Network architecture and radio communication services
Network architecture and radio communication services
This domain tests how radio links become networks: cellular reuse, mobility, backhaul, core functions, QoS, and service categories. Expect capacity and reuse calculations plus architecture-level reasoning.
Core rules
- Cellular cluster size N=i^2+ij+j^2. Co-channel reuse ratio Q=D/R=sqrt(3N), where D is reuse distance and R is cell radius. Larger N reduces co-channel interference but lowers capacity per area.
- Handover maintains a session; cell reselection is an idle-mode process. Location update and paging trade signaling load against reachability.
- FDD uses paired uplink/downlink bands with duplex spacing; TDD uses one band with time splitting and needs guard periods.
- Backhaul can be fiber, microwave, or satellite. Latency, jitter, and availability matter for real-time services and for synchronization.
- Radio services include fixed, mobile, broadcasting, and satellite. Coverage and capacity are designed together: sectorization and densification raise capacity but increase handover and interference complexity.
Worked example
A network uses N=7 and cell radius R=2 km. Q=sqrt(3x7)=sqrt21=4.58. Reuse distance D=QR=9.17 km. If the operator shrinks clusters to N=3, Q=sqrt9=3, so D=6 km: capacity rises, but co-channel cells are closer and interference grows. The design must then improve antenna downtilt, power control, or sectorization rather than simply assuming the new plan works.
Traps
Using N=i^2+ij+j (missing j^2), treating Q as capacity, and confusing handover with roaming. Also do not quote peak rates without stating bandwidth, MIMO layers, and scheduling assumptions.