Wi-Fi Performance Negatively Affected By An Increased Cell Phone Data Use

With more awareness placed on the use of the internet, causing competition in cell data network use, then the issue: the bandwidth and speed it operates may be limited due to the plethora of options of Wi-Fi network signals available.

Researchers at the University of Chicago, not oblivious of this, decided to demonstrate how the stated network competition will have a negative impact on internet connection service for the common users.

Network competition intensifies when they operate on shared frequency ranges for electromagnetic waves. The Wi-Fi network uses an unlicensed spectrum; the implication of this is that any network or device can use the spectrum as long as it’s in tandem with the rules of the Federal Communications Commission. This shows an unfettered use of unlicensed spectrum by different networks, leading to impaired effectiveness.

Monisha Ghosh, a Research Professor in the Pritzker School of Molecular Engineering and an associate member in the Department of Computer Science at the University of Chicago had opined that  “The unlicensed spectrum is literally a free-for-all; anybody can use it, within the bounds set by FCC,”

Although with an FCC providers license, Internet services on the cellular phone relies mostly on separate spectra band, via spectrum auctions, that has shifted with the growing demand for cellular data and limited bandwidths.

When a spectrum band is licensed from the FCC by a cellular provider, it is reserved for its exclusive use and this gives the leverage of little interference on networks operating on licensed band, allowing providers establish faster, reliable services.

But then this isn’t easy as it appears, as it comes at a cost. Professor Ghosh enumerated the implications of a licensed spectrum when he said:

“In the last five years, the cellular world has grown in its number of users and the amount of data they need. Cellular service providers have begun running short on spectrum, and the licensed spectrum costs billions.”

With the cost of a licensed spectrum screaming in the face of network providers, they began to tweak the process by using the unlicensed spectrum via cellular networks, with the use of a mode called licensed assisted access (LAA), which operates on the same bands used for Wi-Fi.

 Professor Ghosh and his team’ decided to take a look at how the shared use of the unlicensed spectrum, called coexistence, impacted both Wi-Fi and cellular users.

“We actually found an LAA station located on the Chicago campus, on a pole in front of the bookstore, and in this outside space campus Wi-Fi is also in use. That provided an experimental platform in our backyard, so we started taking measurements.”

Muhammad Rochman, a Computer Science graduate student and postdoctoral researcher Vanlin Sathya in the process had set up five laptops and smartphones, using them to access the local Wi-Fi networks or connect to LAA using cellular data.

They took a cursory look at different types of data to determine the demand on these networks, from low (such as accessing text on a website) to high (streaming a video). Each of the devices was equipped with applications that allowed the group to know the quality of each network connection.

The group discovered that there was decreased performance (reduction in amount of data transmitted, speed of transmission and signal quality) due to competition when they simultaneously accessed the multiple networks.

The resultant competition was grossly detrimental to Wi-Fi as it was noted that when LAA was in use, data transmitted by Wi-Fi users decreased up to 97% while LAA data only had a 35% decrease when Wi-Fi was also in use.

The non-alignment between Wi-Fi and LAA partly due to different protocols used by each of them to deal with high internet traffic was explained by Ghosh when he opined:

 “If everybody starts using the spectrum at the same time, it creates interference and no one’s information gets through, but Wi-Fi and cellular have developed very different mechanisms for dealing with this issue.”, he said.

As Wi-Fi uses unlicensed spectra, it depends on a protocol that is unpredictable in demand. The protocol dubbed: ‘Listen-before-talk has the capacity to use the principle of interactions of what is known as Polite Party-Goers. In the Polite-Party-Goers Interaction method, participants listen on the other end and wait for a gap in the conversation to speak. Two  people cannot talk effectively at once and once that happens, one has to politely  stop  talking to  allow the other speak, then wait for a gap to respond.

This Polite-Party-Goers principle is then infused into the Wi-Fi spectra; If two or more Wi-Fi users are using the network at once, each of them will be given a brief wait time to allow seamless transition. The wait time reduces the probability of collision.

Cellular providers can actually predict demand based on cellular access, and then assign a specific user a specific transmission time. Thus, LAA users are more like speakers in tightly scheduled colloquia than at an informal party.

Cellular providers using the Licensed spectra encounter little issues but when they switch to the unlicensed spectra, the channel access parameters LAA uses makes it difficult for Wi-Fi users to get equal access to the medium. In spite of the fact that LAA recently modified the tight scheduling used in cellular bands to implement listen-before-talk, it still operates with different parameters. One crucial difference is how long each system holds the medium once it gains access: LAA can transmit for up to 10 milliseconds, whereas Wi-Fi transmissions are only up to 4 milliseconds long.

Competition in the shared spectrum occurs not just between Wi-Fi and cellular providers, but also within each network type.

“In our experiments, we compare Wi-Fi/Wi-Fi coexistence with Wi-Fi/LAA coexistence. “Wi-Fi/Wi-Fi coexistence isn’t too bad because of the listen-before-talk procedure, so we used this as a standard of fairness. But Wi-Fi/LAA behaves worse, and we were surprised by how much worse.”, Ghosh said.

Ghosh further advised regulatory agencies on how to align network protocols based on her research.

“These changes have resulted in better coexistence and better sharing mechanisms. But there’s still a long way to go,” she said.

Reference: “Hidden-nodes in coexisting LAA & Wi-Fi: a measurement study of real deployments” by Vanlin Sathya, Muhammad Iqbal Rochman and Monisha Ghosh.
PDF