Diversity Techniques
For Wireless Communication
Sahar Foroughi Farsani
saharforoughi@gmail.com
Azad University of Najafabad
December, 2014

Outline
1- Introduction
• Wireless Systems
• Wireless Channel Impairments
• Classification of Fading Channels
2- Diversity Techniques For Wireless Communication
• What is Diversity?
2
• What is Diversity?
• Classification of Diversity
3- Cooperative Diversity in Wireless Networks
• Introduction
• Cooperative Transmission Protocols
• Challenging Issues at Different Protocol Layers
4- Conclusions
5- References

Outline
1- Introduction
• Wireless Systems
• Wireless Channel Impairments
• Classification of Fading Channels
2- Diversity Techniques For Wireless Communication
• What is Diversity?
3
• What is Diversity?
• Classification of Diversity
3- Cooperative Diversity in Wireless Networks
• Introduction
• Cooperative Transmission Protocols
• Challenging Issues at Different Protocol Layers
4- Conclusions
5- References

Introduction
Wireless Systems
• Future generations of cellular communications requires higher data rates
and a more reliable transmission link.
• The transmission data rates can be increase by:
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• The transmission data rates can be increase by:
• Increasing the transmission bandwidth
• Using higher transmitter power.
• Wireless communication channels suffer from various factors.
• FADING problem is the major impairment problem.

• To improve the performance of those fading channels, diversity
techniques are used.
• In diversity technique:
• Communication channel is supplied with multiple Transmitting and Receiving
antennas.
• The signal is transmitted and received through multiple paths.
• As a result, the probability that all replicas of signals will fade simultaneously is
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• As a result, the probability that all replicas of signals will fade simultaneously is
reduced considerably.

Wireless Channel Impairments
• Noise
• Thermal noise (modeled as AWGN).
• Path Loss
• The loss in power as the radio signal propagates.
• Shadowing
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• Shadowing
• Due to the presence of fixed obstacles in the radio path.
• Fading
• Combines the effect of multiple propagation paths, rapid movement of mobile
units and reflectors.

Classification of Fading Channels
Fading
Large Scale Fading Small Scale Fading
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Attenuation with
distance
Variation about
mean
Time delay spread
/Multipath
Doppler shift / time
variance of channel
Flat Fading
Frequency Selective
Fading Fast Fading
Slow
Fading

Outline
1- Introduction
• Wireless Systems
• Wireless Channel Impairments
• Classification of Fading Channels
2- Diversity Techniques For Wireless Communication
• What is Diversity?
8
• What is Diversity?
• Classification of Diversity
3- Cooperative Diversity in Wireless Networks
• Introduction
• Cooperative Transmission Protocols
• Challenging Issues at Different Protocol Layers
4- Conclusions
5- References

Diversity Techniques For Wireless Communication
What is Diversity?
• Diversity is a powerful communication technique that provides wireless
link improvements at relatively low cost.
• It provides two or more inputs at the receiver such that the fading
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• It provides two or more inputs at the receiver such that the fading
phenomena among these inputs are uncorrelated.
• If one radio path undergoes deep fade another independent path may
have a strong signal at that input.

• Requirements for Diversity:
1- Multiple branches
2- Low correlation between branches
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Classification of Diversity
• Macro Diversity
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• Micro Diversity

• Space Diversity
• Using antennas spaced enough (at Tx or Rx).
Classification of Diversity
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• Using more than one antenna to receive the signal.
• More hardware (antennas).

• Frequency Diversity
• Is implemented by transmitting same information on more than one carrier
frequency.
• The separation between the carriers should be at least the coherent bandwidth
(Δf)c.
• Different copies undergo independent fading.
• Only one antenna is needed.
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• Time Diversity
• Repeatedly transmits information at the time spacing that exceeds the coherence
time of the channel.
• The interval between transmission of same symbol should be at least the
coherence time (Δt)c.
• Different copies undergo independent fading.
• Reduction in efficiency (effective data rate < real data rate).
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• Modern implementation of time diversity involves the use of RAKE
receiver for spread spectrum CDMA.
15

• Polarization Diversity
• Uses antennas of different polarizations i.e. horizontal and vertical.
• The antennas take advantage of the multipath propagation characteristics to
receive separate uncorrelated signals.
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Outline
1- Introduction
• Wireless Systems
• Wireless Channel Impairments
• Classification of Fading Channels
2- Diversity Techniques For Wireless Communication
• What is Diversity?
17
• What is Diversity?
• Classification of Diversity
3- Cooperative Diversity in Wireless Networks
• Introduction
• Cooperative Transmission Protocols
• Challenging Issues at Different Protocol Layers
4- Conclusions
5- References

Cooperative Diversity in Wireless Networks
• Introduction
• Cooperative communication allows single-antenna mobiles to reap some of the
benefits of MIMO systems.
• The basic idea is that single-antenna mobiles in a multi-user scenario can “share”
their antennas in a manner that creates a virtual MIMO system.
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• System Model
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• In non-cooperative communication, the received signal can be written as:
• In cooperative wireless:

Cooperative Transmission Protocols
• Amplify And Forward Method
• Decode and Forward Method
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• Decode and Forward Method
• Detect And Forward Method

Challenging Issues at Different Protocol Layers
• Challenges at the Physical Layer
• Developing different cooperative strategies.
• Adds complexity to the physical layer.
• Challenges at the MAC Layer
• It is crucial to develop adaptive MAC protocols that use cooperation only when it
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• It is crucial to develop adaptive MAC protocols that use cooperation only when it
is needed.
• Select the optimal cooperating entities among all available entities.
• Challenges at the Network Layer
• Define a routing protocol to deliver the data packets between the source and
destination nodes.
• New Link Definition

• Challenges at the Transport Layer
• In resource aggregation, multi-path routing is employed.
• Several IP addresses are used by the source and destination nodes.
• The traditional transport layer protocols, TCP and UDP are not designed to
handle several IP addresses for a single node.
• SCTP standard.
• Cross-Layer Design
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• Cross-Layer Design
• Cross-layer design for cooperative communication is mainly introduced between
the physical and MAC layers.
• Mobility
• Supporting user mobility is one of the most prominent features of wireless
communications.
• Node mobility can greatly affect the cooperation decision and the selection of
the cooperating entities.

Outline
1- Introduction
• Wireless Systems
• Wireless Channel Impairments
• Classification of Fading Channels
2- Diversity Techniques For Wireless Communication
• What is Diversity?
23
• What is Diversity?
• Classification of Diversity
3- Cooperative Diversity in Wireless Networks
• Introduction
• Cooperative Transmission Protocols
• Challenging Issues at Different Protocol Layers
4- Conclusions
5- References

Conclusions
• The diversity techniques is used to provide the receiver with several replicas of the
transmitted signal, used to overcome the fading problem and to improve the
performance of the radio channel without increasing the transmitted power and
improves the SNR.
• Among the various diversity techniques spatial diversity is best suitable for the
wireless communication.
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wireless communication.
• Multi-input-multi-output (MIMO) wireless communication uses spatial diversity
techniques.
• Potential benefits of cooperation in wireless communication networks include:
improved reliability and throughput, reduced service cost and energy
consumption, and supporting seamless service provision.
• The benefits come with various challenging issues at different layers of the
network protocol stack.

References
1- Pravin, W., and SL Badjate. " Diversity Techniques for Wireless
Communication." International Journal 2013.
2- Garg, Juhi, Priyanka Mehta, and Kapil Gupta. "A Review on Cooperative
Communication Protocols in Wireless World." International Journal of Wireless &
Mobile Networks 5.2 2013.
3- Laneman, J. Nicholas. Cooperative diversity in wireless networks: algorithms and
architectures. Diss. Massachusetts Institute of Technology, 2002.
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architectures. Diss. Massachusetts Institute of Technology, 2002.
4- Laneman, J. Nicholas, David NC Tse, and Gregory W. Wornell. "Cooperative
diversity in wireless networks: Efficient protocols and outage
behavior."Information Theory, IEEE Transactions on 50.12 2004.
5- Vishal K. Shah, Anuradha P. Gharge, " A Review on Relay Selection Techniques in
Cooperative Communication" , International Journal of Engineering and Innovative
Technology (IJEIT) Volume. 2, Issue 5, 2012.
6- Zhuang, Weihua, and Muhammad Ismail. "Cooperation in wireless communication
networks." Wireless Communications, IEEE 19.2, 2012.

With Special Thanks To You!