Per-hop Basis Research Articles

Mobility-Aware Relay Selection in 5G D2D Communication Using Stochastic Model

Challenges in relay selection for device-to-device (D2D) communication arise due to the mobility of nodes, which brings uncertainty in various network parameters. We first developed a network-assisted stochastic integer programming (SIP) model to incorporate uncertainty that predicts the network parameters for upcoming time instance based on information available at current time instance. We converted the SIP model to an equivalent deterministic mixed integer non-linear program (MINLP) model and proved its hardness result. By exploiting the constraints of MINLP, we developed a distributed greedy metric, termed as connectivity factor (CF), which is calculated locally at each node on per-hop basis. It captures the nodes mobility and, hence, takes care of link reliability that in turn controls packet loss and delay. It can be computed in O ( n ) time, where n is the number of transmitters interfering with the given link. Our approach is applicable to any mobility model with relevant distributions of mobility parameters known. We constructed perceived graph based on CF values to devise network-assisted and device-controlled relay selection algorithms for given source-destination pairs. Extensive simulation results show significant improvements in packet loss and average end-to-end delay by our approach over a recent implementation of an ad-hoc on-demand distance vector (AODV) based algorithm.

Spectrum-aware Beaconless Geographical Routing Protocol for Cognitive Radio Enabled Vehicular Networks

The FCC and ETSI have allocated spectrum in the 5.9 GHz band for intelligent transportation systems. However, this spectrum supports short-range transmissions (up to 1000 m) and limited bandwidth (up to 75 MHz), which are not enough to meet the increasing demand for in-car infotainment services. In this paper, we propose a distributed routing protocol for vehicular ad hoc networks, where cognitive radio enabled vehicles (CRVs) dynamically share the TV-band channels. In the proposed protocol, CRVs jointly select relay nodes, channels, transmission powers, and transmission rates so that their total transmission rates are maximized while meeting their rate demands and power constraints. This selection process is carefully executed so that ongoing communications between primary radios (PRs) and between other CRVs are not disrupted. Once the relay nodes are selected, they continue to relay more messages as long as they stay in a predefined forwarding area. By doing so, the overhead for selecting relay nodes can be substantially reduced. Channels, powers, and rates are changed on a per-packet and per-hop basis so that the proposed protocol can efficiently adapt to spectrum dynamics. Simulation results show that our protocol increases the end-to-end network throughput by up to 250 % and decreases the end-to-end delay by up to 400 % compared with other geographical routing protocols.

Distributed admission control protocol for end-to-end QoS assurance in ad hoc wireless networks

Abstract To reserve end-to-end bandwidth in quality of service (QoS) supported wireless ad hoc networks, local bandwidth requirement should be carefully determined by considering the number of contending nodes in an interference range. In this article, we propose a novel admission control protocol, called DACP (distributed admission control protocol), which is implemented over a reactive ad hoc routing protocol with minimal overhead. DACP computes the required bandwidth for end-to-end band-width provision at each node and estimates the available bandwidth at the medium access control layer. After that, DACP makes a decision for admitting a flow in a per-hop basis. Extensive simulations are carried out via the OPNET simulator. The simulation results demonstrate that DACP not only provides guaranteed end-to-end resource but also reduces the control overhead to provide QoS support, compared with the existing admission control schemes.

TCP Performance in IEEE 802.11-Based Ad Hoc Networks with Multiple Wireless Lossy Links

We propose a packet-level model to investigate the impact of channel error on the transmission control protocol (TCP) performance over IEEE-802.11-based multihop wireless networks. A Markov renewal approach is used to analyze the behavior of TCP Reno and TCP Impatient NewReno. Compared to previous work, our main contributions are listed as follows: 1) modeling multiple lossy links, 2) investigating the interactions among TCP, Internet Protocol (IP), and media access control (MAC) protocol layers, specifically the impact of 802.11 MAC protocol and dynamic source routing (DSR) protocol on TCP throughput performance, 3) considering the spatial reuse property of the wireless channel, the model takes into account the different proportions between the interference range and transmission range, and 4) adopting more accurate and realistic analysis to the fast recovery process and showing the dependency of throughput and the risk of experiencing successive fast retransmits and timeouts on the packet error probability. The analytical results are validated against simulation results by using GloMoSim. The results show that the impact of the channel error is reduced significantly due to the packet retransmissions on a per-hop basis and a small bandwidth delay product of ad hoc networks. The TCP throughput always deteriorates less than ~ 10 percent, with a packet error rate ranging from 0 to 0.1. Our model also provides a theoretical basis for designing an optimum long retry limit for IEEE 802.11 in ad hoc networks.

Fair early drop marker for improving TCP fairness in multiple domain DiffServ networks

The differentiated services (DiffServ) model, proposed as a scalable way of providing quality of service in the Internet, provides packet level service differentiation on a per-hop basis. To provide the end-to-end service differentiation more efficiently for the assured services, as well as a source marker, an interdomain marker placed at the boundary edge routers connecting network domains is necessary because an Internet connection usually spans through a path involving one or more network domains. Such an interdomain marker should be operated at the aggregate flow level due to the scalability problem. The random early demotion and promotion (REDP) marker was proposed as an interdomain marker. It introduces randomness and early decisions on the three-color packet marking process at the aggregate flow level to remove the phase effect that brings about the unfairness in the demotion and promotion among different flows. The REDP marker achieves good UDP fairness in demoting and promoting packets through random and early marking decisions on packets. However, TCP fairness of the REDP marker is not obvious as for UDP sources. In this paper, we propose a new interdomain marker to resolve the problem of the REDP marker. Instead of unfair packet droppings at the RIO buffers in the core routers which cause unfairness of TCP flows, it fairly drops the green packets of each TCP flow with a token filling rate configuration method before they enter into the core routers. By doing this fair early packet dropping, it increases TCP fairness at a minor expense for the total throughput.

A random early demotion and promotion marker for assured services

The differentiated services (DiffServ) model, proposed to evolve the current best-effort Internet to a quality-of-service-aware Internet, provides packet level service differentiation on a per-hop basis. The end-to-end service differentiation may be provided by extending the per-hop behavior over multiple network domains through service level agreements between domains. The edge routers of each of the domains monitor the aggregate flow of the incoming packets and demote packets when the aggregate incoming traffic exceeds the negotiated interdomain service agreement. A demoted packet may encounter other edge routers on its path that have sufficient resources to route the packet with its original marking. In this paper, we propose a random early demotion and promotion (REDP) technique that works at the aggregate traffic level and allows (1) fair demotion of packets belonging to different flows, and (2) easy and fair detection and promotion of the demoted packets. Using early and random decisions on packets REDP ensures fairness in promotion and demotion. It uses a three color marking mechanism, reserving one color fur differentiating between a demoted packet and a packet with the original out-of-profile marking. We experiment with the proposed REDP scheme using the ns2 simulator for both TCP and UDP streams. The results demonstrate the fairness of REDP scheme in demoting and promoting packets. Furthermore, we show a variety of results that demonstrates that REDP provides better assured services compared to the previously proposed RIO scheme with or without the provision of promotion.