Spectrum Sharing by Space-Time Waveform Shaping

TL;DR

This work tackles spectrum sharing by designing a dynamic MIMO link that coexists in an occupied band through joint space-time waveform shaping. By optimizing the transmit beam weights and time-domain pulse code sequence to minimize energy per symbol while enforcing a pre-detection SINR, the approach achieves interference avoidance and protection of existing links using the occupancy autocorrelation $O_{f_c}$. A closed-form solution is derived for fixed waveform components and a practical search-based method is provided for the joint optimization, with an algorithmic outline (Algorithm 1). Numerical results in light and heavily congested bands show substantial SINR and energy efficiency gains for the joint space-time waveform compared to space-only, time-only, and non-adaptive schemes, with larger gains as code length increases. The findings suggest strong practical potential for autonomous spectrum sharing in dense wireless environments, particularly for high-dimensional MIMO configurations.

Abstract

In this paper, we consider the task of introducing a new wireless data link over a given occupied frequency band using a multi-antenna transmitter and receiver. We design formally a dynamic multiple-input multiple-output (MIMO) wireless link that can coexist in the fixed congested frequency band by (a) optimally avoiding sensed interference in the joint space-time domain, and (b) protecting existing links by minimizing its own transmitted power in the band. In particular, the transmit beam weight vector and time domain pulse code sequence are jointly optimized to minimize the transmit energy per bit per antenna, while maintaining a pre-defined signal-to-interference-plus-noise ratio (SINR) at the output of the joint space-time maximum SINR receiver filter. Extensive numerical studies are carried out to demonstrate the derived algorithmic solution in light and heavily congested band scenarios with non-cooperative co-channel links. We show that the proposed autonomously reconfigurable 4x4 MIMO link outperforms a non-adaptive transceiver and other forms of waveform shaping in terms of the pre-detection SINR performance and the capability to protect ongoing non-cooperative links by not occupying the band with redundant transmissions.

Figures (2)

• Figure 1: Pre-detection SINR of $4\times 4$ optimal waveform shaping MIMO system ($\gamma =18$ dB): (a) $L=4$, (b) $L=8$.
• Figure 2: Optimal total transmit energy per symbol over ${{N}_{0}}$ ($4\times 4$, $\gamma =18$ dB): (a) $L=4$, (b) $L=8$.