Glossary – Simulation of telesystems

Matlab and Simulink

MATLAB – Matrix Laboratory.

Simulink – A graphically programmed data-flow oriented tool within Matlab for modeling and analysis of dynamic systems.

Matlab function - .m-file that starts with the reserved word “function”. May also be an internal function or a compiled function.

Matlab script – .m-file that does not include a function header. Runes in the workspace.

Toolbox – a set of Matlab-functions and scripts

Blockset – a library of Simulink models.

Signals and signal processing

Signal: A varying physical quantity, for example a voltage or a current, that can carry information.

Digital signal: A signal with a finite number of levels and a certain symbol rate or sample rate. This may be a bit stream transmitted as a pulse train over a baseband channel. A digital signal may be a representation of a quantified and discrete-time signal, for example a sampled and digitized analog signal.

Quantization: Analog-to-digital conversion.

Sampel Rate – The number of samples per second taken from a analogue continous signal to make a time-discrete signal.

Periodic waveform: A signal that repeats it self at regular intervals, the so called period time. Some named examples are since wave, sawtooth wave, square wave and triangle wave.

Fundamental frequency: Number of periods per second of a periodic wave form. One divided by the period time.

Amplitude: Peak voltage or peak current. A nonnegative scalar measure of a wave's magnitude of oscillation, that is, the magnitude of the maximum disturbance in the medium during one wave cycle.

Complex representation of a sinewave: A sinewave of constant amplitude and phase can be divided into an Inphase signal with amplitude I, and a Quadrature phase signal, with amplitude Q. The phase difference between the I and Q signals is 90°. The sinewave can be represented by a constant complex number C = I + jQ, where j is the imaginary unit. This number can be represented graphically by a two-dimensional vector. The amplitude of the sinewave is the absolute value of C (the distance between the point C and origin in the graphical representation), which can be found using Pythagoras’ theorem. The phase of the sinewave is the argument of C (the angle of the graphical vector representation). The real component of C is I, and the imaginary component of C is jQ.

RMS voltage: Root mean square (in Volt). The quadratic mean of a voltage signal. The power or energy of a signal depends on the RMS value rather than the amplitude. In case of a sine wave, the RMS voltage is 71% of the amplitude (the peak voltage). In case of a square wave, the RMS voltage is equal to the amplitude. In case of a stochastic (random) signal with mean value 0, the RMS value corresponds to the standard deviation of the signal.

Power: Energy per time unit, for example radiated as heat from a resistor, or radio waves from an antenna. Measured in Watt and defined as, where is the RMS voltage, and R is the resistance. Sometimes measured in Volt² (V²), defined as .

Signal processing: The analysis, interpretation and manipulation of signals, for example filtering, equalization, noise cancellation, source coding, measuring, etc.

Analog signal processing: Processing of a signal by means of analog components, for example passive components such as capacitors, inductors and resistors, but also active components such as transistors and operational amplifiers.

Digital signal processing: Processing of a digitized and sampled analog signal, by means of digital electronic components and perhaps also software.

Harmonics: Frequency components of a periodic signal. A periodic signal can be described as a sum of sine waves, each with different amplitudes and phases. This is called Fourier series development. If the fundamental frequency (the first harmonic) is f, the second harmonic has the frequency 2f, the third harmonic the frequency 3f, etc.

DC (direct current) component: Mean value of a voltage or a current.

Spectrum: The frequency domain description of a signal. The spectrum is typically illustrated as a plot where the horizontal axis is the frequency, and the vertical axis may be the amplitude (in Volt), the power (in Watt), the power density (in Watt/Hz) and/or the (in radians or degrees). The spectrum may correspond to the fourier series development of a periodic (cyclic) waveform, or the fourier transform of a non-periodic signal, expressed as a mathematical function of the frequency.

Components and algorithms of a digital communication systems

Source coding: Sampling, digitalization and/or compression. The aim is to minimize the number of bit/s but achieve sufficient signal quality.

Channel coding: Addition of forward error correction (FEC) codes and bit interleaving. See below. Sometimes modulation is also included in the term, but not always.

Multiplex method: A scheme for combining many analog signals or digital bit streams into a single transmission circuit or channel. Examples are:

- Time Division Multiplexing (TDM), using a frame consisting of a a fixed number of timeslots.

- Frequency Division Multiplexing (FDM), using modulation and a frequency channel per signal.

- Statistical Multiplexing, for example packet mode communication.

- Code Division Multiplexing, also known as spread spectrum communication, for example frequency hopping or direct sequence code division multiplexing.

Multiple access method, or channel access method: a scheme that allows several terminals connected to the same physical medium to transmit over it, and to share its capacity. Examples of multiple access methods are time division multiple access (TDMA) and carrier sense multiple access with collision detection (CSMA/CD). A multiple access protocol is synonym to media access control (MAC).

Examples of circuit mode channel access methods, providing fixed bit rate and delay: (You are not expected to know all these methods.)

- Frequency division multiple access (FDMA)

- Time-division multiple access (TDMA)

- Code division multiple access (CDMA) or spread spectrum multiple access (SSMA), for example

- Direct-sequence CDMA (DS-CDMA)

- Frequency-hopping

Examples of packet mode channel access methods, providing varying bit rate and delay:

- Contention based random access methods:

- Aloha

- Slotted Aloha

- Multiple Access with Collision Avoidance (MACA)

- Multiple Access with Collision Avoidance for Wireless (MACAW)

- Carrier Sense Multiple Access (CSMA)

- Carrier sense multiple access with collision detection (CSMA/CD)

- Carrier sense multiple access with collision avoidance (CSMA/CA)

- Token passing:

- Token ring

- Token bus

- Polling

- Resource reservation (scheduled) packet-mode protocols:

- Dynamic Time Division Multiple Access (Dynamic TDMA)

- Reservation ALOHA (R-ALOHA)

Where these methods are used for dividing forward and reverse communication channels, they are known as duplexing methods, such as:

- Time division duplex (TDD)

- Frequency division duplex (FDD)

Modulation: The process of varying a carrier signal, typically a sinusoidal signal, in order to use that signal to convey a message signal and transfer it over an analog bandpass channel. Analog and digital modulation facilitate frequency division multiplex (FDM), where several low pass information signals are transferred simultaneously over the same shared physical medium, using separate bandpass channels.

Analog modulation: The aim of analog modulation is to transfer an analog lowpass message signal, for example an audio signal or TV signal, over an analog bandpass channel, for example a limited radio frequency band or a cable TV network channel. Example of analog modulation methods are:

- Amplitude modulation (AM)

- Frequency modulation (FM)

- Phase modulation (PM)

- Qaudrature modulation (AM), where a cosine and a sine carrier wave of the same frequency are modulated by two channels, the inphase message signal (I) and the Quadrature phase message signal (Q) and sumarized. This results in a combination of AM and PM.

Digital modulation: The aim of digital modulation is to transfer a digital bit stream over an analog bandpass channel, for example over the public switched telephone network (where a filter limits the frequency range to between 300 and 3400 Hz) or a limited radio frequency band. An analog carrier signal is modulated by a digital bit stream. This can be described as a form of analog-to-digital conversion. The changes in the carrier signal are chosen from a finite number of alternative symbols (the modulation alphabet).

Example of digital modulation methods are:

- Frequency Shift Keying (FSK), where a finite number of frequencies are used, typically two frequencies.

- Amplitude Shift Keying (ASK), where a finite number of frequencies are used, typically two amplitudes.

- Phase shift Keying (PSK), where a finite number of phases are used for example two (2PSK = BPSK = Binary PSK), 4 (4PSK = QPSK = Quadruple PSK), 8 (8PSK), 16 (16PSK), etc.

- Differential PSK (DPSK) and Differential QPSK (DQPSK). Not sensitive to constant phase shift.

- Continuous phase modulation (CPM), for example Minimum-shift keying (MSK) and Gaussian minimum-shift keying (GMSK). These can be seen as a mix of PSK and FSK.

- Quadrature Amplitude Modulation (QAM), for example 8QAM, 16QAM, etc.

- Orthogonal Frequency Division Multiplexing (OFDM), also known as Discrete Multitone (DMT).

Each of these phases, frequencies or amplitudes are assigned a unique pattern of binary bits. Usually, each phase, frequency or amplitude encodes an equal number of bits. This number of bits comprises the symbol that is represented by the particular phase.

If the symbol alphabet consists of M = 2^N alternative symbols, each symbol represents a message consisting of N bits. If the symbol rate (also known as the baud rate) is f_S symbols/second (or baud), the data rate is Nf_S bit/second.

In the case of QAM, an inphase signal (the I signal, for example a cosine waveform) and a quadrature phase signal (the Q signal, for example a sine wave) are amplitude modulated with a finite number of amplitudes. It can be seen as a two channel system. The resulting signal is a combination of PSK and ASK, with a finite number of at least two phases, and a finite number of at least two amplitudes.

In the case of PSK, ASK and QAM, the modulation alphabet is often conveniently represented on a constellation diagram, showing the amplitude of the I signal at the x-axis, and the amplitude of the Q signal at the y-axis, for each symbol.

PSK and ASK, and sometimes also FSK, can be generated and detected using the principle of QAM. The I and Q message signals can be combined into a complex valued signal called the equivalent lowpass signal or equivalent baseband signal. This is a representation of the real valued modulated physical signal (the so called passband signal or RF signal).

These are the general steps used by the modulator to transmit data:

Group the incoming data into codewords;
Map the codewords to attributes, for example amplitudes of the I and Q signals (the equivalent low pass signal), or frequency or phase values.
Apply pulse shaping and/or other filtering to limit the bandwidth and form the spectrum, typically using digital signal processing.
Digital-to-analog conversion (DAC) of the I and Q signals. Sometimes the next step is also achieved using DSP, and then the DAC should be done after that.
Pulse-amplitude modulate (multiply) the high-frequency sine and cosine carrier waveform by the I and Q signals, resulting in that the equivalent low pas signal is frequency shifted into a modulated passband signal or RF signal.
Amplification and analog bandpass filtering to avoid harmonic distortion and periodic spectrum.

At the receiver, the demodulator typically performs:

Bandpass filtering
Automatic gain control, AGC (to compensate for varying attenuation)
Frequency shifting of the RF signal to baseband I and Q signals, or to an intermediate frequency (IF) signal.
Sampling and analog-to-digital conversion (ADC). (Sometimes before the above point.)
Filtering, for example equalization (channel-adaptive filtering).
Detection of the amplitudes of the I and Q signals, or the frequency or phase of the IF signal;
Quantization of the amplitudes, frequencies or phases to the nearest allowed values, using mapping.
Map the quantized amplitudes, frequencies or phases to codewords (bit groups);
Parallel-to-serial conversion of the codewords into a bit stream
Pass the resultant bit stream on for further processing such as removal of any error-correcting codes.

Orthogonal Frequency Division Multiplex (OFDM), essentially the same thing as Coded OFDM (COFDM) and Discrete multit-tone mulation (DMT), is based on the idea of Frequency Division Multiplex (FDM), but is utilized as a digital modulation scheme. The bit stream is split into several parallel data streams, each transferred over its own sub-carrier using some conventional digital modulation scheme. The sub-carriers are summarized into an OFDM symbol. The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions — for example, multipath and narrowband interference — without complex equalization filters. Channel equalization is simplified because OFDM may be viewed as using many slowly-modulated narrowband signals rather than one rapidly-modulated wideband signal.

Capacity and performance of a communication system

Bandwidth: May denote one of the following:

- Analog bandwidth in Hertz (Hz) of a signal or communication channel. Measured in Hertz (Hz). In case of a baseband channel or baseband signal, the bandwidth is equivalent to the upper cut-off frequency of the signal spectrum or the lowpass filter. In case of a passband signal, it is the upper cut-off frequency minus the lower cut-off frequency of the signal spectrum or the bandpass filter.

- Digital bandwidth consumption in bit/s. Proportional to the analog bandwidth of the signal. This may be equivalent to the raw bitrate (inclusive of forward error correction codes, synchronization and other physical layer protocol overhead), net bit rate (exclusive of forward error correction codes), throughput, or goodput.

- Channel capacity in bit/s. Maximum possible net bit rate. Can be calculated by the Shannon-Hartley formula for a certain analog channel bandwidth and signal-to-noise ratio.

Latency – Delay from transferring a message. It may include:

- Transmission delay – time from the first until the last bit of a message or packet has left the transmitter. (Message or packet length in bits divided by the bit rate.)

- Propagation delay – time from the message haft left the transmitter until it has reached the receiver.(Distance divided by the propagation speed).

- Packet queuing delay in store-and-forward packet mode nodes.

- Protocol overhead, caused by flow control, congestion avoidance, automatic repeat request retransmissions, etc.

- Processing delay, due to slow electronic circuits, etc.

Bit Error Rate (BER) is the percentage of bits with errors divided by the total number of bits that have been transmitted, received or processed over a given time period.

Symbol Error Rate (SER) is the percentage of the modulated symbols with errors divided by the total number of symbols that have been transmitted, received or processed over a given time period.

Packet Error Rate (PER) is the percentage of the data packets that are affected by at least one bit error.

Channel impairments

Noise - Fluctuations in and the addition of external factors to the stream of target information (signal) being received at a detector.

White Noise - Statistically random radio noise characterized by a wide frequency spectrum with a constant spectral density N₀ (expressed as W/Hz) over a specified frequency band. If the noise signal is sampled (time discrete), consequtive samples are independent, i.e. non-correlated.

Noise power spectral density N₀. Expressed as W/Hz, watts per hertz of bandwidth. If the noise is white, the noise power is N = N₀B, where the B is the bandwidth.

Additive Gaussion White Noise (AWGN) channel – A communication channel model where the only impairment is linear addition of white noise with Gaussian distribution of voltage or current values. Wideband Gaussian noise comes from many natural sources, such as the thermal vibrations of atoms in antennas (referred to as thermal noise or Johnson-Nyquist noise), black body radiation from the earth and other warm objects, cross-talk from and from celestial sources such as the sun. Sometimes interference (crosstalk) from wideband signal sources, for example radio transmitters, is included in the noise concept.

Signal-to-noise ratio (SNR) - the power ratio between a signal (useful information) and the background noise:

S/N = Signal power / Noise power

= (Signal RMS voltage/ Noise RMS voltage)²

SNR in dB = 10 log₁₀(S/N)

= 20 log₁₀ (Signal RMS voltage/ Noise RMS voltage)

Carrier-to-noise ratio (CNR). Often the equivalent to the SNR. Used to analyze a modulated signal. C/N = carrier power / Noise power. CNR in dB = 10 log₁₀ (C/(I+N))

Co-channel interference – cross-talk between transmitters sending at the same frequency channel.

Carrier-to-interference and noise ratio (CINR): Includes co-channel interference. C/(I+N) or in dB 10 log₁₀ (C/(I+N)). Often equivalent to SNR.

E_b/N_o – Energy per bit per noise power spectral density: A normalized CNR measure, often used when comparing the bit error rate (BER) of different modulation methods without taking the bit rate or bandwidth into consideration. See the example below.

The CNR can be calculcated as follows:

where R is the bitrate in bit/s and B is the channel bandwidth in Hertz.

E_s/N_o – Energy per symbol per noise power spectral density. A normalized measure of the CNR. Similar usage as E_b/N_o.

BERTool – a graphical user interface (GUI) in Matlab that enables you to analyze BER vs E_s/N_o performance of a communications links. via simulation-based, semianalytic, or theoretical approach.

Phase Noise – variation of the channel phase shift. May be caused by variating multi-path propagation, Doppler shift and synchronization problems between the sender and receiver local oscillators.

Forward error correction (FEC): Is a method of obtaining error control in data transmission in which the source (transmitter) sends redundant data and the destination (receiver) recognizes only the portion of the data that contains no apparent errors.

Block Coding: Is the technique by which the encoder intersperses parity bits into the data sequence using a particular algebraic algorithm.

Convolutional code: Is the process of encoding intersperses parity bits into the data sequence in symbol streams of arbitrary length.

Error detection: Is the ability to detect errors that are made due to niose or other impairments in the course of the transmission from transmitter to receiver

Code Rate = Message length(K)/Code word length(N)

N=2^M -1, where M>=3 and K= N – M

Cyclic Redundancy Check (CRC): It is a type of hash function used to produce a checksum error detection code - which is a small, fixed number of bits - against a block of data, such as a packet of network traffic or a block of a computer file.

Cyclic Redundancy Check (CRC): An error checking technique used to ensure the accuracy of transmitting digital data. CRC Block Generator is used to achieve this function in Simulink.

Scrambler – In telecommunications, a scrambler is a device that transposes or inverts signals or otherwise encodes a message at the transmitter to make the message unintelligible at a receiver not eq>uipped with an appropriately set descrambling device.

Samples, Frames and events

Multirate models = A model that contains signals with different sample times.

A Frame is a sequence of samples combined into a single vector

Sample time = Updating a signal integer multiples of a fixed time interval called the sample time

Samples per frame = How many samples each frame contains.

Sample time = Frame period / Samples per frame

In frame-based processing all the samples in a frame are processed simultaneously.

In sample-based processing samples are processed one at a time.

Signals

A signal is a function representing some variable that contains some information about the behavior of a natural or artificial system.

Scalability - Spectrum’s software reconfigurable platforms

Spectral Analysis:- The goal of spectral estimation is to describe the distribution (over frequency) of the power contained in a signal, based on a finite set of data.

Bandwidth:- Compute the frequency response bandwidth, or Bandwidth is the name for the frequency range that a signal requires for transmission, and is also a name for the frequency capacity of a particular transmission medium.

Sampling is the process of converting continuous data into discrete data.

Sample refers to a value or set of values at a point in time and/or space

The sampling theorem is written as follows:

$\int_{-\infty}^\infty f(t)\delta(t - \alpha) dt = f(\alpha)$

using this theory, we can extract a single value from a continuous function by mulitplying with an impulse, and then integrating.

Quantization:-

The conversion from an infinitely precise amplitude to a binary number is called quantization.´

Sampling frequency or Sampling rate

The sampling frequency or sampling rate defines the number of samples per second taken from a continuous signal to make a discrete signal.

Continuous signal or a Continuous time signal

A continuous signal or a continuous time signal is a varying quantity (a signal) that can be, or is expressed, as a continuous function of an independent variable, usually time.

discrete signal

A discrete signal is a signal that has been sampled from a continuous signal. Unlike a continuous signal, a discrete signal is not a continuous function but a sequence.

Source Coding:-

Source coding, also known as quantization or signal formatting, is a way of processing data to reduce redundancy or prepare it for later processing.

LF = Low Frequency sonar system, operating from 60 kHz to 120 kHz.

HF = High Frequency sonar system, operating from 135 kHz to 200 kHz.

Pulse: A precisely characterized transmission of acoustic energy from a transducer. A short burst of sound at the operating frequency of the sonar (Echoview glossary).

Recorded Signal: A time-series of acoustic energy recorded for a specific duration of time by the transducer immediately following the transmission of a pulse.

Maximum Response Axis (MRA) - The MRA (or acoustic axis, or beam axis) of a beam is defined as the direction in which the acoustic response has its maximum value.

Spectrum Viewer for estimating and analyzing a signal's power spectral density (PSD).

Filtering and FFTs

There are two types of filters in the digital realm: Infinite Impulse Response (IIR) filters, and Finite Impulse Response (FIR) filters.

1.1 FIR Filters

FIR filters, which are conceptually the easiest to understand and the easiest to design. However, FIR filters suffer from low efficiency, and creating an FIR to meet a given spec requires more hardware then an equivalent IIR filter. FIR filters have no feedback elements in the filters.

1.2 IIR Filters

IIR filters are harder to design then the FIR filters, but the benefits are extraordinary: IIR filters are an order of magnitude more efficient then an equivalent FIR filter. even though FIR is easier to design, IIR will do the same work with fewer components, and fewer components translate directly to less money. IIR filters differ from FIR filters because they contain feedback elements in the circuit, which can make the transfer functions more complicated to work with.

Digitizing, or Digitization

Digitizing, or digitization, is the process of turning an analog signal into a digital representation of that signal

Anti-Aliasing Filter

An anti-aliasing filter is commonly used in conjuction with digital signal processing and is a filter to restrict the bandwidth to approximately satisfy the Shannon-Nyquist sampling theorem.

e hertz is defined as one cycle per second. => 1 Hz = 1 s⁻¹

1.3 SI multiples

Multiple	Name	Symbol	Multiple	Name	Symbol
10⁰	hertz	Hz
10¹	decahertz	daHz	10^–1	decihertz	dHz
10²	hectohertz	hHz	10^–2	centihertz	cHz
10³	kilohertz	kHz	10^–3	millihertz	mHz
10⁶	megahertz	MHz	10^–6	microhertz	µHz
10⁹	gigahertz	GHz	10^–9	nanohertz	nHz
10¹²	terahertz	THz	10^–12	picohertz	pHz
10¹⁵	petahertz	PHz	10^–15	femtohertz	fHz
10¹⁸	exahertz	EHz	10^–18	attohertz	aHz
10²¹	zettahertz	ZHz	10^–21	zeptohertz	zHz
10²⁴	yottahertz	YHz	10^–24	yoctohertz	yHz

Sequence generators

To generate sequence of bits as an input or source of our model we can use sequence generators.

Pseudoramdom sequences

Following blocks generate PN (pseudonoise sequences)

Gold sequence generator , kasami sequence generator and PN sequence generator.

Synchronization codes

The Barker Code Generator block generates Barker codes to perform synchronization. Barker codes are subsets of PN sequences.

Orthogonal codes

Orthogonal codes are used in systems in which the receiver is perfectly synchronized with the transmitter

Gaussian noise

Rayleigh noise

Rician noise

Different type of noises in the channel

SAMPLE TIME

For sample based signals it is the time interval between successive updates of the signal. For frame based matrix signals it is the time interval between successive rows of frame based matrix.

Seed

It is the initial value for a random sequence generator (recommended to use a prime number greater than 30)

Eye diagram

It is a tool to represent intersymbol interference and other impairments in digital transmision.

Scatter diagram
A scatter plot of a signal plots the signal value at its dicision points. The decision points is the one where signal parameter(like strenght, direction, frequency, amplitude) changes

Trajectory diagram
We can plot the points on a two dimentional graph which is some times called trajectory diagram.

Error rate

Errors occuring per second in the channel.