Simulcast Systems for Public Safety · Presentation8 29-Nov-11 Backround: Review of Eye Patterns...

Presentation1 29-Nov-11

Simulcast Systems for Public Safety

Rick TaylorSenior Scientist, PSPC

Lynchburg, Va1 Dec 2011

Presentation2

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

Presentation3

Near Ubiquitous Coverage

• Coverage Reliability Requirement is Typically 95-98% • Service Areas: From Small Towns Through Statewide• 3 Watts Portable Output Power

Portable In-Building

Portable In-Basement

Mobile

Towers Typically Spaced 2- 20 miles

30 dB Building Loss Typical

100 W Base Station Output Power + Ant Gain Typical

Presentation4 June 8, 2007

P25IP Trunked Sites

P25IP Trunked Multisite System

IP Consoles

IP WAN

NetworkSwitchingCenter

Network ManagementNetwork Administration

Interoperability Gateways

Presentation5 June 8, 2007

P25IP Simulcast Sites

P25IP Simulcast Systems

IP Consoles

IP WAN

NetworkSwitchingCenter

Network ManagementNetwork Administration

Interoperability Gateways

ControlPoint & Voters

• Used Since the Late 80’s Primarily in Urban Areas


Simulcast System Transmit Overlap

Delay Spread = Abs(tb – ta)Too Much Causes Communications Loss!

tb propagation delay

Both Towers Transmit the Same Signal at Essentially the Same Time

Typically > 3 milesSite Separation

ta propagation delay

Note: Typical Harris simulcast systems have more than two sites(Delay Spread Only Significantly Effects the Sites’ TX Signal)

Presentation7

Delay Spread from a P25 (C4FM) 3-Site Simulcast System

29-Nov-11

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?


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

EDACS Demodulated SignalSystemView

10.45e-3

10.45e-3

10.65e-3

10.65e-3

10.85e-3

10.85e-3

11.05e-3

11.05e-3

11.25e-3

11.25e-3

1

500e-3

0

-500e-3

-1

Amplitude

Time in Seconds

Extracted from w0 (Samples 1000 to 1100)

2-LEVEL EDACS DEMODULATED SIGNAL

SystemView

0

0

20e-6

20e-6

40e-6

40e-6

60e-6

60e-6

80e-6

80e-6

100e-6

100e-6

120e-6

120e-6

140e-6

140e-6

160e-6

160e-6

180e-6

180e-6

1

500e-3

0

-500e-3

-1

Ampl

itude

Time in Seconds

Sliced w0 (No Repeat, Start = 1,006, Length = 20)

Eye Pattern Showing Two Bit Periods


Background: Recovering the Informationfrom a 2-Level FSK Modulation

An “Open” Eye Reduces Errors in Data Recovery (i.e. Lowers Bit Error Rate)

SystemView

45e-6

45e-6

65e-6

65e-6

85e-6

85e-6

105e-6

105e-6

125e-6

125e-6

145e-6

145e-6

165e-6

165e-6

1

500e-3

0

-500e-3

-1

Eye

Threshold

Declare “1”

Declare “0”

Desired Sample Point


Eye Pattern of P25 Phase 1 4-Level C4FM Modulation

SystemView

0

0

100e-6

100e-6

200e-6

200e-6

300e-6

300e-6

400e-6

400e-6

500e-6

500e-6

600e-6

600e-6

4

2

0

-2

-4

Ampl

itude

Time in Seconds

Sliced w3 (No Repeat, Start = 200, Length = 60)

Desired Sample Points

0,10,0

1,0

1,1

3 Thresholds

Di-Bits Declared:

(Figure shows three symbol periods)


Deterioration of P25 Eye Due to Simulcast Delay Spread

Strong Signal, no Fading

SystemView

65e-6

65e-6

85e-6

85e-6

105e-6

105e-6

125e-6

125e-6

2

0

-2

-4

Am

plit

ude

Time in Seconds


SystemView

85e-6

85e-6

105e-6

105e-6

125e-6

125e-6

145e-6

145e-6

2

0

-2

-4

Am

plit

ude

Time in Seconds


Strong Signal, 25 usec Delay Spread Fading

Strong Signal, 50 usec Delay Spread Fading

SystemView

85e-6

85e-6

105e-6

105e-6

125e-6

125e-6

145e-6

145e-6

2

0

-2

-4

Am

plit

ude

Time in Seconds



Model of Delay Spread’s Effect On the Eye

Wider is Better!

1st Path Eye

Delay Spread

2nd Path Eye

Path1+Path2 Usable Eye


Eye Patterns of Different Modulations

SystemView

0

0

100e-6

100e-6

200e-6

200e-6

300e-6

300e-6

400e-6

400e-6

500e-6

500e-6

600

600

3

2

1

0

-1

-2

-3

Am

plitu

de

Time in Seconds

Sliced w4 (No Repeat, Start = 1,000, Length = 30)SystemView

0

0

100e-6

100e-6

200e-6

200e-6

300e-6

300e-6

400e-6

400e-6

500e-6

500e-6

600

600

3

2

1

0

-1

-2

-3A

mpl

itude

Time in Seconds

Sliced w8 (No Repeat, Start = 1,000, Length = 30)SystemView

0

0

100e-6

100e-6

200e-6

200e-6

300e-6

300e-6

400e-6

400e-6

500e-6

500e-6

600

6003

2

1

0

-1

-2

-3

Am

plitu

de

Time in Seconds


SystemView

0

0

100e-6

100e-6

200e-6

200e-6

300e-6

300e-6

400e-6

400e-6

500e-6

500e-6

600e

600e

2

1

0

-1

-2

Ampl

itude

Time in Seconds


C4FM, α =0.2 (Present P25) CQPSK, α = 0.2 C4FM, α =1

CQPSK, α =1

SystemView

0

0

100e-6

100e-6

200e-6

200e-6

300e-6

300e-6

400e-6

400e-6

500e-6

500e-6

600e-6

600e-6

2

1

0

-1

-2

Ampl

itude

Time in Seconds


Preferred Wide CQPSK

(Denoted WCQPSK)Note: α is the

filter rolloff factor


WCQPSK π/4 Differential Phase Modulation

Sy stemView

20.5e-3

20.5e-3

22.5e-3

22.5e-3

24.5e-3

24.5e-3

26.5e-3

26.5e-3

28.5e-3

28.5e-3

30.5e-3

30.5e-3

32.5e-3

32.5e-3

34.5e-3

34.5e-3

1

500e-3

0

-500e-3

-1

-1.5

Amplitud

e

Time in Seconds

Sink 335

Variable Envelope Modulated Signal To Linearized PA

Modulated Time Domain SigRaised Cosine

Filter (α)

Raised Cosine Filter(α)

Table Lookup

I

Q

I

Q

“Constant Envelope”

Signal To PAI, Q

Modulator4 Level Symbols

In

-3,-1,1,3

I

α is Raised Cosine Filter Rolloff Factor

CQPSK I, Q Constellation

Syst emView

-40

-40

-20

-20

0

0

20

20

40

4060

40

20

0

-20

-40

-60

w0

Am

plit

ude

w1 Am plit ude

Sink 484 vs Sink 485 (w0 vs w1)

I

Q


Symbol Period

Symbol Period

Our Patented WCQPSK Modulation Filter ‘s 2nd Zero Crossing Impulse Response Enables a Wider Eye

2nd Zero Crossing


Discernible WCQPSK Eyes Remain Even for 120 usec Delay Spread

Faded, Delay Spread=0

SystemView

0

0

100e-6

100e-6

200e-6

200e-6

300e-6

300e-6

400e-6

400e-6

500e-6

500e-6

600e-6

600e-6

20e+3

0

-20e+3

Ampl

itude

Time in Seconds


Faded, Delay Spread=40 usec

SystemView

0

0

100e-6

100e-6

200e-6

200e-6

300e-6

300e-6

400e-6

400e-6

500e-6

500e-6

600e-6

600e-6

20e+3

0

-20e+3

Ampl

itude

Time in Seconds


Static, Strong Signal

SystemView

0

0

100e-6

100e-6

200e-6

200e-6

300e-6

300e-6

400e-6

400e-6

500e-6

500e-6

600e-6

600e-6

30e+3

20e+3

10e+3

0

-10e+3

-20e+3

-30e+3

Ampl

itude

Time in Seconds


Faded, Delay Spread=120 usec

SystemView

0

0

100e-6

100e-6

200e-6

200e-6

300e-6

300e-6

400e-6

400e-6

500e-6

500e-6

600e-6

600e-6

20e+3

0

-20e+3

Ampl

itude

Time in Seconds



BER Versus Delay Spread Comparison

2.0% BER for DAQ 3.4 Voice Quality

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 10 20 30 40 50 60 70 80 90 100

BER

%

Delay Spread (usec)

BER Versus Delay Spread Measurements

P25 C4FM

WCQPSK6 KHz RX Filter Approx 2X Improvement Over C4FM


WCQPSK Spectrum Out Of Our Base Station’s Linearized PA Meets the Stringent 210d NB Mask

• Peak Hold Measurement

• 100 W Avg Power


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

Presentation20

Questions?

29-Nov-11

Contact Info: [email protected]

Simulcast Systems for Public Safety · Presentation8 29-Nov-11 Backround: Review of Eye Patterns...

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