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Optimal transmit strategy for the 2×1 MISO bidirectional broadcast channel

: Oechtering, T.J.; Wyrembelski, R.F.; Boche, H.


Institute of Electrical and Electronics Engineers -IEEE-:
IEEE 9th Workshop on Signal Processing Advances in Wireless Communications, SPAWC 2008. Vol.1 : Recife, Brazil, 6 - 9 July 2008
Piscataway, NJ: IEEE, 2008
ISBN: 978-1-4244-2045-2
Workshop on Signal Processing Advances in Wireless Communications (SPAWC) <9, 2008, Recife>
Conference Paper
Fraunhofer HHI ()
antenna array; broadcast channel; protocol; wireless channel

We consider the broadcast phase of a three-node network, where a relay node with multiple antennas establishes a bidirectional communication between the two other nodes each equipped with a single antenna using a spectrally efficient two phase protocol. In the first phase, both nodes transmit a message to the relay node, which decodes the messages. In the second phase the relay broadcasts a re-encoded composition of them. In this work, we show that for two transmit antennas at the relay node transmitting a single beam is always an optimal transmit strategy. We show that if a single beam is optimal the beamforming vector is a linear combination of the two single-user optimal strategies. Further, we analyze the dependency of the capacity region on the correlation between the two channels.