  Delivering Gbps high user rate over long distances (around 1 km) is
challenging, and the abundant spectrum available in millimeter wave band cannot
solve the challenge by its own due to the severe path loss and other
limitations. Since it is economically challenging to deploy wired backhaul
every few hundred meters, relays (e.g., wireless access points) have been
proposed to extend the coverage of a base station which has wired connection to
the core network. These relays, deployed every few hundred meters, serve the
users in their vicinity and are backhauled to the base station through wireless
connections. In this work, the wireless relayed backhaul design has been
formulated as a topology-bandwidth-power joint optimization problem, and the
influence of path loss, angular spread, array size, and RF power limitation on
the user rate has been evaluated. It has been shown that for a linear network
deployed along the street at 28 GHz, when high joint directional gain (50 dBi)
is available, 1 Gbps user rate within cell range of 1 km can be delivered using
1.5 GHz of bandwidth (using single polarization antennas). The user rates drop
precipitously when joint directional gain is reduced, or when the path loss is
much more severe. When the number of RF chains is limited, the benefit of
larger arrays will eventually be surpassed by the increased channel estimation
penalty as the effective beamforming gain saturates owing to the channel
angular spread.
