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Capacity of TimeSlotted ALOHA Packetized MultipleAccess Systems over the AWGN Channel
"... We study di#erent notions of capacity for timeslotted ALOHA systems. In these systems multiple users synchronously send packets in a bursty manner over a common additive white Gaussian noise (AWGN) channel. The users do not coordinate their transmissions, which may collide at the receiver. For s ..."
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Cited by 21 (3 self)
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We study di#erent notions of capacity for timeslotted ALOHA systems. In these systems multiple users synchronously send packets in a bursty manner over a common additive white Gaussian noise (AWGN) channel. The users do not coordinate their transmissions, which may collide at the receiver. For such a system we define both singleslot capacity and multipleslot capacity. We then construct a coding and decoding scheme for singleslot capacity that achieves any rate within this capacity region. This coding and decoding scheme for a single time slot combines aspects of multiple access rate splitting and of broadcast codes for degraded AWGN channels. This design allows some bits to be reliably received even when collisions occur, and more bits to be reliably received in the absence of collisions. The exact number of bits reliably received under both of these scenarios is part of the code design process, which we optimize to maximize the expected rate in each slot.
A Distributed Scheme for Achieving EnergyDelay Tradeoffs With Multiple Service Classes over a Dynamically Varying Network
"... We consider a dynamical probabilistic traffic model for the number of users transmitting at any time. This model captures both user mobility and traffic burstiness. Moreover, we assume no centralized controller, such as a scheduler, is available. When multiple users transmit simultaneously, multiple ..."
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Cited by 9 (1 self)
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We consider a dynamical probabilistic traffic model for the number of users transmitting at any time. This model captures both user mobility and traffic burstiness. Moreover, we assume no centralized controller, such as a scheduler, is available. When multiple users transmit simultaneously, multiple access interference affects throughput considerably. Most queue control schemes assume individual users know the states of their own queues (local queue information) along with the states of other users queues (shared queue information) and address issues of scheduling; but this sharing of information may be onerous in a practical system. While shared queue information has recently been shown [1] not to affect the capacity of such systems, it has a considerable impact on delay. We introduce a scheme, where for each user, a bit of shared queue information specifies whether its queue length is above or below a threshold. Our scheme relies on two different service classes implemented through a superposition coding scheme (first proposed in [2], further studied and expanded in [1]). The first class experiences no delay due to multiple access interference while second class requires retransmissions when such an event occurs. We show how our scheme affords an energydelay tradeoff. Moreover, when configured properly, our scheme can be can attain boundary points of the region corresponding to minimum energy with no shared queue information for 0 delay along with minimum energy subject to system stability. We derive bounds on the performance of the multiple access system using our proposed scheme by introducing Lyapunov function bounds in a manner similar to [3].
On Queueing and MultiLayer Coding
, 2004
"... A singleserver queue concatenated with a multilevel channel encoder is considered. The main focus of this work is on minimization of the average delay of a packet from entering the queue until completion of successful service. Tight bounds are derived for the average delay for different numbers of ..."
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Cited by 4 (1 self)
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A singleserver queue concatenated with a multilevel channel encoder is considered. The main focus of this work is on minimization of the average delay of a packet from entering the queue until completion of successful service. Tight bounds are derived for the average delay for different numbers of coded layers. Numerical optimization is applied to find the optimal resource allocation minimizing the average delay. Delay bounds are also derived for continuous layering (single user broadcast approach). The optimizing power distribution of the minimal delay is approximated, and numerically evaluated. It is demonstrated that code layering may give pronounced performance gains in terms of delay, which are more impressive than those associated with throughput. This makes layering more attractive when communicating under stringent delay constraints.
Communication Through Jamming Over a Slotted ALOHA Channel
, 2005
"... This work derives bounds on the jamming capacity of a slotted ALOHA system. A system with n legitimate users, each with a Bernoulli arrival process is considered. Packets are temporarily stored at the corresponding user queues, and a slotted ALOHA strategy is used for packet transmissions over the s ..."
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Cited by 2 (0 self)
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This work derives bounds on the jamming capacity of a slotted ALOHA system. A system with n legitimate users, each with a Bernoulli arrival process is considered. Packets are temporarily stored at the corresponding user queues, and a slotted ALOHA strategy is used for packet transmissions over the shared channel. The scenario considered is that of a pair of covert users that jam legitimate transmissions in order to communicate over the slotted ALOHA channel. Jamming leads to binary signaling between the covert users, with packet collisions due to legitimate users treated as (multiplicative) noise in this channel. Further, the queueing dynamics at the legitimate users stochastically couples the jamming strategy used by the covert users and the channel evolution. By considering various i.i.d. jamming strategies, achievable jamming rates over the slotted ALOHA channel are derived. Further, an upper bound on the jamming capacity over the class of all ergodic jamming policies is derived. These bounds are shown to be tight in the limit where the offered system load approaches unity.
1 Successive Refinement via Broadcast: Optimizing Expected Distortion of a Gaussian Source over a Gaussian Fading Channel
"... Abstract—We consider the problem of transmitting a Gaussian source on a slowly fading Gaussian channel, subject to the mean squared error distortion measure. The channel state information is known only at the receiver but not at the transmitter. The source is assumed to be encoded in a successive re ..."
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Abstract—We consider the problem of transmitting a Gaussian source on a slowly fading Gaussian channel, subject to the mean squared error distortion measure. The channel state information is known only at the receiver but not at the transmitter. The source is assumed to be encoded in a successive refinement manner, and then transmitted over the channel using the broadcast strategy. In order to minimize the expected distortion at the receiver, optimal power allocation is essential. We propose an efficient algorithm to compute the optimal solution in linear time O(M), when the total number of possible discrete fading states is M. Moreover, we provide a derivation of the optimal power allocation when the fading state is a continuum, using the classical variational method. The proposed algorithm as well as the continuous solution is based on an alternative representation of the capacity region of the Gaussian broadcast channel. Index Terms—Broadcast strategy, joint sourcechannel coding, power allocation, successive refinement. I.
Covert Communication over Slotted ALOHA Systems
"... This paper uses jamming legitimate transmissions over a slotted ALOHA system as a means of covert communication. The resulting covert channel is found to be source dependent, and to have infinite memory. Hence, a characterization of the capacity of covert communication over such a medium is an inher ..."
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This paper uses jamming legitimate transmissions over a slotted ALOHA system as a means of covert communication. The resulting covert channel is found to be source dependent, and to have infinite memory. Hence, a characterization of the capacity of covert communication over such a medium is an inherently complex problem. Employing i.i.d. jamming strategies, this paper derives achievable rates for this channel. Finally, we derive an outer bound over the set of all ergodic jamming policies for this channel. 1