1 ptp and pmp links rf links overview. 2 full duplex communications two stations can talk and...

1

PTP and PMP LinksPTP and PMP Links

RF Links Overview

2

Full Duplex CommunicationsFull Duplex Communications

Two stations can talk and listen to each other at the same Two stations can talk and listen to each other at the same time.time.

This requires two separate media.This requires two separate media. In the case of a wireless link, 2 separate channels are In the case of a wireless link, 2 separate channels are

required. This is referred to as Frequency Division Duplex required. This is referred to as Frequency Division Duplex (FDD)(FDD)

Station 1 Station 2Channel 1

Channel 2TX RX

TXRX

3

Half Duplex CommunicationsHalf Duplex Communications

Two stations have to take turns talking and listening. Two stations have to take turns talking and listening. Simultaneous communications is not possible. Requires Simultaneous communications is not possible. Requires handshaking.handshaking.

Two stations share a common mediaTwo stations share a common media This is referred to as time division duplex (TDD)This is referred to as time division duplex (TDD)

Station 1 Station 2Channel 1

TX

RX

TX

RX

4

Advantages of FDDAdvantages of FDD

More efficient data transfer due to lower overhead More efficient data transfer due to lower overhead (required for handshaking). (required for handshaking).

More efficient use of spectrum in high traffic systemsMore efficient use of spectrum in high traffic systems

Most ITU frequency bands are structured for FDD.Most ITU frequency bands are structured for FDD.

Half the data rate for equivalent data transfer as TDD.Half the data rate for equivalent data transfer as TDD.

Does not have latency issues associated with Does not have latency issues associated with handshaking.handshaking.

5

Advantages of TDDAdvantages of TDD

Easier to coordinate channels than FDD.Easier to coordinate channels than FDD.

RF Hardware is potentially less complicated and thus RF Hardware is potentially less complicated and thus lower cost.lower cost.

Installation may be simpler.Installation may be simpler.

Only one antenna per T/ROnly one antenna per T/R

In low traffic networks the spectrum is utilized more In low traffic networks the spectrum is utilized more efficiently.efficiently.

6

Point to Point (PTP) LinksPoint to Point (PTP) Links

A point to point link is one station communicating with A point to point link is one station communicating with another station, 1 to 1.another station, 1 to 1.

Both stations are usually similar in data-rate, modulation Both stations are usually similar in data-rate, modulation and overhead format.and overhead format.

FDD PTP links do not require media access control which FDD PTP links do not require media access control which reduces overhead.reduces overhead.

7

Point to Point (PTP) LinksPoint to Point (PTP) Links

FDD PTP links do not require handshaking, this FDD PTP links do not require handshaking, this minimizes latency.minimizes latency.

PTP links are usually used in constant bit rate PTP links are usually used in constant bit rate applications, such as synchronous data transport and applications, such as synchronous data transport and trunking applications.trunking applications.

PTP links can be built with extra margin to deal with fades PTP links can be built with extra margin to deal with fades and other impairments.and other impairments.

8

System Power LevelsSystem Power Levels

Point to point link has extra system gain to increase Point to point link has extra system gain to increase availability.availability.

Low probability of interference to or from other stations.Low probability of interference to or from other stations.

P to P links typically have narrow beam antennas.P to P links typically have narrow beam antennas.

9

System Power Levels PTP LinksSystem Power Levels PTP Links

Station 1 Station 2

TX = +18 dBm

Antenna Gain 30 dB Antenna Gain 30 dB

RX = -42 dBm

RX Threshold = -72 dBm

Path loss = -116 dB

10

Point to Multipoint (PMP) LinksPoint to Multipoint (PMP) Links

One base station communicating with more than one One base station communicating with more than one subscriber on shared media.subscriber on shared media.

PRIZM 2400

11

Point to Multipoint (PMP) LinksPoint to Multipoint (PMP) Links

Downstream path is from the hub to the sub.Downstream path is from the hub to the sub.

Upstream path is from the sub to the hub.Upstream path is from the sub to the hub.

Can use either FDD or TDDCan use either FDD or TDD

With many subscribers PMP is more economical than With many subscribers PMP is more economical than PTP in both hardware and spectrum utilization. PTP in both hardware and spectrum utilization.

12

Point to Multipoint (PMP) LinksPoint to Multipoint (PMP) Links

Data-rates and modulation tend to be asymmetrical to Data-rates and modulation tend to be asymmetrical to reflect the the asymmetric flow of data in this type of reflect the the asymmetric flow of data in this type of system.system.

Media Access Control (MAC) is mandatory for a PMP Media Access Control (MAC) is mandatory for a PMP system.system.

Typically IP based, does not work well for constant bit rate Typically IP based, does not work well for constant bit rate applications.applications.

13

System Power Levels PMP LinksSystem Power Levels PMP Links

In a point to multi-point system power levels must be In a point to multi-point system power levels must be controlled to prevent self interference.controlled to prevent self interference.

The Hub TX has a fixed output power.

The Hub RX has a fixed gain.

The Sub TX has a variable output power that is controlled by the RSL at the Hub RX.

The Sub RX will adjust its gain for proper RSL.

14

System Power Level PMP LinksSystem Power Level PMP Links

HUB

TX Pwr = +18 dBm

RSL = -72 dBm

Ant. Gain = 20 dBi

TX Pwr = +6 dBm

RSL = -60 dBm

Ant. Gain = 20 dBi

TX Pwr = +12 dBm

RSL = -66 dBm

Ant. Gain = 20 dBi

TX Pwr = +18 dBm

RSL = -72 dBm

Ant. Gain = 20 dBi

Sub 3

Sub 2

Sub 1

Path loss = -130 dB

Path loss = -124 dB

Path loss = -118 dB

15

System Power Levels PMP LinksSystem Power Levels PMP Links

If an unlimited number of channels are available then self If an unlimited number of channels are available then self interference is not a consideration.interference is not a consideration.

Within a sector subscribers will not interfere with each Within a sector subscribers will not interfere with each other due to TDMA.other due to TDMA.

Between Sectors of the same channel interference can Between Sectors of the same channel interference can occur, TDMA control no longer applies.occur, TDMA control no longer applies.

Co-channel interference occurs due to antenna side Co-channel interference occurs due to antenna side lobes, back lobes, improperly aimed antennas and lobes, back lobes, improperly aimed antennas and reflections.reflections.

16

System Power Levels PMP LinksSystem Power Levels PMP Links

To minimize self interference... To minimize self interference...

Use minimum necessary hub TX power to reach farthest out subscriber.

Keep farthest out subscribers in center of beam if possible.

Carefully adjust elevation angle to give good signal to farthest out subscribers while still providing useable signal to close in Subs.

Make sure Sub antennas are pointed correctly, use elevation brackets if necessary.

Use maximum number of channels that is practical.

All links should be LOS, avoid reflections and obstructions.

17

Media Access ControlMedia Access Control

The MAC is implemented by the hub modem and controls The MAC is implemented by the hub modem and controls access of the subscriber modems to the shared channel. Spike access of the subscriber modems to the shared channel. Spike uses the DOCSIS (IEEE 802.14) MAC.uses the DOCSIS (IEEE 802.14) MAC.

Each Subscriber is assigned one or more exclusive time slots in Each Subscriber is assigned one or more exclusive time slots in which they may transmit data. This is referred to as time domain which they may transmit data. This is referred to as time domain multiple access (TDMA).multiple access (TDMA).

The Hub modem adjusts the power level of the Sub TX.The Hub modem adjusts the power level of the Sub TX.

The Hub modem synchronizes all subs with the Hub and The Hub modem synchronizes all subs with the Hub and equalizes path delay. equalizes path delay.

18

Media Access ControlMedia Access Control

The MAC provides a means for new subscribers to join The MAC provides a means for new subscribers to join the network.the network.

The MAC also provides for equitable sharing of bandwidth The MAC also provides for equitable sharing of bandwidth and arbitrating contention among subscribers.and arbitrating contention among subscribers.

The MAC must assure that all similarly provisioned The MAC must assure that all similarly provisioned subscribers have similar quality of service regardless of subscribers have similar quality of service regardless of their location.their location.

19

Broadband Wireless ExampleBroadband Wireless Example

TransceiverTransceiver Modulation TechniquesModulation Techniques Path AnalysisPath Analysis Amplifier ParametersAmplifier Parameters Filter TypesFilter Types Filter TechnologiesFilter Technologies PLL and AttenuatorsPLL and Attenuators

20

Transceiver Design OutlineTransceiver Design Outline

OverviewFunctionality Versions

Design Features Basic RF Concepts

21

Key RF Parameters for Wireless SystemsKey RF Parameters for Wireless Systems

• Antenna• Gain• Sidelobe Level

• Transceiver• Frequency Accuracy• Spurious Response (Regulatory Agency)• RMS Phase Error• Output Power

• Modem• Data rates• Required Signal to Noise• Spurious Response (Regulatory Agency)

22

(0000) (0001) (0010) (0011)(0000) (0001) (0010) (0011)

(0100) (0101) (0110) (0111)(0100) (0101) (0110) (0111)

(1000) (1001) (1010) (1011)(1000) (1001) (1010) (1011)

(1100) (1101) (1110) (1111)(1100) (1101) (1110) (1111)

(00) (00)

(01) (10)(01) (10)

(11)(11)

Modulation TechniquesModulation Techniques

BPSK

QPSK

16QAM

(0) (1)(0) (1)

23

Modulation With NoiseModulation With Noise

BPSK

QPSK

16QAM

24

Manufacturer: SPIKE Technologies Path Length 15.0 mi.

Subscriber Station Base Station

Transmit Frequency 3.550 GHz Transmit Frequency 3.450 GHz

Antenna Transmit Gain 19.0 dBi Antenna Transmit Gain 20.0 dBi

Antenna Receive Gain 19.0 dBi Antenna Receive Gain 19.6 dBi

IF Bandwidth 6.000 MHz IF Bandwidth 6.000 MHz

Receiver Noise Figure 6.5 dB Receiver Noise Figure 5.5 dB

UPLINK DOWNLINK Subscriber Unit Tx Output 25.0 dBm Base Transmitter Output 27.0 dBm

Output Backoff 5.0 dB Output Backoff 5.0 dB

Subscriber Transmit Power 20.0 dBm Base Transmit Power 22.0 dBm

Back-off to Balance Path 0.0 dB Back-off to Balance Path 0.0 dB

Tx Filter Loss 0.0 dB Tx Filter Loss 0.0 dB

Transmission Line Loss 1.0 dB Transmission Line Loss 1.2 dB

Tx Duplexer Loss 0.0 dB Tx Duplexer Loss 1.5 dB

Subscriber Tx Antenna Gain 19.0 dBi Base Tx Antenna Gain 20.0 dBi

Subscriber EIRP (dBm) 38.0 dBm Base EIRP (dBm) 39.3 dBm

Subscriber Average EIRP (Watts) 6.3 W Base Average EIRP (Watts) 8.5 W

Subscriber Max EIRP (Watts) 20.0 W Base Max EIRP (Watts) 26.9 W

Up Link Path Loss 131.1 dB Down Link Path Loss 130.9 dB

Base Rx Antenna Gain 19.6 dBi Subscriber Rx Antenna Gain 19.0 dBi

Transmission Line Loss 1.0 dBi Transmission Line Loss 1.2 dB

Base Rx Signal Level -74.5 dBm Sub Rx Signal Level -73.8 dBm

Thermal Noise Power -102.1 dBm Thermal Noise Power -100.8 dBm

Required C/N (LanCity) 25.0 dB Required C/N (LanCity) 25.0 dB

Final Margin 2.6 dB Final Margin 2.0 dB

Downlink Limited By: 0.6 dB

Usable Margin: 2.0 dB

PRIZM 3500 RF PATH ANALYSIS

25

Receive

LNA Gain

10 MHzReferenceOscillator

IF

Transmit

BPFSAWS

PA

LD1

AnalogAtten

GainBPFCeramic

AnalogAtten

Transceiver Block DiagramTransceiver Block Diagram

DigitalAtten

DigitalAtten

PLL#1

PLL#2

ExternalReference

BPFHelical

Gain

BPFCeramic

MCU &Control

Loop

Loop

Loop

Loop

BPFCeramic

BPFCeramic

DU

PL

EX

ER

Res.Coup.RSSI

26

Amplifiers - Critical ParametersAmplifiers - Critical Parameters

• Gain / Stability• Linearity / Output 3rd Order Intercept

Point ( OIP3 )• Output Power / 1dB Compression Point Noise Figure

27

““Ideal” Amplifier GainIdeal” Amplifier Gain

Linear Gain Amplifier

1

10

100

1000

10000

100000

0.01 0.1 1 10 100 1000

Pin (milliwatts)

Pout

(milli

watts

)

Linear Gain Amplifier

0

10

20

30

40

50

60

-30 -20 -10 0 10 20 30 40

Pin (dBm)

Pout

(dBm

)

28

Actual Amplifier PerformanceActual Amplifier Performance

F1 F2

F1-

Frequency (MHz)

F1+

F2-F1

F2+F1

29

MixersMixers• Mixers are the key component for Frequency Conversion

• Can be used for either Up or Down Conversion

• The output response is actually: N LO + M RF

RF IN

Radio Frequency ( RF )

IF IN

( IF ) Intermediate Frequency = LO + RF

X35.75 MHz

LO

IN

384.25 MHzLocal Oscillator

420 MHz( 360 MHz )

30

Filter TypesFilter Types

Am

pli

tud

e fo

Frequency

Band Pass

Low Pass

High Pass

Band Stop

Diplexer

31

Filter TechnologiesFilter Technologies

Type Advantages Disadvantages

- Lumped Element Small size, Low cost Low Freq Limit

- Microstrip/Stripline Planar, High Repeatability Large in Size

- Ceramic Small size, Low Cost Low Freq Limit

- Cavity High Q High Cost, Large

- SAW High Rejection "in Close" High Loss ( Surface Acoustic Wave )

32

Transceiver Block Diagram

ReceiveReceive

LNA Gain

10 MHzReferenceOscillator

IFIF

TransmitTransmit

BPFSAWS

PA

AnalogAtten

GainBPFCeramic

AnalogAtten

DigitalAtten

DigitalAtten

PLL#1

PLL#2

ExternalExternalReferenceReference

BPFHelical

Gain

BPFCeramic

Loop

Loop

Loop

Loop

BPFCeramic

BPFCeramic

DU

PL

EX

ER

Res.Coup.

RSSIPLL1a & 2a

PLL1b & 2b

•Phase Locked Loops ( PLLs ) -Stabilize the VCOs to a Reference Oscillator

33

Basic Phase Locked LoopBasic Phase Locked Loop

X LoopFilter

VtuneOutput

Div by N

Div by R~ReferenceOscillator

10 MHzPhase

Comparator

V3.0 Only

Div by 4Prescaler

PLL ChipVCO

34

BaseStation

SU

r = 1000 ftPr = -53 dBmLoss = -90 dB

SU

r = 1 milePr = -67 dBmLoss = -104 dB

SU

r = 6 milePr = -83 dBmLoss = -120 dB

ERP=5W

• Subscriber Receive power estimated and measured at installation

• Modem Power Control will compensate for approx +15 dB of signal variation

• Same attenuator setting used on Transmit side

• Base Station will receive power at same level from all Subscribers

• Subscriber Receive power estimated and measured at installation

• Modem Power Control will compensate for approx +15 dB of signal variation

• Same attenuator setting used on Transmit side

• Base Station will receive power at same level from all Subscribers

System Power ControlSystem Power Control

35

•Digital Attenuators

• Coarse gain selection

• Step Size / 2dB

•Analog Attenuators

• Fine Step Size / < .1 dB

• Fine gain selection and temperature compensation

Variable AttenuatorsVariable Attenuators