5,711 research outputs found
Interference Alignment Through User Cooperation for Two-cell MIMO Interfering Broadcast Channels
This paper focuses on two-cell multiple-input multiple-output (MIMO) Gaussian
interfering broadcast channels (MIMO-IFBC) with cooperating users on the
cell-boundary of each BS. It corresponds to a downlink scenario for cellular
networks with two base stations (BSs), and users equipped with Wi-Fi
interfaces enabling to cooperate among users on a peer-to-peer basis. In this
scenario, we propose a novel interference alignment (IA) technique exploiting
user cooperation. Our proposed algorithm obtains the achievable degrees of
freedom (DoF) of 2K when each BS and user have transmit antennas and
receive antennas, respectively. Furthermore, the algorithm requires only
a small amount of channel feedback information with the aid of the user
cooperation channels. The simulations demonstrate that not only are the
analytical results valid, but the achievable DoF of our proposed algorithm also
outperforms those of conventional techniques.Comment: This paper will appear in IEEE GLOBECOM 201
Robust Lattice Alignment for K-user MIMO Interference Channels with Imperfect Channel Knowledge
In this paper, we consider a robust lattice alignment design for K-user
quasi-static MIMO interference channels with imperfect channel knowledge. With
random Gaussian inputs, the conventional interference alignment (IA) method has
the feasibility problem when the channel is quasi-static. On the other hand,
structured lattices can create structured interference as opposed to the random
interference caused by random Gaussian symbols. The structured interference
space can be exploited to transmit the desired signals over the gaps. However,
the existing alignment methods on the lattice codes for quasi-static channels
either require infinite SNR or symmetric interference channel coefficients.
Furthermore, perfect channel state information (CSI) is required for these
alignment methods, which is difficult to achieve in practice. In this paper, we
propose a robust lattice alignment method for quasi-static MIMO interference
channels with imperfect CSI at all SNR regimes, and a two-stage decoding
algorithm to decode the desired signal from the structured interference space.
We derive the achievable data rate based on the proposed robust lattice
alignment method, where the design of the precoders, decorrelators, scaling
coefficients and interference quantization coefficients is jointly formulated
as a mixed integer and continuous optimization problem. The effect of imperfect
CSI is also accommodated in the optimization formulation, and hence the derived
solution is robust to imperfect CSI. We also design a low complex iterative
optimization algorithm for our robust lattice alignment method by using the
existing iterative IA algorithm that was designed for the conventional IA
method. Numerical results verify the advantages of the proposed robust lattice
alignment method
Rate-Splitting for Max-Min Fair Multigroup Multicast Beamforming in Overloaded Systems
In this paper, we consider the problem of achieving max-min fairness amongst
multiple co-channel multicast groups through transmit beamforming. We
explicitly focus on overloaded scenarios in which the number of transmitting
antennas is insufficient to neutralize all inter-group interference. Such
scenarios are becoming increasingly relevant in the light of growing
low-latency content delivery demands, and also commonly appear in multibeam
satellite systems. We derive performance limits of classical beamforming
strategies using DoF analysis unveiling their limitations; for example, rates
saturate in overloaded scenarios due to inter-group interference. To tackle
interference, we propose a strategy based on degraded beamforming and
successive interference cancellation. While the degraded strategy resolves the
rate-saturation issue, this comes at a price of sacrificing all spatial
multiplexing gains. This motivates the development of a unifying strategy that
combines the benefits of the two previous strategies. We propose a beamforming
strategy based on rate-splitting (RS) which divides the messages intended to
each group into a degraded part and a designated part, and transmits a
superposition of both degraded and designated beamformed streams. The
superiority of the proposed strategy is demonstrated through DoF analysis.
Finally, we solve the RS beamforming design problem and demonstrate significant
performance gains through simulations
A Systematic Approach for Interference Alignment in CSIT-less Relay-Aided X-Networks
The degrees of freedom (DoF) of an X-network with M transmit and N receive
nodes utilizing interference alignment with the support of relays each
equipped with antennas operating in a half-duplex non-regenerative mode
is investigated. Conditions on the feasibility of interference alignment are
derived using a proper transmit strategy and a structured approach based on a
Kronecker-product representation. The advantages of this approach are twofold:
First, it extends existing results on the achievable DoF to generalized antenna
configurations. Second, it unifies the analysis for time-varying and constant
channels and provides valuable insights and interconnections between the two
channel models. It turns out that a DoF of \nicefrac{NM}{M+N-1} is feasible
whenever the sum of the
- …