1. Enhancing the capacity of Spectrum Sharing in Cognitive Radio Network
Presented By:
Tapeshwar Narayan

2. Contents Introduction Challenges State-of-the-Art Observations
Objectives
Methodology
Conclusion
References

3. Introduction Cognitive Radio(CR)
"Cognitive radio" is an emerging technique to improve the utilization of radio frequency spectrum in wireless networks.
In CR terminology
Licensed Users of fixed frequency band are Primary Users(PU).
Users who access spectrum opportunistic are Secondary Users(SU).
In fixed frequency allocation strategies large portion of spectrum is either not used or partially utilized.
According to FCC spectrum utilization varies from 15-85% at different place in different times.[9]

4. Introduction Contd… Cognitive Radio(CR)
CR is a transceiver that automatically detect available channel in wireless spectrum to offers dynamic and opportunistic spectrum access to SU’s in fixed allocated spectrum.
So, CR provide access to SU’s without causing interference to PU’s when spectrum in free.

5. Introduction Contd… Spectrum Sensing(SS)
Spectrum Sensing is done in order to determine the presence of primary users or in order to determine the spectral hole.
Sensing the spectrum determine transmission from PU’s.
Basically in spectrum sensing CR sense spectrum to determine spectral hole that can be accessed by SU’s.
In SS we have two hypothesis on the basis of which we decide spectrum is utilized or free.[5]
x(t)= w(t) <t≤T H0
x(t)= s(t) + w(t) 0<t≤T H1

6. Introduction cont. Spectrum Sharing
Two methods of spectrum access by SU:-
Opportunistic Spectrum Access:
Here a secondary user accesses a frequency band only when it is detected not being used by the primary users.
Spectrum Sharing :
Here a secondary users coexist with the primary users under the condition of protecting the primary users from harmful interference.

7. Introduction Cont. Conventional method of spectrum sharing:
Frame Frame-2
In this method of spectrum sharing the secondary user first perform spectrum sensing for t units of time in order to determine the status(active/ideal) of frequency band.
The remaining frame duration (T-t) is used by the secondary user for data transmission.
Sensing (t)
Data Transmission(T-t)
Sensing (t)
Data Transmission(T-t)

8. Challenges Spectrum scarcity problem
Sensing-throughput tradeoff problem
This frame structure disrupts the continuity of communication in spectrum sharing cognitive radio networks
Total interference power at the licensed receiver must remains below a certain threshold.

9. State-of-the-Art
In 2005: Spectrum sharing in fading environments by A. Ghasemi.
In 2007: Spectrum sharing in cognitive radios based on multiple cyclic frequencies.
In 2008: Sensing throughput tradeoff for cognitive radio networks by Y .C Liang.
In 2009: Sensing-based spectrum sharing in cognitive radio networks.
In 2010: Throughput Maximization of Spectrum Sharing Cognitive Radio Networks.
In 2010: Distributed Shared Spectrum Techniques for Cognitive Wireless Radio Networks by Rajni Dubey and Sanjeev Sharma.

10. Observations
Spectrum sharing increase the spectrum utilization up to a large extent.
If the primary user signals under dection are very weak then it leads to very high sensing time.
There is a tradeoff between sensing time and throughput i.e if the sensing time is high than the data transmission time become less , which leads to reduce the throughput.

11. Objectives To enhance the spectrum sharing capicity.
To overcome the sensing-throughput tradeoff problem.
To maximise the the achievable throughput from conventional method.

12. Methodology

13. Methodology Cont.
The Received signal at the receiver of the secondary user is
y = θxp + xs + n
here θ is the status of the frequency band(if θ=1, frequency band is active active, if it is zero frequency band is idle).
xp= Signal from primary user
Xs= Signal from secondary transmitter
Signal y is passed through decoder, then we get signal
y’ = θxp + n
is used to perform spectrum sensing.

14. Methodology Cont.
Based on the decision of spectrum sensing, the secondary users communicate using higher transmit power P0 if the channel is detected to be idle.
Otherwise transmit data with a lower power p1 if the channel is under utilization under the condition of protecting primary user from interferences.

15. Conclusion
Spectrum sensing and data transmission times are simultaneously maximized.
Overcomes the sensing-throughput tradeoff problem by performing spectrum sensing and data transmission at the same time.
Continuous spectrum sensing can be achieved under the proposed method, which ensures better protection of the primary networks.
Increased data transmission time leads to maximize the throughput

16. References
[1] J. Mitola, III and G. Q. Maguire, Jr., “Cognitive radios: Making software radio more personal,” IEEE Pers. Commun., vol. 6, no. 4, pp. 13–18, Aug
[2] J. M. Peha, “Approaches to spectrum sharing,” IEEE Commun. Mag., vol. 43, no. 2, pp. 10– 12, Feb
[3] A. Ghasemi and E. S. Sousa, “Fundamental limits of spectrum sharing in fading environments,” IEEE Trans. Wireless Commun., vol. 6, no. 2, pp. 649–658, Feb
[4] Y.-C. Liang, Y. Zeng, E. C. Y. Peh, and A. T. Hoang, “Sensing throughput tradeoff for cognitive radio networks,” IEEE Trans. Wireless Commun., vol. 7, no. 4, pp. 1326–1337, Apr
[5] A. Ghasemi and E. S. Sousa, “Capacity of fading channels under spectrum-sharing constraints,” in Proc. IEEE Int. Conf. Commun. (ICC), Istanbul, Turkey, June 2006, pp. 4373– 4378.

17. References Cont.
[6] A. Attar, M. R. Nakhai and A. H. Aghvami, "Cognitive Radio Game for Secondary Spectrum Access Problem," IEEE Trans. on Wireless Commun., Vol. 8, No. 4, pp , April 2009.
[7] Rajni Dubey, Sanjeev Sharma, "Distributed Shared Spectrum Techniques for Cognitive Wireless Radio Networks", International Conference on Computational Intelligence and Communication Networks, /10,2010 IEEE
[8] Stergios Stotas, Arumugam Nallanathan, "On the Throughput Maximization of Spectrum Sharing Cognitive Radio Networks", IEEE Globecom 2010 proceedings, /10,2010 IEEE.
[9] Xu Ling, Song Li, "Enhancing the Capacity of Spectrum Sharing Cognitive Radio Networks", IEEE Transactions on Vehicular Technology, Vol ume.60, No.8, , IEEE