1,008 research outputs found
Weighted Compressive Sensing Based Uplink Channel Estimation for TDD Massive MIMO Sytems
In this paper, the channel estimation problem for the uplink massive multi-input multi-output (MIMO) system is considered. Motivated by the observations that the channels in massive MIMO systems may exhibit sparsity and the channel support changes slowly over time, we propose one efficient channel estimation method under the framework of compressive sensing. By exploiting the channel impulse response (CIR) estimated from the previous OFDM symbol, we firstly estimate the probabilities that the elements in the current CIR are nonzero. Then, we propose the probability-weighted subspace pursuit (PWSP) algorithm exploiting these probability information to efficiently reconstruct the uplink massive MIMO channel. Moreover, noting that the massive MIMO systems also share a common support within one channel matrix due to the shared local scatterers in the physical propagation environment, an antenna collaborating method is exploited for the proposed method to further enhance the channel estimation performance. Simulation results show that compared to the existing compressive sensing methods, the proposed methods could achieve higher spectral efficiency as well as more reliable performance over time-varying channel
Orthogonal Time Frequency Space for Integrated Sensing and Communication: A Survey
Sixth-generation (6G) wireless communication systems, as stated in the
European 6G flagship project Hexa-X, are anticipated to feature the integration
of intelligence, communication, sensing, positioning, and computation. An
important aspect of this integration is integrated sensing and communication
(ISAC), in which the same waveform is used for both systems both sensing and
communication, to address the challenge of spectrum scarcity. Recently, the
orthogonal time frequency space (OTFS) waveform has been proposed to address
OFDM's limitations due to the high Doppler spread in some future wireless
communication systems. In this paper, we review existing OTFS waveforms for
ISAC systems and provide some insights into future research. Firstly, we
introduce the basic principles and a system model of OTFS and provide a
foundational understanding of this innovative technology's core concepts and
architecture. Subsequently, we present an overview of OTFS-based ISAC system
frameworks. We provide a comprehensive review of recent research developments
and the current state of the art in the field of OTFS-assisted ISAC systems to
gain a thorough understanding of the current landscape and advancements.
Furthermore, we perform a thorough comparison between OTFS-enabled ISAC
operations and traditional OFDM, highlighting the distinctive advantages of
OTFS, especially in high Doppler spread scenarios. Subsequently, we address the
primary challenges facing OTFS-based ISAC systems, identifying potential
limitations and drawbacks. Then, finally, we suggest future research
directions, aiming to inspire further innovation in the 6G wireless
communication landscape
Seventy Years of Radar and Communications: The road from separation to integration
Radar and communications (R&C) as key utilities of electromagnetic (EM) waves have fundamentally shaped human society and triggered the modern information age. Although R&C had been historically progressing separately, in recent decades, they have been converging toward integration, forming integrated sensing and communication (ISAC) systems, giving rise to new highly desirable capabilities in next-generation wireless networks and future radars. To better understand the essence of ISAC, this article provides a systematic overview of the historical development of R&C from a signal processing (SP) perspective. We first interpret the duality between R&C as signals and systems, followed by an introduction of their fundamental principles. We then elaborate on the two main trends in their technological evolution, namely, the increase of frequencies and bandwidths and the expansion of antenna arrays. We then show how the intertwined narratives of R&C evolved into ISAC and discuss the resultant SP framework. Finally, we overview future research directions in this field
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