This paper investigates adaptive streaming codes over a three-node relayed network. In this setting, a source transmits a sequence of message packets through a relay under a delay constraint of$T$time slots per packet. The source-to-relay and relay-to-destination links are unreliable and introduce a maximum of$N_{1}$and$N_{2}$packet erasures respectively. Recent work has proposed adaptive (time variant) and nonadaptive (time invariant) code constructions for this setting and has shown that adaptive codes can achieve higher rates. However, the adaptive construction deals with many possibilities, leading to an impractical code with very large block lengths. We therefore propose a simplified adaptive code construction which greatly improves the practicality of the code, with only a small cost to the achievable rates. We analyze our construction in terms of the achievable rates and field size requirements, and perform numerical simulations to estimate packet loss probabilities over statistical channels.

This paper studies streaming erasure codes in a relayed multicast setting, where a source wishes to transmit a sequence of messages to two different destinations through a common relay. Our construction extends previously proposed works on the single-destination setting studied in Fong et al. and Facenda et al. to the multicast setting, where each destination can recover the source packets with a correspondingly different delay. A key property of our construction is that it does not require prior knowledge of the maximum number of erasures on the relay-destination link. Instead, it enables the recovery of the source stream with a decoding delay that depends on the number of erasures on the relay-destination links. We demonstrate that if some divisibility conditions are satisfied, then the proposed construction can simultaneously achieve the single-destination delay in Fong et al. for both receivers. Finally we also explain how our proposed construction can be applied in the setting of a single destination when the maximum number of erasures on the relay-destination link is not known beforehand.

This paper studies packet repetition strategies over erasure channels with memory and a long feedback delay. The problem is initially formulated as a communications problem where a source wishes to transmit one message packet to a destination while minimizing both the delay and the number of transmissions. At each time instant, the sender is provided a delayed acknowledgement feedback about past attempts, and must decide whether to attempt a new transmission or not. This problem is then re-formulated as an episodic reinforcement learning problem, where an agent attempts to learn the optimal transmission policy, provided delayed feedback about past transmission attempts. The agent is helped by a channel estimator, which attempts to capture the channel memory and use that to predict probabilities of erasures in a future window. This channel estimator is also data-driven and learns the channel model without anya priorichannel knowledge. The paper presents a lower bound on the achievable trade-off between delay and number of transmissions for any channel modeled as a Markov process. Experimental results show that the combination of the proposed channel estimator and the agent can noticeably outperform naive strategies for channels with memory, and achieves results close to the lower bound.

Many emerging multimedia streaming applications involve multiple users communicating under strict latency constraints. In this paper we study streaming codes for a network involving two source nodes, one relay node and a destination node. In this paper’s setting, each source node transmits a stream of messages, through the relay, to a destination, who is required to decode the messages under a strict delay constraint. For the case of a single source node, a class of streaming codes has been proposed by Fong et al., using the concept of delay-spectrum. The current paper presents a novel framework, which constructs streaming codes for a relayed multi-user setting by sequentially constructing the codes for each link. This requires a characterization of the set of all achievable delay spectra for a given rate, blocklength and number of erasures, beyond the specific choice considered by Fong et al. This characterization is presented in the paper for systematic codes. Using this novel framework, the first proposed scheme involves greedily selecting the rate on the link from relay to destination and using properties of the delay-spectrum to find feasible streaming codes that satisfy the required delay constraints. A closed form expression for the achievable rate region is provided, and conditions for when the proposed scheme is optimal are established by a natural outer bound. The second proposed scheme builds upon this approach, but uses a numerical optimization-based approach to improve the achievable rate region over the first scheme. Experimental results show that the proposed schemes achieve significant improvements over baseline schemes based on single-user codes.

This paper investigates adaptive streaming codes over a three-node relayed network. In this setting, a source node transmits a sequence of message packets to a destination with help of a relay. The source-to-relay and relay-to-destination links are unreliable and introduce at most$N_{1}$and$N_{2}$packet erasures, respectively. The destination node must recover each message packet within a strict delay constraint$T$. The paper presents a new construction of streaming codes for all feasible parameters$\{N_{1}, N_{2}, T\}$. Our work improves upon the construction in Fong et al. by adapting the relaying strategy based on the erasure patterns from source to relay. Specifically, the code employs the notion of symbol estimates, which allows the relay to forward information about symbols before it can decode that symbol, and variable-rate encoding, which decreases the rate used to encode a packet as more erasures affect that packet. The codes proposed in this paper achieve rates higher than the ones proposed by Fong et al. whenever$N_{2} > N_{1}$, and achieve the same rate when$N_{2} \leq N_{1}$, in which case the rate is optimal. The paper also presents an upper bound on the achievable rate that takes into account erasures in both links in order to bound the rate in the second link. The upper bound is shown to be tighter than a trivial bound that considers only the erasures in the second link.

This paper investigates low-latency adaptive streaming codes for a three-node relay network. A source node transmits a sequence of source packets (messages) to the destination through a relay node. We focus on a particular case where the link connecting the source and relay nodes is almost reliable, but the link connecting the relay to the destination is not. The relay node can observe the erasure pattern that has occurred in the transmission between the source node and itself and adapt its relaying strategy based on that observation. Every source packet must be perfectly recovered by the destination with a strict delay T, as long as the number of erasures in the relay-to-destination link lies below some design parameter. We then characterize capacity as a function of such design parameter. The achievability scheme employs two different relaying strategies, based on whether an erasure has or has not occurred in the link from source to relay. The converse is proven by analyzing a periodic erasure pattern and lower bounding the minimum redundancy across channel packets. We show that the achievable rate can be improved compared to non-adaptive schemes previously proposed, indicating that exploiting the knowledge of the erasure pattern by the relay node is essential in achieving capacity.

Applications where multiple users communicate with a common server and desire low latency are common and increasing. This paper studies a network with two source nodes, one relay node and a destination node, where each source nodes wishes to transmit a sequence of messages, through the relay, to the destination, who is required to decode the messages with a strict delay constraint$T$. The network with a single source node has been studied in [1]. We start by introducing two important tools: the delay spectrum, which generalizes delay-constrained point-to-point transmission, and concatenation, which, similar to time sharing, allows combinations of different codes in order to achieve a desired regime of operation. Using these tools, we are able to generalize the two schemes previously presented in [1], and propose a novel scheme which allows us to achieve optimal rates under a set of well-defined conditions. Such novel scheme is further improved in order to achieve higher rates in the scenarios where the conditions for optimality are not met.

We study the problem of transmitting a sequence of messages (streaming messages) through a multi-link, multi-hop packet erasure network. Each message must be reconstructed in-order and under a strict delay constraint. Special cases of our setting with a single link on each hop have been studied recently - the case of a single relay-node, is studied in Fong et al [1]; the case of multiple relays, is studied in Domanovitz et al [2]. As our main result, we propose an achievable rate expression that reduces to previously known results when specialized to their respective settings. Our proposed scheme is based on the idea of concatenating single-link codes from [2] in a judicious manner to achieve the required delay constraints. We propose a systematic approach based on convex optimization to maximize the achievable rate in our framework.

In this paper, we investigate streaming codes over a three-node relay network. Source node transmits a sequence of message packets to the destination via a relay. Source-to-relay and relay-to-destination links are unreliable and introduce at most N1and N2packet erasures, respectively. Destination needs to recover each message packet with a strict decoding delay constraint of T time slots. We propose streaming codes under this setting for all feasible parameters $\{N_{1},\ N_{2},\ T\}$. Relay naturally observes erasure patterns occurring in the source-to-relay link. In our code construction, we employ a channel-state-dependent relaying strategy, which rely on these observations. In a recent work, Fong et al. provide streaming codes featuring channel-state-independent relaying strategies, for all feasible parameters $\{N_{1},\ N_{2},\ T\}$. Our schemes offer a strict rate improvement over the schemes proposed by Fong et al., whenever $N_{1}\lt N_{2}$.

This article investigates the massive random access Gaussian channel with a focus on small payloads. For this problem, grant-based schemes have been regarded as inefficient due to the necessity of large feedbacks and the use of inefficient scheduling request methods. This articles attempts to answer whether grant-based schemes can be competitive against state-ot-art grantless schemes and worthy of further investigation. In order to compare these schemes fairly, a novel model is proposed, and, under this model, a novel grant-based scheme is proposed. The scheme uses Ordentlich and Polyanskiy's grantless method to transmit small coordination indices in order to perform the scheduling request, which allows both the request from the users to be efficient and the feedback to be small. We also present improvements to the Ordentlich and Polyanskiy's scheme, allowing it to transmit information through the choice of sub-block, as well as to handle collisions of the same message, significantly improving the method for very small messages. Simulation results show that, if a small feedback is allowed, the proposed scheme performs closely to the state-of-art while using simpler coding schemes, suggesting that novel grant-based schemes should not be dismissed as a potential solution to the massive random access problem.