Digital modulation schemes transform
digital signals like the one shown below into waveforms that are compatible
with the nature of the communications channel.
There are two major categories of digital
modulation. One category uses a constant amplitude carrier and the other
carries the information in phase or frequency variations (FSK, PSK). The other
category conveys the information in carrier amplitude variations and is known
as amplitude shift keying (ASK).
The past few years has seen a major
transition from the simple amplitude modulation (AM) and frequency modulation
(FM) to digital techniques such as Quadrate Phase Shift Keying (QPSK),
Frequency Shift Keying (FSK), Minimum Shift Keying (MSK) and Quadrate Amplitude
Modulation (QAM).
For designers of digital terrestrial
microwave radios, their highest priority is good bandwidth efficiency with low
bit-error-rate. They have plenty of power available and are not concerned with
power efficiency. They are not especially concerned with receiver cost or complexity
because they do not have to build large numbers of them.
On the other hand, designers of hand-held
cellular phones put a high priority on power efficiency because these phones
need to run on a battery. Cost is also a high priority because cellular phones
must be low-cost to encourage more users.
Accordingly, these systems sacrifice
some bandwidth efficiency to get power and cost efficiency. Every time one of
these efficiency parameters (bandwidth, power or cost) is increased, another
one decreases, or becomes more complex or does not perform well in a poor
environment. Cost is a dominant system priority. Low-cost radios will always be
in demand.
In the past, it was possible to make a
radio low-cost by sacrificing power and bandwidth efficiency. This is no longer
possible. The radio spectrum is very valuable and operators who do not use the
spectrum efficiently could lose their existing licenses or lose out in the
competition for new ones. These are the tradeoffs that must be considered in
digital RF (Radio Frequency) communications design. If you understand the
building blocks, then you will be able to understand how any communications
system, present or future, works.
HDMI Encoder Modulator,16in1 Digital
Headend, HD RF Modulator at Soukacatv.com
SKD3013 3 Channel HD Encode Modulator
SKD121X Encoding & Multiplexing Modulator
SKD19 Series 1U Rack 12CH Encode Modulator
Household Universal Encoding & Modulation Modulator
Why
use Digital Modulation?
The move to digital modulation provides
more information capacity, compatibility with digital data services, higher
data security, better quality communications, and quicker system availability.
Developers of communications systems face these constraints:
available bandwidth
permissible power
inherent noise level of the system
The RF spectrum must be shared, yet every
day there are more users for that spectrum as demand for communications
services increases. Digital modulation schemes have greater capacity to convey
large amounts of information than analogue modulation schemes. The Fundamental
Trade-off:
Industry trends over the past few years a
major transition has occurred from simple analogue Amplitude Modulation (AM)
and Frequency/Phase Modulation (FM/PM) to new digital modulation techniques.
Examples of digital modulation include:
FSK (Frequency Shift Keying)
QPSK (Quadrature Phase Shift Keying)
QAM (Quadrature Amplitude Modulation)
MSK (Minimum Shift Keying)
Now that we understand the basic principles
of modulation you should be ready to take the first tutorial.
Established in 2000, the Soukacatv.com main
products are modulators both in analog and digital ones, amplifier and
combiner. We are the very first one in manufacturing the headend system in
China. Our 16 in 1 and 24 in 1 now are the most popular products all over the
world.
For more, please access to
https://www.soukacatv.com.
CONTACT
US
Company:
DingShengwei Electronics Co., Ltd
Address:
BldgA,the first industry park of Guanlong, Xili
Town,Nanshan,Shenzhen,Guangdong,China
Tel: +86
0755 26909863
Fax: +86
0755 26984949
Mobile:
13410066011
Email:
ken@soukacatv.com
Website:
https://www.soukacatv.com
Source: ukessays
没有评论:
发表评论