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OpenBTS: A New Approach to Cellular David A. Burgess Kestrel Signal Processing, Inc. Fairfield, California.

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Presentation on theme: "OpenBTS: A New Approach to Cellular David A. Burgess Kestrel Signal Processing, Inc. Fairfield, California."— Presentation transcript:

1 OpenBTS: A New Approach to Cellular David A. Burgess Kestrel Signal Processing, Inc. Fairfield, California

2 GSM 2G Core Network From GSM The key pieces: MS - Mobile station. BTS - Base transceiver subsystem (Um L1/L2). BSC - Basestation controller (L3 RR) MSC - Mobile switching center (L3 CC). HLR/VLR - Location registers (L3 MM). Must have all 5! ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

3 Understanding “Um” Um is the GSM subscriber interface. Think ISDN, not WiFi. ~108 kb/s sync serial PHY, TDM’d into logical channels shared channels for radio management Dm signaling channels (~1.4 kb/s) Bm media channels (~13.5 kb/s) ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

4 OpenBTS Open-source Um implementation with a pure SIP/RTP network interface. Manages radio resources internally (no BSCs). Maps mobility management, call control and SMS to SIP operations (no MSCs, H/VLR). Through OpenBTS, GSM handsets appear to VoIP network as SIP endpoints. Through OpenBTS, VoIP network appears to handsets as a GSM carrier. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

5 ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY OpenBTS Node

6 Peer-to-peer APs. No BSCs, no MSCs, no hair- pinning. Network interface is a SIP PBX. Network can be as small as a single node, but with a range of 35 km. OpenBTS Core Network ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

7 OpenBTS Advantages Backhaul GSM through any SIP/IAX carrier. Replace GSM core network with commodity HW and open source SW. Minimum network is a single cell. Use $5 refurb handset as a wireless VoIP terminal. Installation/management similar to WISP. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

8 What OpenBTS Doesn’t Do (Yet) Handovers of active calls between cells. GPRS data services. Encryption. Multiple ARFCNs. We expect to find funding to complete these features in They will just be software upgrades. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

9 OpenBTS Source Code OpenBTS copyrights assigned to Free Software Foundation in October Kestrel still holds a blanket license. Distributed publicly under GPLv3. Licensing options and developer copyright assignment similar to Asterisk. About 15k lines of C++ in 2.5 release. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

10 OpenBTS in 2010 Airline application in South America. GSM PBX in Netherlands, UK. Rural development projects in Brazil and India. Rapid deployment system for US DoD. Law enforcement and intelligence projects. Carrier pilot projects in Polynesia and US. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

11 Operating in GSM900 band to avoid contention w/AT&T. MCC=001, MNC=01 ARFCN 29 (940.8 MHz down, MHz up) Downlink power is about 100 mW. Quad-band phone? Try finding us. Handsets are unmodified refurbs with a mix of SIMs. Demo particulars. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

12 Where to test Um? Some things are hard to simulate. physical propagation heavy loads from many handset models Need an open-air range with ready users, but without strong user expectations. Need a place within a day’s drive of the SF Bay Area so we can avoid crazy freight costs. We have a sense of humor, too: Burning Man. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

13 Fabulous Black Rock City Aerial view of 2009 Burning Man site. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

14 First Time Around: BRC 2008 Experimental license WD9XKN. Spectrum consent from Churchill County Communications (GSM850, B-block). PSTN gateway from Link2VoIP. Static IP and backhaul from Playanet. Very tight budget, <$5k. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

15 What it looks like when you build a BTS from eBay and Home Depot. No real packaging; just assembled the components on a table. Antenna was 10 dBi omni on a 30- ft portable mast. Connected about 100 speech calls in last 24 hours. Camp 3:15&G ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

16 Camp 3:15&G ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

17 Once More Unto the Breach: BRC 2009 Experimental license WD9XSP. Spectrum consent from Verizon (GSM850, A- block). Camp placement (“Papa Legba”, 4:30&H), early access. PSTN gateway from Link2VoIP; iNum gateway from Voxbone. Static IP and backhaul from Playanet. Discussions with BMOrg about social aspects. Budget of about $20k. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

18 Papa Legba’s Services Auto-provisioning via SMS. Local SMS and speech calls. SMS gateways to iNum and . Speech gateways to iNum and PSTN. Expected service radius of about 1.5 miles within BRC, >10 miles in the open desert. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

19 Mobility Strategy Every BTS a different “location area”. Moving to a new location area causes a handset to perform a “location update”. Location update maps to a SIP registration. SIP registry for each user points to IP of BTS for most recent location update. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

20 Putting SMS into SIP SMS is sessionless, page-mode. Most IP messaging protocols are session-oriented and inappropriate for cellular. OpenBTS SMS interface is RFC smqueue: RFC-3428 store & forward server, uses Asterisk for address resolution. Tested integration with Voxbone’s RFC interface. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

21 Radio Hardware Power Amp (40 dB, 10 W) USRP + 2 RFX900 w/clock Mini-ITX 1.6 GHz Atom Uplink BPF (90 dB) Duplexer (70 dB) LNA (40 dB) Power Buses (GND, +6, +12) Pelican Case ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

22 Power System ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

23 Camp “Papa 4:30&G ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

24 Camp “Papa 4:30&G ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

25 Camp “Papa 4:30&G ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

26 Papa Legba IP Network ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

27 Papa Legba GSM Network ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

28 Service Radius Over BRC Esplanade Far edge of BRC Propagation inside BRC follows Hata suburban model. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

29 Service Radius Over BRC ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

30 Service Radius Beyond BRC Propagation outside BRC follows Hata open rural model: much longer range. gate road & Hwy 34 ??? Gerlach, NV ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

31 Successes Hardware and packaging satisfactory. Coverage slightly better than predictions. Mobility strategy worked. Provisioned ~1,300 users via SMS. Connected ~1,000 PSTN calls. Delivered ~270 user-to-user SMS (and ~3,800 other non-user SMS). ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

32 Back in the Real World Carrier pilot project scheduled for March Island microstate, 260 sq-km,1,600 residents. Cover 90% of population from a single tower. Total cost estimate <$50k, including trans-Pacific freight, travel and local network integration. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

33 Building stuff is fun. Now let’s talk about politics and economics. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

34 Regulatory Barriers Cellular uses licensed spectrum. Most countries have licensed out all of their cellular spectrum already. New auctions are rare. Yet most of the spectrum is fallow, especially in rural areas. These things are true all over the world. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

35 Idiotic License Policies Most US cellular licenses are whole counties or multiple counties. You usually can’t get a rural license without getting cities in the deal. Rural customers cost a lot more to serve. Once you pay to cover a city, you have no motivation to serve rural customers. These things are true all over the world. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

36 ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

37 Little Motivation to Change Spectrum policy might change if there were political pressure. Rural areas are typically served by CLECs. A minimum GSM network is $100ks. Nobody will lobby to get access to spectrum they can’t afford to use. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

38 Changing the Equation? OpenBTS can lower cost of entry to $20k for an existing WISP or CLEC. The only barrier is a spectrum licensing policy that lets ATT, VZN, etc. lock down huge swaths of fallow rural spectrum. If we demonstrate this, will there be more pressure to change the policies? ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

39 We Will Try A temporary network in rural Colorado starting in Spring Existing WISP with tower site, VoIP, trunks. Just add OpenBTS. Prove by doing: You don’t need $300k CAPEX. Profitable network with <200 subs. A showpiece for spectrum reform lobbies. ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

40 Thanks to... Harvind Samra (the other half of KSP) John Gilmore Glenn Edens Black Rock City, LLC Many others ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY

41 More Information l l ANIMAL FARM SALT LAKE CITY ANIMAL FARM SALT LAKE CITY


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