Adaptive interference mitigation requires significant resources due to recursive processing. Specific to satellite systems, interference mitigation by employing adaptive beamforming at the gateway or at the satellite both have associated problems. While ground based beamforming reduces the satellite payload complexity, it results in added feeder link bandwidth requirements, higher gateway complexity and suffers from feeder link channel degradations. On the other hand, employing adaptive beamforming onboard the satellite gives more flexibility in case of variation in traffic dynamics and also for changing of beam patterns. However, these advantages come at the cost of additional complexity at the satellite.In pursuit of retaining the benefits of onboard beamforming and to reduce the complexity associated with adaptive processing, we here propose a novel semi-adaptive beamformer for a Hybrid TerrestrialSatellite Mobile System. The proposed algorithm is a dual form of beamforming that enables adaptive and non-adaptive processing to coexist via a robust gradient based switching mechanism. We present a detailed complexity analysis of the proposed algorithm and derive bounds associated with its power requirements. In the scenarios studied, results show that the proposed algorithm consumes up to 98% less filter computing power as compared to full-adaptive case without compromising on system performance.
Global connectivity cannot be guaranteed by terrestrial networks due to the lack of infrastructure in rural areas. Neither can satellite networks assure this due to lack of signal penetration and capacity coverage issues in densely populated areas. To bridge this gap, we propose an Orthogonal Frequency Domain (OFDM) based hybrid architecture where users are provided service by existing mobile networks in urban areas and are served by satellite in the rural areas. In such a system terrestrial and satellite networks can reuse the portion of spectrum dedicated to each of these systems resulting in significant increase in overall capacity, wider coverage and reduced cost. This frequency reuse induces severe Co-Channel Interference (CCI) at the satellite end and our work focuses on its mitigation using OFDM based adaptive beamforming.
exhibits a high degree of sensitivity to the pilot sub-carriers. Increasing the number of reference pilots significantly improves BF performance as well as system performance. However, this increase comes at the cost of data throughput which inevitably shrinks due to transmission of additional pilots. Hence an approach where reference signals available to the BF process can be increased without transmitting additional pilots can exhibit superior system performance without compromising throughput.Thus, in this paper we present a novel three-stage Iterative Turbo Beamforming (ITBF) algorithm for an OFDM based Hybrid Terrestrial-Satellite Mobile System which utilises both pilots and data to perform interference mitigation. Data sub-carriers are utilised as virtual reference signals in the BF process. Results show that when compared to non-iterative conventional BF, the proposed ITBF exhibits Bit Error Rate Gain (BERG) of up to 2.5 dB with only one iteration.
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