41 research outputs found
Mirror Prox Algorithm for Large-Scale Cell-Free Massive MIMO Uplink Power Control
We consider the problem of max-min fairness for uplink cell-free massive
multiple-input multiple-output (MIMO) subject to per-user power constraints.
The standard framework for solving the considered problem is to separately
solve two subproblems: the receiver filter coefficient design and the power
control problem. While the former has a closed-form solution, the latter has
been solved using either second-order methods of high computational complexity
or a first-order method that provides an approximate solution. To deal with
these drawbacks of the existing methods, we propose a mirror prox based method
for the power control problem by equivalently reformulating it as a
convex-concave problem and applying the mirror prox algorithm to find a saddle
point. The simulation results establish the optimality of the proposed solution
and demonstrate that it is more efficient than the known methods. We also
conclude that for large-scale cell-free massive MIMO, joint optimization of
linear receive combining and power control provides significantly better user
fairness than the power control only scheme in which receiver coefficients are
fixed to unity.Comment: in IEEE Communications Letters, 202
Dilaton in Two-Time Physics as trigger of electroweak phase transition and inflation
Within the SP(2, R) symmetry, the Two-time model (2T model) has six dimension
with two time dimensions. The model has a dilaton particle that makes the
symmetry breaking differently from the Standard Model. By reducing the 2T
metric to the Minkowski one (1T metric), we consider the electroweak phase
transition picture in the 2T model with the dilaton as the trigger. Our
analysis shows that Electro-weak Phase Transition (EWPT) is a first-order phase
transition at the GeV scale, its strength is about and the
mass of dilaton is in interval GeV. Furthermore, the metric of 2T
model can be reduced to the Randall-Sundrum model, so the dilaton acts as
inflaton with the slow-roll approximation. Therefore the 2T-model indirectly
suggests that extra-dimension can be also a source of EWPT and inflation. The
EWPT problem can be used to determine scale parameters that refer to
relationships between two metrics.Comment: 25 pages, 2 figure
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
Cell-free Massive MIMO and SWIPT: Access Point Operation Mode Selection and Power Control
This paper studies cell-free massive multiple-input multiple-output
(CF-mMIMO) systems incorporating simultaneous wireless information and power
transfer (SWIPT) for separate information users (IUs) and energy users (EUs) in
Internet of Things (IoT) networks. To optimize both the spectral efficiency
(SE) of IUs and harvested energy (HE) of EUs, we propose a joint access point
(AP) operation mode selection and power control design, wherein certain APs are
designated for energy transmission to EUs, while others are dedicated to
information transmission to IUs. We investigate the problem of maximizing the
total HE for EUs, considering constraints on SE for individual IUs and minimum
HE for individual EUs. Our numerical results showcase that the proposed AP
operation mode selection algorithm can provide up to and
performance gains over random AP operation mode selection with and without
power control, respectively.Comment: 6 pages, 2 figures, to be presented at GLOBECOM 2023, Kuala Lumpu
Network Coding with Multimedia Transmission and Cognitive Networking: An Implementation based on Software-Defined Radio
Network coding (NC) is considered a breakthrough to improve throughput, robustness, and security of wireless networks. Although the theoretical aspects of NC have been extensively investigated, there have been only few experiments with pure NC schematics. This paper presents an implementation of NC under a two-way relay model and extends it to two non-straightforward scenarios: (i) multimedia transmission with layered coding and multiple-description coding, and (ii) cognitive radio with Vandermonde frequency division multiplexing (VFDM). The implementation is in real time and based on software-defined radio (SDR). The experimental results show that, by combining NC and source coding, we can control the quality of the received multimedia content in an on-demand manner. Whereas in the VFDM-based cognitive radio, the quality of the received content in the primary receiver is low (due to imperfect channel estimation) yet retrievable. Our implementation results serve as a proof for the practicability of network coding in relevant applications
New Forests and New Forest People in Central Vietnam: The Acacia Boom
Vietnam is the country with the largest area of plantations of Australasian Acacia species (‘wattles’) in South-East Asia. Between 6 and 9% of the national land area is cultivated with tropical wattles (A. auriculiformis, A. mangium and A. × mangiiformis). From the perspective of its promoters, the wattle plantation industry in Vietnam may be seen as a success beyond expectations. We review the origins of this boom and ask what it has done to and for the coun- try’s landscape and people. The chapter combines findings and insights from an interdisciplinary research project in Thừa Thiên Huế province, north-central Vietnam. Research took place across upland and lowland wattle-growing regions, with ethnic minorities as well as the Kinh majority, and with long-term wattle growers as well as new en- trants. It drew on questionnaires, interviews and observations, as well as information from remote sensing, eco- logical surveys and hydrological assessments. We first describe how substantial areas of ‘new forest’ (short-rotation wattle plantations) were created, initially in degraded bushland, but now sometimes through clearing of highly bi- odiverse natural forest stands. These wattle plantations alter local hydrology, soils and biodiversity, and are exposed to risks including soil erosion and plant pathogens. The plantations provide wood chips and timber, supporting rev- enue, employment and a strong forestry industry. Incomes have risen appreciably for many, although unequally, and a class of successful entrepreneurs has emerged. These plantations alter the livelihoods and identities of upland ‘forest people’, historically shifting cultivators, contributing to what might be called ‘new forest people’. Ethnic mi- nority villagers are building new identities around the wattle economy and around their contracts with state forest agencies, seeing themselves increasingly as forest growers and protectors. We conclude by raising some questions regarding the social changes and issues of environmental sustainability linked to this wattle boom
Network Coding with Multimedia Transmission and Cognitive Networking: An Implementation based on Software-Defined Radio
Network coding (NC) is considered a breakthrough to improve throughput, robustness, and security of wireless networks. Although the theoretical aspects of NC have been extensively investigated, there have been only few experiments with pure NC schematics. This paper presents an implementation of NC under a two-way relay model and extends it to two\ua0non-straightforward scenarios: (i) multimedia transmission with layered coding and multiple-description coding, and (ii) cognitive radio with Vandermonde frequency division multiplexing (VFDM). The implementation is in real time and based on software-defined radio (SDR). The experimental results show that, by combining NC and source coding, we can control the quality of the received multimedia content in an on-demand manner. Whereas in the VFDM-based cognitive radio, the quality of the received content in the primary receiver is low (due to imperfect channel estimation) yet retrievable. Our implementation results serve as a proof for the practicability of network coding in relevant applications