73 research outputs found
Integrated Sensing and Communications with Joint Beam Squint and Beam Split for Massive MIMO
Integrated sensing and communications (ISAC) has attracted tremendous
attention for the future 6G wireless communication systems. To improve the
transmission rates and sensing accuracy, massive multi-input multi-output
(MIMO) technique is leveraged with large transmission bandwidth. However, the
growing size of transmission bandwidth and antenna array results in the beam
squint effect, which hampers the communications. Moreover, the time overhead of
the traditional sensing algorithm is prohibitive for practical systems. In this
paper, instead of alleviating the wideband beam squint effect, we take
advantage of joint beam squint and beam split effect and propose a novel user
directions sensing method integrated with massive MIMO orthogonal frequency
division multiplexing (OFDM) systems. Specifically, with the beam squint
effect, the BS utilizes the true-time-delay (TTD) lines to steer the beams of
different OFDM subcarriers towards different directions simultaneously. The
users feedback the subcarrier frequency with the maximum array gain to the BS.
Then, the BS calculates the direction based on the subcarrier frequency
feedback. Futhermore, the beam split effect introduced by enlarging the
inter-antenna spacing is exploited to expand the sensing range. The proposed
sensing method operates over frequency-domain, and the intended sensing range
is covered by all the subcarriers simultaneously, which reduces the time
overhead of the conventional sensing significantly. Simulation results have
demonstrated the effectiveness as well as the superior performance of the
proposed ISAC scheme.Comment: 13 pages, 11 figures, submitted to IEEE journa
Time-Domain Channel Estimation for Extremely Large MIMO THz Communications with Beam Squint
In this paper, we study the problem of extremely large (XL) multiple-input
multiple-output (MIMO) channel estimation in the Terahertz (THz) frequency
band, considering the presence of propagation delays across the entire array
apertures, which leads to frequency selectivity, a problem known as beam
squint. Multi-carrier transmission schemes which are usually deployed to
address this problem, suffer from high peak-to-average power ratio, which is
specifically dominant in THz communications where low transmit power is
realized. Diverging from the usual approach, we devise a novel channel
estimation problem formulation in the time domain for single-carrier (SC)
modulation, which favors transmissions in THz, and incorporate the beam-squint
effect in a sparse vector recovery problem that is solved via sparse
optimization tools. In particular, the beam squint and the sparse MIMO channel
are jointly tracked by using an alternating minimization approach that
decomposes the two estimation problems. The presented performance evaluation
results validate that the proposed SC technique exhibits superior performance
than the conventional one as well as than state-of-the-art multi-carrier
approaches
FDD Channel Estimation Via Covariance Estimation in Wideband Massive MIMO Systems
[Abstract] A method for channel estimation in wideband massive Multiple-Input Multiple-Output systems using hybrid digital analog architectures is developed. The proposed method is useful for Frequency-Division Duplex at either sub-6 GHz or millimeter wave frequency bands and takes into account the beam squint effect caused by the large bandwidth of the signals. To circumvent the estimation of large channel vectors, the posed algorithm relies on the slow time variation of the channel spatial covariance matrix, thus allowing for the utilization of very short training sequences. This is possibledue to the exploitation of the channel structure. After identifying the channel covariance matrix, the channel is estimated on the basis of the recovered information. To that end, we propose a novel method that relies on estimating the tap delays and the gains as sociated with each path. As a consequence, the proposed channel estimator achieves low computational complexity and significantly reduces the training overhead. Moreover, our numerical simulations show better performance results compared to the minimum mean-squared error solution.Xunta de Galicia; ED431G2019/01Agencia Estatal de InvestigaciĆ³n de EspaƱa; TEC2016-75067-C4-1-RAgencia Estatal de InvestigaciĆ³n de EspaƱa; RED2018-102668-TAgencia Estatal de InvestigaciĆ³n de EspaƱa; PID2019-104958RB-C4
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