Appendices A. Estimation of cell phone coverage Cell phone signals are ultra high frequency radio signals. Radio propagation follows the laws of physics so it is possible to use an electromagnetic signal propagation model to calculate predicted coverage. Cell phone signals’ primary propagation mode is direct wave, and the signal strength decreases proportionally with the inverse of squared distance. The signal strength can also be greatly reduced by objects, such as hills, buildings, or dense foliage, lying on the line of sight. Even if an object does not block the line of sight but lies in the Fresnel zone, it can reduce the signal (Parsons 2000). Therefore, for a given cell tower height and transmission strength, the signal strength in a given location is primarily determined by distance to the tower and whether the receiver (i.e. mobile phone) is in line of sight of the tower. Because I do not have access to the technical details of the cell phone towers, I approximate the parameters needed for the calculation. The end result can therefore be considered as an augmented line of sight analysis, where the ITM is used to define a potential coverage area, as determined by the cell tower locations and plausible parameter values. Intuitively, I take into account if a given point is within the maximum range to receive a signal, and whether there exists a line of sight between that point and a cell tower. I apply the irregular terrain model (ITM), also known as Longley-Rice model, to calculate the predicted coverage area. To apply the ITM, I use a freely available software for RF propagation simulation, called Radio Mobile.12 I start by defining the maximum allowed path loss. Maximum allowed path loss is defined as: Transmitter power (dBm) − Transmitter attenuation (dB) + Antenna gains (dBi) − Receiver line loss (dB) − Receiver sensitivity (dB). If the free space path loss—i.e. path loss due to distance—and the propagation loss due to topography are less than the maximum allowed path loss, the signal is sufficiently strong for reception. The surface area of Myanmar is divided into 200∗200 m grids, and the prediction is calculated for each grid cell. I approximate the cell phone tower parameters so as to mimic transmission in a rural area. Antenna height is assumed to be 35 meters, and antennas are assumed to be omnidirectional. In reality antennas are usually directional, and there are a couple of antennas in a cell tower that cover different segments around the tower. Cell phone tower heights vary a lot, and 30–40 meter towers can be considered high. I limit the maximum range of the signal to 25 km. Due to timing advance, the theoretical maximum range for a standard GSM equipment is 35 kilometers. Because of limitations of network architecture and poor performance of cell phone antennas, in practice the maximum range will be much 12. Radio Mobile is copyright of Roger Coudé VE2DBE. 26