잔향 환경에서의 인공 음향 신호를 이용한 음향 센서 위치 추정 기술

학위논문 (박사)-- 서울대학교 대학원 공과대학 전기·컴퓨터공학부, 2017. 8. 김남수.Widespread use of smart devices has brought a growth of user-customized services. In particular, localization techniques have been gaining attention due to increase of location-based services (LBS). Most of LBS services such as navigation systems, traffic alerts or augmented reality (AR) services depend on the GPS for its accuracy and speed, however, its operation is limited to the outdoor environments. The demand of indoor LBS is rapidly growing due to the growth of automated home and IoT technology. There have been studies via WiFi, Bluetooth or RFID, but their performance has been unsatisfactory for their limitation such as the requirement of additional equipment or guarantee of the line of sight. Among various sensors used for indoor localization, we focus on the acoustic sensors, i.e. microphones. There are several advantages in using the acoustic signals for indoor localization. There is no need for additional apparatus since loudspeakers are pre-installed in most of the buildings for the purpose of announcement or playing background music and mobile devices such as cellphones or tablets are equipped with microphones and loudspeakers. Even the prevailing popularity of IoT services helps accessibility of acoustical sensors and loudspeakers. In addition, acoustic signals have advantages of being able to detect signals through obstacles unlike cameras of RFID. In this thesis, we propose a position estimation system using acoustic signals to maximize these advantages. We aim to estimate the position of the target user with an acoustic sensor based on the recording of signals from the fixed loudspeakers installed around the room. We target to estimate the position of the acoustic sensor with high accuracy and low-complexity in a large space with high reverberation. Particularly, we try not to affect human hearing by using inaudible frequency bands. In order to estimate the position, it is important to estimate the direct path signal rather than the signal due to reverberation or reflection. To do this, we present various localization techniques as following. First, we propose the source data structure to operate in the large reverberant environments. In the large space, the consideration of the near-far effect is required which refers to a situation when the desired signal is far away, it is difficult to receive the desired signal due to the interference of closer unwanted signals. In wireless communications, it can be dealt with by interaction of transmitter and receiver by feedback of channel information. However, it is difficult in the acoustic system since there is no feedback between the transmitter and receiver. We borrowed the structure called OFDMA-CDM and modified it to deal with the near-far effect. In the reverberant environment, the amplitude of reverberation is often larger than the direct path signal. We proposed the technique to estimate the direct path signal. Second, we propose a method for accurate location estimation in the highly reverberant environments. In the high reverberation condition, more spurious reflections occur, which makes it difficult to estimate the time delay of the direct path signal. If the time delay estimation is wrong, it is likely that the position estimate does not converge by an estimation method. In the proposed method, position candidates are obtained from most of the received signals including signals even from spurious reflections. The unreliable candidates are filtered out by the agreement test and rank the rest candidates by their reliability to find accurate target position. We can estimate the receiver's position even in the condition of attenuated direct path signal or high reverberation by using the proposed method. Third, we proposed a low-complexity localization method to work in the highly reverberant environment. This method is based on the particle filter that estimates the position by weighted particles whose weights are computed by the likelihood. We designed likelihood function that efficiently calculates likelihood in the region with the direct path signal so that more reliable position can be obtained. The proposed method enables location estimation with high precision with a relatively small amount of computation in severe reverberation. The proposed methods are evaluated in simulated environments with different reverberation time. The performances are verified in different parameters and compared with other localization methods. In addition, the performance is evaluated in the real reverberant environment with a large space. A series of experiments has shown the superiority of the proposed methods and it is appropriate to apply in the actual environment.1 Introduction 1 2 Acoustic Receiver Localization System 7 2.1 Source data structure 8 2.2 Localization from the received signal 12 2.3 TDE in reverberant environments 16 2.4 Near-far effect 18 3 Indoor Localization using Inaudible Acoustic Signals 21 3.1 Introduction 21 3.2 Acoustic source design and synchronization 22 3.2.1 Reverberation in multipath environments 23 3.2.2 Source data structure for ARL 23 3.2.3 Signal presence detection 30 3.2.4 Direct path detection 30 3.3 Performance evaluation 32 3.3.1 Experimental setup and system configuration 33 3.3.2 Evaluation of acoustic data structure 34 3.3.3 Performance of the direct path detection algorithm 36 3.3.4 Performance in a real room 36 3.4 Summary 38 4 Robust Time Delay Estimation for Acoustic Indoor Localization in Reverberant Environments 39 4.1 Introduction 39 4.2 Robust TDE 40 4.3 Performance evaluation 45 4.3.1 Performance evaluation in a real room 46 4.3.2 Performance evaluation in simulated reverberant conditions 47 4.4 Summary 50 5 Indoor Localization Based on Particle Filtering 53 5.1 Introduction 53 5.2 A framework of positioning method using particle filter 54 5.2.1 State and dynamic models 55 5.2.2 Bayesian framework using particle filter 56 5.2.3 Likelihood function 57 5.3 ARL in reverberant environment 59 5.3.1 Peak quality 59 5.3.2 Efficient calculation of the likelihood function 60 5.3.3 Finding the direct path region 61 5.4 Performance evaluation 64 5.4.1 Performance in a simulated environment 65 5.4.2 Performance in the actual environment 87 5.5 Summary 89 6 Conclusions 91 Bibliography 95 요약 105Docto

decision of optimal stop bar location in ramp metering design

학위논문 (석사)-- 서울대학교 대학원 : 건설환경공학부, 2012. 2. 전경수.미국 및 유럽등지의 여러 나라에서는 효율적인 도로운영의 한 전략으로 램프미터링을 시행중에 있다. 그러나 아직 우리나라에서는 그 활용이 미비하며 정지선에 관한 명확한 설치기준은 우리나라뿐 아니라 외국에도 없다. 본 연구는 본선 및 인접도로의 혼잡을 최소화하기 위한 정지선의 위치 결정을 목적으로 한다. 가속차로의 길이와 대기공간의 길이는 램프의 정지선의 위치에 따라 변하게 된다. 가속차로의 길이가 충분히 길지 않다면 가속차로의 끝부분, 즉 합류부에서 합류차량의 속도가 본선의 주행차량보다 속도가 느리므로 본선의 최대 통과 가능 교통량에 영향을 미칠 것이다. 또한 대기공간의 길이 역시 지나치게 짧을 경우 램프미터링으로 인한 대기행렬이 쉽게 인접도로로 넘어갈 것이며 이로 인하여 인접도로의 최대 통과 가능 교통량에 영향을 미칠 것이다. 따라서 가속차로의 길이와 대기공간의 길이의 충분한 확보가 필요 하지만 우리나라의 경우 도로의 설계시 램프미터링을 염두에 두고 설계를 하지 않아 램프미터링의 실시가 효율적인 구간에도 설치할 공간이 부족한 곳이 많다. 이러한 공간에선 적정한 수준의 경계선이 필요할 것이며 이 적정한 수준을 결정하는 합리적인 근거가 필요할 것이다. 본 연구에서는 가속차로의 길이가 본선의 최대 통과 가능 교통량에 미치는 영향을 합류시 속도와 임계밀도의 곱을 최대 통과 가능 교통량으로 간주하여 본선의 BPR식의 용량항에 적용하였고, 대기공간의 길이가 인접 하부도로에 미치는 영향을 대기행렬이 인접도로로 넘어가는 순간부터 사고시 용량을 적용하여 인접도로의 BPR식의 용량항에 적용하였다. 계산결과를 토대로 본선 및 하부도로의 통행시간이 가장 적게 걸린 경우를 최적 정지선의 위치로 결정하였다. 가상의 진입로에 교통량을 세 가지 상황으로 가정하여 모델을 적용시켜 본 결과 총 통행시간이 가장 적게 걸린 정지선의 위치를 찾을 수 있었으며 이를 최적 정지선 위치로 결정하였다. 이 연구에서 소개한 방법으로 정지선의 위치를 결정하였을 경우 본선 뿐만 아니라 하부도로까지 고려한 총 통행시간의 절감이 가능하며 또한 향후 우리나라에 램프미터링이 도입되었을 시 정지선의 위치를 효율적으로 결정하는 근간이 될 것이다.In many countries like america and in europe, they use ramp metering for useful management of road. But in KOREA, they don't use ramp metering yet. Moreover there are no clear standards of stopbar not only in KOREA but foreign. This research has a purpose of deciding the location of stopbar to minimize the congestion of main stream and adjacent road. The length of acceleration lane changes as the location of stopbar. If there is not enough length of acceleration lane, the maximum throughout volume of traffic should be decresed because the speed of the car entering the highway is slower than passing cars in the main highway. And if there is not enough space, queuing will exceed the capacity of the storage space so it will impact to the adjacent road. So it is necessary to keep enough length of acceleration lane and storage space, but it is not easy to secure enough length because they designed the road without ramp metering. So it is difficult to apply the ramp metering where effect is expectable if ramp metering is conducted. It is necessary to decide proper location of stop bar in this area and it is also important that it should be based on reasonable basis. In this research, we apply the capacity to the BPR function by multiplying the speed of joining point and critical density in order to reflect the effect how the length of acceleration lane influence the maximum throughout volume of main stream. And we also consider the effect of storage space by applying the capacity of accident to the BPR function when the queuing starts exceeding to the adjacent road. We decide the best location of stop bar when the travel time is minimum. We assume the volume and apply to the imaginary intersection. As a result we could find the location of stop bar where the travel time was minimum, and decided the best location of stop bar. If the location of stop bar is decided by this method introduced in this research, the travel time which contain not only main highway but also adjacent road could be reduced. So it can be a basis for reasonable location of stop bar if ramp metering is implemented in KOREA in the future.Maste