266,136 research outputs found
A new approach to the, design of MAC Protocols for wireless LANs: Combining QoS guarantee with power saving
An alternative WLAN protocol which could be
adapted in the HCF access scheme defined by IEEE 802.11e, in
place of the HCCA mechanism, is introduced. LEPOAC-QG (Low
Energy Priority Oriented Adaptive Control with QoS Guarantee)
is a centralized access mechanism that supports low energy
consumption, guarantees QoS for all types of multimedia network
applications, enhances the parameterized traffic with priorities,
and supports time division access. It instantly negotiates the
quality levels of the traffic streams trying to support multiple
streams with best possible quality. LEPOAC-QG, compared with
HCCA, exhibits generally superior performance
On the Total Energy Efficiency of Cell-Free Massive MIMO
We consider the cell-free massive multiple-input multiple-output (MIMO)
downlink, where a very large number of distributed multiple-antenna access
points (APs) serve many single-antenna users in the same time-frequency
resource. A simple (distributed) conjugate beamforming scheme is applied at
each AP via the use of local channel state information (CSI). This CSI is
acquired through time-division duplex operation and the reception of uplink
training signals transmitted by the users. We derive a closed-form expression
for the spectral efficiency taking into account the effects of channel
estimation errors and power control. This closed-form result enables us to
analyze the effects of backhaul power consumption, the number of APs, and the
number of antennas per AP on the total energy efficiency, as well as, to design
an optimal power allocation algorithm. The optimal power allocation algorithm
aims at maximizing the total energy efficiency, subject to a per-user spectral
efficiency constraint and a per-AP power constraint. Compared with the equal
power control, our proposed power allocation scheme can double the total energy
efficiency. Furthermore, we propose AP selections schemes, in which each user
chooses a subset of APs, to reduce the power consumption caused by the backhaul
links. With our proposed AP selection schemes, the total energy efficiency
increases significantly, especially for large numbers of APs. Moreover, under a
requirement of good quality-of-service for all users, cell-free massive MIMO
outperforms the colocated counterpart in terms of energy efficiency
A Hybrid MAC Protocol with Channel-dependent Optimized Scheduling for Clustered Underwater Acoustic Sensor Networks
We propose a novel optimal time slot allocation scheme for clustered underwater acoustic sensor networks that leverages physical (PHY) layer information to minimize the energy consumption due to unnecessary retransmissions thereby improving network lifetime and throughput. To reduce the overhead and the computational complexity, we employ a two-phase approach where: (i) each member node takes a selfish decision on the number of time slots it needs during the next intra-cluster cycle by solving a Markov decision process (MDP), and (ii) the cluster head optimizes the scheduling decision based on the channel quality and an urgency factor. To conserve energy, we use a hybrid medium access scheme, i.e., time division multiple access (TDMA) for the intra-cluster communication phase and carrier sense multiple access with collision avoidance (CSMA/CA) for the cluster head-sink communication phase. The proposed MAC protocol is implemented and tested on a real underwater acoustic testbed using SM-75 acoustic modems by Teledyne Benthos. Simulations illustrate an improvement in network lifetime. Additionally, simulations demonstrate that the proposed scheduling scheme with urgency factor achieves a throughput increase of 28 % and improves the reliability by up to 25 % as compared to the scheduling scheme that neither use MDP nor optimization. Furthermore, testbed experiments show an improvement in throughput by up to 10 % along with an improvement in reliability. 1
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