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

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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

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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

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3C Tradeoff in Wireless

The 3C (Capacity, Cost, Cwality)

Tradeoff

The more things changes, the more

remain the same (Alphonse Karr, 1808) High Capacity Good Quality Low Cost

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What is the fundamental issue for wireless communications?

Spectrum Efficiency

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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.

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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？

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RF Spectrum – 1.39 to 5.923 GHz

Mid-Band High-Band

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Spectrum Allocation for Unlicensed Use

7,500 MHz 3.1 – 10.6 GHz UWB 300 MHz 5.15 -5.35 GHz 5.75-5.85 GHz U-NII at 5 GHz 83.5 MHz 2.4 – 2.4835 GHz ISM at 2.4 GHz Bandwidth Frequency of

• peration

Unlicensed bands

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Evolution of Wireless Communications

Unlicensed band Licensed band Both licensed/unlicensed band

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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)

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Current Situation of Spectrum Usage

Allocated spectrum does not mean

licensed.

Licensed does not mean used.

佔著____，不_____。

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Efficient Spectrum Sharing

Near-term wireless developments:

802.11x (WiFi), 802.11n – 200Mb/ s Wifi 802.16 (WiMax) – long range 3G Cellular

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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, Taiwan 14 Source: Fantasma

Basic Idea of UWB

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How Wide in UWB signals?

• Any signal that occupies more than 500 MHz

absolute bandwidth (f2 – f1) in the 3.1 to 10.6 Hz band and meet the spectrum mask.

• Fractional bandwidth is larger than 20%

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Why UWB?

Shannon Capacity Theorem

C = Information Capacity in bps B = Information Bandwidth in Hertz PR = Received Power in watts k = Baltzmann’s constant (1.38× 10-23 J/ oK) T = Temperature in oK

Conclusion: Capacity increases faster as a

function of bandwidth than as a function of power.

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Basic Idea of Cognitive Radio

Cognitive frequency-agile radios can be allowed to intelligently “switch lanes” and adjust parameters.

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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

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An Example for Cognitive Radio

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An Example for Cognitive Radio

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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

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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

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Cognitive Radio has come into your daily life!

A preliminary CR demonstration: A service is transmitted through heterogeneous wireless systems.

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Definition

Cognitive Radio (CR) is a radio that can

change its parameters based on interaction with the environment in which it operates.

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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

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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

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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.

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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。

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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。

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Spectrum Leasing

Spectrum Pooling, first defined by Joseph Mitola III, is the concept that a non-licensed radio may use a given frequency when the original licensee is not. There are two approaches to the leasing of spectrum pools with which the license owner may operate:

1.

The license owner is aware of other radios using its allocated frequency band. It may avoid other radios, but has the right to reclaim any frequency.

2.

The license owner is completely unaware of the presence of other radios, forcing them to change.

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Key Properties for CR

RF technology to listen to huge

spectrum.

Knowledge of primary users’ spectrum

usage in terms of location and time.

Rules of sharing the available resource

(time, frequency, location)

Intelligence to determine the optimal

transmission parameters (bandwidth, power, QoS).

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CR Network Architecture

On licensed band

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CR Network Architecture (Cont’d)

On unlicensed band

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CR Network Applications

Leased network Cognitive mesh network Emergency network Military network

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Don’t miss your prime time!

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Thank You! lichun@cc.nctu.edu.tw http: / / cmbsd.cm.nctu.edu.tw/ ~ lichun 王蒞君