Multi Channel Protocols In Cognitive Radio Networks

Multi-Channel MAC Protocols in
Cognitive Radio Networks

Prepared by:
Mohammad J. Abdelhadi
Muhammad K. Mustafa

King Abdullah II School of Electrical Engineering
Princess Sumaya University for Technology

Outline
Multi-channel MAC
Multi-channel MAC Approaches
What is Cognitive Radio(CR)?
Overview of some Cognitive multi-channel
MAC protocols.

King Abdullah II School of Electrical Engineering - Princess Sumaya University for Technology 1

Multi-channel MAC

 Multi-channel means that there are more than one channel
available for communication in a system.

 Why Multi-channel MAC?
• Reducing collusion among users
• Higher throughput
• Less normalized propagation delay


Multi-channel MAC


Multi-channel MAC Approaches

 There are three main approaches for Multi-channel
MAC
• Common Control Channel Approach(CCC).
• Split Phase Approach(SP).
• Common Hopping Approach(CH).


Common Control Channel Approach

 The CCC approach applies a single dedicated common control channel.
 Usually uses more than one transceiver, one of them is tuned to the
common control channel at all time.
 Advantages:
• Solves the hidden terminal problem( when using more than one
transceiver).
• Doesn't require time synchronization.
 Disadvantages:
• Congestion can occur.
• Energy inefficient
• Bandwidth inefficient.


Common Control Channel Approach


Split phase Approach

 It splits all channels into two phases:
• Control phase
• Data phase.
 During a control phase, all nodes tune to a common control channel.
 During the data phase, nodes tune to negotiated channels for data
transmission.
 Advantages:
• Uses Only one transceiver
• Does not allow the hidden terminal problem
• Energy Efficient
 Disadvantages:
• Precise time Synchronization is required
• Data Channels are wasted during the control phase
• Data Channel negotiation is only during the control phase


Split phase Approach


Common Hopping Approach

 Every node hops through all available channels following a common
hopping pattern.
 After sending the control packets and agree to send data, a node pair
stop hopping until the transmission is completed.

 Advantages:
• Using only one transceiver
• No common Control channel
• Data channel negotiation is performed simultaneously on different
channels.
 Disadvantages:
• The hidden terminal problem
• There is a high Channel switching delay
• Time Synchronization


Common Hopping Approach


Default Hopping Sequence Approach

 Every node determines its default hopping pattern using the seed
of a pseudo random generator which is known by all nodes.
 same communication procedure that used in CH but with a
scheduled sequence.
 Same advantages and disadvantages of CH.


What is Cognitive Radio

 The main aim behind CR is to utilize the unused spectrum at
a given time and place, thereby creating virtual unlicensed band.
 Two kinds of users in CR networks; primary users(PU) and
secondary users(SU).
 A great principle of CR is the using of the spectrum from SU must
not affect the communication of PU.
 Once the PU returns to a channel, the communication of the SU in
that channel must stop immediately.
 SUs can exchange spectrum information with each other.


FCC: In most places, Over 70% of
the allocated spectrum is not used !


Cognitive MAC protocols and its
Fundamentals

 Cognitive MAC protocols allow unlicensed users to share the
licensed spectrum.
 The presence of PU distinguishes cognitive MAC protocols from
other multi-channel MAC protocols.
 Sensing and distribution of channels is a major concern in CR MAC
protocols.
 Each Cognitive MAC protocol may use more than one approach of
multi-channel MAC approaches.
 Cognitive MAC protocols are in its infancy.


Some Cognitive MAC protocols

 Hang Su and Xi Zhang's MAC Protocol.

 HC-MAC protocol.

 Noun Choi et al protocol.


Hang Su and Xi Zhang's MAC Protocol.

 This protocol assumes that each SU is equipped with two transceivers
 One is for a dedicated control channel and the other is for a data
channel.
 In the control channel the time is divided into time slots and each slot
contains two phases; reporting phase and negotiation phase.
 When a node wants to transmit data, it first senses the channels and
reports the channel state.
 If one channel is idle, it negotiates with the destination over the
control channel on which channel to be used.
 Two sensing policies are used:
• Random Sensing Policy(RSP)
• Negotiation-based sensing policy (NSP)


Hang Su and Xi Zhang's MAC Protocol.


HC-MAC protocol

 Assumes that a control channel is available for secondary users
at any time.
 Each SU is equipped with single transceiver.
 Time frame is divided into three time slots, each with three
phases; contention phase, sensing phase, and transmission phase.
 In contention phase, secondary users content the spectrum and reserve
channels.
 In sensing phase, they conduct sensing in each channel.
 In transmission phase, secondary user will transmit data in channels
sensed ideal.

Contention Sensing Transmission
Phase Phase Phase


HC-MAC protocol


Noun Choi et al MAC Protocol

 This protocol assumes that there are two transceivers at least for each
node.
 One is used for transmitting data while the other is used for receiving
data.
 Each node chooses an available channel and keep it as its Home
Channel (HCh) which its information are broadcasted into a common
control channel to its neighbors.
 If a node wants to transmit data to another one, it has to tune its
transmitting radio to the HCh of the destination node.
 Another HCh is selected in the following cases:
o PU returns to use the same channel.
o Any disagrees with the node's HCh.
o The selected HCh is noisy.


Noun Choi et al MAC Protocol


A comparison between some
Cognitive Radio MAC protocols


Summary
 The use of Multi-channel facilitates and
improves many communication systems.
 Multi-channel MAC protocols have many categories and ways to
be established.
 Cognitive Radio is a new idea aims to utilize the maximum
bandwidth available.
 Cognitive Radio MAC protocols are based on Multi-channel MAC
protocols with a lot of concern in channel sensing and distribution.


THANK YOU

King Abdullah II School of Electrical
Engineering - Princess Sumaya University
for Technology

Multi Channel Protocols In Cognitive Radio Networks

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