Brains & Brawn

Advertising the voice clarity of your wireless network is one thing. Making it happen is another. If quality is poor, your subscribers will not hesitate to switch to another carrier.

THE BRAWNImproving voice quality is a fine art that takes brains and brawn. The muscle comes courtesy of several devices -- voice-activity detectors, noise-reduction circuits and a new generation of T&M equipment.

Voice-activity detectors are found in newer handsets and carriers' network software. They adjust the voice signal to a target power level. For example, D2's voice-activity detector adapts to different background ambient noise or line noise. It also adapts to echo when used with the company's network echo canceller. The result is clear speech because the available bandwidth in a given cell is used more efficiently. However, when network software is not correctly tuned for cutting-in/cutting-out, you can hear a disturbing clicking noise when speaking. This clicking noise can be detected with QVoice, a test-drive-analysis system from Ascom.

To improve voice quality, wireless carriers also add noise-reduction circuits that remove background noise created by passing trucks and motorcycles. There is a drawback: Noise-reduction circuits require good timing optimization and must be able to differentiate between noise and the desired signal. Otherwise, the phone users' words also are lost with the suppression.

To overcome these limitations, carriers are beginning to realize that they need to invest in a new generation of voice T&M equipment to optimize their network performance. Unlike earlier-generation T&M tools, which only measured quality based on parameters such as bit error rates or subjective, non-reproducible mean opinion scoring (MOS) ratings, these new products can measure what the subscriber actually hears.

The advantage to new T&M tools is that they give carriers a true indication of how a phone user will perceive its quality.

Objective test methods have replaced MOS listener panels with electronic speech samples, tones and phonetic sound tests that generate signals emulating what subscribers hear. To assess the speech quality of a transmission link, a reference speech sample is transmitted and compared with a received sample of what the subscriber hears. This comparison results in accurate and reproducible MOS values.

The major players in wireless T&M are marketing new products to address these requirements. Safeco offers VoicePrint with its easy-to-use FieldPak. It allows a single technician to measure voice quality indoors. Q-Voice from Swiss-based Ascom uses differential GPS/dead reckoning technology to pinpoint voice measurements to within a few feet. This is important in cities where the trend is moving toward smaller cell size to handle greater traffic.

THE BRAINSThe brains part of the equation comes in through new speech-evaluation algorithms. These algorithms give carriers a way to measure speech quality objectively. Think of it this way: Algorithms define; testing tools measure and help enforce.

One of the most promising algorithms is Ascom's PACE. In a recent test of various algorithms, the PACE algorithm predicted speech quality accurately in the presence of transmission errors. PACE also performed well when tested in English, French, Italian and Japanese. Other algorithms were less robust and exhibited substantial variations among different languages.

PACE now is being introduced in Ascom's QVoice/QNet network-testing product line. The system evaluates both uplink and downlink speech quality, indoors and outdoors.

SPEECH-QUALITY TESTINGMore wireless carriers are turning to objective speech-quality testing to improve the network and revenues. Monitoring voice quality and optimizing network RF parameter settings can avoid adding unnecessary sites and channels. Also, intelligent centralized monitoring reduces the need for sending field engineers to troubleshoot questionable problems.

Moreover, quality of service (QoS) voice statistics can be used in acceptance testing of new or expanded networks. Carriers can use criteria based on what subscribers actually hear -- not hypothetical engineering values -- to design, expand and maintain networks to ensure optimum speech quality.

Finally, tests of competitive networks can prove important marketing tools, providing a true comparison regardless of the air-interface technology. In addition to price comparisons and coverage-area maps, carriers now advertise QoS test results to gain and keep subscribers.

If you are not implementing competitive measures already, it is only a matter of time before competitors will use the technology to conduct tests on your network and point out the weak spots to your subscribers.

Subscribers also value QoS results. They like to know where coverage is weak and where calls can be placed without retries. Today, it is difficult for subscribers to obtain such information. By providing them with information on speech quality, carriers have the opportunity to set expectations and better educate subscribers.

FUTURE DEVELOPMENTSAs speech quality becomes more important, carriers are rethinking how they can define, monitor and guarantee speech quality in a variety of areas. A few carriers already have signaled that they will investigate using objective test measures to improve speech quality for voice over IP.

Speech-quality tests also can be used to assess the negative effect that the cascading of networks can have on speech. These days, it is increasingly likely that a call will be routed through several networks. On its way, the speech signal could be compressed and expanded repeatedly, or it could undergo several analog-to-digital and digital-to-analog conversions, all of which contribute to voice-quality degradation. With speech-quality measures, carriers can predict where problems in other networks will occur and work to resolve them.

If a carrier can use objective tests to monitor and guarantee high levels of speech quality without armies of human testers and inaccurate, non-reproducible and subjective MOS values, they will attract more subscribers and improve their competitive advantage.