209 research outputs found
Elements of Cellular Blind Interference Alignment --- Aligned Frequency Reuse, Wireless Index Coding and Interference Diversity
We explore degrees of freedom (DoF) characterizations of partially connected
wireless networks, especially cellular networks, with no channel state
information at the transmitters. Specifically, we introduce three fundamental
elements --- aligned frequency reuse, wireless index coding and interference
diversity --- through a series of examples, focusing first on infinite regular
arrays, then on finite clusters with arbitrary connectivity and message sets,
and finally on heterogeneous settings with asymmetric multiple antenna
configurations. Aligned frequency reuse refers to the optimality of orthogonal
resource allocations in many cases, but according to unconventional reuse
patterns that are guided by interference alignment principles. Wireless index
coding highlights both the intimate connection between the index coding problem
and cellular blind interference alignment, as well as the added complexity
inherent to wireless settings. Interference diversity refers to the observation
that in a wireless network each receiver experiences a different set of
interferers, and depending on the actions of its own set of interferers, the
interference-free signal space at each receiver fluctuates differently from
other receivers, creating opportunities for robust applications of blind
interference alignment principles
Joint Scheduling and ARQ for MU-MIMO Downlink in the Presence of Inter-Cell Interference
User scheduling and multiuser multi-antenna (MU-MIMO) transmission are at the
core of high rate data-oriented downlink schemes of the next-generation of
cellular systems (e.g., LTE-Advanced). Scheduling selects groups of users
according to their channels vector directions and SINR levels. However, when
scheduling is applied independently in each cell, the inter-cell interference
(ICI) power at each user receiver is not known in advance since it changes at
each new scheduling slot depending on the scheduling decisions of all
interfering base stations. In order to cope with this uncertainty, we consider
the joint operation of scheduling, MU-MIMO beamforming and Automatic Repeat
reQuest (ARQ). We develop a game-theoretic framework for this problem and build
on stochastic optimization techniques in order to find optimal scheduling and
ARQ schemes. Particularizing our framework to the case of "outage service
rates", we obtain a scheme based on adaptive variable-rate coding at the
physical layer, combined with ARQ at the Logical Link Control (ARQ-LLC). Then,
we present a novel scheme based on incremental redundancy Hybrid ARQ (HARQ)
that is able to achieve a throughput performance arbitrarily close to the
"genie-aided service rates", with no need for a genie that provides
non-causally the ICI power levels. The novel HARQ scheme is both easier to
implement and superior in performance with respect to the conventional
combination of adaptive variable-rate coding and ARQ-LLC.Comment: Submitted to IEEE Transactions on Communications, v2: small
correction
A High-Diversity Transceiver Design for MISO Broadcast Channels
In this paper, the outage behavior and diversity order of the mixture
transceiver architecture for multiple-input single-output broadcast channels
are analyzed. The mixture scheme groups users with closely-aligned channels and
applies superposition coding and successive interference cancellation decoding
to each group composed of users with closely-aligned channels, while applying
zero-forcing beamforming across semi-orthogonal user groups. In order to enable
such analysis, closed-form lower bounds on the achievable rates of a general
multiple-input single-output broadcast channel with superposition coding and
successive interference cancellation are newly derived. By employing
channel-adaptive user grouping and proper power allocation, which ensures that
the channel subspaces of user groups have angle larger than a certain
threshold, it is shown that the mixture transceiver architecture achieves full
diversity order in multiple-input single-output broadcast channels and
opportunistically increases the multiplexing gain while achieving full
diversity order. Furthermore, the achieved full diversity order is the same as
that of the single-user maximum ratio transmit beamforming. Hence, the mixture
scheme can provide reliable communication under channel fading for
ultra-reliable low latency communication. Numerical results validate our
analysis and show the outage superiority of the mixture scheme over
conventional transceiver designs for multiple-input single-output broadcast
channels.Comment: The inner region is evaluated. The single-group SIC performance is
evaluate
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