1 A network that can see

1.1 The idea

A mobile network spends every second of the day pushing radio energy into the air and listening to what comes back. Today it does that to carry your data.

Sensing is the proposal that the same energy and the same listening can tell the network something else as well — that there is an object out there, where it is, how fast it is moving, which way it is pointing.

That is radar, done by equipment that is already on the roof.

1.2 What was actually missing

A 5G network is not blind today. It can work out where a device that is talking to it sits. What it has no rule for is noticing something that is not talking to it at all.

The radio side wrote that gap into the front of its study proposal.

1.3 One radio, two jobs

The short name for the subject is ISAC — integrated sensing and communication. The word "integrated" is the whole point of the name.

One signal, two jobs, at the same time. The network has to keep being a network while it senses, and that constraint is what makes this a 3GPP subject rather than a radar subject.

1.4 The words 3GPP uses for it

The requirements document, TS 22.137, defines the vocabulary everything else leans on. Three of its definitions are worth knowing before any conversation about this.

• 5G wireless sensing is a feature of the 5G system that gets information about the environment and the objects in it — shape, size, orientation, speed, location, distance, relative motion — using the network's own radio signals ^[4].

• 3GPP sensing data is data derived from those signals after an object or an environment has reflected, refracted or diffracted them ^[5].

• A sensing result is that data once it has been processed for whoever asked for it ^[6].

The gap between the second and the third is where most of the design work lives. Somebody has to ask for a sensing result, somebody has to be allowed to ask, and something in the network has to turn raw echoes into an answer.

That something has been given a name already. A Sensing Function is the logical function that supports the sensing service ^[7] — a new box in the diagram of a 5G core, which is why so many other documents have to change to make room for it.

1.5 How far along this is

Sensing was studied in Release 19 and is being turned into rules for Release 20. Those two releases split the paperwork almost in half, and the larger half is the unfinished one — 1416 documents are marked Rel-19 ^[8] and 2069 Rel-20 ^[9].

So this is a subject you can read about in full and cannot buy. The homework is largely finished; the rules are being written now.

1.6 Why anyone proposed it

The requirements proposal put the reason in the most general terms it could.

The architecture proposal was more concrete about who it thought would want this, and named the industries its authors expected to be changed by it — automotive, healthcare, drones, smart cities ^[10].

The next chapter goes through that list, and through the much shorter list of what is actually being built.

1.7 Where to read this yourself

The definitions in this chapter are in TS 22.137, the requirements specification. It is the shortest document in the whole area and the one to open first.

This school does not carry the text of TS 22.137 or of any other 3GPP document. It tells you which number to fetch and what is in it.