Simulcast Radio Network Design Jay M. Jacobsmeyer, P.E. Pericle Communications Co. 1910 Vindicator Drive, Suite 100 Colorado 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 Denver 554,000 residents (2.8 million in metro area) 150 square miles One major airport 1,405 sworn police officers Over 2,000 radio users
Project Background City 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 Overview 800 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 Analysis Denver 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 Specification 95% 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 Identified Downtown Denver Tech Center Green Valley Ranch Cherry Creek Stapleton Hampden Bear Valley
Green Valley Downtown Stapleton Cherry Creek Hampden Bear Valley Tech Center Tech Center
Candidate Technologies Repeater Sites High Power Simulcast network Wide Area Multi-site network Hybrid: combination of simulcast and multi-site Channelized Amplifiers Also called bidirectional amplifiers Distributed Antenna Systems Specific to each building Low Power Small Area
Modeling vs. Measurements Radio 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 σ = 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 Survey Survey 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 Survey Site 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, 40λ 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 40λ 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)
FS2 AMO JOS STA LHU FPS
Amoco Building Republic Plaza (Tallest Denver Bldg.) Amoco (500 AGL)
950 Josephine
Survey Results Strong 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 Site Antenna Time Gain Mt. Morrison Directional NA 17 dbd Amoco Bldg. Omni 0 9 dbd Four Points Sheraton Directional 17 µs 14 dbd Fire Station 2 Omni 34 µs 10 dbd Plus Voting Receivers at Josephine Plus DAS Systems in 11 Public Buildings These Buildings Cannot be Covered by Outdoor Repeaters
Lessons Learned Start 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-Independent Modeling, Simulation and Verification, With Addendum 1, May, 2005. [2] W.C. Jakes, ed., Microwave Mobile Communications, IEEE Press Reissue, 1994. [3] W. C. Y. Lee, Mobile Cellular Telecommunications Systems, McGraw-Hill, 1989. [4] R. J. Larsen, M. L. Marx, An Introduction to Mathematical Statistics 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
F27 AMO JOS MTR LHU HWT
Vendor 6-Site Simulcast
Service Area Reliabilities -99 dbm -79 dbm Mt. Morrison (Existing Sys.) 99.5% 47% Vendor 6-Site Simulcast 100% 74% 3-Site Simulcast + Morrison 100% 82%