Microwave technology can provide ultra-low latency network transport that is comparable or faster than fiber under the right conditions. Key factors that influence latency include air latency, angular deviation from the direct line of sight path, regulatory constraints on spectrum availability and power levels, the number of hops, and modem and RF performance. While equipment latency is important, optimizing the overall route design, planning, and use of repeaters is more significant for achieving the lowest end-to-end latency. Emerging technologies such as specialized modems, all-outdoor radio repeaters, increased capacity solutions, and potential beyond-microwave options may further reduce latency in the future.
2. AVIAT NETWORKS
MICROWAVE IS FASTER THAN FIBER AND IS QUICKLY BECOMING
DEFACTO STANDARD FOR ULTRA LOW LATENCY TRANSPORT
3. AVIAT NETWORKS
Air Latency is the dominant
Factor
Angular deviation comes at a high
cost
Regulatory
Availability of licensed spectrum
Infrastructure
Equipment Operating Modes
Repeaters and Regenerators
Number of Hops
Modem and RF Performance
Equipment Latency
LOW LATENCY MICROWAVE FACTS
4. AVIAT NETWORKS
Air Latency is the dominant
Factor
Angular deviation comes at a high
cost
Regulatory
Availability of licensed spectrum
Infrastructure
Equipment Operating Modes
Repeaters and Regenerators
Number of Hops
Modem and RF Performance
Equipment Latency
Angular
Deviation
Increased
Distance
Increased
Latency
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 path
will cause a significant latency penalty
735 Miles
AIR LATENCY
5. AVIAT NETWORKS
REGULATORY
We are all bound in our microwave designs and planning
by 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
6. 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
Regenerator
Node
Regenerator
Node
Repeater
Node
Repeater
Node
30% reduction
8. 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
9. AVIAT NETWORKS
MODEM TECHNOLOGY
Forward Error Correction
Modulations and Bandwidths
Diversity Protection
Improves 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
BW
30 MHz
40 MHz
Mod
16QAM
32QAM
50 MHz
128QAM
64QAM
256QAM
QPSK
11. 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
12. AVIAT NETWORKS
EQUIPMENT LATENCY
Payload Interface
Interface Alternatives (Ethernet, L1 Interfaces, Proprietary)
Switch Forwarding (Store and Forward, Early Packet Forwarding)
Switch Buffering
Serialization Delay
Interface 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
13. 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
14. 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 goal
Optimal blend of above features Lowest end to end latency + Highest availability
~3-20 µs
Regenerator
Node
Repeater
Node
~100-500 ns
15. AVIAT NETWORKS
LOW LATENCY = LOW LINK RELIABILITY
To achieve low latency multiple modem aspects are sacrificed
Coding gain
Interleaving
Reduced equalization
Additional signal processing techniques
Adaptive repeaters
IF combining – Space Diversity
Adaptive pre-distortion
Combined Signal
Main - Distorted Diversity -DistortedMultipath
16. AVIAT NETWORKS
LOW LATENCY = LOW EQUIPMENT RELIABILITY
Low latency can be built on a field proven platform with very high MTBF
17. AVIAT NETWORKS
HIGH SITE COUNT IS OK IF PATH IS OPTIMAL
Can be offset by having more repeaters
Noise Accumulation
Noise accumulates over a higher number of nodes
Points of Failure
Have more active elements in the network
Operational Complexity
More equipment to manage, troubleshoot (link and network) and maintain
CAPEX + OPEX
Initial spending, cost of leasing towers and maintenance
18. 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
19. AVIAT NETWORKS
LOWER LATENCY
Increase number of repeaters
Through Signal Processing techniques enhance the repeater operation
Able to meet regulatory requirements over a larger number of repeaters
Specialized modems
Optimally combine ASIC and FPGA technologies
Dual/Quad header modems to create repeaters
Minimize transfer delay in the pipeline
All outdoor radio repeaters
Eliminate cable latency
Place modem and RF on the tower
20. AVIAT NETWORKS
INCREASED CAPACITY
Multi-carrier
Outdoor branching for up to 8 channels in a single antenna
Use dual or quad header modems
XPIC + Diversity
Cross polar cancelling for lowest possible latency
Regulatory requirements internationally – Efficient channel utilization (H & V)
Channel bonding
Create wider carriers by bonding 2 to 4 channels together
Single RF for concatenated wide channel
Higher Modulations
Higher bits per Hz efficiencies using up to 1024 QAM
Better signal processing in the modem and cleaner RF
21. AVIAT NETWORKS
BEYOND MICROWAVE
FSO
Higher 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
MMW
Higher 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