Power efficient CDMA broadcast system doing without any channel knowledge at the receivers, a nonobvious modification of THP

For CDMA broadcast transmission recently the linear receiver oriented scheme transmit zero forcing (TxZF) was proposed, in which the receiver algorithms are a priori determined, whereas the transmitter algorithms follow a posteriori. A main asset of this scheme is its low receiver complexity. In addition, it does without sacrificing downlink transmission resources to training signals for channel estimation, which is beneficial for capacity, and its combination with MlMO antenna structures is straightforward. A nonlinear modification of the scheme TxZF termed transmit nonlinear zero forcing (TxNZF) is presented with a view to reduce the required transmit power considerably, a feature mitigating intercell interference in cellular systems and, thereby, further enhancing capacity, and being also attractive with respect to the growing electro-phobia of the public. The crux of TxNZF consists in using multiply connected decision regions in the detectors of the receivers and in advantageously selecting the partial decision regions from the possible set of such regions depending on the messages to be transmitted. TxNZF is particularly effective in the case of relatively large attenuation differences of the channels between the transmitter and the individual receivers. The envisaged practical application of the scheme TxNZF are CDMA mobile radio downlinks. In such systems due to shadowing and to largely different distances between the base station and the mobile terminals, large attenuation differences prevail. The ideas presented in this paper are related to the well known concept of Tomlinson-Harashuna precoding (THP).