Tommi Koivisto

Design and Evaluation of LTE-Advanced Double Codebook

In this paper we address codebook design for LTE-Advanced downlink. In order to meet the peak spectral efficiency requirements of up to 30 bit/s/Hz, LTE-Advanced supports up to eight transmit antennas in downlink, enabling spatial multiplexing transmissions with up to eight parallel streams. In addition to high-order single-user (SU-) MIMO transmissions, LTE-Advanced provides state-of-the-art multi-user (MU-) MIMO support with seamless operation between SU-MIMO and MU-MIMO. Codebook design is the basis of such precoded closed-loop multi-antenna schemes. We investigate multiple options for LTE-Advanced codebook design, providing a solution flexible enough to support both single-user and multi-user operation as well as different base station antenna setups while taking into account practical system design constraints. We provide thorough codebook performance evaluation in realistic LTE-Advanced system scenarios.

Network-Assisted Widely Linear Receivers for LTE

In order to improve cell-edge performance in LTE downlink, several techniques (e.g., Coordinated multi-point transmission) are investigated in the literature which rely on coordination of transmitting nodes without further optimization of receiver algorithms. This paper introduces a new coordination method where the radio network coordinates its transmitted modulation alphabet to assist a widely-linear MMSE (WL-MMSE) receiver to mitigate more effectively the received interference. Assistance from the network ensures that a WL-MMSE receiver is exposed to PAM-type interference which is afterwards mitigated. The technique exploits the fact that complex-valued baseband received samples are split in in-phase (I) and quadrature-phase (Q) parts. These I-Q samples are filtered independently using widely-linear processing. Consequently, better signal estimation is achieved under conditions of PAM-type interference as it is shown by the available literature in widely linear filtering. Finally, simulation results for the introduced scheme show up to 88% coverage gain.