studying the stability region for cooperative cognitive radio networks with finite relaying buffer

1. On the Stable Throughput of Cooperative Cognitive
Radio Networks with Finite Relaying Buffer
Reference: A. M. Elmahdy, A. El-Key, T. ElBatt, and K. G. Seddik, On the Stable Throughput of Cooperative Cognitive
Radio Networks with Finite Relaying Buffer, International Symposium on Personal, Indoor and Mobile Radio
Communications, Sept. 2014.
Abdulmoneam Ali
Wireless Intelligent Network Center (WINC), Nile University, Egypt
June 27, 2016
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 1 / 19

2. Agenda
Introduction
Problem Definition
System Model
Cooperation strategy
Stable Throughput Region
1 Queue Stability
2 DTMC Analysis of relaying queue
3 Stable throughput Characterization problem
Numerical Results
Conclusion
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 2 / 19

3. Introduction
The concept of Cognitive radio was motivated by spectrum scarcity
and inefficient utilization of the licensed spectrum
Cooperative Communication: some nodes forward transmission of
other nodes towards intended receiver ” Relay ”
Incorporating cooperation into cognitive radio networks ”Win-Win”
Situation
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 3 / 19

4. Problem Definition
Characterize the stable throughput region when relaying buffer at the
SU has finite capacity
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 4 / 19

5. System Model
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 5 / 19

6. System Assumption
The system is time-slotted
The instantaneous length evolution :
Qt+1
i = (Qt
i − Y t
i )+ + Xt
i , i ∈ {P, S, SP}
Conflict free system so the only reason for packet loss is link outage
The Mobility of the nodes is ignored
SU has better channel to the destination than PU (fsd > fpd )
Instantaneous and error-free ACK , heard by all the nodes
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 6 / 19

7. Cooperation Strategy
When PU is backlogged,it transmits a packet
If the destination correctly decodes the PU packet, it sends ACK and
packet dropped from Qp and exits the system
If the destination fails to decode the PU packet, but SU correctly
decodes it, Qsp buffers it w.p ai ,i=0,1,...,K.
If neither the destination nor the SU successfully receives PU packet
then the PU keeps it and re-transmit in the next time slot.
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 7 / 19

8. Cooperation Strategy
When PU is idle ( Qp is empty), the SU accesses the channel
SU transmits a packet either from Qsp w.p. 1-bi , i=0,1,...,K or from
Qs w.p. bi i=0,1,..,K
If the destination correctly decodes the SU packet, it sends back an
ACK , then the packet is dropped from either Qsp or Qs and exits the
system.
The queue selection probability bi and the admission probability
depend on the of packets in Qsp
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 8 / 19

9. Cooperation Strategy
When relaying queue is full(Qsp=K packets) , ak=0
When relaying queue is empty , b0=1
It is non-work-conserving System
However, the non-work-conserving policy achieves the same stable
throughput region of work conserving policy in infinite relaying buffer.
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 9 / 19

10. Stable Throughput Region
The System is stable when all of its queues are stable.
Theorem (Loynes’s Theorem)
If the arrival and the service processes of a queue are stationary, then the
queue is stable if and only if the arrival rate is strictly less than the service
rate
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 10 / 19

11. A.Queue Stability
for Qp stability : λp < µp
µp = fpd + (1 − f pd)fpsΣK
i=0ai πi
For Qs : µs = (1 −
λp
µp
)fsd ΣK
i=0bi πi
Stable Throughput region
R = {(λp, λs)|λp < fpd + (1 − f pd)fpsΣK
i=0ai πi , λs < fsd (1 −
λp
µp
)ΣK
i=0bi πi }
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 11 / 19

12. B.DTMC Analysis of Qsp
λi =
λp
µp
(1 − fpd )fpsai , i = 0, 1, ..., K
µi = (1 −
λp
µp
)fsd (1 − bi ), i = 0, 1, ..., K
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 12 / 19

13. B.DTMC Analysis of Qsp
Using balance equation , the steady state probabilities :
πj+1 =
λj
µj+1
πj , j = 0, 1, ..., K − 1
πj+1 =
λb(1−fpd )fps aj
(µp−λp)(1−bj+1)fsd
πj , j = 0, 1, ..., k − 1
Applying normalization condition
ΣK
i=0πi = 1
we can obtain π0 and, hence completely characterize the steady state
distribution of Qsp
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 13 / 19

14. C.Stable throughput characterization Problem
Maximizing service rate of the SU for a given arrival rate of Primary
traffic while satisfying stability constraints of all queues in the system
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 14 / 19

15. Finding Stable throughput region
Transforming non-convex Optimization Problem into a linear
Program
Introduce new variables xi = ai πi and yi = bi πi
At given value of µp the problem reduces into a linear Program in the
variables {ai , bi , πi }
The feasible values of µp over which the linear program runs is :
max(λp, fpd ) ≤ µp ≤ fpd + (1 − fpd )fps
Our goal is to identify the value of µp that corresponds to the
maximum achievable value of objective function
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 15 / 19

16. Numerical Results
System Parameters : fpd = 0.3, fps = 0.4, fsd = 0.8
Baseline Comparison with work conserving scheme in which SU fully
cooperates with PU via an infinite length queue
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 16 / 19

17. Conclusion
Studying effect of the finite size of relaying queue on the stable
throughput region of cooperative cognitive radio network
Formulating constrained optimization problem for maximizing
secondary user throughput while guaranteeing the stability of primary
user queue
Numerical results reveal that cooperation is always advantageous to
PU and SU in terms of expanding their stable throughput region
System doesn’t lose much in terms of the stable throughput region
despite the limited relaying capacity
Future Work : other Performance metrics of the network can be
studied
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 17 / 19

18. Thank you !
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 18 / 19

19. Acknowledge
”This day wouldn’t be possible without the grace of Allah then, the
dedication of Dr. Amr A. El-Sherif and support from my dearest friends
Ahmed Magdy, Ahmed Roshdy , Belal Essam and Osama Ashraf. Thanks
to all of you.”
Abdulmoneam Ali (Nile University) On the Stable Throughput of Cooperative Cognitive Radio Networks with Finite Relaying BJune 27, 2016 19 / 19