Relay Assisted MIMO Transmission System - Seminar Report

Relay Assisted MIMO Transmission System

       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.

         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 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 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.

       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.

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