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Low latency Microwave: Fact, Fiction & Future
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.
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Low latency Microwave: Fact, Fiction & Future
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- 2. AVIAT NETWORKS MICROWAVE ISFASTER THAN FIBER AND IS QUICKLY BECOMING DEFACTO STANDARD FOR ULTRA LOW LATENCY TRANSPORT
- 3. AVIAT NETWORKS Air Latencyis 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 Latencyis 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 areall 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 NUMBERAND 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
- 7. AVIAT NETWORKS Regenerator Node Repeater Node Repeater Node Regenerator Node Repeater Node Repeater Node Regenerator Node Repeater Node Repeater Node Regenerator Node Repeater Node Regenerator Node ADAPTIVE REPEATERTECHNOLOGY 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
- 8. AVIAT NETWORKS RF ANDMODEM 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 ForwardError 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
- 10. AVIAT NETWORKS RF TECHNOLOGY IFPreprocessing Adaptive Predistortion Higher Output Power Clean LOs
- 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 PayloadInterface 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, MISCONCEPTIONSAND 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-THEMOST 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 SITECOUNT 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 LATENCYMICROWAVE 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 Increasenumber 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 Outdoorbranching 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 Highercapacity 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
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