Perspectives and Challenges for Cognitive Radio Li-Chun Wang ( ) - PowerPoint PPT Presentation

Perspectives and Challenges for Cognitive Radio Li-Chun Wang ( 王蒞君 ) Department of Communications Engineering National Chiao Tung University Hsinchu,Taiwan lichun@cc.nctu.edu.tw Wireless Network Lab, NCTU, 1 Taiwan

Outline � Introduction to Wireless Standards and Radio Spectrum Allocation � What is Cognitive Radio (spectrum overlay technique) ? � Challenges in Cognitive Radio � Location Awareness and Dynamic Spectrum Access � Coexistence Issues of Hybrid Infrastructure-based and overlaying ad hoc networks � Cognitive MAC protocol Design � QoS Provisioning � Concurrent Transmission MAC Protocol � Conclusions Wireless Network Lab, NCTU, 2 Taiwan

3C Tradeoff in Wireless � The 3C (Capacity, Cost, Cwality) Tradeoff High Capacity Good Quality Low Cost � The more things changes, the more remain the same (Alphonse Karr, 1808) Wireless Network Lab, NCTU, 3 Taiwan

What is the fundamental issue for wireless communications? Spectrum Efficiency Wireless Network Lab, NCTU, 4 Taiwan

Spectrum Allocation for Licensed Use � Predetermined licensed users have the right to transmit at a given frequency. � Non-licensed users became “harmful interference.” � In most cases, side bands were implemented to ensure interference was not an issue. � Some frequency bands were sold at auction bringing considerable revenue to the government. Wireless Network Lab, NCTU, 5 Taiwan

無線電發展的歷史 � 無線電頻譜本來海闊天空，但過去受限於硬體 與技術，各種無線服務只能使用其中少數頻 帶，造成僧多粥少的擁擠局面。 � 你設定收音機的頻道時，是在調整天線的接收 電路，讓它只收取這個廣播電台的無線電波頻 率，因為你最喜歡的廣播電台以特定頻率發射 無線電波。 � 如果有其他發射器干擾你接收無線電波，唯一 的辦法是等問題自行消失。 � 假如這干擾影響的是緊急求救行動電話通話， 又該怎麼辦呢？ Wireless Network Lab, NCTU, 6 Taiwan

RF Spectrum – 1.39 to 5.923 GHz Mid-Band High-Band Wireless Network Lab, NCTU, 7 Taiwan

Spectrum Allocation for Unlicensed Use Frequency of Bandwidth Unlicensed operation bands ISM at 2.4 GHz 2.4 – 2.4835 83.5 MHz GHz U-NII at 5 GHz 5.15 -5.35 GHz 300 MHz 5.75-5.85 GHz UWB 3.1 – 10.6 GHz 7,500 MHz Wireless Network Lab, NCTU, 8 Taiwan

Evolution of Wireless Communications Both licensed/unlicensed band Licensed band Unlicensed band Wireless Network Lab, NCTU, 9 Taiwan

IEEE 802 LAN/ MAN/ RAN Standards � WLAN (IEEE 802.11) � WiFi 802.11a/ b/ g � WPAN (IEEE 802.15) � Bluetooth 802.15.1 � Co-existence 802.15.2 � High-data-rate UWB 802.15.3a � High-data-rate UWB 802.15.4a (Zigbee) � WMAN (IEEE 802.16) � WBWA (IEEE 802.20) � WRAN (IEEE 802.22) Wireless Network Lab, NCTU, 10 Taiwan

Current Situation of Spectrum Usage � Allocated spectrum does not mean licensed. � Licensed does not mean used. � 佔著 ____ ，不 _____ 。 Wireless Network Lab, NCTU, 11 Taiwan

Efficient Spectrum Sharing � Near-term wireless developments: � 802.11x (WiFi), 802.11n – 200Mb/ s Wifi � 802.16 (WiMax) – long range � 3G Cellular Wireless Network Lab, NCTU, 12 Taiwan

Future Spectrum Sharing � New unlicensed bands � 60 GHz � Spectrum underlay � Ultra-wideband radios � 802.15.3a, 802.15.4a � Spectrum overlay � Cognitive radios Wireless Network Lab, NCTU, 13 Taiwan

Basic Idea of UWB Source: Fantasma Wireless Network Lab, NCTU, 14 Taiwan

How Wide in UWB signals? •Any signal that occupies more than 500 MHz absolute bandwidth (f 2 – f 1 ) in the 3.1 to 10.6 Hz band and meet the spectrum mask. •Fractional bandwidth is larger than 20% Wireless Network Lab, NCTU, 15 Taiwan

Why UWB? � Shannon Capacity Theorem C = Information Capacity in bps B = Information Bandwidth in Hertz P R = Received Power in watts k = Baltzmann’s constant (1.38 × 10 -23 J/ o K) T = Temperature in o K � Conclusion: Capacity increases faster as a function of bandwidth than as a function of power. Wireless Network Lab, NCTU, 16 Taiwan

Basic Idea of Cognitive Radio Cognitive frequency-agile radios can be allowed to intelligently “switch lanes” and adjust parameters. Wireless Network Lab, NCTU, 17 Taiwan

Why Cognitive Radio? � Pros and Cons for Cognitive Radio: � 解決佔著 ____ ，不 _____ 的問題。 � 你幹嘛管我家廁所有沒有人用 ? � The true is � Current unlicensed bands are too crowded. � Emergency application � Provide ubiquitous wireless services by heterogeneous wireless networks Wireless Network Lab, NCTU, 18 Taiwan

19 An Example for Cognitive Radio Wireless Network Lab, NCTU, Taiwan

20 An Example for Cognitive Radio Wireless Network Lab, NCTU, Taiwan

Outline � Introduction to Wireless Standards and Radio Spectrum Allocation � What is Cognitive Radio (spectrum overlay technique) ? � Challenges in Cognitive Radio � Location Awareness and Dynamic Spectrum Access � Coexistence Issues of Hybrid Infrastructure-based and overlaying ad hoc networks � Cognitive MAC protocol Design � QoS Provisioning � Concurrent Transmission MAC Protocol � Conclusions Wireless Network Lab, NCTU, 21 Taiwan

What is Cognitive Radio? � Not CR in your keyboard! � Co-exists with legacy wireless systems � Utilize the spectrum resource of the legacy system. � Does not cause interfere to them Wireless Network Lab, NCTU, 22 Taiwan

Cognitive Radio has come into your daily life! A preliminary CR demonstration: A service is transmitted through heterogeneous wireless systems. Wireless Network Lab, NCTU, 23 Taiwan

Definition � Cognitive Radio (CR) is a radio that can change its parameters based on interaction with the environment in which it operates. Wireless Network Lab, NCTU, 24 Taiwan

Two Main Characteristics for CR � Cognitive capability: � The ability of the radio to capture or sense the information from its radio environment � Monitoring the power in some frequency band is NOT enough � Sophisticated techniques are needed to capture the temporal and spatial variations in the radio environment � Re-configurability: � Enable the radio to be dynamically programmed Wireless Network Lab, NCTU, 25 Taiwan

Key Functions for CR � Sensing Radio � Wideband antenna, PA, and LNA � High speed A/ D & D/ A � Scalable for MIMO � PHY layer � OFDM transmission? � Dynamic frequency selection, adaptive modulation and coding, power control � MAC layer � Transmission parameter optimization � Rate adaptation � Feedback mechanism � Negotiate and opportunistically use of radio resource Wireless Network Lab, NCTU, 26 Taiwan

Frequency-Agile Radios � Software-Defined Radios introduce the ability for instantaneous frequency reconfiguration. � Evolution of the SDR concept leads to Cognitive Radio, defined as “an SDR that additionally senses its environment, tracks changes, and reacts upon its findings.” [ Jondral-06] � A preliminary step in achieving true “open spectrum” is the implementation of a cooperative Primary User-Secondary User system. Wireless Network Lab, NCTU, 27 Taiwan

軟體無線電（ SDR ） � 目前無線電頻譜壅塞的現象，大多起因於上個世紀製 造的老式硬體設備在成本與效能上受到限制。舉例來 說，由於 1950 年代末，真空管電視機的設計過於老 舊，新的電晶體機種被迫只能接收 VHF 信號，過了好 多年，工程師才得以大幅修改電視機。適應性軟體式 無線設計出現後，正可解決這些硬體上的障礙。 � 這種新一代無線技術稱為軟體無線電（ SDR ），採用 嵌入式信號處理演算法，來找出微弱的無線電信號， 並且使用可改變設定的編碼結構，以收發新的無線電 通訊協定。專家預測再過不久，這個以軟體為主的進 展將為無線電設計帶來重大改變。 Wireless Network Lab, NCTU, 28 Taiwan

CR and SDR � 感知無線電緊跟在 SDR 技術後出現，以其為設計基 礎。這個新的無線技術典範採用的 SDR 系統，能改變 自己的類比 RF 輸出設定，同時吸收「自我意識」與傳 輸通訊協定、禮節和常規等知識。以這些發展製作出 來的感知無線電裝置，能感應所在的 RF 環境與地點， 進而調整功率、頻率、調變及其他運作參數，以便靈 活運用所有可用的頻譜。 � 自我意識是指這類裝置知道本身的狀況，以及自己和 周圍無線電網路的關係。工程師要賦予這些功能時， 可以使用裝置和環境的運算模型，將它定義成身為 「無線電」的獨立個體（也就是「自我」），模型還 會定義「使用者」，好讓系統學習。 Wireless Network Lab, NCTU, 29 Taiwan