Testing's Inherent Evolution
Alongside the development of today’s increasingly complex HFC networks,
the tools techs rely on for testing and measurement are evolving to include
digital technology, smaller form factors, and greater functionality
as operators migrate to advanced services.
For years, much of the technology used for testing and analysis of cable network performance went relatively unchanged. Headend operators had a select set of testing tools, which mainly served the purpose of troubleshooting video delivery systems in the RF realm, and their toolsets performed relatively simple tasks to ensure quality video delivery.
But today, the cable operator marketplace is in flux, and the future seemingly rests on operators' ability to move beyond simple video transmission. Future fortunes will be made in advanced services, and networks have undergone radical change to meet the perceived demand for high-speed data, video-on-demand, and other new interactive services that require a busier, faster, more complex HFC network.
So, it should come as no surprise that as network performance and reliability become increasingly essential with the introduction of advanced services, tools that maintain a raised level of performance are finding their way into operator headends and technician trucks.
New testing products from the industry's leading toolmakers are trending in similar directions. New testing tools are providing technicians more power, more functionality, and more portability in the field. Advances in chip form factors, and new all-digital signal analysis technologies are making for some incredibly small, yet imminently powerful tools for techs to bring into the field, into their trucks, and even worn on their belts. With network intelligence being distributed further and further out on the network, technicians are increasingly required to perform more complex measurements and analysis while in the field. And testing gear makers are introducing new products to meet that demand.
The other major trend affecting test and measurement in the cable world is dealing with new data traffic, as well as maintaining both the upstream and return paths of the network. The carriage of DOCSIS cable modem traffic presents new performance thresholds that techs must now maintain. And as operators move into more two-way interactive services, tools that maintain the once-neglected return path are in demand more than ever.
The people at test equipment provider Trilithic are trying to wrap their arms around each of these major trends with the introduction of a new modular HFC testing product–the 860DSP Multifunction HFC Analyzer–described by Trilithic Marketing Manager Jim Harris as "a platform that operates as an instrument." The portable tester, weighing in at just 4.5 pounds, provides the basic functionality of a high-performance signal level meter, but adds other measurement capabilities through custom options added to the platform via firmware upgrade. In a sense, the 860DSP alleviates the problem of having to design hardwired changes and introduce entirely new products in order to add new functionality.
"We're trying to rise above the notion that we're building a 'brick' that makes a certain measurement," Harris explains. "We're building something that potentially can contain anything that a technician wants to do that runs on batteries that he can hang from a shoulder strap. But the real issue was to address things we haven't thought of yet."
Harris really means it when he says "anything." For an additional $500, users can add the functionality of a high-performance spectrum analyzer, with a resolution range from 3 MHz down to 10 kHz. QAM analysis is another available option. The 860DSP also can emulate the two popular Trilithic return products–the general purpose SSR for return sweeping and ingress hunting, and the handheld RSVP emulator.
DSP, or digital signal processing, is the technology behind the development of the 860DSP, and was the catalyst to getting the product out of the drawing board phase and into reality, Harris says. For Trilithic, DSP was a way to quickly convert signals into data without spending a lot of money on RF hardware to get that signal turned into large blocks of data. In the 860, Trilithic digitizes the band in 8 MHz blocks, and strings them along like beads. Each "bead" in the string gets digitally crunched down to spans of 10 kHz from there.
In terms of functionality, software options to the DSAM-2500 can increase the meter's capacity, and other features include a one-button Auto Test feature that ensures digital, analog and DOCSIS tests are conducted the same way by all technicians, from grizzled veteran field techs down to novices new to the job. Test results can also be archived for later analysis, and the meter itself includes more than 100 pages of on-board context-sensitive help pages in four languages.
A recent addition to the line of service meters from Sunrise Telecom–the CM500IP Installer Profiler–also aims to provide techs (from expert to novice) the ability to qualify signal paths for new high-speed data services, though not in a DSP environment. It also communicates with a network CMTS via non-intrusive in-band signals, and adds one-button automated functionality called SMART (Selectable Measurement Automated Routine Tests).
ComSonics’ Sniffer Shadow
Following the trend of giving technicians more portable, and yet more powerful tools for the field, come new products developed for use with the many handheld PCs out there. One product from Pangrac & Associates, called the Tech Assistant, aims to enable these types of handhelds for installers. The software platform provides a way for technicians to store a wide assortment of system information on their handheld PCs, including more than 1,000 miles of system maps. It also has embedded software to automatically calculate things like C/N specifications and return path loss, among others. Guides for troubleshooting and test instrument procedures are also included to enable handhelds with more auto capabilities than previously available to technicians. Pangrac is also working on coupling its Tech Communicator cable plant voice/data radio with the Tech Assistant, which will bring even more functionality to installer handhelds in the future.
Sencore’s new SLM 1453
As noted earlier, the nature of cable network traffic is changing as new advanced services are rolled out. As networks evolve, so too must the instrumentation that keeps networks operating at a new reliability threshold.
The MTS300 MPEG Test System from Tektronix
Specifically, network technicians are increasingly testing for signal leakage more and more in their return paths; enabling fast two-way data services requires that network operators get a handle on the problems of ingress and signal leakage along the return path.
This is the idea behind a new near-field leakage detector from ComSonics, a premises tool for "sniffing" out signal leakage. Called the Sniffer Shadow, it offers unique dual-mode operation for both monitoring, and the consequent measuring, of RF leakage along the plant. The cell phone-sized detector works off of Lithium batteries, and in its "active sleep" Monitoring mode, can run detection tests for more than 100 hours. When leakage is detected, the technician flips up the LCD cover to reveal an integrated antenna to measure the leakage in microvolts per meter. Readings also feature "leakage validation," which tells whether the signal being measured is electrical noise or true RF leakage. This feature bypasses some of the transmitted "tagging" required by other leakage identification systems, and keeps monitoring and measurement functionality in one small, powerful unit.
A new digital signal level meter from Sencore– the new SLM1453–also addresses leakage in its new design. Sencore has added leakage monitoring and measurement to the meter's basic digital level functionality, and has made leakage detection a simple task for even the greenest field techs. The new SLM1453 also has two antennas: one to monitor and gauge the direction of the leakage, and a second dipole antenna for measurement tasks. Because it doesn't employ any sort of tagging method for signal tracking, the new Sencore meter can't distinguish between true RF leakage and other types of noise in the plant. However, it can work with other tagging systems by tuning in any frequencies set up for tagging by technicians. Battery life is a bit less than with the Sniffer; the Sencore meter operates for 14 hours when charged, but can operate off of a vehicle's battery for non-battery operation.
New platforms for leakage analysis are being looked at more closely as well. At Cable Leakage Technologies, its Wavetracker platform adds a geographical component to the hunt for signal leakage. By utilizing standard GPS technology, the dual-antenna Wavetracker not only listens for RF, but assigns a positioning fix via satellite every second. With the combined functionality, a technician can fully automate the process. Point files are collected to tell exactly what the amplitude of a signal is, on a certain street, at a certain time, in front of a certain house. Analysis software the company calls APLAS (Automatic Positional Leakage Analysis) looks at the leaks in a relative environment, peaks them out, assigns a street address and signal amplitude, assigns a repair and cost code, does pass-fail calculations, and then writes up a work order. APLAS even creates the required FCC CLI Form 320 from collected information, which for years was the only reason to measure cable leakage. Today, it's a more important measurement in achieving overall network health.
"Originally, (measuring for leakage) was a 'have-to' kind of thing. It was a mandate from the government," says Perry Havens, owner/operator of CLT. "Now it's a proactive issue with regard to customer service and signal integrity."
Tempo Research has included some leakage detection capabilities in its line of analyzers and fault locators. Specifically, Tempo's SignalScout RFM151 helps technicians do troubleshooting and maintenance anywhere in the network. It provides requisite signal level measurement tasks, and adds spectrum analysis, ingress and digital channel RF measurement as part of the package.
Another result of increased data carriage is a byproduct called "group delay," a situation similar to chromatic dispersion in the fiber optic world. When an operator sends digital data, there will be a certain level of linear distortion and a difference in delay when the frequencies get to their destination points at different times. The result is intersymbol interference, or ISI, which can wreak havoc on digital data.
To combat the problem, a small testing company called Holtzman Inc. has developed a system employing DSP to measure for the presence of group delay without having to take the plant out of service. A technician sets up a black box transmitter to a tap, fires a signal upstream, where it is captured by a digital oscilloscope, downloaded to a PC and then analyzed. It's a system operators heretofore have overlooked, but with more DOCSIS rollouts nationwide, group delay is creeping into lots of networks.
Cable leakage, intersymbol interference, group delay, ingress, noise…When will it all end? Unfortunately, never, but with the right sets of tools and measurement platforms, operators can get a needed grip on their afflicted networks. It's an easy way of getting ahead of the increasingly important customer service curve.