Stable Throughput-Cooperative Cognitive Radio with Finite Relaying Buffer

On the Stable Throughput of Cooperative CognitiveRadio Networks with Finite Relaying Buffer

Reference: A. M. Elmahdy, A. El-Key, T. ElBatt, and K. G. Seddik, On the Stable Throughput of Cooperative CognitiveRadio 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 BufferJune 27, 2016 1 / 19

Agenda

Introduction

Problem Definition

System Model

Cooperation strategy

Stable Throughput Region1 Queue Stability2 DTMC Analysis of relaying queue3 Stable throughput Characterization problem

Numerical Results

Conclusion


Introduction

The concept of Cognitive radio was motivated by spectrum scarcityand inefficient utilization of the licensed spectrum

Cooperative Communication: some nodes forward transmission ofother nodes towards intended receiver ” Relay ”

Incorporating cooperation into cognitive radio networks ”Win-Win”Situation


Problem Definition

Characterize the stable throughput region when relaying buffer at theSU has finite capacity


System Model


System Assumption

The system is time-slotted

The instantaneous length evolution :Qt+1

i = (Qti − Y t

i )+ + X ti , 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


Cooperation Strategy

When PU is backlogged,it transmits a packet

If the destination correctly decodes the PU packet, it sends ACK andpacket dropped from Qp and exits the system

If the destination fails to decode the PU packet, but SU correctlydecodes it, Qsp buffers it w.p ai ,i=0,1,...,K.

If neither the destination nor the SU successfully receives PU packetthen the PU keeps it and re-transmit in the next time slot.



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 fromQs w.p. bi i=0,1,..,K

If the destination correctly decodes the SU packet, it sends back anACK , then the packet is dropped from either Qsp or Qs and exits thesystem.

The queue selection probability bi and the admission probabilitydepend on the of packets in Qsp



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 stablethroughput region of work conserving policy in infinite relaying buffer.


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 thequeue is stable if and only if the arrival rate is strictly less than the servicerate


A.Queue Stability

for Qp stability : λp < µp

µp = fpd + (1− f pd)fpsΣKi=0aiπi

For Qs : µs = (1− λp

µp)fsdΣK

i=0biπi

Stable Throughput region

R = {(λp, λs)|λp < fpd + (1− f pd)fpsΣKi=0aiπi , λs < fsd(1− λp

µp)ΣK

i=0biπi}


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


B.DTMC Analysis of Qsp

Using balance equation , the steady state probabilities :

πj+1 =λj

µj+1πj , j = 0, 1, ...,K − 1

πj+1 =λb(1−fpd )fpsaj

(µp−λp)(1−bj+1)fsdπj , j = 0, 1, ..., k − 1

Applying normalization condition

ΣKi=0πi = 1

we can obtain π0 and, hence completely characterize the steady statedistribution of Qsp


C.Stable throughput characterization Problem

Maximizing service rate of the SU for a given arrival rate of Primarytraffic while satisfying stability constraints of all queues in the system


Finding Stable throughput region

Transforming non-convex Optimization Problem into a linearProgram

Introduce new variables xi = aiπi and yi = biπi

At given value of µp the problem reduces into a linear Program in thevariables {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 themaximum achievable value of objective function


Numerical Results

System Parameters : fpd = 0.3, fps = 0.4, fsd = 0.8Baseline Comparison with work conserving scheme in which SU fullycooperates with PU via an infinite length queue


Conclusion

Studying effect of the finite size of relaying queue on the stablethroughput region of cooperative cognitive radio network

Formulating constrained optimization problem for maximizingsecondary user throughput while guaranteeing the stability of primaryuser queue

Numerical results reveal that cooperation is always advantageous toPU and SU in terms of expanding their stable throughput region

System doesn’t lose much in terms of the stable throughput regiondespite the limited relaying capacity

Future Work : other Performance metrics of the network can bestudied


Thank you !


Acknowledge

”This day wouldn’t be possible without the grace of Allah then, thededication of Dr. Amr A. El-Sherif and support from my dearest friendsAhmed Magdy, Ahmed Roshdy , Belal Essam and Osama Ashraf. Thanksto all of you.”


Engineering

Stable Throughput-Cooperative Cognitive Radio with Finite Relaying Buffer