Advanced Mobile Phone Service (AMPS) - Theory
1. Introduction to AMPS
Advanced Mobile Phone Service (AMPS) was the first generation (1G) analog cellular phone system developed by Bell Labs and introduced in the Americas in 1983. It represented a revolutionary shift from limited-capacity car phones to a true cellular system with handoff capability and frequency reuse.
2. Cellular Concept
The fundamental innovation of AMPS was the cellular concept developed by Bell Labs engineers. The service area is divided into cells, each served by a base station with lower power. By reducing transmitter power, frequencies can be reused at shorter distances, dramatically increasing capacity.
- • Hexagonal Cell Geometry: Idealized model for coverage planning
- • Frequency Reuse: Same channels used in non-adjacent cells
- • Cell Splitting: Dividing congested cells into smaller cells
3. System Architecture Components
Mobile Station (MS)
The subscriber equipment including the transceiver and control unit. Operates at 3 watts maximum ERP.
Base Station (BS)
Fixed station serving one cell. Contains transceivers, antennas, and interface equipment to connect to the MSC.
Mobile Switching Center (MSC)
The central coordinator managing calls, handoffs, and connection to the Public Switched Telephone Network (PSTN).
4. Frequency Plan & Spectrum Allocation
The 45 MHz duplex spacing prevents interference between transmitter and receiver in the mobile unit. Frequency modulation (FM) with ±12 kHz deviation is used for voice transmission.
5. Channel Types
Control Channels (21 per band)
Digital signaling for call setup, paging, and access. Continuously broadcast by base stations.
Voice Channels (395 per band)
Analog FM channels for conversation. Include Supervisory Audio Tone (SAT) and Signaling Tone (ST).
6. Handover (Handoff) Mechanism
Handover maintains connectivity as mobile users move between cells. AMPS uses Mobile Assisted Handoff (MAHO):
- Mobile continuously measures signal strength from serving and neighboring base stations
- Measurements reported to MSC via reverse voice channel
- MSC initiates handover when signal drops below threshold (typically -100 dBm)
- New channel assigned in target cell; call seamlessly transferred
Key Parameter: Handover threshold is typically 6-12 dB above receiver sensitivity to prevent ping-pong effect.
Key Formulas
Laboratory Procedure
A Architecture Study
System Components Identification
Navigate to the Architecture simulation. Hover over each component (MSC, Base Stations, Mobile Stations) to identify their functions and interconnections.
Network Topology Analysis
Observe the star topology connecting base stations to the MSC. Note the redundancy paths and understand how this architecture supports the handover mechanism.
Interface Documentation
Record the interfaces: Air interface (Um) between MS and BS, and terrestrial links between BS and MSC. Note the protocol types used.
B Frequency Plan Analysis
Cluster Configuration
Access the Frequency Plan simulation. Set cluster size N=7 (standard AMPS). Observe the hexagonal grid pattern and color-coded frequency groups.
Reuse Distance Measurement
Calculate the co-channel reuse ratio D/R = √(3N). For N=7, verify D/R ≈ 4.58. Switch to N=4 and observe the reduced reuse distance.
Capacity vs. Quality Trade-off
Compare cluster sizes. Document how smaller clusters increase capacity but reduce signal quality due to increased interference.
C Channel Structure Investigation
Spectrum Exploration
Open the Channels simulation. Use the slider to scan through all 832 channels. Identify the boundary between control channels (1-21) and voice channels (22-832).
Frequency Calculation
Verify the frequency calculation: f = 869.04 + 0.03(n-1) MHz for forward channel n. Calculate reverse channel frequency by subtracting 45 MHz.
Channel Spacing Analysis
Observe the 30 kHz channel spacing. Understand why this spacing was chosen to accommodate FM deviation (±12 kHz) plus guard bands.
D Handover Simulation
Simulation Setup
Launch the Handover simulation. Set mobile speed to medium (5). Observe the three base stations with overlapping coverage areas.
Signal Strength Monitoring
Watch the signal strength display as the mobile moves. Note the gradual decrease in signal from the serving BS and increase from the target BS.
Handover Trigger Observation
Identify the exact moment of handover. Verify that it occurs when the target BS signal exceeds the serving BS signal by the hysteresis margin (typically 6 dB).
Speed Variation Analysis
Adjust mobile speed to minimum and maximum. Observe how handover frequency changes with velocity. Document any dropped calls at high speeds.
Safety & Best Practices
- • Record all observations systematically in your lab notebook
- • Take screenshots of critical simulation states for your report
- • Verify theoretical calculations against simulation results
- • Repeat simulations multiple times to ensure consistency
System Architecture
AMPS is a 1G analog cellular system. It uses a Hexagonal Cell Grid to cover geographic areas. The system consists of three main components:
- MS Mobile Station: The user handset.
- BS Base Station: Tower handling radio traffic for a cell.
- MSC Mobile Switching Center: The brain connecting cells to PSTN.
Laboratory Report Guidelines
Format Requirements
- • Font: Times New Roman, 12pt
- • Spacing: 1.5 line spacing
- • Margins: 1 inch all sides
- • Page limit: 15-20 pages
- • File format: PDF only
- • Naming: RollNo_AMPS_Lab.pdf
Grading Rubric
1. Title Page
Include experiment title, student name, roll number, course code, date of submission, and instructor name. Use university template if provided.
2. Abstract / Executive Summary
Maximum 250 words summarizing: objectives, methodology, key findings, and conclusions. Write this section last after completing the report.
3. Objectives
List specific learning objectives (minimum 4):
- Understand AMPS cellular architecture and components
- Analyze frequency reuse patterns and cluster geometry
- Investigate channel allocation and control channel functions
- Observe and analyze handover mechanisms
4. Theory (Brief)
Concise summary of AMPS principles. Maximum 2 pages. Include:
- Cellular concept and hexagonal geometry
- Frequency reuse equation and cluster size trade-offs
- Channel structure and signaling
- Handover algorithm and hysteresis
5. Simulation Procedure & Observations
Document step-by-step procedure followed. For each simulation module, include:
Screenshot of network topology with labeled components. Table listing MS, BS, MSC functions.
Screenshots for N=4,7,12. Table comparing reuse distances and calculated S/I ratios.
Spectrum screenshots at Ch #1, #100, #800. Frequency calculation verification table.
Event log screenshots. Signal strength vs distance plot. Handover latency measurement.
6. Analysis & Discussion
Critical analysis of results (minimum 500 words). Address:
- Q1. Why is N=7 the standard AMPS cluster size? Calculate S/I for N=4 and discuss trade-offs.
- Q2. How does the 45 MHz duplex spacing prevent self-interference in mobile units?
- Q3. What is the ping-pong effect in handover? How does hysteresis prevent it?
- Q4. Compare AMPS channel spacing (30 kHz) with GSM (200 kHz). Why the difference?
7. Conclusion
Summarize key learnings. State whether objectives were achieved. Mention any difficulties encountered and how they were resolved. Maximum 200 words.
8. References
Minimum 3 references in IEEE format:
[1] V. H. MacDonald, "The Cellular Concept," The Bell System Technical Journal, vol. 58, no. 1, pp. 15-41, Jan. 1979.
[2] T. S. Rappaport, Wireless Communications: Principles and Practice, 2nd ed. Upper Saddle River, NJ: Prentice Hall, 2002.
[3] EIA/TIA, "Mobile Station - Base Station Compatibility Standard for Dual-Mode Cellular System," IS-54-B, 1992.