4,675 research outputs found
Error Floor Analysis of Coded Slotted ALOHA over Packet Erasure Channels
We present a framework for the analysis of the error floor of coded slotted
ALOHA (CSA) for finite frame lengths over the packet erasure channel. The error
floor is caused by stopping sets in the corresponding bipartite graph, whose
enumeration is, in general, not a trivial problem. We therefore identify the
most dominant stopping sets for the distributions of practical interest. The
derived analytical expressions allow us to accurately predict the error floor
at low to moderate channel loads and characterize the unequal error protection
inherent in CSA
An error floor in tone calibrated transmission
Use of a low level pilot tone has been shown to eliminate the error floor in fading channels. This paper demonstrates that non-idealities in the receiver's pilot tone filter cause reappearance of the error floor. It also presents the bit error rate (BER) in closed form, in contrast to the multidimensional numerical integration of previous work
Lowering the Error Floor of LDPC Codes Using Cyclic Liftings
Cyclic liftings are proposed to lower the error floor of low-density
parity-check (LDPC) codes. The liftings are designed to eliminate dominant
trapping sets of the base code by removing the short cycles which form the
trapping sets. We derive a necessary and sufficient condition for the cyclic
permutations assigned to the edges of a cycle of length in the
base graph such that the inverse image of in the lifted graph consists of
only cycles of length strictly larger than . The proposed method is
universal in the sense that it can be applied to any LDPC code over any channel
and for any iterative decoding algorithm. It also preserves important
properties of the base code such as degree distributions, encoder and decoder
structure, and in some cases, the code rate. The proposed method is applied to
both structured and random codes over the binary symmetric channel (BSC). The
error floor improves consistently by increasing the lifting degree, and the
results show significant improvements in the error floor compared to the base
code, a random code of the same degree distribution and block length, and a
random lifting of the same degree. Similar improvements are also observed when
the codes designed for the BSC are applied to the additive white Gaussian noise
(AWGN) channel
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