This paper presents a methodology for determining the ratio of interference power to noise power at the input of a point-to-point receiver in the fixed service (FS) due to operation of a high altitude platform system (HAPS) station at any point visible to the FS receiver. Detailed description about the parameters, models, and possible I/N criteria that might be applied are mentioned in this research paper. The outcome methodology is described, applied and the results obtained with it are presented in a tables and graphs when HAPS platform transmitting to only one gateway station or aggregate interference when HAPS platform transmitting to a ten Gateway symmetrically.