Introduction System Model DC-MAC Design Network Initialization DC-MAC Working Data Transfer on Home Channel Data Transfer on a Foreign Channel Performance Analysis Conclusion References

1. Authors:
Mishra Vishram,
Lau Chiew Tong, and
Chan Syin
Presented By:
Iffat Anjum
Date:
20-11-14

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3.  The recent outburst of high definition content delivery
over wireless network
 exist a paradox between the shortage of the frequency
spectrum and its underutilization
 Cognitive radio based dynamic spectrum access
technique has been proposed to alleviate such paradox
by opportunistically utilizing the spectral holes in the
channels
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4.  In MAC protocols for CRN
 The idea is to develop a mechanism sharing the media (channel)
such that:
 interference is minimized and
 CR nodes can communicate with each other effectively.
 MAC scheme requires exchange of control signals
 Over a common signaling channel
 control channel saturation problem, can create a bottleneck for the
communication
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5.  hopping based control channel less protocol can be used
 which utilizes rendezvous channel as a common channel for
information exchange.
 But, it requires a tight synchronization among all nodes
 ensuring a grade of QoS
 traffic from different application need to be prioritized in order to
mitigate the detrimental effects of uniform resource allocation.
 service latency, signal-to-noise ratio, response time, bandwidth
etc, should be maintained too.
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6.  In DC-MAC
 a control channel less, non-channel-hopping MAC protocol for
single-hop cognitive radio network
 distributes the contention for channel access onto respective
channel.
 A time slotted beacon based structure is utilized on each channel
to distribute the contention
 solving the problem of control channel saturation.
 Four priorities of data type is supported by utilizing different
inter-frame spaces
 ensuring of QoS provisioning.
 Four way handshakes are utilized
 mitigating the problem of hidden terminals (if any)
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7.  Distributed ad-hoc cognitive radio network comprising of N CR
nodes and Z licensed users
 Each CR user equipped with a single half-duplex transceiver for
communication purpose.
 A rendezvous channel (RC) selected similar process of C-MAC
[Cordeiro C., Challapali K., "C-MAC: A Cognitive MAC Protocol for Multi-Channel Wireless Networks,"IEEE DySPAN 2007, pp.
147-157]
 Four priority classes
[WMM: Wi-Fi Alliance. "Wi-fi certified for wmm - support for multimedia applications with Quality of Service in Wi-Fi networks,"
Technical report, Wi-Fi Alliance, 2004.
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8.  The CR network is non-hopping network
 a CR node in the network stay on the selected channel until the
channel ceases to be free or the node has to move to other channel
for some reason.
 The channel on which a node resides is called as home channel
while all other channels w.r.t. it are termed as foreign channels.
 Each channel has a representative which broadcasts the
information about the nodes residing on the home channel
onto RC.
 The representative node (RN) is selected periodically
 Periodic Quiet periods are used for the purpose of sensing an
incumbent user on a channel.
 A node can perform in-band sensing or out-of-band sensing.
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Figure: Superframe structures for channels in DC-MAC

10.  The superframe of RC is composed of three separate intervals:
 Rendezvous channel beacon (RCB),
 Data transfer and
 Quiet period.
 A RCB has time-slotted architecture, where the size of RCB
depends on
 the number of channels used in the system+2 (C+2)
 During RCB, RN from all channels transmit their beacons on their
respective slots
 During quiet period of RC, all nodes which have home channel as
RC stop their communication and perform in-band sensing.
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11.  A superframe of data channel is composed of four separate
intervals:
 Home channel beacon (HCB),
 Home channel information beacon (HCI),
 data transfer and
 quiet period.
 A home channel beacon has a time-slotted architecture
 size of HCB depends upon the number of nodes on home channel.
 number of time-slot = number of nodes on home channel + 1
 RN distributes the information gained from RCB
 all the nodes on a home channel know about the information about
the home channels of all other nodes in the network
 distribution of quiet period
 channel conditions
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12.  A superframe of data channel is composed of four separate
intervals:
 Home channel beacon (HCB),
 Home channel information beacon (HCI),
 data transfer and
 quiet period.
 A home channel beacon has a time-slotted architecture
 size of HCB depends upon the number of nodes on home channel.
 The number of time-slot equals the number of nodes on home
channel + 1.
 RN distributes the information gained from RCB,
 all the nodes on a home channel know about the information about
the home channels of all other nodes in the network including the
distribution of quiet period and channel conditions.
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13.  A HCI is used to elect a RN from the set of all home nodes.
 The home node which has the least amount of load is elected
as a RN.
 Assume, the load metric to be weighted average of
packets sent/received in last 5 frames.
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Ni: represents the number of packets
sent/received in last ith frame

14.  Rendezvous Channel (RC) is established
 all nodes join through Rendezvous Channel Beacon (RCB)
 Initially nodes on RC perform out-of-band sensing to gather
information about other channels and this information is used for
migration purpose.
 If no node exists on a channel, then a new node migrates from RC
to that channel and starts its own beacon so that other nodes can
follow up (migrate).
 Assume
 all node uniformly select a channel as home channel.
 average N/C CR users on each channel.
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Network Initialization

15.  The data transfer on RC and data channel follows RTS/CTS
mechanism similar to 802.11.
 Here a four way handshake is employed to handle the multi-channel
hidden terminal problem.
 RTS/CTS packet contains network allocation vector (NAV) to
indicate the duration of transmission.
 The size of NAV can be calculated as:
 This allows other nodes in the network to go into doze mode
for power saving
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DC-MAC Working

16.  The system employs different set of inter-frame spaces for the
purpose of provisioning of QoS.
 An IFS is a random duration of time defined in [0, interval]
 Before transmitting any message a node perform sensing of the
channel
 decreases its counter at each step when the channel is sensed
free;
 if the channel is sensed busy the counter is freezed.
 sends the packet when the counter has reached zero.
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DC-MAC Working

17.  Depending upon the home channels of transmitter and
receiver
 the communication may take place on either of the home
channels of participating node.
 If the specified channel characteristics are not available on any
of the home channels,
 then the communication may take place over a foreign channel
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DC-MAC Working

18.  If both transmitter and receiver are on the same channel
 then communication takes place using RTS/CTS/DATA/ACK
mechanism, after IFS.
 All nodes which overhear the transmission
 Back-off their own transmission and goes into doze mode until the current
communication is finished.
 If the destination node lies on a channel other than that of the
home channel of sender
 the sender moves to the home channel of destination node
 Once the communication is finished or HCI of the home channel of
the sender starts, the sender moves back to its own home channel.
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Data Transfer on Home Channel

19.  A sender first moves to the home channel of the destination
node
 sends MOV packet which contains the destination ID along with
the channel the channel to which the destination node should
move on.
 If the receiver agrees, it replies with an acknowledgement.
 Immediately after acknowledgement, both transmitter and
receiver moves to the foreign channel
 Once the communication is finished or the HCI of the home
channel of the nodes starts, the nodes move back to their home
channels.
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Data Transfer on a Foreign Channel

20.  A sender first moves to the home channel of the destination
node
 sends MOV packet which contains the destination ID along with
the channel info
 If the receiver agrees, it replies with an acknowledgement.
 Immediately after acknowledgement, both transmitter and
receiver moves to the foreign channel
 Once the communication is finished or the HCI of the home
channel of the nodes starts, the nodes move back to their home
channels.
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Data Transfer on a Foreign Channel

21.  All C channels are modeled as ON-OFF source depending upon
the presence or absence of the PU respectively.
 The probability that a given channel will be available is
calculated by,
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22.  Performance evaluation of the system done in a discrete event
simulator in MATLAB which simulates the system up to MAC
frame level.
 The proposed scheme is compared against similar literature work
(C-MAC) done in [5].
 proposed a distributed contention based MAC scheme for ad-hoc
cognitive radio network with QoS provisioning.
 distributes the contention of channel access onto different channels
 reduces the control channel saturation problem.
 simple temporal synchronization across all channels with non-hopping
nodes in the network.
 four different access categories to data packets based on different
priorities.
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