A radio design is a link budget with hardware attached. Every decision — transmit power, antenna gain, noise figure, bandwidth, modulation, coding — is a term in the same equation, and a design that optimises one term without the others produces a radio that works on a bench and not on a site.
| Term | Set by | Engineering lever |
|---|---|---|
| Transmit power | Amplifier and regulatory limit | Efficiency, not magnitude — the limit is usually legal |
| Antenna gain | Aperture and pattern | Placement and matching; a detuned antenna loses more than an amplifier gains |
| Path loss | Distance, frequency, environment | Frequency selection and siting |
| Receiver noise figure | Front-end design, first-stage amplifier | The first stage dominates; everything after it matters less |
| Bandwidth | Channel plan and data rate | Narrower bandwidth improves sensitivity directly |
| Modulation and coding | Throughput requirement | Robustness traded against rate, adaptively where possible |
| Implementation margin | Real hardware imperfection | Honest accounting; optimism here is discovered on site |
Sensitivity improves as bandwidth narrows, which is why low-power wide-area links reach kilometres at kilobits while broadband links reach hundreds of metres at megabits. It is the same physics, differently spent.
In time-division duplex, transmit and receive share a frequency and alternate in time. The guard period between them has to cover the propagation delay to the furthest served user plus the time the front end takes to switch, and if it does not, a transmission arrives while a neighbour is still receiving.
Which makes it a coexistence problem rather than a local one. Get it wrong and the symptom appears in someone else's network, discovered by them, and attributed to you. This is also why network-wide time synchronisation is not optional in a TDD deployment — every site has to agree on when the boundaries are, which is what IEEE 1588 distribution is for.
The link budget: transmit power, antenna gain, path loss, receiver noise figure, bandwidth, modulation and coding, and an honest implementation margin. Range is the output of that equation, not a property of a radio.
Narrower bandwidth. Receiver sensitivity improves directly as bandwidth narrows, so a link spending its budget on range rather than rate reaches kilometres at kilobits per second. It is the same physics, differently allocated.
Because it must cover propagation delay to the furthest user plus front-end switching time. If it does not, a transmission arrives while a neighbouring site is still receiving — so the symptom appears in someone else's network and is attributed to you.
Antenna detuning. Metal, liquid, curvature and enclosure material shift a small antenna's match, and the loss is frequently larger than anything the amplifier could recover.
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