Transcript
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
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