Cognitive Radio. Master Universitario en Ingeniería de Telecomunicación. I. Santamaría. Universidad de Cantabria

Transcription

1 Cognitive Radio Master Universitario en Ingeniería de Telecomunicación I. Santamaría Universidad de Cantabria

2 Contents Introduction Interweave CR Underlay CR Cognitive Radio 1 / 22 1/22

3 NAT IO NS & INFORMATIO N ADMINISTRAT EXPLORATION GOVERNMENT EXCLUSIVE NON-GOVERNMENT EXCLUSIVE IO N LAND LAND METEOROLOGICAL AIDS METEOROLOGICAL SERVICE EXAMPLE DESCRIPTION Primary Capital Letters Secondary 1st Capital with lower case letters GOVERNMENT/ NON-GOVERNMENT SHARED This chart is a graphic single-point-in-time portrayal of the Table of Frequency Allocations used by the FCC and NTIA. As such, it does not completely reflect all aspects, i.e., footnotes and recent changes made to the Table of Frequency Allocations. Therefore, for complete information, users should consult the Table to determine the current status of U.S. allocations. Office of Spectrum Management October 2003 ASTRONOMY DETERMINATION OPERATION RESEARCH STANDARD FREQUENCY AND TIME SIGNAL STANDARD FREQUENCY AND TIME SIGNAL Aeronautical Radionavigation (Radio Beacons) ( BEACONS) ** * EXCEPT AERO (R) Amateur ( BEACONS) Aeronautical 36.0 NOT ALLOCATED 36.0 MET. SAT (S-S) Fixed SAT SAT. BCST SAT ISM ±.02 MHz ** EXCEPT AERO WAVELENGTH RES SAT EXPL Earth Expl FX-SAT BCST SAT. BAND DESIGNATIONS ACTIVITIES Aeronautical Radionavigation Meteorological Satellite Spectrum Usage The spectrum is a regulated resource (ITU, FCC) -SAT (TLM) LAND (TLM) ( TELEMETERING) SAT. ** (Space to Earth) SAT. SAT. (Space to Earth) (Space to Earth) (Aero. TLM) (space to Earth) FX LAND FX FI XED ** (TV CHANNELS 21-36) AIDS - SAT RES (TV CHANNELS 2-4) ISM 5.8 ±.075 GHz TV ISM ±.250 GHz GHz IS DESIGNATED FOR UNLICENSED DEVICES Fixed (TV CHANNELS 5-6) (AM ) (FM ) * * (TV CHANNELS 7-13) S) * LAND ISM 6.78 ±.015 MHz ISM ±.007 MHz ISM ±.163 MHz Fixed MET MET. SAT. Aids EXPLORATION RESEARCH ASTRONOMY LAND Maritime UNITED STATES THE SPECTRUM 3 khz 300 khz 300 khz 3 MHz (R) (OR) 3 MHz * ( BEACONS) Aeronautical Maritime Radionavigation (Radio Beacons) (R) Aeronautical * (R) (OR) * (DISTRESS AND CALLING) ( BEACONS) (SHIPS ONLY) STANDARD FREQ. AND TIME SIGNAL (5000 KHZ) STANDARD FREQ. Space Research ( BEACONS) (R) (OR) * (R) (OR) (R) (OR) STANDARD FREQ. AND TIME SIGNAL (10,000 khz) STANDARD FREQ. Space Research (R) (OR) (R) (OR) (R) ASTRONOMY * STANDARD FREQ. AND TIME SIGNAL (15,000 khz) STANDARD FREQ. Space Research (OR) (R) (OR) STAND. FREQ. & TIME SIG. Space Research STANDARD FREQUENCY & TIME SIGNAL (20,000 KHZ) STANDARD FREQ. Space Research (R) (TELEPHONY) (DISTRESS AND CALLING) (TELEPHONY) ** STANDARD FREQ. AND TIME SIGNAL (2500kHz) Space Research STANDARD FREQ. STANDARD FREQ. AND TIME SIGNAL STANDARD FREQ. AND TIME SIGNAL (25,000 khz) STANDARD FREQ. Space Research LAND LAND ** ASTRONOMY LAND ** ** ** LAND Radionavigation (Radio Beacons) Aeronautical Radionavigation (Radio Beacons) Aeronautical ( BEACONS) LAND (R) 30 MHz SERVICES COLOR LEGEND LAND LAND LAND LAND Radio Astronomy LAND ASTRONOMY LAND LAND LAND (R) (R) (R) (R) (R) NAV- 30 MHz 300 MHz STD. FREQ. & TIME SIGNAL SAT. (400.1 MHz) EXPL Earth Expl. Earth Expl Sat Satellite MET. AIDS EXPL Earth Expl Sat (Radiosonde) METEOROLOGICAL AIDS (SONDE) ASTRONOMY RESEARCH Amateur LAND LAND LAND LAND LAND (TV CHANNELS 14-20) ASTRONOMY Amateur RES.. ** Amateur Amateur ** BCST- METEOROLOGICAL 300 MHz 3 GHz (Ground) AERO. SAT. NAV.(Ground) ASTRONOMY Space Research AERO. NAV. SAT NAVIGATION NAVIGATION RESEARCH Satellite Satellite Satellite ** EXPL. Satellite EXPL. Satellite (no airborne) EXPL. Satellite (no airborne) RESEARCH (deep space only) RESEARCH Meteorological NAV. METEOROLOGICAL Amateur Amateur- sat (s-e) Amateur SAT Amateur Amateur Amateur Amateur Satellite RESEARCH EXPL. SAT. ASTRONOMY Space Research EXPL. ASTRONOMY RESEARCH RESEARCH (Deep Space) NAV. Space Research Time Signal Satellite SAT. Land Research NAVIGATION SAT. Satellite Land ** Satellite Land Fixed SAT. Satellite Fixed FX SAT. L M Sat Space Research Space Research Space Research ASTRONOMY RESEARCH EXPL. SAT. Fixed Earth Expl Sat Space Res. LOC. Radioloc. BCST SAT. FX SAT RES. FX SAT EXPL. SAT. ASTRONOMY RES. EXPL. SAT. Earth Expl. Satellite (Active) Standard Exploration Frequency and Time Signal Satellite Earth Satellite (S-S) Exploration e-e-sat SAT. & Satellite time (S-S) e-e-sat (s-s) SAT. Earth Exploration Satellite (S-S) Earth std freq SAT EXPLORATION RESEARCH ASTRONOMY E A R T H SAT. RES. EXPL. SAT NAVIGATION NAVIGATION Fixed MET. SAT. (s-e) NAVIGATION NAVIGATION EXPLORATION RESEARCH ASTRONOMY NAVIGATION LAND LAND LAND LAND (OR) MOB. SAT. RES. OPN. MET. SAT. Mob. Sat. RES. OPN. MET. SAT. MOB. SAT. RES. OPN. MET. SAT. Mob. Sat. RES. OPN. MET. SAT. LAND (R) (space to Earth) Satellite (S- E) (R) (space to Earth) (Space to Earth) (R) (space to Earth) LAND LAND LAND LAND Land Fixed Radio- LAND NAV. (Space to Earth) AERO. DET. SAT. SAT AERO. NAV. DET. SAT. SAT. ASTRONOMY AERO. NAV. DET. SAT. SAT. Sat. ASTRONOMY SAT. ASTRONOMY RESEARCH METEOROLOGICAL ASTRONOMY AIDS (SONDE) METEOROLOGICAL (s-e) METEOROLOGICAL AIDS (Radiosonde) (LOS) (LOS) RESEARCH OPERATION EXPLORATION SAT. (s-e)(s-s) (s-e)(s-s) (s-e)(s-s) SAT. Fixed DETERMINATION SAT. BCST - SAT. ** FX-SAT (S - E) E-Expl Sat Radio Ast Space res. MOB** B- SAT. FX-SAT ASTRON. RESEARCH EXPL SAT ISM ±.500 GHz NAVIGATION ASTRONOMY LAND ISM ± GHz ISM ± 1GHz Amateur (TELEPHONY) SPA CE RESEARCH ( Passive) ** -SAT ** LAND ASTRONOMY EXPL SAT LAND Fixed (TLM) LAND (TLM) (TLM) Fixed ISM ± 13 MHz ** Standard Freq. and Space TRAVELERS INFORMATION STATIONS (G) AT 1610 khz 3 x 10 7 m 3 x 10 6 m 3 x 10 5 m 30,000 m 3,000 m 300 m 30 m 3 m 30 cm 3 cm 0.3 cm 0.03 cm 3 x 10 5 Å 3 x 10 4 Å 3 x 10 3 Å 3 x 10 2 Å 3 x 10Å 3Å 3 x 10-1 Å 3 x 10-2 Å 3 x 10-3 Å 3 x 10-4 Å 3 x 10-5 Å 3 x 10-6 Å 3 x 10-7 Å VERY LOW FREQUENCY (VLF) LF MF HF VHF UHF SHF EHF INFRARED VISIBLE ULTRAVIOLET X-RAY GAMMA-RAY COSMIC-RAY Audible Range AM Broadcast FM Broadcast P L S C X Radar Bands Radar Sub-Millimeter Visible Ultraviolet Gamma-ray Cosmic-ray Infra-sonics Sonics Ultra-sonics Microwaves Infrared X-ray FREQUENCY 0 10 Hz 100 Hz 1 khz 10 khz 100 khz 1 MHz 10 MHz 100 MHz 1 GHz 10 GHz 100 GHz 1 THz Hz Hz Hz Hz Hz Hz Hz Hz Hz Hz Hz Hz Hz 3 khz MAGNIFIED ABOVE 300 GHz Amateur ISM ± 50 MHz PLEASE NOTE: THE SPACING ALLOTTED THE SERVICES IN THE SPEC- TRUM SEGMENTS SHOWN IS NOT PROPORTIONAL TO THE ACTUAL AMOUNT OF SPECTRUM OCCUPIED Aeronautical FREQUENCY ALS ** ** SAT * AERO NAV SAT Space Res.(act.) STANDARD FREQ. AND TIME SIGNAL (20 khz) SAT. LAND LAND LAND LAND LAND LAND BROADCAST STANDARD FREQ. AND TIME SIGNAL (60 khz) * ASTRONOMY LAND LAND BROADCAST LAND LAND LAND LAND LAND LAND LAND R- LOC. B-SAT FX MOB FX AIDS Amateur Fixed ** MOB. R- LOC. B-SAT RES. EXPL. OP. (s-s) SAT. (s-s) (s-s) FX. FX MOB Fixed Fixed location MET. AIDS. RES. Space Opn. (Radiosonde) SAT. MET. AIDS (Radiosonde) SAT. OPN. MET-SAT. Met-Satellite MET-SAT. Met-Satellite SAT. BROADCAST FX SAT STD FREQ. & TIME FX SAT SAT RES. EXPL. SAT. ** RAD.AST ** EXPL. SAT. RES. Amateur Earth Expl. Satellite (Active) SAT RES.. LOC. Amatuer BILE 3 GHz 30 GHz ACTIVITY CODE AL USAGE DESIGNATION Standard Frequency and Time Signal Satellite Stand. Frequency and Time Signal Satellite 30 GHz ASTRONOMY RESEARCH EXPLORATION SAT. RESEARCH (deep space) RES. SAT RE. EXPL.. SAT. RESEARCH (space-to-earth) SAT. - Sat (s - e) SAT RES. BROAD- CASTING BROAD- CASTING ** ASTRONOMY NAV. SAT. NAV.SAT. MOB. SAT SAT SAT RESEARCH EXPLORATION EXPLORATION RESEARCH RES. SAT EXPL-SAT SAT RES. -ES RES. -ES SAT EXPLORATION SAT. INTER EXPLORATION SAT. RESEARCH EXPLORATION SAT. ** EXPLORATION RESEARCH ** NAVIGATION NAVIGATION LOC. Amateur LOC. Amateur Amateur Sat. LOC. SAT Amateur Amateur Satellite BROAD- BROAD- CASTING CASTING EXPL. RESEARCH RESEARCH EXPL SAT. MO- RESEARCH EXPL SAT. Amateur Amateur Satellite EXPL. SAT. RES. EXPLORATION RES. ASTRONOMY RESEARCH EXPLORATION SAT. RESEARCH EXPLORATION ASTRONOMY RES. EXPLORATION SAT. RES. EXPL. SAT. Amateur Satellite Amateur EXPLORATION RES. 300 GHz U.S. DEPARTMENT IONAL TELEC O MM UNICAT OF COMMERCE U.S. DEPARTMENT OF COMMERCE National Telecommunications and Information Administration THE SPECTRUM Figure 1.1: Frequencies allocation chart of the Unites States. Cognitive Radio 2 / 22 2/22 5

4 The spectrum is underutilized Band ( MHz) Measurements averaged over six locations in USA Report by M. McHenry NSF Spectrum Occupancy Measurements, 2005 Average use 5.5% Max. utilization 25% NYC average 13.1% Significant white spaces even in cellular bands Cognitive Radio 3 / 22 3/22

5 Introduction Introduction Spectrum SensingInterweave CR Extensions Underlay IEEE CR Introduction Spectrum Sensing Extensions IEEE Licensed Licensed bands offer bands aoffer lota lot of of spectrum opportunities Licensed bands offer a lot of spectrum opportunities Cognitive Radio I. Santamaría Cognitive Radio 4 / 22 4/22

6 General concepts In a Cognitive Radio network we have Primary users (PUs): Users that have a license to access the spectrum Secondary users (SUs): Users that do not have license to access the spectrum, they are allowed to access the spectrum as long as they do not cause harmful interference to the PUs We need spectrum sharing techniques between PUs and SUs Cognitive Radio 5 / 22 5/22

7 Spectrum sharing paradigms 1. Interweave (a.k.a. Dynamic or Opportunistic Spectrum Access) The SU is allowed to transmit only in unoccupied bands Spectrum sensing and interference avoidance 2. Underlay The SU can always transmit as long as the interference to the PU is below a prescribed level Interference control techniques Cognitive Radio 6 / 22 6/22

8 Introduction We consider an interweave SISO CR network composed of: PUs: use a licensed portion of the spectrum, but do no transmit neither all the time nor across all frequency bands/channels SUs: try to detect time-frequency spectral holes and then transmit over them without causing harmful interference to the PUs A critical component of interweave CR networks is therefore spectrum sensing The sensing requirements in CR applications are typically very stringent, so it is a difficult operation For instance, sensing requirements for Digital TV channels in the IEEE standard are Channel detection time: smaller than 2 seconds Sensitivity: 116 dbm (over 6 MHz) Probability of detection: 0.9 Probability of false alarm: 0.1 SNR: 20.8 db Cognitive Radio 7 / 22 7/22

9 Spectrum Sensing: Problem statement Primary user SISO channel (unknown) h Secondary user At each sensing period, the SU acquires N samples and has to solve a binary hypothesis testing problem H 1 : x[n] = hs[n] + v[n], n = 0,..., N 1 H 0 : x[n] = v[n], n = 0,..., N 1 where v[n] is AWGN, that is v[n] CN (0, σ 2 v ) The sensing process is repeated periodically Spectrum sensing problem SU transmits if H0 Sensing Payload transmission Sensing Decision H1/H0 Decision H1/H0 Cognitive Radio 8 / 22 8/22

10 Depending on the prior knowledge of the SU about the problem parameters (s[n], h, σ 2 v ), different detectors can be applied All of them use a test statistic T (x) (which is a function of the observations) and take a decision by comparing it with a predefined threshold λ T ( ) : C N R = T (x) H1 H 0 λ T (x) is a function of the observations x = [x[0], x[1],..., x[n 1]] T, and it is therefore a random variable To characterize the performance of a detector, (Pd, P fa, we need the pdf of T (x) under each hypothesis This might be difficult for some detection problems Cognitive Radio 9 / 22 9/22

11 ROC curve To compare the performance of two detectors we use the receiver operating characteristic (ROC) curve pd Detector 1 Detector p fa Cognitive Radio 10 / 22 10/22

12 Matched filter & Energy detectors Assuming that the PU signal, s[n], and the channel, h, are fully known, the optimal test statistic is the matched filter ( T (x) = 1 N 1 ) N Re x[n](hs[n]) For the energy detector both the channel and the PU signal are assumed to be unknown, the test statistic is n=0 T (x) = 1 N 1 x[n] 2 N n=0 Cognitive Radio 11 / 22 11/22

13 Comparison Matched filter Energy detector pd N Cognitive Radio 12 / 22 12/22

14 Multiantenna detectors Let s assume that the SU is equipped with L > 1 antennas v 1 [n] h 1 + x 1 [n] = h 1 s[n] + v 1 [n] h 2 v 2 [n] Primary user h L + v L [n] x 2 [n] = h 2 s[n] + v 2 [n]. + x L [n] = h L s[n] + v L [n] The detection test is H 1 : x[n] = hs[n] + v[n], n = 0,..., N 1 H 0 : x[n] = v[n], n = 0,..., N 1 Cognitive Radio 13 / 22 13/22

15 Notice that the L L covariance matrix under both hypotheses has different structure H 1 : R 1 = E [ x[n]x[n] H] = hh H E[ s[n] 2 ] + R v, H 0 : R 0 = E [ x[n]x[n] H] = R v Typically R 0 = R v is a diagonal matrix and R 1 is different from diagonal The presence of a PU introduces correlation among antennas This is the key idea behind most multiantenna detectors proposed in the literature Cognitive Radio 14 / 22 14/22

16 Sphericity detector Assumptions: The noise across antennas is spatially and temporally i.i.d. v[n] CN (0, σ 2 I) The PU signal(s) and channel(s) are unknown and arbitrary s[n] is Gaussian (OFDM signals are typically modeled as Gaussian signals) Under these assumptions the test to detect the presence of a PU becomes a test on the structure of the covariance matrix of Gaussian data where R0 = σ 2 I H 1 : x[n] CN (0, R 1 ) H 0 : x[n] CN (0, R 0 ) R1 is an arbitrary covariance matrix (Hermitian and positive definite) Cognitive Radio 15 / 22 15/22

17 The Generalized Likelihood Ratio test for this problem (derived by J. Mauchly in 1940) is given by where det(ˆr) (1/L) 1 L tr(ˆr) H 0 H 1 λ ˆR = 1 N 1 x[n]x H [n] N n=0 is the sample covariance matrix, and λ is a threshold selected to achieve a given P fa Sphericity Test This test is known as the sphericity test, and it is widely used in multivariate data analysis Cognitive Radio 16 / 22 16/22

18 Underlay cognitive radio Primary network (minimum performance requirement) Secondary network Interference Interference constraint Underlay Cognitive Radio: secondary users (SUs) are allowed to coexist with the primary users (PUs) as long as they guarantee them a given performance The PU performance can be guaranteed, for instance, by fixing a minimum rate requirement R PU R Cognitive Radio 17 / 22 17/22

19 The SISO case Tx PU Rx PU n 1 P 1 h 11 R PU R h 21 p2 P 2 Tx SU h 12 h 22 Rx SU n 2 The PU transmits its maximum power P 1 unaware of the SU The SU controls its transmitted power p 2 P 2 The noises are Gaussian with variance σ 2 The PU rate requirement is established in terms of its point-to-point capacity without interference ) R = α log (1 + P1 h11 2, α [0, 1] σ 2 Cognitive Radio 18 / 22 18/22

20 For a given alpha, there is a maximum level of interference (interference temperature) tolerated by the PU This interference temperature determines, in turn, the maximum power transmitted by the SU log (1 + P 1 h 11 2 ) σ 2 + p 2 h 12 2 α log (1 + P 1 h 11 2 ) σ P 1 h 11 2 (1 σ 2 + p 2 h P 1 h 11 2 ) α σ 2 p 2 h 12 2 P 1 h 11 2 ( ) α σ P1 h11 2 σ 1 2 The rate achieved by the SU is R SU = log (1 + p 2 h 22 2 ) σ 2 + P 1 h 21 2 Cognitive Radio 19 / 22 19/22

21 The multiantenna case Tx PU Rx PU P 1 x PU = s 1 h 11 n 1 Tx SU h 12 h 21 Rx SU x SU = w 2 p SU s 2 P 2 h 22 n 2 The PU transmits its maximum power P 1 unaware of the SU The SU can control the level of interference by Designing its transmit beamformer wsu Reducing its transmit power p2 P 2 Cognitive Radio 20 / 22 20/22

22 Scheme 1: Interference avoidance The PU does not tolerate any interference (α = 1) and achieves a rate R PU = log (1 + P 1 h 11 2 ), The SU applies zero-forcing beamforming: any w SU with w SU = 1 such that w T SUh 12 = 0 is a valid solution The SU achieves a rate R SU = log (1 + P 2 wsu T h 22 2 ) σ 2, + P 1 h 21 σ 2 Cognitive Radio 21 / 22 21/22

23 Scheme 2: MRT with power control The PU tolerates some interference (α < 1) and has a rate requirement R PU = α log (1 + P 1 h 11 2 ), The SU applies maximum ratio transmission σ 2 w SU = h 22 h 22 and controls its power to satisfy the rate requirement of the PU The signal transmitted by the SU is x SU = βw SU s 2, 0 β 1 The SU achieves a rate R SU = log (1 + P 2β h 22 2 ) σ 2, + P 1 h 21 Cognitive Radio 22 / 22 22/22