Purpose of writing this report, is to describe about
high speed, single carrier digital communication system. The author has
mentioned about processing blocks of signals which remove interference with
help of Fast Fourier Transforms. He has described how single carrier modulation
(SCM) is being used again to remove barriers from digital communication system.
Author has made comparison between SCM and orthogonal frequency division multiplexing
(OFDM), which is multicarrier modulation system.
SCM is again rising as an effective alternate to
OFDM, and its reason is implementation of nonlinear equalizer structure in
frequency domains. To form a nonlinear equalizer, liner filter and canceller are
used in intersymbol infrastructure. Author has used equalizer as receiver which
brings capacity of SCM equal to OFDM in highly dispersive channels. Author has
mentioned impact of SCM transmission on frequency offset, diffusion because of
high power amplifiers and noise etc.
Overview
of Nonlinear Equalization Methods:
Equalization is reimbursement for linier distortion
that takes place due to selection of channels of different frequencies. This is
very important component for a digital communication system whose data symbol
rate is much higher than typical channels bandwidth. Linear filtering equalizer is used form last
many years to mitigate serial data transmission. In dispersive channels it gives
ideal performance by removing interference and noise distortion in terms of
errors. With guidance of nonlinear structure other types of equalizers are also
developed. Decision feedback equalizer (DFF), in which first transversal filter
reduces precursor at detection point, and then detect past data symbols to
remove other errors as well by using canceller.
Author has used nonlinear structure to detect data
symbol, but DFE is difficult to analyze. Its performance is far better than
other equalizers, and it can easily compete with optimum sequence detectors.
Blocks of signals which are using DFT work better; they provide lower complexity
per data and due to this DFT is today preferred for next generation broadband
wireless system. Author has proposed it for new wireless systems because it can
provide bit rates of hundreds of megabits.
SCM which work with serial fashion data symbol
transmitters are oldest format used for digital communication. Against this
liner transmission, as an alternate to it multicarrier transmission was
introduced. This transmits multiple data streams, each of them construct a
narrow waveform in order to separate all factors. Author has mentioned that
this kind is popular from last two decades because of its brilliant performance
in controlling data symbol rates of coherence bandwidths. Links generated with
this carrier result as flexible and easily adoptable by other factors.
For the first time KATHRYN used DFT as sender and
receiver with realization of benefits from linear system. Author also described
that how they implement DFT with multicarrier signals and gets better results. This
result as increase in wireless and wired system data rates, and people then
demanded better results. Author has used different multicarrier transmissions
in accordance to demand. It was used in digital subscriber line transmission
standards, IEEE 802.11a wireless LAN and digital audio and
video broadcast standards. At that time OFDM got success within days, and then
these processing techniques were used to facilitate SCM systems. Author has
mentioned that this new combination leads us towards nonlinear frequency domain
equalizers.
SCM waveforms give strength to signal power and it’s
used with DFE improved performance level again. Range of amplitude and peak to
average ratio was recorded as less then multicarrier signals which improved its
transmitted spectra and level of power. It is also cheaper and more efficient
mode to transmit signals with best robustness to frequency. Today SCM is not
used a replacement tool, instead it is used as a complement with OFDM.
International Mobile Telecommunications Advanced is getting benefits through
these initiatives. Author has used all this data at time of writing this report
when standards were not finalized but they were being considered for purpose of
uplink.
Further in this report author has mentioned about
wireless mobile transmission, its circular and linear convolutions, methods to
generate signals with improved signal strength, better methods for equalization
and systems to compare performance of extensions. All these factors are
computed with proper calculations and figures, to obtain best and accurate
results.
Pros:
1. Single
carrier modulation have hardware implementation advantage over multicarrier
2. Its
beneficial to use for low power and low cost user wireless terminals
3. It
reduce complexities due to time to time domain implementations
4. SCM
has advantage of lower peak to average power ratio
5. It
can be extended to multi antenna system easily
Cons:
1.
It is not suited with download
transmission
2.
It cannot obtain channel stare
information form user terminal receivers
3.
SCM does not provide with same
spectral efficiency
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