172 research outputs found
Performance Analysis of Channel Extrapolation in FDD Massive MIMO Systems
Channel estimation for the downlink of frequency division duplex (FDD)
massive MIMO systems is well known to generate a large overhead as the amount
of training generally scales with the number of transmit antennas in a MIMO
system. In this paper, we consider the solution of extrapolating the channel
frequency response from uplink pilot estimates to the downlink frequency band,
which completely removes the training overhead. We first show that conventional
estimators fail to achieve reasonable accuracy. We propose instead to use
high-resolution channel estimation. We derive theoretical lower bounds (LB) for
the mean squared error (MSE) of the extrapolated channel. Assuming that the
paths are well separated, the LB is simplified in an expression that gives
considerable physical insight. It is then shown that the MSE is inversely
proportional to the number of receive antennas while the extrapolation
performance penalty scales with the square of the ratio of the frequency offset
and the training bandwidth. The channel extrapolation performance is validated
through numeric simulations and experimental measurements taken in an anechoic
chamber. Our main conclusion is that channel extrapolation is a viable solution
for FDD massive MIMO systems if accurate system calibration is performed and
favorable propagation conditions are present.Comment: arXiv admin note: substantial text overlap with arXiv:1902.0684
Spectral Efficiency of MIMO Millimeter-Wave Links with Single-Carrier Modulation for 5G Networks
Future wireless networks will extensively rely upon bandwidths centered on
carrier frequencies larger than 10GHz. Indeed, recent research has shown that,
despite the large path-loss, millimeter wave (mmWave) frequencies can be
successfully exploited to transmit very large data-rates over short distances
to slowly moving users. Due to hardware complexity and cost constraints,
single-carrier modulation schemes, as opposed to the popular multi-carrier
schemes, are being considered for use at mmWave frequencies. This paper
presents preliminary studies on the achievable spectral efficiency on a
wireless MIMO link operating at mmWave in a typical 5G scenario. Two different
single-carrier modem schemes are considered, i.e. a traditional modulation
scheme with linear equalization at the receiver, and a single-carrier
modulation with cyclic prefix, frequency-domain equalization and FFT-based
processing at the receiver. Our results show that the former achieves a larger
spectral efficiency than the latter. Results also confirm that the spectral
efficiency increases with the dimension of the antenna array, as well as that
performance gets severely degraded when the link length exceeds 100 meters and
the transmit power falls below 0dBW. Nonetheless, mmWave appear to be very
suited for providing very large data-rates over short distances.Comment: 8 pages, 8 figures, to appear in Proc. 20th International ITG
Workshop on Smart Antennas (WSA2016
A Low-Complexity Double EP-based Detector for Iterative Detection and Decoding in MIMO
We propose a new iterative detection and
decoding (IDD) algorithm for multiple-input multiple-output
(MIMO) based on expectation propagation (EP) with application
to massive MIMO scenarios. Two main results are presented.
We first introduce EP to iteratively improve the Gaussian approximations of both the estimation of the posterior by the MIMO
detector and the soft output of the channel decoder. With this
novel approach, denoted by double-EP (DEP), the convergence
is very much improved with a computational complexity just
two times the one of the linear minimum mean square error
(LMMSE) based IDD, as illustrated by the included experiments.
Besides, as in the LMMSE MIMO detector, when the number of
antennas increases, the computational cost of the matrix inversion
operation required by the DEP becomes unaffordable. In this
work we also develop approaches of DEP where the mean and
the covariance matrix of the posterior are approximated by using
the Gauss-Seidel and Neumann series methods, respectively. This
low-complexity DEP detector has quadratic complexity in the
number of antennas, as the low-complexity LMMSE techniques.
Experimental results show that the new low-complexity DEP
achieves the performance of the DEP as the ratio between the
number of transmitting and receiving antennas decreasesProyectos Nacionales Españoles del Gobierno de España TEC2017-90093-C3-2-
- …