1,703 research outputs found
A Survey on MIMO Transmission with Discrete Input Signals: Technical Challenges, Advances, and Future Trends
Multiple antennas have been exploited for spatial multiplexing and diversity
transmission in a wide range of communication applications. However, most of
the advances in the design of high speed wireless multiple-input multiple
output (MIMO) systems are based on information-theoretic principles that
demonstrate how to efficiently transmit signals conforming to Gaussian
distribution. Although the Gaussian signal is capacity-achieving, signals
conforming to discrete constellations are transmitted in practical
communication systems. As a result, this paper is motivated to provide a
comprehensive overview on MIMO transmission design with discrete input signals.
We first summarize the existing fundamental results for MIMO systems with
discrete input signals. Then, focusing on the basic point-to-point MIMO
systems, we examine transmission schemes based on three most important criteria
for communication systems: the mutual information driven designs, the mean
square error driven designs, and the diversity driven designs. Particularly, a
unified framework which designs low complexity transmission schemes applicable
to massive MIMO systems in upcoming 5G wireless networks is provided in the
first time. Moreover, adaptive transmission designs which switch among these
criteria based on the channel conditions to formulate the best transmission
strategy are discussed. Then, we provide a survey of the transmission designs
with discrete input signals for multiuser MIMO scenarios, including MIMO uplink
transmission, MIMO downlink transmission, MIMO interference channel, and MIMO
wiretap channel. Additionally, we discuss the transmission designs with
discrete input signals for other systems using MIMO technology. Finally,
technical challenges which remain unresolved at the time of writing are
summarized and the future trends of transmission designs with discrete input
signals are addressed.Comment: 110 pages, 512 references, submit to Proceedings of the IEE
Adaptive Mode Selection in Multiuser MISO Cognitive Networks with Limited Cooperation and Feedback
In this paper, we consider a multiuser MISO downlink cognitive network
coexisting with a primary network. With the purpose of exploiting the spatial
degree of freedom to counteract the inter-network interference and
intra-network (inter-user) interference simultaneously, we propose to perform
zero-forcing beamforming (ZFBF) at the multi-antenna cognitive base station
(BS) based on the instantaneous channel state information (CSI). The challenge
of designing ZFBF in cognitive networks lies in how to obtain the interference
CSI. To solve it, we introduce a limited inter-network cooperation protocol,
namely the quantized CSI conveyance from the primary receiver to the cognitive
BS via purchase. Clearly, the more the feedback amount, the better the
performance, but the higher the feedback cost. In order to achieve a balance
between the performance and feedback cost, we take the maximization of feedback
utility function, defined as the difference of average sum rate and feedback
cost while satisfying the interference constraint, as the optimization
objective, and derive the transmission mode and feedback amount joint
optimization scheme. Moreover, we quantitatively investigate the impact of CSI
feedback delay and obtain the corresponding optimization scheme. Furthermore,
through asymptotic analysis, we present some simple schemes. Finally, numerical
results confirm the effectiveness of our theoretical claims.Comment: 11 pages,6 figures, 4 tables IEEE Transactions on Vehicular
Technology, 201
Modulation-Specific Multiuser Transmit Precoding and User Selection for BPSK Signalling
Motivated by challenges to existing multiuser transmission methods in a low
signal to noise ratio (SNR) regime, and emergence of massive numbers of low
data rate ehealth and internet of things (IoT) devices, in this paper we show
that it is beneficial to incorporate knowledge of modulation type into
multiuser transmit precoder design. Particularly, we propose a transmit
precoding (beamforming) specific to BPSK modulation, which has maximum power
efficiency and capacity in poor channel conditions. To be more specific, in a
multiuser scenario, an objective function is formulated based on the weighted
sum of error probabilities of BPSK modulated users. Convex optimization is used
to transform and solve this ill-behaved non-convex minimum probability of error
(MPE) precoding problem. Numerical results confirm significant performance
improvement. We then develop a low-complexity user selection algorithm for MPE
precoding. Based on line packing principles in Grassmannian manifolds, the
number of supported users is able to exceed the number of transmit antennas,
and hence the proposed approach is able to support more simultaneous users
compared with existing multiuser transmit precoding methods
Learning-Based Adaptive Transmission for Limited Feedback Multiuser MIMO-OFDM
Performing link adaptation in a multiantenna and multiuser system is
challenging because of the coupling between precoding, user selection, spatial
mode selection and use of limited feedback about the channel. The problem is
exacerbated by the difficulty of selecting the proper modulation and coding
scheme when using orthogonal frequency division multiplexing (OFDM). This paper
presents a data-driven approach to link adaptation for multiuser multiple input
mulitple output (MIMO) OFDM systems. A machine learning classifier is used to
select the modulation and coding scheme, taking as input the SNR values in the
different subcarriers and spatial streams. A new approximation is developed to
estimate the unknown interuser interference due to the use of limited feedback.
This approximation allows to obtain SNR information at the transmitter with a
minimum communication overhead. A greedy algorithm is used to perform spatial
mode and user selection with affordable complexity, without resorting to an
exhaustive search. The proposed adaptation is studied in the context of the
IEEE 802.11ac standard, and is shown to schedule users and adjust the
transmission parameters to the channel conditions as well as to the rate of the
feedback channel
Fundamental Green Tradeoffs: Progresses, Challenges, and Impacts on 5G Networks
With years of tremendous traffic and energy consumption growth, green radio
has been valued not only for theoretical research interests but also for the
operational expenditure reduction and the sustainable development of wireless
communications. Fundamental green tradeoffs, served as an important framework
for analysis, include four basic relationships: spectrum efficiency (SE) versus
energy efficiency (EE), deployment efficiency (DE) versus energy efficiency
(EE), delay (DL) versus power (PW), and bandwidth (BW) versus power (PW). In
this paper, we first provide a comprehensive overview on the extensive on-going
research efforts and categorize them based on the fundamental green tradeoffs.
We will then focus on research progresses of 4G and 5G communications, such as
orthogonal frequency division multiplexing (OFDM) and non-orthogonal
aggregation (NOA), multiple input multiple output (MIMO), and heterogeneous
networks (HetNets). We will also discuss potential challenges and impacts of
fundamental green tradeoffs, to shed some light on the energy efficient
research and design for future wireless networks.Comment: revised from IEEE Communications Surveys & Tutorial
Power Efficient Resource Allocation for Full-Duplex Radio Distributed Antenna Networks
In this paper, we study the resource allocation algorithm design for
distributed antenna multiuser networks with full-duplex (FD) radio base
stations (BSs) which enable simultaneous uplink and downlink communications.
The considered resource allocation algorithm design is formulated as an
optimization problem taking into account the antenna circuit power consumption
of the BSs and the quality of service (QoS) requirements of both uplink and
downlink users. We minimize the total network power consumption by jointly
optimizing the downlink beamformer, the uplink transmit power, and the antenna
selection. To overcome the intractability of the resulting problem, we
reformulate it as an optimization problem with decoupled binary selection
variables and non-convex constraints. The reformulated problem facilitates the
design of an iterative resource allocation algorithm which obtains an optimal
solution based on the generalized Bender's decomposition (GBD) and serves as a
benchmark scheme. Furthermore, to strike a balance between computational
complexity and system performance, a suboptimal algorithm with polynomial time
complexity is proposed. Simulation results illustrate that the proposed GBD
based iterative algorithm converges to the global optimal solution and the
suboptimal algorithm achieves a close-to-optimal performance. Our results also
demonstrate the trade-off between power efficiency and the number of active
transmit antennas when the circuit power consumption is taken into account. In
particular, activating an exceedingly large number of antennas may not be a
power efficient solution for reducing the total system power consumption. In
addition, our results reveal that FD systems facilitate significant power
savings compared to traditional half-duplex systems, despite the non-negligible
self-interference.Comment: Submitted for possible journal publicatio
Performance Analysis of Massive MIMO for Cell-Boundary Users
In this paper, we consider massive multiple-input multiple-output (MIMO)
systems for both downlink and uplink scenarios, where three radio units (RUs)
connected via one digital unit (DU) support multiple user equipments (UEs) at
the cell-boundary through the same radio resource, i.e., the same
time-frequency slot. For downlink transmitter options, the study considers
zero-forcing (ZF) and maximum ratio transmission (MRT), while for uplink
receiver options it considers ZF and maximum ratio combining (MRC). For the sum
rate of each of these, we derive simple closed-form formulas. In the simple but
practically relevant case where uniform power is allocated to all downlink data
streams, we observe that, for the downlink, vector normalization is better for
ZF while matrix normalization is better for MRT. For a given antenna and user
configuration, we also derive analytically the signal-to-noise-ratio (SNR)
level below which MRC should be used instead of ZF. Numerical simulations
confirm our analytical results.Comment: accepted at IEEE Transaction on Wireless Communicatio
Symbol-level and Multicast Precoding for Multiuser Multiantenna Downlink: A Survey, Classification and Challenges
Precoding has been conventionally considered as an effective means of
mitigating the interference and efficiently exploiting the available 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- and symbol-level precoding, ii) the number of users that
each stream is addressed to, hence unicast-/multicast-/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.Comment: Submitted to IEEE Communications Surveys & Tutorial
Detection and Estimation Algorithms in Massive MIMO Systems
This book chapter reviews signal detection and parameter estimation
techniques for multiuser multiple-antenna wireless systems with a very large
number of antennas, known as massive multi-input multi-output (MIMO) systems.
We consider both centralized antenna systems (CAS) and distributed antenna
systems (DAS) architectures in which a large number of antenna elements are
employed and focus on the uplink of a mobile cellular system. In particular, we
focus on receive processing techniques that include signal detection and
parameter estimation problems and discuss the specific needs of massive MIMO
systems. Simulation results illustrate the performance of detection and
estimation algorithms under several scenarios of interest. Key problems are
discussed and future trends in massive MIMO systems are pointed out.Comment: 7 figures, 14 pages. arXiv admin note: substantial text overlap with
arXiv:1310.728
Stepwise Transmit Antenna Selection in Downlink Massive Multiuser MIMO
Due to the large power consumption in RF-circuitry of massive MIMO systems,
practically relevant performance measures such as energy efficiency or
bandwidth efficiency are neither necessarily monotonous functions of the total
transmit power nor the number of active antennas. Optimal antenna selection is
however computationally infeasible in these systems. In this paper, we propose
an iterative algorithm to optimize the transmit power and the subset of
selected antennas subject to non-monotonous performance measures in massive
multiuser MIMO settings. Numerical results are given for energy efficiency and
demonstrate that for several settings the optimal number of selected antennas
reported by the proposed algorithm is significantly smaller than the total
number of transmit antennas. This fact indicates that antenna selection in
several massive MIMO scenarios not only reduces the hardware complexity and
RF-costs, but also enhances the energy efficiency of the system.Comment: To be presented in 22nd International ITG Workshop on Smart Antennas
(WSA 2018); 8 pages, 3 figure
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