Making the Case for AMI Part 5: Understand Your Network Options

This is the fifth installment of Making the Case for Advanced Metering Infrastructure.

Deploying an advanced metering infrastructure (AMI) system is a large investment and commitment to a technology road map that will impact utility operations for many years. Making the proper choice here can either help or hinder future distribution system improvements.

In this post: Will your AMI network help or handcuff you as your needs change over time?

Power line networks, point-to-multipoint networks, mesh or mesh-hybrid networks: What is the best AMI network type for your utility?

There are a lot of differing AMI network options on the market today, and each has its own advantages and disadvantages. This is my take on the many AMI network options.

Power Line Networks

Power line networks use the actual power lines to transmit communications from the substation to the endpoints. While this may seem logical on the surface, power lines are not well suited for fast, near real-time data communications.

Troubleshooting signal issues is often tricky when poor connections, worn or faulty line hardware, feeder switching and other power line issues cause signal interference. If you hope to push meter data from the field into your SCADA system or other applications, this could be difficult to do in any volume in near real-time.

Power line networks also provide a lower redundancy than other technologies due to their dependency on “one path home” and costly injection equipment. While these types of networks were once the only option for rural applications, new technologies have increased radio coverage capabilities in most areas.

Still, power line networks are sometimes the only option for extremely rural applications. But before resigning your utility to a power line solution, make sure you’ve ruled out the many wireless options.

Point-to-multipoint Networks

Given the challenges with power line networks, point-to-multipoint networks began to gain popularity. These networks depend on high power transmitters to talk directly to each endpoint (or repeater) on the network.

While point-to-multipoint networks are an improvement over power line networks, they still depend on a limited number of radio paths between the endpoints and a radio base station. This makes these networks more susceptible to signal fading or shadowing caused by hills, valleys and radio-reflective or radio-absorbing obstructions. Sometimes, the only remedy is an additional high power base station or repeater, which can be relatively expensive.

Some providers of point-to-multipoint solutions require FCC licensing for their high power networks. While sometimes sold as an advantage due to the designated spectrum on which they operate, FCC licensed spectrum has been subject to reallocation as recently as a last year when the VHF paging spectrum was “narrow banded.” As a result, any devices not capable of accommodating a new, narrower channel were left abandoned in the field or now require a mass hardware or firmware upgrade, or possibly both.

Operating under an FCC license does give the user a certain degree of legal recourse if someone or something accidentally or purposely encroaches on the dedicated frequency. But this in no way guarantees a “clean” channel.

Tracking down and finding sources of interference can be a difficult endeavor, and even then, this requires FCC action to enforce spectrum protections once any violators are identified.

Mesh or Mesh-hybrid Networks

Newer AMI trends are now favoring mesh or mesh-hybrid solutions. This architecture actually consists of two network types: the local area network (LAN) and the wide area network (WAN).

The LAN consists of meters and other endpoints that create a mesh network among themselves in the field. Installed among this mesh of devices are collection points. These collection points relay data from the meshed devices over the WAN to the network head end.

Advantages of this type of network design include:

Redundancy

In the event of a downed collection point, endpoint traffic is capable of failing over to another collection point on the mesh network.

Flexibility

The WAN section of the system is not dependent on any specific radio technology. WAN options include anything from fiber to WiMAX to 900/220 MHz solutions and in any combination.

This means you can strategically choose the best long-range radio for each area inside your utility’s service territory. In the event your WAN radios go obsolete, you only need to replace the head end radio and the limited number of collection point radios.

All mesh radios on the LAN section of the system (meters, load control devices, etc.) remain unaffected.

Performance

Some mesh networks use a lower power 900 MHz spectrum, prompting competitors to employ the “baby monitor” argument citing interference from everyday household devices.

In reality, mesh networks use frequency-hopping techniques (across up to 64,000 possible channels in some cases) to provide fast and highly redundant communications even while using less power and existing in a more crowded spectrum.

The “baby monitor” argument simply doesn’t hold water if you understand radio technology basics.

What Is the Best AMI Network Type?

Is there one AMI network type that is best for everyone? Unfortunately, no. There is, however, a best solution for each utility, and in some cases, each area inside any one utility’s service territory.

Whatever your specific needs from an AMI system, make sure the network is capable of supporting your future distribution automation endeavors. If it doesn’t lock you into a specific back-haul technology, all the better.

If you’re considering a comprehensive AMI system, make sure you know what questions to ask before it’s too late.

Stay tuned as this series continues, and reach out to your Border States representative or me for a discussion on your long-term technology needs.