  The design of cell-free massive MIMO (CF-mMIMO) systems requires accurate,
measurement-based channel models. This paper provides the first results from
the by far most extensive outdoor measurement campaign for CF-mMIMO channels in
an urban environment. We measured impulse responses between over 20,000
potential access point (AP) locations and 80 user equipments (UEs) at 3.5 GHz
with 350 MHz bandwidth (BW). Measurements use a "virtual array" approach at the
AP and a hybrid switched/virtual approach at the UE. This paper describes the
sounder design, measurement environment, data processing, and sample results,
particularly the evolution of the power-delay profiles (PDPs) as a function of
the AP locations, and its relation to the propagation environment.
