Routing in cognitive radio ad hoc network
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Routing in Cognitive Radio Ad-hoc Network. By Payel Bandyopadyay. What am I going to deal about?. What is an ad-hoc network? That doesn't depend on any infrastructure ( eg . Access points, routers) for setting up a wireless connection

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Routing in Cognitive Radio Ad-hoc Network

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Routing in Cognitive Radio Ad-hoc Network


Payel Bandyopadyay

What am I going to deal about?

What is an ad-hoc network? That doesn't depend on any infrastructure (eg. Access points, routers) for setting up a wireless connection

What I am going to deal about?The challenges that cognitive radio network faces in communicating with each other in an ad-hoc manner

Why is it a challenge for CR networks?CR networks have multi-hop architecture and dynamic spectrum access which increases the complexity of designing the communication protocols at different layers

What is the main routing problem in CRAHNs ?

the creation and the maintenance of wireless multi-hop paths among Secondary Users (sus) by deciding both the relay nodes and the spectrum to be used on each link of the path

Routing in multi-hop CRNs

What are the challenges of routing in CRAHNs?

Spectrum awareness:Should always be aware of the available spectrum

set up of Quality routes: Quality of end to end routes is measured not only by throughput, delay, energy efficiency and fairness but also by path stability and PU presence

route maintenance: Sudden appearance of PU may lead to sudden route failure so how to restore the “broken” paths without affecting the quality of routes

Classification of cognitive routing scheme

full spectrum knowledge:nodes in CRNs have full knowledge about the availability of spectrum from the central spectrum database recently promoted by FCC to show the availability of spectrum below 900 MHz and around 3GHz

local spectrumKNOWLEDGE: nodes do not have a full knowledge of the spectrum availability. Each SU has its own spectrum availability knowledge gathered through distributed protocols

Classification of cognitive routing schemes

Graph based routing approach

  • Hey! I am based on full spectrum knowledge

  • I consist of 2 phases

  • Graph abstraction: G =(N, V, f(V)), where N = number of nodes, V =number of edges and f(V) =function which allows to assign a weight to each edge of the graph

  • Route calculation: Designing a path in the graph connecting source–destination pairs

  • I also take care of Channel assignment

Doesn’t this sounds interesting?

Let’s check it out then……………….

Layered-graph creation

Layered graph architecture of 4 nodes of CRNs

What are these edges?

  • Access edges connects each node with it’s suitable sub nodes

  • Horizontal edges connects sub nodes of same logical layers

  • Vertical edges connects sub nodes of various layers of same secondary device to portray the switching ability of secondary device from one channel to another channel to forward incoming traffic.

How are costs assigned to these edges?

  • The cost of vertical edge depends on channel switching overhead and is fixed in routing path computation period

  • The cost of horizontal edge is dependent on link usage

  • The cost of access edge can be set arbitrarily because only access edge of source and destination participate in the path computation

Figure showing how costs are assigned to each edge

How is path designed between these 4 nodes?

  • Suppose, we want to design path from A to D

  • First we choose node A and B

  • Path we choose is A, A1, B1, B

  • As, both sub nodes A1 and B1 are in channel 1, so radios of both A and B is assigned to channel 1

  • As, sub nodes A1 and B1 are taken in the path, they are referred as active node while the sub nodes A2 and B2 are referred as inactive nodes

  • Update the vertical and horizontal edges of the sub nodes

How are edges updated?

  • We remove the horizontal edge between A2 and B2

  • We change the vertical edge between A1 and A2 to unidirectional from A1 to A2. Similarly, vertical edge between B1 and B2 becomes unidirectional from B1 to B2

  • The horizontal edge of B2 and C2 is changed to out going from B2

  • Then we increase the cost of all horizontal edges that are related to the path- cost of horizontal edges between A1, B1 and between B1, C1 is increased

Updated layered graph after path A -> B is computed

Updated edge costs

Then how is total path constructed?

  • Similarly, we compute the path between C and D in the

  • We assign C and D nodes in channel 2 as both of their active sub nodes (C2;D2) lies in channel 2

But how is path from a to d constructed?

  • While computing the total path from A to D, B and C are in different primary channels

  • So, when large number of packets of this path arrives at node B, it switches its channel from channel 1 to channel 2

  • In most link centric channel assignment cases, nodes often fluctuate between channels to maintain the link level connectivity to neighbours

Ok friends I was graph based routing approach! Hope you all enjoyed my approach of designing routing paths. Bye bye!

Welcome to local spectrum knowledge scheme!Ido not have a full knowledge of the spectrum availability. In my scheme Each SU has its own spectrum availability knowledge gathered through spectrum sensing. But I can assure you of providing the best routing paths! Let’s see how……………………..

Interference and power based solutions

  • Mainly based on power consumption for transmission and the interference that is generated along a multi hop path through secondary users

  • It solves the problem of neighbour discovery and routing


(A) Wireless ad hoc network (B) Cognitive wireless ad hoc network

Why is Neighbour discovery a problem?

  • To discover neighbouring terminals, it is necessary for the both terminals of a transmitter and a receiver to be the same wireless system

  • If the primarily active wireless systems of the both terminals are different,the neighbour discovery does not success at all

  • Additionally, even though the active wireless systems of the terminals are the same, the neighbour discover will fail if the radio coverage ranges of them do not reach in each other

Didn’t understand? Wait don’t be depressed!

Neighbour discovery problems

Limitation of routing in cognitive wireless ad hoc

How can these problem be solved?

Don’t worry my protocol is designed in such a manner that it solves these issues! Don’t believe me? Come, let’s check it out then…….

Common link control radio (CLCR)

  • Common link control radio (CLCR) is an active wireless system in each cognitive terminal, which is necessary to be the same wireless system and is required to be as a more energy efficient wireless system and a wider coverage area

  • CLCR enables us to effectively solve the neighbour discovery problem by which every terminal performs neighbour discovery over a common active wireless system

Neighbour discovery and routing over CLCR

But how is routing path constructed?

1. At first, source node (called the transmitter) broadcasts a neighbour discovery request over CLCR

2. When receiving the request, the receivers feed back the information of all available wireless systems to the transmitter over CLCR

3. The transmitter selects a receiver that is reachable by the minimum weight wireless system into the neighbours

4. This steps goes on repeating until destination node is reached.

An example of routing parameters

Hey! Didn’t I solve all the problems that I specified?

Ok, I am done! Hope you all enjoyed my approach of designing routing paths. Bye bye!

Delay based solutions

  • Hey! I take care of delays that occur in establishing, maintaining and sending traffic in multi-hop routes in CRAHNs.

  • The delay metrics that Iconsidered is queuing delay

What is queuing delay?

Queuing delay refers to output transmission capacity of a single node

So how do I take care of delays while designing routing paths?

  • My protocol is based on local coordination of neighbours

  • A node which is common among the neighbour nodes decides whether to keep the incoming flow or to change its direction to its neighbours based on the local work load

Route establishment

Hey didn’t I solve the delay problem?

Ok, I am done! Hope you all enjoyed my approach of designing routing paths. Bye bye!

Link quality/stability based solutions

  • My main aim is to maintain a stable route between secondary source destination pairs with low maintenance costs

  • When PUs become active, one or more links should be altered with a link that is not interfered by PUs

  • SUs coordinate with each other in terms of signalling, which measures cost in terms of power and service interruption time during switching routes

What are epochs?

Epochs means time interval in which the network topology is stable

PU becoming active

Rerouting due to PU activation

Hey didn’t I maintained stable path between SU nodes in spite of PU interference?

Ok, I am done! Hope you all enjoyed my approach of designing routing paths. Bye bye!

Hey wasn’t my approaches interesting? Did I solve the routing issues?

Do you have any questions?

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