Virtual Laboratory: Telecommand & Telemetry Systems

Learning Objectives

Upon completion of this virtual laboratory, the student will be able to:

1. Understand Telecommand Architecture

Explain the structure, encoding, and modulation of satellite telecommand frames including sync patterns, address fields, command words, and error protection mechanisms.

2. Analyze Telemetry Frame Formats

Identify and decode standard telemetry frame structures (minor frames, major frames, sub-commutation), and understand how housekeeping data is organized for downlink transmission.

3. Operate Source & Channel Codecs

Demonstrate the operation of source coding (data compression) and channel coding (error detection/correction) algorithms including Hamming codes, Reed-Solomon, and convolutional coding.

4. Evaluate Link Performance

Measure and analyze Bit Error Rate (BER) versus Signal-to-Noise Ratio (Eb/N0) for different coding schemes and modulation types used in satellite links.

5. Simulate End-to-End Communication

Execute a complete telecommand transmission and telemetry reception cycle, observing the effects of noise, Doppler shift, and coding gain on system performance.

6. Apply CCSDS Standards

Recognize the role of CCSDS (Consultative Committee for Space Data Systems) recommendations in standardizing packet telemetry and telecommand protocols.

Theoretical Background

1. Introduction to Telecommand (TC)

A Telecommand (TC) system provides the uplink communication path from a ground station to a satellite, enabling operators to control spacecraft functions, modify operational parameters, and recover from anomalies. The telecommand link is mission-critical and requires extremely high reliability.

                Key Requirement: The telecommand link must operate with a Command Error Rate typically better than 10-6 per command, necessitating robust error detection and often error correction coding.
            

1.1 Telecommand Frame Structure (CCSDS TC Frame)

The standard telecommand frame consists of several fields designed to ensure reliable delivery and execution:

Figure 1: CCSDS Telecommand Transfer Frame Structure showing the Control Link Control Word (CLCW), Segment Header, Packet Data, Forward Error Correction (FEC), Tail sequence, and Frame Sync marker.

1.2 Telecommand Encoding Chain

The telecommand data passes through several processing stages before RF transmission:

Raw Command Data → Source Encoding → Packet Assembly → Channel Coding (BCH/RS) → Frame Sync Addition → Scrambling → PSK Modulation → Uplink Transmission

Processing Stage	Function	Typical Standard
Source Coding	Compress redundant data, optimize bandwidth	CCSDS Lossless Data Compression
Packet Assembly	Encapsulate data in standardized packets	CCSDS Space Packet Protocol
Channel Coding	Add redundancy for error detection/correction	BCH (63,56) or Reed-Solomon (255,223)
Scrambling	Ensure bit transitions for clock recovery	CCSDS Pseudo-Randomizer (PN sequence)
Modulation	Map bits to RF carrier phase/frequency	PCM/PSK/PM, typically QPSK or BPSK

2. Telemetry (TM) Systems

Telemetry (TM) provides the downlink path from satellite to ground, transmitting spacecraft health status, scientific data, and operational parameters. Modern satellite telemetry follows the CCSDS Packet Telemetry standard.

2.1 Telemetry Frame Hierarchy

Figure 2: Telemetry Frame Hierarchy. A Major Frame (or Master Frame) consists of multiple Minor Frames. Each Minor Frame contains a sync word, frame counter, and multiple data words representing different telemetry channels.

2.2 Source Coding in Telemetry

Source coding reduces the redundancy in telemetry data to optimize bandwidth usage:

Differential PCM (DPCM): Encodes the difference between consecutive samples rather than absolute values.
Adaptive DPCM: Adjusts quantization step size based on signal variance.
CCSDS Lossless Compression: Uses adaptive entropy coding for scientific data.

Compression Ratio (CR) = Uncompressed Size / Compressed Size
For typical housekeeping telemetry: CR ≈ 1.5 to 3.0

3. Channel Coding & The Codec

A Codec (Coder-Decoder) in satellite communications performs both source coding (compression) and channel coding (error protection). The channel encoder adds controlled redundancy to enable error detection and correction at the receiver.

3.1 Hamming Codes

Hamming codes are linear error-correcting codes that can detect up to two-bit errors or correct one-bit errors. The (7,4) Hamming code encodes 4 data bits into 7 bits by adding 3 parity bits:

Parity Bits: p₁ = d₁ ⊕ d₂ ⊕ d₄ p₂ = d₁ ⊕ d₃ ⊕ d₄ p₃ = d₂ ⊕ d₃ ⊕ d₄
Codeword: [p₁, p₂, d₁, p₃, d₂, d₃, d₄]

3.2 Reed-Solomon Codes

Reed-Solomon (RS) codes are non-binary cyclic error-correcting codes particularly effective against burst errors. The CCSDS standard uses RS(255,223) over GF(2⁸):

Block length: n = 255 symbols (8 bits each)
Message symbols: k = 223
Parity symbols: 2t = 32 (can correct up to 16 symbol errors)
Code rate: R = k/n = 223/255 ≈ 0.875

3.3 Convolutional Codes

Convolutional codes operate on continuous data streams using shift registers. The CCSDS standard rate-1/2, constraint length K=7 convolutional code:

Generator Polynomials: G₁ = 171₈ (1111001), G₂ = 133₈ (1011011)
Coding Gain: Approximately 5-6 dB at BER = 10^-5 compared to uncoded BPSK

Figure 3: Convolutional Encoder with constraint length K=7. The six delay elements (D) form the shift register. Modulo-2 adders implement generator polynomials G1=171₈ and G2=133₈. Each input bit produces two output bits (V1, V2), giving a code rate of 1/2.

3.4 Coding Gain

The coding gain represents the reduction in required Eb/N0 to achieve a target BER compared to an uncoded system:

Coding Gain (dB) = (Eb/N0)_uncoded - (Eb/N0)_coded |_{at same BER}

4. Modulation for Satellite Links

Satellite telecommand and telemetry typically employ phase-shift keying (PSK) due to its power efficiency:

Modulation	Bits/Symbol	Bandwidth Efficiency	Power Efficiency	Typical Use
BPSK	1	Low	High	Telecommand uplink
QPSK	2	Medium	Medium	Telemetry downlink
8-PSK	3	High	Low	High-rate science data
O-QPSK	2	Medium	Medium	Constant envelope systems

BPSK Signal: s(t) = A·cos(2πf_ct + π·d(t)) where d(t) ∈ {0,1}
QPSK Signal: s(t) = A·cos(2πf_ct + π/4 + n·π/2), n ∈ {0,1,2,3}

Laboratory Procedure

Experiment 1: Telecommand Frame Generation and Transmission

Initialize the Ground Station

Navigate to Simulation 1: Telecommand Encoder. Set the ground station parameters: carrier frequency (e.g., 2.1 GHz S-band), modulation type (BPSK), and EIRP (Equivalent Isotropically Radiated Power). Verify the link budget calculator shows positive margin.

Construct the Command Message

Enter a spacecraft command from the predefined list (e.g., "Enable Solar Panel Tracking", "Set Attitude Mode: Sun-Pointing", or "Dump Memory Bank A"). Observe how the command is packetized according to the CCSDS Space Packet Protocol.

Apply Channel Coding

Select the channel coding scheme (Hamming, Reed-Solomon, or Convolutional). Observe the frame length increase due to added parity bits. Record the code rate and theoretical coding gain for your selected scheme.

Modulate and Transmit

Apply scrambling and PSK modulation. Observe the time-domain waveform and constellation diagram. Click Transmit to send the command through the simulated satellite channel with adjustable AWGN and Doppler shift.

Analyze Reception

At the satellite receiver, observe the demodulated signal, frame synchronization acquisition, error correction decoding, and command verification. Record the Bit Error Rate (BER) before and after decoding.

Experiment 2: Telemetry Data Reception and Decoding

Configure the Satellite Transmitter

Navigate to Simulation 2: Telemetry Decoder. Select telemetry types: Housekeeping (temperature, voltage, current), Attitude (quaternions, gyro rates), or Payload Science Data. Set the downlink frequency (e.g., 2.3 GHz) and modulation (QPSK).

Generate Telemetry Frames

Observe the automatic generation of Minor Frames and Major Frames. Identify the frame sync word, frame counter, and time stamp. Note how different telemetry channels are sub-commutated into the frame structure.

Simulate Channel Impairments

Introduce controlled impairments: Additive White Gaussian Noise (AWGN), Doppler frequency offset, and phase jitter. Gradually increase noise power and observe the effect on the received constellation diagram.

Decode and Display

At the ground station receiver, perform carrier recovery, symbol synchronization, frame synchronization, and channel decoding. Extract the telemetry parameters and observe their real-time graphical display (gauges, time-series plots).

Measure Performance

Vary Eb/N0 from 0 dB to 12 dB in 2 dB steps. For each step, measure the BER and Frame Error Rate (FER). Plot BER vs Eb/N0 curves for both coded and uncoded transmission.

Experiment 3: Codec Operation Analysis

Source Coding Analysis

Navigate to Simulation 3: Codec Analyzer. Input a sample telemetry data stream (e.g., temperature readings from a spacecraft sensor). Compare the original data size with the compressed size using differential encoding. Calculate the compression ratio.

Channel Coding - Hamming Code

Select the (7,4) Hamming code. Input a 4-bit data word and observe the generated 7-bit codeword. Introduce a single-bit error and demonstrate the error detection and correction capability using the syndrome calculator.

Channel Coding - Convolutional Code

Select the CCSDS K=7, R=1/2 convolutional code. Trace the path through the trellis diagram for a short input sequence. Observe how the Viterbi decoder recovers the original data from a noisy received sequence.

BER Performance Comparison

Run Monte Carlo simulations to generate BER curves. Compare uncoded BPSK, Hamming-coded BPSK, and Convolutional-coded BPSK. Determine the coding gain at BER = 10^-5 for each coding scheme.

Concatenated Coding

Observe the performance of a concatenated coding system (Reed-Solomon outer code + Convolutional inner code). Measure the additional coding gain achieved and discuss the "error floor" phenomenon.

Interactive Simulations

Simulation 1: Telecommand Encoder

Simulation 2: Telemetry Decoder

Simulation 3: Codec Analyzer

🛰️ Telecommand Transmission System

Construct, encode, modulate, and transmit a spacecraft command. Observe the complete signal processing chain from raw command to RF waveform.

Command Type

Spacecraft Address

Channel Code

Modulation

Eb/N0 (dB) 8 dB

Frame Structure Visualization

0xAA

0x1A

0x55

Baseband Signal (Time Domain)

Modulated RF Signal

Constellation Diagram

Power Spectral Density

System Ready. Configure parameters and click 'Generate & Transmit' to begin telecommand simulation.

📡 Telemetry Reception System

Receive, demodulate, and decode satellite telemetry frames. Monitor spacecraft health parameters in real-time.

Telemetry Type

Modulation

Channel Code

AWGN (dB) 10 dB

Doppler (kHz) 0 kHz

Received Signal with Noise

Constellation (Noisy)

Telemetry Parameter Display

Frame Error Rate vs Time

Telemetry receiver ready. Select parameters and click 'Start Reception' to simulate downlink monitoring.

🔧 Codec Operation Analyzer

Study source coding (compression) and channel coding (error correction) algorithms. Visualize encoding, introduce errors, and observe decoding performance.

Data Input (Hex)

Coding Scheme

Error Bits

Eb/N0 Range

Encoder Structure / Trellis

Codec Operation Status

                            Ready for codec analysis...
                        

BER vs Eb/N0 Performance

Coding Gain Analysis

Laboratory Report Guidelines

Report Structure

Your laboratory report should be professionally formatted and contain the following sections. Use clear headings, numbered figures, and captioned tables throughout.

📋 1. Title Page

Experiment title: "Virtual Laboratory: Telecommand and Telemetry Systems"
Student name, registration number, and group
Course code and name (e.g., Satellite Communication Engineering)
Date of submission
Instructor name

🎯 2. Abstract / Executive Summary (150-200 words)

Brief statement of the experiment objectives
Summary of key methods used (simulations performed)
Principal results obtained (BER values, coding gains, frame structures)
Main conclusions drawn from the experiments

📚 3. Introduction and Theory (3-4 pages)

Overview of satellite telecommand and telemetry functions
Description of CCSDS standards for TC and TM
Explanation of frame structures (transfer frames, packets, segments)
Mathematical description of channel coding: Hamming, Reed-Solomon, Convolutional
Modulation theory: BPSK and QPSK signal expressions and constellation diagrams
Definition of key metrics: BER, FER, Eb/N0, Coding Gain
Include at least 3 original diagrams (frame structure, encoder block diagram, constellation)

⚙️ 4. Experimental Procedure (2-3 pages)

Step-by-step description of Simulation 1 (Telecommand Transmission)
Step-by-step description of Simulation 2 (Telemetry Reception)
Step-by-step description of Simulation 3 (Codec Analysis)
Parameter settings used for each simulation run
Screenshots of key simulation states (frame visualizer, constellation, BER curves)

📊 5. Results and Analysis (4-5 pages)

Table 1: Telecommand frame field lengths and values for each command tested
Figure 1: Time-domain waveforms of baseband and modulated telecommand signal
Figure 2: Constellation diagrams for BPSK and QPSK at different Eb/N0 values
Table 2: Measured BER vs Eb/N0 for uncoded and coded transmissions
Figure 3: BER vs Eb/N0 curves (semi-log plot) comparing all coding schemes
Table 3: Coding gain values at BER = 10^-3 and BER = 10^-5
Figure 4: Telemetry parameter time-series plots (temperature, voltage, etc.)
Figure 5: Frame Error Rate (FER) as a function of channel Eb/N0
Analysis of Hamming code error correction: show syndrome calculation for single-bit error
Discussion of the Shannon Limit and how coding approaches it

💡 6. Discussion (2 pages)

Compare theoretical and simulated BER values. Explain any discrepancies.
Discuss the trade-off between bandwidth expansion and power savings in channel coding
Explain why concatenated codes (RS + Convolutional) are used in deep-space missions
Discuss the importance of frame synchronization in telecommand links
Analyze the effect of Doppler shift on QPSK reception and how it is mitigated
Comment on the practical implementation challenges of the Viterbi decoder

✅ 7. Conclusion (1 page)

Summarize whether the experiment objectives were achieved
State the key numerical findings (coding gains, optimal operating points)
Mention any unexpected observations and their possible causes
Suggest improvements to the simulation or real-world system design

📖 8. References

List all textbooks, standards, and papers cited using IEEE referencing format
Include CCSDS Blue Books (e.g., CCSDS 231.0-B-3 for TC, CCSDS 132.0-B-3 for TM)
Cite at least 3 peer-reviewed journal articles on satellite channel coding

📎 9. Appendices (if applicable)

Appendix A: Sample calculations (e.g., Hamming parity bit calculations)
Appendix B: Additional simulation screenshots
Appendix C: MATLAB/Python code if used for verification

Grading Rubric

Component	Weight	Excellence Criteria
Theory & Background	20%	Accurate, comprehensive, well-referenced, original diagrams
Procedure Description	15%	Clear, reproducible, all parameters documented
Results & Data	25%	Complete tables/figures, correct calculations, proper labels
Analysis & Discussion	25%	Critical thinking, physical insight, error analysis
Presentation & Format	10%	Professional layout, grammar, IEEE references
Conclusion	5%	Summarizes key findings, links to objectives

Important Notes

                Plagiarism Policy: All diagrams, tables, and analysis must be your own work based on the virtual laboratory simulations. Copying from internet sources without proper citation will result in disciplinary action.
            

                Submission: Submit your report as a single PDF file via the course learning management system. Maximum file size: 20 MB. Include all figures as embedded images (minimum 300 DPI).
            

                Deadline: Reports must be submitted within two weeks of the laboratory session. Late submissions incur a penalty of 10% per day.
            