In millimeter wave (mmWave) systems, antenna architecture limitations make itdifficult to apply conventional fully digital precoding techniques but call forlow cost analog radio-frequency (RF) and digital baseband hybrid precodingmethods. This paper investigates joint RF-baseband hybrid precoding for thedownlink of multiuser multi-antenna mmWave systems with a limited number of RFchains. Two performance measures, maximizing the spectral efficiency and theenergy efficiency of the system, are considered. We propose a codebook based RFprecoding design and obtain the channel state information via a beam sweepprocedure. Via the codebook based design, the original system is transformedinto a virtual multiuser downlink system with the RF chain constraint.Consequently, we are able to simplify the complicated hybrid precodingoptimization problems to joint codeword selection and precoder design (JWSPD)problems. Then, we propose efficient methods to address the JWSPD problems andjointly optimize the RF and baseband precoders under the two performancemeasures. Finally, extensive numerical results are provided to validate theeffectiveness of the proposed hybrid precoders.
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