ELARA/ODIN > SDRs > Flashcards

SDRs Flashcards

(63 cards)

Study These Flashcards
1
Q

What is an SDR (Software-Defined Radio)?

A

An SDR is a radio where the RF front-end handles only essential hardware functions, while waveform generation, demodulation, and link layer processes are implemented in software using I/Q samples from fast ADCs/DACs.

The SDR acts as a universal modem defined by code and configuration.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Five components are included in the RF front-end of an SDR

A
  • Antenna
  • LNA (Low Noise Amplifier)
  • Filters
  • Mixer/Local Oscillator (LO)
  • Power Amplifier (PA)

These components manage the physical aspects of radio frequency communication.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the purpose of the antenna in an SDR?

A

The antenna couples RF energy efficiently, with poor matching potentially wasting power and triggering PA foldback.

Return Loss and VSWR are key metrics for efficiency.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does LNA stand for and what is its role?

A

LNA stands for Low Noise Amplifier, which sets sensitivity via Noise Figure and filters to prevent desensitization from blockers.

IP3 is an important linearity measurement in this context.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the function of the Local Oscillator (LO) in an SDR?

A

The Local Oscillator sets frequency accuracy and phase noise, with options to discipline them using GPSDO to reduce residual offset.

XO, TCXO, and OCXO are types of oscillators used.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the significance of the Power Amplifier (PA) in SDR transmission?

A

The PA maintains headroom below P1dB and ensures low-impedance power rail to prevent constellation smearing and maintain low EVM.

P1dB defines the output power level at which the amplifier begins to distort.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Fill in the blank: The _______ converts analog signals to digital for further processing in an SDR.

A

ADC (Analog-to-Digital Converter)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the purpose of Decimation and Interpolation in SDR?

A

Decimation and Interpolation reshape rates and bandwidths while preserving information through anti-alias filters.

This process is crucial for optimizing data handling.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the role of RRC filters in SDR?

A

RRC filters implement Nyquist pulse shaping, aligning roll-off between TX/RX to preserve processing gain and minimize ISI (Inter-Symbol Interference).

Roll-off (α) is a key parameter in filter design.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is Timing Recovery in the context of SDR?

A

Timing Recovery aligns sampling to symbol centers to maintain an open eye diagram, essential for effective communication.

TED (Timing Error Detector) methods like Gardner and M&M are commonly used.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What does AGC stand for, and what is its function?

A

AGC stands for Automatic Gain Control, which keeps amplitude within the ADC’s optimal range with time constants tuned to symbol and fade times.

This is critical for maintaining signal integrity.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

True or False: The modulation type in an SDR can be BPSK, QPSK, QAM, or GMSK.

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the purpose of interleaving in SDR?

A

Interleaving transforms burst errors from fading into random errors that can be corrected by FEC, thus improving coding gain and reducing BER.

LDPC and RS are examples of FEC methods used.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What five metrics can be obtained ‘for free’ in SDR operations?

A
  • SNR
  • (E_b/N_0)
  • Constellation plots
  • PSD/waterfall
  • BER/PER vs time/elevation
  • Loop offsets

These metrics assist in adaptive behavior and troubleshooting.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What does RTT stand for in the context of SDR, and why is it important?

A

RTT stands for Round Trip Time, which is crucial for setting ARQ window sizes and timers to prevent pipeline stalls.

In LEO systems, RTT is typically in the tens of milliseconds.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Fill in the blank: An SDR can optimize link margin in software by adjusting the _______.

A

symbol rate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the benefits of SDR flexibility?

A

SDR flexibility allows for quick changes in modulation, coding, and operational parameters, enabling adaptation to varying conditions.

This adaptability is a key advantage over traditional hardware.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What does ‘observability’ in SDR refer to?

A

Observability allows for the recording of I/Q data during issues, enabling offline analysis to troubleshoot and optimize performance.

This includes assessing PER vs (E_b/N_0) to identify problems.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is a concrete mental model for the receive path in SDR?

A

Antenna → LNA → Filters → Mixer/LO → ADC → DDC/Decimation → AGC → RRC Matched Filter → Timing Loop → Carrier Loop → Demod → De-Interleave → FEC → Deframe → ARQ Windows/ACKs.

Each stage serves a specific function critical to the overall performance.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What factors contribute to link margin in SDR?

A
  • Antenna gain/diversity
  • Lower symbol rate
  • Stronger FEC
  • Better NF
  • Tighter RRC matching

Link margin is typically measured as (E_b/N_0) and PER.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the significance of ‘clean constellation’ in SDR?

A

A clean constellation is achieved through adequate PA headroom, low rail impedance, and correct AGC, reflected in low EVM.

EVM (Error Vector Magnitude) is a key performance indicator.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What determines the throughput ceiling in SDR?

A

The throughput ceiling is determined by ACM and the ARQ window size relative to BDP, verified through long-run throughput measurements.

BDP stands for Bandwidth-Delay Product.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the final definition of an SDR?

A

An SDR is a software-programmable PHY and link front-end that digitizes signals, applies matched filtering and synchronization, manages demodulation and FEC, and exposes performance metrics while allowing real-world impairments to be measured and corrected.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is an eye diagram?

A

A type of oscilloscope display generated by overlaying many segments of a digital signal waveform

It resembles the shape of an eye and helps visualize how a signal behaves over many symbol periods.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
In what context is an eye diagram commonly used?
Common in **digital communications**, especially in baseband and passband modulation schemes like QPSK, QAM, etc. ## Footnote It assesses the quality of a digital signal, particularly at the receiver side.
26
What does a **clean, wide-open eye** indicate?
A healthy, easily decodable signal ## Footnote It suggests good signal integrity with minimal jitter, noise, and intersymbol interference.
27
What issues does a **closed or distorted eye** suggest?
Issues with **sampling, timing, or noise** ## Footnote It indicates potential problems in signal processing that may affect decoding.
28
What is the purpose of an eye diagram in **clock recovery and timing**?
Helps determine the optimal **sampling point** ## Footnote Typically, this point is at the center of the eye opening.
29
How is an eye diagram created in **SDR software**?
* Buffering the baseband samples * Slicing the data stream into segments based on symbol timing * Overlaying those segments in time-aligned windows ## Footnote This process visualizes symbol transitions in the signal.
30
What does the **eye opening** in an eye diagram indicate?
Amplitude margin for **noise** ## Footnote A wider eye opening suggests better noise tolerance.
31
What do the **crossing points** in an eye diagram tell you?
Symmetry and **timing** ## Footnote They help assess the timing accuracy of the signal transitions.
32
What does **jitter** in an eye diagram represent?
Horizontal blurring of **transitions** ## Footnote It indicates timing variations that can affect signal integrity.
33
What does **noise** in an eye diagram indicate?
Vertical blurring ## Footnote It reflects the presence of unwanted signals that can distort the original signal.
34
What does **ISI** stand for and what does it indicate in an eye diagram?
Intersymbol Interference; distortion due to **neighboring symbols** ## Footnote It can complicate the decoding process by causing overlap between signal symbols.
35
In the context of designing a **QPSK modem** in GNU Radio, what does a partially closed eye indicate?
Filtering or sampling timing may need **tuning** ## Footnote This observation helps in optimizing the receiver's performance.
36
True or false: An eye diagram is essential for both learning and engineering **digital comms systems**.
TRUE ## Footnote It serves as a real-time, software-generated diagnostic tool.
37
In the context of **spacecraft deployment**, what does the term **constellation** refer to?
A group of satellites working together to provide continuous or global coverage of some service ## Footnote Key characteristics include specific orbital planes, coverage, redundancy, and persistent presence.
38
What are some **uses** of satellite constellations?
* Global Navigation (e.g., GPS, Galileo, GLONASS) * Earth Observation (e.g., Planet Labs) * Global Internet (e.g., Starlink, OneWeb) ## Footnote These applications rely on coordinated satellite operations for effective service.
39
In **SDR and digital communications**, what does the term **constellation** refer to?
A visual representation of the possible symbols used in a modulation scheme ## Footnote Each point corresponds to a unique bit pattern and reflects amplitude and phase changes.
40
What modulation types are associated with **constellation diagrams** in SDR?
* QPSK * 16-QAM * 64-QAM ## Footnote These types are plotted on an I/Q plane to visualize signal characteristics.
41
What is the purpose of a **constellation diagram** in SDR?
To help visualize symbol distortion, phase noise, or interference in real-time ## Footnote It assists in determining if the receiver is correctly demodulating the signal.
42
True or false: A **satellite internet constellation** might consist of 3,000+ LEO satellites.
TRUE ## Footnote Each satellite hands off coverage to another as the Earth rotates, ensuring continuous service.
43
What is the **visual form** of spacecraft constellations?
Orbital map or satellite network diagram ## Footnote This visual representation shows the arrangement and coordination of satellites.
44
What is the **visual form** of SDR constellations?
I/Q plot (Cartesian) of signal symbols ## Footnote This plot represents the modulation scheme and helps in analyzing signal quality.
45
Who typically uses **spacecraft constellations**?
Satellite operators, aerospace engineers ## Footnote These professionals design and manage satellite systems for various applications.
46
Who typically uses **SDR constellations**?
Comms engineers, SDR developers ## Footnote These individuals work on communication systems and signal processing technologies.
47
Fill in the blank: **Spacecraft constellation** = __________ in space.
Satellites ## Footnote This mnemonic helps remember the concept of coordinated satellites.
48
Fill in the blank: **SDR constellation** = __________ in space (I/Q space).
Symbols ## Footnote This mnemonic aids in recalling the representation of modulation schemes.
49
What does **smearing** refer to in the context of Software-Defined Radio (SDR)?
Blurring or spreading of signal features over time or frequency ## Footnote This degradation affects the clarity and integrity of the received signal.
50
Name the **three main types** of smearing.
* Time-Domain Smearing * Frequency-Domain Smearing * Phase Smearing ## Footnote Each type has distinct characteristics and causes.
51
What is **Time-Domain Smearing**?
Symbols in a digital signal bleed into each other ## Footnote Often caused by intersymbol interference (ISI).
52
List the **causes** of Time-Domain Smearing.
* Poor filtering * Insufficient bandwidth * Multi-path propagation * Symbol timing errors ## Footnote These factors contribute to the overlap of symbols.
53
What are the **symptoms** of Time-Domain Smearing?
* Blurred eye diagrams * Increased bit error rate (BER) * Symbols in constellation diagram don't land cleanly ## Footnote These symptoms indicate degradation in signal clarity.
54
What is **Frequency-Domain Smearing**?
A sharp frequency component spreads out over a wider range ## Footnote This reduces frequency resolution.
55
List the **causes** of Frequency-Domain Smearing.
* Windowing artifacts in FFTs * Phase noise in oscillators * Doppler shifts or drift ## Footnote These factors lead to frequency spreading.
56
What are the **symptoms** of Frequency-Domain Smearing?
* Smeared or fuzzy power spectral density plots * Increased adjacent channel interference * Harder to isolate narrowband signals ## Footnote These symptoms indicate issues with frequency resolution.
57
What is **Phase Smearing**?
Random fluctuations in phase over time, leading to distorted modulation ## Footnote This affects the integrity of the signal's modulation.
58
List the **causes** of Phase Smearing.
* Phase noise in local oscillator (LO) * Poor phase synchronization * Carrier frequency drift ## Footnote These factors contribute to phase fluctuations.
59
What are the **symptoms** of Phase Smearing?
* Blurred points in constellation diagram * Difficulty decoding higher-order modulations ## Footnote These symptoms indicate issues with phase stability.
60
How can **smearing** be diagnosed and mitigated in SDR workflows?
* Adjusting symbol synchronizers * Using matched filters * Implementing carrier recovery loops * Utilizing equalizers * Modifying FFT window functions ## Footnote These adjustments can help improve signal clarity.
61
Fill in the blank: **Time-Domain Smearing** is caused by _______.
ISI, multipath, filter misalignment ## Footnote These factors lead to symbols overlapping in time.
62
Fill in the blank: **Frequency Smearing** is caused by _______.
FFT windowing, Doppler, oscillator phase noise ## Footnote These factors cause energy to spread across adjacent frequencies.
63
Fill in the blank: **Phase Smearing** is caused by _______.
LO phase noise, poor carrier recovery ## Footnote These factors lead to constellation points wobbling or drifting.
ELARA/ODIN
flashcards
Decks in class (14)
# Cards
Brainscape helps you reach your goals faster, through stronger study habits.
© 2026 Bold Learning Solutions. Terms and Conditions