This document proposes allowing cognitive radios to opportunistically transmit in the 3GPP-LTE uplink by using channel nulls and peaks. It analyzes the performance of overlay transmission on nulls and peaks in a static and dynamic resource allocation scenario. Transmission during peaks caused less interference than nulls. Further work is needed to analyze performance from the secondary user perspective and incorporate error correction.

1. Cognitive Radio into the 3GPP-LTE Uplink
System. A first Approach
Presented by:
José A. Delgado Penín
Gerardo Agni Medina Acosta & José A. Delgado-Penín
COST TERRA Workshop – 20 June 2011, Brussels, Belgium

2.  Introduction
 Proposal Statement
 Small-Scale Fading
 Hypothesis
 Overlay Model
 3GPP-LTE Multiuser Environment
 System’s Performance Evaluation (Results)
 Conclusions
COST TERRA Workshop – 20 June 2011, Brussels, Belgium

3. COST TERRA Workshop – 20 June 2011, Brussels, Belgium
SC-FDMA Transmitter
Introduction
3GPP-LTE uplink:

4. Introduction
• The establishment of a CR communication highly depends that the surrounding
licensed environment remains unaffected.
• This nondisturbance can be achieved for example by:
 Interweaving communication: The SU transmits where PU’s are not active
(i.e. white spaces).
 Overlay communication: The SU simultaneously transmists without
distorting or slightly distorting the licensed communication.
Time
Power OPPORTUNITY
Time
Power
PU
SUPERIMPOSED OPPORTUNITY
COST TERRA Workshop – 20 June 2011, Brussels, Belgium

5. Proposal
Statement
Frequency
Power
Description:
• The idea behind this proposal consists in deeply analyzing the fluctuations that
occur in the LTE mobile channel aiming at identifying its extreme conditions.
• So, according to this proposal the channel Nulls and Peaks will play the role of the
opportunities to be discovered for co-transmitting opportunistically over the
licensed communication.
COST TERRA Workshop – 20 June 2011, Brussels, Belgium

6. Small-Scale
Fading
• The theoretical foundations of this proposal are directly related with the
small-scale fading mechanisms known as delay-spreading and time-
variance of the channel.
Small Scale Fading
Time Spreading Time Variance
Fast Fading
Non-Flat Fading
Flat Fading
Tm > Ts
f0 < W
T0 > Ts
fd < W
Yes
No
Slow Fading
Yes
No
COST TERRA Workshop – 20 June 2011, Brussels, Belgium

7. Fading Mechanisms:
• Concretely, the frequency selectivity of the channel provides the information
about which subcarriers along the entire transmission bandwidth are undergoing
the best, the worst and the intermediate conditions.
• On the other hand, the fading rapidity indicates (i.e. depending on the carrier
frequency and UE speed) approximately how long time the conditions over those
subcarriers will be steady.
Power
Small-Scale
Fading (continues)
COST TERRA Workshop – 20 June 2011, Brussels, Belgium

8. Proposal Hypothesis:
• The nulls and the peaks constituting an inherent part of any mobile
communication channel could be used in order to transmit opportunistically low
priority (secondary) information without significantly degrading the performance
of the primary system.
Hypothesis
COST TERRA Workshop – 20 June 2011, Brussels, Belgium

9. Model Representation (Simplest Form):
Overlay Comm.
Model
)()()()( kZkXkHkY 
kk 

InterferenceSignal Noise
Conventional Transmission
• Regarding the induced interference, k indicates that exclusively the subcarriers
experiencing either nulls or peaks (i.e. depending on the analysis) are taken into
account.
• This means that the interference induced to the conventional transmission only
holds for a limited number of subcarriers, and that can even disappear when no
extreme conditions are found in the link during certain time interval.
COST TERRA Workshop – 20 June 2011, Brussels, Belgium
)()( kXkH susu



10. Scenario Description:
• Secondary Overlay Communication into a 3GPP-LTE Multiuser Environment.
• Instead of conducting a sensing procedure, the SU would be able to make use of the
feedback information (CSI) coming from the eNode-B.
• The SU would be aware or focused on the information destined to the PU nearest to
its location.
• After an initial listening procedure the SU could conclude which subcarriers are
undergoing the worst/best conditions in order to initiate a low priority
communication strictly over those subcarriers.
Multiuser
Environment
COST TERRA Workshop – 20 June 2011, Brussels, Belgium

11. Multiuser
Environment
(Continues)
3GPP-LTE uplink Scenario subject to the presence of a SU:
(Primary Network View)
(Feedback Awaiting)
(Coherence Time Estimation)
(Opportunistic Transmission nulls/peaks)
COST TERRA Workshop – 20 June 2011, Brussels, Belgium

12. First Approach Results:
• The deployed scenario was analyzed under a static and dynamic (i.e. by using a Channel
Scheduler.REF) allocation of frequency resources.
• Given that the channel scheduler tries to avoid as far as possible the worst channel
conditions, the number of discovered opportunities for the case of transmitting over the
channel nulls was reduced but significantly increased for transmitting over the peaks.
Static Allocation: {4,140 peaks & 230 nulls , consisting of 15KHz each}
Dynamic Allocation:{ 6,295 peaks & 181 nulls , consisting of 15KHz each}
Results
Example of a secondary
transmission
over the Channel
Peaks
(Static Allocation)
Example of a secondary
transmission
over the Channel
Nulls
(Dynamic Allocation)
COST TERRA Workshop – 20 June 2011, Brussels, Belgium
Signal-to-Interference Ratio Signal-to-Interference Ratio
SIR(dB)
SIR(dB)
REF: G. A. Medina-Acosta, and J. A. Delgado-Penín, ‘On the feasibility of a Channel-Dependent Scheduling for the SC-FDMA in 3GPP-LTE (Mobile
Environment) based on a Prioritized-Bifacet Hungarian Method’, EURASIP Journal on Wireless Communications and Networking, (Accepted, to be published
Q1/Q2 2011)

13. • According to our preliminar observations, a transmission over the nulls produces a
higher impact on the primary communication even when the number of discovered
opportunities is lesser than those identified for the peaks.
• An explanation to this has to do with the fact that the equalizer embedded in the
reception chain tends to amplify the induced interference that is located over the
deep fadings.
Results
(continues)
Remove
CP
Serial
to
Parallel
M -
point
FFT
Subcarrier
De-
mapping
Equalizer
(MMSE)
N -
point
IFFT
Q-PSK
De-
Mapping
Parallel
to Serial
Recovered
Symbols
Baseband Receiver
First Approach Results:
COST TERRA Workshop – 20 June 2011, Brussels, Belgium

14. Conclusions
• This proposal revealed that:
• A secondary transmission over the channel nulls is much more harmful than an
opportunistic transmission carried out over the channel peaks.
• It is clear that in real world situations the number of discovered opportunities based
on the coherence time estimation cannot be guaranteed as in theory (Constant
speed cannot be assumed).
• However the feasibility of this proposal could follow the same operation principle as
a channel scheduler, which takes decissions about the channel assuming that will
prevail until next TTI.
COST TERRA Workshop – 20 June 2011, Brussels, Belgium

15. Conclusions
• Work in progress:
• To analyse the performance from the point of view of the SU.
• To incorporate error correction mechanisms (e.g. Turbo Codes) in order to evaluate
once again the performance of the interfered system.
• To identify the most suitable candidate (e.g. OFDMA) to carry out the secondary
communication under the suggested scheme.
COST TERRA Workshop – 20 June 2011, Brussels, Belgium

16.  Thank you !
Presented by:
José Antonio Delgado Penín
delpen@tsc.upc.edu
COST TERRA Workshop – 20 June 2011, Brussels, Belgium