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:''This article deals with coherent space–time block codes (STBCs). For differential space–time block codes, see differential space–time codes. Space–time block coding is a technique used in wireless communications to transmit multiple copies of a data stream across a number of antennas and to exploit the various received versions of the data to improve the reliability of data-transfer. The fact that the transmitted signal must traverse a potentially difficult environment with scattering, reflection, refraction and so on and may then be further corrupted by thermal noise in the receiver means that some of the received copies of the data will be 'better' than others. This redundancy results in a higher chance of being able to use one or more of the received copies to correctly decode the received signal. In fact, space–time coding combines ''all'' the copies of the received signal in an optimal way to extract as much information from each of them as possible. ==Introduction== Most work on wireless communications until the early 1990s had focused on having an antenna array at only one end of the wireless link — usually at the receiver.〔E. Larsson and P. Stoica,''Space-Time Block Coding For Wireless Communications''. Cambridge University Press, UK, 2003 (Chinese Edition, 2006).〕 Seminal papers by Gerard J. Foschini and Michael J. Gans, Foschini and Emre Telatar enlarged the scope of wireless communication possibilities by showing that for the highly scattering environment substantial capacity gains are enabled when antenna arrays are used at both ends of a link. An alternative approach to utilizing multiple antennas relies on having multiple transmit antennas and only optionally multiple receive antennas. Proposed by Vahid Tarokh, Nambi Seshadri and Robert Calderbank, these space–time codes (STCs) achieve significant error rate improvements over single-antenna systems. Their original scheme was based on trellis codes but the simpler block codes were utilised by Siavash Alamouti, and later Vahid Tarokh, Hamid Jafarkhani and Robert Calderbank to develop space–time block-codes (STBCs). STC involves the transmission of multiple redundant copies of data to compensate for fading and thermal noise in the hope that some of them may arrive at the receiver in a better state than others. In the case of STBC in particular, the data stream to be transmitted is encoded in blocks, which are distributed among spaced antennas and across time. While it is necessary to have multiple transmit antennas, it is not necessary to have multiple receive antennas, although to do so improves performance. This process of receiving diverse copies of the data is known as diversity reception and is what was largely studied until Foschini's 1998 paper. An STBC is usually represented by a matrix. Each row represents a time slot and each column represents one antenna's transmissions over time. : Here, is the modulated symbol to be transmitted in time slot from antenna . There are to be time slots and transmit antennas as well as receive antennas. This block is usually considered to be of 'length' The code rate of an STBC measures how many symbols per time slot it transmits on average over the course of one block.〔 If a block encodes symbols, the code-rate is : Only one standard STBC can achieve full-rate (rate 1) — Alamouti's code. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Space–time block code」の詳細全文を読む スポンサード リンク
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