In millimeter wave (mmWave) systems, antenna architecture limitations make it difficult to apply conventional fully digital precoding techniques but call for low cost analog radio-frequency (RF) and digital baseband hybrid precoding methods. This paper investigates joint RF-baseband hybrid precoding for the downlink of multiuser multi-antenna mmWave systems with a limited number of RF chains. Two performance measures, maximizing the spectral efficiency and the energy efficiency of the system, are considered. We propose a codebook based RF precoding design and obtain the channel state information via a beam sweep procedure. Via the codebook based design, the original system is transformed into a virtual multiuser downlink system with the RF chain constraint. Consequently, we are able to simplify the complicated hybrid precoding optimization problems to joint codeword selection and precoder design (JWSPD) problems. Then, we propose efficient methods to address the JWSPD problems and jointly optimize the RF and baseband precoders under the two performance measures. Finally, extensive numerical results are provided to validate the effectiveness of the proposed hybrid precoders. Hybrid precoding design, millimeter wave communication, energy efficient communication, successive convex approximation, power allocation.

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Two new azaphilone derivatives, chaephilones A (1) and B (2), were isolated from the fungus Chaetomium globosum, together with four structurally related analogs 3 - 6. The structures of 1 and 2 were elucidated by comprehensive spectroscopic analyses including HR-ESI-MS and NMR. The known compounds were identified as chaetomugilin Q (3), chaetomugilin D (4), 11-epichaetomugilin A (5), and chaetomugilin S (6) by comparing their NMR data and optical rotation values with those reported. Compound 2 represents the first example of azaphilone with an open furan ring. Compounds 1 and 2 were evaluated for cytotoxic activities against five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW480) by the MTS method.