  In small cell networks, high mobility of users results in frequent handoff
and thus severely restricts the data rate for mobile users. To alleviate this
problem, we propose to use heterogeneous, two-tier network structure where
static users are served by both macro and micro base stations, whereas the
mobile (i.e., moving) users are served only by macro base stations having
larger cells; the idea is to prevent frequent data outage for mobile users due
to handoff. We use the classical two-tier Poisson network model with different
transmit powers (cf [1]), assume independent Poisson process of static users
and doubly stochastic Poisson process of mobile users moving at a constant
speed along infinite straight lines generated by a Poisson line process. Using
stochastic geometry, we calculate the average downlink data rate of the typical
static and mobile (i.e., moving) users, the latter accounted for handoff outage
periods. We consider also the average throughput of these two types of users
defined as their average data rates divided by the mean total number of users
co-served by the same base station. We find that if the density of a
homogeneous network and/or the speed of mobile users is high, it is
advantageous to let the mobile users connect only to some optimal fraction of
BSs to reduce the frequency of handoffs during which the connection is not
assured. If a heterogeneous structure of the network is allowed, one can
further jointly optimize the mean throughput of mobile and static users by
appropriately tuning the powers of micro and macro base stations subject to
some aggregate power constraint ensuring unchanged mean data rates of static
users via the network equivalence property (see [2]).
