Full-packet long-haul microwave architecture can make business sense, reducing cost while improving performance. Market factors to consider include:
- Mobile backhaul - Transition to packet in mobile backhaul is underway. The shift to packet in transport and aggregation networks, where long-haul systems are usually deployed, is the only option that can meet LTE bandwidth needs today and prepare networks for LTE-Advanced tomorrow.
- Fixed aggregation - Providers need to supply bandwidth-hungry residential services. And they need to solve the bottlenecks created by new, high-speed access technologies, such as vectoring, in areas where long-haul microwave connectivity is employed instead of fiber.
- Efficient transition - Packet technologies support a seamless transition from the existing legacy world to the coming all-packet world less expensively than hybrid technologies. They enable TDM traffic through more efficient packet-oriented solutions, as in the case of service emulation.
- Advantages relative to fiber - Compared to fiber, microwave offers:
- Faster time to market. Sometimes burdensome civil works or permissions interfere with new fiber projects.
- Lower cost. Microwave deployment costs tend to be flat regardless of the link distance, and are less impacted by recurring fees associated with the carried capacity.
- Greater flexibility. Traffic changes can be accommodated through a simple spectrum reallocation.
WHAT IS A FULL-PACKET LONG-HAUL MICROWAVE SYSTEM?
Technical characteristics of a full-packet long-haul microwave system include:
- Service convergence - In all packet microwave platforms, Ethernet is used as the sole transport technology to carry all services. Legacy services are translated and adapted to Ethernet -- e.g., through service emulation -- and applications specific SLAs are enforced.
- Capacity scale - Full-packet long-haul microwave systems combine best-in-class packet mechanisms such as packet compression and multichannel transmission with best-in-class RF mechanisms like high modulation, high system gain, and strong modem signature. In particular, multichannel operation leads to new operational modes that increase capacity scale and availability.
- Operational efficiency - Multichannel-based models simplify capacity provisioning, changing the way link design is done. In “old-style” design, the number of T1/E1 or OC3/STM-1 circuits that need to be carried over the air is considered. Multichannel-enabled new-style design is based on the requested throughput expressed in Mbps. The resulting simplified system architecture reduces total cost of ownership.
ADVANTAGES OF A MULTICHANNEL APPROACH
The multi-channel approach allows the system to handle the bundle of radio links as a single big pipe whose capacity is the sum of all of the single links capacities. The overall capacity can be flexibly assigned to any services based on specific SLAs or operator defined rules.
A few elements characterize the multichannel architecture:
- The bundle can be formed by any number of links. Usual deployments include 4 links (N = 4), while complex installations can reach 8-10 links (N = 8, 10).
- No spare channels are needed, thus the name N+0 (the trailing 0 means no reserved protection channels are allocated). This lets operators move away from legacy N+1 implementation, where at least 1 channel is statically reserved for protection, increasing TCO and reducing flexibility.
- There are no restrictions on the frequency band, channel width, or RF mechanisms employed. Any mix of them is allowed. For example a 4+0 application may use 2 14MHz channels in a frequency band and other 2 28MHz channels operating in another frequency band.
- The multichannel engine knows the actual status of the bundle. And the services entering the engine receive proper handling based on their relative priority or SLA.
- Services gets distributed over the link bundle and rebuilt at the receiving end without performance degradation nor delay.
- The distribution of services across the bundle is the key to raise the overall availability.
In N+0 multichannel, a service (e.g., an STM-1) is no longer associated to a specific link, but it is simply spread on the bundle. In legacy N+1 applications if the link carrying that STM-1 had an issue, e.g., a modulation decrease, the service was lost. In N+0 if one of the links experiences an issue and decreases its offered capacity, services gets redistributed over the remaining links in real time. The total capacity of the bundle decreases but high-priority services are unaffected and best effort traffic only is discarded.
EUROPEAN OPERATOR USE CASE
A convergent fixed and mobile European operator wanted to upgrade an existing 2+1 link over the Mediterranean Sea into a 4+0 multichannel system to carry more capacity. Being a 65 km long link over the sea, multipath fading effect is present. The operator request included:
- removal of empty SDH VC-12 containers to free more capacity over the air (utilization of channelized STM-1 interfaces)
- enabling of adaptive modulation up to 1024QAM
- use of a 4+0 multichannel bundle
Post-upgrade system improvements are shown in Figure 2.
The graph shows 2 of the 4 channels (for each channel both the “go” and “return” directions are represented). The Y-axis represents the probability that any of the channels reaches maximum modulation -- i.e., maximum capacity.
At maximum modulation, each bar achieves a probability value very close to 1x100. In other words, every channel works for almost 100% of the time at 1024QAM – a meaningful outcome considering that it is a long link over the sea with strong multi-path effect.
For very short periods the 4 channels decrease their modulation, but the probability of this happening is very low. In some cases, the channel quality is so good that they never go below a certain modulation scheme. For example, the yellow and red bars never decrease below 256QAM and 64QAM respectively.
The overall system performance is in line with a pre-deployment predictive analysis done by Alcatel-Lucent, as shown in Figure 3.
The analysis correlated capacity and availability for different legacy N+1 and multichannel N+0 configurations. X-axis capacity is expressed in Mbps while Y-axis availability is expressed as the probability of achieving the corresponding capacity.
The analysis shows the performance improvement of moving from legacy N+1 models to multichannel N+0 ones, increasing the channels in a bundle.
The yellow stars represent the working conditions of legacy N+1 systems, corresponding to fixed states where capacity and availability are statically determined. For example, the previously installed 2+1 system could provide an availability value of around 1x10-5 and a throughput figure of around 300 Mbps. Results of improving that system to 3+1 or even 4+1 are shown along the dashed yellow line.
The behavior of a multichannel system depends upon a contiguous set of possible states, given by the combination of all the possible working conditions of the bundle. As such, the behavior of a multichannel system is represented by an entire curve. The green curve, corresponding to a multichannel 2+0 system, can easily scale to higher capacity than a legacy 2+1 configuration -- or achieve higher availability. 3+0 and 4+0 configurations are represented by the red and blue curves.
The 4+0 configuration differs significantly from a legacy 4+1 system. Higher capacity, in the order of 700 Mbps, is achieved at the same availability level. That is around 100 Mbps more than legacy 4+1. At 600 Mbps (nominal capacity), higher availability is achieved, moving from around 3x10-4 to 1x10-5.
THE ALCATEL-LUCENT SOLUTION
Alcatel-Lucent launched its 9500 Microwave Packet Radio long-haul version more than a year ago. Since that time, it has fulfilled market expectations:
- The most scalable system in the long-haul segment
- Field-proven throughput of up to 10 Gbps – unmatched on the market – with its multichannel engine
- Strong RF capabilities to counter fading effects
- Allows accurate pre-deployment prediction of system behavior
Packet longhaul deployment – The experience one year later slides on SlideShareAlcatel-Lucent 9500 Microwave Packet Radio product page
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