Wireless Notes
Learn cellular network planning with coverage planning, capacity dimensioning, link budget, site selection, RF optimization, KPIs, drive testing, and SON self-organizing networks for engineering students.
Understanding the cellular network planning process including coverage planning, capacity dimensioning, link budget analysis, propagation modeling, site selection, and network optimization techniques.
The Planning Process
Phase 1: Requirements Analysis
| Parameter | Input Needed | Source |
|---|---|---|
| Coverage target | 95-99% area coverage at -100 dBm | Business/regulatory requirement |
| Capacity demand | Users per km², traffic per user | Market research, forecasting |
| Quality target | Minimum SINR, call drop rate < 1% | Service requirements |
| Spectrum allocation | Band, bandwidth, reuse constraints | License conditions |
| Budget | CapEx per site, total budget | Financial planning |
| Timeline | Coverage milestones per quarter | Business plan |
Phase 2: Dimensioning
Dimensioning calculates how many sites are needed:
Coverage-limited dimensioning: Number of sites = Total area / Coverage area per site Coverage per site = π × R² (R from link budget)
Capacity-limited dimensioning: Number of sites = Total traffic demand / Capacity per site Capacity per site = Channels × Spectral efficiency × Bandwidth
The final site count is the MAXIMUM of coverage-limited and capacity-limited calculations. In urban areas, capacity typically dominates. In rural areas, coverage dominates.
Phase 3: Detailed Planning
Using propagation models and digital terrain data, determine:
- Exact site locations (based on available real estate)
- Antenna height, type, orientation
- Transmit power per sector
- Frequency plan (channel assignment)
- Neighbor cell lists for handover
Link Budget Analysis
Downlink Link Budget (LTE Example)
| Parameter | Value | Unit |
|---|---|---|
| BS transmit power | 46 | dBm |
| BS antenna gain | 18 | dBi |
| Cable/connector loss | -3 | dB |
| EIRP | 61 | dBm |
| Body/penetration loss | -20 | dB (indoor) |
| UE antenna gain | 0 | dBi |
| UE noise figure | 7 | dB |
| Thermal noise (10 MHz) | -104 | dBm |
| Required SINR | -1 | dB (QPSK 1/3) |
| Receiver sensitivity | -98 | dBm |
| Interference margin | 4 | dB |
| Fade margin (shadow, 8 dB std, 95%) | 10.3 | dB |
| Maximum Allowable Path Loss | 144.7 | dB |
From the maximum allowable path loss (MAPL), we determine the maximum cell radius using a propagation model.
Propagation Models
Commonly Used Models
| Model | Frequency | Environment | Accuracy |
|---|---|---|---|
| Free Space (Friis) | Any | LOS reference | Theoretical baseline |
| Okumura-Hata | 150-1500 MHz | Urban/suburban/rural | ±5-8 dB |
| COST-231 Hata | 1500-2000 MHz | Urban/suburban | ±6-8 dB |
| 3GPP TR 38.901 | 0.5-100 GHz | UMa/UMi/InH | ±4-7 dB (calibrated) |
| ITU-R P.1411 | 0.3-100 GHz | Short-range outdoor | ±5-7 dB |
| Ray tracing | Any | Detailed 3D environments | ±2-4 dB (with building data) |
Okumura-Hata Model
The most widely used empirical model for macrocell planning:
PL (dB) = 69.55 + 26.16×log(f) - 13.82×log(hb) - a(hm) + (44.9 - 6.55×log(hb))×log(d)
Where:
- f = frequency (MHz)
- hb = base station height (m)
- hm = mobile height (m)
- d = distance (km)
- a(hm) = mobile antenna correction factor
For f = 900 MHz, hb = 30m, urban environment: R ≈ 1.5-3 km (for MAPL = 145 dB)
For f = 2600 MHz (LTE Band 7), same conditions: R ≈ 0.5-1 km (higher frequency = shorter range)
Capacity Planning
Traffic Modeling
Capacity planning requires predicting traffic demand:
| Parameter | Urban Dense | Suburban | Rural |
|---|---|---|---|
| Population density | 10,000/km² | 2,000/km² | 100/km² |
| Subscriber penetration | 80% | 70% | 50% |
| Active ratio (busy hour) | 10% | 8% | 5% |
| Data per active user (BH) | 50 MB | 30 MB | 10 MB |
| Traffic density | 4000 GB/km²/hr | 336 GB/km²/hr | 2.5 GB/km²/hr |
Cell Throughput
With 3 sectors, 20 MHz bandwidth, LTE:
- Average spectral efficiency: 2.5 bps/Hz/sector
- Sector throughput: 2.5 × 20 = 50 Mbps
- Site throughput: 3 × 50 = 150 Mbps
- Busy hour capacity: 150 Mbps × 3600s × 0.7 (overhead) ≈ 378 GB/hr
Sites needed (urban): 4000 / 378 ≈ 11 sites/km²
Network Optimization
Post-Deployment Optimization
After initial deployment, continuous optimization improves performance:
| Technique | What It Adjusts | Benefit |
|---|---|---|
| Antenna tilt optimization | Downtilt angle (electrical/mechanical) | Reduces interference, improves cell-edge |
| Power optimization | Per-carrier transmit power | Balances coverage vs interference |
| Neighbor list optimization | Handover relationships | Reduces dropped calls |
| Load balancing | Handover thresholds | Distributes traffic evenly |
| Carrier aggregation config | Component carrier assignment | Maximizes user throughput |
| MIMO mode selection | Open-loop vs closed-loop thresholds | Optimizes for user conditions |
Key Performance Indicators (KPIs)
| KPI | Target | Measurement |
|---|---|---|
| Coverage (RSRP > -110 dBm) | > 95% area | Drive test, MDT |
| Call drop rate | < 1% | Network counters |
| Handover success rate | > 98% | Network counters |
| Average user throughput | > 10 Mbps (DL) | User measurements |
| RRC setup success | > 99% | Network counters |
| VoLTE MOS (voice quality) | > 3.5 | Call quality measurement |
Modern Planning Approaches
AI/ML in Network Planning
Modern operators increasingly use machine learning for:
- Traffic prediction: Forecast demand growth per area for proactive capacity upgrades
- Anomaly detection: Automatically identify cells with unusual performance degradation
- Self-Optimizing Networks (SON): Automatic parameter adjustment based on KPI trends
- Site selection: ML models predict optimal locations based on demographics, terrain, and existing coverage
Digital Twins for Planning
Creating a digital twin of the network — a detailed simulation model that mirrors real-world performance — allows planners to test changes virtually before implementing them physically. This reduces optimization time and prevents costly mistakes.
Key Takeaways
- Network planning determines the number and location of base stations based on coverage requirements (link budget → cell radius) and capacity requirements (traffic demand → sites needed)
- The link budget calculates maximum allowable path loss, which determines maximum cell radius through propagation models
- Propagation models (Okumura-Hata, COST-231, ray tracing) predict signal strength at any distance based on frequency, antenna height, and environment type
- Urban planning is typically capacity-limited (need many sites for traffic), while rural planning is coverage-limited (need sites for geographic reach)
- Shadow fade margin (typically 8-10 dB for 95% area coverage probability) is a critical link budget component often underestimated by beginners
- Post-deployment optimization (tilt, power, neighbor lists) can improve network performance by 20-40% without adding new sites
- Modern planning increasingly uses AI/ML for traffic prediction, automatic optimization, and digital twin simulation before physical changes
Exam Focus
Revise definitions, diagrams, examples, and short-answer points for Cellular Network Planning Coverage Capacity Optimization.
Interview Use
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