Decrease interference using adaptive modulation and coding

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Decrease interference using adaptive modulation and coding. This paper was prepared as simulation study of interference decreasing using AMC algorithm where a comparison between ordinary modulation techniques is compared to Multicarrier Modulation MCM and adaptive modulation, results of the simulation was observed and compared for above scenarios.
International Journal of Computer Networks and Communications Security
VOL. 3, NO. 9, SEPTEMBER 2015, 378–383
Available online at: www.ijcncs.org
E-ISSN 2308-9830 (Online) / ISSN 2410-0595 (Print)
Decrease Interference Using Adaptive Modulation and Coding
Osman Mudathir Elfadil1, Y. M. Alkasim2 and Rayan. A. Ali3
1, 2, 3 Department of Electrical and Electronics Engineering, Omdurman Islamic University
E-mail: 1osman7677@yahoo.com, 2yasserm89@hotmail.com, 3eng.ray2014@gmail.com
ABSTRACT
The limitations of channel bandwidth, time varying channel and fading are significant and fundamental
problem in wireless communication, which leads to the difficulty of providing high Quality of Service. The
traditional wireless communication systems are designed to provide good quality of services at the worst
channel conditions. Wherein any attempts to increase the channel bandwidth, interference arises along with
these attempts.
And result in inefficient utilization of the full channel capacity. One of the efficient
techniques to overcome to these problems is known as adaptive modulation and coding (AMC). This paper
was prepared as simulation study of interference decreasing using AMC algorithm where a comparison
between ordinary modulation techniques is compared to Multicarrier Modulation MCM and adaptive
modulation, results of the simulation was observed and compared for above scenarios.
Keywords: MCM, SCM, OFDM, AMC, BER, AWGN, Rayleigh.
1
INTRODUCTION
block diagram and model the received signal and
Communication bandwidth is the range of
frequencies passed by a wireless or wired medium,
the bitrate supported is generally proportional to the
bandwidth, and spectral efficiency is the ratio of
bitrate to bandwidth. On these media spectral
efficiency is limited by interference. In wireless
measured SNR for feedback purposes. The
simulation was introduced in section 4 with
simulation parameters and flow chart for AMC
algorithm achieved, results obtained from the
simulation was introduced and compared in figures
and tables. The conclusion of the paper in section 5.
radio any user’s communications typically share the
same radio channel one user’s communication
2
MULTI CARRIER MODULATION
becomes unwanted interference to another user’s
legitimate communication user’s cannot simply
increase their transmitted power to overcome this
interference because is increase interference as
much as the wanted signal. One of the promising
approaches to 4G is adaptive OFDM (AOFDM). In
AOFDM, adaptive transmission scheme is
employed according to channel fading condition
with OFDM to improve the performance.
In this paper we consider the use of AMC to
decrease the interference and enhance data rate and
bit error rate performance. The paper lies in five
sections. In section 2 SCM is compared to MCM
and investigating MCM and OFDM as MCM which
maximum spectral efficiency obtained due to the
use of orthogonality. Section 3 contains AMC
In this section, multi carrier modulation has been
discussed. In single carrier modulation, data is sent
serially over the channel at a bound rate of
symbols per second. The data is then 1/ . The
time dispersion can be significant compared to the
symbol period, in a multipath fading channel which
results in inter symbol interference ISI. A complex
equalizer is then needed to compensate for the
channel distortion.
The basic idea of multicarrier modulation is
available bandwidth is divided into a number of
of sub bands, commonly called subcarriers, each
of width ∆ = , as shown in fig. 1 the band width
in single carrier modulation compared to MCM.
379
O. M. Elfadil et. al/ International Journal of Computer Networks and Communications Security, 3 (9), September 2015
impossible as a consequence the coherence time of
the channel defines an upper bound for the number
of subcarriers, together with the condition for flat
fading with in the sub bands a reasonable range for
can be derived as / ≪ ≪ .
To
assure
a
high
spectra
efficiency,
the
sub
channel waveforms must have overlapping transmit
Fig. 1. SCM and MCM frequency spectra.
spectra. They need to be orthogonal for enabling
Instead of transmitting the data symbols in serial
way, at a bound rate , a multicarrier transmitter
partitions the data stream into blocks of data
symbols that are transmitted in parallel by
modulating the carrier. The symbol duration for
a multicarrier scheme is = / , as shown in
Fig. 2.
In its most general form the multicarrier signal
can be written as set modulated carriers:
( ) = ∑ , ( − ) (1)
where , is the data symbol modulating the
subcarrier in the signaling interval, is the
waveform for the subcarrier.
The symbol duration can be made long compared
simple separation of these overlapping sub channels
at the receiver. MCM that fulfill these conditions
are called Orthogonal Frequency Division
Multiplexing OFDM system.
A general set of orthogonal waveforms, is given by:
( , ) = [0, ] (2)
0 ℎ
with = + ; = 0,1,…, − 1
The demodulation is based on this orthogonality
of the subcarriers and consists of a bank of
matched filters that implement the relation,
, = ∫( ) ( ) ( − ) (3)
Complete block diagram of OFDM system
shown in fig. 3. [1].
to the maximum excess delay of the channel,
or , by choosing sufficiently high. At
the same time the bandwidth of the sub bands can
3
ADAPTIVE MODULATION
be small compared to the coherence bandwidth of
the channel ( > / ).
Is a term used in wireless communications to
denote the matching of the modulation, coding and
other
signal
and
protocol
parameters
to
the
conditions on the radio link. Adaptive modulation
systems
invariably
require
some
channel
state
information
at
the
transmitter.
This
could
be
acquired
in
time
division
duplex
systems
by
assuming the channel from the transmitter to the
receiver is approximately the same as the channel
from the receiver to the transmitter. Alternatively,
the
channel
knowledge
can
also
be
directly
measured
at
the
receiver,
and
fed
back
to
the
transmitter.
Fig. 2. Multi Carrier Modulation Block diagram
The sub bands then experience flat fading, which
reduces equalization to a single complex multip-
lication per carrier.
Increasing thus reduces the ISI and simplifies
the equalizer into a single multiplication. However
the
performance
in
time
variant
channels
is
degraded by long symbols. If the coherence time
of the channel is small compared to , the
channel frequency response changes significantly
during transmission of one symbol and reliable
Fig. 3. Discrete time baseband equivalent model of an
OFDM system.
detection of the transmitted information becomes