186 research outputs found
Joint Beamforming and Power Control in Coordinated Multicell: Max-Min Duality, Effective Network and Large System Transition
This paper studies joint beamforming and power control in a coordinated
multicell downlink system that serves multiple users per cell to maximize the
minimum weighted signal-to-interference-plus-noise ratio. The optimal solution
and distributed algorithm with geometrically fast convergence rate are derived
by employing the nonlinear Perron-Frobenius theory and the multicell network
duality. The iterative algorithm, though operating in a distributed manner,
still requires instantaneous power update within the coordinated cluster
through the backhaul. The backhaul information exchange and message passing may
become prohibitive with increasing number of transmit antennas and increasing
number of users. In order to derive asymptotically optimal solution, random
matrix theory is leveraged to design a distributed algorithm that only requires
statistical information. The advantage of our approach is that there is no
instantaneous power update through backhaul. Moreover, by using nonlinear
Perron-Frobenius theory and random matrix theory, an effective primal network
and an effective dual network are proposed to characterize and interpret the
asymptotic solution.Comment: Some typos in the version publised in the IEEE Transactions on
Wireless Communications are correcte
Joint Downlink Base Station Association and Power Control for Max-Min Fairness: Computation and Complexity
In a heterogeneous network (HetNet) with a large number of low power base
stations (BSs), proper user-BS association and power control is crucial to
achieving desirable system performance. In this paper, we systematically study
the joint BS association and power allocation problem for a downlink cellular
network under the max-min fairness criterion. First, we show that this problem
is NP-hard. Second, we show that the upper bound of the optimal value can be
easily computed, and propose a two-stage algorithm to find a high-quality
suboptimal solution. Simulation results show that the proposed algorithm is
near-optimal in the high-SNR regime. Third, we show that the problem under some
additional mild assumptions can be solved to global optima in polynomial time
by a semi-distributed algorithm. This result is based on a transformation of
the original problem to an assignment problem with gains , where
are the channel gains.Comment: 24 pages, 7 figures, a shorter version submitted to IEEE JSA
Joint Power Allocation and User Association Optimization for Massive MIMO Systems
This paper investigates the joint power allocation and user association
problem in multi-cell Massive MIMO (multiple-input multiple-output) downlink
(DL) systems. The target is to minimize the total transmit power consumption
when each user is served by an optimized subset of the base stations (BSs),
using non-coherent joint transmission. We first derive a lower bound on the
ergodic spectral efficiency (SE), which is applicable for any channel
distribution and precoding scheme. Closed-form expressions are obtained for
Rayleigh fading channels with either maximum ratio transmission (MRT) or zero
forcing (ZF) precoding. From these bounds, we further formulate the DL power
minimization problems with fixed SE constraints for the users. These problems
are proved to be solvable as linear programs, giving the optimal power
allocation and BS-user association with low complexity. Furthermore, we
formulate a max-min fairness problem which maximizes the worst SE among the
users, and we show that it can be solved as a quasi-linear program. Simulations
manifest that the proposed methods provide good SE for the users using less
transmit power than in small-scale systems and the optimal user association can
effectively balance the load between BSs when needed. Even though our framework
allows the joint transmission from multiple BSs, there is an overwhelming
probability that only one BS is associated with each user at the optimal
solution.Comment: 16 pages, 12 figures, Accepted by IEEE Trans. Wireless Commu
Coordinated multicell beamforming with local and global data rate constraints
© 2016 IEEE.We propose optimization techniques for coordinated multi-cell beamforming in the presence of local users and a global user. The local users are served by only the corresponding basestation (BS) while the global user is served by multiple basestations. The global user, with the aid of multiple antennas, is able to decode multiple data streams transmitted by various transmitters through singular value decomposition of the channels at the receiver and using left dominant singular vectors as the receiver beamforming. The coordinating basestations employ semidefinite programing based transmitter beamforming and agree to perform optimum data rate split for the global user in order to minimise the transmission power
Large System Analysis of Base Station Cooperation for Power Minimization
This work focuses on a large-scale multi-cell multi-user MIMO system in which
base stations (BSs) of antennas each communicate with
single-antenna user equipments. We consider the design of the linear precoder
that minimizes the total power consumption while ensuring target user rates.
Three configurations with different degrees of cooperation among BSs are
considered: the coordinated beamforming scheme (only channel state information
is shared among BSs), the coordinated multipoint MIMO processing technology or
network MIMO (channel state and data cooperation), and a single cell
beamforming scheme (only local channel state information is used for
beamforming while channel state cooperation is needed for power allocation).
The analysis is conducted assuming that and grow large with a non
trivial ratio and imperfect channel state information (modeled by the
generic Gauss-Markov formulation form) is available at the BSs. Tools of random
matrix theory are used to compute, in explicit form, deterministic
approximations for: (i) the parameters of the optimal precoder; (ii) the powers
needed to ensure target rates; and (iii) the total transmit power. These
results are instrumental to get further insight into the structure of the
optimal precoders and also to reduce the implementation complexity in
large-scale networks. Numerical results are used to validate the asymptotic
analysis in the finite system regime and to make comparisons among the
different configurations.Comment: 32 pages, 6 figures, to appear IEEE Trans. Wireless Commun. A
preliminary version of this paper was presented at the IEEE Global
Communication Conference, San Diego, USA, Dec. 201
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