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| Κώδικες Ελέγχου Χαμηλής Πυκνότητας (LDPC)× | Ορθογώνια Διαίρεση Συχνότητας (OFDM)× | |
|---|---|---|
| Πεδίο | Τηλεπικοινωνίες | Τηλεπικοινωνίες |
| Οικογένεια | Process / pipeline | Process / pipeline |
| Έτος προέλευσης≠ | 1962 | 1971 |
| Δημιουργός≠ | Robert Gallager | Weinstein and Ebert |
| Τύπος≠ | linear error-correcting code | multicarrier modulation scheme |
| Θεμελιώδης πηγή≠ | Gallager, R. G. (1962). Low-density parity-check codes. IRE Transactions on Information Theory, 8(1), 21-28. DOI ↗ | Weinstein, S. B., & Ebert, P. M. (1971). Data transmission by frequency-division multiplexing using the discrete Fourier transform. IEEE Transactions on Communication Technology, 19(5), 628-634. DOI ↗ |
| Εναλλακτικές ονομασίες≠ | sparse codes, belief propagation codes | multicarrier modulation |
| Συναφείς | 5 | 5 |
| Σύνοψη≠ | LDPC codes, invented by Robert Gallager in 1962 and rediscovered in the 1990s by MacKay, are linear error-correcting codes defined by sparse parity-check matrices. They achieve performance within 0.4 dB of the Shannon limit with iterative belief-propagation decoding and have become the standard for modern wireless (WiFi-6, 5G NR, Digital Video Broadcasting). Unlike turbo codes, LDPC codes have a more elegant graph-theoretic structure and more mature theoretical analysis. | OFDM is a multicarrier modulation technique that divides a wideband channel into many narrowband orthogonal subcarriers. Introduced by Weinstein and Ebert in 1971, it exploits the duality between time and frequency domains to efficiently use spectrum while mitigating intersymbol interference in frequency-selective channels. OFDM is now the standard for high-speed wireless systems including WiFi, cellular LTE, and digital broadcasting. |
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