--- title: "Techniques to enhance capacity and coverage" subject: "Wireless Communication" chapter: 2 key: "semester_7/wireless_communication:capacity-coverage-enhancement" source: https://www.bctengineer.com/q/semester_7/wireless_communication/capacity-coverage-enhancement site: BCT Engineering --- # Techniques to enhance capacity and coverage Wireless Communication · Chapter 2: Cellular Mobile Communication Concepts - Asked in: 2071 Magh, 8 marks - Video: [Cell Sectoring and Cell Splitting | Improving Coverage and Capacity In Cellular System](https://www.youtube.com/watch?v=7rjmKgMrDpM) — ECIT Engineering - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/wireless_communication/capacity-coverage-enhancement - Whole chapter: https://www.bctengineer.com/md/semester_7/wireless_communication/chapter-2 ## Question Describe the techniques used for enhancing the capacity and coverage in cellular radio network. ## 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. ## Answer 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. ```text 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 | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. If the cell radius is halved in cell splitting, capacity in the area becomes about: A. 8 times B. Unchanged C. 2 times D. 4 times Answer: D. Halving R gives about 4 times as many cells in the same area, so capacity rises about 4 times. (Key point: Cell splitting capacity) 2. For path loss exponent n = 4, how should transmit power of the new half-radius cell compare with the old? A. Pt1/16 B. Pt1/2 C. Same as before D. Pt1/4 Answer: A. Pt2 = Pt1/2^n = Pt1/16, which is 12 dB less. (Key point: Cell splitting power) 3. How does sectoring improve capacity? A. It reduces the number of interfering co-channel cells seen (i0), allowing a smaller cluster B. It removes the need for handoffs C. It increases antenna height D. It adds more channels to the spectrum Answer: A. Directional antennas cut i0 from 6 to 2 or 1, raising S/I so a smaller N can be used. (Key point: Sectoring principle) 4. What is the key advantage of the microcell zone concept? A. Mobile moving between zones of one cell needs no MSC handoff; the base station just switches zones B. It removes co-channel interference completely C. It needs no extra hardware D. It only improves coverage in tunnels Answer: A. All zones connect to one base station, so zone changes keep the same channel without handoff. 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