Cellular Concept & System Design Quiz

Cellular networks divide large areas into smaller regions called cells, each controlled by a base station. This strategy improves frequency reuse and increases capacity.

Key Feature 1: Dividing coverage into small hexagonal cells.
Key Feature 2: Each cell uses specific frequencies to avoid interference with neighboring cells.

System Capacity: The maximum number of users or calls a cellular network can handle simultaneously.
Increasing Capacity Methods:
- Frequency Reuse: Using the same frequencies in non-adjacent cells.
- Cell Splitting: Dividing large cells into smaller ones (microcells).
- Sectoring: Splitting a cell into multiple sectors with directional antennas.
- Additional Spectrum: Allocating more frequency bands.
Quality of Service (QoS): Ensures clear calls, reliable connections, and fast data transfer.
Enhancing QoS:
- Reducing interference.
- Efficient handoff mechanisms.
- Traffic management.
- Optimizing cluster size
Trade-off: Increasing capacity may reduce QoS if interference is not managed.

The radio frequency spectrum is the range of electromagnetic frequencies used for wireless communication.
Common Frequency Bands:
- VLF (3 kHz - 30 kHz): Long-range communication
- LF (30 kHz - 300 kHz): Submarine communication.
- MF (300 kHz - 3 MHz): AM radio.
- HF (3 MHz - 30 MHz): Shortwave radio.
- VHF (30 MHz - 300 MHz): FM radio, moderate range communication
- UHF (300 MHz - 3 GHz): Mobile phones, GPS, Wi-Fi, 4G
- SHF (3 GHz - 30 GHz): Satellite communication.
- EHF (30 GHz - 300 GHz): Millimeter-wave communication (5G).

Management by the National Telecommunications Regulatory Authority (NTRA).
Mobile Spectrum Bands:
- 2G/3G: 900 MHz and 1800 MHz – good coverage, low data capacity.
- 4G: 800 MHz, 1800 MHz, and 2600 MHz – higher speeds and better data capacity.
- 5G: Trials are underway in the 3.5 GHz band, offering ultra-high speeds but requires more infrastructure due to shorter range.

Objective: Explain the concept of frequency reuse and how clusters of cells manage interference.
Description:
- Draw clusters of hexagonal cells, each containing N cells (e.g., N = 7)
- Assign different frequency sets to each cell (e.g., f1, f2, f3).
- These clusters are repeated throughout the network with reused frequencies in different clusters.
- Show that cells in different clusters can reuse the same frequency (e.g., all cells labeled f1.)
- Draw lines between cells that reuse the same frequency set to illustrate the reuse distance (D), ensuring these cells are not directly adjacent

Relationship Between Cluster Size (N) and Reuse Distance (D)
D is the distance between two cells that use the same frequency (must not interfere).
Formula for reuse distance D: D = R√3/√N.
- R is the radius of a cell.
- N is the cluster size.
As N increases, reuse distance D also increases. This means cells using the same frequency are further apart.

Co-channel interference (CCI) occurs when cells too close use the same frequency, causing overlapping signals.
Reuse distance (D) is critical in determining interference levels.
- As N (cluster size) increases, D increases, leading to less interference.

Increased N (cluster size) improves QoS because the reuse distance (D) increases, reducing co-channel interference.
Higher QoS = better signal clarity, fewer call drops, and improved user experience.

Increasing N (cluster size) improves QoS but may limit network capacity.
Fewer calls can be handled simultaneously across the network when N is increased.

The goal is for an optimal N value that balances QoS and system capacity; high N reduces interference but reduces capacity.
Designers need to consider user density, traffic demands, and environmental factors.

What happens to reuse distance (D) as N increases?
How does increasing D reduce interference? Include real-world implications (voice clarity, data transfer rates).
What tradeoffs occur between QoS and capacity as N changes?

CCI is when multiple transmitters use the same frequency channel.
Causes of CCI:
- Frequency Reuse (in non-adjacent cells).
- Insufficient Reuse Distance (cells too close using same freq).
- High Traffic Demand (more frequent reuse).
Mitigation of CCI:
- Optimal Frequency Planning (careful frequency assignment).
- Directional Antennas (focus signal transmission).

ACI is when signals from neighboring frequency channels interfere.
Causes of ACI:
- Spectral Overlap (signals spilling into adjacent channels).
- Wide Bandwidth Signals (more easily causing overlap).
- High Power Transmission
Mitigation of ACI:
- Improved Filtering
- Guard Bands (unused spaces)
- Narrower Bandwidths (for signals).

A technique for increasing network capacity by subdividing large cells into smaller ones (micro or picocells).
When demand increases, a large cell is split.
Frequency channels reused in smaller cells.
Increased capacity.
Improved signal quality if users closer to base stations.
Higher infrastructure cost (due to new base stations).
Applications: Urban areas, high-traffic locations.

Dividing a single cell into multiple (typically 3-6) sectors, each with a directional antenna.
Directional antennas transmit over specific angles.
Reduced interference and improved network performance.
Uses separate frequencies/time slots in sectors.
Sectoring utilizes existing infrastructure (modified antennas).
Reduced interference, higher capacity.
Applications: High-demand cells, long-distance communication.

Handoff is maintaining connections as mobile users move between cells.
- Hard Handoff: disconnects old connection before establishing the new connection. May cause brief disconnection
- Soft Handoff: overlap between the old and new connections to ensure continuity. Easier user experience.