Cooperative TV Spectrum Sensing in Cognitive Radio :for Wi-Fi Networks

PRESENTED BY :DEEPAK KUMAREC6 111424B.TECH NIT KURUKSHETRA

Content

INTRODUCTION

SYSTEM MODEL : WI-FI ZONE

ENERGY DETECTION ALGORITHM

SPECTRUM SENSING:

SINGLE USER

COOPERATIVE SENSING

TOTAL DETECTION ERROR PROBABILITY

OPTIMAL SENSING TIME

NUMERICAL RESULT

CONCLUSION

INTRODUCTION

SHORTAGE OF SPECTRUM

USE OF TV SPECTRUM IN WI-FI NETWORKS

ACCURACY :

• S E N S I N G T I M E

• N O . O F S E N S I N G n O D E S [ S U ’ S ]

OBJECTIVE :

O P T I M A L N O . O F S U ’ S

O P T I M A L S E N S I N G T I M E

M I N I M I Z A T I O N O F D E T E C T I O N E R R O R P R O B A B I L I T Y

SYSTEM MODEL: WI-FI ZONE

CPE : CUSTOMER PREMISES

EQUIPMENT [ SMART PHONE

LAPTOPS ETC. ]

ELEMENTS:

o PU

o SU

o FC [ FUSION CENTER ]

ENERGY DETECTION ALGORITHM

Primary Signal

Y(t) = { 𝑛 𝑡 𝐻𝑜ℎ𝑠 𝑡 +𝑛 𝑡 𝐻1

}n(t) =white noise

h =channel coefficient

False Alarm Probability

𝑃𝑓 = 𝑃 𝑌 > 𝜆 𝐻𝑜

Miss Detection Probability

𝑃𝑚 = 𝑃(𝑌 < 𝜆|𝐻1)

Ho is the hypothesis of absence of primary user

H1 is the hypothesis of presence of primary user

SINGLE USER spectrum SENSING :

FRAME :𝜏 + (𝑇 − 𝜏)

𝝉= SENSING TIME

T−𝝉= DATA TRANSISSION

TIME

Single user SPECTRUM sensing

Transmission throughput: 1. Secondary User Throughput

2. Primary User Throughput

o First term corresponds to the secondary user throughput

o Second term corresponds to the primary user throughput

o T is frame duration and τ is spectrum sensing time.

o P(H0) [P(H1) ] is a probability for primary user being absent [present ].

o C0 (C1) is a secondary user’s channel capacity under the hypothesis H0(H1).

COOPERATIVE SPECTRUM SENSING

Cooperative spectrum sensing schemes :

To determine the presence of primary user (PU) with the collected information from secondary users (SUs) at a fusion center (FC).

Three kind of decision rules :

OR RULE

AND RULE

K OUT-OF- N-RULE

OR-RULE

The OR-rule declares presence of PU as long as at least one SU detects the PU.

The OR-rule has very low mis-detection probability which is helpful to protect the primary user.

Relatively high false alarm probability which makes the spectrum usage inefficient.

AND RULE

The AND-rule declares presence of PU only when all Su’s report of PU presence.

The AND-rule has very low false alarm which makes spectrum usage efficient.

It may not protect the primary user from strong interferences from the secondary users.

Quality of services for primary user is not guaranteed.

K -out -of -n -rule

K-out-of-N-rule which declares the presence of primary user when more than K-out-of-N SUs detect presence of primary user.

Special cases of K-out-of-N-rule with different values of K.

OR RULE : WHEN K=1

AND RULE : WHEN K=N

RULE

RULE

RULE

TOTAL DTECTION ERROR PROBEBILITY

Total detection error probability is defined as the average of mis-detection probability and false alarm probability

P(H0) is a probability for primary user being absent .

P(H1) is a probability for primary user being present.

OPTIMAL KOpT FOR K-OUT –OF –N RULE:

OPTIMAL SENSING TIME FOR MULTIPLE USERS

The longer spectrum sensing time guarantees low detection error probability BUT it reduces transmission throughput because data are not transferred during sensing time.

Throughput consists of two terms:

Secondary user throughput

Primary user throughput.

TOTAL THROUGHPUT

THE PRIMARY USER THROUGHPUT

The total throughput

For Optimal sensing time R_total

has to be differentiated in terms of

spectrum sensing time τ and set

to zero.

It is too complex to obtain

analytical expression for optimal

sensing time.

Instead it can be numerically found

such as the sensing time which

yields the highest total throughput.

SECONDARY THROUGHPUT

NUMERICAL RESULT

Optimal number KOUT of secondary users for K-out-of-N-rule

Compare optimal spectrum sensing time and transmissionthroughput for three detection rules.

Assumption:

o The frame duration is 100ms.

o The frequency bandwidth of primary user is 3MHz.

o The signal-to noise power ratio =20dB.

o C0 = log2(1+SNR) = 6.6582 bps.

o P(H0)=P(H1)=0.5.

Optimal number of secondaRY users

o Three detection error

Probabilities (Pt Pf Pm) versus

number of secondary users K

o Vertical dotted line corresponds

to KOUT .

MATLAB IMPLEMENTion:

o Optimal K increases from

13 to 23 as mis-detection

probability decreases from

0.26 to 0.01.

o Larger K usually increases

mis-detection probability

but decreases false alarm

probability.

o However when mis-

detection probability is

very low larger K is better

to reduce false alarm

probability.

Total throughput:

Blue line for primary user

Red line for secondary user

Green line for total throughput

OPTIMAL SENSING TIME FOR MULTIPLE USERS

Total throughput for three

kinds of detection

rules versus sensing time.

o OR rule: 1.26ms

o AND-rule: 1.56ms

o K out-of-N-rule: 0.84ms

CONCLUSIONS

A cognitive radio system using a vacant TV channel in a Wi-Fi zone to achieve increased data transmission capacity for a Wi-Fi service.

We derived the optimal threshold number of secondary users for K-out-of-N-rule of cooperative spectrum sensing in the constraint of minimum detection error probability.

We also numerically presented the optimal sensing time which maximizes the data throughput.

This proposed CR scheme may solve the spectrum shortage problem due to explosively increasing Wi- Fi data traffic due to smart phones.

THANK YOU PRESENTED BY :DEEPAK KUMAR ROLL NO .111424EC6 B.TECH