmit at least one of cell/packet-formatted signals by a wireless communication link, said interconnection apparatus comprising: 
 a transmitter for transmitting a fixed size frame of n octets comprising a header portion and payload portion, said entire payload of the frame comprising a fill pattern, comprising a sequence of numbers; and    a receiver for detecting the sequence for purposes of acquisition, and for determining where a frame boundary is located for purposes of synchronization.    
     
     
         15 . The apparatus, as set forth in  claim 14 , further comprising an interleaver for interleaving at a depth of I frames and wherein for a single sampling of 2I frames, where I is the interleaver depth, the receiver is operative to adjust the frame boundary to the correct value.  
     
     
         16 . The apparatus, as set forth in  claim 14 , wherein said transmitter comprises means operative, once acquisition has been achieved, for determining whether there is space remaining in a frame payload after insertion of data, and for filling any remaining space with a fill pattern comprising a sequence of numbers.  
     
     
         17 . A method of communication acquisition comprising: 
 at a transmitter, transmitting a fixed size frame of n octets comprising a header portion and payload portion, said entire payload of the frame comprising a fill pattern, comprising a sequence of numbers;    at a receiver, detecting the sequence for purposes of acquisition, and using the detected sequence to determine where the frame boundary is located for purposes of synchronization.    
     
     
         18 . The method as set forth in  claim 17  further comprising, at the transmitter, interleaving at a depth of I frames and, at the receiver, wherein for a single sampling of 2I frames or less, where I is the interleaver depth, adjusting the frame boundary to the correct value.  
     
     
         19 . The method as set forth in  claim 17 , further comprising, once acquisition has been achieved, determining whether there is space remaining in a frame payload after insertion of data, and filling any remaining space with a fill pattern comprising a sequence of numbers.  
     
     
         20 . The method as set forth in  claim 17 , wherein said cell/packets comprise at least one of ATM cells and frame relay Spackets.  
     
     
         21 . A method of frame synchronization for use in receiving cell/packets, in whole or in part, within a transmitted frame comprising: 
 (a) initially choosing an arbitrary receive frame boundary for a frame, said frame comprising at least a header portion and a payload portion defined by a sequence of bits;    (b) receiving and analyzing I frames to determine an offset number,    (c) skipping said offset number of bits after the next frame and then resuming frame bit collection;    (d) receiving and discarding the next I+1 frames;    (e) receiving and inspecting at least the next I frames for validity; and    (f) if all I frames are valid, then deciding that synchronization is achieved and commencing normal operation and if any of the I frames is found invalid, then repeating steps (b) through (e).    
     
     
         22 . The method of  claim 21  wherein, once receive synchronization has been achieved, monitoring further received frames for accuracy.  
     
     
         23 . The method of  claim 21  wherein, if in any T-second period the receiver does not detect a sequence of I correct consecutive frames, then the receiver is declared out-of-synchronization and returns to step (b).  
     
     
         24 . The method of  claim 22  wherein analysis is performed for at least one of decoder errors, frame number accuracy and header fields.  
     
     
         25 . The method as recited in  claim 21  further comprising deinterleaving the receive bit stream and Reed-Solomon decoding the bit stream before collection into a frame.  
     
     
         26 . The method as recited in  claim 25  wherein I frames are received and discarded prior to the deinterleaving step, if convolutional interleaving is used at a transmitter.  
     
     
         27 . The method as recited in  claim 26  wherein frames are not discarded prior to an deinterleaving step if a non-convolutional deinterleaver is used.  
     
     
         28 . The method as recited in  claim 21  wherein the first I frames for a non-convolutional type deinterleaver are received and analyzed.  
     
     
         29 . The method as recited in  claim 21  wherein after receiving N frames, the next I frames for a convolutional type deinterleaver are received and analyzed  
     
     
         30 . The method of synchronization comprising: 
 detecting the frame sequence number field in the header of every frame to match frame number and correct header fields; detecting the Reed-Solomon decoding result for the absence of Reed-Solomon decoder errors; and    verifying and maintaining frame synchronization on the basis of a plurality of frames having the correct incrementing frame sequence number and the Reed-Solomon decoder should declare success in correcting a second plurality of frames.    
     
     
         31 . The method of  claim 30  wherein said plurality of frames comprises all frames.  
     
     
         32 . The method of  claim 30  wherein said frame header comprises a frame sequence number, that is incremented modulo 8 and uniquely assigned to each frame, and said method further comprises using said frame sequence number field in the header of every frame and the Reed-Solomon decoding result to verify and maintain frame synchronization.  
     
     
         33 . The method as set forth in  claim 23 , wherein said cell/packets comprise ATM cells.  
     
     
         34 . The method as set forth in  claim 23 , wherein said cell/packets comprise frame relay packets.  
     
     
         35 . The method as set forth in  claim 23 , wherein said cell/packets comprise Internet packets.