535 research outputs found
Asymptotic and Finite Frame Length Analysis of Frame Asynchronous Coded Slotted ALOHA
We consider a frame-asynchronous coded slotted ALOHA (FA-CSA) system where
users become active according to a Poisson random process. In contrast to
standard frame-synchronous CSA (FS-CSA), users transmit a first replica of
their message in the slot following their activation and other replicas
uniformly at random in a number of subsequent slots. We derive the
(approximate) density evolution that characterizes the asymptotic performance
of FA-CSA when the frame length goes to infinity. We show that, if users can
monitor the system before they start transmitting, a boundary-effect similar to
that of spatially-coupled codes occurs, which greatly improves the decoding
threshold as compared to FS-CSA. We also derive analytical approximations of
the error floor (EF) in the finite frame length regime. We show that FA-CSA
yields in general lower EF, better performance in the waterfall region, and
lower average delay, as compared to FS-CSA.Comment: 5 pages, 6 figures. Updated notation, terminology, and typo
Exploiting Capture Effect in Frameless ALOHA for Massive Wireless Random Access
The analogies between successive interference cancellation (SIC) in slotted
ALOHA framework and iterative belief-propagation erasure-decoding, established
recently, enabled the application of the erasure-coding theory and tools to
design random access schemes. This approach leads to throughput substantially
higher than the one offered by the traditional slotted ALOHA. In the simplest
setting, SIC progresses when a successful decoding occurs for a single user
transmission. In this paper we consider a more general setting of a channel
with capture and explore how such physical model affects the design of the
coded random access protocol. Specifically, we assess the impact of capture
effect in Rayleigh fading scenario on the design of SIC-enabled slotted ALOHA
schemes. We provide analytical treatment of frameless ALOHA, which is a special
case of SIC-enabled ALOHA scheme. We demonstrate both through analytical and
simulation results that the capture effect can be very beneficial in terms of
achieved throughput.Comment: Accepted for presentation at IEEE WCNC'14 Track 2 (MAC and
Cross-Layer Design
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
On Frame Asynchronous Coded Slotted ALOHA: Asymptotic, Finite Length, and Delay Analysis
We consider a frame asynchronous coded slotted ALOHA (FA-CSA) system for
uncoordinated multiple access, where users join the system on a slot-by-slot
basis according to a Poisson random process and, in contrast to standard frame
synchronous CSA (FS-CSA), users are not frame-synchronized. We analyze the
performance of FA-CSA in terms of packet loss rate and delay. In particular, we
derive the (approximate) density evolution that characterizes the asymptotic
performance of FA-CSA when the frame length goes to infinity. We show that, if
the receiver can monitor the system before anyone starts transmitting, a
boundary effect similar to that of spatially-coupled codes occurs, which
greatly improves the iterative decoding threshold. Furthermore, we derive tight
approximations of the error floor (EF) for the finite frame length regime,
based on the probability of occurrence of the most frequent stopping sets. We
show that, in general, FA-CSA provides better performance in both the EF and
waterfall regions as compared to FS-CSA. Moreover, FA-CSA exhibits better delay
properties than FS-CSA.Comment: 13 pages, 12 figures. arXiv admin note: substantial text overlap with
arXiv:1604.0629
ALOHA Random Access that Operates as a Rateless Code
Various applications of wireless Machine-to-Machine (M2M) communications have
rekindled the research interest in random access protocols, suitable to support
a large number of connected devices. Slotted ALOHA and its derivatives
represent a simple solution for distributed random access in wireless networks.
Recently, a framed version of slotted ALOHA gained renewed interest due to the
incorporation of successive interference cancellation (SIC) in the scheme,
which resulted in substantially higher throughputs. Based on similar principles
and inspired by the rateless coding paradigm, a frameless approach for
distributed random access in slotted ALOHA framework is described in this
paper. The proposed approach shares an operational analogy with rateless
coding, expressed both through the user access strategy and the adaptive length
of the contention period, with the objective to end the contention when the
instantaneous throughput is maximized. The paper presents the related analysis,
providing heuristic criteria for terminating the contention period and showing
that very high throughputs can be achieved, even for a low number for
contending users. The demonstrated results potentially have more direct
practical implications compared to the approaches for coded random access that
lead to high throughputs only asymptotically.Comment: Revised version submitted to IEEE Transactions on Communication
Coded Slotted ALOHA: A Graph-Based Method for Uncoordinated Multiple Access
In this paper, a random access scheme is introduced which relies on the
combination of packet erasure correcting codes and successive interference
cancellation (SIC). The scheme is named coded slotted ALOHA. A bipartite graph
representation of the SIC process, resembling iterative decoding of generalized
low-density parity-check codes over the erasure channel, is exploited to
optimize the selection probabilities of the component erasure correcting codes
via density evolution analysis. The capacity (in packets per slot) of the
scheme is then analyzed in the context of the collision channel without
feedback. Moreover, a capacity bound is developed and component code
distributions tightly approaching the bound are derived.Comment: The final version to appear in IEEE Trans. Inf. Theory. 18 pages, 10
figure
Coded Slotted ALOHA with Varying Packet Loss Rate across Users
The recent research has established an analogy between successive
interference cancellation in slotted ALOHA framework and iterative
belief-propagation erasure-decoding, which has opened the possibility to
enhance random access protocols by utilizing theory and tools of
erasure-correcting codes. In this paper we present a generalization of the
and-or tree evaluation, adapted for the asymptotic analysis of the slotted
ALOHA-based random-access protocols, for the case when the contending users
experience different channel conditions, resulting in packet loss probability
that varies across users. We apply the analysis to the example of frameless
ALOHA, where users contend on a slot basis. We present results regarding the
optimal access probabilities and contention period lengths, such that the
throughput and probability of user resolution are maximized.Comment: 4 pages, submitted to GlobalSIP 201
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
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