Digital Communications Quiz
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Questions and Answers

What does a factor of 2 correspond to in decibels?

  • 10 dB
  • -3 dB
  • 3 dB (correct)
  • 0 dB

DBm represents the signal power in Watts.

False (B)

What does the equation X (dB) = 10 log10 X represent?

A logarithmic ratio used in communications.

The unit _____ can be used to express very small signal values in reasonable numbers, such as -100dB for 10^-10.

<p>decibel</p> Signup and view all the answers

Match the following terms with their definitions:

<p>dBW = Signal power in Watts represented in dB dBm = Signal power in milli-Watts represented in dB Factor of 10 = Corresponds to an addition of 10 dB Factor of 1/2 = Corresponds to a subtraction of 3 dB</p> Signup and view all the answers

What is the rate of the convolutional code shown?

<p>1/2 (D)</p> Signup and view all the answers

The convolutional code has a constraint length of 2.

<p>False (B)</p> Signup and view all the answers

What are the two output sequences produced when the input bits are 0 0 1?

<p>1 1, 1 0</p> Signup and view all the answers

The input bit sequence for time t=4 is ______.

<p>0 1 0</p> Signup and view all the answers

Match the values with their corresponding meanings:

<p>R = Rate of the convolutional code K = Constraint length m = Input bit sequence U = Encoded output sequence</p> Signup and view all the answers

What does GSM stand for?

<p>Global System for Mobile communication (B)</p> Signup and view all the answers

The first satellite phone was launched in 1995.

<p>False (B)</p> Signup and view all the answers

What year did the introduction of GPRS occur?

<p>2000</p> Signup and view all the answers

The first commercial launch of CDMA occurred in ______.

<p>1995</p> Signup and view all the answers

Which country introduced mobile TV first?

<p>South Korea (D)</p> Signup and view all the answers

HSDPA was first launched worldwide in 2006.

<p>True (A)</p> Signup and view all the answers

In what decade did 1G technology emerge?

<p>Mid 1980s</p> Signup and view all the answers

What is a characteristic of a regular LDPC code?

<p>Every code digit is contained in the same number of equations. (B)</p> Signup and view all the answers

In an irregular LDPC code, each equation contains the same number of code symbols.

<p>False (B)</p> Signup and view all the answers

How many independent equations are there in a simple LDPC code with n=12?

<p>9</p> Signup and view all the answers

A Tanner graph uses two types of nodes: ____ and ____.

<p>bit nodes, parity nodes</p> Signup and view all the answers

Which of the following statements about LDPC codes is true?

<p>The decoding of LDPC codes can be visualized with Tanner graphs. (B)</p> Signup and view all the answers

A Tanner graph connects bit nodes to parity nodes based on their involvement in parity equations.

<p>True (A)</p> Signup and view all the answers

List the parity check equations for a simple irregular LDPC code with n=6.

<p>c1 Å c2 Å c5 = 0; c1 Å c4 Å c6 = 0; c1 Å c2 Å c3 Å c6 = 0</p> Signup and view all the answers

Match the following terms related to LDPC codes with their definitions:

<p>Regular LDPC Code = Contains the same number of code symbols in each equation Irregular LDPC Code = Lacks uniform restrictions on code symbols across equations Bit Node = Represents a code symbol in a Tanner graph Parity Node = Represents a parity equation in a Tanner graph</p> Signup and view all the answers

What is the primary purpose of pulse shaping?

<p>To fit signals into a spectral mask (B)</p> Signup and view all the answers

A square pulse in the frequency domain results in a sinc function with minimal high frequency components.

<p>False (B)</p> Signup and view all the answers

What is the consequence of having sharp edges in a pulse?

<p>High frequency components and wider bandwidth</p> Signup and view all the answers

To avoid interference to neighboring symbols, pulse shapes must achieve _____ ISI.

<p>zero</p> Signup and view all the answers

Match the following components with their roles in pulse shaping:

<p>Spectral Mask = Defines the frequency range for signals Nyquist Criterion = Ensures zero ISI Pulse Shape = Influences high frequency components Inter-Symbol Interference = Causes signal distortion</p> Signup and view all the answers

What is a potential advantage of using a smooth pulse shape?

<p>Avoidance of high frequency components (C)</p> Signup and view all the answers

Pulses need to interfere with each other for effective transmission.

<p>False (B)</p> Signup and view all the answers

What is the main requirement of the Nyquist criterion for pulses?

<p>A pulse signal should exist at the sampling instance and be zero at other instances</p> Signup and view all the answers

What is one disadvantage of taking a sample at the peak of the pulse for signal detection?

<p>Noise can severely distort the sample (D)</p> Signup and view all the answers

Integrating the signal over a symbol period can help average out noise.

<p>True (A)</p> Signup and view all the answers

What does the term 'integrate and dump' refer to in signal processing?

<p>It refers to the process of integrating a signal over a specified time period and then sampling the result.</p> Signup and view all the answers

A convolution of two square pulses is expressed as $y(t) = \int_{0}^{1} ______(\tau) ______(t - \tau) d\tau$.

<p>rect</p> Signup and view all the answers

Match the following signal processing techniques with their descriptions:

<p>Sample at peak = Directly measures signal at its maximum Integrate over symbol period = Averages out noise for better SNR Convolution = Combines two signals to produce a third Integrate and dump = Computes an integral over a time period and samples once</p> Signup and view all the answers

Flashcards

What does GSM stand for?

A group of mobile phone operators and industry stakeholders who developed the GSM standard, which was a digital mobile communication technology introduced in the 1990s.

What was AMPS?

A technology standard originally developed in the U.S. that introduced analog mobile phone communication in the 1980s.

What is PHS?

A digital mobile technology launched in Japan during the 1990s, known for its personal handheld phone design.

What is CDMA?

A widely adopted 3G technology using code division multiple access, which allows multiple users to share the same spectrum more efficiently.

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What is IMT-2000?

An initiative formed in 1995 to develop standards for future mobile technologies, paving the way for 3G.

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What is GPRS?

A technology focused on providing internet access on mobile devices using a packet-switched network. It became a key feature of 3G networks.

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What is UMTS?

A specific 3G standard, based on a wideband code division multiple access (W-CDMA) technology.

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What is 4G technology?

A mobile technology that brought faster internet speeds to mobile phones, considered an extension of 3G, significantly improving the mobile internet experience.

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Decibel (dB)

A logarithmic unit used to express the ratio of two values, commonly used in communications.

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3dB

A factor of 2 increase in power corresponds to an addition of 3dB.

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10dB

A factor of 10 increase in power corresponds to an addition of 10dB.

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dBW

Represents signal power in Watts on a logarithmic scale.

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dBm

Represents signal power in milliwatts on a logarithmic scale.

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Convolutional Codes

A method of encoding data where the output bits depend not only on the current input bit but also on previous input bits.

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Rate R

The ratio between the number of input bits and output bits in a convolutional encoder. It indicates the efficiency of the encoding process.

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Constraint length K

The number of memory cells in a convolutional encoder, which determines the amount of past input bits influencing the output.

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Input BIT m

The specific set of bits that are shifted into the memory cells at each time step during the encoding process.

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Output sequence

The output produced by the convolutional encoder based on the input bits and the encoding rule.

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LDPC codes

Low-density parity-check (LDPC) codes are a type of error-correcting code used for reliable data transmission over noisy channels. They use a sparse parity-check matrix, meaning it has a low density of 1's, to define relationships between code symbols.

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Regular LDPC code

A regular LDPC code has a parity check matrix where each code symbol participates in the same number of parity check equations, and each parity check equation involves the same number of code symbols.

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Irregular LDPC code

An irregular LDPC code relaxes the constraints of a regular LDPC code. It allows different code symbols to participate in a varying number of equations, and equations can involve a different number of code symbols.

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Parity check matrix

A parity check matrix is a mathematical representation of a LDPC code. It defines the relationships between code symbols and parity check equations.

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Parity check equations

Parity check equations are mathematical equations that define the relationships between code symbols. They ensure that the encoded data satisfies certain conditions for error detection and correction.

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Tanner graph

The Tanner graph is a visual representation of the parity check matrix. It depicts code symbols as bit nodes and parity equations as parity nodes. Connections between nodes indicate that the corresponding code symbol is involved in that parity check equation.

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Bit nodes in the Tanner graph

Bit nodes represent code symbols in the Tanner graph, and they are connected to parity nodes based on the corresponding parity check equations.

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Parity nodes in the Tanner graph

Parity nodes represent parity check equations in the Tanner graph. They are connected to bit nodes indicating the code symbols involved in that particular parity check equation.

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Matched Filter

A technique used to detect a signal by maximizing the signal-to-noise ratio (SNR). It involves correlating the received signal with a reference signal that matches the expected transmitted signal.

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Rectangular Pulse

A rectangular pulse with a fixed duration like a square pulse. If a signal has the shape of a rect function, its duration is considered the pulse length.

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Integration

The process of integrating a signal over a specific duration, often a symbol period. This helps to average out the noise and improve the SNR.

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Convolution of Rectangular Pulses

The convolution process of two rectangular pulses results in a triangular wave, which reaches its peak at half the duration of each individual pulse.

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Sampling at the peak of the Pulse

The process of taking a sample of the received signal at a specific time, often at the peak of the pulse. While simple, this method can be susceptible to noise and may not provide the best SNR.

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Spectral Mask

A range of frequencies specifically allocated for a signal, usually with a defined power level for each band.

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Pulse Shaping

A method used to shape the frequency response of a signal by applying a specific filter to modify its spectral characteristics.

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How does smoothing a pulse reduce high frequency components?

Pulses in a digital signal have sharp transitions, creating a wide range of frequency components that can affect adjacent channels. Smoothing the edges of these pulses reduces high-frequency components, allowing for better channel separation.

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No Inter-Symbol Interference (ISI)

A key principle in pulse shaping that ensures that signals do not interfere with each other, maintaining clarity in communication.

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Nyquist Criterion

A mathematical condition that guarantees no inter-symbol interference (ISI) occurs.

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Sampling Time (Tb)

The time interval between the sampling points in a digital signal where information is extracted.

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Zero ISI Condition

A digital signal can be reconstructed perfectly at the receiver if the pulses are shaped in such a way that only the pulse corresponding to the sampled instance is non-zero, ensuring no interference.

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How does the Nyquist criterion aid in signal reconstruction?

The Nyquist criterion ensures that the received signal is sampled at the correct time by ensuring no inter-symbol interference (ISI), allowing for accurate reconstruction of the transmitted signal.

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Study Notes

Introduction & Background

  • Lecture set 1 covered the introduction and background to digital mobile communication.
  • The course outline included topics like: Course Outline, Introduction, Why Wireless?, History & Modern Development, Wireless = Mobile?, Mobile Challenge, Basic Revision (key concepts, frequency translation, different types of communications, basics of mobile communication)
  • Introduction to specific areas like: Introduction & Background, Baseband digital transmissions, Bandpass digital transmissions, Radio propagation & Diversity, Multiple access techniques, and Cellular network design.
  • Key lecturer information was provided specifying who was responsible for which section of the lecture set.

Course Structure

  • Lectures and surgery sessions were scheduled.
    • Wednesday lectures, specific location and times
    • Surgery sessions included location and times.
  • The assessment schedule was outlined, including:
    • Two courseworks (10% + 10%)
    • Final exam (80%)

Reference Books

  • Several books were referenced. For example, books by T. Rappaport, A. F. Molisch, A. Goldsmith, and S. Haykin and M. Moher.
  • The authors and publication year were listed for each book

Key Learning Points

  • Carefully read the materials for weekly asynchronous activities.
  • Try to attend synchronous lectures and surgery sessions.
  • Ask teachers for clarification when needed.
  • Avoid working until the end of each session to ensure you understand all the material.

Why Digital?

  • Key reasons for using digital communication include:
    • Noise immunity
    • Multiplexing
    • Better security
    • Support for digital signal processing

###Why Wireless?

  • Key benefits of wireless communication include:
    • Mobility
    • Flexibility

Wireless = Mobile?

  • Explains the difference between wireless and mobile communication.

  • Wireless communication: any form of communication that doesn't use wires. Typical examples include speech, hand signals, and electromagnetic waves.

  • Mobile communication: means being able to communicate wirelessly anywhere and anytime. A major focus of mobile communication is through the use of light-weight handheld devices like mobile phones and wireless networks.

Modern Development (1G - 3G)

  • Key milestones in mobile technology development from 1G to 3G were outlined.

Modern Development (3G - 4G)

  • Key technological developments and standards from 3G to 4G were described. For example, the launch of 3G service in UK or the introduction to GPS or W-LAN.

Modern Development (1G - 4G)

  • A timeline chart illustrating the evolution of mobile technology from 1G to 4G was displayed.

Modern Development (5G - 1/3)

  • 3GPP is responsible for 5G standardization
  • Release 15 (Non-Standalone, NSA) is a phase
  • Release 16 (New radio, NR) is a second phase
  • Information on important aspects of 5G evolution.

Modern Development (5G - 2/3)

  • 5G will increase mobile broadband, enabling 3D video, UHD screens, and more.
  • Other applications like smart home/buildings and smart city.
  • The uses for massive machine type communications and ultra-reliable and low latency technologies.
  • Information on use by ITU-R.

Modern Development (5G - 3/3)

  • The targets of 5G technology have various aspects such as peak data rate, user experienced data rate, Area traffic capacity, network energy efficiency, connection density, and latency, along with spectrum efficiency and mobility.

Visions for 6G?

  • Is it too early to talk about 6G?

How to develop 1/2/3/4/5G?

  • The key phases to developing a 1/2/3/4/5G system were provided in a visual chart depicting phases like invention, vision, proof-of-concept, standardization, and trials.

Visions for 6G

  • Several future applications were listed under different categories.

Mobile Challenges

  • Wireless channel impairments, limited bandwidth, and transmission power.
  • Interference and the issues of power consumption and processing power.
  • Historical context including the difficulties in moving a 5MB hard disk in the 1950s.
  • Challenges with size, security, and the health concerns related to the use of wireless technology

Basic Revision (I)

  • Explains the concept of dB and decibels (dB).
  • The use of decibels in various communication scenarios.

Basic Revision (II)

  • Explains the difference between dBW and dBm.
  • The use of dBW and dBm units for power measurement.

Basic Revision (III)

  • Bit error rates (BER) in digital communication systems.
  • SNR per bit in digital communications

Basic Revision (IV)

  • Additive white Gaussian noise (AWGN) is a pervasive noise model in digital communications.
  • The maximum data rate achievable in an AWGN channel.

Basic Revision (V)

  • Capacity calculations for a mobile link under specific conditions.

Frequency Translation

  • Frequency translation shifts the frequency range of a signal from one to another
  • The reasons for the need of this type of translation in communications.
  • A block diagram of a digital mobile transmitter and receiver system.
  • Key components of the structure and their functions were explained.

Types of Communications

  • Different communication types (simplex, half duplex, full duplex) in the context of point to point or point to multipoint communications (broadcast and multicast).

Multi-Point to Multi-Point

  • Multiplexing, such as Frequency Division Multiplexing (FDM).

Types of Communications

  • Explains the concept of multiple access in communications
  • Concepts about FDM, TDMA, CDMA, OFDMA.

Mobile Communications

  • Bidirectional communication and duplex techniques (frequency division and time division).

Summary

  • A concluding summary of the main concepts covered in lecture set 1.

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Lecture Set 1: Introduction & Background (Digital Mobile Communication) PDF

Description

Test your knowledge on digital communications concepts such as decibels, convolutional codes, and the evolution of mobile technologies. This quiz covers fundamental terms, definitions, and historical milestones in the field. Perfect for students and professionals looking to refresh their understanding of communication systems.

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