1,415 research outputs found
On the Throughput of Large-but-Finite MIMO Networks using Schedulers
This paper studies the sum throughput of the {multi-user}
multiple-input-single-output (MISO) networks in the cases with large but finite
number of transmit antennas and users. Considering continuous and bursty
communication scenarios with different users' data request probabilities, we
derive quasi-closed-form expressions for the maximum achievable throughput of
the networks using optimal schedulers. The results are obtained in various
cases with different levels of interference cancellation. Also, we develop an
efficient scheduling scheme using genetic algorithms (GAs), and evaluate the
effect of different parameters, such as channel/precoding models, number of
antennas/users, scheduling costs and power amplifiers' efficiency, on the
system performance. Finally, we use the recent results on the achievable rates
of finite block-length codes to analyze the system performance in the cases
with short packets. As demonstrated, the proposed GA-based scheduler reaches
(almost) the same throughput as in the exhaustive search-based optimal
scheduler, with substantially less implementation complexity. Moreover, the
power amplifiers' inefficiency and the scheduling delay affect the performance
of the scheduling-based systems significantly
Two-Layered Superposition of Broadcast/Multicast and Unicast Signals in Multiuser OFDMA Systems
We study optimal delivery strategies of one common and independent
messages from a source to multiple users in wireless environments. In
particular, two-layered superposition of broadcast/multicast and unicast
signals is considered in a downlink multiuser OFDMA system. In the literature
and industry, the two-layer superposition is often considered as a pragmatic
approach to make a compromise between the simple but suboptimal orthogonal
multiplexing (OM) and the optimal but complex fully-layered non-orthogonal
multiplexing. In this work, we show that only two-layers are necessary to
achieve the maximum sum-rate when the common message has higher priority than
the individual unicast messages, and OM cannot be sum-rate optimal in
general. We develop an algorithm that finds the optimal power allocation over
the two-layers and across the OFDMA radio resources in static channels and a
class of fading channels. Two main use-cases are considered: i) Multicast and
unicast multiplexing when users with uplink capabilities request both
common and independent messages, and ii) broadcast and unicast multiplexing
when the common message targets receive-only devices and users with uplink
capabilities additionally request independent messages. Finally, we develop a
transceiver design for broadcast/multicast and unicast superposition
transmission based on LTE-A-Pro physical layer and show with numerical
evaluations in mobile environments with multipath propagation that the capacity
improvements can be translated into significant practical performance gains
compared to the orthogonal schemes in the 3GPP specifications. We also analyze
the impact of real channel estimation and show that significant gains in terms
of spectral efficiency or coverage area are still available even with
estimation errors and imperfect interference cancellation for the two-layered
superposition system
Exploiting Full-duplex Receivers for Achieving Secret Communications in Multiuser MISO Networks
We consider a broadcast channel, in which a multi-antenna transmitter (Alice)
sends confidential information signals to legitimate users (Bobs) in
the presence of eavesdroppers (Eves). Alice uses MIMO precoding to generate
the information signals along with her own (Tx-based) friendly jamming.
Interference at each Bob is removed by MIMO zero-forcing. This, however, leaves
a "vulnerability region" around each Bob, which can be exploited by a nearby
Eve. We address this problem by augmenting Tx-based friendly jamming (TxFJ)
with Rx-based friendly jamming (RxFJ), generated by each Bob. Specifically,
each Bob uses self-interference suppression (SIS) to transmit a friendly
jamming signal while simultaneously receiving an information signal over the
same channel. We minimize the powers allocated to the information, TxFJ, and
RxFJ signals under given guarantees on the individual secrecy rate for each
Bob. The problem is solved for the cases when the eavesdropper's channel state
information is known/unknown. Simulations show the effectiveness of the
proposed solution. Furthermore, we discuss how to schedule transmissions when
the rate requirements need to be satisfied on average rather than
instantaneously. Under special cases, a scheduling algorithm that serves only
the strongest receivers is shown to outperform the one that schedules all
receivers.Comment: IEEE Transactions on Communication
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