928 research outputs found
Achievable Rates and Training Overheads for a Measured LOS Massive MIMO Channel
This paper presents achievable uplink (UL) sumrate predictions for a measured
line-of-sight (LOS) massive multiple-input, multiple-output (MIMO) (MMIMO)
scenario and illustrates the trade-off between spatial multiplexing performance
and channel de-coherence rate for an increasing number of base station (BS)
antennas. In addition, an orthogonal frequency division multiplexing (OFDM)
case study is formed which considers the 90% coherence time to evaluate the
impact of MMIMO channel training overheads in high-speed LOS scenarios. It is
shown that whilst 25% of the achievable zero-forcing (ZF) sumrate is lost when
the resounding interval is increased by a factor of 4, the OFDM training
overheads for a 100-antenna MMIMO BS using an LTE-like physical layer could be
as low as 2% for a terminal speed of 90m/s.Comment: 4 pages, 5 figure
Massive MIMO performance evaluation based on measured propagation data
Massive MIMO, also known as very-large MIMO or large-scale antenna systems,
is a new technique that potentially can offer large network capacities in
multi-user scenarios. With a massive MIMO system, we consider the case where a
base station equipped with a large number of antenna elements simultaneously
serves multiple single-antenna users in the same time-frequency resource. So
far, investigations are mostly based on theoretical channels with independent
and identically distributed (i.i.d.) complex Gaussian coefficients, i.e.,
i.i.d. Rayleigh channels. Here, we investigate how massive MIMO performs in
channels measured in real propagation environments. Channel measurements were
performed at 2.6 GHz using a virtual uniform linear array (ULA) which has a
physically large aperture, and a practical uniform cylindrical array (UCA)
which is more compact in size, both having 128 antenna ports. Based on
measurement data, we illustrate channel behavior of massive MIMO in three
representative propagation conditions, and evaluate the corresponding
performance. The investigation shows that the measured channels, for both array
types, allow us to achieve performance close to that in i.i.d. Rayleigh
channels. It is concluded that in real propagation environments we have
characteristics that can allow for efficient use of massive MIMO, i.e., the
theoretical advantages of this new technology can also be harvested in real
channels.Comment: IEEE Transactions on Wireless Communications, 201
Initial Characterization of Massive Multi-User MIMO Channels at 2.6 GHz in Indoor and Outdoor Environments
The channel properties have a large influence on user separability in massive multi-user multiple-input multiple-output (massive MIMO) systems. In this paper we present spatio-temporal characteristics obtained from massive MIMO channel measurements at 2.6 GHz. The results are based on data acquired in both indoor and outdoor scenarios where a base station equipped with 64 dual-polarized antenna elements communicates simultaneously with nine single-antenna users. In the outdoor scenarios the base station is placed at two rooftops with different heights and the users are confined to a five-meter diameter circle and move rando mly at pedestrian speeds. In the indoor scenarios, the users are located close to each other in a lecture theater and the base station is placed at various locations in the room. We report on the observed distribution of the delay spreads and angular spreads. Furthermore, the multi-user performance in terms of singular value spread of the MU-MIMO channel is also reported. Finally, statistics of the coherence time and coherence bandwidth of the propagation channel in various scenarios are given. The results are important for the design and analysis of massive MU-MIMO systems, as well as in the development of realistic massive MU-MIMO channel models
Terahertz Wireless Channels: A Holistic Survey on Measurement, Modeling, and Analysis
Terahertz (0.1-10 THz) communications are envisioned as a key technology for
sixth generation (6G) wireless systems. The study of underlying THz wireless
propagation channels provides the foundations for the development of reliable
THz communication systems and their applications. This article provides a
comprehensive overview of the study of THz wireless channels. First, the three
most popular THz channel measurement methodologies, namely, frequency-domain
channel measurement based on a vector network analyzer (VNA), time-domain
channel measurement based on sliding correlation, and time-domain channel
measurement based on THz pulses from time-domain spectroscopy (THz-TDS), are
introduced and compared. Current channel measurement systems and measurement
campaigns are reviewed. Then, existing channel modeling methodologies are
categorized into deterministic, stochastic, and hybrid approaches.
State-of-the-art THz channel models are analyzed, and the channel simulators
that are based on them are introduced. Next, an in-depth review of channel
characteristics in the THz band is presented. Finally, open problems and future
research directions for research studies on THz wireless channels for 6G are
elaborated.Comment: to appear in IEEE Communications Surveys and Tutorial
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