GSM & Wireless Communication Laboratory Manual

Course: Mobile & Wireless Communication Software: Scilab Hardware: GSM & CDMA Trainer Kits

📌 Quick Navigation Menu (Click to Expand / Collapse)

• Exp 1: GSM Architecture
• Exp 2: Basic AT Commands
• Exp 3: Call & Phonebook AT
• Exp 4: SMS Handling AT
• Exp 5: GSM Channels & Users
• Exp 6: HATA Model Simulation
• Exp 7: Knife-Edge Diffraction
• Exp 8: Two-Ray Ground Model
• Exp 9: CDMA Trainer Kit
• Exp 10: Mobile Trainer Kit
• Outcomes & Precautions

Experiment 1: Study of GSM Architecture & Trainer Kit

Aim

To study the overall GSM architecture and identify different blocks of the GSM Trainer Kit.

Key Objectives

• Understand the operational structure of GSM networks.
• Identify hardware functional modules on the GSM Trainer Kit.
• Analyze functions of BTS, BSC, MSC, HLR, VLR, AuC, and EIR.

Apparatus Required

GSM Trainer Kit, GSM Modem, Functional SIM Card, PC, Serial/USB Interface Cable.

Theoretical Overview

GSM (Global System for Mobile Communication) operates primarily across 900 MHz and 1800 MHz bands.

• Mobile Station (MS): Combines the physical handset device with the SIM card.
• Base Transceiver Station (BTS): Handles direct radio transmission with mobile devices.
• Base Station Controller (BSC): Controls radio resources, frequency hopping, and cell handovers.
• Mobile Switching Centre (MSC): Coordinates call switching, setup, and external network routing.
• Home Location Register (HLR): Primary database containing permanent user subscription data.
• Visitor Location Register (VLR): Temporary database storing data of roaming subscribers in the cell region.
• Authentication Centre (AuC): Provides secret keys for SIM/user authentication.
• Equipment Identity Register (EIR): Database maintaining network security lists based on hardware IMEI.

Result

The GSM architecture and module blocks on the trainer kit were successfully studied.

Experiment 2: Basic AT Commands for Modem & SIM Hardware

Aim

To test and analyze essential AT (Attention) commands used for checking modem connectivity and SIM hardware status.

Command Reference Table

Command	Purpose	Expected Response
AT	Check hardware communication link	OK
ATI	Display modem manufacturer & module identity	Module Details
AT+CPIN?	Check SIM security pin & readiness	+CPIN: READY
AT+CSQ	Check signal strength (RSSI & BER)	+CSQ: <rssi>,<ber>
AT+CREG?	Check network registration status	+CREG: 0,1
AT+COPS?	Query connected network operator	+COPS: 0,0,"Operator"

Result

Basic modem diagnostic and SIM hardware commands were verified via serial terminal interface.

Experiment 3: Call Control & Phonebook AT Commands

Aim

To execute call origination, reception, termination, and phonebook storage management via AT commands.

Command List

• ATD<number>; — Initiate a voice call (e.g., ATD9876543210;)
• ATA — Answer incoming call
• ATH — Disconnect active call session
• ATDL — Redial last called contact number
• AT+CPBR=1,10 — Read phonebook index entries 1 through 10
• AT+CPBW=1,"9876543210",129,"Name" — Store phonebook contact at index slot 1
• AT+CPBW=1 — Clear phonebook entry stored at index 1

Result

Call setup sequences and SIM phonebook memory operations were successfully tested.

Experiment 4: Message Handling AT Commands

Aim

To configure text mode and execute Short Message Service (SMS) actions including sending, reading, and deleting messages.

Step-by-Step Execution

1. Set modem to SMS Text Mode: AT+CMGF=1
2. Send SMS: AT+CMGS="9876543210" → Type message body → Send termination key: Ctrl+Z
3. Read incoming inbox messages: AT+CMGL="ALL"
4. Delete specific message entry: AT+CMGD=1

Result

SMS mode configuration, transmission, retrieval, and message clearing were verified successfully.

Experiment 5: Calculation of GSM Channels & Capacity

Aim

To compute total available radio frequency (RF) channels and maximum theoretical user capacity for a standard GSM system.

Theoretical Calculations

Considering a standard GSM-900 primary uplink allocation:

• Total Uplink Bandwidth: \( 25\text{ MHz} \) (\( 890\text{ MHz} - 915\text{ MHz} \))
• Channel Spacing: \( 200\text{ kHz} \) (\( 0.2\text{ MHz} \))
• Total RF Carrier Channels: \( \frac{25\text{ MHz}}{0.2\text{ MHz}} = 125 \) (124 usable active channels)
• TDMA Framing: 8 Time Slots per carrier frequency

Maximum Simultaneous User Capacity Formula: $$ \text{Total Simultaneous Capacity} = 124 \text{ channels} \times 8 \text{ users/channel} = 992 \text{ channels/users} $$

Result

The total GSM-900 active RF channels (124) and maximum simultaneous capacity (992 channels) were derived.

Experiment 6: Scilab Simulation of HATA Path Loss Model

Aim

To simulate the Urban empirical HATA propagation path loss model using Scilab.

Model Equation

$$ L = 69.55 + 26.16\log_{10}(f) - 13.82\log_{10}(h_b) - a(h_m) + (44.9 - 6.55\log_{10}(h_b))\log_{10}(d) $$

Where \( f=900\text{ MHz} \), base station height \( h_b=50\text{ m} \), mobile height \( h_m=1.5\text{ m} \), and correction factor \( a(h_m) = (1.1\log_{10}(f) - 0.7)h_m - (1.56\log_{10}(f) - 0.8) \).

Scilab Script

clc;
clear;

// Parameters Definition
f = 900;       // Frequency in MHz
hb = 50;       // Base station antenna height (m)
hm = 1.5;      // Mobile antenna height (m)
d = 1:0.5:20;  // Distance vector (km)

// Mobile Antenna Correction Factor
a = (1.1*log10(f)-0.7)*hm - (1.56*log10(f)-0.8);

// Path Loss Calculation
L = 69.55 + 26.16*log10(f) - 13.82*log10(hb) - a + (44.9 - 6.55*log10(hb)).*log10(d);

// Plot Resulting Curve
plot(d, L, "r-o");
xlabel("Distance (km)");
ylabel("Path Loss (dB)");
title("HATA Path Loss Model");
xgrid();

Result

Path loss curves plotted in Scilab confirmed logarithmic increase in attenuation over distance.

Experiment 7: Knife-Edge Diffraction Simulation

Aim

To compute Fresnel diffraction parameter (\(v\)) and evaluate obstacle diffraction loss in Scilab.

Equations

$$ v = h\sqrt{\frac{2(d_1+d_2)}{\lambda d_1 d_2}} $$ $$ L_d = 6.9 + 20\log_{10}\left(\sqrt{(v-0.1)^2+1} + v - 0.1\right) \quad (\text{for } v > -0.7) $$

Scilab Script

clc;
clear;

v = -1:0.1:5;
Ld = zeros(v);

for i=1:length(v)
    if v(i) <= -0.7 then
        Ld(i) = 0;
    else
        Ld(i) = 6.9 + 20*log10(sqrt((v(i)-0.1)^2 + 1) + v(i) - 0.1);
    end
end

plot(v, Ld, "b-d");
xlabel("Diffraction Parameter (v)");
ylabel("Diffraction Loss (dB)");
title("Knife-Edge Diffraction Loss");
xgrid();

Result

Simulations demonstrated that diffraction loss increases steadily as the obstacle obstruction parameter grows positive.

Experiment 8: Two-Ray Ground Reflection Model

Aim

To analyze signal power attenuation for the Two-Ray Ground Reflection model in Scilab.

Model Equation

$$ P_r = \frac{P_t G_t G_r h_t^2 h_r^2}{d^4} $$

Scilab Script

clc;
clear;

Pt = 1; Gt = 1; Gr = 1;
ht = 50; hr = 2;
d = 100:100:5000;

Pr = (Pt * Gt * Gr * (ht^2) * (hr^2)) ./ (d.^4);

plot(d, 10*log10(Pr), "m-s");
xlabel("Distance (m)");
ylabel("Received Power (dB)");
title("Two-Ray Ground Reflection Model");
xgrid();

Result

The characteristic \(1/d^4\) long-distance path degradation was successfully verified.

Experiment 9: CDMA Trainer Kit Analysis

Aim

To observe signal spreading and despreading using Pseudorandom Noise (PN) code sequences on a CDMA trainer system.

Core Concepts

• Spreading: Data bits are multiplied by higher frequency PN chip codes.
• Processing Gain (\(PG\)): Calculated as the ratio of chip rate to message data rate (\(B_w / R_b\)).
• Multi-User Capability: Unique orthogonal codes allow simultaneous users on the same radio frequency.

Observation Summary

Parameter	Status / Measurement
PN Sequence Length	Verified via kit logic display
Chip Rate vs. Bit Rate	Validated ratio matches expected processing gain
Despread Signal Output	Successfully reconstructed original input waveform

Result

Direct Sequence Spread Spectrum (DSSS) spreading and signal extraction principles were demonstrated.

Experiment 10: Mobile Trainer Kit Analysis

Aim

To inspect mobile handset architecture including SIM initialization, cell registration, and baseband operations.

Procedure Summary

1. Power on trainer board and monitor initial processor initialization routines.
2. Verify successful SIM detection and cellular network link attachment.
3. Run live voice call tests while logging real-time RF signal strength (\(CSQ\)).

Result

End-to-end cellular telephone operations and internal module interactions were analyzed.

Lab Precautions & Learning Outcomes

Safety & Operational Precautions

• Always switch OFF power prior to inserting or removing SIM cards from hardware modules.
• Ensure terminal serial communication baud rates (e.g., 9600 bps) match hardware setup settings.
• Always verify RF external antennas are firmly attached prior to powering active transmitters.

Learning Outcomes

• Gain comprehensive practical knowledge of GSM and CDMA system architectures.
• Master AT command-line operation for modem control and telemetry.
• Develop analytical models for wireless propagation and attenuation using computational software.