A survey on Spectrum Management in Cognitive Radio Networks

Transcription

1 A survey on Spectrum Management in Cognitive Radio Networks Ian F. Akyildiz, Won-Yeol Lee, Mehmet C. Vuran, Shantidev Mohanty Georgia Institute of Technology Communications Magazine, vol 46, April 2008, pp HY 539 Nov S. Loutou

2 Introduction Current Wireless Networks: Static spectrum Allocation Policy & Spectrum Underutilization Cognitive Radio Technology: Share the wireless channel with licensed users in an opportunistic manner Provide high bandwidth to mobile users via heterogeneous wireless architectures & dynamic spectrum access techniques

3 Emerging Issues Spectrum Management Determine which portions of the spectrum are available: Spectrum Sensing Select the best available channel: Spectrum Decision Coordinate access to this channel with other users: Spectrum Sharing Vacate the channel when a licensed user is detected: Spectrum Mobility

4 Cognitive Radio Technology 1/3 Definition: A radio that can change its transmitter parameters based on interaction with its environment Main Characteristics: Cognitive Capability: Identify the unused spectrum at a specific time or location (Spectrum Holes/ White Spaces) Reconfigurability: Transmit and Receive on a variety of frequencies. Use different access technologies

5 Cognitive Radio Technology 2/3 Spectrum Hole

6 Cognitive Radio Technology 3/3 Architecture CR requires a novel radio frequency (RF) transceiver architecture Main components: Radio front-end, Baseband processing unit Novel characteristic: RF front-end capable of simultaneous sensing over a wide frequency range RF hardware capable of being tuned to any part of a large range of spectrum RF front-end capable to detect a weak signal in a large dynamic range

7 CR Network Architecture 1/3 Network Components Primary Network CR Network Primary Network can have infrastructure (Base Stations) CR network also can have Base Stations and Spectrum Brokers

8 CR Network Architecture 2/3 Spectrum Heterogeneity CR networks : Licensed band operation Unlicensed band operation Licensed band CR focuses on the detection of PUs CR should vacate if PU appears The channel capacity depends on the interference at nearby PUs Unlicensed band CR have the same access rights

9 CR Network Architecture 3/3 Network Heterogeneity CR network access: Access their own CR base station on both licensed and unlicensed spectrum bands define their sharing policy CR ad hoc access: CR users communicate through ad hoc connection on both licensed and unlicensed spectrum bands Primary Network access: CR users access the primary base station through the licensed band require adaptive MAC protocol

10 Spectrum Management Framework 1/15 Challenges: Coexistence with primary networks & Diverse QoS requirements Design challenges: Interference Avoidance QoS Awareness, considering the dynamic and heterogeneous spectrum environment Seamless Communication regardless of the appearance of PU

11 Spectrum Management Framework 2/15 Spectrum Sensing Enables CR users to adapt to the environment by detecting spectrum holes without causing interference to the primary network Through a real-time wideband sensing capability Spectrum sensing techniques: Primary Transmitter Detection Primary Receiver Detection Interference Temperature Management

12 Spectrum Management Framework 3/15 Primary Transmitter Detection Spectrum Sensing Based on the detection of a weak signal from Primary Transmitter. 3 schemes used: Matched Filter Detection: When primary information is known to CR Energy Detection: When primary info is not available. Susceptible in noise power Feature Detection: Detect the built-in periodicity or cyclostationarity that characterize modulated signals. Computational complex. Sensing info from others users required: Cooperative Detection

13 Spectrum Management Framework 4/ 15 Spectrum Sensing Primary Receiver Detection & Interference Temperature Management Most efficient way to detect holes: Detect the PU that are receiving data within the communication range of a CR Interference Temperature: A limit to the amount of new interference the receiver could tolerate

14 Spectrum Management Framework 5/15 Challenges Spectrum Sensing Interference Temperature Measurement: CR user cannot be aware of the precise location of the PU Spectrum-Sensing in multi-user networks: More difficult to sense holes and estimate interference Spectrum-efficient sensing: Sensing cannot be performed while transmitting Minimize sensing time

15 Spectrum Management Framework 6/15 Spectrum Decision Define parameters to represent a particular spectrum band Interference: To estimate the permissible power of a CR. Estimate channel capacity Path Loss: Closely related to distance & frequency Wireless link errors: Depending on the modulation scheme and the interference level Link layer delay: different types required at different bands

16 Spectrum Management Framework 7/15 Decision Procedure Spectrum Decision Considering QoS requirements & Spectrum characteristics -> Configure transmission mode & bandwidth Primary User Activity: New metric to describe the dynamic nature of CR Use of multiple noncontiguous spectrum bands

17 Spectrum Management Framework 8/15 Challenges Spectrum Decision Decision Model: Taking into account QoS requirements at spectrum capacity estimation Cooperation with reconfiguration: Transmissions parameters to be reconfigured for optimal operation in certain bands Spectrum decision over heterogeneous spectrum bands: On both licensed and unlicensed bands

18 Spectrum Management Framework 9/15 Spectrum Sharing Includes much of the functionality of a MAC protocol Classified by 4 aspects -Architecture -Spectrum Allocation Behavior -Spectrum Access Technique -Scope

19 Spectrum Management Framework 10/15 Architecture Spectrum Sharing Centralized spectrum sharing: Controlled by a central unit. Distributed Sensing Procedure Distributed spectrum sharing : Local policies performed by each node distributively Distributed solutions follow the centralized, but at the cost of message exchange

20 Spectrum Management Framework 11/15 Allocation Behavior Spectrum Sharing Cooperative spectrum sharing: The effect of the communication of one node on other nodes is considered. Share interference info locally Non-cooperative spectrum sharing: Only a single node is considered. May result in reduced spectrum utilization Cooperative approaches outperform and result to a certain degree of fairness Non-cooperative perform better at energy consumption

21 Spectrum Management Framework 12/15 Access Technology Spectrum Sharing Overlay spectrum sharing: SUs use a portion of the spectrum not used by Pus Underlay spectrum sharing: The transmission of a CR is regarded as noise by PUs Underlay techniques utilize higher bandwidth but increase slightly the complexity

22 Spectrum Management Framework 13/15 Scope Spectrum Sharing Intranetwork: Spectrum allocation between the entities of a CR network, without interfere to PUs Internetwork: Enable multiple systems to be deployed in overlapping locations and spectrum

23 Spectrum Management Framework 14/15 Challenges Spectrum Sharing Common Control Channel: Infeasible implementation -> Mitigation techniques or local CCC for clusters or nodes Dynamic Radio Range: Due to the interdependency between range and operating frequency, the neighbors change when the frequency change Spectrum Unit: Definition of a channel as spectrum unit Location Information: Assumption that the location and transmit power of PUs are known is not always valid

24 Spectrum Management Framework 15/15 Spectrum Mobility The necessity to change its operating spectrum bands: Spectrum Handoff Ensure smooth and fast transition leading to min performance degradation Challenges: Spectrum mobility in Time domain Space

25 CONCLUSION CR networks will provide a spectrum-aware communication Solve wireless network problems resulting from the limited available spectrum More research required along the lines introduced in this survey