  Cell-free massive multiple-input multiple-output (MIMO) is a potential key
technology for fifth generation wireless communication networks. A mixed
quality-of-service (QoS) problem is investigated in the uplink of a cell-free
massive MIMO system where the minimum rate of non-real time users is maximized
with per user power constraints whilst the rate of the real-time users (RTUs)
meet their target rates. First an approximated uplink user rate is derived
based on available channel statistics. Next, the original mixed QoS problem is
formulated in terms of receiver filter coefficients and user power allocations
which can iteratively be solved through two sub-problems, namely, receiver
filter coefficient design and power allocation, which are dealt with using a
generalized eigenvalue problem and geometric programming, respectively.
Numerical results show that with the proposed scheme, while the rates of RTUs
meet the QoS constraints, the $90\%$-likely throughput improves significantly,
compared to a simple benchmark scheme.
