part_4_error_handling

part_4_error_handling - CIS 6930 Powerline Communications...

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CIS 6930 Powerline Communications Richard Newman Spring 2010
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Error Handling - Outline Analysis Forward Error Correction Copy codes Block codes Convolutional codes Scrambling Concatenated codes Turbo-codes Low Density Parity Check (LDPC) Backward Error Correction (BEC) Stop-and-Wait
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Analysis Measures Nature of errors detected/corrected Efficiency Efficiency: U = Uf Up Ue Uf = framing efficiency = D/(D+H) where D = Data length and H = Header length Up = protocol utilization Depends on protocol, propagation delay, transmission time Ue = error caused utilization efficiency = 1-P where P = frame error rate
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Error Correction Strategies Forward Error Correction Include sufficient redundancy in transmitted units that errors can be corrected Simplifies sender protocol – used in PHY Backward Error Correction Include sufficient redundancy in transmitted units that errors can be detected Retransmit damaged units More efficient – used in MAC and above Limitations Hamming Distance of code limits capabilities
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General ECC Considerations Systematic vs. non-systematic Systematic = data bits appear in coded stream Non-systematic = no data bits identifiable Hamming Distance H(x,y) = number of bits where x and y differ Code C = {x1, x2, . .., xN} set of valid codewords d = H(C) = min{H(x,y) | x and y are distinct codewords in C} Maximum detection ability = d-1 Maximum correction ability = (d-1)/2
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part_4_error_handling - CIS 6930 Powerline Communications...

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