Minming Ni

MPBC: A Mobility Prediction-Based Clustering Scheme for Ad Hoc Networks

Creating a hierarchical structure by clustering has been considered an effective method to improve the performance of ad hoc networks, such as scalability and stability. This is particularly important for networks with mobile nodes, where the mobility can cause randomly and dynamically changed network topology. In this paper, we propose a mobility prediction-based clustering (MPBC) scheme for ad hoc networks with high mobility nodes, where a node may change the associated cluster head (CH) several times during the lifetime of its connection. The proposed clustering scheme includes an initial clustering stage and a cluster maintaining stage. The Doppler shifts associated with periodically exchanged Hello packets between neighboring nodes are used to estimate their relative speeds, and the estimation results are utilized as the basic information in MPBC. In the initial clustering stage, the nodes having the smallest relative mobility in their neighborhoods are selected as the CHs. In the cluster maintaining stage, mobility prediction strategies are introduced to handle the various problems caused by node movements, such as possible association losses to current CHs and CH role changes, for extending the connection lifetime and providing more stable clusters. An analytical model is developed to find the upper and lower bounds of the average connection lifetime and to find the average association change rate of MPBC. Numerical results verify the analysis and further show that the proposed clustering scheme outperforms the existing clustering schemes in ad hoc networks with high mobility nodes.

A Geometrical-Based Throughput Bound Analysis for Device-to-Device Communications in Cellular Networks

Device-to-device (D2D) communications in cellular networks are promising technologies for improving network throughput, spectrum efficiency, and transmission delay. In this paper, we first introduce the concept of guard distance to explore a proper system model for enabling multiple concurrent D2D pairs in the same cell. Considering the Signal to Interference Ratio (SIR) requirements for both macro-cell and D2D communications, a geometrical method is proposed to obtain the guard distances from a D2D user equipment (DUE) to the base station (BS), to the transmitting cellular user equipment (CUE), and to other communicating D2D pairs, respectively, when the uplink resource is reused. By utilizing the guard distances, we then derive the bounds of the maximum throughput improvement provided by D2D communications in a cell. Extensive simulations are conducted to demonstrate the impact of different parameters on the optimal maximum throughput. We believe that the obtained results can provide useful guidelines for the deployment of future cellular networks with underlaying D2D communications.

Performance Analysis of Group-Synchronized DCF for Dense IEEE 802.11 Networks

In dense IEEE 802.11 networks, improving the efficiency of contention-based media access control is an important and challenging issue. Recently, the IEEE802.11ah Task Group has discussed a group-synchronized distributed coordination function (GS-DCF) for densely deployed wireless networks with a large number of stations. By using the restricted access window (RAW) and RAW slots, the GS-DCF is anticipated to improve the throughput substantially, primarily due to relieving the channel contention. However, optimizing the MAC configurations for the RAW, i.e., the number and duration of RAW slots, is still an open issue. In this paper, we first build an analytical model to track the performance of the GS-DCF in saturated 802.11 networks. Then, we study and compare the GS-DCF throughput using both centralized and decentralized grouping schemes. The accuracy of our model has been validated with simulation results. It is observed that the GS-DCF obtains a throughput gain of seven times or more over DCF in a network of 512 or more stations. Moreover, it is demonstrated that the decentralized grouping scheme can be implemented with a small throughput loss when compared with the centralized grouping scheme.

Performance analysis of grouping strategy for dense IEEE 802.11 networks

In IEEE 802.11 networks, how to improve the efficiency of contention-based media access is an important, challenging issue. Recently, the grouping strategy is introduced in the IEEE 802.11ah standard to alleviate the channel contention. In IEEE 802.11ah networks, stations can be divided into groups and each group is only allowed to access wireless channel during the designated channel access period. By limiting the number of stations participating in the channel contention, it is anticipated that such a grouping strategy could substantially improve the communication efficiency. However, how to allocate the channel among different groups and how to adjust the number and sizes of groups are still open issues. In this paper, we first study the impact of the grouping strategy on the network performance, and then propose an analytical model to track the performance under saturated traffic. The accuracy of our model has been validated by simulation results. Our analytical model and results also provide important guidelines in optimizing grouping parameters.

Geometrical-Based Throughput Analysis of Device-to-Device Communications in a Sector-Partitioned Cell

Device-to-device (D2D) communications in cellular networks are considered a promising technology for improving network throughput, spectrum efficiency, and transmission delay. In this paper, the Power Emission Density (PED)-based interference modeling method is applied to explore proper network settings for enabling multiple concurrent D2D pairs in a sector-partitioned cell. With the constraint of the Signal-to-Interference Ratio (SIR) requirements for both the macro-cell and D2D communications, an exclusive region-based analytical model is proposed to obtain the guard distances from a D2D user to the base station, to the transmitting cellular user, and to other communicating D2D pairs, respectively, when the uplink resource is reused. With these guard distances, the bounds of the maximum throughput improvement provided by D2D communications are then derived for different sector-based resource allocation schemes. Extensive simulations are conducted to verify our analytical results. The new results obtained in this work can provide useful guidelines for the deployment of future cellular networks with underlaying D2D communications.

A Pipelined-forwarding, Routing-integrated and effectively-Identifying MAC for large-scale WSN

This paper presents the design of a duty-cycling MAC, called PRI-MAC (Pipelined-forwarding, Routing-integrated, and effectively-Identifying MAC), for large-scale wireless sensor networks. PRI-MAC divides the whole network into grades around the sink node. The higher grade a node is in, logically the further away it is from the sink which is in the lowest grade. Staggered sleep-wakeup schedules are established between any two adjacent grades such that data can be forwarded in a pipelined fashion, largely reducing the packet delivery latency to meet the real-time transmission requirement. Meanwhile, the routing function is seamlessly integrated into PRI-MAC, which reduces the protocol overhead and increases the network scalability. Furthermore, each node utilizes a randomly-generated integer as its identifier only when it is involved in a data transmission, instead of allocating a unique address for each sensor node. The performance of PRI-MAC is evaluated in comparison with PW-MAC by OPNET, in terms of the packet delivery latency, energy efficiency, and throughput.

Connectivity Analysis for Cooperative Vehicular Ad Hoc Networks Under Nakagami Fading Channel

User behaviors like inter-vehicle cooperation have a significant impact on vehicular network connectivity. Intuitively, the network performance can be boosted by introducing cooperation. However, an increasing number of cooperative vehicles may result in increased interference and thus negatively affect the system performance. In this letter, we present an analytical framework to study the impact of the cooperative vehicle ratio on connectivity probability under Nakagami fading channel for both cases of independently non-identically and identically distributed interference. The lower bound of the optimal cooperative ratio is derived to explicitly reveal its relation with system parameters when interference are identically distributed. Numerical results are supplemented by simulations to demonstrate the accuracy of the analytical framework and provide useful guidelines for estimating connectivity performance in the network design for scheduling policy in vehicular networks.

A New Stable Clustering Scheme for Highly Mobile Ad Hoc Networks

This paper addresses the clustering problem for highly mobile ad hoc networks. In the proposed scheme, Doppler shifts associated with received signal are used to estimate the relative speed between cluster head and cluster members. With the estimated speed, a node can predict its stay time in every nearby cluster. In the initial clustering stage, a node joins a cluster that can provide it with the longest stay time in order to reduce the number of re- affiliations. In the cluster maintaining stage, strategies are designed to help node cope with connection loss caused by channel fading and node mobility. Simulation results show that the proposed clustering scheme can reduce the number of re- affiliations and the average disconnection time compared with previous schemes.

A geometrical probability-based approach towards the analysis of uplink inter-cell interference

Interference signal-to-interference ratio (SIR), and other performance metrics in cellular networks depend on the distances between the nodes. As a result, a geometrical probability-based approach can shed light on the analysis of the interference and SIR. In cellular networks, hexagon geometry is considered as the preferred cell shape, as it provides compactness and coverage efficiency. We propose an analytical model for the interference and SIR using the existing knowledge of random distances related to the hexagon geometry. We derive the closed-form expressions for the probability distribution function (PDF) of the interference from one interferer, as well as the PDF of the received signal power of the intended transmission using a geometrical probability-based approach. Moreover, the distributions of the total interference power and SIR are presented in this work. Finally, the analytical results are verified through extensive simulations, which shows the accuracy of our model.

Analytical modeling of link duration for vehicular ad hoc networks in urban environment

Link duration determines the performance of many vehicular applications, especially for urban vehicular wireless communication networks. However, the theoretical analysis on link properties is always complicated, since parameters that should be considered include the inter-vehicle distance, the vehicle speed, the turning ratios in the intersection, the influence of traffic lights in the intersections, and the signal decay caused by the roadside buildings etc. To reduce the analytical complexity, most of the previous works proposed preliminary analysis on link duration property by considering some parameters. Even though some works considered all parameters, their assumptions on the parameters setting were somewhat ideal. For example, the events of meeting traffic lights for two consecutive vehicles in a communication route path were always assumed independent with each other, which is different from the actual situations. This paper proposes a discrete Markov process-based analytical model on link duration by considering a relatively complete set of parameters, including the influence of the inter-vehicle distance, vehicle speed, turning ratios in the intersection, traffic lights in the intersection, and the non-line-of-sight transmission for the intersection. Especially, the theoretical study on the link duration is based on a more realistic traffic lights scenario description model. Finally, simulations are carried to verify the accuracy of our analytical work.