6 research outputs found
Rank-Two Beamforming and Power Allocation in Multicasting Relay Networks
In this paper, we propose a novel single-group multicasting relay beamforming
scheme. We assume a source that transmits common messages via multiple
amplify-and-forward relays to multiple destinations. To increase the number of
degrees of freedom in the beamforming design, the relays process two received
signals jointly and transmit the Alamouti space-time block code over two
different beams. Furthermore, in contrast to the existing relay multicasting
scheme of the literature, we take into account the direct links from the source
to the destinations. We aim to maximize the lowest received quality-of-service
by choosing the proper relay weights and the ideal distribution of the power
resources in the network. To solve the corresponding optimization problem, we
propose an iterative algorithm which solves sequences of convex approximations
of the original non-convex optimization problem. Simulation results demonstrate
significant performance improvements of the proposed methods as compared with
the existing relay multicasting scheme of the literature and an algorithm based
on the popular semidefinite relaxation technique
Multi-Pair Two-Way Relay Network with Harvest-Then-Transmit Users: Resolving Pairwise Uplink-Downlink Coupling
While two-way relaying is a promising way to enhance the spectral efficiency
of wireless networks, the imbalance of relay-user distances may lead to
excessive wireless power at the nearby-users. To exploit the excessive power,
the recently proposed harvest-then-transmit technique can be applied. However,
it is well-known that harvest-then-transmit introduces uplink-downlink coupling
for a user. Together with the co-dependent relationship between paired users
and interference among multiple user pairs, wirelessly powered two-way relay
network suffers from the unique pairwise uplink-downlink coupling, and the
joint uplink-downlink network design is nontrivial. To this end, for the one
pair users case, we show that a global optimal solution can be obtained. For
the general case of multi-pair users, based on the rank-constrained difference
of convex program, a convergence guaranteed iterative algorithm with an
efficient initialization is proposed. Furthermore, a lower bound to the
performance of the optimal solution is derived by introducing virtual receivers
at relay. Numerical results on total transmit power show that the proposed
algorithm achieves a transmit power value close to the lower bound
Symbol-level and Multicast Precoding for Multiuser Multiantenna Downlink: A State-of-the-art, Classification and Challenges
Precoding has been conventionally considered as an effective means of mitigating or exploiting the interference in the multiantenna downlink channel, where multiple users are simultaneously served with independent information over the same channel resources. The early works in this area were focused on transmitting an individual information stream to each user by constructing weighted linear combinations of symbol blocks (codewords). However, more recent works have moved beyond this traditional view by: i) transmitting distinct data streams to groups of users and ii) applying precoding on a symbol-per-symbol basis. In this context, the current survey presents a unified view and classification of precoding techniques with respect to two main axes: i) the switching rate of the precoding weights, leading to the classes of block-level and symbol-level precoding, ii) the number of users that each stream is addressed to, hence unicast, multicast, and broadcast precoding. Furthermore, the classified techniques are compared through representative numerical results to demonstrate their relative performance and uncover fundamental insights. Finally, a list of open theoretical problems and practical challenges are presented to inspire further research in this area