Lecture_9b-09Ross

Lecture_9b-09Ross - ELEC300U: A System View of...

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ELEC300U: A System View of Communications: from Signals to Packets Lecture 09a Burst Error Correction Interleaving Framing Bit Stuffing Error Correcting Coding/Decoding Summary Block Error Probability Analysis ELEC300U 1 Some content taken with permission from material developed for the course EECS6.02 by C. Sodini, M. Perrot and H. Balakrishnan
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Burst Errors Correcting single-bit errors is nice, but in many situations errors come in bursts many bits long (e.g., damage to storage media, burst of interference on wireless channel, …). How does single-bit error correction help with that? Well, can we think of a way to turn a B-bit error burst into B single-bit errors? B Problem: Bits from a particular codeword are transmitted sequentially, so a B-bit burst produces multi-bit errors. Solution: interleave bits from B different codewords. Now a B-bit burst produces 1-bit errors in B different codewords. Row-by-row transmission order B Col-by-col transmission order ELEC300U 2 Some content taken with permission from material developed for the course EECS6.02 by C. Sodini, M. Perrot and H. Balakrishnan
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Framing Looking at a received bit stream, how do we know where a block of interleaved codewords begins ? Physical indication (transmitter turns on, beginning of disk sector, separate control channel) Place a unique bit pattern (frame sync sequence) in the bit stream to mark start of a block Frame = sync pattern + interleaved code word block Search for sync pattern in bit stream to find start of frame Bit pattern can’t appear elsewhere in frame (otherwise our search will get confused), so have to make sure no legal combination of codeword bits can accidentally generate the sync pattern Sync pattern can’t be protected by ECC, so errors may cause us to lose a frame every now and then, a problem that will need to be addressed at some higher level of the communication protocol.
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Lecture_9b-09Ross - ELEC300U: A System View of...

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