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Some of the existing relay schemes for cooperative networks based on one-way relaying protocol are not applicable to the case of two-way relaying protocol. In this letter, a cooperative relay scheme for distributed amplify-and-forward relays working under the two-way relaying protocol is designed in a closed-form, which is asymptotically optimal in the high levels of signal-to-noise ratio (SNR). An upper-bound of the mean squared error (MSE) is derived via a tight approximation of the SNR expression. Based on the minimization of this upper-bound, the two-way relay scheme is then derived as a Rayleigh-Ritz ratio problem. The new relay scheme achieves the minimum MSE for both directional transmissions. Simulation results illustrate the effectiveness of the proposed scheme especially in the high SNR regime.