1

RLAN and C Band Weather Radar Interference Studies*

Paul Joe1, John Scott1, John Sydor2, Andre Brandao2, Abbas Yongacoglu3

1Meteorological Service of Canada, 2Communications Research Centre, 3University of Ottawa

*Study supported by Industry Canada

2

Outline

ITU Resolution R 229 RLANs and RLAN signal The Experiment (Internal, External) Simulation of RLANs in Urban Environment Radar Examples Summary

3

International Telecommunication UnionWorld Radiofrequency Conference 03

RESOLUTION 229 [COM5/16] (WRC-03)

Use of the bands 5150-5 250MHz, 5250-5350MHz and 5470-5725MHz by the

mobile service for the implementation of wireless access systems including

radio local area networks

4

ITU-R Resolution 229 / WRC03(highly condensed and edited)

5470-5725MHz allocated on a primary basis to WAS, RLAN

5250-5725MHz is allocated on a primary basis to the radiodetermination service;

5600-5650MHz, ground-based meteorological radars are extensively deployed and support critical national weather services

Must protect existing primary services Dynamic Frequency Selection (DFS) for mitigation by

RLAN

5

Experimental Setup

RLAN TX

DFS Detector

•Collaborative study with Industry Canada/Communication Research Centre; •Previous work was theoretical, simulations•Inject RLAN signals directly into the radar receiver to determine effect on weather radars of different power outputs, modulations•Introduce RLAN signals in a “typical” rural/urban environment taking into propagation and terrain effects (not comprehensive)•Simulations

6

RLAN Spectrum Single packet (Agilent signal generator)

18 MHz and many peaks

10 channels of 18 MHz wide for RLAN (5625 MHz))

Compared to 1MHz wide for radar (5600-5650MHz)

RLAN looks like white noise to the weather radar – no preferred frequencies within 18 MHz

RLAN are Wireless LANs using Radiofrequencies

Send sequence of information packets; typical 750 usec in length; 18 MHz bandwidth, 30 dBm erip

Point to point or isotropic

7

•Input of signal processor•Propagation compensated - predetermined

Packet Modulations

Frequency Test

Interference Modes

Off-Axis

Backscatter

Direct

8

Dynamic Frequency SelectionRLAN Mitigation Strategy

DFS – a device to detect weather radar interference and shift

DFS detects weather radar, must vacate channel for 30 minutes and then can use frequency immediately again (and interfere). Q: Sensitivity, reaction time? Channel vacate algorithm is unknown?

Canadian proposal on the channel visit algorithm: additional 10 minutes of monitoring (without transmission) before using the channel. Proposal led by Industry Canada. Otherwise, intermittent (mutual) interference every 30 minutes. Adopted in several jurisdictions.

Sensitivity Range of DFS to weather radar

DFS detector can see weather radar easily! (not shown)

9

RLAN Simulation Urban EnvironmentWhat happens with a network of RLANS?

Distribution of RLANS Remaining RLANS with DFSITU specification of distribution.

King City/Toronto – worse case in CanadaTheoretical simulations used London UK.

One Realization of a monte carlo simulation

10

Effect of Network of RLANS on the Weather Radar as a function of the DFS Detection Threshold

MDS of Wx Radar

DFS Sensitivity

0.65o beamwidth antenna has greater sensitivity

1.0o beamwidth antenna sees more RLANS

DFS must have at least this detection sensitivity

11

Low Level PPI of RLAN InterferenceExample for RLAN at 500m and 10 km

500 m 10 km

12

RHI’s through the Intereference Example for RLAN at 500m and 10 km

500 m 10 km

13

Sidelobe Detection4.1o elevation

Main

Sidelobe

Sidelobe

14

Cross-section Perpendicular to Radial/Beam Pattern

15

RLANS and the King City EnvironmentRLANS are licensed now! Non-licensed use in the future!

•Artifacts are out of band RLAN interference•radar is very sensitive•Radar rx needs to filter

24 hr Rainfall Accumulation

16

Summary Spectrum sharing is the reality Must adopt collaborative mitigation strategies

10 minute additional monitor without transmit strategy in DFS

Filtering out of band in wx radar (tx/rx) Experiments show RLAN as white noise and

manageable (for now) Simulations show that DFS will mitigate

RLANS Urban sprawl may change the situation; Increased use of RLAN’s and…

DFS can see weather radar No commercial DFS’ yet, Specification

enforcement?, Non-licensed, No import restrictions Vacate algorithms unknown?

Other frequencies at risk too; particularly passive microwave

Ultrawideband next, support your ITU rep – communications, avoidance radars

Lightning, UAV not even considered yet