A Novel MAC Scheme for Multichannel Cognitive Radio Ad Hoc Networks
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Transcript of 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
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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.
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Reduces data transmission delay
Introduction (2/2)
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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.
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The proposed MAC scheme (2/3)
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.
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The proposed MAC scheme (3/3)
Overall operation that CR node performs with data transceiver.
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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.
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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.
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Reservation of Data Channel(1/4)
Control packets for data transmission.
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Reservation of Data Channel(2/4)
Exchange of control packets during data channel reservation and transmission.
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Reservation of Data Channel(3/4)
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).
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( )A DIFS RREQ RREQ At T T D l w
Reservation of Data Channel(4/4)
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
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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.
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(1)(1) max
(1)
DATADATA
DATA
Performance evaluation (1/6)
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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
Performance evaluation (1/6)
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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
Performance evaluation (1/6)
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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
Performance evaluation (1/6)
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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
Performance evaluation (1/6)
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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
Performance evaluation (3/6)
Effect of es and sensing urgency - Sensing interval.
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Performance evaluation (4/6)
Effect of es and sensing urgency – PU outage probability and average power consumed for sensing during 1 sec.
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Performance evaluation (5/6)
PU outage probability vs PU_ON duration of a channel
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Performance evaluation (5/6)
Control message overhead vs PU_ON duration of a channel
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Performance evaluation (5/6)
Performance comparison of proposed scheme and HPUA – System throughput and average packet delay
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Performance evaluation (5/6)
Performance comparison of proposed scheme and HPUA – PU outage probability and average energy consumed for sensing during 1 sec
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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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THANK YOU FOR YOUR ATTENTION