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In radio technology, symmetrical double-sided two-way ranging (SDS-TWR) is a ranging method that uses two delays that naturally occur in signal transmission to determine the range between two stations:〔IEEE Standard 802.15.4a: Part 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) specifications for low-rate wireless personal area networks (WPANs) Amendment 1: Add Alternate PHYs〕 * Signal propagation delay between two wireless devices * Processing delay of acknowledgements within a wireless device This method is called ''symmetrical double-sided two-way ranging'', because: * It is symmetrical in that the measurements from station A to station B are a mirror-image of the measurements from station B to station A (ABA to BAB). * It is double-sided in that only two stations are used for ranging measurement – station A and station B. * It is two-way in that a data packet (called a test packet) and an ack packet is used. == Signal propagation delay == A special type of packet (test packets) is transmitted from station A (node A) to station B (node B). As time the packet travels through space per meter is known (from physical laws), the difference in time from when it was sent from the transmitter and received at the receiver can be calculated. This time delay is known as the ''signal propagation delay''. 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「Symmetrical double-sided two-way ranging」の詳細全文を読む スポンサード リンク
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