Key parameters in optimising low duty cycle mitigation ETSI STF 411 CEN DSRC/ITS Coexistence Workshop Ispra June 2011 Friedbert Berens STF411 Member

Scope of Work  Use of LDC as passive mitigation technique  Generic LDC for frequency usage optimisation (intra-system)  Specific LDC for co-existence usage (inter-system) GHz WiMAX /UWB Potentially 873 to 876MHz Extended-GSM-R/Specific SRDs  Describe harmonised procedures to define  Application independent LDC mitigation factor  Optimise  Transmission performance  Spectrum utilisation  Spectrum co-existence behaviour ETSI TC ERM STF411: Overview 2

Received Wisdom  Duty cycle (D.C.), Power & Bandwidth can be traded to minimise interference potential between SRDs and other services  Successfully used with narrowband systems  Proposed for broadband systems e.g. draft v EN  All parameters are interchangeable  Not generally true except over a very small range  Interference is progressive and well behaved  Perhaps with older systems  Digital systems are ‘all or nothing’  We sought to re-examine some of the received wisdom to address scope of work 3 ETSI TC ERM STF411: Overview

Interference potential  Operational Parameters (what we can control)  Occupied Bandwidth  Power  Duty cycle  Independent parameters (what we can’t control)  Activity factor  Undesirable consequences (what we’d like to control)  Probability of intercept (inter-system)  Probability of bandwidth overlap (inter-system)  Probability of collision (intra-system) 4 ETSI TC ERM STF411: Overview

Bandwidth  Occupied bandwidth vs available bandwidth  Frequency hoppers have much greater available b/w compared to occupied b/w  Frequency hoppers dwell on any frequency channel for a very short time  Here bandwidth and duty cycle per channel are linked  Bandwidth overlap  Ultra Wideband low power systems already power limited Bandwidth reduction is passive option to limit inter-system interferences Detect and avoid [DAA] is an active solution developed by STF350 5 ETSI TC ERM STF411: Overview

Duty Cycle (i)  The nature of the victim is critical  Digital systems using FEC to protect data are robust to time limited interference  Synchronisation pulses are always sensitive  The nature of the interferer is critical Polled systems are truly duty cycle driven D.C reflects operational constraints Aperiodic systems are activity driven D.C. is irrelevant  Alarmingly  ETSI has 21 definitions! 6

 What should be included?  Whose perspective is important? 7 Duty Cycle (ii) ETSI TC ERM STF411: Overview

8 Duty Cycle (iii) ETSI TC ERM STF411: Overview

Power  Not all systems fail through excess power  Victim selective  Victim RF gain control response time is critical  Inter and Intra System power  In band power will always cause issues – no help from LDC  Here implicit link to bandwidth overlap between victim and interferer Minimise overlap to limit aperture for power capture 9 ETSI TC ERM STF411: Overview

Spectrum Access  Currently implicit that D.C. is an access mechanism  It says nothing about how, Aloha assumed  Listen Before Talk  Widely used technique defining device behaviour  Only really useful with rising channel capacity  All devices must have the same behaviour- difficult in dissimilar systems  LDC  Behaviour defined by operational parameters only Implies extensive knowledge of systems using same frequency band 10 ETSI TC ERM STF411: Overview

Learning points so far  Current D.C. definition includes Activity Factor  Wide variation between current definitions & true D.C. value  Perception of D.C. varies  Engineers’ view, Regulators’ view, etc  Both Victim and Interferer operational parameters need to be considered in any mitigation scheme  Spectrum Access  LBT requires delicate balance between payload and access overhead in lightly loaded conditions  LDC suitable for light channel loading in known environment  LDC may not be "one hat fits all" solution  LDC locks in possible system sharing 11 ETSI TC ERM STF411: Overview