Simulcast Systems for Public Safety Rick Taylor Senior Scientist, PSPC Lynchburg, Va 1 Dec 2011 Presentation1 29-Nov-11
Public Safety Mission Critical Communications Systems • Secure Wide-area Voice and Data Networking • Interoperability and Reliability are Key • Fragmented Frequency Bands • Rapid Access - Sub-second Across Network • Mostly Group Calls (“One to Many”) • Near Ubiquitous Coverage Presentation2
Near Ubiquitous Coverage 100 W Base Station Output Power + Ant Gain Typical Towers Typically Spaced 2- 20 miles Mobile 30 dB Portable In- Building Building Loss Typical Portable In-Basement Coverage Reliability Requirement is Typically 95-98% • Service Areas: From Small Towns Through Statewide • 3 Watts Portable Output Power • Presentation3
P25 IP Trunked Multisite System Network Switching Center I P Consoles Network I P WAN Management Network I nteroperability Gateways Administration P25 I P Trunked Sites Presentation4 June 8, 2007
P25 IP Simulcast Systems • Used Since the Late 80’s Primarily in Urban Areas Network Switching Center I P Consoles Network I P WAN Management Network I nteroperability Gateways Administration Control Point & Voters P25 I P Simulcast Sites Presentation5 June 8, 2007
Simulcast System Transmit Overlap Both Towers Transmit the Same Signal at Essentially the t a t b Same Time propagation propagation delay delay Delay Spread = Abs(t b – t a ) Too Much Causes Communications Loss! Typically > 3 miles Site Separation Note: Typical Harris simulcast systems have (Delay Spread Only Significantly Effects the Sites’ TX Signal) more than two sites Presentation6 29-Nov-11
Delay Spread from a P25 (C4FM) 3-Site Simulcast System Pink Signal Overlap Areas Have Excessive Delay Spread to Communicate Less Pink = Better Coverage What Can Be Done with the Modulation to Improve the Tolerance to Delay Spread? Presentation7 29-Nov-11
Backround: Review of Eye Patterns An Overlay of Time Segments of the Demodulated Digital Signal, with • Each Segment an Integer Multiple of the Bit (or Symbol) Period 2-LEVEL EDACS DEMODULATED SIGNAL EDACS Demodulated Signal S y stem V iew E x tra cted from w 0 (S am ples 1 00 0 to 1 100 ) 10 .4 5e -3 10 .6 5e -3 10 .8 5e -3 11 .0 5e -3 11 .2 5e -3 1 50 0e-3 e d u m p A t l i 0 -50 0e-3 -1 10 .4 5e -3 10 .6 5e -3 10 .8 5e -3 11 .0 5e -3 11 .2 5e -3 Ti m e in S econd s SystemView Sliced w0 (No Repeat, Start = 1,006, Length = 20) 0 20e-6 40e-6 60e-6 80e-6 100e-6 120e-6 140e-6 160e-6 180e-6 1 Eye Pattern 500e-3 Amplitude Showing Two 0 Bit Periods -500e-3 -1 0 20e-6 40e-6 60e-6 80e-6 100e-6 120e-6 140e-6 160e-6 180e-6 Time in Seconds Presentation8 29-Nov-11
Background: Recovering the Information from a 2-Level FSK Modulation Desired Sample Point SystemView Eye 45e-6 65e-6 85e-6 105e-6 125e-6 145e-6 165e-6 1 An “Open” Declare Eye Reduces “1” 500e-3 Errors in Threshold Data 0 Recovery (i.e. Declare Lowers Bit -500e-3 “0” Error Rate) -1 45e-6 65e-6 85e-6 105e-6 125e-6 145e-6 165e-6 Presentation9 29-Nov-11
Eye Pattern of P25 Phase 1 4-Level C4FM Modulation SystemView Sliced w3 (No Repeat, Start = 200, Length = 60) 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e-6 Di-Bits 4 Declared: 0,1 2 0,0 3 Amplitude 0 Thresholds 1,0 -2 1,1 -4 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e-6 Time in Seconds Desired Sample Points (Figure shows three symbol periods) Presentation10 29-Nov-11
Deterioration of P25 Eye Due to Simulcast Delay Spread SystemView SystemView SystemView Sliced w3 (No Repeat, Start = 200, Length = 20) Sliced w3 (No Repeat, Start = 200, Length = 20) Sliced w3 (No Repeat, Start = 200, Length = 20) 65e-6 85e-6 105e-6 125e-6 85e-6 105e-6 125e-6 145e-6 85e-6 105e-6 125e-6 145e-6 2 2 2 Amp litud e Amp litud e Amp litud e 0 0 0 -2 -2 -2 -4 -4 -4 65e-6 85e-6 105e-6 125e-6 85e-6 105e-6 125e-6 145e-6 85e-6 105e-6 125e-6 145e-6 Time in Seconds Time in Seconds Time in Seconds Strong Strong Signal, Strong Signal, Signal, no 25 usec Delay 50 usec Delay Fading Spread Fading Spread Fading Presentation11 29-Nov-11
Model of Delay Spread’s Effect On the Eye 1st Path 2nd Path Eye Eye Path1+Path2 Usable Eye Delay Wider is Better! Spread Presentation12 29-Nov-11
Eye Patterns of Different Modulations C4FM, α =0.2 (Present P25) CQPSK, α = 0.2 C4FM, α =1 SystemView SystemView SystemView Sliced w4 (No Repeat, Start = 1,000, Length = 30) Sliced w8 (No Repeat, Start = 1,000, Length = 30) Sliced w16 (No Repeat, Start = 1,000, Length = 30) 0 100e-6 200e-6 300e-6 400e-6 500e-6 600 0 100e-6 200e-6 300e-6 400e-6 500e-6 600 0 100e-6 200e-6 300e-6 400e-6 500e-6 600 3 3 3 2 2 2 1 1 1 Amplitude Amplitude Amplitude 0 0 0 -1 -1 -1 -2 -2 -2 -3 -3 -3 0 100e-6 200e-6 300e-6 400e-6 500e-6 600 0 100e-6 200e-6 300e-6 400e-6 500e-6 600 0 100e-6 200e-6 300e-6 400e-6 500e-6 600 Time in Seconds Time in Seconds Time in Seconds SystemView SystemView Sliced w20 (No Repeat, Start = 1,000, Length = 30) Sliced w3 (No Repeat, Start = 200, Length = 30) 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e-6 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e Preferred 2 2 Wide 1 1 CQPSK CQPSK, α =1 Amplitude Amplitude 0 0 (Denoted -1 -1 Note: α is the -2 WCQPSK) -2 filter rolloff factor 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e-6 Time in Seconds Time in Seconds Presentation13 29-Nov-11
WCQPSK π /4 Differential Phase Modulation α is Raised Cosine Filter Modulated Time Domain Sig Rolloff Factor “Constant Raised I I Envelope” I Cosine Variable Envelope Signal To Modulated Signal Filter ( α ) PA I, Q To Linearized PA -3,-1,1,3 Table Modulator Lookup Raised Sy stemView 4 Level Sink 335 Q 20.5e-3 22.5e-3 24.5e-3 26.5e-3 28.5e-3 30.5e-3 32.5e-3 34.5e-3 Symbols 1 Cosine 500e- 3 In de plitu m 0 A Q Filter( α ) -500e-3 -1 -1.5 20.5e-3 22.5e-3 24.5e-3 26.5e-3 28.5e-3 30.5e-3 32.5e-3 34.5e-3 Time in Seconds S yst emV i ew S nk 484 vs S i i nk 485 (w 0 vs w 1) -40 -20 0 20 40 60 Q 40 20 de w0 A mpli t u 0 I CQPSK I, Q -20 Constellation -40 -60 -40 -20 0 20 40 1 A w m pl t ude i Presentation14 29-Nov-11
Our Patented WCQPSK Modulation Filter ‘s 2 nd Zero Crossing Impulse Response Enables a Wider Eye Symbol Symbol Period Period 2 nd Zero Crossing Presentation15 29-Nov-11
Discernible WCQPSK Eyes Remain Even for 120 usec Delay Spread SystemView Sliced w3 (No Repeat, Start = 1,000, Length = 30) 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e-6 30e+3 20e+3 Static, Strong 10e+3 Amplitude 0 -10e+3 Signal -20e+3 -30e+3 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e-6 Time in Seconds SystemView Sliced w3 (No Repeat, Start = 1,000, Length = 30) 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e-6 Faded, Delay 20e+3 Amplitude 0 Spread=0 -20e+3 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e-6 Time in Seconds SystemView Sliced w3 (No Repeat, Start = 1,000, Length = 30) 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e-6 Faded, Delay 20e+3 Amplitude 0 Spread=40 usec -20e+3 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e-6 Time in Seconds SystemView Sliced w3 (No Repeat, Start = 1,000, Length = 30) 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e-6 Faded, Delay 20e+3 Amplitude 0 Spread=120 usec -20e+3 0 100e-6 200e-6 300e-6 400e-6 500e-6 600e-6 Time in Seconds Presentation16 29-Nov-11
BER Versus Delay Spread Comparison BER Versus Delay Spread Measurements 5 WCQPSK 6 KHz RX 4.5 Filter Approx 2X 4 Improvement Over C4FM P25 3.5 C4FM 3 BER % 2.5 2.0% BER for 2 DAQ 3.4 Voice Quality 1.5 1 0.5 0 0 10 20 30 40 50 60 70 80 90 100 Delay Spread (usec) Presentation17 29-Nov-11
WCQPSK Spectrum Out Of Our Base Station’s Linearized PA Meets the Stringent 210d NB Mask • Peak Hold Measurement • 100 W Avg Power Presentation18 29-Nov-11
Summary of WCQPSK Conceptual Design Simulcast Delay Spread BER Can Be Greatly • Improved with PSPC’s WCQPSK Linear Modulation that Has “Wider” Eyes > 2X Delay Spread Improvement Over P25 C4FM Meets Required FCC Masks and has Low TX ACP Has Slightly Better Sensitivity than P25 Phase 1 C4FM Systems Presentation19 29-Nov-11
Questions? Contact Info: richard.taylor@harris.com Presentation20 29-Nov-11
Recommend
More recommend
