Implementation of MIMO relays
in Cognitive Radio Networks
Presenter: Chao Kong
1
Outline
Motivation
Challenges in building the system
Theoretical analysis
2
Motivation
In a cognitive radio network, “rich” nodes
(one antenna) can help to relay other nodes
traffic with their otherwise wasted spectrum.
Node can only transmit one
packet in one channel in one
[1,3,4]
time slot
3 packets
3 time slots
[1]
[1,2]
[2,3]
(a) Channel and demand
(b) OFDM transmission
3
Motivation
Node C works as a relay, thus can finish the
transmission in 2 time slots by using DiscontinuousOFDM.
Time slot 21
[1,3,4]
[1]
[3]
[1]
[2]
[1,2]
[2,3]
( c) cooperative relay transmission
[1] Juncheng Jia, Jin Zhang and Qian Zhang ,“ Cooperative Relay for
Cognitive Radio Networks,” in the IEEE INFOCOM 2009
4
Motivation
D-OFDM (discontiguous Orthogonal Frequency
Division Multiplexing)
A OFDM scheme have 16
subcarriers
Combine several continuous
subcarriers together to form
a sub-channel
Sub-channel 1
Sub-channel 2
5
Motivation
Consider the following scenario
[1,3,4]
3 packets
[1,2]
[3,4]
Heavy interference
[3]
[2,3]
[3]
3 packets
[2,3]
[2,4]
6
Motivation
Using a MIMO relay H to replace node C and E
Time slot 21
[1,3,4]
[1]
[3]
[3]
[4]
[1]
[2,3]
[2]
[1,2]
[3,4]
[2,3]
[4]
[2]
[2,3]
[2,4]
( d) cooperative MIMO relay transmission
7
Motivation
Advantages of deploying MIMO relays:
Reduce the cost of relay node deployment
Improve capacity of the network
Achieve diversity gain in some cases
( e) cooperative MIMO relays in one network
8
Motivation
 implementing this system on the USRP (Universal
Software Radio Peripheral) platform
 Using programming languages LABVIEW and
MATLAB.
(f) NI USRP 2920 series
9
Outline
Motivation
Challenges in implementing the system
Theoretical analysis
10
Challenges
There are 3 challenges:
 How to implement D-OFDM?
 Synchronization and coordination
 Obtaining CSI(channel state information)
and precoding
[1,3,4]
D-OFDM: using filters to
select the signals at certain
subchannels that we want
[1]
[1]
[3]
Time slot 21
[2]
[1,2]
[2,3]
11
Challenges
Synchronization and coordination in transmitters
 In time slot 1, node A,D should start transmitting simultaneously
 In time slot 2, node A,D,H should start transmitting simultaneously
Time slot 12
[1,3,4]
[1]
[3]
[3]
[4]
[1]
[2]
[1,2]
[3,4]
[2,3]
[4]
[2]
[2,4]
12
Challenges
Obtaining CSI(channel state information)
and precoding
In time slot 2, link (B,H) and (H,F) may encounter heavy interference,
so we need get the CSI about this two channel and do some precoding
Time slot 2
[3,4]
[1,3,4]
[4]
[1]
[2]
[1,2]
[2,3]
[2]
[2,4]
13
Outline
Motivation
Challenges in implementing the system
Theoretical analysis
14
Theoretical analysis
 If nodes have different number of antennas and
there are several MIMO relays, how could we
allocate the spectrum resources and select the
most efficient MIMO relays?
 We will propose an algorithm to solve it.
Our Wedsite: http://iwct.sjtu.edu.cn/Personal/xwang8/rese
arch-system/MIMO/mimo.html
15
Q&A
16
Q &A
What are the disadvantages of this system?
MIMO relays should be deployed in certain location
The system will be more complicated and brings more
overhead
17
Q &A
What kinds of filter would you use?
square-root raised cosine roll off filter
18
Thank you!
19