22 research outputs found
Non-Data-Aided Parameter Estimation in an Additive White Gaussian Noise Channel
Non-data-aided (NDA) parameter estimation is considered for
binary-phase-shift-keying transmission in an additive white Gaussian noise
channel. Cramer-Rao lower bounds (CRLBs) for signal amplitude, noise variance,
channel reliability constant and bit-error rate are derived and it is shown how
these parameters relate to the signal-to-noise ratio (SNR). An alternative
derivation of the iterative maximum likelihood (ML) SNR estimator is presented
together with a novel, low complexity NDA SNR estimator. The performance of the
proposed estimator is compared to previously suggested estimators and the CRLB.
The results show that the proposed estimator performs close to the iterative ML
estimator at significantly lower computational complexity
On the Exact BER of Bit-Wise Demodulators for One-Dimensional Constellations
The optimal bit-wise demodulator for M-ary pulse amplitude modulation (PAM)
over the additive white Gaussian noise channel is analyzed in terms of uncoded
bit-error rate (BER). New closed-form BER expressions for 4-PAM with any
labeling are developed. Moreover, closed-form BER expressions for 11 out of 23
possible bit patterns for 8-PAM are presented, which enable us to obtain the
BER for 8-PAM with some of the most popular labelings, including the binary
reflected Gray code and the natural binary code. Numerical results show that,
regardless of the labeling, there is no difference between the optimal
demodulator and the symbol-wise demodulator for any BER of practical interest
(below 0.1)
On the Asymptotic Performance of Bit-Wise Decoders for Coded Modulation
Two decoder structures for coded modulation over the Gaussian and flat fading
channels are studied: the maximum likelihood symbol-wise decoder, and the
(suboptimal) bit-wise decoder based on the bit-interleaved coded modulation
paradigm. We consider a 16-ary quadrature amplitude constellation labeled by a
Gray labeling. It is shown that the asymptotic loss in terms of pairwise error
probability, for any two codewords caused by the bit-wise decoder, is bounded
by 1.25 dB. The analysis also shows that for the Gaussian channel the
asymptotic loss is zero for a wide range of linear codes, including all
rate-1/2 convolutional codes
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
All-to-all Broadcast for Vehicular Networks Based on Coded Slotted ALOHA
We propose an uncoordinated all-to-all broadcast protocol for periodic
messages in vehicular networks based on coded slotted ALOHA (CSA). Unlike
classical CSA, each user acts as both transmitter and receiver in a half-duplex
mode. As in CSA, each user transmits its packet several times. The half-duplex
mode gives rise to an interesting design trade-off: the more the user repeats
its packet, the higher the probability that this packet is decoded by other
users, but the lower the probability for this user to decode packets from
others. We compare the proposed protocol with carrier sense multiple access
with collision avoidance, currently adopted as a multiple access protocol for
vehicular networks. The results show that the proposed protocol greatly
increases the number of users in the network that reliably communicate with
each other. We also provide analytical tools to predict the performance of the
proposed protocol.Comment: v2: small typos fixe
Broadcast Coded Slotted ALOHA: A Finite Frame Length Analysis
We propose an uncoordinated medium access control (MAC) protocol, called
all-to-all broadcast coded slotted ALOHA (B-CSA) for reliable all-to-all
broadcast with strict latency constraints. In B-CSA, each user acts as both
transmitter and receiver in a half-duplex mode. The half-duplex mode gives rise
to a double unequal error protection (DUEP) phenomenon: the more a user repeats
its packet, the higher the probability that this packet is decoded by other
users, but the lower the probability for this user to decode packets from
others. We analyze the performance of B-CSA over the packet erasure channel for
a finite frame length. In particular, we provide a general analysis of stopping
sets for B-CSA and derive an analytical approximation of the performance in the
error floor (EF) region, which captures the DUEP feature of B-CSA. Simulation
results reveal that the proposed approximation predicts very well the
performance of B-CSA in the EF region. Finally, we consider the application of
B-CSA to vehicular communications and compare its performance with that of
carrier sense multiple access (CSMA), the current MAC protocol in vehicular
networks. The results show that B-CSA is able to support a much larger number
of users than CSMA with the same reliability.Comment: arXiv admin note: text overlap with arXiv:1501.0338
Unequal Error Protection in Coded Slotted ALOHA
We analyze the performance of coded slotted ALOHA systems for a scenario
where users have different error protection requirements and correspondingly
can be divided into user classes. The main goal is to design the system so that
the requirements for each class are satisfied. To that end, we derive
analytical error floor approximations of the packet loss rate for each class in
the finite frame length regime, as well as the density evolution in the
asymptotic case. Based on this analysis, we propose a heuristic approach for
the optimization of the degree distributions to provide the required unequal
error protection. In addition, we analyze the decoding delay for users in
different classes and show that better protected users experience a smaller
average decoding delay
Probabilistic Handshake in All-to-all Broadcast Coded Slotted ALOHA
We propose a probabilistic handshake mechanism for all-to-all broadcast coded
slotted ALOHA. We consider a fully connected network where each user acts as
both transmitter and receiver in a half-duplex mode. Users attempt to exchange
messages with each other and to establish one-to-one handshakes, in the sense
that each user decides whether its packet was successfully received by the
other users: After performing decoding, each user estimates in which slots the
resolved users transmitted their packets and, based on that, decides if these
users successfully received its packet. The simulation results show that the
proposed handshake algorithm allows the users to reliably perform the
handshake. The paper also provides some analytical bounds on the performance of
the proposed algorithm which are in good agreement with the simulation results