16,411 research outputs found
High-Throughput Random Access via Codes on Graphs
Recently, contention resolution diversity slotted ALOHA (CRDSA) has been
introduced as a simple but effective improvement to slotted ALOHA. It relies on
MAC burst repetitions and on interference cancellation to increase the
normalized throughput of a classic slotted ALOHA access scheme. CRDSA allows
achieving a larger throughput than slotted ALOHA, at the price of an increased
average transmitted power. A way to trade-off the increment of the average
transmitted power and the improvement of the throughput is presented in this
paper. Specifically, it is proposed to divide each MAC burst in k sub-bursts,
and to encode them via a (n,k) erasure correcting code. The n encoded
sub-bursts are transmitted over the MAC channel, according to specific
time/frequency-hopping patterns. Whenever n-e>=k sub-bursts (of the same burst)
are received without collisions, erasure decoding allows recovering the
remaining e sub-bursts (which were lost due to collisions). An interference
cancellation process can then take place, removing in e slots the interference
caused by the e recovered sub-bursts, possibly allowing the correct decoding of
sub-bursts related to other bursts. The process is thus iterated as for the
CRDSA case.Comment: Presented at the Future Network and MobileSummit 2010 Conference,
Florence (Italy), June 201
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
Optimal Networks from Error Correcting Codes
To address growth challenges facing large Data Centers and supercomputing
clusters a new construction is presented for scalable, high throughput, low
latency networks. The resulting networks require 1.5-5 times fewer switches,
2-6 times fewer cables, have 1.2-2 times lower latency and correspondingly
lower congestion and packet losses than the best present or proposed networks
providing the same number of ports at the same total bisection. These advantage
ratios increase with network size. The key new ingredient is the exact
equivalence discovered between the problem of maximizing network bisection for
large classes of practically interesting Cayley graphs and the problem of
maximizing codeword distance for linear error correcting codes. Resulting
translation recipe converts existent optimal error correcting codes into
optimal throughput networks.Comment: 14 pages, accepted at ANCS 2013 conferenc
Tiny Codes for Guaranteeable Delay
Future 5G systems will need to support ultra-reliable low-latency
communications scenarios. From a latency-reliability viewpoint, it is
inefficient to rely on average utility-based system design. Therefore, we
introduce the notion of guaranteeable delay which is the average delay plus
three standard deviations of the mean. We investigate the trade-off between
guaranteeable delay and throughput for point-to-point wireless erasure links
with unreliable and delayed feedback, by bringing together signal flow
techniques to the area of coding. We use tiny codes, i.e. sliding window by
coding with just 2 packets, and design three variations of selective-repeat ARQ
protocols, by building on the baseline scheme, i.e. uncoded ARQ, developed by
Ausavapattanakun and Nosratinia: (i) Hybrid ARQ with soft combining at the
receiver; (ii) cumulative feedback-based ARQ without rate adaptation; and (iii)
Coded ARQ with rate adaptation based on the cumulative feedback. Contrasting
the performance of these protocols with uncoded ARQ, we demonstrate that HARQ
performs only slightly better, cumulative feedback-based ARQ does not provide
significant throughput while it has better average delay, and Coded ARQ can
provide gains up to about 40% in terms of throughput. Coded ARQ also provides
delay guarantees, and is robust to various challenges such as imperfect and
delayed feedback, burst erasures, and round-trip time fluctuations. This
feature may be preferable for meeting the strict end-to-end latency and
reliability requirements of future use cases of ultra-reliable low-latency
communications in 5G, such as mission-critical communications and industrial
control for critical control messaging.Comment: to appear in IEEE JSAC Special Issue on URLLC in Wireless Network
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
Frameless ALOHA with Reliability-Latency Guarantees
One of the novelties brought by 5G is that wireless system design has
increasingly turned its focus on guaranteeing reliability and latency. This
shifts the design objective of random access protocols from throughput
optimization towards constraints based on reliability and latency. For this
purpose, we use frameless ALOHA, which relies on successive interference
cancellation (SIC), and derive its exact finite-length analysis of the
statistics of the unresolved users (reliability) as a function of the
contention period length (latency). The presented analysis can be used to
derive the reliability-latency guarantees. We also optimize the scheme
parameters in order to maximize the reliability within a given latency. Our
approach represents an important step towards the general area of design and
analysis of access protocols with reliability-latency guarantees.Comment: Accepted for presentation at IEEE Globecom 201
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