Addressing Interference – Art or Science?

By    May 14, 2014

Is Creating a High Performance Point to Multipoint System for Noisy Environments an Art or a Science?

No matter how much frequency is added to the unlicensed spectrum, it is only going to get more crowded. The increased cost of licensed spectrum, the proliferation in the number of wireless equipment vendors, and the insatiable demand for connectivity will force companies to adapt and drive innovation — rallying them to find new ways to make wireless systems perform under noisy environments.

The problem is not new, but it has certainly become more complex. Initially noise was controlled by finding an appropriate channel without noise. As the spectrum became crowded, the solution evolved into selecting the least noisy channel and radiating at the highest allowed power level. Today, with no clear channels left, another round of innovation is vital.

I joined Cambium Networks in June 2013. Since then I have worked with the ePMP™ engineering team through two releases focusing largely on solving radio interference issues. The release in October addressed throughput, scalability, and frequency reuse while simultaneously minimizing self-interference. The second, which we are making available today to the market, targets a more indeterminate factor: external interference. It works to optimize performance while dealing with radio interference that is essentially beyond its control. As we approved our final release and celebrated the engineering efforts required to achieve it, I reflected back and started wondering whether addressing radio interference is a science or an art.

If the environment is clean, passing high throughput, making the system scalable, and keeping latency low is a work of science: the solution can be derived by striking a balance between the following four mechanisms: 

  • Rate Adapt enables the system to find the optimum data rate, so that packet error rate is minimized
  • Retry resends the frame to recover failed or corrupted packets
  • Scheduling fixes a time when a particular node will transmit (to decrease contention)
  • Transmit Power Control minimizes interference on the same channel by altering the transmit power

However when there is noise which is random and unpredictable, a sense of art is needed: one must find harmony in the chaos and can no longer follow the same set of rules for performance. Instead devices must collaborate – taking a system view and adapting their behavior to suit the environment. This requires visibility, communication, an unsurpassed knowledge of the wireless environment, and the ability to tie it all together into a single unified product. A holistic approach, and a flexible, dynamic infrastructure, is the solution.

The question of art or science may not have a single answer – science definitely plays a significant role. However the innovation and dynamism required to create unsurpassed performance in a noisy environment is definitely an art.