  Distributed Multiple-Input and Multiple-Output (D-MIMO) is envisioned to play
a significant role in future wireless communication systems as an effective
means to improve coverage and capacity. In this paper, we have studied the
impact of a practical two-level data routing scheme on radio performance in a
downlink D-MIMO scenario with segmented fronthaul. At the first level, a
Distributed Unit (DU) is connected to the Aggregating Radio Units (ARUs) that
behave as cluster heads for the selected serving RU groups. At the second
level, the selected ARUs connect with the additional serving RUs. At each route
discovery level, RUs and/or ARUs share information with each other. The aim of
the proposed framework is to efficiently select serving RUs and ARUs so that
the practical data routing impact for each User Equipment (UE) connection is
minimal. The resulting post-routing Signal-to-Interference plus Noise Ratio
(SINR) among all UEs is analyzed after the routing constraints have been
applied. The results show that limited fronthaul segment capacity causes
connection failures with the serving RUs of individual UEs, especially when
long routing path lengths are required. Depending on whether the failures occur
at the first or the second routing level, a UE may be dropped or its SINR may
be reduced. To minimize the DU-ARU connection failures, the segment capacity of
the segments closest to the DU is set as double as the remaining segments. When
the number of active co-scheduled UEs is kept low enough, practical segment
capacities suffice to achieve a zero UE dropping rate. Besides, the proper
choice of maximum path length setting should take into account segment capacity
and its utilization due to the relation between the two.
