緊急救難無論在任何時候都是無比重要的課題，而各個國家也持續致力於發展並整合相關的求救資源，以達到更有效的保障人身安全，1979年由加拿大，法國，美國和蘇聯四個國家共同發起Cospas-Sarsat國際衛星搜救計劃，目的是以分享使用緊急衛星信號、警報檢測系統和求救訊號的分發轉送，以加速受害者的搜索和救援，為GMDSS(Global Maritime Distress and Safety System, 全球海上遇險及安全系統)的一個部分。多年以來，許多國家作為地面站台的提供與架設者或單純做為該系統之用戶加入了此項目，目前已經是全球最受到廣泛使用的緊急救難系統。
然而緊急救難設備目前對於普羅大眾來說仍是一項十分昂貴的設備，而相關的檢測設備則更是需要一筆龐大的費用，使得一般使用者對其望而卻步。近年來軟體定義無線電(Software-defined Radio, SDR) 發展逐漸成熟，而SDR最廣為人知的優勢就是具有高度的彈性以及低成本的開發環境，因此較容易從中取得有用的資料，本研究經過評估之後使用 SDR 作為開發平台，並利用其優勢來實作救難設備運作的情形，本研究先是使用了GNU Radio 進行整個應急指位無線電示標(Emergency Position Indicating Radio Beacon, EPIRB)系統的架構，而後以輔助硬體 USRP (Universal Software Radio Peripheral) 配合RTL-SDR來進行實際收發的測試。
而在本研究的實驗結果中可以知道，在SDR平台上的確可以完整實現整個緊急救難系統的架構，雖然由於軟硬體的限制，尚無法完美實作EPIRB實際收發系統於SDR平台上，但已經證實緊急救難系統的確具備了實作於SDR的可能性。並且根據測試的結果，發現以通訊的角度而言，具備比現有方式具備更高可靠度的調變方式。

Design and Implementation of Emergency Position Indicating Radio Beacon by Software-Defined Radio
Student: Zhe-Wei Lin
Adviser: Wen-Tzu Chen
Institute of Telecommunications Management, College of Management
SUMMARY
Emergency Position Indicating Radio Beacons (EPIRBs) currently comprise the most widely used emergency rescue system in the world. However, emergency rescue equipment is still expensive for the general public, and relevant testing equipment is even more costly to purchase and maintain. Recently, SDR (Software-Defined Radio) technology has been well developed. The primary advantage of SDR is its low-cost experimental environment and provision of a flexible communication system. Hence, in this research, SDR is used to develop an experimental platform in order to implement EPIRB architecture. Also, a pair of transmitter and receiver is developed by using radio frequency hardware such as Universal Software Radio Peripheral (USRP) and RTL-SDR to test the influences of different modulation methods on communication performance.
Our results show that SDR technology can fully implement the emergency rescue system although hardware and software limitations make it difficult to implement the EPIRB perfectly. However, the results still suggest the possibility of replacing the original design with hardware. Based on the results of the measurement, we find that the modulation method has a higher successful transmission rates than the original method.

Keywords: SDR, Software-Defined Radio, emergency rescue system, GNU Radio, EPIRB
 
INTRODUCTION
mergency relief is an ever present, extremely important issue. In order to achieve more effective personal safety protection, many countries are continuously striving to develop related technologies and to integrate assistance resources. The Cospas-Sarsat, a section of the Global Maritime Distress and Safety System, is a program dedicated to detecting and locating radio beacons activated by people, aircraft, or vessels. In addition, the passing of this alert information to disaster assistance teams leads to rescue actions.
A Cospas-Sarsat distress beacon is a kind of radio transmitter operating at 406MHz, which is classified into three main types: 1) A beacon designed for use in an aircraft is called an emergency locator transmitter (ELT). 2) Another one designed for use as marine ship equipment is called an emergency position-indicating radio beacon (EPIRB). 3) Lastly, one is designed to be miniaturized for personal use, and is known as a personal locator beacon (PLB).
Even though emergency rescue systems have been seriously considered, the testing equipment is too expensive to purchase and maintain at the individual level, which means the transmitter reliability may be questionable. This research analyzes an EPIRB communication system that includes a transmitter and receiver. In the system, BPSK (Binary Phase Shift Keying) modulation with a unique phase offset is used. In order to study the influences of different modulation methods on system performance, we use the other two widely used types of modulation methods, including BPSK without phase offset and DPSK (Differential Phase Shift Keying). The experimental platform will be tested by real transmitter and receiver. The platform performance can be then evaluated according to successful transmission rate.

MATERIALS AND METHODS
The GNU Radio platform is used in this study. It is a free, open source, cross-platform software development platform. It is also widely used by hobbyists and academics to support communications research.
The GNU Radio is used in this study to develop experimental system architecture in order to determine the suitable modulation method to ensure communication quality.

Figure 1. The experimental system architecture

As shown in Figure 1, we build the experimental system architecture, including 2 SDR devices and two personal computers. These devices are used as the transmitter and receiver. For the transmitter, we input the information according to the specification for the COSPAS-SARSAT 406 MHz Distress Beacon. The information includes country code and maritime mobile service identity (MMSI), etc. After the transmitted data is confirmed, GNU Radio is used to read the specified file. The proposed system is modulated using different modulation methods, including the BPSK with the unique EPIRB phase offset, the original BPSK, and differential binary phase shift keying (DBPSK).
Finally, the signal is transmitted into the air at 406.025MHz using the USRP. On the other side, the receiver can receive the radio signal with an antenna. The PC is connected to the SDR device to process the digital signal. After demodulation and the decoding, we use the information sent by the transmitter to measure the correct rates.

RESULTS AND DISSCUSSION
The actual experimental system is shown as Figure 2, where each PC is connected to USRP hardware for transmission and reception. Figure 3 is the spectrum and constellation diagram of the BPSK with a phase offset of 1.1 radius. Figure 3 can also be used to ensure whether the signal is received or not.

Figure 2. The actual experimental setup

Figure 3. Frequency spectrum and constellation diagram of
BPSK with an offset of 1.1 radius.

ur experimental results are presented in Table 1. We find that the BPSK modulation method with a phase offset has a successful transmission rate of 38%. The original BPSK modulation method exhibits a higher successful rate of 62%. Finally, the DBPSK modulation method has a higher successful rate of 89%.
Table 1. Transmission successful rate comparisons
Success Fail Total Success Rate
PSK + 1.1rad 38 62 100 38%
PSK 62 38 100 62%
DPSK 89 11 100 89%

CONCLUSION
Our results show that the SDR technology can fully implement the emergency rescue system, although hardware and software limitations make it difficult to implement the EPIRB system perfectly. However, the results suggest the possibility of replacing the original system with hardware-based design. Based on the results of the experiment, we find that the DPSK modulation method has a much higher successful rate than the original method. The research results can be used to develop software-defined EPIRB test equipment which has a significant advantage of low cost.

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