Abstract
Relay assisted Multiple Input Multiple Output
transmission system (MIMO) are expected to be a part of future infrastructure
based wireless networks. Besides coverage extensions, such relays can posses
high transmission rates, higher speed and larger capacity than its
predecessors. MIMO opens a new dimension for wireless broadband communication,
mobile wireless access. In this paper we present the concept of a relay-assisted MIMO transmission system for
wireless communication, via conceptual study of
relay-assisted MIMO transmission system.
Introduction
It is
believed that next generation wireless network will adopt MIMO technology to
have higher speed and larger capacity than its predecessors [1]. MIMO opens
a new dimension for an effective communication. They can offer multiplexing
gains and diversity gain (robustness of
communication under undesirable channel effects) and are receiving much
attention nowadays thanks to their properties
for increasing the performance
of wireless communication.
It is expected that future wireless broadband
communication systems will operate beyond 5GHz, which relays on the use of
multiple antennas at transmitter/receiver side. It is a very promising
technique to mitigate the channel fading and thus improving the cellular system
capacity. However, it is capable of accomplishing what is undertaken it has to
face some problems, hence relay assisted
MIMO was proposed.
Relay
transmission has been identified as one of the core technologies that could
enable robust high speed information transfer over challenging wireless
environment [2]. By positioning the relays in between source and destination, it is possible to
benefit the transmission in terms of higher transmission rate and wider
coverage, due to such benefits, much research has been devoted in analyzing the
relay channel and realizing its
potential. MIMO system enhances the system’s performance by increasing the
number of relays between them. By replacing the multiple transmitters with
relay nodes, the system is able to achieve the more homogeneous power
distribution by reducing deployment and operational expenditures. Thus the goal
of relay assisted MIMO system is to increase the rank of compound channel
matrix, high throughput and link range without additional bandwidth. It
achieves this by higher spectral efficiency and link reliability. In this paper
we present, a conceptual study of relay-assisted MIMO system in detail.
MIMO
MIMO is an antenna array technology for wireless communication in which multiple antennas are used at both
source and destinations . Antenna array technology is the use of
multiple antennas at the transmitter or the receiver. Antennas at each end of the communications
circuit are combined to minimize errors and optimize data speed. MIMO is one of
several forms of smart antenna technology. By configuring
multiple antennas at both the transmitting and receiving side, the channel
capacity may be improved proportionally to the minimum number of antennas at
the transmitter and the receiver.
In conventional wireless communications,
a single antenna is used at the source, and another single antenna is used at
the destination. In some cases, this gives rise to problems with multipath
effects. When an electromagnetic field is met
with obstructions such as hills, canyons, buildings, and utility wires,
the wave fronts are scattered, and thus they take many paths to reach the
destination. The late arrival of scattered portions of the signal causes
problems such as fading, cut-out and intermittent reception. In digital communications
systems such as wireless Internet, it can cause a reduction in data speed and
an increase in number of errors. The use
of two or more antennas, along with the transmission of multiple signals (one
for each antenna) at the source and the destination, eliminates the trouble
caused by multipath wave propagation, and can even take advantage of this
effect. MIMO technology has attracted in
wireless communication, since it offers significant increase in data throughput
and link range without additional
bandwidth or transmit power. It achieves it by higher spectral efficiency and
link reliability or diversity. Because of these characteristic, MIMO is a current theme of
international wireless research.
Basic Concepts of MIMO Wireless
Antenna Array Technology: MIMO is an
antenna array technology that is the use of multiple antennas at the
transmitter or the receiver.
Spatial Multiplexing: Spatial multiplexing is a transmission technique in MIMO wireless
communication to transmit independent and separately encoded data signals, so called
streams, from each of the multiple transmit antennas.
Forms of MIMO
Single
Input and Single Output (SISO) is a radio system where neither the
transmitter nor receiver have multiple antennas.
Single Input and Multiple Output
(SIMO) is a degenerate case when the transmitter has a single antenna.
Multiple
Input and Single Output (MISO) is a degenerate case when the transmitter
has multiple antennas.
Cooperative MIMO
Cooperative MIMO (CO-MIMO), also known as Network MIMO, utilizes
distributed antennas which belong to other users [3]. CO-MIMO improves the
performance of a wireless network by introducing multiple antenna advantages,
such as diversity, multiplexing and beam forming. If the main interest hinges
on the diversity gain, it is known as cooperative diversity. Cooperative
MIMO is, Multiple Transmitters with
Multiple Antennas each transmits different encoded streams to
a Single Receiver with
Multiple Antennas. In
conventional MIMO, transmitting stations perform MIMO transmission with out
consideration of the other transmitting stations. Therefore if all transmitting
stations have the same number of transmit antennas then all transmitting
stations will transmit identical signals. One notable advantage of CO-MIMO is
that spatial multiplexing gain can be achieved even if the transmitting
stations do not have multiple transmit antennas as long as receiving station as
multiple antennas. The relay station will generate the same encoded result but
will transmit different portions of it, operating as if they were different
antenna elements of a common transmitter. CO-MIMO is a technique useful for
future cellular networks which consider wireless mesh networking.
Why Relay Assisted MIMO ?
Communication becomes ineffective on the MIMO
system when the distance between source and destination large. It is better to provide a short distance,
which makes communication much better. In MIMO transmission system, relays are
added in between the source and destination, which provide a short distance communication
to the destination from the source. This makes communication muchost effective.
That is why relays are assisted on a MIMO system for better and effective
communication.
Relay channels will play a central
role in next-generation wireless systems. If a source wants to send a message
to a distant sink in a relatively dense network, it can
forward the message via several intermediate nodes. This would improve the
overall rate of successful message delivery over a communication channel and
coverage. In this setup, we can exploit the multiple antennas at the source and
the relay to perform, which will lead to improve performance.
The relay assisted transmission system is able to combat, the channel
impairments caused due to the shadowing and path-loss provided in source
destination and relay destination links
cause they are statistically independent, where there is no obstacle.
Relay Assisted MIMO
The relay assisted MIMO system uses
same number of multiple antennas at the
transmitter (source) and at the receiver (destination). In between source and
destination relays are used, which make the transmission better. On using MIMO
alone there exist a single time slot, which will be large and there will be a
propagation delay. When relays are introduced on such cases there will be two
time slots, they are time before receiving and the time after forwarding. Thus
the relays in between transmitter antenna and receiver antenna will make the
transmission better.
Relays
Relays
are the nodes or channels that interconnects the source (transmitter) and
destination (receiver), which they can receive and transmit information from
the source to destination. Relay transmission has been identified as one of the core
technologies that could enable high speed information transfer over challenging
wireless environment[4]. By placing relays between MIMO, it is possible to
improve throughput and coverage, than the system which uses MIMO alone. Relays
has made a major parts in mobile communication and wireless broadband access. Each
assisting relay does a phase rotation of the received signal, so that, the
channel between the relays and the relays and the destination is transformed into
time variant channel.
Infrastructure Relay Assisted MIMO
It is the design
format by which the relays are arranged in a pattern, such that it makes
communication more effective when placed between a MIMO.
In relay
transmission is carried out in two
orthogonal phases, one the relay receive phase and relay transmit phase,
according to the state of the assisting relay[2]. Multiplexing gains are
possible in relays having multiple antenna terminals, although significant
additive capacity gains are still possible. This system contains a multiple
input transmitter (source station), relay station and multiple output receivers
(destination station).
The
relay assisted transmission definition entails a cross-layer architecture. At the physical
layer, algorithm for encoding and signal processing are required at the source
and relay. Additionally, decoding algorithms are also needed at the relay and
destination. Therefore a new paradigm in communication appears, source-
relay-destination. The decoding terminal of the relay terminal should be
defined,[2].
Amplify
and Forward (AF): The
relay amplifies and forwards the signal received during the relay-receive phase.
Decode
and Forward (DF): The
relay decodes the message received in the relay-receive phase, re-encodes and
transmits in the relay-transmit phase.
Compress
and Forward (CF): The
relay compress the estimated symbols of signal received during the
relay-receive phase and transmits in the relay-transmit phase.
The relay-assisted transmission is able to
provide an additive capacity gain compared with the direct transmission. The
relay assisted MIMO transmission can be carried with different topologies.
Application of Relay assisted MIMO
As the characteristics of the relay transmission for wireless
communication has attracted the world towards it. Mobile communication is made
effective through relay assisted MIMO system. It provides high throughput for
wireless mobile access than that in multiple times of a system without relays.
Even on high mobility, relay assisted MIMO possess high throughput. Relay-assisted
MIMO technique will be used in wireless mobile access. As it removes multipath
fading, it is highly preferable in places where multiple reflections of signal
occurs. Hence it has attracted attention in wireless communication, it plays a
major role in future. Relay-assisted MIMO planned to be used in mobile radio
telephone standards such as in recent 3GPP (3rd Generation Partnership Project)
and 3GPP2 (3rd Generation Partnership Project), High Speed
Packet Access Plus (HSPA+) and Long Term Evolution (LTE) standards take
relay-assisted MIMO into account.
Conclusion
This
paper have discussed the basic concepts, evolution, applications of MIMO and
relay-assisted MIMO communication system, also we presented the properties
of the infrastructure relay system, with
different topologies and transmission scheme considering cooperative MIMO. Relay
assisted MIMO transmission system plays a important role in near future
wireless communication. It has been studied that these system possess high
throughput, reduces multi path fading
and suitable for long range transmission. Relay-assisted MIMO transmission strategy
will contribute a lot in future.
No comments:
Post a Comment
leave your opinion