1,988 research outputs found
System level modeling and evaluation of advanced linear interference aware receivers
To cope with the growth of data traffic through mobile networks, efficient utilization of the available radio spectrum is needed. In densely deployed radio networks, User Equipments (UE) will experience high levels of interference which limits the achievable spectral efficiency. In this case, a way to improve the achievable performance is by mitigating interference at the UE side.
Advanced linear interference aware receivers are linear receivers able to mitigate external co-channel interference. Optimum linear interference rejection is obtained with the Interference Rejection Combining (IRC) receiver which relies on the ideal knowledge of the interference covariance matrix. The IRC interference covariance matrix is the sum of all interference channel covariance matrices. In practical radio networks, like LTE-Advanced, the knowledge of interference channel covariance matrices might not always be available. However, the IRC interference covariance matrix estimation can be done with a data-based or reference-symbol-based interference covariance matrix estimation algorithm.
In this thesis, the modeling and evaluation of advanced linear interference aware receivers for LTE-Advanced downlink are studied. In particular, the data-based and reference-symbol-based covariance matrix estimation algorithms are modeled by using the Wishart distribution. This modeling allows the evaluation of advanced linear receivers without explicit need for baseband signals. The evaluation is done with a system level simulator. Later, a comparison of performance between advanced linear interference aware receivers and 3GPP baseline linear receivers for multiple homogeneous and heterogeneous deployment scenarios is presented.
Finally, it is shown that advanced linear interference aware receivers can provide spectral efficiency improvements specially to UEs located at cell borders
A Practical Cooperative Multicell MIMO-OFDMA Network Based on Rank Coordination
An important challenge of wireless networks is to boost the cell edge
performance and enable multi-stream transmissions to cell edge users.
Interference mitigation techniques relying on multiple antennas and
coordination among cells are nowadays heavily studied in the literature.
Typical strategies in OFDMA networks include coordinated scheduling,
beamforming and power control. In this paper, we propose a novel and practical
type of coordination for OFDMA downlink networks relying on multiple antennas
at the transmitter and the receiver. The transmission ranks, i.e.\ the number
of transmitted streams, and the user scheduling in all cells are jointly
optimized in order to maximize a network utility function accounting for
fairness among users. A distributed coordinated scheduler motivated by an
interference pricing mechanism and relying on a master-slave architecture is
introduced. The proposed scheme is operated based on the user report of a
recommended rank for the interfering cells accounting for the receiver
interference suppression capability. It incurs a very low feedback and backhaul
overhead and enables efficient link adaptation. It is moreover robust to
channel measurement errors and applicable to both open-loop and closed-loop
MIMO operations. A 20% cell edge performance gain over uncoordinated LTE-A
system is shown through system level simulations.Comment: IEEE Transactions or Wireless Communications, Accepted for
Publicatio
Advanced Coordinated Beamforming for the Downlink of Future LTE Cellular Networks
Modern cellular networks in traditional frequency bands are notoriously
interference-limited especially in urban areas, where base stations are
deployed in close proximity to one another. The latest releases of Long Term
Evolution (LTE) incorporate features for coordinating downlink transmissions as
an efficient means of managing interference. Recent field trial results and
theoretical studies of the performance of joint transmission (JT) coordinated
multi-point (CoMP) schemes revealed, however, that their gains are not as high
as initially expected, despite the large coordination overhead. These schemes
are known to be very sensitive to defects in synchronization or information
exchange between coordinating bases stations as well as uncoordinated
interference. In this article, we review recent advanced coordinated
beamforming (CB) schemes as alternatives, requiring less overhead than JT CoMP
while achieving good performance in realistic conditions. By stipulating that,
in certain LTE scenarios of increasing interest, uncoordinated interference
constitutes a major factor in the performance of CoMP techniques at large, we
hereby assess the resilience of the state-of-the-art CB to uncoordinated
interference. We also describe how these techniques can leverage the latest
specifications of current cellular networks, and how they may perform when we
consider standardized feedback and coordination. This allows us to identify
some key roadblocks and research directions to address as LTE evolves towards
the future of mobile communications.Comment: 16 pages, 6 figures, accepted to IEEE Communications Magazin
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