Wireless Networked Systems

Transcription

1 Wireless Networked Systems CS 795/895 - Spring 2013 Lec #10: Medium Access Control Advanced Networking Cognitive Network, Software Defined Radio Tamer Nadeem Dept. of Computer Science

2 Spectrum Access Page 2 Spring 2013 CS 795/895 - Wireless Networked Systems

3 Spectrum Utilization Use of radio frequency bands has been regulated through spectrum allocations with licensing procedure. However, measurements on the licensed bands show severe temporal and / or spatial underutilization of the assigned spectral resources. A snapshot of spectrum utilization up to 6 GHz in an urban area at mid-day Page 3 Spring 2013 CS 795/895 - Wireless Networked Systems

4 Motivation Bandwidth becoming scarcer and more valuable Increased demands on wireless applications Users demand higher performance To solve the imbalance between spectrum shortage and spectrum underutilization an innovative spectrum access strategy called spectrum pooling has been envisioned. A concept of cognitive radio (CR) has been proposed to fulfill the unique requirements of intelligence and spectrum agility necessary for successful deployment of such dynamic spectrum access. Page 4 Spring 2013 CS 795/895 - Wireless Networked Systems

5 Motivation Spectrum pooling Allows opportunistic secondary (unlicenced) access to spectral resources unused by their primary (licensed) owners. Secondary transmission must avoid any harmful interference to primary systems. CRs have to regularly perform reliable radio scene analysis to detect the presence of primary user signals with high detection and low false alarm probability. Goal is to support multiple transmissions and increase performance by mitigating interference Page 5 Spring 2013 CS 795/895 - Wireless Networked Systems

6 Background Cognitive radio Smart and spectrally flexible radio (secondary user device, SU) that monitors and senses its radio environment for potential spectrum opportunities. Secondary users operating on licensed Band Required to detect primary users signals (physical-layer) Avoid and yield the channel use to primary users (MAC-layer) In addition, coordination with other secondary users Page 6 Spring 2013 CS 795/895 - Wireless Networked Systems

7 Cognitive Radio Definition by FCC: A radio or system that senses its operational electromagnetic environment and can dynamically and autonomously adjust its radio operating parameters to modify system operation, such as maximize throughput, mitigate interference, facilitate interoperability, access secondary markets. Page 7 Spring 2013 CS 795/895 - Wireless Networked Systems

8 Cognitive Radio CR is an emerging concept designed to enable more efficient use of frequency spectrum and the reuse of licensed frequencies. CR should be adaptive in order to respond to dynamic changes in the spectrum use. Vacate specified frequency bands upon request while service call is in progress Adapt QoS requirements to changing conditions Transmit over non-contiguous frequency bands to take advantage of all available/unused spectrum CR should also be able to sense the environment in which they operate Spectrum sensing => find transmission opportunities Modulation classification => identify competing systems Page 8 Spring 2013 CS 795/895 - Wireless Networked Systems

9 Cognitive Radio Concepts of a spectrum hole and opportunistic spectrum sharing: Page 9 Spring 2013 CS 795/895 - Wireless Networked Systems

10 Cognitive Radio: Definitions Spectrum gap, spectrum hole, white space Spatially & temporally unused part of the radio spectrum, which is considered for use by CR Primary user (PU) Licensed user/privileged user of a frequency band Secondary user (SU) Opportunistic user of a frequency band Waveform Signal model & other essential characteristics of the (PU or SU) communication system Page 10 Spring 2013 CS 795/895 - Wireless Networked Systems

11 Types of CR Systems Underlay systems use wide bandwidth and low-enough power spectral density not to disturb PUs. Spread spectrum, UWB Interweave CR is based on identification of spectral holes. Overlay: the SU RX and TX are assumed to know and utilize info about the PU signal Example: SU TX sends a signal which consists of (1) relayed PU signal and (2) SU signal, possibly with special coding (e.g. dirty paper coding). The relayed PU signal is included to guarantee sufficient SNR for nearby PU receivers. SU receiver detects both PU signal and SU signal, using interference cancellation techniques. Black space systems: Transmitting at relatively low power level on top of powerful PUs. Detection based on interference cancellation, after detecting PU data. Like overlay, but no PU relaying needed Page 11 Spring 2013 CS 795/895 - Wireless Networked Systems

12 Types of CR Systems Underlay transmission Overlay transmission Page 12 Spring 2013 CS 795/895 - Wireless Networked Systems

13 CR Functionalities Higher layers Cognitive cycle, adapting to the environment, learning/predicting the PU characteristics and spectrum usage patterns; game-theoretic approaches Real-time spectrum markets Reliable information about primary usage Cognitive pilot channel Data base of primary users (PUs) & positioning of secondary user (SU) stations Spectrum sensing Dynamic spectrum access (DSA) scheme Spectrum exploitation Flexible, spectrum agile waveforms and signal processing for secondary communications Software defined radio technologies are essential in this context Page 13 Spring 2013 CS 795/895 - Wireless Networked Systems

14 CR Functionalities Page 14 Spring 2013 CS 795/895 - Wireless Networked Systems

15 Levels of Cognitive Radio Functionality Level Capability Comments 0 Pre-programmed A software radio 1 Goal Driven Chooses Waveform According to Goal. Requires Environment Awareness. 2 Context Awareness Knowledge of What the User is Trying to Do 3 Radio Aware 4 Capable of Planning Knowledge of Radio and Network Components, Environment Models Analyze Situation (Level 2& 3) to Determine Goals (QoS, power), Follows Prescribed Plans 5 Conducts Negotiations Settle on a Plan with Another Radio 6 Learns Environment Autonomously Determines Structure of Environment 7 Adapts Plans Generates New Goals 8 Adapts Protocols Proposes and Negotiates New Protocols Adapted From Table 4-1Mitola, Cognitive Radio: An Integrated Agent Architecture for Software Defined Radio, PhD Dissertation Royal Institute of Technology, Sweden, May Page 15 Spring 2013 CS 795/895 - Wireless Networked Systems

16 Cognition Cycle Level 0 SDR 1 Goal Driven 2 Context Aware 3 Radio Aware 4 Planning 5 Negotiating 6 Learns Environment 7 Adapts Plans 8 Adapts Protocols User Driven (Buttons) Outside World Infer from Context Pre-process Parse Stimuli Observe Autonomous Orient Establish Priority Generate Alternate Goals Normal Select Alternate Immediate Normal Urgent Goals New States Infer from Radio Model Learn Plan Decide States Determine Best Plan Determine Act Generate Best Allocate Resources Known Waveform Waveform Initiate Processes Negotiate Protocols Page 16 Spring 2013 CS 795/895 - Wireless Networked Systems

17 Knowledge/detection of primary usage Cognitive pilot channel Dedicated control interface ideally to all local users of the radio channel Could provide explicit information about primary usage In the first stage, expected to be used as a means for closer coordination of wireless networks using existing technologies (e.g., sharing the same frequency band for GSM/WCMDA/HSPA/LTE/WiMAX/... waveforms in a flexible way) Means for exchanging information between spectrum sensing stations (cooperative sensing) Data base of primary users & positioning of secondary user stations Database maintenance is critical Central element in the first CR standard IEEE , along with spectrum sensing Page 17 Spring 2013 CS 795/895 - Wireless Networked Systems

18 Knowledge/detection of primary usage Spectrum sensing Sensing the radio environment to detect on-going primary transmissions Idea is to detect spectral holes as opportunities for secondary transmissions Cooperative sensing by multiple stations helps to mitigate problems, e.g., due to shadow fading. Reliable detection of primaries in a single mobile station is an extremely challenging task Minimum infrastructure needed, suitable for ad-hoc networks. Most challenging scheme to implement from the RF point of view Page 18 Spring 2013 CS 795/895 - Wireless Networked Systems

19 Spectrum Sensing in General Occupancy sensing white spaces or spectral holes grey spaces black spaces Methods (matched filtering) energy-based detection (radiometer) feature-based detection CP autocorrelation for OFDM primaries Cyclo-stationary detection Covariance & eigenvalue based methods (within sample sequence and/ or between antennas) Many others Fixed sample size vs. sequential detection principles Cooperative sensing Page 19 Spring 2013 CS 795/895 - Wireless Networked Systems

20 Dynamic Spectrum Access Scheme MAC protocol for the secondary user system Usually expected to support, in the same region, multiple independent SU systems Cognitive pilots support coordinated use of the same resources by multiple operators / SU systems Opportunistic dynamic spectrum access (DSA) for ad-hoc type operation Distributed coordination, usually no central control element between different SU systems is assumed. Basically different SU systems are competing for the spectral resources To make the idea sensible, some form of distributed co-operation is needed (e.g., good neighbor strategy, fairness) Game theory & other advanced concepts often considered in the developments. Page 20 Spring 2013 CS 795/895 - Wireless Networked Systems

21 Spectrum agile waveforms for secondary communications Very flexible waveforms are needed Waveforms need to be adapted to the radio environment Adjustable center frequency, bandwidth, SNR requirements, etc. Fragmented spectrum use is of interest: The overall transmission band may consist of multiple non-adjacent frequency slots Well-contained spectrum for high spectral efficiency without leakage to adjacent PU frequency channels. Multicarrier modulation has many of the desired features Page 21 Spring 2013 CS 795/895 - Wireless Networked Systems

22 Evolution of Cognitive Radio Cognitive Radio Spectrum Deregulation Drives Software-defined Radio Page 22 Spring 2013 CS 795/895 - Wireless Networked Systems

23 Cognitive Radio & SDR SDR s impact on the wireless world is difficult to predict But what is it good for? Engineer at the Advanced Computing Systems Division of IBM, 1968, commenting on the microchip Some believe SDR is not necessary for cognitive radio Cognition is a function of higher-layer application Cognitive radio without SDR is limited Underlying radio should be highly adaptive Wide QoS range Better suited to deal with new standards Resistance to obsolescence Better suited for cross-layer optimization Page 23 Spring 2013 CS 795/895 - Wireless Networked Systems

24 Software Defined Radio & CR Flexible, intelligent systems allow reconfiguring a radio in software and communication via different protocols at different times Software-Defined Radio Hardware driven radios à parameters are determined by hardware and cannot be changed without hardware changes. Digital radios à perform part of the signal processing or transmission digitally, but is not programmable in the field. SDR à all functions, modes and applications are configured by software and may be adapted in the field. CR incorporates intelligence driving SDR platforms Observe the RF environment in which they operate, learn from past actions, evaluate alternatives, and make decisions on how to better provide services. Page 24 Spring 2013 CS 795/895 - Wireless Networked Systems

25 Software-Defined Radio - SDR Forum Radios that provide software control of a variety of modulation techniques, wide-band or narrow-band operation, communications security functions such as hopping, and waveform requirements of current and evolving standards over a broad frequency range. Page 25 Spring 2013 CS 795/895 - Wireless Networked Systems

26 Software Radio Classification Tier 0: Hardware Radio (HR) No changes to system can by done by so1ware Tier 1: So2ware- Controlled Radio (SCR) Control func8onality implemented in so1ware, but change of a<ributes such as modula8on and frequency band cannot be done without changing hardware Page 26 Spring 2013 CS 795/895 - Wireless Networked Systems

27 Software Radio Classification Tier 2: So2ware- Defined Radio (SDR) Capable of covering substan8al frequency range and of execu8ng so1ware to provide variety of modula8on techniques, wide- band or narrow- band opera8on, communica8ons security func8ons and meet waveform performance requirements of relevant legacy systems Capable of storing large number of waveforms or air interfaces, and of adding new ones by so1ware download System so1ware should be capable of applying new or replacement modules for added func8onality or bug fixes without reloading en8re set of so1ware Separate antenna system followed by some wideband filtering, amplifica8on, and down conversion prior to receive A/D- conversion The transmission chain provides reverse func8on of D/A- conversion, analog up- conversion, filtering and amplifica8on Page 27 Spring 2013 CS 795/895 - Wireless Networked Systems

28 Software Radio Classification Tier 3: Ideal So2ware Radio (ISR) All of capabili8es of so1ware defined radio, but eliminates analog amplifica8on and heterodyne mixing prior to A/D- conversion and a1er D/ A conversion Tier 4: Ul?mate So2ware Radio (USR) Ideal so1ware radio in a chip, requires no external antenna and has no restric8ons on opera8ng frequency Can perform a wide range of adap8ve services for user Intended for comparison purposes rather than implementa8on Page 28 Spring 2013 CS 795/895 - Wireless Networked Systems

29 Future: Shift from Tier 0 to 4 Anil Shukla, QinetiQ Page 29 Spring 2013 CS 795/895 - Wireless Networked Systems

30 SDR Architecture Page 30 Spring 2013 CS 795/895 - Wireless Networked Systems

31 Advantages of SDR Ease of design Reduces design- cycle 8me, quicker itera8ons Ease of manufacture Digital hardware reduces costs associated with manufacturing and tes8ng radios Mul?mode opera?on SR can change modes by loading appropriate so1ware into memory Use of advanced signal processing techniques Allows implementa8on of new receiver structures and signal processing techniques Fewer discrete components Digital processors can implement func8ons such as synchroniza8on, demodula8on, error correc8on, decryp8on, etc. Flexibility to incorporate addi?onal func?onality Can be modified in the field to correct problems and to upgrade Page 31 Spring 2013 CS 795/895 - Wireless Networked Systems

32 Benefits of SDR Flexible/reconfigurable Reprogrammable units and infrastructure Reduced obsolescence Mul8band/mul8mode Ubiquitous connec?vity Different standards can co- exist Enhances/facilitates experimenta?on Brings analog and digital worlds together Full convergence of digital networks and radio science Networkable Simultaneous voice, data, and video Page 32 Spring 2013 CS 795/895 - Wireless Networked Systems

33 How is a Software Radio Different from Other Radios? - Application Conventional Radio Supports a fixed number of systems Reconfigurability decided at the time of design May support multiple services, but chosen at the time of design Software Radio Dynamically support multiple variable systems, protocols and interfaces Interface with diverse systems Provide a wide range of services with variable QoS Cognitive Radio Can create new waveforms on its own Can negotiate new interfaces Adjusts operations to meet the QoS required by the application for the signal environment Page 33 Spring 2013 CS 795/895 - Wireless Networked Systems

34 How is a Software Radio Different from Other Radios? - Design Conventional Radio Traditional RF Design Traditional Baseband Design Software Radio Conventional Radio + Software Architecture Reconfigurability Provisions for easy upgrades Cognitive Radio SDR + Intelligence Awareness Learning Observations Page 34 Spring 2013 CS 795/895 - Wireless Networked Systems

35 How is a Software Radio Different from Other Radios? Upgrade Cycle Conventional Radio Cannot be made future proof Typically radios are not upgradeable Software Radio Ideally software radios could be future proof Many different external upgrade mechanisms Over-the-Air (OTA) Cognitive Radio SDR upgrade mechanisms Internal upgrades Collaborative upgrades Page 35 Spring 2013 CS 795/895 - Wireless Networked Systems

36 Typical Cognitive Radio Applications What does cognitive radio enable?

37 Conceptual example of opportunistic spectrum utilization Primary Signals Random Access TDMA Opportunistic Signals Page 37 Spring 2013 CS 795/895 - Wireless Networked Systems 37

38 Cognitive radio permits the deployment of cheaper radios RF components are expensive Cheaper analog implies more spurs and out-of-band emissions Processing is cheap and getting cheaper Cognitive radios will adapt around spurs (just another interference source) or teach the radio to reduce the spurs Better radios results in still more available spectrum as the need arises. Likely able to exploit SDR Page 38 Spring 2013 CS 795/895 - Wireless Networked Systems

39 Improved Link Reliability Cognitive radio is aware of areas with a bad signal Can learn the location of the bad signal Has insight Radio takes action to compensate for loss of signal Actions available: Power, bandwidth, coding, channel, form an ad-hoc network Radio learns best course of action from situation Signal Quality Good Transitional Poor Radio takes Can aid cellular system Inform system & other radios of identified gaps Page 39 Spring 2013 CS 795/895 - Wireless Networked Systems

40 Automated Interoperability Basic SDR idea Use a SDR as a gateway to translate between different radios Problems Which devices are present? Which links to support? With SDR some network administrator must answer these questions Basic CR idea Let the cognitive radio observe and learn from its environment in an automated fashion. Page 40 Spring 2013 CS 795/895 - Wireless Networked Systems

41 Spectrum Trading Underutilized spectrum can be sold to support a high demand service Currently done in Britain Permitted in US among public safety users Currently has a very long time scale (months) Faster spectrum trading could permit for significant increases in available bandwidth How to recognize need and availability of additional spectrum? Environment + context awareness + memory Page 41 Spring 2013 CS 795/895 - Wireless Networked Systems

42 Collaborative Radio A radio that leverages the services of other radios to further its goals or the goals of the networks. Cognitive radio enables the collaboration process Identify potential collaborators Implies observations processes Classes of collaboration Distributed processing Distributed sensing Page 42 Spring 2013 CS 795/895 - Wireless Networked Systems

43 Summary Cognitive radio evolves the software radio concept to permit intelligent autonomous adaptation of radio parameters Significant variation in definitions of cognitive radio Question of how cognitive the radio is Numerous new applications enabled Opportunistic spectrum utilization, collaborative radio, link reliability, advanced network structures Differing implementation approaches Many applications implementable with simple algorithms Greater flexibility achievable with a cognitive engine approach Many objectives will require development of a cognitive language In a network, adaptations of cognitive radios interact Interaction can be mitigated with policy, punishment, cost adjustments, centralization or potential games Commercial implementations starting to appear , h,y, h And may have been around for a while (cordless phones with DFS) Page 43 Spring 2013 CS 795/895 - Wireless Networked Systems

44 Questions Page 44 Spring 2013 CS 795/895 - Wireless Networked Systems