Paper Submitted to IEEE Transactions on Wireless Communications

We submitted a new paper to IEEE Transactions on Wireless Communications:

Multi-Functional Diversity via Flexible Spatial Partitioning for Massive MIMO ISAC

Evangelos Vlachos and Aryan Kaushik

In massive MIMO ISAC systems, conventional contiguous sub-array partitioning limits spatial degrees of freedom. This work introduces multi-functional selection diversity — a new gain mechanism that arises from assigning spatial beams to communication and radar based on their long-term channel statistics.

Key contributions:

• Scaling laws: We prove that the dominant diversity component — spatial decoupling (leakage avoidance) — scales as log(N) with the array size, while signal alignment saturates.
• DASP algorithm: A covariance-only framework that solves the combinatorial beam assignment with O(N log N) complexity, eliminating the need for instantaneous CSI.
• Regime analysis: An analytical SNR threshold demarcating when spatial partitioning outperforms orthogonal resource slicing (e.g., TDM). Standard mmWave link budgets fall firmly in the partitioning-favorable regime.

Numerical results with up to 256 antennas confirm that flexible interleaved partitioning nearly doubles the spectral efficiency of resource slicing and strictly dominates contiguous sub-array approaches.