  A novel approach to global gyrokinetic simulation is implemented in the
flux-tube code $\texttt{stella}$. This is done by using a subsidiary expansion
of the gyrokinetic equation in the perpendicular scale length of the
turbulence, originally derived by Parra and Barnes [Plasma Phys. Controlled
Fusion, $\textbf{57}$ 054003, 2015], which allows the use of Fourier basis
functions while enabling the effect of radial profile variation to be included
in a perturbative way. Radial variation of the magnetic geometry is included by
utilizing a global extension of the Grad-Shafranov equation and the Miller
equilibrium equations which is obtained through Taylor expansion. Radial
boundary conditions that employ multiple flux-tube simulations are also
developed, serving as a more physically motivated replacement to the
conventional Dirichlet radial boundary conditions that are used in global
simulation. It is shown that these new boundary conditions eliminate much of
the numerical artefacts generated near the radial boundary when expressing a
non-periodic function using a spectral basis. We then benchmark the new
approach both linearly and nonlinearly using a number of standard test cases.
