DYNAMIC SPECTRUM ACCESS

BY SANJANA PRASAD

Research scholarPSG COLLEGE OF TECHNOLOGY

1601RL01

New spectrum sharing paradigm that allows secondary users to access the abundant spectrum holes or white spaces

Promising technology to alleviate the spectrum scarcity problem

Increase spectrum utilization Overcomes two types of interference

◦ Harmful interference caused by device malfunctioning

◦ Harmful interference caused by malicious user

INTRODUCTION

Secondary users dynamically search for idle spectrum bands and temporarily access them for wireless communications

To avoid interference to primary users (PU)’s secondary users continuously monitor the spectrum bands and yield to PU’s whenever PU start using a band .

Dsa-made possible-cr technology

Functions of DSA :◦ Spectrum awareness◦ Cognitive processing◦ Spectrum access

COMPONENTS OF A COGNITIVE RADIO:◦ Analog RF front end◦ A digital processing engine ◦ Digital signal processor◦ Customized FPGA

Dynamic exclusive use Open sharing model Hierarchial access model

Dynamic Exclusive Use model:◦ Basic structure of the current spectrum regulation

policy are maintained in this model◦ Spectrum bands licensed to services for exclusive

use◦ Improves spectrum efficiency by introducing

flexibility

DSA MODELS

2 approaches: Spectrum property rights Dynamic spectrum allocation

Spectrum property rights:Allows licensees to sell and trade spectrum and to choose technology freelyEconomy,profit- play important role with the most profitable use of this limited resource

Dynamic spectrum allocation

◦ Improve efficiency through spectrum assignment by using spatial / temporal traffic statistics of different services

Open sharing model: Spectrum commons model Every user has equal rights to use the

spectrum Applied for wireless services which operates

in unlicensed ISM radio bands(WLAN) 3 TYPES: Uncontrolled commons Managed commons Private commons

Uncontrolled commons No entity has exclusive license to the

spectrum band Managed – commons

◦ Imposes a limited form of structure of spectrum access

◦ Resource which is owned or controlled by a group of individuals or entities

◦ Characterized by restrictions on when and how the resource is used.

Private commons:◦ Introduced by FCC.◦ allows advanced technologies which enable

multiple users to access the spectrum

Hierarchial access models : Interweave Underlay Overlay

Different from overlay and underlay DSA models

SU cannot access a licensed spectrum band as long as PU is active on the band

PU-absolute priority on the spectrum band SU accessing the spectrum band must yield

to PU whenever PU starts to access the band

Also called oppurtunistic spectrum access.

INTERWEAVE MODEL

SU’ s are constrained to oppurtunistically utilise spectrum holes or white spaces in the temporary ,spatial,and/or frequency domain.

SU uses SR –sense the sorounding environment

Selects one or more idle spectrum bands Switches the cognitive radio to the selected

bands to transmit

Allows SU to transmit on a licensed spectrum band regardless of the PU accessing the band or not, subject to a constraint that the accumulated interference from all SU’s is tolerable by the PU ie. below some threshold

2 approaches◦ UWB TECHNOLOGY◦ INTERFERENCE TEMPERATURE

UNDERLAY DSA MODEL

UWB Technology◦ SU transmit power ◦ Interference < threshold

Interference temperature◦ SU transmit with higher power as long as the total

interference from all SU’s on the band is below a threshold.

SU transmit on the licensed spectrum band even when the PU is accessing the band.

Targets maintaining the PU performance SU are allowed to transmit simultaneously

with PU s as long as there is no performance degradation

2 approaches:◦ Channel coding◦ Network coding

OVERLAY DSA MODEL

Channel coding Network coding

Used when a PU transmitter is transmitting a PU packet that is known to a SU transmitter

Su transmitter- can split into two parts-◦ One to transmit its own SU

packet◦ Transmit PU packet to

enhance the total power received such that SINR not degrade

Su-relay – between disconnected or weakly connected nodes.

While relaying a PU packet:◦ SU may encode an SU packet

onto the PU packet through network coding

◦ transport of the SU packet does not incur separate spectrum access ,without degrading the PU performance .

Accurate spectrum sensing Uncertainity of noise PUE attacks

CHALLENGES TO DSA

[1]Min Song,Chunsheng Xin,Yanxiao Zhao,Xiuzhen Cheng “Dynamic Spectrum Access: From Cognitive Radio To Network Radio”,IEEE Wireless Communications,Feb 2012.

[2]Goutam Ghosh,Prasun Das,Subhajit Chatterjee ,“Cognitive Radio And Dynamic Spectrum Access-a Study”,International Journal Of Next Generation Networks,Vol 6,No 1 ,March 2014

REFERENCES