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1、,Cognitive Radio: Next Big Thing,Presented by: Huifang Li,May. 26, 2008,China Telecom Corporation Ltd.,2,Outline Basic Concepts Applications and Markets Key Issues Emerging Standards Challenges to Wide-Scale Deployment,China Telecom Corporation Ltd.,3,Background - current usage of radio resource Acc
2、ording to scanning portions of the radio spectrum below 3GHz some frequency bands in the spectrum are largely; unoccupied most of the time some other frequency bands are only partially occupied remaining frequency bands are heavily used FCC report utilization of the assigned spectrum range from 15%
3、to 85% the licensed bands are abundant but poorly utilized Fig.1 Measurements of spectrum occupancy below 3GHz,China Telecom Corporation Ltd.,4,Background -improvements of spectrum utilization Shortage of spectrum management in traditional way spectrum usage is very low in certain licensed bands the
4、 scarcity of radio resources is becoming a crisis hindering the development of many wireless applications Spectrum hole band of frequencies assigned to a primary user and is not being utilized by that user at a particular time and specific geographic location Ways to improve spectrum utilization mak
5、ing it possible for a secondary user (who is not being serviced) to access a spectrum hole unoccupied by the primary user at the right location and time Cognitive Radio is seen as the solution to the current low usage of the radio spectrum,China Telecom Corporation Ltd.,5,Definition and function of
6、Cognitive Radio Cognitive radio (CR) a radio that can change its transmitter parameters based on interaction with the environment in which it operates Function of CR: spectrum sensing determine which portions of the spectrum is available detect the presence of licensed users spectrum management sele
7、ct the best available channel spectrum sharing coordinate access to this channel with other users spectrum mobility vacate the channel when a licensed user is detected,China Telecom Corporation Ltd.,6,Spectrum hole access with CR Fig.2 usage of spectrum hole with CR CR enables the user access a spec
8、trum hole unoccupied by the licensed user If this band is further used by a licensed user moves to another spectrum hole stays in the same band, altering its transmission power level or modulation scheme to avoid interference,China Telecom Corporation Ltd.,7,awareness,adaptability,intelligence,learn
9、ing,efficiency,Characteristics of CR Cognitive Radio,China Telecom Corporation Ltd.,8,Outline Basic Concepts Applications and Markets Key Issues Emerging Standards Challenges to Wide-Scale Deployment,China Telecom Corporation Ltd.,9,Prominent target application Core application with initial trial de
10、ployments of CR wireless broadband access in rural and remote areas performance comparable to those of existing fixed broadband access technologies FCC selected the TV bands for providing CR service due to lower spectrum of frequencies features is favorable for propagation characteristics many TV ch
11、annels are largely unoccupied most households and businesses rely on cable and satellite TV services unlicensed bands lower costs of electronic devices,China Telecom Corporation Ltd.,10,Other key markets CR can be used in other settings single-family residential multi-dwelling units small office/hom
12、e office (SOHO) small businesses multi-tenant buildings public and private campuses Type of services provided by CR data voice audio and video traffic with appropriate Quality-of-Service (QoS) support,China Telecom Corporation Ltd.,11,Outline Basic Concepts Applications and Markets Key Issues Emergi
13、ng Standards Challenges to Wide-Scale Deployment,China Telecom Corporation Ltd.,12,Physical architecture of CR - transceiver Main components: radio front-end and the baseband processing unit Component can be reconfigured to adapt to the time-varying RF environment Baseband processing unit is essenti
14、ally similar to existing transceivers RF front-end is a novelty of the CR Fig.3 transceiver of CR,China Telecom Corporation Ltd.,13,Physical architecture of CR - RF front-end of transceiver Novel characteristic wideband sensing capability RF hardware technologies wideband antenna, power amplifier, a
15、daptive filter Spectrum sensing enables real-time measurements of spectrum information from radio environment Fig.4 RF front-end of transceiver,14,Fig.5 Basic cognitive cycle,bandwidth of the transmission China Telecom Corporation Ltd.,Cognitive capability - cognitive cycle Three cognitive tasks: 1.
16、 Radio-scene analysis estimation of interference temperature detection of spectrum holes 2. Channel identification estimation of channel-state information prediction of channel capacity 3. Transmit-power control and dynamic spectrum management data rate transmission mode,China Telecom Corporation Lt
17、d.,15,Cognitive capability - cognitive steps Three main steps Spectrum sensing monitors the available spectrum bands, captures their information, detects the spectrum holes. Spectrum analysis estimate the characteristics of the spectrum holes which are detected through spectrum sensing Spectrum deci
18、sion appropriate spectrum band is chosen according to the spectrum characteristics and user requirements Fig.6 Classification of spectrum sensing techniques,China Telecom Corporation Ltd.,16,Reconfigurability Capability of adjusting operating parameters for the transmission Operating frequency Modul
19、ation Transmission power Communication technology Characteristics of reconfigurability Parameters can be reconfigured at any time of a transmission Enables CR to adapt easily to the dynamic radio environment Enables CR to switch to a different spectrum band,China Telecom Corporation Ltd.,17,Outline
20、Basic Concepts Applications and Markets Key Issues Emerging Standards Challenges to Wide-Scale Deployment,China Telecom Corporation Ltd.,18,Standard work overview SDR(software defined radio) Forum chartered two groups on CR CR Working Group standardizing a definition of CR identifying the enabling t
21、echnologies CR Special Interest Group identifying attractive commercial applications IEEE 1900 group with three subgroups 1900.1 standardize definitions and terminology 1900.2 standardizing a process for testing and verifying the operation 1900.3 standardizing approaches for qualifying software modu
22、les IEEE 802 community is currently developing two standards 802.22 intending to provide high bandwidth access in rural areas 802.11h focusing on dynamic frequency selection in WLAN,China Telecom Corporation Ltd.,19,IEEE 802.22 SYSTEM - Topology, Entities and Relationships Specifies a fixed point-to
23、- multipoint wireless air interface: Base Station (BS) Consumer Premise Equipments (CPEs) BS controls the medium access and downstream transmits to CPEs System follows a strict masters/slave relationship BS controls RF characteristics of CPEs CPE is not allowed to transmit before receiving authoriza
24、tion from BS Distributed sensing BS instructs CPEs to perform distributed measurement activities Fig.7 802.22 deployment configuration,China Telecom Corporation Ltd.,20,IEEE 802.22 SYSTEM - Service Coverage and Capacity Service coverage larger coverage range, up to 100 Km higher power favorable prop
25、agation characteristics of TV frequency bands Service capacity broad band operation frequency 54-862 MHz extended range to 41-910 MHz accommodate various TV channel bandwidths of 6, 7, 8 MHz 0.5 bit/(sec/Hz) up to 5 bit/(sec/Hz) Fig.8 802.22 compared to other standards,China Telecom Corporation Ltd.
26、,21,IEEE 802.11h - wlan with cognitive function Cognitive tasks Observation estimate channel characteristics such as path loss and link margin Orientation determine if it is operating in the presence of a radar installation, in a bad channel, in band with satellites, or in the presence of other wlan
27、s Decision decide to change frequency (Dynamic Frequency Selection), adjust the transmit power (Transmit Power Control), or in the case of encountering Action be able to implement decisions,China Telecom Corporation Ltd.,22,Outline Basic Concepts Applications and Markets Key Issues Emerging Standard
28、s Challenges to Wide-Scale Deployment,China Telecom Corporation Ltd.,23,Spectrum sensing challenges Spectrum sensing enables CR to be aware of changes in its surrounding by detecting spectrum holes Challenges for development of spectrum sensing interference measurement no practical way to measure th
29、e interference at nearby primary receivers spectrum sensing in multi-user networks multi-user environment makes it more difficult to sense the primary users and to estimate the actual interference detection capability design complexity increases by using of a large number of carriers in order to red
30、uce overall detection time,China Telecom Corporation Ltd.,24,Spectrum decision challenges Spectrum decision choose appropriate spectrum band according to the spectrum characteristics and user requirements Challenges for development of spectrum decision: decision model how to combine the spectrum cha
31、racterization parameters for the spectrum decision model multiple spectrum band decision how to determine the number of spectrum bands how to select the set of appropriate bands spectrum decision over heterogenous spectrum bands how to support spectrum decision on both licensed and unlicensed bands
32、over the heterogeneous environment,China Telecom Corporation Ltd.,25,Spectrum mobility challenges Spectrum mobility enables changing of frequency to get the best available channel Challenges for development of spectrum mobility mobility model how to decide the best available spectrum based on the ch
33、annel characteristics and the requirements of applications spectrum mobility in time domain how to maintain QoS with changing of available channels over time spectrum mobility in space how to continuous allocate spectrum with changing of available bands when a user moves from one place to another,Thanks for your attention!,