Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Spectral Efficiency of Blind Channel Estimation and
  Synchronization Techniques   In the literature, channel estimation and synchronization (CE/SY) algorithms
are classified as blind, and hence spectrally efficient, if they do not require
pilot symbols. However, we show in this letter that such classification is not
accurate and can be misleading. Consequently, this letter presents a more
reliable and accurate approach to evaluate the spectral efficiency of
communications systems with various CE/SY algorithms. The proposed approach
allows fair spectral efficiency comparison between various systems with blind
or non-blind CE/SY algorithms. In particular, we evaluate the spectral
efficiency of communications systems that incorporates blind CE/SY algorithms
and compare it to other blind and pilot-based algorithms. The obtained results
reveal that, on the contrary to what is widely accepted, blind CE/SY algorithms
with modulation-type constrain do not necessarily improve the spectral
efficiency as compared to pilot-based techniques. Consequently, such techniques
are classified as conditionally blind, to distinguish them from fully blind
techniques.

19
The categories of this paper are: eess
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
13
The categories of this paper are: quant-ph
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
18
The categories of this paper are: econ
8
The categories of this paper are: hep-ex
4
The categories of this paper are: cond-mat
17
The categories of this paper are: q-fin
12
The categories of this paper are: nucl-th
29
The categories of this paper are: funct-an