Cognitive Radio & DSA ;Introduction et concept.ppt
- 1. Cognitive Radio & DSA By : M.R. Heidarpour
- 2. Isfahan University of Technology Page 2/32 Static licensing : • Multiple allocation over all of the band • A crisis of spectrum availability Pros: • Effectively controls interferenc • Simple to design hardware Cons: • Utilization of 0.5% in the 3-4 GHz • And 0.3% in 4-5 GHz A new approach to spectrum licensing is needed
- 3. Isfahan University of Technology Page 3/32 Solutions ( what I want to present) : Cognitive Radio Spectrum management Spectrum mobility Spectrum sharing sensing Analyzing Decision cooperative transmitter Interference based energy Match filter Cyclo stationary A suggested Architecture (CORVUS) Dynamic Spectrum allocation history Different types of DSA Example: UMTS DVBT merging Driving project 1 2
- 4. Isfahan University of Technology Page 4/32 Cognitive radio : • “cognitive Radio” was first introduced by J.Mitola : An intelligent wireless communication system that is An intelligent wireless communication system that is aware of its surrounding environment aware of its surrounding environment (i.e., outside (i.e., outside world), and uses the methodology of understanding- world), and uses the methodology of understanding- by-building to learn from the environment and adapt by-building to learn from the environment and adapt its internal states to statistical variations in the its internal states to statistical variations in the incoming RF stimuli by incoming RF stimuli by making corresponding making corresponding changes in certain operating parameters changes in certain operating parameters (e.g., (e.g., transmit-power, carrierfrequency, and modulation transmit-power, carrierfrequency, and modulation strategy) in real-time, with two primary objectives in strategy) in real-time, with two primary objectives in mind: mind: · · highly reliable communications whenever and highly reliable communications whenever and wherever needed; wherever needed; · efficient utilization of the radio spectrum. · efficient utilization of the radio spectrum.
- 5. Isfahan University of Technology Page 5/32 Cognitive radio : • FCC definition : A ‘‘Cognitive Radio’’ is a radio that can change its transmitter parameters (So must be Reconfigurable) based on interaction with the environment in which it operates. (So must have some capabilities such as sensing)
- 6. Isfahan University of Technology Page 6/32 Spectrum sensing: • An important requirement to sense the spectrum holes. sensing Transmitter detection Cooperative detection Interference- Based detection Match filter Energy Cyclo stationary
- 7. Isfahan University of Technology Page 7/32 Energy sensing: • Energy sensing can be performed in both time domain and frequency domain. • For either case, we consider the received signal of the form y(n) = x(n) + z(n) Time or freq. samples of received signal target signal AWGN Note that |y(n)|2 is a sequence of (IID) random variables with : NB large S :Gaussian random variable with:
- 8. Isfahan University of Technology Page 8/32 Energy detection (con.): • When there is no signal present, i.e. x(n) = 0, the sensing metric is: • When there is signal present, the sensing metric is: Bad behavior in Small buffer size
- 9. Isfahan University of Technology Page 9/32 Match filter detection : • If a priori knowledge of primary user signal (such as modulation type, shaping signal, …) is available , Match filter detection is optimal because it maximizes SNR in AWGN channel • In this case : When there is no signal present : When there is signal present : Better behavior in small buffer size
- 10. Isfahan University of Technology Page 10/32 Cyclo-stationary detection : • modulated signals are characterized as cyclostationarity since their mean and autocorrelation exhibit periodicity. • These features are detected by analyzing a spectral correlation function. Δt T t Δt T t 2 / 2 / * ) 2 - , ( ) 2 , ( 1 1 lim lim ) ( t t T T T t x dt f t X f t X T t f S 2 / 2 / 2 ) ( ) , ( T t T t fu j T du e u x f t X Spectral correlation function can be used for feature detection Sx α is a two dimensional complex transform on a support set (f, α)
- 11. Isfahan University of Technology Page 11/32 Example of Spectral Correlation Function • BPSK modulated signal: – carrier at 125 MHz, bandwidth 20 MHz, square root raised cosine pulse shape with roll-off=0.25, sampling frequency 0.8 GHz Power Spectrum Density Spectrum Correlation Function Power Spectrum Density Spectrum Correlation Function
- 12. Isfahan University of Technology Page 12/32 Cyclostationary Detection Hypothesis testing: Is the primary signal out there? ) ( ) ( ) ( : 1 n w n x n y H ) ( ) ( : 0 n w n y H x(n) is primary user signal with known modulation and Sx α (f) w(n) is noise with zero mean and unknown power N0 that could vary over time Noise is not cyclostationary process thus Sw α (f)=0 for α≠0. ) ( ) ( ) ( : 1 f S f S f S H w x y Spectral correlation function of y(n): ) ( ) ( : 0 f S f S H w y 2 / 2 / 2 ) ( ) , ( T n T n fu j T du e u y f n Y N n T T y f n Y f n Y T N f S 0 * ~ ) 2 - , ( ) 2 , ( 1 1 ) ( For fixed number of samples N compute estimate of SCF: T pt. FFT around nth sample
- 13. Isfahan University of Technology Page 13/32 Cooperative detection : Transmitter detection problems : the sensing information from other users is required for more accurate detection.
- 14. Isfahan University of Technology Page 14/32 Protocol cycle of detection, collection and broadcast Strategy (in an OFDM C.R.): It takes a long time to collect the results from each terminal in the form of the MAC packet Suggested methods to decrease this time: reducing the number of detecting mobile terminals ( not interesting ) physical layer operation instead of MAC layer operation +
- 15. Isfahan University of Technology Page 15/32 Collection of the measurement data: A. First Phase If a mobile terminal encounters a spectral access by a licensed user to a certain subband which was not announced by the access point, then it transmits complex symbols at maximum power level (e.g. 1 + j1) on these OFDM carriers where the new licensed user accesses were etected
- 16. Isfahan University of Technology Page 16/32 Collection of the measurement data(con.): Second Phase One-to-one mapping between allocated and idle subbands Now, only the subbands that remain allocated are boosted
- 17. Isfahan University of Technology Page 17/32 Interference based detection: • Instead of transmitter detection we can measure the interference level in receivers & use the freq. band until a receiver begins suffering from interference. This approach is suitable for underlay (UWB) cognitive radios
- 18. Isfahan University of Technology Page 18/32 Spectrum analysis: enables the characterization of different spectrum bands, which can be exploited to get the spectrum band appropriate to the user requirements. these characteristics are: • Interference • Path loss • Wireless link errors • Link layer delay • Holding time Spectrum decision: Once all available spectrum bands are characterized,appropriate operating spectrum band should be selected for the current transmission considering the QoS requirements and the spectrum characteristics.
- 19. Isfahan University of Technology Page 19/32 Spectrum mobility In spectrum management and spectrum mobility functions, application, transport, routing, medium access and physical layer functionalities are carried out in a cooperative way, considering the dynamic nature of the underlying spectrum. When current channel becomes worse or a primary user appears Spectrum mobility
- 20. Isfahan University of Technology Page 20/32 Spectrum mobility (con.): Network Protocol adaption Changing The channel condition spectrum management Spectrum mobility For example: • FTP packets must be stored & RT packets must be discarded during the mobility process. • TCP parameters must be updated after mobility according to new link conditions such as delay,…
- 21. Isfahan University of Technology Page 21/32 CORVUS ( a Cognitive Radio approach for usage of Virtual Unlicensed Spectrum) 1.Dedicated spectrum for this purpose 2.ISM/UNII 3.UWB Carry a low bit rate signaling • the principle idea of a Spectrum Pooling system in CORVUS: – Each spectrum pool is divided into N sub-channels. – Sub-channels selected to create a SU Link should be scattered over multiple PU frequency.for two reasons: » it limits the interference impact of a SU on a re-appearance of a PU » if a PU appears during the lifetime of a SU Link it would impact very few (preferable one) of the Sub-Channels used by the SU Link – for cooperative detection SUs work in groups & signal to each other via the control channel
- 22. Isfahan University of Technology Page 22/32 CORVUS:( CON.) • Physical layer : – Sensing – Channel estimation – Data transmission ( parameter adjustment) • Link layer : – Group management – Link management (choosing ,setupping ,maintaini ng a connection) – MAC (resolve the competition)
- 23. Isfahan University of Technology Page 23/32 Dynamic Spectrum Allocation : (DSA) • Spectrum is valuable and our current regularity wastes it • DSA aims to manage the spectrum utilized by a converged radio system and share it between participating radio networks over space and time to increase overall spectrum efficiency. Must be re-regulated to
- 24. Isfahan University of Technology Page 24/32 History : • Introduced at the World Radio Conference (WRC) 2000 • Discussed at WRC 2003 and suggested as an agenda item for WRC 2010 ; further studies will he done until that time. • Discussions have also started on a national level : • U.K : – spectrum trading should be implemented in the UK as soon as possible – Broadcasters should he given the ability to lease spectrum to other uses and/or users. • U.S : – FCC: “preliminary data and general observations indicate that many portions of the radio spectrum are not in use for significant periods of time, and that spectrum use of these ‘white spaces’ (both temporal and geo- graphic) can he increased significantly” These regulatory developments show that there is a perceived need to bring regulations up to date
- 25. Isfahan University of Technology Page 25/32 Methods for DSA: Fixed : current regulations Contiguous : contiguous blocks of spectrum with variable boundaries allocated to different RANs Fragmented : any RAN can he assigned an arbitrary piece of spectrum anywhere in the band
- 26. Isfahan University of Technology Page 26/32 Example : ( UMTS , DVBT merging ) Temporal DSA Spatial DSA
- 27. Isfahan University of Technology Page 27/32 Fix vs. dynamic allocation :
- 28. Isfahan University of Technology Page 28/32 DSA requirements: • Flexible frequency carrier tuning • Variable duplex distances between the for- ward and reverse links for frequency division duplex (FDD)-based systems • Flexible receiver signal filtering 1. Network 2. Physical layer ( we focus on it ) The required flexibility for DSA can be achieved with SDR-based reconfigurable equipment If you want to know Current and breakthrough key enabling technologies for reconfigurable equipment, click here
- 29. Isfahan University of Technology Page 29/32 Drive : Dynamic Radio for IP Services in Vehicular Environments • aims at coordination of existing radio networks into a hybrid network to ensure spectrum efficient provision of mobile multimedia services • Provide mechanisms for spectrum sharing between systems using Dynamic Spectrum Allocation (DSA)
- 30. Isfahan University of Technology Page 30/32 Driving : (con.) • Has two approaches to increase spectrum efficiency : – System selection : • Spectrum efficiency can be increased by choosing the optimum transmission technology for a given load scenario. – As an example: Transmission via a DAB broadcast link should be preferred in a scenario where many mobile users are requesting the same data. Several point-to-point UMTS links would considerably waste bandwidth – Dynamic spectrum allocation (DSA) The dynamic nature of this network is a major challenge to the routing itself and also on the update of the routing tables
- 31. Isfahan University of Technology Page 31/32 References : • NeXt generation/dynamic spectrum access/cognitive radio wireless networks: A survey ,by Ian F. Akyildiz, Won-Yeol Lee, Mehmet C. Vuran *, Shantidev Mohanty @ ELSERVIER • L. Xu, R. Tonjes, T. Paila, W. Hansmann, M. Frank, M.Albrecht, DRiVE-ing to the internet: dynamic radio for ip services in vehicular environments, in: Proc. of 25th AnnualIEEE Conference on Local Computer Networks, November2000, pp. 281–289. • T.A. Weiss, J. Hillenbrand, A. Krohn, F.K. Jondral,Efficient signaling of spectral resources in spectrum pooling systems, in: Proc. 10th Symposium on Communications and Vehicular Technology (SCVT), November 2003. • T.A. Weiss, F.K. Jondral, Spectrum pooling: an innovative strategy for the enhancement of spectrum efficiency, IEEE Radio Communication Magazine 42 (March) (2004) 8–14. • R.W. Brodersen, A. Wolisz, D. Cabric, S.M. Mishra, D.Willkomm, Corvus: a cognitive radio approach for usage of virtual unlicensed spectrum, Berkeley Wireless Research Center (BWRC) White paper, 2004. • P. Leaves, K. Moessner, R. Tafazoli, D. Grandblaise, D.Bourse, R. Tonjes, M. Breveglieri, Dynamic spectrum allocation in composite reconfigurable wireless networks, IEEE Comm. Magazine, vol. 42, May 2004, pp. 72–81. • Some Physical Layer Issues of Wide-band Cognitive Radio Systems by Haiyun Tang @ IEEE 2005 • Thanks from Anant Sahai, Danijela Cabric for their slides on cyclostationary detection
- 32. Isfahan University of Technology Page 32/32 The end Thank you for your listening