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| 直交周波数分割多重 (OFDM)× | スロット付きALOHAランダムアクセスプロトコル× | |
|---|---|---|
| 分野 | 通信工学 | 通信工学 |
| 系統 | Process / pipeline | Process / pipeline |
| 提唱年≠ | 1971 | 1970 |
| 提唱者≠ | Weinstein and Ebert | Norman Abramson and Lawrence Roberts |
| 種類≠ | multicarrier modulation scheme | random access protocol |
| 原典≠ | 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 ↗ | Roberts, L. G. (1975). ALOHA packet system with and without slots and capture. ACM SIGCOMM Computer Communication Review, 5(2), 28-42. DOI ↗ |
| 別名≠ | multicarrier modulation | random access, medium access |
| 関連≠ | 5 | 3 |
| 概要≠ | 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. | Slotted ALOHA is a fundamental random access protocol enabling multiple devices to share a wireless channel without centralized coordination. Introduced by Abramson (1970) and refined by Roberts (1975), it divides time into fixed slots and allows devices to transmit at the beginning of a slot with a fixed probability. While simple and elegant, Slotted ALOHA achieves only 37% channel utilization under saturation (optimal traffic load), a fundamental limit discovered by Abramson. Despite this limitation, Slotted ALOHA remains a teaching tool and appears in modern systems like satellite and IoT networks. |
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