- 2071 Magh · 8 marks
Techniques to enhance capacity and coverage
Short answer
Cell splitting divides congested cells into smaller ones, multiplying capacity but adding handoffs. Sectoring with directional antennas reduces co-channel interferers, enabling smaller cluster size at the cost of trunking efficiency. The microcell zone concept lowers interference without extra handoffs by switching zones. Repeaters improve coverage in dead spots without adding capacity.
Describe the techniques used for enhancing the capacity and coverage in cellular radio network.
As demand grows, the channels per cell become insufficient. Capacity and coverage are improved mainly by cell splitting, sectoring, the microcell zone concept, and repeaters for coverage.
1. Cell splitting
- A congested cell is divided into smaller cells (microcells), each with its own base station, lower antenna height and lower transmit power.
- Since more cells fit in the same area, the cluster is repeated more times and channel reuse increases.
- If the radius is halved (R → R/2), the number of cells in the area becomes about 4 times, so capacity is about 4 times.
- Power of the new cell: to keep the same received power at the edge, Pt2 = Pt1/2ⁿ; for n = 4, Pt2 = Pt1/16 (12 dB less).
- Drawbacks: more base stations, more handoffs, and old and new cells must coexist during the transition.
2. Sectoring
- A single omnidirectional antenna is replaced by 3 directional antennas (120° sectors) or 6 antennas (60° sectors). Each sector uses a subset of the cell's channels.
- A sector receives interference from only part of the first-tier co-channel cells: i₀ drops from 6 to 2 (120°) or 1 (60°).
- Higher S/I allows a smaller cluster size (e.g. N = 7 → N = 4 or 3), which raises capacity.
- Drawbacks: more antennas, loss of trunking efficiency, and extra handoffs between sectors.
120° sectoring Interferers seen
/\ Omni : 6
/α \ 120° : 2
/----\ 60° : 1
| β γ |
3. Microcell zone concept
- A cell is divided into zones (usually 3). Each zone site is connected to a single base station by fibre or microwave.
- The mobile is served by the zone with the strongest signal; when it moves between zones in the same cell, the base station just switches zones and no handoff at the MSC is needed. The channel stays the same.
- Since only one zone transmits on a channel at a time, interference is local, D/R improves and capacity can rise (about 2.33 times in the textbook example) without extra handoffs.
4. Coverage enhancement: repeaters
- Repeaters (range extenders) receive, amplify and retransmit signals to cover holes, tunnels, buildings and remote roads.
- Distributed antenna systems and in-building systems improve indoor coverage.
| Technique | Main gain | Cost |
|---|---|---|
| Cell splitting | More reuse, more capacity | More BS, more handoffs |
| Sectoring | Less CCI, smaller N | Trunking loss, more antennas |
| Zone concept | Less CCI, no extra handoff | Extra zone hardware |
| Repeaters | Better coverage | No capacity gain |
✓ Answer checked by Claude Opus 5.5 (high effort)
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