1,727,864 research outputs found
Enhanced Contention Resolution Aloha - ECRA
No full textRandom Access (RA) Medium Access (MAC) protocols
are simple and effective when the nature of the traffic
is unpredictable and random. In the following paper, a novel
RA protocol called Enhanced Contention Resolution ALOHA
(ECRA) is presented. This evolution, based on the previous
Contention Resolution ALOHA (CRA) protocol, exploits the
nature of the interference in unslotted Aloha-like channels for
trying to resolve most of the partial collision that can occur
there. In the paper, the idea behind ECRA is presented together
with numerical simulations and a mathematical analysis of
its performance gain. It is shown that relevant performance
increases in both throughput and Packet Error Rate (PER) can
be reached by ECRA with respect to CRA. A comparison with
Contention Resolution Diversity Slotted ALOHA (CRDSA) is also
provided
The Throughput of Slotted Aloha with Diversity
No full textIn this paper, a simple variation of classical Slotted Aloha is introduced and analyzed. The enhancement relies on adding multiple receivers that gather different observations of the packets transmitted by a user population in one slot. For each observation, the packets transmitted in one slot are assumed to be subject to independent on-off fading, so that each of them is either completely faded, and then does not bring any power or interference at the receiver, or it arrives unfaded, and then may or may not, collide with other unfaded transmissions. With this model, a novel type of diversity is introduced to the conventional SA scheme, leading to relevant throughput gains already for moderate number of receivers. The analytical framework that we introduce allows to derive closed-form expression of both throughput and packet loss rate an arbitrary number of receivers, providing interesting hints on the key trade-offs that characterize the system. We then focus on the problem of having receivers forward the full set of collected packets to a final gateway using the minimum possible amount of resources, i.e., avoiding delivery of duplicate packets, without allowing any exchange of information among them. We derive what is the minimum amount of resources needed and propose a scheme based on
random linear network coding that achieves asymptotically this bound without the need for the receivers to coordinate among them
Delay distributions of slotted ALOHA and CSMA
No full textWe derive the closed-form delay distributions of slotted ALOHA and nonpersistent carrier sense multiple access (CSMA) protocols under steady state. Three retransmission policies are analyzed. We find that under a binary exponential backoff retransmission policy, finite average delay and finite delay variance can be guaranteed for G<2S and G<4S/3, respectively, where G is the channel traffic and S is the channel throughput. As an example, in slotted ALOHA, S<(ln2)/2 and S<3(ln4-ln3)/4 are the operating ranges for finite first and second delay moments. In addition, the blocking probability and delay performance as a function of r/sub max/ (maximum number of retransmissions allowed) is also derived
Performance Enhancements for Asynchronous Random Access Protocols over Satellite
No full textIn this paper, a novel enhancement of the well known
ALOHA random access mechanism is presented which largely extends the achievable throughput compared to traditional ALOHA and provides significantly lower packet loss rates. The novel mechanism, called Contention Resolution - ALOHA (CRA), is based on transmitting multiple replicas of a packet in an unslotted ALOHA system and applying interference cancellation techniques. In this paper the methodology for this new random access technique is presented, also w.r.t. existing Interference Cancellation (IC) techniques. Moreover numerical results for performance comparison with state of the art random access mechanisms, such as Contention Resolution Diversity Slotted ALOHA (CRDSA) are provided. Finally the benefit of taking strong forward error correcting codes for the performance of CRA is shown
Penentuan Batasan Parameter Komunikasi Data Dengan Teknik Aloha
No full textAloha adalah nama protokol dalam bidang komunikasi data melalui satelit yang dikembangkan selama akhir 1960 di Universitas Hawaii. Makalah ini membahas bagaimana menentukan lebar kanal, dan jumlah pemakai. Teori Nyquist dan Shannon yang telah ditampilkan secara grafik, dilengkapi dengan data energi bit per sinyal per kerapatan derau (Eh/No) untuk Bit Error Rate dan modulasi tertentu, dan data keperluan "Random Multiple ACCESS" (RAM) bagi berbagai pelayanan komunikasi digital, gambaran singkat tentang Aloha murni, Aloha bercelah, dan sebagainya untuk mendukung penentuan tersebut.hlm. 12-2
High-Throughput Random Access via Codes on Graphs
No full textRecently, 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
Aloha Eagles Papers, 1966-1977
No full textThe Aloha Eagles Papers document her long and distinguished career as a state legislator, serving in the N.D. House of Representatives from 1967 to 1985 and her active support of women's issues. She introduced legislation that would have legalized North Dakota's abortion law in 1969 and in 1973 she introduced a resolution in favor of the Equal Rights Amendment
An Enhanced Multiple Random Access Scheme for Satellite Communications
No full textIn this paper, we introduce Multi-Slots Coded ALOHA (MuSCA) as a multiple random access method for satellite communications. This scheme can be considered as a generalization of the Contention Resolution Diversity Slotted Aloha (CRDSA) mechanism. Instead of transmitting replicas, this system replaces them by several parts of a single word of an error correcting code. It is also different from Coded Slotted ALOHA (CSA) because collided data are used in the iterative decoding of the frame. In MuSCA, the entity in charge of the decoding mechanism collects all bursts of the same user (including the interfered slots) before decoding and implements a successive interference cancellation process to remove successfully decoded signals. Simulations show that the achievable total normalized throughput is greater than 1.25 and 1.4 for a frame of 100 and 500 slots, resulting in a gain of 85% and 75% with respect to CRDSA and CSA respectively. This gain comes from the combination between diversity introduced by the random distribution of the data on the frames and MuSCA decoding algorithm, allows the system to transmit on average more than one packet per slot. This paper is a first analysis of the proposed scheme and opens several perspectives
Antonio Saavedra, Yolanda Meave, Jorge Meave, and University President David Mathews at the International Students Reception
No full textAntonio Saavedra, Yolanda Meave, Jorge Meave, and University President David Mathews are standing together at the International Students Reception in 1978
Protocolli Framed Slotted Aloha
No full textIl protocollo Aloha è un noto protocollo di accesso al mezzo a contesa indicato per canali di tipo broadcast. In questo lavoro si studiano alcune innovazioni del protocollo Aloha recentemente proposte che riescono a incrementarne le prestazioni in termini di throughputope
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