402 research outputs found
Interference Cancellation trough Interference Alignment for Downlink of Cognitive Cellular Networks
In this letter, we propose the interference cancellation through interference
alignment at the downlink of cognitive cellular networks. Interference
alignment helps the spatial resources to be shared among primary and secondary
cells and thus, it can provide higher degrees of freedom through interference
cancellation. We derive and depict the achievable degrees of freedom. We also
analyse and calculate the achievable sum rates applying water-filling optimal
power allocation
-Box Optimization for Green Cloud-RAN via Network Adaptation
In this paper, we propose a reformulation for the Mixed Integer Programming
(MIP) problem into an exact and continuous model through using the -box
technique to recast the binary constraints into a box with an sphere
constraint. The reformulated problem can be tackled by a dual ascent algorithm
combined with a Majorization-Minimization (MM) method for the subproblems to
solve the network power consumption problem of the Cloud Radio Access Network
(Cloud-RAN), and which leads to solving a sequence of Difference of Convex (DC)
subproblems handled by an inexact MM algorithm. After obtaining the final
solution, we use it as the initial result of the bi-section Group Sparse
Beamforming (GSBF) algorithm to promote the group-sparsity of beamformers,
rather than using the weighted -norm. Simulation results
indicate that the new method outperforms the bi-section GSBF algorithm by
achieving smaller network power consumption, especially in sparser cases, i.e.,
Cloud-RANs with a lot of Remote Radio Heads (RRHs) but fewer users.Comment: 4 pages, 4 figure
Retrospective Interference Alignment for the 3-user MIMO Interference Channel with delayed CSIT
The degrees of freedom (DoF) of the 3-user multiple input multiple output
interference channel (3-user MIMO IC) are investigated where there is delayed
channel state information at the transmitters (dCSIT). We generalize the ideas
of Maleki et al. about {\it Retrospective Interference Alignment (RIA)} to be
applied to the MIMO IC, where transmitters and receivers are equipped with
antennas, respectively. We propose a two-phase transmission scheme
where the number of slots per phase and number of transmitted symbols are
optimized by solving a maximization problem. Finally, we review the existing
achievable DoF results in the literature as a function of the ratio between
transmitting and receiving antennas . The proposed scheme improves
all other strategies when .Comment: Draft version of the accepted manuscript at IEEE ICASSP 1
On the Degrees of freedom of the K-user MISO Interference Channel with imperfect delayed CSIT
This work investigates the degrees of freedom (DoF) of the K-user
multiple-input single-output (MISO) interference channel (IC) with imperfect
delayed channel state information at the transmitters (dCSIT). For this
setting, new DoF inner bonds are provided, and benchmarked with
cooperation-based outer bounds. The achievability result is based on a
precoding scheme that aligns the interfering received signals through time,
exploiting the concept of Retrospective Interference Alignment (RIA). The
proposed approach outperforms all previous known schemes. Furthermore, we study
the proposed scheme under channel estimation errors (CEE) on the reported
dCSIT, and derive a closed-form expression for the achievable DoF with
imperfect dCSIT.Comment: Draft version of the accepted manuscript at IEEE ICASSP 1
Sum-Rate Analysis for High Altitude Platform (HAP) Drones with Tethered Balloon Relay
High altitude platform (HAP) drones can provide broadband wireless
connectivity to ground users in rural areas by establishing line-of-sight (LoS)
links and exploiting effective beamforming techniques. However, at high
altitudes, acquiring the channel state information (CSI) for HAPs, which is a
key component to perform beamforming, is challenging. In this paper, by
exploiting an interference alignment (IA) technique, a novel method for
achieving the maximum sum-rate in HAP-based communications without CSI is
proposed. In particular, to realize IA, a multiple-antenna tethered balloon is
used as a relay between multiple HAP drones and ground stations (GSs). Here, a
multiple-input multiple-output X network system is considered. The capacity of
the considered M*N X network with a tethered balloon relay is derived in
closed-form. Simulation results corroborate the theoretical findings and show
that the proposed approach yields the maximum sum-rate in multiple HAPs-GSs
communications in absence of CSI. The results also show the existence of an
optimal balloon's altitude for which the sum-rate is maximized.Comment: Accepted in IEEE Communications Letter
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