ed to data transmission over the air, but increasing data traffic due to HSDPA or LTE is already a significant part of overall CAPEX and OPEX of a mobile radio system. T1/E1 lines with a data rate of a few megabits per second are quite common in current radio networks; required enhancements in this area are now a big challenge for MNOs. Generally, there are several options for providing broadband data connections to eNB sites over so-called S1 or between eNBs over so-called X2 interfaces as defined by 3GPP for LTE: Fibers are the most powerful technology and provide, in combination with GB Ethernet, almost 1 Gb/s or, in conjunction with so-called GPON sys- items, even several gigabits per second. A drawback is the typically high construction costs if fibers are not available. u-wave links are commonly used for NB site connections. Today, several mega- bits per second are typical, but, given enough spectra, several 100 Mb/s would be feasible. There are mainly two possible drawbacks: increasing HW expendi- tures for higher data rate links and relatively large delays for u-wave systems. An interesting alternative is optical free space feeder links, which might provide for distances well below the 1-km data rates of more than 1 Gb/s. Up to now, HW costs have been very high; however, given a larger usage of these systems, this might be changing in the future. For very high digital subscriber lines (VDSLs), digital spectrum manage- ment (DSM) level-3 techniques have been investigated to exploit existing wireline connections more effectively. Over short distances of a few hun- dred meters, several hundreds of megabits per second might be possible. Cooperative relaying combines cooperation gains with in-band wireless backbone functionality. This assumes optimum channel conditions for the first links from the serving NBs to neighboring NBRs SO that overall system performance loss due to in-band relaying is minimal. For this reason, LOS connections are assumed, which are further enhanced by directional anten- nas and MIMO 