Stating the obvious, networks are evolving rapidly and so too, are the configurations of microwave backhaul systems. Today network operators can choose among three distinct configurations: all-indoor, all-outdoor and split-mount systems. Each has three key components: a radio that transmits and receives, interfaces that connect the radio link to one or more TDM or IP pipes, and an antenna that shapes and directs the signal. While all-indoor and split-mount systems have been the preferred choice for many applications, the transition to all-IP networks will make all-outdoor designs preferred. All-outdoor systems will not only be easier to install and maintain, but will be a greener choice for energy conservation.
Before the industry can move to all-outdoor microwave backhaul systems exclusively, however, there are key hurdles to overcome. Let’s first examine today’s available configurations and the considerations for choosing one over the other two.
Why All-Indoor?
All-indoor microwave backhaul systems incorporate the radio, interfaces and modem in a rack mountable enclosure typically installed inside an environmentally controlled hut or building with the antenna mounted outdoors. A transmission line, typically waveguide, connects the microwave radio to the antenna. This alternative offers convenient access to all the system electronics without requiring tower climbs and minimizes the length of cabling from the radio interfaces to other transport or termination equipment in the building. This is especially valuable in TDM applications.
In addition, these designs have been popular with large carriers, tower companies and rights-of-way companies (e.g., railroads) because it is less expensive to pay and insure ground-based personnel than the specialized personnel required to climb towers while working on active electronics. Trade unions in particular are often reluctant to approve tower climbing by their members in the United States, so all-indoor designs are more popular in the United States. All these benefits reduce OPEX for mobile operators and reduce repair time because technicians can repair or replace equipment on site – even in inclement weather – without the need to work outdoors.
All-indoor designs, however, require more expensive and careful installation because a pressurized waveguide is required to keep the losses from radio to antenna at a minimum. This keeps the practical implementation of all-indoor systems below 12 GHz. Plus all-indoor systems generally require installation in an environmentally controlled building, and rack space may be a challenge depending on the size of the unit.
Why Split-Mount?
Split-mount microwave backhaul systems eliminate the need for expensive waveguide runs while still providing the convenience and interface accessibility of an all-indoor system. In the split mount design, the modem and interfaces are mounted indoors (IDU) and the RF (ODU) is mounted outdoors with or alongside the antenna. This design is the most popular configuration outside of North America for both carrier and enterprise customers because all the TDM and Ethernet interfaces are readily accessible, the network operator can easily replace the IDU in case of failure and installation costs are comparatively low due to the low-cost coaxial cable used to interconnect the IDU to the ODU.
Similar in requirements to the all-indoor design, the split-mount configuration requires the building, rack space and environmental control for the IDU and a tower climb for the ODU.
Why All-Outdoor?
In an all-outdoor configuration, all electronics including radio, interfaces and modem are housed in a hardened enclosure that can be mounted on a tower or rooftop. All-outdoor microwave backhaul systems are fully integrated and have been popular in wireless networking and Ethernet bridging applications. Similarly, as mobile infrastructure applications transition to Ethernet and IP, driven by LTE and WiMAX, the all-outdoor configuration will become the dominant choice for microwave backhaul systems.
The key advantage of an all-outdoor system is its “zero-footprint” design: This configuration requires no internal cabinet space or cooling, so it is more energy-efficient than other designs. Additionally, the all-outdoor system can deliver higher performance due to design efficiencies possible in a fully integrated system. It also minimizes and virtually eliminates the RF loss between the radio and the antenna.
With an all-outdoor system, a single Cat5 cable is required to power the radio (PoE) and carry Ethernet traffic to a LAN switch or router. Some all-outdoor radios on the market also support native TDM, such as 4xT1/E1, via two additional CAT-5 cables, making it convenient and practical to deploy an outdoor wireless bridge with native voice support for PBX interconnection in enterprise applications, or simultaneous backhaul of 2G base station traffic in mobile applications.
All-outdoor designs are popular with enterprises because these companies tend to own the real estate where the radio system resides, so they typically have no issues in gaining access to rooftops or towers in order to perform radio maintenance or configuration. Moreover, all-outdoor designs are physically more secure because they are not as accessible and can be powered via solar energy for remote surveillance or other connectivity applications.
These systems do require installation and maintenance personnel to climb towers or access rooftops, and this may not be easy during harsh weather conditions. That’s why all-outdoor radios must be highly reliable and rated to withstand extreme variations in temperature and harsh weather environments.
Mobile infrastructure evolution reduces the need for split-mount and indoor systems
Although all-outdoor configurations have not been the most popular microwave backhaul systems to date, several factors are now changing the equation for choosing this type of configuration.
The world is transitioning to IP, and IP/Ethernet networks will be designed differently than TDM networks. Ring and mesh designs leveraging protocols such as RSTP will replace “hub and spoke” as the default network configuration. This approach will minimize the need for multi-radio nodal systems, which require an indoor component. Radio systems will also need only one cable connecting the radio with the network, rather than requiring one line for each T1/E1 connection.
There is also a trend toward forcing equipment outside of enclosures to promote greener designs, reduce costs and place equipment closer to the point of use. Space is becoming more expensive in general, and companies are trying to cut costs by reducing real estate, power and cooling costs.
The need for higher network capacity is forcing the deployment of more nodes, so network operators need more backhaul locations in the network. This also tends to force radios outside because new radio locations often lack existing space for indoor units.
All-outdoor systems on the rise
All of these factors point toward much greater use of all-outdoor systems, particularly in the edge and first-tier aggregation layers of the network. Split-mount or all-indoor systems may remain in use for large hub aggregation points, high capacity long-haul backbone connections, or sites in which the tower is inaccessible (e.g. utility sites), but all-outdoor systems will handle most edge and outer-tier aggregation links.
Given the realities of the move to IP, the trends toward reducing data center costs and the need to deploy far more backhaul systems to increase capacity, outdoor systems offer the best approach for several reasons:
- Zero-footprint designs are the greenest because they minimize the need for space, power and cooling resources.
- Small, compact systems are far easier to deploy.
- All-in-one systems reduce sparing and inventory costs compared with split-mount systems.
- Integrated designs deliver higher efficiency with lower power consumption while minimizing RF losses between the radio and antenna.
- Closer proximity to the antenna also tends to minimize antenna size, wind loading, and visual pollution, making it easier to obtain the necessary zoning permits.
- All-outdoor units are easier to maintain – there are no line cards or chassis to troubleshoot.
- The attributes of all-outdoor systems are perfectly aligned with various green initiatives across the industry and government agencies.
All-outdoor microwave backhaul systems are the way of the future because they deliver the same or better performance and reliability in a configuration that is much greener, more easily deployable, more cost-effective and easier to maintain. IP migration and a desire to reduce costs will gradually make split-mount and all-indoor radio systems less attractive.
As enterprises and mobile operators seek to conserve energy and reduce costs through IP migration and footprint reduction, all-outdoor microwave backhaul systems will prove their real value.
It’s only a matter of time.
Amir Zoufonoun is president and CEO of Exalt Communications.
Filed Under: Infrastructure
