1,722 research outputs found
A Data-Aided Channel Estimation Scheme for Decoupled Systems in Heterogeneous Networks
Uplink/downlink (UL/DL) decoupling promises more flexible cell association
and higher throughput in heterogeneous networks (HetNets), however, it hampers
the acquisition of DL channel state information (CSI) in time-division-duplex
(TDD) systems due to different base stations (BSs) connected in UL/DL. In this
paper, we propose a novel data-aided (DA) channel estimation scheme to address
this problem by utilizing decoded UL data to exploit CSI from received UL data
signal in decoupled HetNets where a massive multiple-input multiple-output BS
and dense small cell BSs are deployed. We analytically estimate BER performance
of UL decoded data, which are used to derive an approximated normalized mean
square error (NMSE) expression of the DA minimum mean square error (MMSE)
estimator. Compared with the conventional least square (LS) and MMSE, it is
shown that NMSE performances of all estimators are determined by their
signal-to-noise ratio (SNR)-like terms and there is an increment consisting of
UL data power, UL data length and BER values in the SNR-like term of DA method,
which suggests DA method outperforms the conventional ones in any scenarios.
Higher UL data power, longer UL data length and better BER performance lead to
more accurate estimated channels with DA method. Numerical results verify that
the analytical BER and NMSE results are close to the simulated ones and a
remarkable gain in both NMSE and DL rate can be achieved by DA method in
multiple scenarios with different modulations
Defining Urban Boundaries by Characteristic Scales
Defining an objective boundary for a city is a difficult problem, which
remains to be solved by an effective method. Recent years, new methods for
identifying urban boundary have been developed by means of spatial search
techniques (e.g. CCA). However, the new algorithms are involved with another
problem, that is, how to determine the characteristic radius of spatial search.
This paper proposes new approaches to looking for the most advisable spatial
searching radius for determining urban boundary. We found that the
relationships between the spatial searching radius and the corresponding number
of clusters take on an exponential function. In the exponential model, the
scale parameter just represents the characteristic length that we can use to
define the most objective urban boundary objectively. Two sets of China's
cities are employed to test this method, and the results lend support to the
judgment that the characteristic parameter can well serve for the spatial
searching radius. The research may be revealing for making urban spatial
analysis in methodology and implementing identification of urban boundaries in
practice.Comment: 26 pages, 5 figures, 7 table
- …