IEEE 802.22Wireless Regional Area Network

Bahar RadfarShiraz University CSE Department

OverViewWhat is IEEE 802.22?

Why IEEE 802.22?

Cognitive Radio (CR)

Why TV bands ?!

Advantages & Disadvantages

The market for the IEEE 802.22

Topology of IEEE 802.22

Technology of IEEE 802.22

The enhanced IEEE 802.22 standard

Spectrum sensing

03WHAT ?!!!

The IEEE 802.22 standard is the first standard based on Cognitive Radios (CR) for Wireless Regional Area Networks (WRAN).

An air interface which is defined for allowing unlicensed users to work in TV bands when the incumbents (primary users) are not present in the network.

0104WHY ?!!!high requirements to frequency spectrum, the spectrum utilization is not optimum.

The measurements for the frequency bands below 3GHz from January/2004 to August/2005 showed that only about 5.2% of the spectrum is actually in use in the US.

The previous geographical coverage is not enough large to service the remote/rural areas, than the half of the population of many country are located in remote/rural areas.

0105Cognitive Radio (CR)

An intelligent radio that can be programmed and configured dynamically.

0106Cognitive Radio (CR)

Why TV bands? 0107

The first reason is the broadband access of this standard in remote and rural areas.

It has been realized that many TV channels are largely unoccupied in many parts of the US .

802.22 devices in the TV bands will be unlicensed, so lowers cost and is conducive to providing a more affordable service

Advantages 0108

The IEEE 802.22 users are in lower frequencies but some of previous standards may use the higher frequency bands which are more available .

high frequencies disadvantages: The cost of electronics for a given transmit power is higher.

The Doppler effect on mobile transmissions is exacerbated.

Advantages 0109

802.22 cover area much larger than other IEEE 802 standards

It can provide various type of services like data, voice, audio & video with appropriate Quality-Of-Service (QOS) support.

The users are unlicensed users in TV bands and this decreases the cost.

higher utilization of spectrum than the other standards

Disadvantages 0110

The propagation delay is more considerable in this standard in comparison to the others.

the self-coexistence and hidden incumbent problem

0111The market for the IEEE 802.22

The most important reason for developing technologies like WRAN 802.22 standard is the availability of broadband access in rural and remote areas as well as that in urban and suburban areas .

Two reasons for considering this standard as a suitable business case is providing wireless broadband access in large geographical coverage and incumbent considerations.

0112Topology of IEEE 802.22

a single Base Station (BS) and zero or more Consumer Premise Equipments (CPEs) .

The relations between these components is a master/slave relation.

The operations : sensing and transmitting/ receiving data.

BS does this spectrum sensing periodically itself and by the reports receiving from the CPEs, chooses the appropriate vacant channel to communicate with CPEs.

Each CPE has two antennas: one directional for communicating with the BS and the other omni-directional for sensing and performing measurements.

0113Topology of IEEE 802.22

0114Technology of IEEE 802.22

Because the random behavior of the vacancy of the TV channels, PHY and MAC ( Media Access Control ) layers both should be considered in our design.

The design of the layers is less innovative, and builds instead upon the structures already developed in IEEE 802.16 .

0115The PHY considerations

It should be high performance and low cost and complexity .

Must be able to adapt to different conditions and also needs to be flexible for jumping from channel to channel without errors in transmission or losing clients (CPEs).

This flexibility is also required for being able to dynamically adjust the bandwidth, modulation and coding schemes.

With OFDMA it will be possible to achieve this fast adaptation needed for the BS's and CPEs.

Another important consideration in the 802.22 PHY layer, is the Transmission Power Control (TPC) and frequency agility.

0116The MAC considerations Media Access Control

the master role of the BS that means no CPE can initialize, continue or stop communication without the authorization of the BS.

listen before talk

The CPE should find a proper channel to look for and aware the BS of its presence in the network.

Periodic spectrum sensing by the BS and receiving the feedback from the CPEs continues during the communication in order to change the channel appropriately in any time.

BS send preamble signal at the start of each frame to CPE’s to separate it’s message from TV broadcasts

Spectrum measurements and spectrum sensing is one of the most important issues

0117The enhanced IEEE 802.22 standard

In this subsection we introduce an enhanced version of the IEEE 802.22 standard in which two major problems have been solved.

1. Self-coexistence

2. The hidden incumbents

0118Self-coexistence

One of the most important features is coexistence with the incumbents and self-coexistence between the overlapping 802.22 networks.

The coexistence with the incumbents is achieved by accurate and fast spectrum sensing, measurements, detection algorithms, and spectrum management, which are done by the CPEs and the BS.

Solving by the graph coloring model 0119

G = { V , E }

Solving by the graph coloring model 0120

Each color shows the bandwidth of its corresponding BS.

Solving by the graph coloring model 0121

G is m-colorable check each node in G if it can be made color i without conflict to the other nodes’ colormade by traditional graph coloring algorithm ; for each color i {store the information of occurrences of each color after this iteration ;}color graph G with traditional graph coloring algorithm

Solving by the graph coloring model 0122

By this method the channel utilization increases while the self- coexistence is considered as well as possible.

The hidden incumbents 0123

We can say hidden incumbents are the primary users which can be sensed by the CPE but not by the BS.

In this case suppose that while the CPE and the BS are communicating, the hidden incumbent becomes present in the network.

In another manner, suppose that the CPE is switched on while an hidden incumbent is present in the channel .

Solving by multiple broadcasting 0124

Use dynamic multiple broadcasting in different frequencies (candidate frequencies) periodically.

The number of broadcast messages by BS is updated dynamically depending on the feedback received from the CPEs.

When CPE find encounters an in-band licensed incumbent transmission (hidden to the BS) report it to BS on another candidate channel.

The BS then changes the channel to some other unused band thus overcoming the hidden incumbent problem.

Spectrum sensing 0125

Make observations of the radio frequency (RF) spectrum to identify unused television channels

It is undertaken within the Customer Premises Equipments, CPEs.

Spectrum sensing 0126

In band spectrum sensing

Out of band spectrum sensing : locate possible alternative channels

Ensures sufficient guard band between the channels in use by the BS and any TVs stations that may be using adjacent channels.

In-band spectrum sensing 0128

Fast sensing:accomplished quicklyuses a simple energy detection algorithmcomplete within 1 ms

Fine sensing: if the BS believes there is need for a more accurate measurementtakes around 25-30 ms. the CPE looks at the signatures of signals that may be the primary user, i.e. television.

Spectrum sensing 0129

Any Question?See you next t ime, have nice day