The problem of interference management is considered in the context of a linear interference network that is subject to long term channel fluctuations due to shadow fading. The fading model used is one where each link in the network is subject independently to erasure with probability p. It is assumed that each receiver in the network is interested in one unique message, which is made available at M transmitters. Optimal schemes from a Degrees of Freedom (DoF) viewpoint are analyzed for the setting of no erasures, and new schemes are proposed with better average DoF performance at higher probabilities of erasure. Additionally, for M=1, the average per user DoF is characterized for every value of p, and optimal message assignments are identified. For M>1, it is first established that there is no strategy for assigning messages to transmitters in networks that is optimal for all values of p. The optimal cooperative zero-forcing scheme for M=2 is then identified, and shown to be information-theoretically optimal when the size of the largest subnetwork that contains no erased links is at most five.
Channel state information (CSI) in systems with multiple antennas at both sides of the transmission link (multiple input multiple output, MIMO) is beneficial for many transmission schemes. However, a transceiver station can only estimate the channel transfer functions (CTFs) of the channels over which the received signals propagate which are different from the channels over which the transmitted signals will propagate in FDD systems. This paper shows a technique to obtain the CSI of the channels over which the transmitted signal will propagate based on the CSI of the channels over which the received signals propagate. By means of estimating the directions of arrival (DOAs) and times of arrival (TOAs), the shift of the previously estimated CSI to the CSI which cannot be estimated based on training signals can be calculated. The quality of the proposed algorithm depends on the quality of the parameter estimation. In scenarios with many scatterers the estimation of the DOAs and TOAs may not be precise enough or there may be paths with similar parameters which cannot be resolved. Thus, the proposed algorithm performs better in non-rich scattering environments. Having the channel state information of the channels over which the signals propagate from the transmitter to the receiver available at both sides of the transmission link is beneficial in many wireless applications. However, in frequency division duplex systems, a base station can only estimate the channel transfer function of the uplink channel based on the transmission of a-priori known training signals from the mobile station. A mobile station can only estimate the channel transfer function of the downlink channel based on the transmission of a-priori known training signals from the base station. Due to the frequency selective behavior of the mobile radio channel, the channel transfer functions of the uplink channel are different from the channel transfer functions of the downlink channel. In order to obtain the channel state information of the downlink channel in the base station or the channel state information of the uplink channel in the mobile station it is possible to feed back this information from the mobile station to the base station or from the base station to the mobile station. However, this feedback of the channel state information decreases the spectral efficiency. This paper introduces novel techniques to obtain the channel state information of the downlink channel in the base station based on the channel state information of the uplink channel in multiple antenna systems. Measurement results show the good performance of the investigated techniques. Thus, the signalling overhead can be reduced. 