526 research outputs found
Multi-slot Coded ALOHA with Irregular Degree Distribution
This paper proposes an improvement of the random multiple access scheme for
satellite communication named Multislot coded ALOHA (MuSCA). MuSCA is a
generalization of Contention Resolution Diversity Slotted ALOHA (CRDSA). In
this scheme, each user transmits several parts of a single codeword of an error
correcting code instead of sending replicas. At the receiver level, the decoder
collects all these parts and includes them in the decoding process even if they
are interfered. In this paper, we show that a high throughput can be obtained
by selecting variable code rates and user degrees according to a probability
distribution. With an optimal irregular degree distribution, our system
achieves a normalized throughput up to 1.43, resulting in a significant gain
compared to CRDSA and MuSCA. The spectral efficiency and the implementation
issues of the scheme are also analyzed.Comment: 6 pages, 8 figure
Network Coding Tree Algorithm for Multiple Access System
Network coding is famous for significantly improving the throughput of
networks. The successful decoding of the network coded data relies on some side
information of the original data. In that framework, independent data flows are
usually first decoded and then network coded by relay nodes. If appropriate
signal design is adopted, physical layer network coding is a natural way in
wireless networks. In this work, a network coding tree algorithm which enhances
the efficiency of the multiple access system (MAS) is presented. For MAS,
existing works tried to avoid the collisions while collisions happen frequently
under heavy load. By introducing network coding to MAS, our proposed algorithm
achieves a better performance of throughput and delay. When multiple users
transmit signal in a time slot, the mexed signals are saved and used to jointly
decode the collided frames after some component frames of the network coded
frame are received. Splitting tree structure is extended to the new algorithm
for collision solving. The throughput of the system and average delay of frames
are presented in a recursive way. Besides, extensive simulations show that
network coding tree algorithm enhances the system throughput and decreases the
average frame delay compared with other algorithms. Hence, it improves the
system performance
Analysis of Network Coding in a Slotted ALOHA-based Two-Way Relay Network
This paper deals with a two-way relay network (TWRN) based on a slotted ALOHA
protocol which utilizes network coding to exchange the packets. We proposed an
analytical approach to study the behavior of such networks and the effects of
network coding on the throughput, power, and queueing delay of the relay node.
In addition, when end nodes are not saturated, our approach enables us to
achieve the stability region of the network in different situations. Finally,
we carry out some simulation to confirm the validity of the proposed analytical
approach
Towards a System Theoretic Approach to Wireless Network Capacity in Finite Time and Space
In asymptotic regimes, both in time and space (network size), the derivation
of network capacity results is grossly simplified by brushing aside queueing
behavior in non-Jackson networks. This simplifying double-limit model, however,
lends itself to conservative numerical results in finite regimes. To properly
account for queueing behavior beyond a simple calculus based on average rates,
we advocate a system theoretic methodology for the capacity problem in finite
time and space regimes. This methodology also accounts for spatial correlations
arising in networks with CSMA/CA scheduling and it delivers rigorous
closed-form capacity results in terms of probability distributions. Unlike
numerous existing asymptotic results, subject to anecdotal practical concerns,
our transient one can be used in practical settings: for example, to compute
the time scales at which multi-hop routing is more advantageous than single-hop
routing
Interference-Based Optimal Power-Efficient Access Scheme for Cognitive Radio Networks
In this paper, we propose a new optimization-based access strategy of
multipacket reception (MPR) channel for multiple secondary users (SUs)
accessing the primary user (PU) spectrum opportunistically. We devise an
analytical model that realizes the multipacket access strategy of SUs that
maximizes the throughput of individual backlogged SUs subject to queue
stability of the PU. All the network receiving nodes have MPR capability. We
aim at maximizing the throughput of the individual SUs such that the PU's queue
is maintained stable. Moreover, we are interested in providing an
energy-efficient cognitive scheme. Therefore, we include energy constraints on
the PU and SU average transmitted energy to the optimization problem. Each SU
accesses the medium with certain probability that depends on the PU's activity,
i.e., active or inactive. The numerical results show the advantage in terms of
SU throughput of the proposed scheme over the conventional access scheme, where
the SUs access the channel randomly with fixed power when the PU is sensed to
be idle
On Coding for Reliable Communication over Packet Networks
We present a capacity-achieving coding scheme for unicast or multicast over
lossy packet networks. In the scheme, intermediate nodes perform additional
coding yet do not decode nor even wait for a block of packets before sending
out coded packets. Rather, whenever they have a transmission opportunity, they
send out coded packets formed from random linear combinations of previously
received packets. All coding and decoding operations have polynomial
complexity.
We show that the scheme is capacity-achieving as long as packets received on
a link arrive according to a process that has an average rate. Thus, packet
losses on a link may exhibit correlation in time or with losses on other links.
In the special case of Poisson traffic with i.i.d. losses, we give error
exponents that quantify the rate of decay of the probability of error with
coding delay. Our analysis of the scheme shows that it is not only
capacity-achieving, but that the propagation of packets carrying "innovative"
information follows the propagation of jobs through a queueing network, and
therefore fluid flow models yield good approximations. We consider networks
with both lossy point-to-point and broadcast links, allowing us to model both
wireline and wireless packet networks.Comment: 33 pages, 6 figures; revised appendi
Sign-Compute-Resolve for Random Access
We present an approach to random access that is based on three elements:
physical-layer network coding, signature codes and tree splitting. Upon
occurrence of a collision, physical-layer network coding enables the receiver
to decode the sum of the information that was transmitted by the individual
users. For each user this information consists of the data that the user wants
to communicate as well as the user's signature. As long as no more than
users collide, their identities can be recovered from the sum of their
signatures. A splitting protocol is used to deal with the case that more than
users collide. We measure the performance of the proposed method in terms
of user resolution rate as well as overall throughput of the system. The
results show that our approach significantly increases the performance of the
system even compared to coded random access, where collisions are not wasted,
but are reused in successive interference cancellation.Comment: Accepted for presentation at 52nd Annual Allerton Conference on
Communication, Control, and Computin
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