725 research outputs found
Pilot Optimization and Channel Estimation for Multiuser Massive MIMO Systems
This paper proposes novel pilot optimization and channel estimation algorithm
for the downlink multiuser massive multiple input multiple output (MIMO) system
with decentralized single antenna mobile stations (MSs), and time division
duplex (TDD) channel estimation which is performed by utilizing pilot
symbols. The proposed algorithm is explained as follows. First, we formulate
the channel estimation problem as a weighted sum mean square error (WSMSE)
minimization problem containing pilot symbols and introduced variables. Second,
for fixed pilot symbols, the introduced variables are optimized using minimum
mean square error (MMSE) and generalized Rayleigh quotient methods. Finally,
for and settings, the pilot symbols of all MSs are optimized using
semi definite programming (SDP) convex optimization approach, and for the other
settings of and , the pilot symbols of all MSs are optimized by applying
simple iterative algorithm. When , it is shown that the latter iterative
algorithm gives the optimal pilot symbols achieved by the SDP method.
Simulation results confirm that the proposed algorithm achieves less WSMSE
compared to that of the conventional semi-orthogonal pilot symbol and MMSE
channel estimation algorithm which creates pilot contamination.Comment: Accepted in CISS 2014 Conferenc
Inter-micro-operator interference protection in dynamic TDD system
Abstract. This thesis considers the problem of weighted sum-rate maximization (WSRM) for a system of micro-operators subject to inter-micro-operator interference constraints with dynamic time division duplexing. The WSRM problem is non-convex and non-deterministic polynomial hard. Furthermore, micro-operators require minimum coordination among themselves making the inter-micro-operator interference management very challenging. In this regard, we propose two decentralized precoder design algorithm based on over-the-air bi-directional signalling strategy. We first propose a precoder design algorithm by considering the equivalent weighted minimum mean-squared error minimization reformulation of the WSRM problem. Later we propose precoder design algorithm by considering the weighted sum mean-squared error reformulation. In both approaches, to reduce the huge signalling requirements in centralized design, we use alternating direction method of multipliers technique, wherein each downlink-operator base station and uplink-operator user determines only the relevant set of transmit precoders by exchanging minimal information among the coordinating base stations and user equipments. To minimize the coordination between the uplink-opeator users, we propose interference budget allocation scheme based on reference signal measurements from downlink-operator users. Numerical simulations are provided to compare the performance of proposed algorithms with and without the inter-micro-operator interference constraints
Transceiver design for single-cell and multi-cell downlink multiuser MIMO systems
This thesis designs linear transceivers for the down link multiple user
multiple input multiple output single-cell and multiple-cell systems. The
transceivers are designed by assuming perfect and imperfect channel state
information at the BS and mobile stations (MS). Different signal to
interference plus noise ratio, mean square error and rate-based design criteria
are considered. These design criteria are formulated by considering total BS,
per BS antenna, per user, per symbol or a combination of per BS antenna and per
user (symbol) power constraints. To solve these problems generalized down link
up link and down link interference duality approaches are proposed.
We have also shown that the weighted sum rate maximization problem can be
equivalently formulated as weighted sum mean square error minimization problem
with additional optimization variables and constraints. We also develop
distributed transceiver design algorithms to solve weighted sum rate and mean
square error optimization problems for coordinated BS systems. The distributed
transceiver design algorithms employ modify matrix fractional minimization and
Lagrangian dual decomposition methods.Comment: PhD Thesi
Interference pricing mechanism for downlink multicell coordinated beamforming
We consider the downlink coordinated beamforming problem in a cellular network in which the base stations (BSs) are equipped with multiple antennas and each user is equipped with a single antenna. The BSs cooperate in sharing their local interference information, and they aim to maximize the sum-rate of the users in the network. A decentralized interference pricing beamforming (IPBF) algorithm is proposed to identify the coordinated beamformer, where a BS is penalized according to the interference it creates to its peers. We show that the decentralized pricing mechanism converges to an interference equilibrium, which is a KKT point of the sum-rate maximization problem. The proofs rely on the identification of rank-1 solutions of each BSs' interference-penalized rate maximization problem. Numerical results show that the proposed iterative mechanism reduces significantly the exchanged information with respect to other state-of-the-art beamforming algorithms with very little sum-rate loss. The version of the algorithm that limits the coordination to a cluster of base stations (IPBF-L) is shown to have very small sum-rate loss with respect to the full coordinated algorithm with much less backhaul information exchange.The work was partially supported by NSF grant CCF-1017982 and SICCNALS project (TEC2011-28219). The work of A. GarcĂa was partially supported by NSF grant CCF-1017982. A. GarcĂa-Armada’s work has been partially funded by research projects COMONSENS (CSD2008-00010) and GRE3N (TEC2011-29006-C03-02)Publicad
Precoder design for multi-antenna transmission in MU-MIMO with QoS requirements
Abstract. A multiple-input multiple-output (MIMO) interference broadcast channel (IBC) channel is considered. There are several base stations (BSs) transmitting useful information to their own users and unwanted interference to its neighboring BS users. Our main interest is to maximize the system throughput by designing transmit precoders with weighted sum rate maximization (WSRM) objective for a multi-user (MU)-MIMO transmission. In addition, we include the quality of service (QoS) requirement in terms of guaranteed minimum rate for the users in the system. Unfortunately, the problem considered is nonconvex and known to be non-deterministic polynomial (NP) hard. Therefore, to determine the transmit precoders, we first propose a centralized precoder design by considering two closely related approaches, namely, direct signal-to-interference-plus-noise-ratio (SINR) relaxation via sequential parametric convex approximation (SPCA), and mean squared error (MSE) reformulation. In both approaches, we adopt successive convex approximation (SCA) technique to solve the nonconvex optimization problem by solving a sequence of convex subproblems. Due to the huge signaling requirements in the centralized design, we propose two different distributed precoder designs, wherein each BS determines only the relevant set of transmit precoders by exchanging minimal information among the coordinating BSs. Initially, we consider designing precoders in a decentralized manner by using alternating directions method of multipliers (ADMM), wherein each BS relaxes inter-cell interference as an optimization variable by including it in the objective.
Then, we also propose a distributed precoder design by solving the Karush-Kuhn-Tucker (KKT) expressions corresponding to the centralized problems. Numerical simulations are provided to compare different system configurations with QoS constraints for both centralized and distributed algorithms
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