block 3 unit 5
(Frequency shift keying) FSK
Changes the frequency (how often in a second) of the analog signal carrying the data and this increases or decreases depending on whether the binary data is a zero or one.
Amplitude shift keying (ASK)
Changes the voltage level to represent the binary bit of one while the frequency and phase stay constant.
mobile station
Consists of the mobile equipment and a smart card called the subscriber identity module (SIM).
GSM
Digitizes and compresses data, then sends it down a channel, each of these channels is divided into 8 time slots.
amplitude frequency phase
During the modulation process, the analog signal is modified to represent the digital information by altering one of three characteristics:
BTS ( Base transceiver station )
Houses the radio transceivers that defines a cell and handles the radio link protocols with the mobile station (cell phone)
amplitude modulation
If the amplitude of the output frequency (carrier)) is changed by the amplitude of the input signal (intelligence), that process is known as
CDMA wimax WLAN satellite DVB cable modem
QPSK can be seen inmultiple system applications
Bandwidth
In electronic communications, ____________ is the width of the range (or band) of frequencies that an electronic signal uses on a given transmission medium. In this usage, bandwidth is expressed in terms of the difference between the highest-frequency signal component and the lowest-frequency signal component
Symbol
Referred to as a waveform change or signaling even. Each symbol can represent one bit of data, but it can also represent several bits of data.
spread spectrum
Is a method in which electromagnetic energy in a particular bandwidth is spread across the frequency domain, resulting in a signal with a wider bandwidth. This technique is used to establish secure communications and to increase resistance to natural interference and jamming.
BSC (Base station controller)
Is the connection between the mobile station and network substystem.
Pulse code modulation (PCM - digital conversion process)
One of the largest concerns in communications systems is the conversion of an analog signal to a digital signal.
Phase shift keying (PSK)
A digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave). It uses a process called phase modulation.
DAMA (demand assigned multiple access)
A technique used to assign satellite channels on a per-request basis.
BPSK (binary phase shift keying)
A very popular digital modulation scheme. ____, shifts phases of the carrier sine wave 180 degrees for each change in binary state. Every time the binary bit of the intelligence changes from a "0" to a "1" or from a "1" to a "0", the phase of the carrier signal changes 180 degrees. Therefore the state of each bit is determined according to the state of the preceding bit. If a series of bits are the same, the phase of the wave will not change. However if the state changes so will the phase of the wave change by 180 degrees.
Bit rate
An important factor in determining computer efficiency because it's a measure of how long it takes a computer to process information.
ASK
As the signal travels down the it can encounter interference from the voltages that the line itself is carrying inadvertently changing the one to a zero a zero to a one. This interference is known as "noise" and ___ is very susceptible to this type of interference.
QPSK BPSK
BPSK vs QPSK ____ can either be used to double the data rate compared with a ____ system while maintaining the same bandwith of the signal or to maintain the data-rate of BPSK but halving the bandwith needed.
modulation
Based on what characteristic is caused to change
Quantizing
Second step in PCM. it is the process of assigning a decimal value to each voltage level (amplitude) created in the sampled signal.
Return channel Control order wire (RCCOW)
Slot provides limited transmit system and control information from the subscriber to the channel controller.
mobile station base station network subsystem
The GSM network can be divided into three parts
SIM
The ___ is a detachable smart card contains the users subscription information. This allows the user to retain their information after switching terminals.
Base Station
The ____ _____ is composed of two parts Base transceiver station (BTS) Base controller station (BSC)
DAMA
The _____ network takes a single 25kHz channel and breaks it up into a time division multiple access format which allows a number of users onto a singl channel simultanesouly. It is predicted to be the satellite communications network of the future. Rather than putting up more satellites, DAMA allows for better use of the existing satellite resources.
BSC (Base station Controller)
The base station controller manages one or more BTS.
sampling
The first step in PCM.
samples
The more _________ taken across the same timeframe the more accurate the receiving modem can reconstruct the original signals.
phase Phase modulation
The most common way to modulate is to change the _____ of the output signal, this is called ______ ______________
advantages of digital technology
The recording doesn't degrade over time. As long as the numbers can be read, you will always get exactly the same wave. Groups of numbers can often be compressed based on patterns. Special computers called digital signal processors (DSPs) can be used to easily process and modify number streams.
ASK
The simplest and most common form of ASK operates as a switch, using the presence of a carrier wave to indicate a binary one and its absence to indicate a binary zero. This type of modulation is called on-off keying (OOK), and is used at radio frequencies to transmit morse code (referred to as continuous wave operation.
Encoding
The third step in the PCM process. It is simply changing the decimal values of each quantum step into a binary. Several PCM streams could be multiplexed into a larger combined data stream used by many time division multiplexers.
symbol
The type of modulation used can determine bits per _______
BPSK (binary phase shift keying) QPSK (quadrature phase shift keying)
There are several types of phase shift keying varying in complexity. One method is ____, another is ____.
sampling
To accurately reconstruct a digitized analog signal, the original analog signal must be sampled at a rate at least twice as high as the highest radio FREQUENCY.
Bandwidth
Used as a synonym for data transfer rate; the amount of data that can be carried from one point to another in a given time period (usually a second). this kind of bandwidth is typically expressed in bits of data per second (bps).
frequency modulation
When the frequency of the output signal is changed by the intelligence (input signal)
FSK
a receiving device looks for specific frequency changes to decode a signal and ignores the voltage spikes caused by noise interference; therefore it is far less susceptible to noise interference from the line.
analog signal
an ________ ________'s amplitude is constantly changing and can be one of an infinite number of amplitude values at any given instant. This uncertainy as to what the value will be is referred to as INDISCRETE. The amplitude is constantly changing over the time of the cycle.
DAMA
assigns a pair of available channels based on a request from a user. Once the call is completed, the channels are returned to the pool for use by another user.
QPSK
can be used either to double the data rate compared with a BPSK system while maintaining the same bandwidth of the signal, or to halve the bandwidth needed while maintaining the data-rate of BPSK.
digitalization
conversion of an analog signal to a digital form is called __________________ and in most long-haul (long distance) digital communications systems, analog signals are digitized by PCM.
(Amplitude shift keying) ASK (Frequency shift keying) FSK (Audio frequency-shift keying) AFSK
digital modulation techniques
symbol
each ________ can represent one bit of data, but it can also represent several bits of data.
Digital signal
has limited and finite values also called DISCRETE values.
CDMA
in ____ special code schemes allow multiple users to be multiplexed over the same physical channel. Each user in a CDMA system uses a differernt code to modulate their signal.
analog technology
in _________ _____________ a wave is recorded or used in its original form.
DAMA
increases the number of users in a pool of satellite channels available to any station in a network. It is assumed that not all users will need access to the same communications channel simultaneously.
CDMA (Code division multiple access)
is a channel access method utilized by various radio communication technologies. CDMA employs spread spectrum technology.
PCM
is a method of converting an analog signal into a digital format
QPSK
is bandwidth efficient as each symbol represents two bits. It converts two binary bits, represented simultaneously at the input, to the complex signal which selects one of the four phases based on the two binary digits.
QPSK (quadrature phase shift keying)
is bandwidth efficient as each symbol represents two bits. It converts two binary bits, represented simultaneously at the input, to the complex signal which selects one of the four phases based on the two binary digits.
digital signal
is either a logic high or logic low, on or off, current or no currnt. It is divided up into short elements called bits. TTY teletype and computer data signals are usually expressed in this form.
DAMA
is often used in military environments due to the relatively simple implementation, ease of modeling and the fact that military usage profiles are a very good fit. In military SATCOM it has the added advantage that it can function in a bent pipe (frequency amplification) environment, thus requires no special security or coordination hardware on the satellite. This allows the master and secondary ground stations to be upgraded repreatedly to change or improve security and compression without requiring an expensive satellite replacement.
Phase modulation
is the method of modulation in which the amplitude of the modulated wave remains constant, but varies the phase of the carrier wave based on the amplitude of the modulating signal.
Symbol Rate
is the number of symbol changes made to the transmission medium per second using a digitally modulated signal. A symbol ratae is measred in baud (Bd).
Ranging time slot
is the time during which the users equipment determines the range between the user terminal and the satellite to set the transmitter synchroninzation required for timing
Link test slsot
is used to evaluate the performance of the satellite link.
Bit Rate
measure of throughput or rate of data transfer and represents the number of bits that are transmitted within a second and it is measured in bits per sonds (bps or b/s)
modulation
modifying the characteristics of one waveform with the variations in another signal.
GSM networks
operate in 4 different frequency ranges. Most networks operate in the 900MHz or 1800 MHz bands; however the US uses the 850 MHz and 1900Mhz bands because the 900 MHz and 1800 frequncy bands are already allocated.
sampling
process generates DISCRETE voltage samples representing the amount of amplitude in the signal at the time the sample was taken.
Network Subsystem
provides the connection to the fixed networks. The central component of the network subsystem is the Mobile Switching Center (MSC). It provides all the functions needed to handle a mobile subscriber, such as registration, location updating, handovers and call routing.
intelligence
relates to the input signal
carrier
relates to the output frequency
CCOW (Channel control order wire)
slot is used to transmit system timing and control information from the channel controller to subscriber unit.
Data time
slots are the time slots during which users transmit or receive data. The number of circuits in each group depends on the data rate and the transmission rate of the satellite link.
DAMA
the ____ multiplexed data stream is divided into frames with each frame being 1.386 seconds long. Each frame is subdivided into time slots. Most of the DAMA frame formats are derived from this basic format.
GSM (global system for mobile communication)
the most popular standard for mobile phones in the world and uses a form of air interface called time division multiple access (TDMA).
BTS (Base transceiver station) BSC (Base station controller)
two parts of the base station
DAMA
typically a single hop satellite transmission network that allows direct connection between any two computers in a network.
QPSK
uses two bianry bits for a combination of four binary possibilities, each related to a 90 degree phase of the signal.
BPSK
when modulating a ____ signal, a transceiver can process data at 1 bit per symbol, but is not as susceptible to noise as ASK