Data transfer and real-time communication via wireless access points are set to for a boost with the development of an algorithm that improves bandwidth efficiencies.
© 2009 istockphoto.com/mikdam
When we connect to the internet through a wireless network, few of us appreciate the complex actions required to transmit information error-free over the airwaves. Now, the team of Peng Hui Tan, Yan Wu and Sumei Sun at the A*STAR Institute for Infocomm Research in Singapore has developed a new algorithm that improves wireless bandwidth efficiencies. This development sets the stage for faster data transfers and enhanced real-time communication.
Because numerous factors can affect wireless communication—distance, physical interference, weather, to name a few—signals over networks must be dynamically adjusted to meet actual transmission-channel conditions using a process called link adaptation. Recently, a new technique, adaptive modulation and coding (AMC), was created to improve link adaptation. With AMC, the best modulation and coding scheme—the modification of analog signals by digital bits—is chosen to adapt to current channel conditions, helping to maximize transmission efficiency.
Decisions on modulation and coding schemes are made by examining the packet error rate (PER), which measures the ratio of incorrect to correct data packets received under real-time communication link conditions. According to Sun, predicting PERs is key to achieving high network efficiency in multiple-in, multiple-out orthogonal frequency-division multiplexing (MIMO-OFDM), which is one of the most important wireless infrastructures in use today.
“Perfect PER prediction leads to an optimum modulation and coding scheme selection,” says Sun. “On the other hand, unreliable PER prediction can result in suboptimum performance or link failure.”
Typically, PERs are chosen by evaluating the instantaneous signal-to-noise ratio in a transmission channel, but it is difficult to calculate the best link adaptation with just a single parameter. A generous safety margin must be incorporated into the AMC, which reduces system throughput.
Sun and co-workers’ new algorithm uses extrinsic information transfer (EXIT) functions—analytical tools that measure how much of a data bit is known after transmission over a noisy channel—to characterize PER performance. By measuring the output of the detector between a wireless access point and a transmitting station, such as a laptop, the EXIT functions can model the real channel conditions and generate accurate PER predictions.
The low complexity, high flexibility and easy implementation of this link adaptation algorithm promises to help meet the bandwidth needs of our information-driven society. “Our research is primarily focused on improving the spectral efficiency and robust performance of wireless communications,” says Sun. “This project will help support the increasing demands of high-throughput applications, one example of which is real-time video streaming.”
The A*STAR-affiliated authors in this highlight are from the Institute for Infocomm Research.
