Topology-transparent Scheduling Research Articles

A Framework of Topology-Transparent Scheduling Based on Polynomial Ring

Topology transparent scheduling (TTS) has been widely studied over the last two decades, which provides guaranteed throughput for each node in the network with only knowledge of global parameters. Leveraging different mathematical approaches, the existing TTSs briefly fall into three board categories: 1) the Galois field (GF)-based; 2) the combinatory-based; and 3) the number theory-based schemes. In this letter, a new scheme via the polynomial ring is proposed as a generalization of Chinese remainder theorem (CRT)-based TTS presented recently. It brings significant improvement over the theoretic bounds of both maximum nodal degree supported and frame length required. In addition, we prove that the proposed scheme is also a generic framework of both GF and CRT-based TTS.

Steiner system‐based topology‐transparent priority scheduling for wireless ad hoc networks

Topology‐transparent scheduling (TTS) for wireless networks involves generation of schedules which do not need update even when the network topology is constantly changing. TTS schemes designed with Steiner systems support the largest number of nodes—among all cover‐free families—for a given frame length. In this paper, we propose a TTS scheme using Steiner systems for a network in which nodes are divided into multiple classes of different priorities. Our proposed scheme called “Steiner system‐based Topology‐transparent Priority Scheduling” (STPS) produces priority‐sensitive schedules using different Steiner systems for the different priority classes. We explain our proposed method through illustrative examples and show its superiority over a competitive scheme in the literature with respect to the frame length.

Topology-Transparent Scheduling Based on Reinforcement Learning in Self-Organized Wireless Networks

Topology-transparent scheduling policies do not require the maintenance of accurate network topology information and therefore are suitable for highly dynamic scenarios in self-organized wireless networks. However, in topology-transparent scheduling, it is a very challenging problem to make individual nodes efficiently select their transmission slots in a distributed manner. It is desirable for individual nodes, through time slot selection, to avoid collision on the one hand and utilize as many time slots as possible (i.e., minimize the number of redundant slots) on the other. In this paper, learning-based approaches are employed to solve the time slot scheduling problem. Specifically, the proposed method uses a temporal difference learning approach to address the collision issue and use a stochastic gradient descent approach to reduce the number of redundant slots. Unlike previous works, this learning approach is trained through self-play reinforcement learning without incurring communication overhead for the exchange of reservation information, thereby improving the network throughput. Extensive simulation results validate that our proposal can achieve better efficiency than the existing approaches.

Variable-weight topology-transparent scheduling

In this paper, topology-transparent scheduling for mobile multi-hop wireless networks is extended from constant-weight to variable-weight schedules. A construction of variable-weight topology-transparent schedules – the first of its kind – is provided based on transversal designs from the finite field. The schedules are integrated into the VWATT medium access control (MAC) protocol, enabling nodes to dynamically select their schedule weights to accommodate both their local traffic load and local topology while maintaining a guarantee on maximum delay. Simulations show VWATT to increase throughput compared to constant-weight topology-transparent schedules, to reduce both maximum and expected delay relative to schedules whose weights are not constrained to the set of weights, and to adapt rapidly to changes in topology and traffic load. The results suggest variable-weight topology-transparent scheduling as a viable approach to medium access control when a bound on delay is required.

A Survey of Topology-Transparent Scheduling Schemes in Multi-Hop Packet Radio Networks

The aim of topology-transparent scheduling in multi-hop packet radio networks is to find a schedule for the nodes in such a way that the schedule of the existing nodes need not be recomputed when the network topology changes. It caters to highly dynamic scenarios where topology changes occur faster than the speed at which schedule updates can be orchestrated. Hence, the scheduler is typically expected to use only global network parameters like upper bounds on the number of nodes in the network and on the maximum degree of any node in the network. The problem is non-trivial if there are restrictions on the frame length or the minimum throughput of a node in a frame. Over the years, several innovative solutions have been proposed using a variety of mathematical techniques. We present a lucid tutorial-style survey of the approaches using an integrative taxonomy and a comparative analysis. We also outline a few directions for future research in the field.

A Note on Topology-Transparent Scheduling via the Chinese Remainder Theorem

Topology-transparent scheduling (TTS) via the Chinese remainder theorem (CRT) has succeeded in providing guaranteed collision-free transmissions in each schedule without the need to know the maximum nodal degree of the graph representing connectivity of a mobile ad hoc network. Its main limitation is due to the restriction on the moduli imposed by the CRT. To address the shortcoming, this letter proposes an application of the general Chinese remainder theorem (GCRT) to TTS, which provides a unified framework for TTS that is developed via the CRT. The proposed GCRT-based scheme not only employs integer sequences to form the moduli, but also repeats the moduli to enhance TTS via the CRT. To determine how to repeat moduli in a systematic way, this letter formulates an integer programming problem, which is solved by the branch-and-bound technique. Numerical results are presented, demonstrating that the proposed GCRT-based scheme outperforms earlier works with much shorter schedule lengths.

Topology-Transparent Scheduling via the Chinese Remainder Theorem

This paper proposes a novel scheme for the design of topology-transparent scheduling (TTS) in mobile ad hoc networks (MANETs), based on the Chinese remainder theorem (CRT). TTS can provide each node with guaranteed success in each schedule without any detailed topology information and yields a guaranteed upper bound on the transmission delay of each packet at every node in a MANET. In general, TTS requires two global constraints on the number of nodes in the MANET and the maximum nodal degree of the graph representing connectivity of the MANET. Due to the inherent mobility of MANETs, the maximum nodal degree, however, cannot be available or easily estimated. To eliminate the requirement for the maximum nodal degree, this paper proposes TTS via the CRT. By the redundancy property of the Chinese remainder representation, the proposed CRT-based scheme not only preserves the advantages of providing guaranteed success in each schedule with only the global constraint on the number of nodes in the MANET, but also offers flexibility in constructing TTS. To have a better transmission delay bound for a node with lower interference, this paper also introduces two threaded counterparts of the proposed CRT-based scheme. This paper provides performance analyses for the proposed CRT-based scheme and its threaded counterparts. Numerical results demonstrate that TTS via the CRT can outperform existing schemes, especially in scenarios with harsh interference, and is a versatile approach for the design of TTS.

Topology-Transparent Scheduling in Mobile Ad Hoc Networks With Multiple Packet Reception Capability

Recent advances in the physical layer have enabled wireless devices to have multiple packet reception (MPR) capability, which is the capability of decoding more than one packet, simultaneously, when concurrent transmissions occur. In this paper, we focus on the interaction between the MPR physical layer and the medium access control (MAC) layer. Some random access MAC protocols have been proposed to improve the network performance by exploiting the powerful MPR capability. However, there are very few investigations on the schedule-based MAC protocols. We propose a novel m-MPR-l-code topology-transparent scheduling ((m, l)-TTS) algorithm for mobile ad hoc networks with MPR, where m indicates the maximum number of concurrent transmissions being decoded, and l is the number of codes assigned to each user. Our algorithm can take full advantage of the MPR capability to improve the network performance. The minimum guaranteed throughput and average throughput of our algorithm are studied analytically. The improvement of our (m, l)-TTS algorithm over the conventional topology-transparent scheduling algorithms with the collision-based reception model is linear with m. The simulation results show that our proposed algorithm performs better than slotted ALOHA as well.

Performance Improvement of Topology-Transparent Broadcast Scheduling in Mobile Ad Hoc Networks

Broadcasting is a key function in mobile ad hoc networks. Topology-dependent scheduling algorithms depend on the detailed network connectivity information and cannot adapt to dynamic topological changes in mobile networks. To overcome this limitation, topology-transparent broadcast scheduling algorithms have been proposed. Due to the large overhead of implement- ing the acknowledgement mechanism in broadcast communica- tions and to guarantee that there is at least one collision-free transmission in each frame, most existing topology-transparent broadcast scheduling algorithms require a node to transmit the same packet repeatedly at multiple slots during one frame. This is very inefficient. In this paper, we propose an efficient topology- transparent broadcast scheduling algorithm. First, instead of transmitting the same packet repeatedly during one frame, each node collects transmission codes of its two-hop neighbors and transmits several different packets during one frame. Second, noting that many unassigned slots are not utilized, we propose several methods to utilize the unassigned slots efficiently in a collision-free and traffic-adaptive manner. Thus, our algorithm provides a guaranteed throughput and achieves a much better average throughput. The analytical and simulation results show that our proposed algorithm outperforms other existing topology- transparent broadcast algorithms dramatically.

Joint Topology-Transparent Scheduling and QoS Routing in Ad Hoc Networks

This paper considers the problem of joint topologytransparent scheduling (TTS) and quality-of-service (QoS) routing in ad hoc networks and presents a joint scheme for the problem. Due to its ability to guarantee single-hop QoS support, TTS is chosen as the underlying medium-access-control (MAC) protocol. By being built on top of TTS, this paper first designs methods for bandwidth estimation and allocation (BWE and BWA, respectively) to provide QoS support without knowledge of slot status information, and then, estimates and allocates nonassigned eligible bandwidth for best effort (BE) flows. With these bandwidth management methods, this paper proposes a QoS routing protocol for a mixture of QoS and BE flows. Idealized simulation results based on the standard radio model, which ignores external sources of radio interference and protocol inefficiencies, reveal that the proposed joint scheme can provide a reduction of at least 93% in QoS violation rates and a reduction of 78%-89% in control overhead compared with the conventional dynamic source routing (DSR)/IEEE 802.11 technique. A comparison with another conventional technique, i.e., DSR/carrier sense multiple access (CSMA), also reveals that the proposed joint scheme can reduce QoS violation rates by at least 93%. In addition, the proposed joint scheme can provide an increase of 31%-104% in aggregate throughput over two representative QoS routing protocols while achieving a reduction of approximately 93% in QoS violation rates. The performance improvement to be achieved under a realistic radio model is yet to be determined.

Is Topology-Transparent Scheduling Really Inefficient in Static Multihop Networks?

Topology-transparent scheduling algorithms are oblivious to the network topology changes and can provide throughput and delay guarantees in mobile multihop networks. However, it has been argued that topology-transparent scheduling algorithms are inefficient when the network is static, compared to topology-dependent scheduling algorithms. In this paper, we propose to utilize both assigned and unassigned slots efficiently to boost the performance of topology-transparent scheduling algorithms. We conclude that, in certain cases, the performance of the proposed topology-transparent scheduling algorithm can be comparable to or better than that of some topology-dependent algorithms even when the network topology remains unchanged. Yet, the proposed algorithm also works even when the network topology is dynamic.

Topology-Transparent Broadcast Scheduling with Erasure Coding in Wireless Networks

Broadcasting is an important function in wireless networks. Ensuring broadcast efficiency and reliability with low communication overhead is challenging, especially with error-prone links. In this letter, we employ erasure coding together with topology-transparent scheduling as a coded transmission strategy in the MAC (Medium Access Control) layer rather than the physical layer to combat collisions and channel errors, implementing an efficient and reliable broadcast algorithm in wireless networks without introducing any additional communication overhead. We achieve the optimal frame structure that maximizes the average network throughput, and investigate the performance of our proposed algorithm in terms of the average network throughput and the packet failure probability. Simulation results show that our proposed algorithm with erasure coding outperforms other existing topology-transparent broadcast algorithms and the conventional TDMA dramatically.

Bounds and parameter optimization of medium access control coding for wireless ad hoc and sensor networks

The use of codes to schedule transmissions is an attractive technique able to guarantee a non-zero throughput medium access performance for the nodes of a wireless ad hoc or sensor network regardless of network topology variations. Some authors refer to this technique as topology-transparent scheduling. In this paper, we use the term MAC coding in order to emphasize the exclusive use of codes to achieve topology-transparency within the MAC sub-layer. We present a new upper bound expression on the guaranteed throughput achievable by any linear code used in a MAC coding context. This bound proves to be tighter than the one obtained when the minimum distance of the code is equal to its length. Additionally, we derive new and simple closed analytical expressions for the parameters of maximum distance separable codes that maximize the minimum, average, or joint minimum–average throughput of MAC coding. The optimization methods presented here are also applicable to other codes with available analytical expressions for their minimum distance and distance distribution. Finally, we present system-level simulation results of MAC coding on static and dynamic topologies with mobility and including wireless channel errors. Throughput simulation results are compared with their corresponding analytical expressions and to a random scheduling approach. The results show agreement with analysis and confirm the robustness of MAC coding in maintaining minimum levels of performance with good average performance and graceful degradation.

An Algorithm for Improving Throughput Guarantee of Topology-Transparent MAC Scheduling Strategy

Topology-transparent MAC scheduling strategies nowadays are all based on combinatorial design. To get throughput guarantee, a cover-free set is output as scheduling strategy of network. In this paper, we aim to modify the cover-free set so that better throughput can be guaranteed. At the first step, the redundant slot of the cover-free set is proposed and found to have negative influence on the minimal guaranteed throughput. Second, we prove that any subset of a cover-free set is still a cover-free set after its redundant slots were squashed out. Our algorithm chooses the subset which has the maximal number of redundant slots, squashes all of its redundant slots, and then designates it as the network scheduling strategy. Therefore, better through- put can be guaranteed if the squashed subset is adopted as network scheduling strategy. For any topology- transparent node scheduling strategy, both the increased minimal throughput and decreased maximal transmission delay can be gotten by just using our algorithm as an extra accessory.

Rateless Forward Error Correction for Topology-Transparent Scheduling

Topology-transparent scheduling for mobile wireless ad hoc networks has been treated as a theoretical curiosity. This paper makes two contributions towards its practical deployment: (1) We generalize the combinatorial requirement on the schedules and show that the solution is a cover-free family. As a result, a much wider number and variety of constructions for schedules exist to match network conditions. (2) In simulation, we closely match the theoretical bound on expected throughput. The bound was derived assuming acknowledgments are available immediately. We use rate less forward error correction (RFEC) as an acknowledgment scheme with minimal computational overhead. Since the wireless medium is inherently unreliable, RFEC also offers some measure of automatic adaptation to channel load. These contributions renew interest in topology-transparent scheduling when delay is a principal objective.

Transport schemes for topology-transparent scheduling

Transport protocols provide reliable, end-to-end communication between a source and a destination in a network. The Transmission Control Protocol (TCP) uses backward error correction, where the destination explicitly returns feedback to the source. Forward error correction (FEC) can also be used for transport; here the source includes enough redundancy in the encoding symbols to allow the destination to decode the message. In this paper, we compare the performance of two transport schemes, TCP and LT, a scheme based on rateless FEC codes, in a wireless ad hoc network when topology-transparent scheduling is used for channel access. These schedules are derived from cover-free families, a type of combinatorial design. They provide a mechanism to guarantee collision-free communication between any two nodes provided that each of the N nodes of the network has at most a specified number D of active (transmitting) neighbours. We find that LT outperforms TCP in more strenuous network conditions.

The effects of synchronization on topology-transparent scheduling

Topology-transparent scheduling is an attractive medium access control technique for mobile ad hoc networks (MANETs) and wireless sensor networks (WSNs). The transmission schedule for each node is fixed and guarantees a bounded delay independent of which nodes are its neighbours, as long as the active neighbourhood is not too dense. Most of the existing work on topology-transparent scheduling assumes that the nodes are synchronized on frame boundaries. Synchronization is a challenging problem in MANETs and in WSNs. Hence, we study the relationships among topology-transparent schedules, expected delay, and maximum delay, for successively weaker models of synchronization: frame-synchronized, slot-synchronized, and asynchronous transmission. For each synchronization model, we give constructive proofs of existence of topology-transparent schedules, and bound the least maximum delay. Perhaps surprisingly, the construction for the asynchronous model is a simple variant of the slot synchronized model. While it is foreseen that the maximum delay increases as the synchronization model is weakened, the bound is too pessimistic. The results on expected delay show that topology-transparent schedules are very robust to node density higher than the construction is designed to support, allowing the nodes to cope well with mobility, and irregularities of their deployment.

Topology-transparent schedule with reservation and carrier sense for multihop ad hoc networks

To solve collisions of topology-transparent schedules in multihop ad hoc networks, we propose a topology-transparent schedule with reservation and carrier sense. Our schedule is based on slotted architecture in which each slot is divided into reservation phase and data phase. Each node resolves possible collisions in its assigned slots by reservation and utilizes free ones among its non-assigned slots by carrier sense. By analysis, we derive the optimal parameter for the best performance. Compared results show that our schedule is better than others.

Slot synchronized topology-transparent scheduling for sensor networks

We propose a slot synchronized topology-transparent medium access control (MAC) protocol for sensor networks. Most of the earlier scheduled approaches require a stronger form of synchronization where nodes are synchronized on frame boundaries. Synchronizing on slot boundaries is simpler to achieve since it does not require global time, making the protocol practical for sensor networks. The benefit of topology-transparency is that it ensures a bounded delay to each neighbour as long as the number of actively transmitting nodes in a neighbourhood is at most D max . The node schedules are independent of which nodes are active. Such a topology-transparent solution is particularly suitable for sensor networks, where nodes may not have unique identifiers, eliminating costly neighbour discovery. We formulate the problem as a combinatorial design problem on cyclic superimposed codes and give a constructive proof of existence along with a delay bound.

Cover-Free Families and Topology-Transparent Scheduling for MANETs

We examine the combinatorial requirements of topology-transparent transmission schedules in a mobile ad hoc network (MANET). Specifically, if each of the N nodes has at most D active neighbors, we require the schedule to guarantee a collision-free transmission to each neighbor. This requirement is met by a cover-free family. We show that existing constructions for topology-transparent schedules correspond to an orthogonal array. Moreover, we show that Steiner systems support the largest number of nodes for a given schedule length. Both of these combinatorial objects are special cases of cover-free families. Analytically and numerically, we examine slot guarantees, expected throughput, and normalized expected throughput for systems of small strength, exploring the sensitivity of the response to D. Expected throughput provides a better performance metric than the minimum throughput results obtained earlier. The impact of a more realistic model of acknowledgments is also examined. The extension of the schedule to multiple frames returns us to the orthogonal arrays. The very density of Steiner systems that afforded an improvement over orthogonal arrays in one frame impedes the best extension to more frames.