17 research outputs found
On Low-Resolution ADCs in Practical 5G Millimeter-Wave Massive MIMO Systems
Nowadays, millimeter-wave (mmWave) massive multiple-input multiple-output
(MIMO) systems is a favorable candidate for the fifth generation (5G) cellular
systems. However, a key challenge is the high power consumption imposed by its
numerous radio frequency (RF) chains, which may be mitigated by opting for
low-resolution analog-to-digital converters (ADCs), whilst tolerating a
moderate performance loss. In this article, we discuss several important issues
based on the most recent research on mmWave massive MIMO systems relying on
low-resolution ADCs. We discuss the key transceiver design challenges including
channel estimation, signal detector, channel information feedback and transmit
precoding. Furthermore, we introduce a mixed-ADC architecture as an alternative
technique of improving the overall system performance. Finally, the associated
challenges and potential implementations of the practical 5G mmWave massive
MIMO system {with ADC quantizers} are discussed.Comment: to appear in IEEE Communications Magazin
Error Correction with Systematic RLNC in Multi-Channel THz Communication Systems
The terahertz (THz) frequency band (0.3-10THz) has the advantage of large
available bandwidth and is a candidate to satisfy the ever increasing mobile
traffic in wireless communications. However, the THz channels are often
absorbed by molecules in the atmosphere, which can decrease the signal quality
resulting in high bit error rate of received data. In this paper, we study the
usage of systematic random linear network coding (sRLNC) for error correction
in generic THz systems with with 2N parallel channels, whereby N main
high-bitrate channels are used in parallel with N auxiliary channels with lower
bit rate. The idea behind this approach is to use coded low-bit rate channels
to carry redundant information from high-bit rate channels, and thus compensate
for errors in THz transmission. The analytical results evaluate and compare the
different scenarios of the THz system in term of the amount of coding
redundancy, a code rate, transmission rate of auxiliary channels, the number of
THz channels, the modulation format and transmission distance as required
system configurations for a fault tolerant THz transmission.Comment: 6 pages, 5 figure
Performance Analysis of Indoor THz Communications with One-Bit Precoding
In this paper, the performance of indoor Terahertz (THz) communication systems with one-bit digital-to- analog converters (DACs) is investigated. Array-of- subarrays architecture is assumed for the antennas at the access points, where each RF chain uniquely activates a disjoint subset of antennas, each of which is connected to an exclusive phase shifter. Hybrid precoding, including maximum ratio transmission (MRT) and zero-forcing (ZF) precoding, is considered. The best beamsteering direction for the phase shifter in the large subarray antenna regime is first proved to be the direction of the line-of-sight (LoS) path. Subsequently, the closed-form expression of the lower- bound of the achievable rate in the large subarray antenna regime is derived, which is the same for both MRT and ZF and is independent of the transmit power. Numerical results validating the analysis are provided as well
Dynamical visualization of anisotropic electromagnetic re-emissions from a single metal micro-helix at THz frequencies
微小金属らせんとテラヘルツ光との相互作用を可視化 --次世代超高速移動通信などにおける高性能アンテナへ応用--. 京都大学プレスリリース. 2021-02-09.The capability for actual measurements—not just simulations—of the dynamical behavior of THz electromagnetic waves, including interactions with prevalent 3D objects, has become increasingly important not only for developments of various THz devices, but also for reliable evaluation of electromagnetic compatibility. We have obtained real-time visualizations of the spatial evolution of THz electromagnetic waves interacting with a single metal micro-helix. After the micro-helix is stimulated by a broadband pico-second pulse of THz electromagnetic waves, two types of anisotropic re-emissions can occur following overall inductive current oscillations in the micro-helix. They propagate in orthogonally crossed directions with different THz frequency spectra. This unique radiative feature can be very useful for the development of a smart antenna with broadband multiplexing/demultiplexing ability and directional adaptivity. In this way, we have demonstrated that our advanced measurement techniques can lead to the development of novel functional THz devices
Improving THz Quality-of-Transmission with Systematic RLNC and Auxiliary Channels
In this paper, we propose a novel solution that can improve the quality of
THz transmission with systematic random linear network coding (sRLNC) and a
low-bitrate auxiliary channel. To minimize complexity of channel coding, we
complement a generic low complexity FEC code by a low complexity sRLNC. To
increase the overall throughput of THz transmission, we propose to send the
native data and coding redundancy in parallel over 2 differently configured THz
channels, i.e., over 1 high bit rate main channel and 1 low bit rate low error
rate auxiliary channel. The results show, that the main THz channel supported
by low bit rate auxiliary channel can use a higher level modulation format and
sent over longer distances with a higher throughput.Comment: 7 pages, 6 figures, accepted at IEEE ICC'20 Workshop - TeraCo