  Massive multiple-input multiple-output (mMIMO) antenna systems and inter-band
carrier aggregation (CA)-enabled multi-band communication are two key
technologies to achieve very high data rates in beyond fifth generation (B5G)
wireless systems. We propose a joint optimization framework for such systems
where the mMIMO antenna spacing selection, precoder optimization, optimum
sub-carrier selection and optimum power allocation are carried out
simultaneously. We harness the bandwidth gain existing in a tightly coupled
base station mMIMO antenna system to avoid sophisticated, non-practical antenna
systems for multi-band operation. In particular, we analyze a multi-band
communication system using a circuit-theoretic model to consider physical
characteristics of a tightly coupled antenna array, and formulate a joint
optimization problem to maximize the sum-rate. As part of the optimization, we
also propose a novel block iterative water-filling-based sub-carrier selection
and power allocation optimization algorithm for the multi-band mMIMO system. A
novel sub-carrier windowing-based sub-carrier selection scheme is also proposed
which considers the physical constraints (hardware limitation) at the mobile
user devices. We carryout the optimizations in two ways: (i) to optimize the
antenna spacing selection in an offline manner, and (ii) to select antenna
elements from a dense array dynamically. Via computer simulations, we
illustrate superior bandwidth gains present in the tightly-coupled colinear and
rectangular planar antenna arrays, compared to the loosely-coupled or
tightly-coupled parallel arrays. We further show the optimum sum-rate
performance of the proposed optimization-based framework under various power
allocation schemes and various user capability scenarios.
