Research On High Energy-efficient Distributed Antenna System

Distributed antenna system (DAS), is a new wireless network, consists of spatiallyseparated antenna nodes including contral antenna unit (CAU) and remote antenna unit(RAU). In DAS, the RAUs are distributed geographically apart and connected via opticalfiber, to the CAU which is responsible for the primary signal processing. Widely separatelyantenn units contributed to the shorter access distances between the transmitter and receiver.Moreover, DAS has the merits of better coverage in contrast with the co-locatedmultiplut-input and multiplut-output (C-MIMO). Although the DAS was originally proposedto cover the indoor dead point, recently studies identified that DAS had many advantagessuch as higher capacity and better spectral efficiency and higher diversity. Now, thecoordinated multipoint (CoMP) based on DAS has been adopted by3GPP in theLTE-Advance. Moreover, DAS shows better power and spectral efficient comparing with thestate of art solutions such as mirco cell and femtocell.Nowadays, the seamless and ubiquitous wireless communiation has enhanced the quality ofour everyday life. However, this blanket wireless service comes at the cost of ever-increasinghigh power consumption and CO2emission. The growing conerng over the powerconsumption has triggered the research on green wireless communication. Therefore thepower-efficient techniques in wirelss communications are receiving considerable researchattention. Motivated by these observations, this paper focus on the power efficient techniquesin DAS, specifically, we aim to the minmize the transmit power of all the antenna nodes inmulticell DAS, while fulfill the quality of service (QoS) of all the mobile users. It is alsoreferred to as power control problems in what follows. Compared with the existing studies onDAS, the main contributions of this paper are following:Quasi-static power control for multicell DAS:We propose two robust-beamforming schemes for downlink of multi-cell DAS. One isbased on S-procedure; the other is based on Bernstein ineqaulity, which is suitable for signalcell C-MIMO.We first formulate our problem as a SDP and then prove the solution of this SDP isalways rank-one which guarantees the relaxation is tight, i.e. the optimal solution of relaxproblem is equivalent to the original problem.Considering channel state information at transmitter (CSIT) error, the most robust andenergy efficient AS scheme subject to QoS guarantee for all the users in multiccell DAS, ismade through extensive simulations. Dynamic power control for multicell DAS:Assuming the channel changes continuously, CSI is firstly modeled by employingstochastic differential equation (SDE). The considered dynamic beamforming problem is thentransformed into stabilization for SDE using primal-dual interior point (PDIP) method forsemidefinite program (SDP). By exploiting the theory of stochastic stability, the proposedmethod can be shown to be asymmetrically stable in the sense of probability.Using the channel prediction methods (such as Berg, modified convriance), the proposedmethods can be extened to the delayed CSI cenarios.Dynamic system performance of multicell DAS:Considering the delay of CSIT in the presence of pathloss, we analysis the systemperformance of DAS. In particular, we derive the closed-form outage probability undernoise-limied and unequal power CCI cenarios. Monte Carlo simulations verify our analysis.