Microwave Transport
Microwave transport covers wireless backhaul for mobile and fixed access sites using Nokia Wavence platforms. The exam tests link budgeting, modulation and adaptive coding, E-band and traditional bands, XPIC, protection, and latency planning.
Link design and capacity
A microwave link is designed from transmit power, antenna gain, path loss, fade margin, and receiver threshold. Higher-order modulation increases capacity but reduces sensitivity and reach. Adaptive modulation and coding changes capacity as the link degrades. XPIC uses cross-polarization to double capacity on one frequency channel, but it depends on cross-polar discrimination. E-band offers wide channels and high capacity over shorter distances, with rain fade as a major constraint. Protection options include 1+1 hot standby and space diversity.
Rules to apply
- A link budget must include fade margin, not just free-space path loss.
- Higher QAM is not free capacity; it trades sensitivity and reach.
- ACM changes capacity during fading; it does not guarantee the same availability at peak modulation.
- XPIC requires good cross-polar discrimination and correct antenna alignment.
- Latency and synchronization matter for fronthaul and backhaul services.
Worked example
A link has 20 dBm transmit power, 40 dBi gain at each antenna, and 130 dB path loss. Received power is 20 + 40 + 40 − 130 = −30 dBm. If the receiver threshold for the target modulation is −70 dBm, the margin is 40 dB. The reasoning: the available margin must cover rain fade, interference, and aging before the link can claim the target availability at that modulation.
Traps that cost marks
Using free-space loss only; ignoring rain fade; assuming ACM guarantees peak capacity at all times; and deploying XPIC without checking cross-polar discrimination.