Efficient Messaging Services for Interactive Satellite Networks. Dr. Sandro Scalise, DLR (German Aerospace Center)

Transcription

1 Chart 1 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Efficient Messaging Services for Interactive Satellite Networks Dr. Sandro Scalise, DLR (German Aerospace Center) 19 th Ka and Broadband Communications [ ] Conference 31 st AIAA International Communications Satellite Systems Conference Florence, Italy

2 Chart 2 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 M2M and Alike: an Opportunity for SatCom? - Many types of Machine-to-Machine (M2M) services are mainly based on the transmission of short messages from/to remote sensors or mobile devices used to track specific events or monitor automatic systems: - industrial SCADA (Supervisory Control And Data Acquisition) systems - fleet management or containers tracking - public systems, such as automatic highway tollgates, traffic light controllers - energy systems, e.g. current sensors in a solar panel array, water level sensors in a dam, etc - Some of these services require - truly worldwide availability even in very remote areas - high resilience even in case of large scale natural or man-made disasters - cost effectiveness even across national borders

3 Chart 3 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Satellite-Based M2M and Alike: a SWOT Analysis Coverage Resilience against large-scale disasters and black-outs Bandwidth Cost Terminal Cost Terminal Size & Weight General Trends regarding: Traceability of freights Safety of transportation (aircraft, vessels, trains) Unmanned operations Regulatory Hurdles WW-Availability of Spectrum Compliance with safety regulations (aircraft, vessels, trains) Lower roaming fees of terrestrial celullar systems

4 Chart 4 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Motivation (cont d) - For such classes of services, satellite communication represents the ideal complement to 2G/3G/4G wireless terrestrial networks M2M Wireless Market Size (# of subscribers) 3.4 M (total) 2.3 M (mobile) Revenues 500 M$ Actual Share of Satellite Services Revenue 0,5% (total) 8-10% (mobile) Potential Share relevant for Satellite 45% of the total market Current Satellite Penetration < 5% of relevant market ca 2% of total market Total M2M connections (2010) 66 millions Sold M2M satellite terminals (2009) (2010) New M2M connections (millions) 10 (2009) 12 (2010) Forecast for the next 10 years 2 millions new connections per year - Historical note: the provision of M2M services dates back to the late 1980s / early 1990s, with OmniTRACS/EutelTRACS, a localization and messaging system for trucks, still active today

5 Chart 5 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Motivation (cont d) - Main reasons for low penetration: - high cost of the satellite airtime - costly and/or bulky terminals. The availability of a cost effective solutions remarkable reducing OPEX could further contribute to the market share expansion for satellite based M2M services - Based on these premises, S-MIM (S-Band Mobile Interactive Multimedia) was recently standardised within ETSI SES SCN as TS S-MIM offers a low cost though very bandwidth and power efficient solution to send short messages: - modest power requirements on the terminal side (as low as 0 dbw EIRP for an S-Band Uplink to GEO) - widely reusing 3GPP Wideband Code Division Multiple Access (W- CDMA) technology properly adapted to the scope - very simple terminal design, also thanks to the use of Random Access techniques

6 Chart 6 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Back to 1971 in Hawaii?!? The ALOHAnet System (courtesy of N.M. Abramson)

7 Chart 7 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Back to 1971 in Hawaii?!? Throughput of Pure Aloha and Slotted Aloha shown on vs. Traffic Load

8 Chart 8 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Challenges of Conventional Random Access Schemes - Aggregated Throughput Limitation - PLR Limitation - Stability Issues - Delay (consequence of the previous two ) For these reasons, Random Access today is mainly used *only* for network logon (e.g. DVB-RCS), i.e. for signalling - S-MIM (together with DVB-RCS2) ist the first SatCom Standard using Random Access also for data traffic in the RTN link - Originally developed for S-Band, it can be easily adapted to other frequency bands (VHF, L-Band, C-Band, Ku-Band, Ka-Band)

9 Chart 9 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Aggregate Throughput / Packet Loss Rate - From the transmitter side, S-MIM is using a purely spread spectrum ALOHA (SSA) - Normalised throughput well above 1 is obtained thanks to a Successive Interference Cancellation (SIC) algorithm in the PLR < 10-3 (over mobile fading channel) Throughput (Mbit/s) Pkt Size=600 bits Ricean Channel C/M=10 db, 50 km/h Canc. Eff.=95% Rmax=3 db Throughput PLR 1.E Offered traffics (Pkt/s) 1.E+00 1.E-01 1.E-02 1.E-03 Packet Loss Rate

10 Chart 10 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Successive Interference Cancellation: Basic Principle codes E-SSA E-SSA E-SSA E-SSA E-SSA E-SSA E-SSA E-SSA time - Most powerful bursts are decoded first and then cancelled from the received signal System is self-interference limited! - Two-dimensional (frequency-time) preamble search down to C/(N+I) in the range db (ESA Patent)

11 Chart 11 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 S-MIM Key Components: Enhanced SSA Demodulator - Fully SDR (Software Defined Radio) implementation of S-MIM E- SSA Demodulator - implements Successive Interference Cancellation as per ESA patent to reach high aggregate MAC throughput - runs over COTS HW platforms such as e.g. Dual Xeon CPU servers equipped with NVIDIA Tesla C2050 GPUs (courtesy of MBI,

12 Chart 12 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Enhanced SSA Demodulator PLR Performance σ =STD of the power demod. Input Power terminal plays a key role Theory tells us, that throughput is maximised if the received power distribution is uniform (in db)

13 Chart 13 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Power Control - Uniformly distributed power randomisation at the terminal based on an open loop algorithm - Additional effects due to: - FWD link SNR-estimation - G/T variation within the beam - Terminal antenna pattern - Terminal amplifier power setting accuracy All these effects are typically lognormally distrbuted The resulting power distribution is the sum of a uniform + lognormal RVs: - if the uniform component is dominating smashed uniform distr. - if the lognormal one is dominating close to lognormal

14 Chart 14 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Power Control: an Example Ideal Real

15 Chart 15 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Stability - Operation at the maximum throughput desirable BUT unpredictable traffic fluctuations move the operating point - Higher load reduces throughput asymptotically to zero 1. Without retransmissions or with a max. number of retransmissions: - Packets lost, but channel can always return to low load inherently stable 2. With retransmissions - Risk of avalanche effect resulting in total saturation and requiring a system reset Techniques to analyse the system Behaviour and set the relevant parameters so to ensure stability have been developed by DLR Still (for both cases), a practical issue is is related to the time after which the system will return in high throughput region load control

16 Chart 16 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Example: Load/Rate Control in S-MIM ARQ: - Transparent / ACK / uack Modes - Cumulative ACK - Retransmissions in next TX opportunity after ACK-timeout expiration Load Control (@ Hub): - Hub senses the offered load - Decide status - Tailor rate control parameters in signalling tables - Broadcast signalling tables Rate Control (@ Terminal) : - Deterministic Backoff Time (BOT) between consecutive LL packets of same PDU - Random Persistence index (P): to use or dismiss a transmission opportunity TERMINALS HUB ARQ + Tx CTRL ACK SIGNALLING TABLES SIGNALLING LL PACKET LOAD CTRL ARQ + Tx CTRL LL PACKET DEMOD/ DECAPS

17 Chart 17 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 S-MIM in a Nutshell - Re-use of any standardised (broadcast) radio interface in FWD link such as DVB-SH, DVB-NGH, DVB-S/S2, ETSI SDR, anything capable of carrying IP traffic - Enhanced Spread Spectrum Aloha Random Access (E-SSA) in the RTN link - ESA Patent, largely based on 3GPP W-CDMA / S-UMTS - MAC Throughput up to ca. 1.8 b/s/hz thanks to successive interference cancellation in the demodulator - For S-Band: - Different chip rates / channelisations: 0.24, 1,92 and 3.84 Mchip/s - Short Messages (300, 600, or 10 kbps - Re-use of existing link layer protocols with minimal adaptations 1. Header Compression to reduce the overhead 2. Encapsulation/Fragmentation to transport IP over the air interfaces based on RLE 3. System-specific MAC addressing to allow transmission of unicast traffic 4. Authentication and security features similar to UMTS 5. Joint ARQ / Load Control for link layer reliable transmission allowing QoS support 6. Open Loop TX Control (crucial for E-SSA demodulator operations) 7. Mobility management (Handover, Roaming and Cell Selection ) 8. Management of System Signalling (FWD link signalling is carried in compliance to PSI/SI)

18 Chart 18 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Some Trials Results: Overview - DLR ESA S-Band Workshop (Noordwijk, NL, 2012cMay 15th) Nocturnal measurements (Noordwijk, NL, 2012 May 14th) (courtesy of SafeTRIP Project,

19 Chart 19 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Some Trials Results: Vehicle Tracking

20 Chart 20 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 Acknoledgements - S-MIM was designed in a project led by DLR and co-funded by ESA and Solaris Mobile Ltd. - More info: - The standardisation effort within ETSI was supported by DLR, Fraunhofer IIS, ESA-ESTEC, Eutelsat, Skylogic and SES

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22 Chart 22 > Efficient Messaging Services for Interactive Satellite Networks > S.Scalise > 14/10/2013 The Advanced Satellite Multimedia Systems Conference and the Signal Processing for Space Communications Workshop has been initiated by the DEIS and ARCES Institutions of the University of Bologna, the DLR Institute for Communications and Navigation and the European Space Agency. The 2014 joint event will be organised by University of Pisa and MBI, and endorsed by the Integral SatCom Initiative European Technology Platform, the SatNEx Network of Experts and the regional network Toscana Spazio. More Info: