15,222 research outputs found
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
LPDQ: a self-scheduled TDMA MAC protocol for one-hop dynamic lowpower wireless networks
Current Medium Access Control (MAC) protocols for data collection scenarios with a large number of nodes that generate bursty traffic are based on Low-Power Listening (LPL) for network synchronization and Frame Slotted ALOHA (FSA) as the channel access mechanism. However, FSA has an efficiency bounded to 36.8% due to contention effects, which reduces packet throughput and increases energy consumption. In this paper, we target such scenarios by presenting Low-Power Distributed Queuing (LPDQ), a highly efficient and low-power MAC protocol. LPDQ is able to self-schedule data transmissions, acting as a FSA MAC under light traffic and seamlessly converging to a Time Division Multiple Access (TDMA) MAC under congestion. The paper presents the design principles and the implementation details of LPDQ using low-power commercial radio transceivers. Experiments demonstrate an efficiency close to 99% that is independent of the number of nodes and is fair in terms of resource allocation.Peer ReviewedPostprint (author’s final draft
Sign-Compute-Resolve for Tree Splitting Random Access
We present a framework for random access that is based on three elements:
physical-layer network coding (PLNC), signature codes and tree splitting. In
presence of a collision, physical-layer network coding enables the receiver to
decode, i.e. compute, the sum of the packets that were transmitted by the
individual users. For each user, the packet consists of the user's signature,
as well as the data that the user wants to communicate. As long as no more than
K users collide, their identities can be recovered from the sum of their
signatures. This framework for creating and transmitting packets can be used as
a fundamental building block in random access algorithms, since it helps to
deal efficiently with the uncertainty of the set of contending terminals. In
this paper we show how to apply the framework in conjunction with a
tree-splitting algorithm, which is required to deal with the case that more
than K users collide. We demonstrate that our approach achieves throughput that
tends to 1 rapidly as K increases. We also present results on net data-rate of
the system, showing the impact of the overheads of the constituent elements of
the proposed protocol. We compare the performance of our scheme with an upper
bound that is obtained under the assumption that the active users are a priori
known. Also, we consider an upper bound on the net data-rate for any PLNC based
strategy in which one linear equation per slot is decoded. We show that already
at modest packet lengths, the net data-rate of our scheme becomes close to the
second upper bound, i.e. the overhead of the contention resolution algorithm
and the signature codes vanishes.Comment: This is an extended version of arXiv:1409.6902. Accepted for
publication in the IEEE Transactions on Information Theor
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