198 research outputs found
Stability Region of a Slotted Aloha Network with K-Exponential Backoff
Stability region of random access wireless networks is known for only simple
network scenarios. The main problem in this respect is due to interaction among
queues. When transmission probabilities during successive transmissions change,
e.g., when exponential backoff mechanism is exploited, the interactions in the
network are stimulated. In this paper, we derive the stability region of a
buffered slotted Aloha network with K-exponential backoff mechanism,
approximately, when a finite number of nodes exist. To this end, we propose a
new approach in modeling the interaction among wireless nodes. In this
approach, we model the network with inter-related quasi-birth-death (QBD)
processes such that at each QBD corresponding to each node, a finite number of
phases consider the status of the other nodes. Then, by exploiting the
available theorems on stability of QBDs, we find the stability region. We show
that exponential backoff mechanism is able to increase the area of the
stability region of a simple slotted Aloha network with two nodes, more than
40\%. We also show that a slotted Aloha network with exponential backoff may
perform very near to ideal scheduling. The accuracy of our modeling approach is
verified by simulation in different conditions.Comment: 30 pages, 6 figure
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
ALOHA With Collision Resolution(ALOHA-CR): Theory and Software Defined Radio Implementation
A cross-layer scheme, namely ALOHA With Collision Resolution (ALOHA-CR), is
proposed for high throughput wireless communications in a cellular scenario.
Transmissions occur in a time-slotted ALOHA-type fashion but with an important
difference: simultaneous transmissions of two users can be successful. If more
than two users transmit in the same slot the collision cannot be resolved and
retransmission is required. If only one user transmits, the transmitted packet
is recovered with some probability, depending on the state of the channel. If
two users transmit the collision is resolved and the packets are recovered by
first over-sampling the collision signal and then exploiting independent
information about the two users that is contained in the signal polyphase
components. The ALOHA-CR throughput is derived under the infinite backlog
assumption and also under the assumption of finite backlog. The contention
probability is determined under these two assumptions in order to maximize the
network throughput and maintain stability. Queuing delay analysis for network
users is also conducted. The performance of ALOHA-CR is demonstrated on the
Wireless Open Access Research Platform (WARP) test-bed containing five software
defined radio nodes. Analysis and test-bed results indicate that ALOHA-CR leads
to significant increase in throughput and reduction of service delays
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
On the Stability of Random Multiple Access with Stochastic Energy Harvesting
In this paper, we consider the random access of nodes having energy
harvesting capability and a battery to store the harvested energy. Each node
attempts to transmit the head-of-line packet in the queue if its battery is
nonempty. The packet and energy arrivals into the queue and the battery are all
modeled as a discrete-time stochastic process. The main contribution of this
paper is the exact characterization of the stability region of the packet
queues given the energy harvesting rates when a pair of nodes are randomly
accessing a common channel having multipacket reception (MPR) capability. The
channel with MPR capability is a generalized form of the wireless channel
modeling which allows probabilistic receptions of the simultaneously
transmitted packets. The results obtained in this paper are fairly general as
the cases with unlimited energy for transmissions both with the collision
channel and the channel with MPR capability can be derived from ours as special
cases. Furthermore, we study the impact of the finiteness of the batteries on
the achievable stability region.Comment: The material in this paper was presented in part at the IEEE
International Symposium on Information Theory, Saint Petersburg, Russia, Aug.
201
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