Abstract-The present paper studies the asymptotic performance of dual-hop amplify-and-forward multiple-input multipleoutput relay communication systems. In the corresponding setup, a relay amplifies the signal received from a source, retransmitting it towards a destination, while the direct source-destination link is absent. Ergodic achievable rates under separate decoding, along with the average bit error rate under various detection schemes are derived in the regime where the number of antennas at each terminal grows without bound. To overcome the mathematical difficulty of averaging over both channel realizations and input signals we apply large-system analysis based on the replica method from statistical physics. The validity of the large-system analysis is further verified through Monte Carlo simulations, providing particularly good accuracy at low SNR.
I. INTRODUCTIONMultiple-input multiple-output (MIMO) relaying has been proved a promising technology that allows for reliable communication at increased coverage and data rates [1]. Understanding the fundamental limits of the relay channel has therefore become one of the recent research challenges. The relay MIMO channel (depicted in Fig. 1) -consisting of a source (S), a relay (R) and a destination (D) -is a fundamental building block for complex cooperative networks [2], [3]. It has therefore been regarded as an important milestone in the research efforts within the field.The relays in a cooperative network may realize different cooperative strategies. For instance, a regenerative strategy (e.g., decode-and-forward [4]) involves decoding of the noisy signal from the source, re-encoding the underlying message and retransmitting it upstream. A non-regenerative strategy (e.g., amplify-and-forward (AF) [2]) involves simple amplification of the received noisy signal and subsequent retransmission towards the destination. Non-regenerative relaying, being simple in implementation and independent of the modulation schemes at the source terminal, is of particular interest.In fading environment, the achievable data rate of such cooperative communication systems is measured by the endto-end ergodic mutual information (MI). Hence, performance evaluation requires averaging over the channel randomness. This, in general, prevents one from having closed-form expressions and motivates the need for alternative approaches to