A Novel MAC Scheme for Multichannel Cognitive Radio Ad Hoc Networks

Presented by Le The DungDept. of Electronics & Computer Engineering in Graduate School, Hongik Universty

A Novel MAC Scheme for Multichannel Cognitive Radio Ad Hoc Networks

Wha Sook Jeon, Senior Member, IEEE , Jeong Ae Han, Dong Geun Jeong, Senior Member, IEEE

IEEE Transaction on Mobile Computing, vol. 11, no. 6, June 2012

Contents

Introduction The proposed MAC scheme

Collaborative Channel Sensing Data Transmission Scheme

Reservation of Data Channel Packet Transmission on Data Channel

Performance evaluation Conclusions

Hongik University 1Ubiquitous Networks and Convergence Lab

Introduction (1/2)

Cognitive based ad hoc networks are networks operating on multiple channels in order to fully utilize the spectrum access opportunity without a centralized controller. Just-before-transmission sensing: to

carry out channel sensing before data transmission.

Opportunistic sensing: to sense channel in advance whether they have any opportunity for channel sensing and maintain the list of empty channel.


Reduces data transmission delay

Introduction (2/2)


Issues in opportunistic sensing: Fresh level of sensing results: the PU

disturbance by CRs may higher than just-before-transmission sensing.

Partial PU signal coverage area: PU signal covers only a part of the network, thus the nodes should sense individually all channels.

To investigate how much a PU is disturbed by CR

system adopting opportunistic sensing

To collaborative

opportunistic sensing

The proposed MAC scheme (1/3)

The authors propose a novel MAC scheme for multichannel CR ad hoc networks who only a part is influenced by PU activation.



Features of proposed MAC scheme: Collaborative sensing: to sense channel

opportunistically and adjust sensing priorities of channels through collaboration with other nodes.

Transmission power control for PU protection: to transmit traffic with controlled power to protect potential hidden PUs.

Multiple packet transmission the reserved channel: to transmit multiple packets on the reserved channel during channel occupancy time.



Overall operation that CR node performs with data transceiver.


Collaborative Channel Sensing

Sensing Priorities of Channel: Urgent Sensing: a responsible node k (i.e. the

node k which firstly detects PU signal on channel i through

opportunistic sensing, announced by RN_ON/RN_OFF) urges other nodes to sense the channel i as soon as possible by sending US_REQ.

Opportunistic Sensing: when CR node does not have data packets to transmit as well as channels waiting for urgent sensing.

The proposed MAC gives precedence to urgent sensing over opportunistic sensing.


Data Transmission Scheme (4/4) Data Transmission Scheme includes:

Reservation of Data Channel To determine candidate channel priority for data

transmission. To select channel reserved duration.

Packet Transmission on Data Channel To protect potential hidden PU by calculate the

number of multiple packet transmissions during the reserved duration.

To transmit data packets with the power lower than the maximum allowable power.


Reservation of Data Channel(1/4)

Control packets for data transmission.



Exchange of control packets during data channel reservation and transmission.



Reservation time (DRREQ) calculation:

w: worst case channel i.e. the channel having the longest elapsed time since the last sensing.

lA(w): the last sensing finish time of the channel w.

: parameter for compensating the miss detection of PU and random backoff delay of RREQ packet; 0 1.

: detection delay limit ( = 1 sec in this paper).


( )A DIFS RREQ RREQ At T T D l w


Reservation time (DRREQ) calculation (cont’)

Number of multiple data transmissions during channel reserved duration:

Vdf : transmission time of data packet at default transmission rate Rdf.

Tcntl = TRREQ + TRRSP + TEREQ + TERSP


max

( ) 2

2A A cntl DIFS SIFS

df ACK SIFS

l w t T T Tk k

V T T

2 ( 2 )RREQ RRSP EREQ ERSP SIFS df ACK SIFSD T T T T k V T T

Packet Tx on Data Channel

To adjust transmission power of data packets Node A sends EERQ through channel i with maximum

allowable power max. Node B calculates channel gain GEREQ = XEREQ/ max and

replies with ERSP that contain GEREQ.

Node A estimates channel gain: DATA(1) = × GEREQ and determine the transmission power of first packet.

DATA(1) : lowest channel gain under with Tx rate RDATA(1) is allowed.


(1)(1) max

(1)

DATADATA

DATA

Performance evaluation (1/6)


Simulation model PU networks

40 data channels, each has bandwidth 1 MHz

PU_ON, PU_OFF: exponential distribution, mean = 300s

PU transmitter: randomly located in a circle with radius of 600m

PU receiver: randomly located in a circle with radius of 100m from PU transmitter



Simulation model (cont’) CR networks

CR node are located randomly over a circle with radius of 200m, positioned at the center of the distribution area of PUs

Number of CR: 30 nodes Mobility model: Random Walk with v =

0~4km/h, time tick = 0~10s Data traffic: Poisson distribution with rate =

18.75pk/s, packet size = 1000 bytes, data generation rate = 150kbps



Simulation model (cont’) Channel model

Path loss model: gain = C×d-3.5 (C = -72.92dB _ control channel; C = -66.08dB _ data channel)

Multipath fading: Jake’s spectrum model; central frequency = 915 MHz; PU transmission outage if IPU > -103 dBm; noise density = -163 dBm/Hz



Simulation model (cont’) Tx power and Tx rate

Control channel: 27 dBm; 1 Mbps Data channel: Rtx = 1, 1.5, 2, 3, and 4.5 Mbps;

Required SNR = 6, 9, 13, 16, and 22 dB, repectively; Rdf = 2 Mbps

Size of packets RN_ON, RN_OFF, US_REQ = 21 bytes RREQ, RRSP, EREQ, ERSP, ACK/NACK, CH_REL

= 32, 27, 21,23, 21 byte, respectively



Simulation model (cont’) Other settings

= 1 sec; = 0.5; = 0.95; c = 6 CR nodes access control channel according

to CSMA/CA Maximum retransmission = 3 Maximum allowable transmission power max

= 7 dBm


Effect of es and sensing urgency - Sensing interval.



Effect of es and sensing urgency – PU outage probability and average power consumed for sensing during 1 sec.



PU outage probability vs PU_ON duration of a channel



Control message overhead vs PU_ON duration of a channel



Performance comparison of proposed scheme and HPUA – System throughput and average packet delay



Performance comparison of proposed scheme and HPUA – PU outage probability and average energy consumed for sensing during 1 sec


Conclusions

The authors propose a new MAC scheme based on opportunistic sensing, for multichannel CR ad hoc networks.

CR node efficiently senses the entire channel pool by adjusting the sensing priorities of channels.

With controlled Tx power, the proposed CR system effectively protects hidden Pus and give higher throughput.

By allowing multiple packet transmission on reserved channel, traffic load on control channel is reduced.


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A Novel MAC Scheme for Multichannel Cognitive Radio Ad Hoc Networks