NICT C-Band Channel Measurement Towards Deploying UAS for Disaster Mitigations (Rev1)

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AERONAUTICAL COMMUNICATIONS PANEL (ACP)

30th MEETING OF WORKING GROUP F

Pattaya, Thailand 13-19 March 2014

NICT C-band Channel Measurement towards Deploying UAS for Disaster Mitigations

(Prepared by Kenichi Takizawa, Fumie Ono, Hiroyuki Tsuji, and Ryu Miura)

(Presented by Fumie Ono)

1. INTRODUCTION

1.1 Background

1.1.1 National Institute of Information and Communications Technology (NICT) has conducted measurement campaign for characterizing radio propagation in C-band CNPC channel for unmanned aircraft systems (UAS). This campaign has been supported by Ministry of Internal affairs and Communications (MIC) as “R&D on Cooperative Technologies and Frequency Sharing between Unmanned Aircraft Systems (UAS) Based Wireless Relay Systems and Terrestrial Networks.” Target application of UAS in this R&D is disaster mitigation. For example, unmanned aircrafts (UA) is deployed to see disaster areas suffered from tsunami or volcanic eruption by taking video images and sending the images to headquarter of disaster mitigation for drawing up a disaster relief plan. This type of application is included in Report ITU-R M.2171 as one of promising UAS applications. In such usage models related to disaster mitigation, it is not realistic that a fixed ground control station (GCS) dedicated to UA is established in each local government body. One of possible deployment scenarios is that small-size UAs are deployed with an ad-hoc GCS. Based on such a deployment scenario, this measurement campaign has been conducted, in which radio propagation characteristics in CNPC channel on air-to-ground (A2G) between small-size UA and ad-hoc GCSs.

1.1.2 The previous work conducted by NASA has been presented at ACP WG-F/29 as IP 05 in 2013, in which measurement results on C-band CNPC channel has been shown thoroughly. The measurement has been conducted based on a deployment scenario in which UA is controlled by a remotely pilot station (RPS) as illustrated in ICAO Circular 328-AN/190. Therefore, the RPS is a dedicated station for UAS, which has functionalities. The results shown in the IP are valuable to evaluate availability of CNPC channels for the scenario.

1.1.3 The purpose of conducting our measurement campaign is to provide a set of radio propagation channel models that are available to evaluation on availability of CNPC channels for small-size UAs. The typical usage scenarios in our measurement are focused on disaster mitigations by using small-size UAs controlled by an ad-hoc GCS for monitoring disaster areas and so on. One of differences between small-size and large-size UAs is their flight altitude in operation. On their deployment of the small-size UAs, it is expected that typical altitude in operation ranges from 1000 to 3000 feet in AGL. As a result, it is noticeable to characterize multipath effect caused by ground or surface reflections in CNPC channels for the small UAs. Since relatively little works on characterization of CNPC channels in C-band for small-UAs has been done, NICT, which is a movement sector research institute on radio communications technologies in Japan, has a plan to conduct a measurement campaign. This IP presents a plan for the measurement in order to gather comments on the measurement plan.

2. measurement plan

2.1 Measurement setup

2.1.1 This measurement is for clarifying radio propagation characteristics on the frequency band between 5030 and 5091 MHz. As metrics of radio propagation characteristics, both received signal strength (RSS) and channel impulse response (CIR) will be recorded.

2.1.2 A block diagram of the measurement setup is shown in Fig. 1.At the transmitter side, which is on a manned small-size airplane, a vector signal generator (VSG) outputs a designed waveform with frequency bandwidth of 10 MHz for channel sounding at the center frequency of 5060 MHz. The output signal is amplified by a power amplifier up to +37 dBm in EIRP. After passing through bandpass filters (BPF), the waveform is sent from an antenna on the airplane. In this measurement, two separated signal generators are used in order to transmit the waveform for channel sounding alternately from either left-side or right-side wing tip in order to avoid shadowing due to the airplane. At the receiver side, which is a ground-side station in this measurement, the received signal is amplified by a low noise amplifier (LNA) followed by BPF. The received signals are down-converted into baseband signals at a vector signal analyzer (VSA), and then the signals are recoded. The VSA has capability of recording the baseband signals during more than 1 hour when setting the sampling ratio to 50 MHz. As antennas for the ground-side station, up to 4 antennas are acceptable to use for the measurement.

2.1.3 All the antennas utilized in this measurement are small-size and not-active antennas since UAS deployed for disaster relief or mitigation is expected that its ground station is deployed with a small-size and not-active antenna in most cases. Thus, antennas on the airplane for measurement are V-polarized antennas with omni-directional radiation pattern in horizontal plane. One antenna is attached on both sides of airplane’s wingtip in order to reduce blocking effect due to the airplane’s body. For the antennas on the ground stations, both liner- and circular-polarized patch antennas without any tracking mechanism are used to provide a comparison between different polarization types.

2.1.4 In this measurement, in order to characterize frequency offset due to its mobility of airplane, frequency synchronization between the transmitter (airplane) and receiver (ground station) is achieved by installing a 10-MHz reference sine wave regulated by Rubidium oscillator at both the transmitter and receiver. Time synchronization between them is also achieved by GPS 1PPS. These synchronizations enable us to characterize radio propagation in C-band channel between airplane and ground on various metrics including Doppler frequency or spectrum and propagation delay. This measurement setup brings receiver sensitivity of around -90 dBm at the input of the LNA. Therefore, acceptable propagation loss for transmit power of +37 dBm becomes around 127 dB, which is equivalent to free-space distance of around 10 km.

Figure 1 - Measurement setup for C-band radio channel characterization.

2.2 Airplane for measurement

2.2.1 In this measurement, a small-size manned airplane is used as a transmitter for realizing the A2G channel sounding. Its outlook of the airplane is shown in Fig. 2 (left). Antennas for measurement are mounted on the wingtips, as shown in Fig. 2 (right). The material of the wingtips is polyurethane covered by Kevlar, which is the same as a type of commercially available UAs. During the measurement, an on-board flight recorder stores information on the airplane’s status including latitude, longitude, altitude above ground level (AGL), posture angles, etc., with GPS time stamp.

Figure 2 - Airplane for this measurement (left). The antenna attached firmly on the wingtip (right).

2.3 Flight route

2.3.1 An expected flight route in this measurement is shown in Fig. 3. This measurement will be conducted in Oahu Island, HI, USA in March 2014. Two ground stations as channel sounding waveform receiver are settled as shown in the figure. The distance between these stations is around 10 km. The airplane, which plays a roll of transmitter, flies over these ground stations in a round-trip way as shown in the figure. Around right above each ground station, the airplane as transmitter flies circularly, which imitates UA when taking video images in disaster areas. The circular flight route near the coast imitates tsunami monitoring. The flight altitude of the airplane in this measurement is in the range between 1000 to 3000 feet in AGL.

Figure 3 – An expected flight route for the C-band radio channel measurement in Oahu Island, HI.

2.4 Post processing

2.4.1 In order to characterize the A2G radio channels, the recorded waveform is calibrated with a waveform taken by back-to-back at ground. The calibrated waveform provides us various channel characteristics including RSS, CIR, Doppler shift and spectrum, and so on. By analyzing the measurement results with the flight information (location and posture angles of the airplane) stored during the measurement flight gives us additional insights on A2G channels. The obtained RSS and CIR with flight information are applicable into evaluation of availability of CNPC channels for the en-route radio links.

3. Conclusion

3.1 This IP presents a summary of a measurement plan for characterizing radio propagation in C-band CNPC channels. The measurement plan is based on usage scenarios of UAS for disaster reliefs by deploying a small-size UAs. Measurement results will be shown in the following meeting.