| As a realization of the matched filter (MF), the RAKE receiver is optimal under the assumption that multiple access interference (MAI) is an additive white Gaussian noise. On the forward link of a WCDMA network, MAI is not spectrally white. Thus, there been interest development of the generalized RAKE (GRAKE) as a whitened matched filter (WMF). See papers by G. E. Bottomley, et.al.
This paper is motivated by the Mobile User Objective System (MUOS), which is a WCDMA network over geostationary satellites. The forward link is segmented by satellite beams, which corresponds to terrestrial cells. In a terrestrial system, interference from other cells experiences independent multipath fading. In the satellite system, however, all beams are transmitted from a common source (the satellite), and hence, interfering beams experience a common fading channel. This fundamental observation leads to the innovation of this paper. Unlike the terrestrial case, the satellite-GRAKE can utilize the same pilot code channel trackers as used in the RAKE finger channel estimation to determine inter-beam MAI spectral shaping.
The paper will develop the satellite-GRAKE as follows. First, we shall present a formula for the GRAKE output SIR in terms of (1) the fading channel state, (2) the combining weights. This formula is similar to analysis found in the literature, with modifications for satellite link. Second, we shall derive the optimum combining weights, which leads to the satellite-GRAKE architecture. Finally, we shall present simulation results to establish the performance gain of the satellite G-RAKE. These results show a performance gain of approximately 1 dB on stressed MUOS channels.
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