ETSI TR 103 067 V1.1.1 (2013-05)

Reconfigurable Radio Systems (RRS); Feasibility study on Radio Frequency (RF) performance for Cognitive Radio Systems operating in UHF TV band White Spaces

DTR/RRS-01008

General Information

• Status: Published
• Publication Date: 21-May-2013
• Technical Committee: RRS 1 - RRS System Aspects & Cognitive functionalities
• Current Stage: 12 - Completion
• Due Date: 22-May-2013
• Completion Date: 22-May-2013
• Mandate: M/512

Standards Content (Sample)

Technical Report
Reconfigurable Radio Systems (RRS);
Feasibility study on Radio Frequency (RF) performance for
Cognitive Radio Systems operating in
UHF TV band White Spaces
2 ETSI TR 103 067 V1.1.1 (2013-05)

Reference
DTR/RRS-01008
Keywords
CRS, GLDB, performance, UHF, white space
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3 ETSI TR 103 067 V1.1.1 (2013-05)
Contents
Intellectual Property Rights . 5
Foreword . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 6
3 Definitions and abbreviations . 8
3.1 Definitions . 8
3.2 Abbreviations . 9
4 Advanced incumbent protection techniques and implementations . 11
4.1 Advanced sensing techniques . 11
4.1.1 General . 11
4.1.2 Cooperative Sensing . 12
4.1.2.1 Use of Correlation Information in Cooperative Sensing . 12
4.1.3 Event Driven Sensing . 15
4.1.3.1 Example Measurement for Event Triggering . 17
4.1.3.2 Silent period start time . 18
4.1.4 Coordinated Silencing. 18
4.1.4.1 Silencing in an LTE-Based System . 19
4.1.4.1.1 Gap Definition through Clustering . 21
4.1.4.1.2 Silencing through the Absence of Scheduling . 25
4.1.4.1.3 A Quiet Period Scheme for LTE-TDD . 25
4.1.4.2 Silencing in a WiFi-Based System . 34
4.2 Advanced Geo-location Database Design . 36
4.2.1 General . 36
4.2.2 Output Power Control Techniques to Address an Aggregated Interference Problem due to
Simultaneous Transmission of Multiple WSDs defined in ECC REPORT 186 and its Feasibility
Study Analysis . 36
4.2.2.1 Target scenario . 37
4.2.2.2 Information Flow Among Relevant Entities . 39
4.2.2.3 Analysis on the system overhead reduction when considering output power level control at each
connected WSD taking into account the number of active/actual WSD interferes . 41
4.2.2.4 Numerical simulation results . 44
4.2.2.4.1 Simulation methodology. 44
4.2.2.4.2 Simulation results . 48
4.2.2.5 Conclusions . 52
4.3 Combined Sensing and Geo-location Database Design . 52
4.3.1 General . 52
4.3.2 Combined geo-location and sensing for identification of the available spectrum . 52
4.3.2.1 Example use of combined sensing and geo-location applied to the FCC regulatory framework . 53
4.3.2.1.1 FCC regulatory framework . 53
4.3.2.1.2 Main operation. 53
4.3.2.1.3 Information flows among relevant entities . 54
4.3.2.2 Use of primary user sensing capability for system channel allocation . 57
4.3.3 Using combined sensing and geo-location to enhance the protection/identification of incumbent
services . 60
4.3.3.1 Introduction . 60
4.3.3.2 Identify TV broadcast services . 61
4.3.3.3 Geo-location database aided feature sensing description . 61
4.3.3.4 Information Flow Among Relevant Entities . 61
4.3.3.5 Performance evaluation on geo-location database aided sensing design . 62
4.3.3.6 Conclusions . 65
4.4 Combined Interference Monitoring and Geo-location Database Design . 65
4.4.1 Introduction. 65
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4 ETSI TR 103 067 V1.1.1 (2013-05)
4.4.2 System Model . 66
4.4.3 Interference Monitoring . 67
4.4.3.1 Concept . 67
4.4.3.2 General Operations. 68
4.4.3.2.1 Procedures . 68
4.4.3.2.2 CIR Estimation in Single Sensor Case . 69
4.4.3.2.3 CIR Estimation in Multiple Sensor Case . 70
4.4.3.2.4 Allowable Transmit Power Calculation . 71
4.4.4 Performance of Interference Monitoring . 71
4.4.5 Conclusions. 72
4.5 Spectral Pre-coding . 73
4.5.1 Introduction. 73
4.5.2 Protecting TV receivers by pre-coded OFDM . 73
4.5.3 Pre-coder design . 75
4.5.4 Signalling related to pre-coding . 79
4.6 WSD operating parameters based on WSD emission characteristics . 80
4.6.1 Approaches for determining the allowed WSD operating parameters based on WSD emission
characteristics . 80
4.6.1.1 DB-centric model . 81
4.6.1.2 WSD-centric model . 83
4.6.1.3 Discussion of the DB-centric and WSD-centric models . 85
5 Co-existence studies out of CEPT responsibility . 85
5.1 Coexistence between Incumbent and Cognitive Radio Systems in UHF TV band White Spaces . 85
5.1.1 RF performance of LTE systems under adjacent channel interference from DTT systems . 86
5.1.1.1 Coexistence scenario . 86
5.1.1.2 Analysis/simulation results . 90
5.1.1.3 Coexistence suggestions . 94
5.1.2 RF performance of LTE systems in presence of co-channel signals from DTT systems . 95
5.1.2.1 Coexistence scenario . 95
5.1.2.2 Analysis/simulation results . 95
5.1.2.3 Coexistence suggestions . 97
5.2 Coexistence between Cognitive Radio Systems in UHF TV band White Spaces . 97
5.2.1 CRSs coexistence scenario description . 98
5.2.2 Non-coordinated coexistence mechanisms . 100
5.2.3 Coordinated coexistence mechanism . 101
5.2.4 New potential coexistence mechanisms . 101
5.2.4.1 Coexistence Gaps for coexistence between CSMA and non-CSMA systems . 101
5.2.4.1.1 Simulation Configuration . 103
5.2.4.1.2 Simulation Results . 105
5.2.4.1.3 Example Implementations for Coexistence Gaps . 106
6 Device classes . 108
6.1 Classification based on WSD role in operation enablement . 109
6.2 WSD parameters to geo-location database . 111
Annex A: Definition of interfere-victim reference point [i.3] . 114
Annex B: UL Data channel performance of LTE system Operating in Channels Adjacent to
DTMB . 115
B.1 Coexistence scenario . 115
B.2 System simulation . 116
B.3 Coexistence conclusion . 119
History . 120

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5 ETSI TR 103 067 V1.1.1 (2013-05)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://ipr.etsi.org).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Technical Report (TR) has been produced by ETSI Technical Committee Reconfigurable Radio Systems (RRS).
ETSI
6 ETSI TR 103 067 V1.1.1 (2013-05)
1 Scope
The present document aims to identify the relevant Radio Frequency (RF) scenarios and RF performance applicable to:
• Cognitive Radio Systems (CRS) for the coexistence between CRSs when they are operating in UHF TV band
White Spaces.
• Both broadcasting service and Cognitive Radio Systems for the deployment of CRS in the UHF TV band
White Spaces when advanced incumbent protection techniques and implementations such as cooperative
sensing and advanced geo-location database are considered.
• Both broadcasting service and Cognitive Radio Systems for the coexistence studies in UHF TV band White
Spaces in regions outside of CEPT responsibility.
The scenarios described in the preset document are based on [i.22] and [i.3].
2 References
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references,only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee
their long term validity.
2.1 Normative references
The following referenced documents are necessary for the application of the present document.
Not applicable.
2.2 Informative references
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] FCC 10-174: "Second Memorandum Opinion and Order", Sept. 23, 2010.
[i.2] OFCOM, Consultation on license-exempting cognitive devices using interleaved spectrum,
Feb. 2009.
[i.3] ECC Report 159 (January 2011): "Technical and Operational Requirements for the Possible
Operation of Cognitive Radio Systems in the 'White Spaces' of the Frequency Band
470-790 MHz".
[i.4] IEEE 802.22 (2011): "Standard for Wireless Regional Area Networks. Part 22: Cognitive Wireless
RAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Policies and
procedures for operation in the TV bands".
[i.5] IEEE 802.11n (2009): "IEEE Standard for Information technology. Part 11: Wireless LAN
Medium Access Control (MAC) and Physical Layer (PHY) Specifications".
[i.6] Recommendation ITU-R P.1546-4 (October 2009): "Method for point-to-area predictions for
terrestrial services in the frequency range 30 MHz to 3 000 MHz".
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7 ETSI TR 103 067 V1.1.1 (2013-05)
[i.7] IEEE Communications Letters, Vol. 14, no. 10, pp. 886-888, October 2010: "Orthogonal
multiplexing in a subspace of frequency well-localized signals", Jaap van de Beek.
[i.8] IEEE Transactions on Communications, Vol. 54, no. 12, pp. 2173-2185, December 2006:
"Spectrally precoded OFDM", Char-Dir Chung.
[i.9] IEEE Communications Letters, Vol. 10, no. 6, pp. 444-446, June 2006: "Subcarrier weighting: a
method for sidelobe suppression in OFDM systems", Ivan Cosovic, Sinja Brandes,
Michael Schnell.
[i.10] IEEE Communications Letters, Vol. 13, no. 12, pp. 881-883, December 2009: "Sculpting the
multicarrier spectrum: a novel projection precoder", Jaap van de Beek.
[i.11] IEEE Transactions on Communications, Vol. 59, no. 3, pp. 844-853, March 2011: "Optimal
orthogonal precoding for power leakage suppression in DFT-based systems", Meng Ma,
Xiaojing Huang, Bingli Jiao and Y. Jay Guo.
[i.12] ETSI TS 136 211: "LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical
channels and modulation (3GPP TS 36.211)".
[i.13] Proc. First European Conference on Antennas and Propagation (EuCAP), November 2006:
"Deterministic propagation prediction method developed by the European broadcasting union",
R. Grosskopf.
[i.14] ERC Report 85: "Compatibility Analysis of Radio Astronomy in the Frequency Range
608-614 MHz within DVB-T".
[i.15] CEPT Chester 97: "The Chester 1997 Multilateral Coordination Agreement relating to Technical
Criteria, Coordination Principles and Procedures for the introduction of DVB-T".
[i.16] ETSI TS 136 101 (V10.6.0): "LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); User
Equipment (UE) radio transmission and reception (3GPP TS 36.101 version 10.6.0 Release 10)".
[i.17] ETSI TS 136 104: "LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Base Station
(BS) radio transmission and reception".
[i.18] IEEE International Conference on Communications, June 2006, Vol. 4, pp. 1658-1663:
"Cooperative Sensing Among Cognitive Radios", S.M. Mishra, A.Sahai, and R.W. Brodersen.
[i.19] IEEE Signal Processing Letters, vol. 15, pp. 649-652, 2008: "Blindly combined energy detection
for spectrum sensing in cognitive radio", Y. H. Zeng, Y.-C. Liang, and R. Zhang.
[i.20] ETSI EN 300 744 (V1.6.1) (01-2009): "Digital Video Broadcasting (DVB); Framing structure,
channel coding and modulation for digital terrestrial television".
[i.21] Wenshan Yin, Pinyi Ren, Jun Cai and Zhou Su. A pilot-aided detector for spectrum sensing of
Digital Video Broadcasting-Terrestrial signals in cognitive radio networks. Wireless
Communications and Mobile Computing 2011.
[i.22] ETSI TR 102 907: "Reconfigurable Radio Systems (RRS); Use Cases for Operation in White
Space Frequency Bands".
[i.23] ECC Report 186 (January 2013): "Technical and operational requirements for the operation of
WSDs under geo-location approach".
[i.24] Document Number D2.2 Scenario Definitions, Project: Flexible and Spectrum Aware Radip
Access through Measurements and Modeling in Cognitive Radio Systems (FARAMIR).
[i.25] Recommendation ITU-R M.2241 (11/2011): "Compatibility studies in relation to Resolution 224
in the bands 698-806 MHz and 790-862 MHz".
[i.26] Electrical Engineering and Computer Sciences, University of California at Berkeley/Technical
Report No. UCB/EECS-2009-3, "How much white space is there".
NOTE: Available at http://www.eecs.berkeley.edu/Pubs/TechRpts/2009/EECS-2009-3.html.
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8 ETSI TR 103 067 V1.1.1 (2013-05)
[i.27] ETSI TR 136 942: "LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Radio
Frequency (RF) system scenarios (3GPP TR 36.942)".
[i.28] IEEE 802.11af: "IEEE Standard for Information technology--Telecommunications and
information exchange between systems Local and metropolitan area networks--Specific
requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)
Specifications-- Amendment 4: TV White Spaces Operation-D2.0".
[i.29] IEEE 802.11: "IEEE Standard for Information technology--Telecommunications and information
exchange between systems Local and metropolitan area networks--Specific requirements
Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)
Specifications".
[i.30] IEEE 802.11ac: "IEEE Standard for Information technology--Telecommunications and
information exchange between systems Local and metropolitan area networks--Specific
requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)
Specifications-- Amendment 4: Enhancements for Very High Throughput for Operation in Bands
below 6 GHz-D5.0".
[i.31] ECMA 392: "MAC and PHY for Operation in TV White Space".
[i.32] 3GPP TR 36.814: "Evolved Universal Terrestrial Radio Access (E-UTRA); Further advancements
for E-UTRA physical layer aspects".
[i.33] IEEE 802.11g: "IEEE Standard for Information technology--Telecommunications and information
exchange between systems Local and metropolitan area networks--Specific requirements Part 11:
Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications--
Amendment 4: Further Higher Data Rate Extension in the 2.4 GHz Band-2003".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
cognitive radio: radio, which has the following capabilities:
• to obtain the knowledge of radio operational environment and established policies and to monitor usage
patterns and users' needs;
• to dynamically and autonomously adjust its operational parameters and protocols according to this knowledge
in order to achieve predefined objectives, e.g. more efficient utilization of spectrum; and
• to learn from the results of its actions in order to further improve its performance.
program making and special events: equipment that is used to support broadcasting and special events in general
NOTE 1: Special events include culture events, concerts, sport events, conferences, trade fairs, etc.
NOTE 2: These devices operate in different frequency bands. In the present document we focus on devices using
the band 470 MHz - 862 MHz, also referred to as professional wireless microphone systems.
radio system: system capable to communicate some user information by using electromagnetic waves
NOTE: Radio system is typically designed to use certain radio frequency band(s) and it includes agreed schemes
for multiple access, modulation, channel and data coding as well as control protocols for all radio layers
needed to maintain user data links between adjacent radio devices.
silent period: period of time during which a radio system or a subset of devices in a radio system abstain from any
transmission (data, control, reference, etc) over a particular band or channel
NOTE: Silencing refers to the act of a device or set of devices to create a silent period.
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9 ETSI TR 103 067 V1.1.1 (2013-05)
white space: part of the spectrum, which is available for a radiocommunication application (service, system) at a given
time in a given geographical area on a non-interfering/nonprotected basis with regard to primary services and other
services with a higher priority on a national basis.
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
ACIR Adjacent Channel Interference Ratio
ACLR Adjacent Channel Leakage Ratio
ACS Adjacent Channel Selectivity
AP Access Point
ATSC Advanced Television Systems Committee
AWGN Additive White Gause Noise
BLER Block Error Rate
BS Base Station
BW Band Width
CCA-ED Clear Channel Assessment Energy Detection
CCDF Complementary Cumulative Distribution Function
CCE Control Channel Element
CCP Central Control Point
CDF Cumulative Distribution Function
CEPT Commission of European Post and Telecommunications
CG Coexistence Gap
CIR Carrier to Interference Ratio
CMMB China Multimedia Mobile Broadcasting
CNR Carrier to Noise Ratio
CP Cyclic Prefix
CQI Channel Quality Indication
CQI Average Channel Quality Indication
AVG
CR Cognitive Radio
CRC Cycle Redundancy Check
CRS Cognitive Radio System
CSMA Carrier Sense Multiple Access
DB Database
DCI Downlink Control Information
DL Down Link
DRX Discontinuous Reception
DTMB Digital Terrestrial Television Multimedia Broadcasting
DTT Digital Terrestrial Television
DTV Digital Television
DVB-T Digital Video Broadcasting-Terrestrial
ECC Electronic Communications Committee
EIRP Effective Isotropic Radiated Power
ERP Effective Radiated Power
ETU Extended Typical Urban
EVM Error-Vector-Magnitude
FCC Federal Communications Commission
FDD Frequency Division Duplex
FFT Fast Fourier Transform
GAP Gap
GD Guard Duration
GI Guard Interval
GLDB Geo-Location Database
GNSS Global Navigation Satellite System
GP Guard Period
HARQ Hybrid Acknowledge Request
HW Hardware
HW/SW Hardware/Software
ICIC Inter Cell Interference Coordination
I Interference from the DTT system
DTT
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IFFT Inverse Fast Fourier Transform
IM Interference Margin
ISD Inter Site Distance
ISDB Integrated Services Digital Broadcasting
ISM Industrial Scientific and Medical (frequency band)
ITU-R International Telecommunication Union - Radio
KW Kilo-Watt
LE License Exempt
LOS Line of Sight
LP Location Probability
LTE-CR Long Term Evolution-Cognitive Radio
MAC Medium Access Control
MBSFN Multicast/Broadcast over a Single Frequency Network
MCH Multicast Channel
MET Maximum Eigen-value to Trace
MHz Mega Hertz
MI Multiple interference
MME Mobility Management Entity
MS-BS Mobile Station/Base Station
OFCOM Independent regulator and competition authority for the UK communications industries
OFDM Orthogonal Frequency Division Multiplexing
OPNET A tool for application and network performance management
PA Power Amplifier
PC Power control
PDCCH Physical Downlink Control Channel
PDSCH Physical Dedicated Shared Channel
P Transmit power of the DTT broadcast station
DTT
PHY Physical Layer
IM
P Transmit power of the Interference Monitoring
I
PE
P Transmit power of the WSD based on the propagation estimation
I
PL Path loss of DTT
DTT
PN Pseudo Noise
PRBS Pseudo-Random Binary Sequence
PSD Power Spectral Density
QP Quiet Period
QPSK Quadrature Phase Shift Keying
RAT Radio Access Technology
REG Resource Element Group
RF Radio Frequency
RRC Radio Resource Control
RRM Radio Resource Management
RSRP Reference Signal Received Power
RSRQ Reference Signal Received Quality
RX Reception
SINR Signal to Interference plus Noise Ratio
SISO Single Input Single Output
SM Safety Margin
SNR Signal to Noise Ratio
SRS Sounding Reference Signal
STA Station
SVD Singular Value Decomposition
TA Timing Advance
TB Technical Board
TDD Time Division Duplex
TD-LTE Time Division Long Term Evolution
TDM Time Division Multiplex
T the length of guard period
GP
TOFF Period of no transmission
TON Period of transmission
TRX Transmitter-Receiver
TS Technical Specification
TTT Time To Trigger
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11 ETSI TR 103 067 V1.1.1 (2013-05)
TV Television
TVWS Television White Space
TX/RX Transmitter-Receiver
UE User Equipment
UHF Ultra High Frequency (300 Mhz - 3 000 Mhz)
UL Up link
UL/DL Up link/Down link
UTRA Universal Terrestrial Radio Access
VS Versus
Wi-Fi Wireless Local Area Network product certified by Wi-Fi Alliance
WLAN Wireless Local Area Network
WM Wireless Microphone
WRAN Wireless Regional Area Network
WS White Space
WSD White Space Device
4 Advanced incumbent protection techniques and
implementations
4.1 Advanced sensing techniques
4.1.1 General
Sensing has been considered as one kind of protection technique by regulatory bodies in order to protect incumbents
from Cognitive Radio Systems which may opportunistically use the UHF TV band WS. Sensing has the following
advantages:
1) It can be used by devices that are unable to access a geo-location database. One example of such a device is
the so called "sensing only device" as described in the FCC Second Memorandum Opinion and Order [i.1].
2) It can be used to improve protection of the incumbent compared to geo-location database use only.
3) It can be used to find further opportunities for use of WS beyond what is available in the geo-location
database.
A large degree of study has been done on sensing algorithms in the literature. The main property of any sensing
algorithm remains the sensitivity, i.e. the minimum incumbent signal power that it can detect reliably in noise with the
required probability of detection and false alarm. Regulatory bodies have defined minimum sensitivity requirements for
incumbent protection in the WS:
• Federal Communications Commission (FCC):
- The FCC requires that TV band devices be capable of sensing analog and digital TV signals at a level of
-114 dBm within defined receiver bandwidths. It also requires that TV band devices be capable of
sensing wireless microphone signals at a level of -107 dBm [i.1].
• Commission of European Post and Telecommunications (CEPT)
- CEPT presents sensitivity threshold calculations which yield detection thresholds which depend on the
WSD characteristics, deployment scenarios, and BS/receiver configurations. The thresholds calculated
by CEPT range from -155dBm to -91 dBm [i.3]. OFCOM UK, for instance, has set the minimum
sensitivity for TV signal and wireless microphone signal detection to -114 dBm and -126 dBm
respectively [i.2].
Detection of incumbent users through sensing poses several challenges:
• Detection of incumbents at the sensitivity levels required by regulatory bodies requires considerably complex
sensing hardware that may not be feasible or economical for most wireless devices which will use the TV
bands.
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12 ETSI TR 103 067 V1.1.1 (2013-05)
• The effect of multipath and shadowing further complicates incumbent detection. When the sensing node
exhibits multipath and shadowing, the required sensitivity of the algorithm will become unreasonably large.
• Identification of incumbents through sensing when other WSDs are transmitting can result in the need for
feature detection algorithms which can be difficult, and in some cases not feasible.
4.1.2 Cooperative Sensing
In cooperative sensing, multiple sensing nodes perform the task of detection of an incumbent and the detection decision
is made based on the fused results of each node. The main motivation behind cooperative sensing is to lighten the
burden of sensing that a single sensing node would need to carry by distributing the detection among multiple nodes.
When a single node exhibits multipath or shadowing and therefore has higher sensitivity requirements on its sensing
algorithm, cooperative sensing can be used to effectively decrease the sensitivity requirements by relying on other
nodes which may not exhibit these same unfavorable conditions.
Efficient cooperative sensing requires:
• Exploiting information from each of the sensing nodes to effectively choose the nodes that will be involved in
the detection task. This could include location, relative signal correlation, etc.
• Effectively dividing the sensing task based on factors such as minimizing power consumption and properly
exploiting the sensing capabilities of each node.
• Coordinating the location and method in which the fusion of sensing results from the individual nodes is
performed.
4.1.2.1 Use of Correlation Information in Cooperative Sensing
In spectrum sensing, if a particular node is experiencing a multipath fade or shadowing at a particular moment or
geographical location, it is sensing requirements are suddenly much more stringent since that node needs to detect the
presence of a primary user at a power level that is now much lower than just the path loss from the primary user to the
node in question. As a result, the sensing requirements (also known as sensitivity) of the sensing algorithm may become
unreasonably large when considering that sensing is performed in a time shared fashion with actual data transmission.
The problem of requiring a sensing node to be able to handle the worst-case signal attenuation that may arise due to the
presence of multipath or shadowing could be alleviated through cooperative sensing. If multiple nodes are involved in
the sensing decision, then the fact that a particular node is in a fading situation could be offset by the sensing
information of another node which may be in a more favourable fading environment. By merging or fusing the
decisions between these nodes, the required sensitivity for each of the nodes can effectively be decreased.
Figure 1 illustrates the decrease in sensitivity with cooperative sensing under different fading conditions [i.18]. As the
number of users is increased, the required sensitivity of the sensing devices decreases and approaches the path loss. In a
practical system, however, the number of users is limited and only a limited amount of gain can be achieved through
cooperative sensing. As figure 1 illustrates, the gain per additional user is greater in the case of multipath fading only.
This happens as multipath at different radios is generally uncorrelated since a small change in distance between the
radios will result in loss of correlation. On the other hand, shadowing results in high correlation if two radios are
blocked by the same obstacle. For this reason, the case of shadowing shows less gain on average as the number of nodes
is increased.
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Figure 1: Sensitivity Increase with Cooperative Sensing [i.18]
In cooperative sensing, generally a central fusion node performs fusion of sensing information coming from different
sensing nodes. In order for fusion of sensing information to result in a better estimate of the presence of a primary user
and thus decrease the required sensing sensitivity of the individual sensing nodes, the fusion node can ensure that the
sensing information received from each CR node is uncorrelated. This means that two nodes providing sensing
information or sensing decisions should not both be located simultaneously in a fade with respect to the primary user.
As long as each additional sensing node which contributes to the cooperative sensing decision is uncorrelated with the
others, adding the information from additional sensing node increases the performance of the fused decision made by
the fusion node.
A sensing scheme which uses correlation information to tailor its cooperative sensing can consist of two phases:
1) an initial phase of correlation determination whereby the central fusion collects information to determine the
correlation between the nodes; and
2) a sensing and fusion phase whereby sensing is scheduled and fusion is performed based on the information
obtained from the initial phase.
The initial phase may be repeated continuously based on the size of network, the expected mobility of sensing nodes,
and the frequency in which the actual sensing is performed.
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14 ETSI TR 103 067 V1.1.1 (2013-05)

Figure 2: Two stage approach for cooperative sensing
An initial phase of determining the users which are uncorrelated in the network can be performed using sensing
information received during periodic sensing periods. This information can consist of coarse sensing information (such
as a power spectral density over a wide bandwidth) which can also be used for the purpose of actual sensing. Other
methods can also be used to collect the coarse sensing information that is used for correlation determination.
Each sensing node sends sensing information to the fusion node periodically. The fusion node will use this sensing
information to determine which of the nodes in the network are uncorrelated so that future information from
uncorrelated nodes can be used for fusion. In addition, when two nodes are determined to be correlated, future sensing
tasks performed by these nodes can be divided so as to achieve faster sensing for a particular set of channels, or battery
savings for the correlated nodes which can share the sensing load for a set of channels. As a result, the correlation
information obtained from the correlation determination stage could be used to determine:
• Which users' sensing results should be combined/fused to obtain a single decision about the presence or
absence of a primary user on a particular channel.
• Which users should instead cooperate in order to split the sensing task over multiple channels and assign each
user a subset of the channels.
The flowchart in figure 3 shows a possible sequencing of events in the two stage cooperative sensing scheme where the
correlation information is collected in the initial sensing operation.
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15 ETSI TR 103 067 V1.1.1 (2013-05)

Figure 3: Flow diagram of Potential Two-Stage Cooperative Sensing Scheme
Several challenges exist with the two-stage cooperative sensing scheme, including:
• Determining how often to perform the initial step and dealing with mobility (the scheme may not be suitable
for high mobility cases but could be used in fixed sensor networks operating in TVWS).
• Determining the algorithm for correlation determination.
4.1.3 Event Driven Sensing
In order to make use of the UHF TV band WS, sensing devices will need to periodically perform these sensing
operations while the WS is being used for data communication. The period of sensing operation should be a tradeoff
between power consumption for the sensing devices and the agility of the network to leave the WS frequencies
occupied by a newly arriving incumbent. One method to improve agility is to make use of events to trigger non-periodic
(or asynchronous) sensing. The occurrence of an event can be communicated to the sensing nodes to trigger a
non-periodic sensing occasion. These events could, for example, be relative to the change in performance of a network
(e.g. a drop in CQI) which may indicate the immediate need for sensing to determine whether an incumbent is present.
In event driven sensing, it is assumed that a "Central Control Point (CCP)" controls, configures, and manages one or
many WS devices. Sensing done in the WS devices is triggered by the CCP when certain conditions are met. Compared
to continuous or periodic sensing, event driven sensing is only performed following the occurrence of a specific event.
This procedure has the advantage of conserving battery power (as the sensing frequency may be reduced) and
improving throughput (as the actual sensing time and the amount of silencing periods may be reduced).
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16 ETSI TR 103 067 V1.1.1 (2013-05)
While event driven sensing may not replace periodic sensing that is required by some regulations such as the FCC (in
the case of sensing only devices under this regulation), it may serve
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