PLC Technology - IEEE Xplore

7 downloads 1837 Views 1MB Size Report
laboratory demonstrator using commercial PLC technology. • Environmental (DO-160) ... Centralized master/Slave logical architecture. • Adaptive Dynamic ...
The Application of Commercial Power Line Communications Technology for Avionics Systems 31st Digital Avionics Systems Conference (DASC) October 14-18, 2012 – Williamsburg, VA Stephen Dominiak Sabina Serbu Lucerne University of Applied Sciences & Arts (HSLU) Lucerne, Switzerland

Stefan Schneele Franz Nuscheler EADS-Innovation Works Ottobrunn, Germany

Tobias Mayer Diehl Aerospace Nuremberg, Germany

Contents • Introduction • PLC Technology and Standards • PLC as an Avionics Data Bus • PLC-Enabled Cabin Demonstrator & Testing • Deficiencies of Commercial PLC Technology • Conclusion

Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

-2-

Introduction • An investigation into the use of Power Line Communications (PLC) technology in commercial aircraft has recently been completed in the EU FP7 TAUPE project • Investigation focused on two reference applications for the A380: • Cabin Lighting System (CLS) – Cabin Illumination • Cabin Communication System (CCS) – PAX Services • PLC prototype avionics equipment was developed and integrated into a laboratory demonstrator using commercial PLC technology • Environmental (DO-160),, functional and performance er testing were w performed • Project-level highlights: • TRL4 successfully demonstrated • Weight reduction of 110 kg per aircraft • 40% reduction in the aircraft cabling

Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

Presentation Focus: Results & Evaluation -3-

PLC Technology • PLC refers to a general communications technology in which a data signal is transmitted over a wiring network not designed for high-speed communications • PLC provides robust communication protocols optimized for a harsh communications channel (e.g. OFDM, powerful FEC, hybrid-ARQ, etc.) • PLC includes a broad range of protocols typically divided into two categories Category

Signal Band

Max. Data Rates

Narrowband PLC (NPL)

3 kHz – 500 kHz

500 kbps

Broadband PLC (BPL)

2 MHz – 30 MHz 2 MHz – 80 MHz

200 Mbps 500+ Mbps

• BPL has been targeted for avionics applications due to: • Relatively short communication links • Lower noise levels (> 2 MHz) • Higher potential data rates and lower latency times • The consumer in-home market (Internet/multimedia distribution) is the main driver for the development of commercial BPL technology and standards Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

-4-

Broadband PLC Standardization Status • Until recently the BPL market consisted of a number of proprietary solutions or industry specifications • PLC technology used in the TAUPE project is based on the industry specification from the Universal Powerline Association (UPA) • Since the start of the TAUPE project, standards’ bodies for PLC have been very active • For BPL, this has led to the recent ratification of multiple international and industry standards • IEEE P1901 • ITU-T G.hn (G.9960/G.9961) • HomePlug Alliance • HomePlug AV/AV2 • HomePlug Green PHY • These standards still focus on the consumer in-home market Stephen Dominiak, Oct. 18, 2012 S

The Application of Commercial Power Line Communications Technology for Avionics Systems

-5-

UPA/OPERA Specification • UPA specification has been developed within the EU FP6 project OPERA • Design targeted low-voltage access networks for last-mile consumer services, e.g. Internet, Video streaming • Configurable frequency bands: • Supported signal band: 2 - 34MHz • Supported signal bandwidth: 10, 20, 30 MHz • Flexible power masking is supported • PHY Layer: OFDM with adaptive bit loading • Subcarriers: 1536 • BPSK – 1024 QAM (1-10 bpc) • Approx. 200 Mbps max. raw data rate • Two modes for bit mapping: HURTO or adaptive • HURTO: highly robust mode - max. data rate of 4 Mbps • MAC Layer: • Centralized master/Slave logical architecture • Adaptive Dynamic TDMA (ADTDM) channel access scheduling • Access assignment distributed through a virtual token • IP/Ethernet compatible network Stephen he Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

-6-

PLC-Enabled Avionics Data Bus Architecture • Single interface for power and data • PLC chipset, filtering and coupling elements must be introduced • Integrated approach provides maximum weight savings taking advantages of available synergies, e.g. shared power supply • Data interface to backbone networks typically within the PDB Data Backbone Network

PDB

PLC Head end Chip set

Filter & coupler

e.g 115 VAC/400 Hz

Power Distribution Box

Appliance #1

Appliance #2

Appliance #3

PLC PLC chipset Coupler chip set & filter

A/C appliance subsystem

Appliance #n Primary Power Network

Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

-7-

PLC as an Avionics Data Bus • Introducing PLC as an avionics data bus is not straightforward largely due to the following characteristics • Harsh transmission channel varies over frequency, time and position • Strict limits on unwanted EMC conducted and radiated emissions • Unshielded single wire power distribution • Crosstalk between wires in complex bundles • Multi-drop bus wiring topologies • Optimizations to the power distribution network can mitigate some negative effects1 • A PLC data bus therefore provides an unreliable and shared communications medium • There are also further factors which must be taken into consideration • Potentially large number of application devices • Safety critical applications require strict real-time delivery requirements • Proper coordination of the available communications resources is just as essential as achieving sufficient link capacity and reliability [1] Dominiak, S., H. Widmer, M. Bittner, U. Dersch, 2011, “A Bifilar Approach to Power and Data Transmission over Common Wires in Aircraft,” 2011 IEEE/AIAA 30th Digital Avionics Systems Conference (DASC), p. 7.

Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

-8-

TAUPE Verification and Validation • Extensive V&V campaign was performed in the TAUPE project • PLC technology was verified against a set of over 350 requirements derived from the actual aircraft systems & equipment

PSU 16 PTU-28 24 PTU-115

• Environmental testing according to DO-160 included: • Power input & lightning • EMC conducted and radiated susceptibility • EMC conducted and radiated emissions Full DO-160F emissions compliance achieved2

Application Server HIBU

Equipment Harness

Main Harness

PHEU 28VDC Supply 115VAC Supply

• An integrated demonstrator was developed for functional and performance testing [2] Dominiak, S., G. Vos, T. ter Meer, H. Widmer, 2012, “Achieving EMC Emissions Compliance for an Aeronautics Power Line Communications System,” 2012 Proceedings ESA Workshop on Aerospace EMC, no. 1.

Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

-9-

PLC Demonstrator • CLS/CCS integrated into a demonstrator with 41 PLC-enabled application equipment • 24 Hybrid Illumination Ballast Units (HIBU) • 16 Passenger Service Units (PSU) • 1 application server

Laboratory Power Supply 115VAC

Application Server

Laboratory Power Supply 28VDC

Legend 28VDC-Normal

SPDB / PHEU

28VDC-Emergency 100 Mbps Ethernet

115VAC

28VDC 28VDC NORM EMER

115VAC-Var. Freq. 100Mbps Ethernet RS485

Redundant Data Lines

• 5 power lines with 2 different power networks: • 3 - 115 VAC variable frequency lines • 2 - 28 VDC lines (w/ emergency) • PLC Terminal Units (PTU) interfaced to existing equipment

Stephen Dominiak, Oct. 18, 2012

PTU-115 #2

HIBU #3

HIBU #23

HIBU #24

PSU #1

PSU #2

PTU-28 #2

PTU-115 #3

HIBU #22

PTU-28 #1

...

• Single logical PLC network controlled by the master in the SPDB

HIBU #2

Equipment Wiring Harness

PTU-115 #1

...

• Demonstrator wiring harness designed and verified to be representative of an actual aircraft harness

HIBU #1

Main Wiring Harness

PTU-115 #22 PTU-115 #23

PTU-28 #15 PTU-28 #16

PSU #15 PSU #16

PTU-115 #24

The Application of Commercial Power Line Communications Technology for Avionics Systems

- 10 -

CCS Performance Testing • CCS application traffic consisted of: • Audio streams related to passenger announcements and cabin music • Control of PAX indicator, reading lights and call functions • Audio streams and commands were sent as multicast UDP frames • Audio requirements were to support at least 10 concurrent channels • Combined data rate of 10 Mbps • Max. latency of 10 ms • Max. audio jitter between two different PSUs of 㼼 1 ms (synchronized playback) • Performance measurements were made using a hardware packet analyzer (Anritsu Data Quality Analyzer MD1230B) Application Server

Wiring Switch

PHEU

PTU-28

Switch

PSU

Harness

Packet Analyzer

Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

- 11 -

CCS Performance Testing Results – Throughput • Throughput measured between the SPDP and different PSUs with different frame lengths • Maximum throughput bounded by the Fast Ethernet interface of the PLC modems (~95 Mbps for UDP) 100 90 Throughput [Mbps]

80 70

PSU01

60

PSU05

50

PSU08

40

PSU09

30

PSU11

20

PSU16

10

Average

0 64

128

256

512

1024

1280

1518

Frame Length [Bytes]

Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

- 12 -

CLS Performance Testing Results – Frame Loss & Delay • Frame loss rate and delay as a function of the offered throughput for different frame sizes • Measurements made between the SPDB and different PSUs Æ results show the average of all measurements 10

20

8

15

7

64 128 10

256 512 1024

5

Delay [ms]

Frame Loss Rate [%]

9

64

6

128

5

256

4

512

3

1024

1280 1518

1280

2

1518

1 0

0 0

20

40

60

80

Offered Throughput [Mbps]

Stephen Dominiak, Oct. 18, 2012

100

0

20

40

60

80

100

Offered Throughput [Mbps] The Application of Commercial Power Line Communications Technology for Avionics Systems

- 13 -

CCS Performance Testing Results – Results Arrival Time Variation Difference in Arrival Time [ms]

4 3 2 1 0 -1 -2 -3 0

2000

Application Server

4000

6000 Frame Count

8000

10000

PTU-28

Switch

PSU

PTU-28

Switch

PSU

12000

Wiring PHEU Harness

Packet Analyzer Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

- 14 -

CLS Performance Testing • CLS data traffic consists of: • A command sent every 32 ms as a broadcast UDP packet with a payload size of 144 bytes • Status messages sent by each HIBUs within a unicast UDP packet with a payload size of 2 bytes • Status messages must be delivered by all HIBUs to the server within a 32 ms interval • Performance was observed using a packet sniffer • Results showed • It takes 60 – 70 ms to deliver all status messages (2.5 ms per message) • Some commands were lost when CCS audio streams were running in parallel • Functional tests also showed that a very high network setup time was observed as high as 10 minutes!

Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

- 15 -

Deficiencies of Commercial PLC Technology • CLS & CCS are not safety critical, but can be considered as real-time control applications with the following characteristics: • Relatively high number of application devices • Low delay and jitter requirements • Majority of the traffic is broadcast/multicast • High required aggregate bandwidth (10 Mbps) • Through testing, we have identified three principle deficiencies of the commercial UPA PLC technology • Lack of support for native multicast and efficient broadcast transmission • Medium access control scheduling algorithm is non-deterministic and notoptimized for real-time automation and control applications • Network setup time is much too high • Further analysis shows that these deficiencies may be common to other competing commercial BPL technologies

Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

- 16 -

Multicast/Broadcast Transmission with BPL • For PLC networks the channel between each pair of nodes may vary • Similar to wireless networks, a common transmission scheme for multicast/broadcast must be selected to ensure distribution to all receivers • In BPL, this is handled in one of two ways: • Robust transmission with a common modulation and redundancy • Unicast conversion: a copy of the multicast frame is made and sent per unicast with an optimal modulation and coding • Robust transmission data rate is limited to 2% of the max. unicast data rate • Unicast conversion may provide a higher overall data rate but is detrimental for the transport of real-time traffic in large networks B A

MF1

Transported Frames

C Stephen Dominiak, Oct. 18, 2012

Application Frames

MF2

MF1B

MF1C

MF2B

MF2C

time The Application of Commercial Power Line Communications Technology for Avionics Systems

- 17 -

Channel Access Scheduling • ADTDM scheduling provides • Collision free channel access • Dynamic channel scheduling which can adapt to the number of nodes in the network, different offered traffic loads and various traffic types • Channel access determined by master using a proprietary (closed) algorithm • Bidirectional exchange of a logical token between master and slave allows: • Master to distribute the current channel allocation • Slaves to inform the master about their traffic requirements • Channel assignment can be influenced through QoS provisioning • QoS mechanism has been optimized around the requirements of VoIP traffic Æ maximum latency upper bound on the order of 100 ms • The scheduling algorithm has been shown to be not suitable for • Networks with a high number of nodes • Application traffic with very small frame sizes • Dynamic nature of the algorithm does not provide determinism

Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

- 18 -

Network Setup Time • Network setup time: the time between when all PLC-enabled equipment are powered on until when all necessary connections have been established and application data traffic can be delivered • BPL standards strive to support plug and play functionality • UPA access protocol: • Each slave must perform an access handshake with the master before enabling communication • Access mechanism uses the logical command channel with robust transmission mode (HURTO mode) • Access mechanism is contention based and designed for smaller networks • High network setup time due to: • Large number of collisions in the contention based access mechanism Æ nodes need to retry in next round • Contention with broadcast data traffic also sharing the command channel Æ poor scheduler prioritization Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

- 19 -

Deterministic PLC Data Bus • As with any avionics data bus, PLC must be able to provide sufficient redundancy, fault tolerance and determinism • Providing determinism and fault tolerance must be considered in the protocol design • There is a common misconception that commercial solutions may be directly applied in the avionics environment: • Protocol framework may not support determinism (especially protocols for designed for consumer applications) • Proprietary algorithms mean that technology provider support is required Æ unlikely due to the relatively small aeronautics market size • A deterministic PLC MAC must be developed • There is the potential to make use of existing protocols which may be independent of the underlying PHY layer, e.g. Time-Triggered Protocol (TTP) • However, it is important to consider • Unreliable communications medium • Characteristics of the PLC PHY (FEC, H-ARQ, adaptive bit-loading, etc.) • Requirements of the avionics applications

Stephen Dominiak, Oct. 18, 2012

The Application of Commercial Power Line Communications Technology for Avionics Systems

- 20 -

Conclusions

The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement 213645

• EU research project TAUPE has shown positive results for the use of PLC as an avionics data bus • Performance testing on a laboratory demonstrator has shown PLC can provide data rates approaching 100 Mbps and low latency times (