Cognitive radio is a paradigm for wireless communication in which either a network or a wireless node changes its transmission or reception parameters to communicate efficiently avoiding interference with licensed or unlicensed users. This alteration of parameters is based on the active monitoring of several factors in the external and internal radio environment, such as radio frequency spectrum, user behaviour and network state. this presentation discusses main approaches and protocols of multichannel cognitive radio networks.

1. 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

2. Outline
Multi-channel MAC
Multi-channel MAC Approaches
What is Cognitive Radio(CR)?
Overview of some Cognitive multi-channel
MAC protocols.
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3. 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
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4. Multi-channel MAC
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5. 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).
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6. 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.
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7. Common Control Channel Approach
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8. 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
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9. Split phase Approach
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10. 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
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11. Common Hopping Approach
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12. 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.
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13. 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.
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14. FCC: In most places, Over 70% of
the allocated spectrum is not used !
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15. 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.
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16. Some Cognitive MAC protocols
 Hang Su and Xi Zhang's MAC Protocol.
 HC-MAC protocol.
 Noun Choi et al protocol.
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17. 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)
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18. Hang Su and Xi Zhang's MAC Protocol.
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19. 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
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20. HC-MAC protocol
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21. 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.
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22. Noun Choi et al MAC Protocol
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23. A comparison between some
Cognitive Radio MAC protocols
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24. 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.
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25. THANK YOU
King Abdullah II School of Electrical
Engineering - Princess Sumaya University
for Technology