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August 2007 | Volume 10 / Nuber 8
Packet Voice over Wireless

Dual Mode Cellphones Promise Better Sound Quality

The cellular industry has been monstrously successful, but the sound quality of cellular calls remains abysmal. This proves that people like you and me don’t care about sound quality, right? Wrong. Most of us do most of our calls on our cellphones, and we use our cell phones more with each passing year; but we do this only because we value mobility higher than sound quality, not because we don’t care about sound quality. The ongoing success of Polycom speaker phones shows that at least in some circumstances people are willing to pay for good sound quality, and one of the success factors for Skype is its use of wideband codecs.

On both fixed and mobile calls, the telephonic journey from mouth to ear, often thousands of miles in tens of milliseconds, traverses a chain of many weak links, each compounding the impairment of the sound. Whether you are talking through a headset, a handset or a speaker-phone, the microphone and speakers may be incapable of reproducing high quality sound. The digital encoding of the call is almost always done with a narrow-band codec, which discards the higher frequencies that enable you to distinguish between an “F” and an “S.” The media stream is often transcoded, for example from GSM to G.711 and back, losing fidelity each time. On VoIP calls, packets are often lost or delayed. Over wireless connections, whether cellular or WiFi, interference, crowding and imperfect coverage cause even more packets to be lost, and calls are sometimes dropped in mid-sentence.

The premise of this column is that Voice-over-WiFi sounds better than traditional phone service. Not just better than cellular voice, but better than toll-quality wireline voice.

Suspend your disbelief for a moment, and contemplate what it would be like if conversations over your cellphone were in CD quality sound. This is technically achievable today with Voice-over-WiFi on a dual-mode (cellular plus WiFi) phone.

Because they must handle polyphonic ring tones and iPod-type capabilities, the speakers on most cell phones can easily carry the full frequency range of the human voice. Cellphone microphones can also pick up the required range, and DSP techniques can mitigate the physical acoustic design challenges of the cell phone form factor.

Smart phone processors have the power to run modern wideband codecs for superior sound quality. Using a wideband codec you can easily hear the difference between an “F” and an “S,” and calls gain an agreeable clarity and immediacy.

Unfortunately, without a major overhaul, neither cellular networks nor wireline voice networks can transport high

definition sound. So even if you have a wideband-capable phone the chances are that your sound quality will be limited by the network.

But this limitation doesn’t apply to the IP network. Voice-over-IP can use a wideband codec as easily as a narrowband one. This benefit is lost if there is a transcoding step, but WiFi provides a direct connection to the IP network, and if the call remains on the IP network end to end the callers can enjoy the wideband experience. Dual-mode phones can connect directly to the Internet in the two places where most people spend most of their time: at work and at home. These phones must be open enough to run VoIP software; Nokia’s smart phones and Windows-based smart phones fit this description, though the iPhone doesn’t yet.

In large enterprises many calls are internal. With VoIP phones deployed around the entire company, all internal calls can use wideband codecs. Even better, both large and small companies can federate their voice systems with each other over their data networks; calls between them don’t touch the public voice network, so they can stay in wideband format. This is viral. As more companies experience the benefits of high definition sound internally and with their suppliers and customers, they will encourage those who haven’t made the switch to do so.

If the analysts’ projections are correct, and hundreds of millions of cellphones sold in 2010 are WiFi voice-capable, businesses won’t have to make the decision to buy VoIP phones. Our cellphones will come with VoIP capability; we will be enjoying much better sound quality on many of our calls even if the public voice networks aren’t yet wideband-capable.

Check out the V2oIP Quality Alliance website ( for an industry initiative on improved call quality. IT

Michael Stanford has been an entrepreneur and strategist in Voice-over-IP for over a decade. His strengths are technical depth, business analytic skills and the ability to communicate clearly. In his current consulting practice, Michael specializes in VoIP wireless networks, both WiFi and WiMAX. Internet Telephony Magazine recognized him as one of “The Top 100 Voices of IP Communications” and VoIP News named him one of “The 50 Most Influential People in VoIP”.

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