Sojourn time in a $M^{[X]}/M/1$ Processor Sharing Queue with batch arrivals (II)

For the $M^{[X]}/M/1$ processor Sharing queue with batch arrivals, the sojourn time $\Omega$ of a batch is investigated. We first show that the distribution of $\Omega$ can be generally obtained from an infinite linear differential system. When further assuming that the batch size has a geometric distribution with given parameter $q \in [0,1[$, this differential system is further analyzed by means of an associated bivariate generating function $(x,u,v) \mapsto E(x,u,v)$. Specifically, denoting by $s \mapsto E^*(s,u,v)$ the one-sided Laplace transform of $E(\cdot,u,v)$ and defining $$\Phi(s,u,v) = P(s,u) \, (1-v) \, F^*(s,u,uv), \quad 0 < \vert u \vert < 1, \, \vert v \vert < 1,$$ for some known polynomial $P(s,u)$ and where $$F^*(s,u,v) = \frac{E^*(s,u,v)-E^*(s,q,v)}{u-q},$$ we show that the function $\Phi$ verifies an inhomogeneous linear partial differential equation (PDE) $$\frac{\partial \Phi}{\partial u} - \left [ \frac{u - q}{P(s,u)} \right ] v(1-v) \, \frac{\partial \Phi}{\partial v} + \ell(s,u,v) = 0$$ for given $s$, where the last term $\ell(s,u,v)$ involves both $E^*(s,q,v)$ and the first order derivative $\partial E^*(s,q,v)/\partial v$ at the boundary point $u = q$. Solving this PDE for $\Phi$ via its characteristic curves and with the required analyticity properties eventually determines the one-sided Laplace transform $E^*$. By means of a Laplace inversion of this transform $E^*$, the distribution function of the sojourn time $\Omega$ of a batch is then given in an integral form. The tail behavior of the distribution of sojourn time $\Omega$ is finally derived.