7,045 research outputs found
On Buffer-Aided Multiple-Access Relay Channel
The paper treats uplink scenario where M user equipments (UEs) send to a Base
Station (BS), possibly via a common Relay Station (RS) that is equipped with a
buffer. This is a multiple-access relay channel (MARC) aided by a buffer. We
devise a protocol in which the transmission mode is selected adaptively, using
the buffer at the RS in order to maximize the average system throughput. We
consider the general case in which the RS and the BS can have limits on the
maximal number of transmitters that can be received over the multiple access
channel. In each slot there are three type possible actions: (A1) multiple UEs
transmit at rates that enable BS to decode them (A2) multiple UEs transmit, the
BS can only decode the messages partially, while the RS completely; (A3) RS
forwards the side information to BS about the partially decoded messages, which
are going to be combined and decoded entirely at the BS, while simultaneously a
number of UEs sends new messages to the BS. The results show that the adaptive
selection of direct and buffer-aided relay transmissions leads to significant
average throughput gains.Comment: 13 pages, 3 figures, accepted to IEEE Communications letter
Decoupled Uplink and Downlink in a Wireless System with Buffer-Aided Relaying
The paper treats a multiuser relay scenario where multiple user equipments
(UEs) have a two-way communication with a common Base Station (BS) in the
presence of a buffer-equipped Relay Station (RS). Each of the uplink (UL) and
downlink (DL) transmission can take place over a direct or over a relayed path.
Traditionally, the UL and the DL path of a given two-way link are coupled, that
is, either both are direct links or both are relayed links. By removing the
restriction for coupling, one opens the design space for a decoupled two-way
links. Following this, we devise two protocols: orthogonal decoupled UL/DL
buffer-aided (ODBA) relaying protocol and non-orthogonal decoupled UL/DL
buffer-aided (NODBA) relaying protocol. In NODBA, the receiver can use
successive interference cancellation (SIC) to extract the desired signal from a
collision between UL and DL signals. For both protocols, we characterize the
transmission decision policies in terms of maximization of the average two-way
sum rate of the system. The numerical results show that decoupling association
and non-orthogonal radio access lead to significant throughput gains for
two-way traffic.Comment: 27 pages, 10 figures, submitted to IEEE Transactions on
Communication
Adaptive Mode Selection and Power Allocation in Bidirectional Buffer-aided Relay Networks
In this paper, we consider the problem of sum rate maximization in a
bidirectional relay network with fading. Hereby, user 1 and user 2 communicate
with each other only through a relay, i.e., a direct link between user 1 and
user 2 is not present. In this network, there exist six possible transmission
modes: four point-to-point modes (user 1-to-relay, user 2-to-relay,
relay-to-user 1, relay-to-user 2), a multiple access mode (both users to the
relay), and a broadcast mode (the relay to both users). Most existing protocols
assume a fixed schedule of using a subset of the aforementioned transmission
modes, as a result, the sum rate is limited by the capacity of the weakest link
associated with the relay in each time slot. Motivated by this limitation, we
develop a protocol which is not restricted to adhere to a predefined schedule
for using the transmission modes. Therefore, all transmission modes of the
bidirectional relay network can be used adaptively based on the instantaneous
channel state information (CSI) of the involved links. To this end, the relay
has to be equipped with two buffers for the storage of the information received
from users 1 and 2, respectively. For the considered network, given a total
average power budget for all nodes, we jointly optimize the transmission mode
selection and power allocation based on the instantaneous CSI in each time slot
for sum rate maximization. Simulation results show that the proposed protocol
outperforms existing protocols for all signal-to-noise ratios (SNRs).
Specifically, we obtain a considerable gain at low SNRs due to the adaptive
power allocation and at high SNRs due to the adaptive mode selection.Comment: arXiv admin note: substantial text overlap with arXiv:1303.373
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