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SATWAYS addresses the installation of remote site controllers equipped with radio and telephony interfaces at isolated heliports countrywide. They will relay radio & telephony communications, control/monitor data and surveillance videos to and from HCAA headquarters over satellite connections and use IP as the transport protocol.
Upon approach to the remote heliport, VHF communication on the VFR frequency is either difficult or impossible to achieve, so the Flight Plan is usually closed with the helicopter landing report being sent over mobile telephones, often an hour after landing.
During that period, it is unknown whether the helicopter has landed or crashed. Additionally, there is no way to relay heliport equipment maintenance information to HCAA, unless a person actually goes there. For instance during a helicopter approach, the approach lights may be malfunctioning or severe meteorological conditions may be encountered, without FIC being aware. Moreover, communication with ground maintenance personnel and pilots after landing or before takeoff relies on the mobile telephony network, which seldom provides coverage. Finally, heliport sites are unsupervised, so additional risks to landing safety are posed, since unauthorized people or even animals may be inside the heliport when the helicopter lands.
The SATWAYS objectives are to provide remote control and monitoring of all heliport equipment and resolve the issue of communication loss during approach. This will be done by maintaining radio contact via switching to the heliport local frequency which is relayed to the flight controller over satellite.
As far as the radio communication is concerned the long-term objective is to implement a TWR (tower) service in a centralized manner for all heliports. The envisioned system is actually an extension to the VFR procedure for the airspace above heliports.
Figure 1: SATWAYS operational deployment
The key issue addressed in SATWAYS is to achieve the performance targets certifying efficient radio over IP over satellite communications for ATC (Air Traffic Control) applications, particularly those handling helicopter flights, over a private DAMA satellite network and under the effect of dynamic satellite bandwidth allocation mechanisms.
For this purpose the voice service requirements have been analyzed extensively from a quality viewpoint to end up with system requirements that affect the design of the SATWAYS system, as well as with requirements on the necessary satellite capacity and bandwidth allocation strategy in order to implement them.
The operational system has been designed to comply with the ICAO guidelines on performance of VSAT networks for ground-to-ground radio communications. This means 400 ms of absolute one-way delay, call setup time less than or equal to 2 sec, 10-7 BER, and 99.8% service availability.
SATWAYS employs the HellaSat2 geo-stationary satellite to implement the space segment. Based on the service availability, the bandwidth, the satellite, the BER requirements and the geographical location, link budget calculation has been carried out to reveal that 200 kHz of satellite bandwidth are sufficient to accommodate a single heliport implementing the whole of the envisioned functionality. Bearing in mind that this is a DAMA system, this in turn means that the system can be seamlessly expanded.
The major expected benefits brought by the project will be to:
Other major expected operational benefits will be to:
The satellite transport network selected for the project is based on the NDSatCom SkyWan product line but any other network capable of proper IP traffic routing over satellite could be utilised, provided it is in line with the ICAO guidelines on performance of VSAT networks in Airports.
Remote Site Controllers will be installed at every heliport to provide:
An Audio Gateway will be installed at HCAA headquarters to provide:
A remote monitoring and control network will also be installed at HCAA to provide:
Prior to its engagement in the SATWAYS project, inAccess Networks had extensive experience in building centralized control/monitoring systems and providing autonomous intelligent controllers to a variety of customers, mainly in the telecom sector. The products of the company are built around two principal components:
The overall architecture is presented in Figure 2.
Figure 2: Monitoring and Control service architecture
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A typical RSC10 system (see Fig. 3) consists of a rack-mountable chassis that carries an eight- or sixteen-slot backplane. The backplane interconnects a power-supply module, a processor module and up to eight or sixteen slave modules. The slave modules implement field I/O ports, network interfaces, instrumentation bus interfaces, and other such amenities. A fully loaded RSC10 controller can interface directly with up to 512 field I/Os. Up to 8192 I/Os can be supported if external instrumentation buses are used.
Figure 3: The RSC10 Modular Controller designed and developed by inAccess Networks
Figure 4:The SATWAYS RSC10-560 Radio/FXS Voice Module designed and developed by inAccess Networks
A Radio and FXS RSC10-560TM interface card (see Fig. 4) and a high-performance VoIP/DSP framework for low latency call handling and media streaming have been developed within the project to provide audio gateway functionality to the controller. Figure 6 presents the proposed Voice Extension Function software architecture, designed to operate within the RSC10 platform. The MGC and MGW software entities of the endpoints (at the heliport and at HCAA headquarters) involved in a radio or telephone call interact via SIP and RTP protocols respectively in order to implement the voice service. The voice network topology of the SATWAYS system is depicted in Figure 7.
Figure 5: Overview of the RSC10 Embedded Software Architecture
Figure 6: VEF Software Architecture
The heliport state, controls of and alarms from all monitored equipment as well as video surveillance images are provided to the user through a custom HMI (see Fig. 8).
|Figure 7: The voice network topology of the SATWAYS system
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Figure 8: The Control, Monitoring and Video Surveillance service HMI
The project will evolve within an 18-month framework, which includes a field trial installation and pilot operation phase, with direct participation from the Hellenic Civil Aviation Authority (HCAA).
The SATWAYS system has been fully developed, validated and documented. Prior to its deployment, the services provided by the SATWAYS system were rigorously tested in the lab and in an end-to-end manner under a variety of strenuous conditions representing extreme system and network loads.
The peak call setup delay that was recorded was 1.06 seconds, while the peak end-to-end delay equaled 392 msecs. The packet loss remained below 0.5% at all times, so the voice quality requirements that were put forth in the beginning of the project were covered. Consequently, the objective voice quality metrics indicated a very good quality of service. The remaining services (control/monitoring, video surveillance and weather monitoring) were also functionally and performance tested to prove that they operated as expected.
The system was installed at the heliport of Patmos and HCAA headquarters and the pilot phase was initiated at 20:00 Hours on September 18, 2008. In the meantime, the pilot trial experienced two long interruptions. On the 20th of January 2009, the ODU at HCAA headquarters failed and was finally replaced on the 6th of March 2009 due to supply chain problems. On the 18th of December 2009, the project partners were informed that the carrier the system was using could no longer be used, due to ESA release of HellasSat2 capacity, so SATWAYS was once more shut down. HCAA, together with inAccess Networks put a lot of effort in finding access to another carrier via the Hellenic Ministry of Transportation and Communications and they finally achieved their goal on the 30th of April 2010. The new carrier resides on a different transponder, such that a change of the RF head was required. The necessary components were purchased and installed. The SATWAYS system resumed operation on the 17th of May 2010 and the pilot testing phase was resumed to proceed with a final review on October 6, 2010. The carrier is still available to HCAA, so the pilot phase still continues.
With the invaluable help of HCAA, a user acceptance test plan was compiled, so that flight controllers could evaluate the operation of the system in operational conditions. The approach used was based on questionnaires inspired by the CARS (Controller Acceptance Rating Scale) method devised by USA’s Federal Aviation Authority to test new systems for radio communications in ATC. User ratings were impressive and revealed full compliance to the above mentioned requirements and proper operation of the QoS mechanisms which enforce them.
The users rated the system with an average of 8.67 on a scale from 1 to 10 (10 is best) regarding voice quality and an average of 1.44-1.61 on a scale from 1 to 10 (1 is best) regarding the effect of delay on their perception, effectiveness, timing, correct phraseology and speech rate. The SATWAYS system has been used numerous times for operational activities, however, the controllers were rating it in writing only when their workload was reduced and flight safety was not compromised by their actions.
It has to be noted that the SATWAYS system has been used and evaluated not only during the control of VFR flights (that is helicopters which were the original target), but also for IFR flights, i.e. speedy airplanes rushing through the Greek skies through extremely dense regions of our airspace. Taking into consideration that, to the best of the knowledge of the authors, there exist no publications that present a similar system or a similar trial, this outcome is considered truly original.
To put the SATWAYS project in a nutshell, the use of Radio over IP over satellite can be used in the ATC environment, in support of even the most demanding missions, such as control of a jumbo jet doing 950 km/h just 5 nautical miles away from another one, when delays can be lethal. The biggest reward was Report #18, within which the responsible controller wrote:
“This was a flight with destination the Patmos heliport. The frequency was checked upon departure from the heliport of Mykonos (translation note: another island about 45 miles West of Patmos) and throughout the flight until landing at the heliport of Patmos. At a distance of 15 nautical miles east of the RIPLI region (translation note: controller jargon for an area within the Greek airspace), the pilot reported a 5/5 radio communications quality and so did the flight controller with little noise. At 20 nautical miles west of Patmos and at a flight level of 1500 feet, both the pilot and controller reported a 5/5 quality. Beginning the descent to the Patmos heliport, both the transmission and reception were exceptional. On the ground, the communication quality was also exceptional and the flight plan has been closed using radio comms. The pilot has expressed to me his admiration, since traditionally this area had no radio coverage. I consider that the use of satellite communications is a success and covers our requirements for the heliport up to ground level”
“Albert Einstein once said imagination is more important than knowledge. We combined both, in the development of SATWAYS,” remarked Mr. Constantine Simaiakis, Chief of HCAA’s Communications, Navigation and Surveillance Division, Communications sector and responsible for the SATWAYS project on behalf of HCAA. “We are creating an anthropocentric system aiming at the provision of communication and a variety of other services both reliably and efficiently in the Air Traffic Management domain, in environments where legacy systems fail.”
Selected project dissemination includes a highlighted publication in the IEEE Communication Magazine, D&I series, August 2008 issue, introduced by a flattering editorial, which has already generated significant feedback, as well as a presentation in Space Application Days, Toulouse Space Show, France, April 22-25, 2008. Moreover, a research paper on E-model adaptation for satellite IP radio calls in Air Traffic Control is currently under evaluation by IEEE JSAC. Furthermore, a press release on the successful installation and operation of the system appeared on the ESA Telecom web news on 05 Nov 2008. A Springer book publication summarizing the most important results achieved throughout the SATWAYS project is also under preparation.
|Figure 9: Antenna installation on top of the Athens International Airport approach tower at Hellenicon, Athens, together with Mr. Simeakis, HCAA representative for SATWAYS
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Figure 10: Heliport antenna assembly
Figure 11: The heliport equipment rack
Figure 12: The heliport VHF antenna and IP camera
Figure 13: The heliport Vaisala AWS520 meteo station