1. Cooperative MIMO Paradigms for Cognitive Radio Networks
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Wei Chen & Liang Hong
College of Engineering
Tennessee State University
APDCM 2013
Boston, MA, May 20, 2013

2. Cooperative MIMO Paradigms for Cognitive Radio Networks
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Outline
Introduction
Problem Statement
Cooperative MIMO Network Model and Communication Schemes
Cooperative MIMO Paradigm for Overlay Systems
Cooperative MIMO Paradigm for Underlay Systems
Numerical Analysis and Experiments
Conclusions

3. Cooperative MIMO Paradigms for Cognitive Radio Networks
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Introduction
MIMO Technology
Multiple antennas transmit same data streams simultaneously: it can be used to reduce energy, or extending communication range and error rate.
Multiple antennas transmit different data streams simultaneously: it can be used to provide higher data rate (multiplexing gain)
MIMO transceiver
Wireless MIMO network
diversity gain
multiplexing gain
However, it is unrealistic to equip multiple antennas to small and inexpensive wireless devices (e.g., wireless sensor nodes).

4. Cooperative MIMO Paradigms for Cognitive Radio Networks
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Cooperative Communication MIMO Technology
– Distributed individual single-antenna nodes cooperating on information transmission and reception as a multiple antenna array
MIMO links
SIMO Link
MISO Link
MIMO Link
SISO Link
Cooperative MIMO Schemes
First hop
Other hops

5. Cooperative MIMO Paradigms for Cognitive Radio Networks
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Cognitive radio A promising paradigm in wireless communication that enables efficient use of frequency resources
Coexistence of licensed primary users (PUs) and unlicensed secondary users (SUs) in the same frequency band
Cognitive capabilities
Basic approaches: (1) spectrum overlay, (2) underlay, and (3) interweave
Overlay
Underlay
Interweave
Primary users PT PR
Secondary
users
A cooperative SIMO link
A cooperative MISO link
Secondary Users PT PR
an mt×mr cooperative MIMO link SR ST
Primary Users
time

6. Cooperative MIMO Paradigms for Cognitive Radio Networks
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Problem Statement
Existing overlay schemes require the relay SUs to be in the convenient location, typically halfway between source and destination
Existing underlay schemes cannot guarantee that the aggregated interference generated by SUs is maintained below the threshold
This Research
Develop energy efficient cooperative MIMO paradigms that can maximize the diversity gain and significantly improve the performance of both overlay and underlay systems.

7. Network Model and Communication Schemes
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Network Model and Communication Schemes
Underlying network: Network G = (V,E) of single-antenna radio nodes.
d-Clustering: the distance between two nodes in a cluster ≤ d. d-clusters are called Cooperative MIMO nodes, and the nodes of G are called primary nodes.
D-Cooperative-MIMO links: Let A and B be two d-clusters, and A’ and B’ be the subsets of A and B, respectively. Suppose there are mt nodes in A’ and mr nodes in B’. If the largest distance between any node of A’ and any node of B’ is not larger than D, a D-mt×mr virtual MIMO transmission link can be defined between A and B.
Heterogeneity: The size and the diameter of a cluster, and the length of virtual MIMO links can be different.
3×2 MIMO link

8. Cooperative MIMO Paradigm for Overlay System
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Cooperative MIMO Paradigm for Overlay System
SUs assistant PUs’ communication:
(SUs can use the PUs channel when PUs’ communication completed)
Primary users PT PR
Secondary
users
A cooperative SIMO link
A cooperative MISO link
Step 1: data transmission from the primary transmitter to m SUs via 1×m SIMO link
Step2: data transmission from m SUs to the primary receiver via a m×1 MISO link
Optimization (at SUs)
Maximize the distance that the secondary users can be away from the primary users.
Minimize the energy usage at the secondary users.

9. Cooperative MIMO Paradigm for Underlay System
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Cooperative MIMO Paradigm for Underlay System
Secondary Users PT PR
mt×mr cooperative MIMO link SR ST
Primary Users
SUs utilize PUs’ channel obliviously:
SUs share the PUs’ frequency resource without any knowledge about the PUs’ signals and under the strict constraint that the spectral density of their transmitted signals fall below the noise floor at the primary receivers
Optimization at SUs
Maximize the communication performance (minimize error rate)
Minimize the energy usage at the secondary users.

10. Numerical Analysis and Experiments
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Numerical Analysis and Experiments
Energy Model
Energy consumption per bit at each primary node for local/intra data transmission
Energy consumption per bit at each primary node for local/intra reception

11. Cooperative MIMO Paradigms for Cognitive Radio Networks
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Energy consumption per bit at each primary node for data transmission in long-haul mt × mr cooperative MIMO link
Energy consumption per bit at each primary node for data reception in long-haul mt × mr cooperative MIMO link

12. Cooperative MIMO Paradigms for Cognitive Radio Networks
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Parameters
Pct = mw
Pcr = 62.5 mw
Psyn = 50 mw
Nf = 10 dB
Ttr = 5 μs
σ2 = N0/2 = -174 dBm/Hz
GtGr = 5 dBi
λ =
Gd = G1dkMl (G1 = 10 mw, k = 3.5, Ml = 40 dB)

13. Numerical analysis in Overlay System
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Numerical analysis in Overlay System
Secondary Users PT PR
mt×mr cooperative MIMO link SR ST
Primary Users
Step 1: data transmission from the primary transmitter to m SUs via 1×m SIMO link
Step2: data transmission from m SUs to the primary receiver via a m×1 MISO link

14. Numerical Analysis in Underlay System
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Numerical Analysis in Underlay System
Since only transmission energy brings interference from SUs to primary receiver, only the transmission energy is considered
Intra/local transmission
Long-haul transmission
Secondary Users PT PR
mt×mr cooperative MIMO link SR ST
Primary Users

15. Numerical Analysis Results
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Numerical Analysis Results
In overlay systems the SUs can assist/relay the PUs’ transmission even when SUs are far away from primary transmitter (Pt) and primary receiver (Pr)

16. Cooperative MIMO Paradigms for Cognitive Radio Networks
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
In underlay systems the SUs are able to share the PUs’ frequency resource without any knowledge about the PUs’ signals and under the strict constraint that the spectral density of their transmitted signals fall below the noise floor at the primary receivers.

17. Cooperative MIMO Paradigms for Cognitive Radio Networks
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
System Evaluation in Real Wireless Environment
Build a cooperative cognitive testbed using the universal software radio peripheral (USRP) platform and GNU Radio
Each node consists: an USRP motherboard + RFX2400 daughterboard
signal processing module implemented in GNU Radio running in a general purpose computer under Ubuntu operating system
BPSK modulation and demodulation is used for all experiments
Overlay System
Underlay System
Licensed Primary Transmitter
Licensed Primary Receiver
unlicensed Secondary Transmitter
unlicensed Secondary Receiver
unlicensed Secondary Users as Relay
unlicensed Secondary Cooperative Transmitter

18. Overlay System Underlay System
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Overlay System Underlay System
(Bit error rate performance) (Packet error rate performance)
Single-relay Cooperation
Multiple-relay cooperation
Amplitude
With Cooperation
Without Cooperation
800
24.85%
600
6.12%
70.28%
400
13.72%
97.1%
Average
6.61%
64.08%
Trial
(Node distance: 2 m)
With Cooperation
Without Cooperation 1
2.21%
9.13% 2
2.27%
12.73% 3
2.89%
10.76%
Average
2.46%
10.87%
Multiple Relays Coop.
(Node Distance: 30 ft)
Single Relay Cooperation
Without Cooperation
2.93%
2.21%
9.13%

19. Cooperative MIMO Paradigms for Cognitive Radio Networks
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Conclusions
Proposes energy efficient cooperative MIMO paradigms for cognitive radio networks.
In overlay systems, SUs can relay the primary transmissions even when they are far away from the primary users
In underlay systems, SUs are able to share the primary users’ frequency resources without any knowledge about the PUs’ signals, even when they are close to the primary receivers
Performance evaluation in real wireless environment verified the advantage of the proposed paradigms.

20. Cooperative MIMO Paradigms for Cognitive Radio Networks
Dr. Liang Hong
(615)
College of Engineering
Tennessee State University
Cooperative MIMO Paradigms for Cognitive Radio Networks
Thank you!
Questions?