隨著技術的成熟，機器人在各個層面的功能性越來越多元化，例如：導覽機器人，打掃機器人、服務類型機器人等，這些類型的機器人在執行任務時需要到處移動，因此定位的準確性便非常重要，必須解決機器人本身以及感測器所造成的量測誤差，例如多重路徑傳播(Multipath propagation)所造成的干擾，因為超音波是以全方向性的方位進行傳送，因此多重路徑會在超音波訊號跟障礙物產生碰撞時發生，訊號可能會被障礙物分割，當訊號從物體彈回，便會產生較長的路徑和較大量的延遲。當訊號受到多重路徑傳播通道影響，而導致量測時間與實際傳送時間不同時，抵達時間定位法以及抵達時間差定位法比較容易產生誤差，使得定位準確度降低。為了解決這些誤差，我們透過架構簡單、價格便宜、精準度高的超音波室內定位系統，應用在各個層面上，預期能提高室內定位系統的精準度，可以大幅降低機器人或感測器對位置的誤判，提供機器人做出更好更精準的動作行為。
本研究欲運用複合M序列編碼(Composite M-sequences)架構在超音波室內定位系統中，利用訊號處理(Signal Processing)進行並行碼存取以及抵達時間差定位法(Time Difference of Arrival, TDOA)來分析訊號和訊號之間的關係來取得訊號的飛行時間值，再將抵達飛行時間值參數帶入抵達時間差定位法來最佳化以估測目標物位置，目標物位置會隨著我們抵達訊號飛行時間值的誤差而有所差異，最後再進一步分析並探討複合M序列編碼存取功能對定位精確度的影響。

With the mature technology, the functionality of robots is more and more pluralism. For example, the navigation robot, the cleaning robot, and other service type of robots, when robots execute their task, they need to move around. Therefore, the accuracy of positioning is very important, and the error of measurements between robot and sensor must be solved. For example, the multipath propagation is caused by the interference, because the ultrasonic wave is transmitted at all directions. As a result, multipath propagation will occur when the ultrasonic wave collide obstacles. Transmitting signals may be cut by obstacles so that a longer distance and a larger time delay are produced. Time of Arrival Positioning and Time Difference of Arrival are easily influenced by errors so that the positioning accuracy is reduced. In order to solve these problems, we through construct a simple, inexpensive and high-accuracy indoor ultrasonic positioning system to apply to all applications, and expect to improve the accuracy of indoor positioning systems. The positioning error can be much reduced by robot and sensor and provides robots with better and more precise movement behaviors.
Our research uses composite M-sequences to construct the indoor ultrasonic positioning system. Using signal processing and Time Difference of Arrival to analyze the relation between the transmitting signal and the local signal, the time of flight is obtained. Then the time of flight is used to estimate the target location. The target location is varied by the error of the time delay. Finally, the effects of access function of composite M-sequences on positioning accuracy are further analyzed.

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