EFFICIENT UTILIZATION OF RADIO

SPECTRUM BASED ON DSA

Ali Fotowat Ahmady – Faculty of EE, Sharif University Of Tech

12th Session of SATRC Feb. 28, 2011

WHY DSA? Value of frequency spectrum in wireless systems Fixed freq allocation Increase of users, needs and introduction of new

services Scarcity of freq spectrum

2

Cognitive Radio

Dynamic Spectrum Allocation

Dynamic Spectrum Access

3

MATURITY OF CR

4

SDR

Complete adjustability through software of all radio operating parameters.

Hardware Architecture of SDR

5

CR

When a radio is aware, adaptive, and learns, it is a CR.

Cognition cycle

6

CR NEEDS

Sensors creating awareness in the environment.

Actuators enabling interaction with the environment.

Memory and a model of the environment. Learning and modeling of specific beneficial

adaptations. Specific performance goals Autonomy Constraint by policy and use of inference

engine to make policy-constrained decisions 7

COMMERCIALIZATION ROADMAP OF COGNITIVE RADIO

8

CR SPECTRUM SHARING

9

TRANSMIT POWER ALLOCATION COMPARISON WITH UWB

10

TECHNICAL CHALLENGES

Spectrum sensing Detect spectral holes to opportunistically use

bands without causing harmful interference to legacy systems

RF front-end and signal path Wideband elements Nonlinearity and LO Harmonics Adequate IP2 Dynamic frequency selection: DFS Adaptive modulation

Power control, Sharing Management11

SENSING DETAILS

12

SENSING CHALLENGES

Hardware High sampling rate, High resolution ADCs with large dynamic range High speed signal processors Broad band RF components

Hidden Primary User Detecting Spread Spectrum users such as FHSS or

DSSS Sensing Duration and Freq(period). Security

13

HIDDEN PRIMARY USER PROBLEM

14

SPECTRUM SENSING METRICS

Bandwidth Resolution Freq Trade-off between the detection time and the

detection bandwidth and the sensing resolution

15

SPECTRUM SENSING METHODS

Energy Detection Time domain Freq domain

Feature based detection Matched filter Cyclostationary detection

16

ENERGY DETECTOR

Output is compared to the predefined threshold. Non-coherent, optimal, low signal processing.

Binary hypothesis

17

FEATURE BASED SENSING

Known patterns: Preambles, Midambles, Regularly transmitted pilot patterns, Spreading sequences.

Correlative sensing with a known copy of signal.

Applicable to systems with known signal patterns

More performance with longer length known signal patterns.

18

A/D N pt. FFTCorrelate

X(f+a)X*(f-a)Averageover T

x(t)Featuredetect

COOPERATIVE SENSING Solve noise uncertainty, fading, and shadowing Solve hidden primary user problem Decrease sensing time Spatial spectral joint detection Wide-band sensing1. centralized sensing(a central unit collects sensing

information from cognitive devices, identifies the available spectrum, and broadcasts this information to other cognitive radios or directly controls the cognitive radio traffic.)

2. Distributed sensing(cognitive nodes share information among each other but they make their own decisions as to which part of the spectrum they can use)

3. External sensing(an external agent performs the sensing and broadcasts the channel occupancy information to cognitive radios)

19

RELATED STANDARDS IEEE 802.22 WRAN fixed wireless access services support 6, 7 and 8 MHz channels OFDMA PHY layer Each station in an 802.22 network is required to perform spectrum

sensing final decision as to the availability of a channel is made by the base

station. Sensing is required for analog television, digital television and wireless

microphones. required detection time for all types is 2 seconds. the probability of detection is 0.9 probability of false alarm is 0.1

20

OTHER STANDARDS FOR UNLICENSED ACCESS AND SENSING CAPABILITIES

802.16h – Unlicensed WiMAX license-exempt operation of 802.16 networks,

that is defines a set of cognitive radio capabilities for Wimax networks.

802.11af – TV white space WiFi CogNeA – Industry standard for

personal/portable application on the TV white spaces

802.19.1 - TV White Space coexistence standard

21

EXAMPLE OF IMPLEMENTED CIRCUITS

receiver with a CR spectrum sensing capability in the UHF band A Fully Integrated UHF-Band CMOS Receiver With Multi-Resolution Spectrum

Sensing (MRSS) Functionality for IEEE 802.22 Cognitive Radio Applications, Jongmin Park, Taejoong Song,, Joonhoi Hur, Sang Min Lee, Jungki Choi, Kihong Kim, Kyutae Lim, Chang-Ho Lee, Haksun Kim, and Joy Laskar, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 44, NO. 1, JANUARY 2009.

22

23

RESULTS

24

EXAMPLE OF IMPLEMENTED CIRCUITS

Injection locking based sensing method A Novel RF Sensing Circuit Using Injection Locking and Frequency

Demodulation for Cognitive Radio Applications”, Chien-Jung Li, Fu-Kang Wang, Tzyy-Sheng Horng, and Kang-Chun Peng, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 57, NO. 12, DECEMBER 2009.

25

EXAMPLE OF COMMERCIAL PRODUCTSXG TECHNOLOGY

BSN250 Base Station TX70 Mobile VoIP handset xMSC mobile switching center

Advanced cognitive radio capabilities (detect and avoid, edge-device driven handoffs, proactive alternate channel/path determination)

translates the concept of mobile phones to the (unlicensed) band of 900MHz.

The core of technology is it capability of sensing for other systems in the band and determine if interference has reached unacceptable levels, and in such case change band.

26

Thanks.

27