In downlink cellular multiple users in multiple cells systems using beams, the should cooperate to generate beams to improve the spectrum efficiency. A mathematical model for the multi-cell multi-user downlink transmission is established, and the gradients of the variables including beamfonning filters, receiving filters and transmitting power are calculated. Then, a gradient-project-based cooperative beamforming scheme is proposed in which each user iteratively adjusts bearnforming variables in the direction of the gradients and projects onto feasible spaces. The information exchange protocol needed to support the scheme is also described. Simulation results show that the proposed scheme can achieve an average spectral efficiency of about 5 bit/（ s · Hz · cell）. The results show that cooperative beamforming can improve the spectrum efficiency of the cellular systems.
This paper investigates the multi-beam selection algorithms for transmit correlation channels by using statistical channel state information （SCSI） and instantaneous channel state information. Unlike the conventional codebook-based transmission scheme, the proposed multi-beam selection with the single channel quality indicator （CQI） feedback （MBS- SCF） algorithm determines the preferred beam vector by exploiting the SCSI and only feeds back CQI at each timeslot. The performance of the MBS-SCF algorithm is nearly the same as that of the conventional scheme. In order to further improve the average sum rate, a novel multi-beam selection with the dual CQIs feedback （MBS-DCF） algorithm is proposed, which determines dual preferred statistical eigen- directions and feeds back dual CQIs at each timeslot. The theoretical analysis and simulation results demonstrate that the MBS-DCF algorithm can increase the multiuser diversity and multiplexing gain and exhibits a higher average sum rate.
Based on the conflict graph model which is formulated as a binary integer optimization problem, a resource allocation method to support device-to-device （D2D） communications in ceUular networks is proposed. First, a frequency resource assignment algorithm is presented which assigns each D2D link one frequency resource block. For this algorithm, frequency resource blocks are assigned so that the frequency resource spatial reuse opportunities in the cellular networks can be fully exploited. Then a slot scheduling algorithm is presented which schedules time slots among D2D links assigned the same frequency resource block. For this algorithm, time slot resources are scheduled so that the proportional fairness among D2D links which are assigned the same frequency resource block can be achieved. The performance of the proposed method is evaluated via computer simulations. The simulation results show that the proposed method can well support D2D communications in cellular networks.
