20 research outputs found
On the Achievability of Interference Alignment in the K-User Constant MIMO Interference Channel
Interference alignment in the K-user MIMO interference channel with constant
channel coefficients is considered. A novel constructive method for finding the
interference alignment solution is proposed for the case where the number of
transmit antennas equals the number of receive antennas (NT = NR = N), the
number of transmitter-receiver pairs equals K = N + 1, and all interference
alignment multiplexing gains are one. The core of the method consists of
solving an eigenvalue problem that incorporates the channel matrices of all
interfering links. This procedure provides insight into the feasibility of
signal vector spaces alignment schemes in finite dimensional MIMO interference
channels.Comment: submitted to IEEE Workshop on Statistical Signal Processing (SSP09
Maximizing the Sum Rate in Cellular Networks Using Multi-Convex Optimization
In this paper, we propose a novel algorithm to maximize the sum rate in
interference-limited scenarios where each user decodes its own message with the
presence of unknown interferences and noise considering the
signal-to-interference-plus-noise-ratio. It is known that the problem of
adapting the transmit and receive filters of the users to maximize the sum rate
with a sum transmit power constraint is non-convex. Our novel approach is to
formulate the sum rate maximization problem as an equivalent multi-convex
optimization problem by adding two sets of auxiliary variables. An iterative
algorithm which alternatingly adjusts the system variables and the auxiliary
variables is proposed to solve the multi-convex optimization problem. The
proposed algorithm is applied to a downlink cellular scenario consisting of
several cells each of which contains a base station serving several mobile
stations. We examine the two cases, with or without several half-duplex
amplify-and-forward relays assisting the transmission. A sum power constraint
at the base stations and a sum power constraint at the relays are assumed.
Finally, we show that the proposed multi-convex formulation of the sum rate
maximization problem is applicable to many other wireless systems in which the
estimated data symbols are multi-affine functions of the system variables.Comment: 24 pages, 5 figure
MIMO Interference Alignment Over Correlated Channels with Imperfect CSI
Interference alignment (IA), given uncorrelated channel components and
perfect channel state information, obtains the maximum degrees of freedom in an
interference channel. Little is known, however, about how the sum rate of IA
behaves at finite transmit power, with imperfect channel state information, or
antenna correlation. This paper provides an approximate closed-form
signal-to-interference-plus-noise-ratio (SINR) expression for IA over
multiple-input-multiple-output (MIMO) channels with imperfect channel state
information and transmit antenna correlation. Assuming linear processing at the
transmitters and zero-forcing receivers, random matrix theory tools are
utilized to derive an approximation for the post-processing SINR distribution
of each stream for each user. Perfect channel knowledge and i.i.d. channel
coefficients constitute special cases. This SINR distribution not only allows
easy calculation of useful performance metrics like sum rate and symbol error
rate, but also permits a realistic comparison of IA with other transmission
techniques. More specifically, IA is compared with spatial multiplexing and
beamforming and it is shown that IA may not be optimal for some performance
criteria.Comment: 21 pages, 7 figures, submitted to IEEE Transactions on Signal
Processin
Dynamic Interference Mitigation for Generalized Partially Connected Quasi-static MIMO Interference Channel
Recent works on MIMO interference channels have shown that interference
alignment can significantly increase the achievable degrees of freedom (DoF) of
the network. However, most of these works have assumed a fully connected
interference graph. In this paper, we investigate how the partial connectivity
can be exploited to enhance system performance in MIMO interference networks.
We propose a novel interference mitigation scheme which introduces constraints
for the signal subspaces of the precoders and decorrelators to mitigate "many"
interference nulling constraints at a cost of "little" freedoms in precoder and
decorrelator design so as to extend the feasibility region of the interference
alignment scheme. Our analysis shows that the proposed algorithm can
significantly increase system DoF in symmetric partially connected MIMO
interference networks. We also compare the performance of the proposed scheme
with various baselines and show via simulations that the proposed algorithms
could achieve significant gain in the system performance of randomly connected
interference networks.Comment: 30 pages, 10 figures, accepted by IEEE Transaction on Signal
Processin
User Arrival in MIMO Interference Alignment Networks
In this paper we analyze a constant multiple-input multiple-output
interference channel where a set of active users are cooperating through
interference alignment while a set of secondary users desire access to the
channel. We derive the minimum number of secondary transmit antennas required
so that a secondary user can use the channel without affecting the sum rate of
the active users, under a zero-forcing equalization assumption. When the
secondary users have enough antennas, we derive several secondary user
precoders that approximately maximize the secondary users' sum rate without
changing the sum rate of the active users. When the secondary users do not have
enough antennas, we perform numerical optimization to find secondary user
precoders that cause minimum degradation to the sum rate of the active users.
Through simulations, we confirm that i) with enough antennas at the secondary
users, gains equivalent to the case of all the users cooperating through
interference alignment is obtainable, and ii) when the secondary users do not
have enough antennas, large rate losses at the active users can be avoided.Comment: 17 pages, 6 figures, submitted to IEEE Transactions on Wireless
Communication