השוואת שיטות

	קוד בלוק מרחב-זמן של אלאמוטי	קודים בעלי צפיפות נמוכה של בדיקת זוגיות (LDPC)	תורת אפנון תדר רב-נושא אורתוגונלי (OFDM)	משפט קיבולת ערוץ של שאנון
תחום	תקשורת	תקשורת	תקשורת	תקשורת
משפחה	Process / pipeline	Process / pipeline	Process / pipeline	Process / pipeline
שנת המקור	1998	1962	1971	1948
הוגה השיטה	Siavash Alamouti	Robert Gallager	Weinstein and Ebert	Claude Shannon
סוג	space-time coding scheme	linear error-correcting code	multicarrier modulation scheme	fundamental theoretical bound
מקור מכונן	Alamouti, S. M. (1998). A simple transmit diversity technique for wireless communications. IEEE Journal on Selected Areas in Communications, 16(8), 1451-1458.	Gallager, R. G. (1962). Low-density parity-check codes. IRE Transactions on Information Theory, 8(1), 21-28.	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.	Shannon, C. E. (1948). A mathematical theory of communication. Bell System Technical Journal, 27(3), 379-423.
כינויים	space-time coding, transmit diversity	sparse codes, belief propagation codes	multicarrier modulation	channel capacity, information theory bound
קשורות	5	5	5	5
תקציר	The Alamouti code is an elegant space-time coding scheme that provides full transmit diversity using two antennas and a simple linear receiver. Introduced by Siavash Alamouti in 1998, it requires no channel state information at the transmitter, achieves the same bit-error rate as a single-antenna system with receiver diversity, and uses linear processing for decoding. The Alamouti code has become the de facto standard for transmit diversity in cellular systems and is adopted in LTE, WiFi, and many 5G protocols.	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.	Shannon's channel capacity theorem, published in 1948, establishes the maximum rate at which information can be reliably transmitted over a noisy channel. Expressed as C = B log2(1 + S/N) for additive white Gaussian noise (AWGN), it is a fundamental bound in information theory and communications engineering. Shannon proved that reliable communication is possible at any rate below capacity, and impossible above it. This theorem underpins the design of all modern communication systems and motivates coding theory, modulation, and signal processing techniques.