Spatial Reuse Time-division Multiple Access Research Articles

Modeling Impact of Concurrent Transmissions in Cluster Based Mobile Caching Networks

Dissemination of cached contents on device-to-device (D2D) links is one promising technique to relieve network load. In this correspondence paper, we extend our Markov chain model (A. Ahmed, H. Shan, and A. Huang, 2019) to analyze the impact of both node mobility and multiple concurrent transmissions in a cluster based mobile caching network. To unearth the impact of the former factor, we derive the steady-state probability of nodes in different clusters under the Markov mobility model. To reveal the impact of the latter factor, the per-node collision-free transmission chance in each active cluster is tunable by building the network with spatial reuse time division multiple access (STDMA) and the receiver based code division multiple access (R-CDMA) codes. Diverse network performance metrics are derived from the analytical framework. Simulation results verify the accuracy of the analysis and examine the impact of system parameters.

Leveraging the Near–Far Effect for Improved Spatial-Reuse Scheduling in Underwater Acoustic Networks

We present a spatial reuse resource allocation scheme for underwater acoustic networks that organizes communications so as to avoid destructive collisions. One prime source of collisions in underwater acoustic networks is the so called near–far effect, where a node located farther from the receiver is jammed by a closer node. While common practice considers such a situation a challenge, in this paper we consider it a resource, and use it to increase the network throughput of spatial-reuse time-division multiple access. Our algorithm serves two types of communications: 1) contention-free and 2) opportunistic. Our objective is to maximize the time slot allocation, while guaranteeing a minimum per-node packet transmission rate. The result is an increase in the number of contention-free packets received, and a decrease in the scheduling delay of opportunistic packets. Numerical results show that, at a slight cost in terms of fairness, our scheduling solutions achieve higher throughput and lower transmission delay than benchmark spatial-reuse scheduling protocols. These results are verified in a field experiment conducted in the Garda Lake, Italy, where we demonstrated our solution using off-the-shelf acoustic modems. To allow the reproducibility of our results, we publish the implementation of our proposed algorithm.

Spatial Reuse TDMA/CDMA in Multi-hop MIMO Relay Systems with Imperfect CSI

In multi-hop relay systems, due to considerably small allocation times in a perfectly orthogonal time division multiple access (TDMA) protocol or greatly large length of sequence in a perfectly orthogonal code division multiple access (CDMA) protocol, a channel capacity of multi-hop relay systems is deteriorated. In order to improve the channel capacity, a spatial reuse TDMA/CDMA protocol is proposed, a performance of both protocols is analyzed and compared in perfect and imperfect channel state information. The optimal number of phases in the spatial reuse TDMA protocol and the optimal length of sequence in the spatial reuse CDMA protocol that can achieve the maximal channel capacity will be discussed in this paper. The numerical evaluation result indicates the channel capacity of spatial reuse TDMA/CDMA is higher than that of systems have perfect orthogonality or without TDMA/CDMA.

A Quality-of-Service Routing Protocol with Supplementary Cooperation for Wireless Ad Hoc Networks

End-to-end quality-of-service (QoS) in wireless multihop ad hoc networks is a challenging issue, especially when the wireless channels suffer from time-varying fading. In this paper, we develop a spatial-reuse time-division multiple access (STDMA)-based QoS routing protocol, named supplementary-cooperation routing (SC-routing). SC-routing can provide the service guarantee of target data rate and maximum end-to-end outage probabilities for data flows in the multihop ad hoc networks. For each arriving data flow, SC-routing determines a route, and schedules STDMA slot and transmit power to each link of this route. To effectively combat the fading channels, SC-routing employs supplementary cooperation, which utilizes cross-hop overhear to gain transmit diversity, and thus saves the relay transmission in usual cooperative communication. Simulation results show the network capacity can be improved by incorporating transmit diversity into end-to-end transmission.

An SINR-based routing and MAC design for QoS in wireless ad hoc networks

In this paper, we propose a cross routing and MAC QoS protocol design, named Signal-to-Interference-plus-Noise-Ratio and Quality-of-Service (SINR-QoS), for wireless ad hoc networks. SINR-QoS is spatial-reuse time division multiple access (STDMA)-based. Unlike most of the conventional approaches, SINR-QoS manages the spatial reuse based on SINR. When a data flow with end-to-end throughput requirement arrives, the routing part of SINR-QoS, called SINR-QoS-routing (SQ-routing), determines a route, and assigns STDMA slots, transmission rate, and transmission power for each link on the route. The assignment is SINR-based, and thus requires some SINR-related information to coordinate the co-channel interference. Hence, the MAC part of SINR-QoS, called SINR-QoS-MAC (SQ-MAC), is proposed for nodes to acquire and update the SINR-related information. With the specific design of SQ-MAC, SINR-QoS can precisely manage the spatial reuse without explicit channel-gain exchange between interfering neighbors. Simulation results show SINR-QoS outperforms the existing QoS approaches in both total end-to-end throughput and reliability.

Optimization Decomposition for Scheduling and System Configuration in Wireless Networks

Who gets to use radio spectrum, and when, where, and how? Scheduling (who, where, when) and system configuration (how) are fundamental problems in radio communication and wireless networking. Optimization decomposition based on Lagrangian relaxation of signal quality requirements provides a mathematical framework for solving this type of combined problem. This paper demonstrates the technique as a solution to spatial reuse time-division multiple access (STDMA) scheduling with reconfigurable antennas. The joint beam steering and scheduling (JBSS) problem offers both a challenging mathematical structure and significant practical value. We present algorithms for JBSS and describe an implemented system based on these algorithms. We achieve up to 600% of the throughput of TDMA with a mean of 234% in our experiments. The decomposition approach leads to a working distributed protocol producing optimal solutions in an amount of time that is at worst linear in the size of the input. This is, to the best of our knowledge, the first actually implemented wireless scheduling system based on dual decomposition. We identify and briefly address some of the challenges that arise in taking such a system from theory to reality.

Rapid Dissemination of Public Safety Message Flows in Vehicular Networks

We consider a Road Side Unit (RSU) that aims to broadcast critical public safety message flows to vehicles that travel along a linear highway. The RSU is able to transmit such message flows directly to only a limited group of vehicles travelling in its close vicinity. To assure delivery of these messages to all other vehicles traveling along the highway, we make use of a Vehicular Ad Hoc Network (VANET) system to provide vehicle-to-vehicle multi-hop transport of these messages. We propose a VANET networking scheme that is identified as a Vehicular Backbone Network (VBN), under which vehicles that are located close to properly selected nominal positions are elected to serve as Relay Nodes (RNs). We study the optimal cross-layer design of such a network system, by presenting an analytical model to jointly select the operational data rate, scheduling mechanism and the inter-RN targeted distance levels. We show that a high level of coverage of highway vehicles, coupled with very low incurred queueing delays, can be achieved by employing a flow admission control mechanism at the source. We consider a high intensity vehicular traffic flow regime under which vehicles that are elected to serve as RNs are generally located close to designated nominal positions, as well as lower rate stochastic traffic flow conditions. Furthermore, we demonstrate the capability of the system, when properly configured, to employ a vehicular Carrier Sense Multiple Access/ Collision Avoidance (CSMA/CA) access scheme to well emulate the operations of the system when managed by the use of spatial-reuse Time Division Multiple Access (TDMA) scheduling scheme. Our mathematical analyses and designs are well confirmed through the execution of system simulation analyses.

Distributed Robust Scheduling and Power Control For Cognitive Spatial-Reuse TDMA Networks

We investigate the distributed robust transmission scheduling and power control problem in a cognitive spatial-reuse time division multiple access (STDMA) network. In particular, we address the problem of minimizing the transmission length (in terms of time-slots) of the secondary links under their minimum quality-of-service (QoS) requirements without violating the maximum tolerable interference limit for the primary receivers. Traditionally, the joint transmission scheduling and power control problem only considers the average link gains; therefore, QoS violation can occur due to improper power allocation with respect to instantaneous channel gain realization. To overcome this problem of QoS violation, our problem formulation takes the channel gain uncertainty into account. Since an optimal solution cannot be obtained due to the NP-completeness of the problem, we propose a novel distributed two-stage algorithm based on the distributed column generation method to obtain the near-optimal solution for the robust transmission schedules in an ad-hoc cognitive radio network. To demonstrate its relative efficiency, our algorithm is compared with previously proposed algorithms. For the proposed algorithm, we also derive the bounds on the probability of signal-to-interference-plus-noise ratio (SINR) constraint violation and the expected number of additional time-slots required to satisfy the traffic demand requirements of secondary links.

Robust Scheduling and Power Control for Vertical Spectrum Sharing in STDMA Wireless Networks

We study the robust transmission scheduling and power control problem for spectrum sharing between secondary and primary users in a spatial reuse time-division multiple access (STDMA) network. The objective is to find a robust minimum-length schedule for secondary users (in terms of time slots) subject to the interference constraints for primary users and the traffic demand of secondary users. We consider the fact that power allocation based on average (or estimated) link gains can be improper since actual link gains can be different from the average link gains. Therefore, transmission of the secondary links may fail and require more time slots. We also consider this demand uncertainty arising from channel gain uncertainty. We propose a column generation-based algorithm to solve the scheduling and power control problem for secondary users. The column generation method breaks the problem down to a restricted master problem and a pricing problem. However, the classical column generation method can have convergence problem due to primal degeneracy. We propose an improved column generation algorithm to stabilize and accelerate the column generation procedure by using the perturbation and exact penalty methods. Furthermore, we propose an efficient heuristic algorithm for the pricing problem based on a greedy algorithm. For the simulation scenario considered in this paper, the proposed stabilized column generation algorithm can obtain the optimal schedules with 18.85% reduction of the number of iterations and 0.29% reduction of the number of time slots. Also, the heuristic algorithm can achieve the optimality with 0.39% of cost penalty but 1.67×10-4 times reduction of runtime.

Electromagnetic Interference-Aware Transmission Scheduling and Power Control for Dynamic Wireless Access in Hospital Environments

We study the multiple access problem for e-Health applications (referred to as secondary users) coexisting with medical devices (referred to as primary or protected users) in a hospital environment. In particular, we focus on transmission scheduling and power control of secondary users in multiple spatial reuse time-division multiple access (STDMA) networks. The objective is to maximize the spectrum utilization of secondary users and minimize their power consumption subject to the electromagnetic interference (EMI) constraints for active and passive medical devices and minimum throughput guarantee for secondary users. The multiple access problem is formulated as a dual objective optimization problem which is shown to be NP-complete. We propose a joint scheduling and power control algorithm based on a greedy approach to solve the problem with much lower computational complexity. To this end, an enhanced greedy algorithm is proposed to improve the performance of the greedy algorithm by finding the optimal sequence of secondary users for scheduling. Using extensive simulations, the tradeoff in performance in terms of spectrum utilization, energy consumption, and computational complexity is evaluated for both the algorithms.

Mathematical decomposition techniques for distributed cross-layer optimization of data networks

Network performance can be increased if the traditionally separated network layers are jointly optimized. Recently, network utility maximization has emerged as a powerful framework for studying such cross-layer issues. In this paper, we review and explain three distinct techniques that can be used to engineer utility-maximizing protocols: primal, dual, and cross decomposition. The techniques suggest layered, but loosely coupled, network architectures and protocols where different resource allocation updates should be run at different time-scales. The decomposition methods are applied to the design of fully distributed protocols for two wireless network technologies: networks with orthogonal channels and network-wide resource constraints, as well as wireless networks where the physical layer uses spatial-reuse time-division multiple access. Numerical examples are included to demonstrate the power of the approach