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This presentation talks about the fact, the fiction and the future of low latency microwave solutions and compares it to the alternative - fiber.
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LOW LATENCY MICROWAVE
Fact, Fiction & Future
AVIAT NETWORKS
MICROWAVE IS FASTER THAN FIBER AND IS QUICKLY BECOMING DEFACTO STANDARD FOR ULTRA LOW LATENCY TRANSPORT
AVIAT NETWORKS
Air Latency is the dominant Factor Angular deviation comes at a high cost
RegulatoryAvailability of licensed
spectrum
Infrastructure
Equipment Operating ModesRepeaters and Regenerators
Number of HopsModem and RF Performance
Equipment Latency
LOW LATENCY MICROWAVE FACTS
AVIAT NETWORKS
Air Latency is the dominant Factor Angular deviation comes at a high cost
RegulatoryAvailability of licensed
spectrum
Infrastructure
Equipment Operating ModesRepeaters and Regenerators
Number of HopsModem and RF Performance
Equipment Latency
Angular Deviation
IncreasedDistance
IncreasedLatency
Percentage
5 Degrees 2.8 Miles 15.0 µs 0.38%
10 Degrees 11.3 Miles 60.5 µs 1.54%
15 Degrees 25.9 Miles 138.4 µs 3.53%
20 Degrees 47.2 Miles 251.8µs 6.42%
Even with microwave working at the speed of light a less than ideal pathwill cause a significant latency penalty
735 MilesAIR LATENCY
AVIAT NETWORKS
REGULATORY
• We are all bound in our microwave designs and planningby the availability of licensed spectrum
- Optimal frequency bands are scarce on primary routes
- Channel sizes (bandwidth) and efficiency (bits per Hz) are regulated
- Limitations to the total carrying capacity of the pipeline
- Emission Masks and Interference Regulations
- Power Control
AVIAT NETWORKS
REDUCE NUMBER AND COMPLEXITY OF THE HOPS
INTRODUCTION OF THE REPEATER CONCEPT
- Latency in Nx10 ns- RF Repeater
- Limited RF Options- Mask Limitations
- IF Repeater- Frequency Agile- Mask Limitations
- Digital Repeater- Frequency Agile- Less Susceptible to Mask Limitations
RegeneratorNode
RegeneratorNode
RepeaterNode
RepeaterNode
30% reduction
AVIAT NETWORKS
RegeneratorNode
RepeaterNode
RepeaterNode
RegeneratorNode
RepeaterNode
RepeaterNode
RegeneratorNode
RepeaterNode
RepeaterNode
RegeneratorNode
RepeaterNode
RegeneratorNode
ADAPTIVE REPEATER TECHNOLOGY
Ultra Low End-End Latency
Low End-End Latency (still better than fiber)
99% of time
1% of time
Continuous monitoring of the received signal quality
AVIAT NETWORKS
RF AND MODEM PERFORMANCE
WHERE DOES IT HELP?
• Antenna Size
• Number of Repeaters
- FEC Coding
- Rx Threshold
- Higher Quality Oscillators
Ultimately all revolves around having better System Gain !!!
• Link Distance
• Number of Hops
• Link Availability
TECHNIQUES INCLUDE:
- Tx Power
- Rx Sensitivity
- Diversity
AVIAT NETWORKS
MODEM TECHNOLOGY
Forward Error Correction
Modulations and Bandwidths
Diversity ProtectionImproves link availability and hence low latency availability
Adaptive Modulation and Adaptive Coding Latency Increase
Phase noise reduction
FEC Method
Linear and Iterative
Convolutional Codes
Algorithm
LPDC, Turbo Codes
Viterbi
Latency
High
Medium
Block Codes
No FEC
Reed Solomon
- - -
Low*
Lowest
SG Imp.
High
Good*
None
Good
BW30 MHz
40 MHz
Mod
16 Q
AM
32 Q
AM
50 MHz
128
QA
M
64 Q
AM
256
QA
M
QP
SK
AVIAT NETWORKS
RF TECHNOLOGY
IF Preprocessing
Adaptive Predistortion
Higher Output Power
Clean LOs
AVIAT NETWORKS
QUANTIFY RF / MODEM PERFORMANCE
• Example: Chicago rain zone, 99.999 Availability, 6 Ft Antenna, 64QAM
Frequency Band
6 GHz
11 GHz
Std System Gain
51.6 Miles
35.1 Miles
+3dB
55.8 Miles
38.5 Miles
AVIAT NETWORKS
EQUIPMENT LATENCY
Payload InterfaceInterface Alternatives (Ethernet, L1 Interfaces, Proprietary)
Switch Forwarding (Store and Forward, Early Packet Forwarding)
Switch Buffering
Serialization DelayInterface speed differentials force store and forward stages and buffering
Modem Technology (Traditional)Scrambling / Descrambling
Encoding / Decoding
Interleaving / Deinterleaving
Modulation / Demodulation
Analog Front End
Reduce or Eliminate
AVIAT NETWORKS
FICTION, MISCONCEPTIONS AND MYTHS
Equipment latency is most important
Focus in In and Out of the box
latency
Reduced Latency = Reduced
Reliability
Link Reliability
Equipment Reliability
High site count is OK if path is optimal
AVIAT NETWORKS
EQUIPMENT LATENCY-THE MOST IMPORTANT FACTOR
Equipment latency is important but not the most important factor
Route design
Path and Frequency planning
Maximizing the number of repeaters
RF / Modem performance
Reduce the number of hops
Improve link availability
Equipment Latency
End to end latency is the goalOptimal blend of above features Lowest end to end latency + Highest availability
~3-20 µs
RegeneratorNode
RepeaterNode
~100-500 ns
AVIAT NETWORKS
LOW LATENCY = LOW LINK RELIABILITY
To achieve low latency multiple modem aspects are sacrificed
Coding gain
Interleaving
Reduced equalization
Additional signal processing techniquesAdaptive repeaters
IF combining – Space Diversity
Adaptive pre-distortion
Combined Signal
Main - Distorted Diversity -DistortedMultipath
AVIAT NETWORKS
LOW LATENCY = LOW EQUIPMENT RELIABILITY
Low latency can be built on a field proven platform with very high MTBF
AVIAT NETWORKS
HIGH SITE COUNT IS OK IF PATH IS OPTIMAL
Can be offset by having more repeaters
Noise AccumulationNoise accumulates over a higher number of nodes
Points of FailureHave more active elements in the network
Operational ComplexityMore equipment to manage, troubleshoot (link and network) and
maintain
CAPEX + OPEXInitial spending, cost of leasing towers and maintenance
AVIAT NETWORKS
LOW LATENCY MICROWAVE FUTURE
Lower Latency
Increase number of repeaters
Specialized Modems
All outdoor radio repeaters
Increased Capacity
Multi-Carrier
XPIC
Channel Bonding
Higher Modulations
Beyond Microwave
AVIAT NETWORKS
LOWER LATENCY
Increase number of repeatersThrough Signal Processing techniques enhance the repeater operation
Able to meet regulatory requirements over a larger number of repeaters
Specialized modemsOptimally combine ASIC and FPGA technologies
Dual/Quad header modems to create repeaters
Minimize transfer delay in the pipeline
All outdoor radio repeatersEliminate cable latency
Place modem and RF on the tower
AVIAT NETWORKS
INCREASED CAPACITY
Multi-carrierOutdoor branching for up to 8 channels in a single antenna
Use dual or quad header modems
XPIC + DiversityCross polar cancelling for lowest possible latency
Regulatory requirements internationally – Efficient channel utilization (H & V)
Channel bondingCreate wider carriers by bonding 2 to 4 channels together
Single RF for concatenated wide channel
Higher ModulationsHigher bits per Hz efficiencies using up to 1024 QAM
Better signal processing in the modem and cleaner RF
AVIAT NETWORKS
BEYOND MICROWAVE
FSOHigher capacity than microwave, minimizes serialization delay
Limited to short distances due to physical and atmospheric disturbances
Must reduce cost and increase usability for wide scaled adoption
MMWHigher capacity than microwave, minimizes serialization delay
Limited to short distances due to atmospheric disturbances
Prone to interference in heavily congested areas
Further ahead than FSO in adoption but requires tighter regulation and
more efficient use of the bandwidth
W W W . A V I A T N E T W O R K S . C O M