SimulcastRadio

NetworkDesign

Jay M. Jacobsmeyer, P.E.Pericle Communications Co.

1910 Vindicator Drive, Suite 100Colorado Springs, CO 80919

Outline

Company Overview

Background Information

Needs Analysis

Requirements Specification

System Design

Comparison with Competing Design

Company Overview

Pericle Communications Company– Founded in 1992– Headquartered in Colorado Springs, CO– Specializing in wireless communications– 10 employees, six are electrical engineers

Services Include:– Public safety radio network design, testing, & troubleshooting– Interference mitigation for wireless carriers– Radio frequency exposure surveys

City and County of Denver554,000 residents(2.8 million inmetro area)150 square milesOne major airport1,405 swornpolice officersOver 2,000 radiousers

Project BackgroundCity and County of Denver Radio System– 800 MHz, single site, trunked radio system– Constructed in 1988– Main repeater site on Mt. Morrison in Jefferson County, CO

Radio Coverage Weak in Some Areas– Especially southeast Denver in Denver Tech Center– Inside certain buildings

Vendor (M/A-COM) asked to Quote Improvements (2005)– Proprietary system made competition impractical– Solution originally budget driven, not requirements driven– Pericle asked to provide independent design

Technology Overview800 MHz Trunked Radio Systems– Repeater site transmit frequency: 851 - 869 MHz– Repeater site receive frequency: 806 - 824 MHz– Frequencies first available in late 1970s (TV Ch’s 70 - 83)– Multiple frequencies controlled by a single switch– Until recently systems were proprietary and not interoperable

Trunking Concept– Similar to telephone switch– Control channel is gateway to voice channels– Radio channels are shared– “Talk group” is a virtual channel

Denver Particulars– 24 channel system– Vendor = M/A-COM, a Tyco Electronics Company

Needs AnalysisDenver Staff Conducted User Surveys– Primarily to identify weak service areas– Specific buildings to be covered also identified

Process was Imperfect– Needs should be independent of current state– But only those buildings with problems made the list– Danger is that new system improves coverage in some

areas, but worsens in other, equally important areas

Requirements Specification95% Coverage Requirement– Outside coverage in Denver County– Inside each problem area– Inside listed buildings

Channel Assumptions– Multipath fading channel, Rayleigh distribution

Figure of Merit = 12 dB SINAD– Vendor radio performance threshold = -99 dBm

Measurement Requirements (see TIA TSB-88)– Service area reliability (SAR) = 95%– 90% confidence level, +/- 2% confidence interval– Requires at least 1,702 samples– Drive test “tile” size ≤≤≤≤ 400 meters

System Design

Problem Areas IdentifiedDowntownDenver Tech CenterGreen Valley RanchCherry CreekStapletonHampdenBear Valley

Tech Center

Tech Center

Stapleton

Green Valley

Downtown

Cherry Creek

Bear Valley

Hampden

Candidate TechnologiesRepeater Sites– Simulcast network– Multi-site network– Hybrid: combination of simulcast and multi-site

Channelized Amplifiers– Also called bidirectional amplifiers

Distributed Antenna Systems– Specific to each building

High PowerWide Area

Low PowerSmall Area

Modeling vs. MeasurementsRadio Propagation Models– Lack of complete database is key shortcoming– Mathematical models tend to be crude– No consensus on accuracy of sophisticated models– Best models have σσσσ = 8 dB

Measurements– Not perfect either, but much more accurate– Measurement accuracy +/- 1.5 dB– Main disadvantage is cost– Some prospective sites cannot be tested

Objectives of SurveySurvey All Candidate Sites– City wide on-street measurements– In-building measurements

Quantify Contribution of Each Site– Improved service reliability on street– Improved service reliability inside buildings

Find Logical Breakpoints– Identify sites with high pay-off– Identify weak sites– Identify isolated buildings, if any

RF SurveySite Preparation– Repeater and omni antenna installed at each site– Unique frequency at each site– Each site transmits continuously

On-Street Measurements– Drive entire city using 0.25 mile grid– Drive every street in the seven problem areas– Per EIA-TSB-88A, 40λλλλ averaging, > 50 samples per meas.– Over 12,000 measurements collected city-wide– Measurements collected from multiple sites simultaneously

In-Building Measurements– From building list, 46 structures– 40λλλλ averaging, > 50 samples per measurement– Multiple measurements per floor, over 1,000 total

RF Survey Results

Mt. Morrison(Current System)

7,700’ AMSL

2,500’ Above Denver

12 miles West of City

60° BW Antennas

Candidate Sites

AMO = Amoco Building (Downtown)

FPS = Four Points Sheraton (DTC)

FS2 = Fire Station 2 (Green Valley Ranch)

JOS = 950 Josephine (Cherry Creek, Stapleton)

STA = CCNC Tower (Hampden, Stapleton)

LHU = Loretto Heights (Bear Valley)

AMO JOS

LHU FPS

FS2

STA

Amoco Building

Amoco(500’ AGL)

RepublicPlaza(Tallest

Denver Bldg.)

950Josephine

Survey ResultsStrong Sites– Mt. Morrison– Amoco Building– Four Points Sheraton– Fire Station 2

Weak Sites– Josephine (when compared to Amoco, voting)– State Tower

Both Problem Area and Site Are Questionable– Loretto Heights (Bear Valley Area)

Mt. Morrison Is Still Strongest Server in Some Locations

Network Design

Hybrid Design Summary

10 dBd34 µµµµsOmniFire Station 2

14 dBd17 µµµµsDirectionalFour Points Sheraton

9 dBd0OmniAmoco Bldg.

17 dBdNADirectionalMt. Morrison

GainTimeAntennaSite

Plus Voting Receivers at JosephinePlus DAS Systems in 11 Public Buildings– These Buildings Cannot be Covered by Outdoor Repeaters

Lessons LearnedStart From Requirements, not Budget

Bad Assumption Leads to Wrong Answer– I.e., the “omni” site in simulcast network

Avoid Vendor Conflicts of Interest– Vendor should not set requirements– Objective test plan must be in contract– How to test is as important as pass/fail criteria– Use independent party for acceptance testing

References[1]EIA TSB-88-B, “Wireless Communications Systems —

Performance in Noise and Interference-Limited Situations,Recommended Methods for Technology-IndependentModeling, Simulation and Verification,” With Addendum 1,May, 2005.

[2] W.C. Jakes, ed., Microwave Mobile Communications, IEEEPress Reissue, 1994.

[3]W. C. Y. Lee, Mobile Cellular Telecommunications Systems,McGraw-Hill, 1989.

[4]R. J. Larsen, M. L. Marx, An Introduction to MathematicalStatistics and its Applications, Prentice-Hall, 1986, pp. 281.

Design Comparison

Vendor Proposal

What is it?– Six-site simulcast with 20 channels per site– “Fork-lift” upgrade to replace public safety radio system

Issues From Outset– Lack of evidence to support coverage assertions– Does not provide wide area coverage outside Denver– Zoning issues with at least two of the proposed sites– No evidence that alternatives were considered

Problems Discovered During Coverage Survey– Bear Valley problem is not weak signals– Amoco Building should be the omni site, not Josephine– If Amoco is omni, Josephine offers negligible improvements

JOS

LHU

MTR

AMO

F27

HWT

Vendor 6-Site Simulcast

Service Area Reliabilities

-99 dBm -79 dBmMt. Morrison (Existing Sys.) 99.5% 47%Vendor 6-Site Simulcast 100% 74%3-Site Simulcast + Morrison 100% 82%