1 A network that detects things, not only carries them

1.1 The gap somebody noticed

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

The proposal behind this whole area of work is that the same energy and the same listening can also tell you that something is out there — where it is, how big it is, how fast it is moving.

The radio side wrote the gap it wanted to close into the front of its study proposal.

The last sentence is the one that matters. A 5G network can already work out where a device that is talking to it sits. What it has no rule for is noticing a thing that has no subscription, no radio of its own, and no interest in being found.

1.2 What the first proposal said the point was

The requirements side stated it more generally, and without any mention of a network at all.

That is a description of radar, written for a standards body. The 3GPP contribution is not the physics. It is the answer to a narrower question: what has to be added to a network that already exists, so that the sensing is a service somebody can ask for, be charged for, and be refused.

The architecture proposal opened by pointing at the industries the proposers expected to be changed by it — automotive, healthcare, drones, smart cities ^[6].

1.3 Three words the requirements document defines

The requirements document is TS 22.137, and it is short. Its most useful pages are the definitions, because every later document leans on them.

Two things are worth pulling out of that. The list of characteristics is wide: not just where a thing is, but its shape, its size, which way it is pointing and how fast it is going. And the signals named are the network's own radio signals, not a new sensor bolted on.

The other two words split the raw from the useful:

• 3GPP sensing data is data derived from 3GPP radio signals that an object or environment has reflected, refracted or diffracted, and optionally processed inside the 5G system ^[7].

• A sensing result is that data once it has been processed for whoever asked for it ^[8].

The gap between those two definitions is where most of the architecture work lives: somebody has to ask, somebody has to be allowed to ask, and somebody has to turn measurements into an answer.

1.4 How the two jobs share one radio

The short name for the area is ISAC — integrated sensing and communication. The word "integrated" is doing real work in that name.

One signal, two jobs, at the same time. That is what makes this a 3GPP subject rather than a radar subject: the sensing has to happen without the network stopping being a network.

1.5 What is actually being built first

The studies talked about cars, factories, hospitals and shipping. The specification being written now does not.

Two limits sit in that sentence. The target is aerial objects — drones — and nothing else. And stage 2, in 3GPP's ladder, is how the system is put together: what talks to what. Stage 1 is what the system must do; stage 3 is the bytes on the wire. Different groups own each rung.

The other limit is who does the sensing. The architecture study defines gNB-based sensing as the base station acting as the sensing entity, and adds that this says nothing about where the sensing result is worked out ^[9].

1.6 Not one document, and not one group

The local record holds 18 entries in the 3GPP work plan for this subject ^[10], carrying 14 different acronyms between them ^[11], with 3492 meeting documents filed against those acronyms ^[12].

Two acronyms have more than one work plan entry, which is why those two numbers differ. A statement like "there are 18 sensing work items" is only meaningful if it says whether it is counting entries or acronyms.

Every count in this course is a floor rather than a total. A further 440 documents whose title says "integrated sensing" or "ISAC" carry no work item acronym at all, and are in none of these figures ^[13].

1.7 Where to read this yourself

The definitions in this chapter come from TS 22.137, the requirements specification, and from TR 23.700-14, the architecture study. The narrow scope comes from TS 23.137, the stage 2 specification now being drafted.

This school does not carry the text of any of those three documents. It tells you which one to open and what you will find when you do.