Transcript System Power Levels - International Centre for Theoretical

RF Links Overview
PTP and PMP Links
1
Full Duplex Communications
 Two stations can talk and listen to each other at the same
time.
 This requires two separate media.
 In the case of a wireless link, 2 separate channels are
required. This is referred to as Frequency Division Duplex
(FDD)
TX
Station 1
Channel 2 RX
RX Channel 1
Station 2
TX
2
Half Duplex Communications
 Two stations have to take turns talking and listening.
Simultaneous communications is not possible. Requires
handshaking.
 Two stations share a common media
 This is referred to as time division duplex (TDD)
TX
TX
Station 1
Station 2
RX
Channel 1
RX
3
Advantages of FDD
 More efficient data transfer due to lower overhead
(required for handshaking).
 More efficient use of spectrum in high traffic systems
 Most ITU frequency bands are structured for FDD.
 Half the data rate for equivalent data transfer as TDD.
 Does not have latency issues associated with
handshaking.
4
Advantages of TDD
 Easier to coordinate channels than FDD.
 RF Hardware is potentially less complicated and thus
lower cost.
 Installation may be simpler.
 Only one antenna per T/R
 In low traffic networks the spectrum is utilized more
efficiently.
5
Point to Point (PTP) Links
 A point to point link is one station communicating with
another station, 1 to 1.
 Both stations are usually similar in data-rate, modulation
and overhead format.
 FDD PTP links do not require media access control which
reduces overhead.
6
Point to Point (PTP) Links
 FDD PTP links do not require handshaking, this
minimizes latency.
 PTP links are usually used in constant bit rate
applications, such as synchronous data transport and
trunking applications.
 PTP links can be built with extra margin to deal with fades
and other impairments.
7
System Power Levels
 Point to point link has extra system gain to increase
availability.
 Low probability of interference to or from other stations.
 P to P links typically have narrow beam antennas.
8
System Power Levels PTP Links
Antenna Gain 30 dB
Antenna Gain 30 dB
Path loss = -116 dB
Station 1
Station 2
TX = +18 dBm
RX = -42 dBm
RX Threshold = -72 dBm
9
Point to Multipoint (PMP) Links
 One base station communicating with more than one
subscriber on shared media.
PRIZM 2400
10
Point to Multipoint (PMP) Links
 Downstream path is from the hub to the sub.
 Upstream path is from the sub to the hub.
 Can use either FDD or TDD
 With many subscribers PMP is more economical than
PTP in both hardware and spectrum utilization.
11
Point to Multipoint (PMP) Links
 Data-rates and modulation tend to be asymmetrical to
reflect the the asymmetric flow of data in this type of
system.
 Media Access Control (MAC) is mandatory for a PMP
system.
 Typically IP based, does not work well for constant bit rate
applications.
12
System Power Levels PMP Links
 In a point to multi-point system power levels must be
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.
13
System Power Level PMP Links
TX Pwr = +6 dBm
RSL = -60 dBm
Path loss = -118 dB
Sub 1
Ant. Gain = 20 dBi
TX Pwr = +12 dBm
Path loss = -124 dB
RSL = -66 dBm
Sub 2
HUB
Ant. Gain = 20 dBi
Path loss = -130 dB
TX Pwr = +18 dBm
TX Pwr = +18 dBm
RSL = -72 dBm
RSL = -72 dBm
Ant. Gain = 20 dBi
Ant. Gain = 20 dBi
Sub 3
14
System Power Levels PMP Links
 If an unlimited number of channels are available then self
interference is not a consideration.
 Within a sector subscribers will not interfere with each
other due to TDMA.
 Between Sectors of the same channel interference can
occur, TDMA control no longer applies.
 Co-channel interference occurs due to antenna side
lobes, back lobes, improperly aimed antennas and
reflections.
15
System Power Levels PMP Links
 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.
16
Media Access Control
 The MAC is implemented by the hub modem and controls
access of the subscriber modems to the shared channel. Spike
uses the DOCSIS (IEEE 802.14) MAC.
 Each Subscriber is assigned one or more exclusive time slots in
which they may transmit data. This is referred to as time domain
multiple access (TDMA).
 The Hub modem adjusts the power level of the Sub TX.
 The Hub modem synchronizes all subs with the Hub and
equalizes path delay.
17
Media Access Control
 The MAC provides a means for new subscribers to join
the network.
 The MAC also provides for equitable sharing of bandwidth
and arbitrating contention among subscribers.
 The MAC must assure that all similarly provisioned
subscribers have similar quality of service regardless of
their location.
18
Broadband Wireless Example
 Transceiver
 Modulation Techniques
 Path Analysis
 Amplifier Parameters
 Filter Types
 Filter Technologies
 PLL and Attenuators
19
Transceiver Design Outline
 Overview
Functionality
Versions
 Design Features
 Basic RF Concepts
20
Key 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)
21
Modulation Techniques
BPSK
(0)
(1)
(00)
(01)
(10)
QPSK
(11)
(0000)
(0001)
(0010)
(0011)
(0100)
(0101)
(0110)
(0111)
(1000)
(1001)
(1010)
(1011)
(1100)
(1101)
(1110)
(1111)
16QAM
22
Modulation With Noise
BPSK
QPSK
16QAM
23
PRIZM 3500 RF PATH ANALYSIS
Manufacturer:
SPIKE Technologies
Subscriber Station
Transmit Frequency
Path Length
15.0 mi.
Base Station
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
Receiver Noise Figure
6.000 MHz
6.5 dB
UPLINK
Subscriber Unit Tx Output
Output Backoff
Subscriber Transmit Power
IF Bandwidth
Receiver Noise Figure
6.000 MHz
5.5 dB
DOWNLINK
25.0 dBm
5.0 dB
20.0 dBm
Base Transmitter Output
Output Backoff
Base Transmit Power
27.0 dBm
5.0 dB
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)
Subscriber Max EIRP (Watts)
Up Link Path Loss
6.3 W
20.0 W
131.1 dB
Base Rx Antenna Gain
19.6 dBi
Transmission Line Loss
1.0 dBi
Base Rx Signal Level
-74.5 dBm
Thermal Noise Power
-102.1 dBm
Required C/N (LanCity)
Final Margin
25.0 dB
2.6 dB
Base Average EIRP (Watts)
Base Max EIRP (Watts)
Down Link Path Loss
Subscriber Rx Antenna Gain
Transmission Line Loss
Sub Rx Signal Level
Thermal Noise Power
Required C/N (LanCity)
Final Margin
8.5 W
26.9 W
130.9 dB
19.0 dBi
1.2 dB
-73.8 dBm
-100.8 dBm
25.0 dB
2.0 dB
Downlink Limited By:
0.6 dB
Usable Margin:
2.0 dB
24
Transceiver Block Diagram
BPF
LNA
Ceramic
BPF
Helical
BPF
Ceramic
Analog
Atten
Gain
Gain
Digital
Atten
Loop
Receive
PLL#1
Loop
DUPLEXER
RSSI
Res.
Coup.
IF
MCU &
Control
10 MHz
Reference
Oscillator
LD1
Loop
Transmit
BPF
Ceramic
PA
BPF
Ceramic
PLL#2
Analog
Atten
Gain
Loop
Digital
Atten
BPF
SAWS
External
Reference
25
Amplifiers - Critical Parameters
• Gain / Stability
• Linearity / Output 3rd Order Intercept
Point ( OIP3 )
• Output Power / 1dB Compression Point
Noise Figure
26
“Ideal” Amplifier Gain
Pout (dBm)
60
50
40
100000
10000
1000
30
20
10
0
-30
-20
-10
100
10
Pout (milliwatts)
Linear Gain Amplifier
Linear Gain Amplifier
1
0
10
Pin (dBm)
20
30
40
0.01
0.1
1
10
100
1000
Pin (milliwatts)
27
Actual Amplifier Performance
F1
2515.0
F2-F1
0.1
F1-D
2514.9
F2
2515.1
F1+D
2515.2
F2+F1
5030.2
Frequency (MHz)
28
Mixers
• Mixers are the key component for Frequency Conversion
• Can be used for either Up or Down Conversion
• The output response is actually:
Radio Frequency ( RF )
35.75 MHz
( IF ) Intermediate Frequency = LO + RF
X
IF IN
420 MHz
( 360 MHz )
LO IN
RF IN
N LO + M RF
384.25 MHz
Local Oscillator
29
 Band Pass
Amplitude
Filter Types
fo
 Low Pass
 High Pass
 Band Stop
 Diplexer
Frequency
30
Filter 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 )
31
Transceiver Block Diagram
BPF
LNA
Ceramic
BPF
Helical
BPF
Ceramic
Analog
Atten
Gain
Gain
Digital
Atten
Loop
Receive
PLL#1
Loop
Res.
Coup.
DUPLEXER
PLL1a & 2a
IF
RSSI
10 MHz
Reference
Oscillator
PLL1b & 2b
Loop
Transmit
BPF
Ceramic
PA
BPF
Ceramic
Analog
Atten
PLL#2
Gain
Loop
Digital
Atten
BPF
SAWS
External
Reference
•Phase Locked Loops ( PLLs ) -Stabilize the VCOs to a Reference Oscillator
32
Basic Phase Locked Loop
PLL Chip
10 MHz
~
VCO
Phase
Comparator
Div by R
X
Loop
Filter
Vtune
Output
Reference
Oscillator
Div by N
Div by 4
Prescaler
V3.0 Only
33
System Power Control
SU
r
= 6 mile
Pr = -83 dBm
Loss = -120 dB
SU
Base
Station
ERP=5W
SU
r
= 1000 ft
Pr = -53 dBm
Loss = -90 dB
r
= 1 mile
Pr = -67 dBm
Loss = -104 dB
•
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
34
Variable Attenuators
•Digital Attenuators
• Coarse gain selection
• Step Size / 2dB
•Analog Attenuators
• Fine Step Size / < .1 dB
• Fine gain selection and temperature
compensation
35