Consider a network with one source, one destination and multiple relays. It is shown that multiplexing gains that are higher than that of the direct link are possible for any finite SNR, in such a network, under any fading statistics. Thus relaying can offer not only stronger link reliability, but also higher spectral efficiency, compared with non-relay transmission. Several schemes for the decode-and-forward protocol are proposed and are shown to offer the same outage probability and diversity-multiplexing tradeoff (DMT) as if the transmit antennas at the source and the relay(s) were co-located, under certain power constraints. Thus a higher multiplexing gain than that of the direct link can be obtained if the destination has more antennas than the source.
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