## 1. Introduction

[2] In the band of frequencies above 10 GHz rain attenuation is considered to be a principal factor affecting the availability and performance of a satellite communication system. Interference effects must be carefully taken into account, also for the reliable design of an Earth-space path. In the present work, we assume that the dominant interference source comes from the differential rain attenuation from an adjacent Earth-space system operating at the same frequency.

[3] So far, the outage performance analysis has been based on the assumption that the thermal noise is dominant [*Ha*, 1986], and consequently, the outage time is mainly dictated by the fact that the rain attenuation A_{c} of the wanted carrier signal should exceed a certain rain fade level, called margin M (in dB). The contribution of the interference to the total outage time effects can be further taken into account by calculating the degradation of the carrier-to-interference ratio (C/I), under the condition that the system is working properly (A_{c} < M). For this reason, some models have been so far proposed [*Kanellopoulos and Houdzoumis*, 1990; *Kanellopoulos et al.*, 1993; *Kanellopoulos and Margetis*, 1997] dealing with the prediction of the differential rain attenuation ΔA = A_{c} − A_{I}, under the above condition of proper operation (A_{c} < M). Validation of the above models has been made by comparing the theoretical results with a set of simulated data in Montreal area [*Rogers et al.*, 1982]. Some recent experimental results derived from rain attenuation measurements in Italy for two frequency bands (11.6 and 20 GHz) [*Matricciani and Mauri*, 1996; *Matricciani*, 1997] have been also used for this purpose, and the agreement is found to be quite satisfactory [*Kanellopoulos et al.*, 2000].

[4] In recent years, taking into account the expected aggravation in the frequency and orbital congestion, the complicated problem of predicting the degradation of the total carrier-to-noise plus interference ratio (CNIR), under the presence of rain fades, has been carefully examined [*Kanellopoulos and Livieratos*, 1997; *Livieratos and Kanellopoulos*, 2000]. This is an important subject contributing toward the much desirable accurate estimation of the total outage time of an interfered satellite link without any condition regarding the thermal noise. This is even more imperative for systems working under the interference domination consideration, a quite probable situation for modern satellite paths as previously mentioned.

[5] The subject of the present paper is an extension of the previous analysis in order to include interfered Earth-space systems located in regions representing heavy rain climatic conditions. In this case, the demand of using the possible low fade margins can lead to the employment of the site diversity technique. The extended method assumes again the model of convective rain cells for the spatial rainfall structure and the lognormality for the point rainfall statistics. The more complicated case, where another interference source such as the cross-polarization is also present, will be examined in a future work. The numerical results presented in the last part of the paper are concerned with the proper use of the CNIR statistics toward the reliable design of an interfered site diversity system suffering from differential rain attenuation.