  Motivated by applications such as battery-operated wireless sensor networks
(WSN), we propose an easy-to-implement energy-efficient two-way relaying
scheme. In particular, we address the challenge of improving the standard
two-way selective decode-and-forward protocol (TW-SDF) in terms of
block-error-rate (BLER) with minor additional complexity and energy
consumption. By following the principle of soft relaying, our solution is the
two-way one-bit soft forwarding (TW-1bSF) protocol in which the relay forwards
the one-bit quantization of a posterior information metric about the
transmitted bits, associated with an appropriately designed reliability
parameter.
  In WSN-related standards (such as IEEE802.15.6 and Bluetooth), block codes
are adopted instead of convolutional and other sophisticated codes, due to
their efficient decoder hardware implementation. As the second main
contribution, we derive tight upper bounds on the BLER performance for both
TW-SDF and TW-1bSF, when the two-way relaying network employs block codes and
hard decoding. The error probability analysis confirms the superiority of
TW-1bSF. Moreover, we derive the asymptotic performance gain of TW-1bSF over
TW-SDF, which further suggests that the proposed protocol is a good choice,
especially when long block codes are used.
