I was working through M.Chiang’s Networked Life: 20 Questions and Answers which is an awesome textbook touching on a wide range of networks topics.

The first chapter, “What makes CDMA work for my smartphone” covers mobile station power control which plays a crucial role in communication systems in terms of interference management, energy management, and connectivity management. Power control helps address the near-far problem faced in non-orthogonal wireless systems like CDMA.

I created a d3 visualization that lets you explore a basic formulation of the distributed power control algorithm (with a fixed signal to interference ratio) over a narrow range of inputs. You can play around with it on bl.ocks.org.

Each receiving channel is assigned a target SIR that is randomly sampled from a uniform distribution with range 1-3. Each mobile station is assigned an initial transmit power level that is randomly sampled from a uniform distribution with range 1-3mW. Gains for interference channels are randomly sampled from a uniform distribution with range 0.01-0.10. These inputs are displayed in tables where each row corresponds to a given mobile station. The input values used here are arbitrary and don’t reflect actual numerical values observed in real cellular networks.

The transmit power of each mobile station is plotted as a line over time (i.e. over the DPC algorithm iterations). If there exists a set of transmit powers that satisfies all target SIRs, the minimal power solution is displayed in a table to the right of the input tables. Otherwise “No Solution” is displayed.

Users can:

  • alter the seed for the random number generator (this will generate different inputs)
  • set the number of mobile stations (3-9)
  • set the receiver noise (0.1-0.5mW) which is assumed to be the same for all channels
  • set the number of iterations for the DPC algorithm

Source Code: gist.github.com/renschler

Reference: M. Chiang, P. Hande, T. Lan, and C.W. Tan, “Power control for cellular networks”, Foundation and Trends in Networking, vol. 2, no. 4, pp. 381-533, July 2008.