Thread by @steve_larrison

1/61 The testing process of BlueWalker 3 - A look at what happens in the ground stations - a thread

AST SpaceMobile
$ASTS
#SpaceMob

2/61 I believe that if people are truly going to understand the testing process of BlueWalker 3, not only is at least a general understanding of the major architectural components of the SpaceMobile network needed, but it is necessary to take a step back and understand the goal…

3/61 …that @AbelAvellan had when he founded AST back in 2017.

4/61 Therefore, even though BlueWalker 3 was just launched on September 10, 2022 and it is attracting attention because of the capabilities provided by the large phased antenna array on the satellite, we need to take a few steps back.

5/61 The technical goal of the company is to allow unmodified cell phones to make calls and connect to the internet in places where cell towers don't provide coverage.

6/61 The only possible way to accomplish this goal is to provide a signal to the cellphone that looks and behaves the same regardless of whether that signal originates from a cell tower, or from a satellite.

But this thread is about ground stations.

7/61 And there hasn't been a lot of material provided by SpaceMob on the ground station component of SpaceMobile. So let's take a look at a systems flow chart (drawings created by @NomadBets and consulting on technical details provided by @CatSE___ApeX___ )\\

8/61 The SpaceMobile network doesn't just consist of satellites in a Low Earth Orbit and user cell phones. SpaceMobile requires ground stations to work.

Each country will need between 1 and 3 ground stations to provide nationwide coverage.

9/61 These ground stations connect to data sources (phone and internet) and connect those data sources to satellites that end user cell phones talk to.

But before we get into details on how this magic works, we need to go another step backwards.

10/61 As mentioned earlier, if we want to work with unmodified cell phones, the cell phone can't know whether it is talking to an AST ground station and satellite, or if it is talking to a conventional cell tower.

11/61 So let's take a minute and talk about what a cell tower does, then we will show how the work of a cell tower is split between an AST ground station and an AST satellite.

So let's talk about how cell towers work.

12/61 Here is what a prototype of a cell tower site might look like

13/61 Before going farther, let me call attention to the power generator. A remote site far removed from an electric grid may require a power generator to operate.

14/61 This adds a great deal to the expense of connecting the unconnected - not only do you have to purchase the power generator initially, but fuel and maintenance (re-fueling as well as maintaining the generator itself) is an ongoing expense.

15/61 In the past, there have been attempts to require cell towers to maintain backup power supplies in the United States, but cell tower operators have resisted these efforts because of the expense involved.

16/61 Next - the Backhaul - this is the term used to describes the side of the network that connects to the global phone and internet networks. In other words, the backhaul provides data to the cellular site for broadcase to end users.

BTS/Node B

17/61 BTS stands for Base Transceiver Station. Sometimes it is called an RBS (Radio Base Station) or simply a BS (Base Station). But regardless of what it is called, the term is used to describe a base station that is used for 2nd generation wireless technologies.

18/61 The base station is used to process data from the backhaul (global phone and/or internet network) prior to transmitting it through antennas.

19/61 Examples of 2nd generation wireless technology are GSM (Global System for Mobile Communication) and CDMA (Code Division Multiple Access).

Node B

20/61 Functionally, the Node B serves the same purpose as a BTW - it is used to process data from the backhaul prior to transmission through antennas.

21/61 The difference between BTW and Node B is that Node B is designed to work with the 3rd generation UMTS (Universal Mobile Telecom System) networks instead of 2nd generation networks like GSM and CDMA.

22/61 Once data has been processed by the BTS or Node B, it is sent to a transceiver/antenna pairing at the top of a cell tower via cable.

That's it.

It's greatly simplified - after all, I am tweeting, not writing a book. But that's the basics of how a cell tower works.

23/61 Now remember, the goal of SpaceMobile is to work with unmodified cell phones. The only way to accomplish that goal is to make everything that happens between a user and the phone system and duplicate it as closely as possible.

24/61 If a phone can't tell whether it is connected to a cell tower or to the SpaceMobile network, it should just work.

Conceptually, the following drawing is what a SpaceMobile ground station looks like.

25/61 (We will start looking at things from the conceptual level, then get into specific implementations as the thread continues)

26/61 The only difference between this conceptual drawing of a SpaceMobile ground station and a standard cell tower site is that the antenna mast, transceiver, and antenna(s) have been replaced by a satellite dish that is capable of talking to SpaceMobile satellites over Q/V…

27/61 …band.

The reason I mentioned that this is a conceptual drawing is because the physical implementation differs. But it is useful to solidify things that have been covered before introducing new concepts.

RAN/VRAN/OpenRAN/CloudRAN

28/61 First let's talk RAN - the acronym stands for Radio Access Network. You may think of your cell phone as a phone, but it's really a radio. The transceiver/antenna pairing at the cell tower site that broadcasts signal to end users uses radio spectrum.

29/61 You communicate over the radio waves to talk to a cellular site, and that cellular site will route your conversation to the phone network via the BTS or NodeB.

VRAN is an acronym that stands for Virtualized Radio Access Network.

30/61 Like RAN, VRAN provides the network that connects your cell phone and the cell tower site.

31/61 Where VRAN differs from RAN is that rather than using specialized hardware, VRAN uses General Purposes Processors (i.e. x86 computers that are common everywhere) instead of specialized hardware that is purpose built for RAN functionality.

32/61 VRAN is becoming popular in the telecom industry for the same reason that virtualization is becoming popular in enterprise computing:

33/61 ORAN is the next topic of interest. ORAN is an acronym that stands for Open Radio Access Network. Software people reading this thread can probably guess where this is going. Open RAN is a Radio Access Network built on Open Source standards.

34/61 The reason that open source standards are preferable to closed source standards is largely related to cost. But security and flexibility are also important considerations.

35/61 On the side of flexibility, there aren't very many RAN vendors who offer a full stack of proprietary RAN products needed to build out an installation.

36/61 By having an open standard for RAN hardware and software, best of breed components may be chosen from multiple different vendors in the construction of a telecom stack. This flexibility offers both performance and pricing advantages.

37/61 Finally, CloudRAN - sometimes referred to as CRAN. If RAN hardware can be virtualized, then it only makes sense that it can be run in the cloud as well as on premises.

38/61 Hosting RAN in the cloud offers additional cost benefits in that elasticity can be applied cross cell tower site, and the cost to build out individual cell sites is reduced.

39/61 If it isn't already obvious, there is a reason that I have diverted into a discussion on various flavors of RAN.

Early in the partnership between AST and Rakuten, Rakuten provided AST with access to 3rd party software from AltioStar.

40/61 This software is one of the keys to Rakuten's plans for it's future as an MNO. Since the partnership between AST and Rakuten was formed in early 2020, Rakuten has purchased the company AltioStar ( altiostar.com/rakuten-group-… ).

41/61 AltioStar is an ORAN software offering that uses VRAN technologies and enables CloudRAN hosting.

42/61 As such, it offers tremendous cost advantages in the construction and operation of ground stations needed to connect AST satellites to the phone network, and the broader internet.

43/61 Now let's talk about another important piece of technology that enables AST ground stations to function - the Nokia AirScale base station. The Nokia AirScale base station provides 2g, 3g, 4g, and 5g compliant RAN through what is called "SingleRAN".

44/61 If you want to work with any cell phone ever made, the Nokia AirScale is a very good choice. It not only works with "any g" technology, it works with every cell phone frequency of every cell phone commercially made.

45/61 And the AirScale base station provides this connectivity to all relevant forms of wireless communication at massive scale. The AirScale base station is one of the keys to offering Multiple Input Multiple Output (MIMO) capabilities when the SpaceMobile network is built out.

46/61 So if you read the technical documentation on AltioStar software, and if you read the technical documentation on the Nokia AirScale, you will find that while each platform does offer some unique and compelling features, there is also a lot of overlap between the systems.

47/61 Is that a concern?

Does it pose an integration risk if you are using both platforms in a single ground station?

The answer is no.

What AST is doing with an integration between AltioStar and the Nokia AirScale base station is not unique.

48/61 This is something that has been done before in terrestrial cellular networks, and the technical stack has been thoroughly de-risked and has been proven to perform at scale.

49/61 (Performance at scale is one of the technical items that needs to be de-risked during the testing process of BlueWalker 3)

50/61 There are numerous examples of integrations between Nokia AirScale and AltioStar software that I could point to, but none is more compelling than what partner Raktuen has done - in 2019, Rakuten built Japan's 4th MNO on a foundation of AltioStar software and Nokia…

51/61 …AirScale - commsupdate.com/articles/2019/…

Raktuen has been able to provide first hand experience to AST in the construction of complex mobile networks using the same fundamental technical stack that AST ground stations will be using.

52/61 As for the concept of pairing satellites using a "bent pipe" architecture with ground stations connected to the internet and phone networks, AST is not a first mover in this systems architecture.

53/61 Rather, they are using a design pattern that has been used in a production environment for over 20 years.

54/61 If you are familiar with the architecture of the SpaceMobile network and take a look at the GlobalStar network (GlobalStar has provided a global satellite phone service similar to Iridium since 1999 and recently has been attracting attention for providing the satellite…

55/61 …services behind Apple's SOS Messaging service), you will see that the concepts are very similar.

The following drawing was taken from an article on ResearchGate at researchgate.net/publication/33…

56/61 Rather than using C band for duplex communications between the ground station and satellites, SpaceMobile will be using Q/V bands. The frequencies that AST will be using allow much higher data rates than C band.

57/61 Other key differences between the GlobalStar network and SpaceMobile is that GlobalStar, being older technology, uses a 2nd generation network - CDMA. Whereas SpaceMobile uses a 3rd generation network - UMTS.

58/61 This allows greater scalability even before you consider the fact that GlobalStar has a total of 24 ground stations spread throughout the world. Whereas AST will be operating between 1 and 3 ground stations per country that they offer services in.

59/61 On the satellite side, though the Apple deal with GlobalStar will be bringing new satellites into their constellation, their most recent satellites were designed in 2007, and deployed beginning in 2009. Also, their entire constellation currently consists of 48 satellites.

60/61 But the basic component architecture is the same and has been proven to work.

The task of making the ground stations work with SpaceMobile is one of systems integration. This is technology that has been used in commercial settings before and has been proven to scale well.

61/61 While there is always a risk of schedule slippage in any technical implementation, the technical risk inherent in the ground systems is negligible.