Powering Up for Wireless Data

The data revolution continues to escalate as wireless carriers and application providers offer data-intensive services to attract, retain and satisfy customer demands. Wireless data capabilities like e-mail access, fax capabilities, and specialized navigational tools now play critical roles in today's business and consumer transactions.

With the growth of wireless data, a dropped transmission may no longer be a simple issue of a loss in billable minutes. Being the conduit for what may be millions of dollars in transactions, wireless carriers have greater responsibility for quality of service. For many carriers, this is a key differentiator in a very competitive market.

Due to the critical nature of most communications, many of today's data and voice systems have moved from the central office space to facilities specifically designed to provide continuous availability. Often called co-location facilities or carrier hotels, these organizations provide connectivity, security and environmental control over power and cooling systems. These ultra-secure facilities form what can be considered a model of protection for the newly empowered wireless marketplace.

Hybrid Power Considerations

Previous generations of voice communications systems were centered on analog equipment, which relied primarily on DC power. This is quite different from systems that store and distribute data, which require AC as a source of power. The emergence of data over wireless (Figure 1) creates a situation where there is both voice and data equipment in the same operating environment. With the convergence of these two systems comes the necessity to have both AC and DC power supply and protection.

There are a variety of methods for powering these converged data and voice systems in wireless sites and facilities having both AC- and DC-powered equipment. Different power configurations include the use of a DC plant with inverters for AC loads, a DC plant for DC loads and an AC UPS for the AC loads, and an AC UPS for the AC loads with rectifiers for the DC loads.

There are advantages and disadvantages to each of these different approaches, and determining the right balance in a hybrid power system is really a matter of application criteria and budgetary considerations.

For reliability, a hybrid distributed redundant power system may be the best approach for power availability and protection (Figure 2). Configurations of this type use distributed, redundant DC rectifier systems supplied from large, dual redundant AC UPS systems.

Small, self-contained DC rectifier systems along with AC power distribution units (PDUs) can be located throughout a facility to supply either AC or DC power to the load equipment.

The “best practices” of large data centers are merged with telecom DC power systems to optimize reliability. Redundant, standby generators can be used to provide dependable power in the event of a sustained utility power failure. A configuration of this kind ensures that the air conditioning system is powered as well, since heat buildup within the room can shut down the load in as little as five minutes.

A hybrid distributed redundant power configuration provides substantial reliability for wireless systems by using dual redundant AC UPSs with redundant power distribution paths. A high degree of fault tolerance is obtained without any single points of failure in the AC or DC power system. Any component within the AC or DC power system can fail or be maintained without disrupting the critical load equipment operation.

Continuous Availability

Continuous availability starts with an infrastructure that ensures and maintains clean, conditioned power throughout wireless facilities and structures. Primary protection solutions include advanced UPS and TVSS technologies that create a barrier between critical systems and problems with the power supply.

TVSS can protect anything from a single server to an entire facility. Today's surge suppressors are often the first lines of defense for cable, data and electrical lines. This is especially true for remote telecom sites with delicate and sophisticated electronic equipment, which is typical of cellular and PCS applications.

TVSS provides high frequency noise filters that suppress small surges, minimizing interference with normal utility power. Instead of cutting off power disturbances, the surge suppressor continuously limits distortion at every point of the sine wave, whether it's a surge or spike. This unique filtration feature is one of the few methods of limiting ring waves, which are created by a rapid reduction, or increase in the power load.

Small TVSS units may be mounted to electrical distribution panels to protect both linear and non-linear loads from damaging transients and electric line noise. These units are designed to limit peak amplitude of large surges on telephone and data lines while eliminating lesser power glitches as well. Through detection circuits, these units alert to all modes of failure through local indicator or status contacts. In addition, advances in sine wave tracking circuitry provide high frequency noise filtering.

Surge suppression technology is an integral part of a cost-effective power protection strategy for telecom equipment. Using TVSS as the first line of defense against power problems reduces UPS usage, which in turn preserves battery life and lowers maintenance costs. Compared to a UPS, surge suppression equipment is less expensive to maintain and replace, which makes this initial layer of protection a significant cost savings for many organizations.

Advanced UPS Systems

A UPS provides clean, reliable power to protect sensitive communications equipment from power problems and outages. For situations where a cost-effective solution is needed, an offline UPS may be all that is needed.

Offline UPS topologies prevent most spikes, but do not maintain perfect power during minor sags and surges. The next level in protection offered by a UPS is a line-interactive topology. These systems offer power conditioning to protect against sags, spikes, surges and brownouts, as well as providing battery backup.

For critical wireless systems, a true online double conversion UPS is the best alternative for true isolation from problems originating from utility or generator power. In this configuration, power is continuously supplied to the batteries via the rectifier (Figure 3) at the same time the inverter is providing a constant flow of power to the load. This allows for a seamless transition in the event of a power outage while supplying the load with a continuous source of superior-quality AC voltage.

Power Protection and Generators

The use of standby generators provides a power supply that can withstand a variety of power disturbances as well as keep a system up and running for hours, or even days. As a viable alternative to substantial battery backup, a power system that includes generators could potentially replace the need to site large, heavy batteries that still have a finite amount of runtime.

Specific to wireless organizations that have hundreds of sites in a geographic area, a cost-effective alternative might include the use of portable generators that can be dispatched as needed. These portable units can provide a significant cost savings and eliminate the hassles of obtaining permits for permanently sited generators, which can be rather difficult in certain states such as California.

A frequent problem that occurs during a power outage involves the starting of loads on a generator, which causes output frequency to vary, thereby triggering an offline or line-interactive UPS to cycle to battery operation. The problem is especially pronounced with natural-gas power generation. This repetitive battery cycling can cause the battery to discharge completely, which significantly shortens battery life.

Another potential problem is the generator instability that occurs when the UPS load is moved to the generator. The UPS load transfer causes the generator voltage and frequency to sag, which triggers the UPS to go back to battery operation. Once the UPS senses stable generator output, it transfers the load back to the generator. If generator output dips again, the load will transfer back to battery operation.

For systems that include the use of generators, a UPS that provides double-conversion technology is preferred. A double-conversion UPS can accommodate large swings in power supply frequency while continuing to provide regulated, stable output power frequency, without the use of a battery.

Incoming AC power is rectified to DC power to supply the internal DC bus of the UPS. The output inverter takes the DC power and produces regulated AC power to support the critical load. Batteries attached to the DC bus are float charged during normal operation. When the input power is beyond the normal operating parameters, the batteries provide power to support the inverter and critical load. During this switch in power from the utility to the generator, the UPS provides the control bridge between the utility and generator while it ramps up to full capacity. The UPS system thus balances the load until generators reach full capacity.

In addition, a successful power protection strategy includes redundancy configurations, both in systems and within the common elements. N+1 redundancy provides substantial improvements in reliability and can be cost-effective and easy to implement.

Continuously Available

Continuous availability requires dual bus architectures, with redundancy throughout, to eliminate single points of failure and maintainability. For power protection, a dual bus configuration provides a mirrored system, which may be electronically tied together. In the event that one of the buses goes down, the duplicated system is available to carry the load for a seamless transition.

Monitoring and management of infrastructure support systems is critical to the performance and availability of communications networks, particularly for remote wireless sites and unmanned shelters.

The latest solutions for monitoring of support systems include a variety of methods that can be used together for multiple paths of communication. Out-of-band monitoring is achieved using a modem or a Web-based system, while in-band monitoring is provided through an internal network connection. For continuous communications capabilities, an in-band connection can be used with out-of-band access in the event that the network goes down or is not available.

Monitoring

Most network monitoring systems allow for management and control of infrastructure supports using either SNMP (Simple Network Management Protocol) or http access. Alarm notification and escalation, as well as the capability to shut down and reboot systems are just some of the critical functions performed by today's monitoring and management technologies.

Some monitoring capabilities include trending and analysis reports, which provide a way to trace events. In many cases, it's possible to map out the root cause of a problem by looking at historical logs and reports. This is provided by equipment messaging, event and status logs and time stamps, which can point to a specific reason and the time of occurrence for a particular problem.

Web-based monitoring may be particularly useful for certain applications such as remote sites and shelters. As an integral part of a communications system, a single site has the potential to bring down an entire network. Therefore, the ability to monitor and control power at a remote site from any location in the world is an advantageous capability.

It's inevitable that wireless data will continue to grow as it expands the capabilities and services of wireless providers. Being prepared with power and environmental control that keeps data-intensive wireless traffic up and running will play an essential role in customer satisfaction and loyalty. For many carriers, a power protection strategy that offers continuous availability will be a critical element in preparing for the future of a dynamic and growing competitive wireless market.

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James Hall (james.hall@liebert.com) is Liebert's telecom market manager.