Ad-hoc network probes links for smoother calls

2019-02-27 08:03:07

By Michael Reilly An “ad-hoc” wireless network that probes the strength of connections before configuring itself could make it easier for cellphone users to hop smoothly between different open networks during calls. Ad-hoc wireless networks require each device to transmit as well receive. By passing signals between each other, more devices can connect to the network and the coverage can be extended. Eventually, entire cities might be covered with a wireless blanket this way, with all sorts of wireless communications devices sharing signals. It has been hard to incorporating voice traffic into this vision, however, even in the laboratory. Researchers have found it difficult to transmit voice data smoothly while devices share signals and users jump between networks. Calls made over data networks typically use voice over internet protocol (VoIP), which normally relies on a strong, reliable network to deliver a clear audio signal. On an ad-hoc network, however, signal strength fluctuates as a user moves around and the distance between each node varies. As an ad-hoc network reconfigures itself, the relay of data can be disrupted. Delays of a few hundred milliseconds are not enough to interfere with email or web browsing, but beyond about 230 milliseconds the human ear will detect choppiness in a voice call. With voice data bundled into 10-to-30-millisecond packets it is easy for pieces of a voice communication to go astray. Hai Jiang of the University of Alberta, Canada, and colleagues have developed a trick that could help deal with the problem. Using computer models to simulate mobile ad-hoc networks, they sent a lower-power probe from the caller’s node to test the viability of each potential connection. If the caller’s probe reaches the destination node without being degraded too much, a connection is established. If a connection drops below a quality threshold during a call, new probes are launched to hunt for a more robust path through the network. Rajit Gadh of the University of California, Los Angeles says the research points the way towards truly cheaper or even free mobile telephony. “Ad-hoc networks are a fantastic opportunity for voice,” he told New Scientist. “Within a city, with enough nodes, this could provide a secondary network for people to make calls.” Such a network could function outside of VoIP or connect to it via internet access points, he says. But the idea has its detractors too. Mohsen Kavehrad of Pennsylvania State University says under some circumstances the ever-shifting nodes of an ad-hoc network could still cause disruption to voice data,