At the advent of their third generation, large-scale wireless networks continue to struggle with capacity limitations brought about by the very nature of the cellular architecture. In addition to capacity, the problems of power, battery consumption, and resilience are ever present. Most variations of broadband wireless access that have been deployed, or planned, have hinged on the compromise of mobility for higher data rates. Higher data rates over the air have been available in the form of wireless local area networks, (WLANs), and ad hoc networks, which are restricted in geographic scope. In the recent years, network architectures that take advantage of high bandwidth in close proximity, and low power communications have been receiving serious consideration for larger scale operation, despite sacrificing continuous coverage. On the other hand, each type of network is accessible only by specialized mobile terminals. We present a new approach to wireless networking: “elec! tromagnetic spectrum should be use d by all devices, mobile and fixed, capable of transmitting and receiving in a manner that is locally optimal, in time and space.” We follow the trend in mobile transceiver technologies towards providing access to a multiplicity of networks, enabling a new network design philosophy.
The following topics are being addressed by the Networking Group in 2002:
Dynamic Utility Maximization for Infostations
N. Mandayam, Rutgers
In this project, we analyze dynamic transmission strategies (for transmitter power and data rate) for mobile data users. Energy consumption, system throughput, and the QoS requirements (such as time delay, outage probability) are important objectives of our optimization problems. Our goal is to design transmission policies for every user to maximize the network throughput, and to minimize the consumed energy while satisfying all QoS requirements. In this project, time-varying channels due to the mobile’s movement, shadowing and fading, are taken into account. We believe the work here is a realistic representation of data transmission over time-varying channels and can be used to gain insights into dynamic power and rate control for data. This year, the following specific problems will be addressed: 1) the transmission of finite amount of data under energy constraints: Under a two-state fading channel model, optimal power control schemes will be explored to minimize the! transmission delay of a file tran sfer while guaranteeing that the probability of successful transmission satisfies a threshold requirement. 2) Dynamic power control policies for packet data systems: The QoS requirements are the average packet waiting time and the packet loss probability. With the two-state fading channel model, we will optimize the transmission policy to minimize the energy consumption on a time-varying channel.
Wireless Geolocation
H. Kobaysashi, Princeton and S. Tekinay, NJIT
In the area of “NLOS (non-line-of-sight) geolocation,” we will pursue the following two aspects of the problem. First, we will continue our simulation study to evaluate our geolocation method in more realistic environments, including a multi-path environment. Adaptive schemes will be investigated to update various parameters in the position tracking problem, such as the speed of MS. Second, we plan to extend our current theoretical study by incorporating prior information concerning system parameters such as the delay in an NLOS signal. Then the optimum geolocation solution should take into account such information and better position accuracy is expected. In this context, we will explore the use of the EM (expectation and maximization) algorithm in deriving an optimum geolocation estimator.
Geolocation Estimation
S. Schwartz and V. Poor, Princeton
We plan to expand our project in the general area of geolocation, since there is an increasing level of interest in this topic. Specific research directions are to be formulated in consultation with an industrial sponsor as well as the student’s interest.
Geolocation methods and services or applications for which the location information will be used need to be tightly coupled in order to optimize the overall operation in terms of capacity and performance. Specifically, state of the art standards and recommendations for geolocation will be considered in the context of 2G, 3G and 4G systems. The significance of peer to peer communications will be underlined. The role of mobility modeling, and the trajectory prediction as an aid to service provisioning and routing decisions will be demonstrated.
Radio Resource Management
S. Tekinay, NJIT
We have proposed a new architecture to promote capacity and network lifetime. Ad hoc networking is used as a means to augment the cellular architecture in an effort to maximize capacity and coverage while improving performance. We will devise algorithms taking into account physical layer issues, specifically the channel models, in making routing decisions through the ad hoc subnetwork.
Multi-tiered Cellular Structures for Heterogeneous Wireless Users
S. Schwartz, V. Poor,Princeton and S. Tekinay, NJIT
We plan to continue our study of issues related to tiered networks and heterogeneous users. Our focus will be on the interaction of the network and the physical layer issues. The two conflicting issues of increased capacity and maximum coverage will be studied. Our study will continue to focus on hotspot microcells embedded in a CDMA macrocell system. Hotspots consist of a high density of users in a small geographic area. We will study channel impairments, multiple access interference, power control. Random location of users will help characterize capacity and coverage performance issues. The goal is to develop partition design rules to maximize the number of users in the overall system. In the limit, microcells become infostations, which are high-speed, very small range base stations which we are studying jointly with Rutgers and NJIT under NSF sponsorship, as candidates for a 4th generation system. In the ad hoc augmented network architecture developed last year, t! here is room for accommodating the 3G overlay/underlay concept by creating ad hoc subnets imitating microcells. We will exploit this concept and improve the mobility performance of 3G systems.
Handoff for Wireless ATM
S. Tekinay and N. Ansari, NJIT
We will conduct further analytical and simulation studies on the adaptive handoff prioritization method we have proposed and published for reserving resources and queuing WATM cells. Instead of being forced to terminate a connection when existing QoS (Quality of Service) demands cannot be fulfilled in a new access point, the connection may be maintained with a degraded QoS. With QoS adaptation, improvement of handoff performance in terms of cell loss probability and handoff failure probability can be achieved.
Traffic Modeling and Bandwidth Allocation
N. Ansari and Y. Shi, NJIT
This work focuses on new methods, which can capture both the first order and second order statistics of the video data. Refinement of proposed models are still being investigated. Traffic models are important to network design, performance evaluation, bandwidth allocation, and bit-rate control. Video traffic will be occupying a major portion of network resources. Yet, traditional models fall short in describing the video traffic because video traffic is strongly correlated and bursty.
Traffic Scheduling
N. Ansari, NJIT
As data are piped from the mobile hosts through the network, the ability to schedule transmission of cells for provisioning Quality of Service (QoS) is essential for various multimedia applications. Our efforts will focus on developing switch scheduling algorithms that are fair and scalable, and at the same time can provide QoS guarantees.
Resource Allocation for Video Transmission
N. Ansari and Y. Shi, NJIT
Among multimedia traffic, video traffic is increasingly occupying the major trunk of the network, and demands stringent QoS requirements. These constraints are difficult to meet if high network utilization is desired. We are looking into the idea of allocating bandwidth dynamically that is applicable to real-time video delivery. Some results have been reported, and more exciting results are expected.
QoS Routing
N. Ansari, NJIT
Finding a feasible path subject to multiple constraints in a network is an NP-complete problem. Yet, it is an important problem as many applications require QoS provisioning. In this endeavor, we are looking into a theoretical framework for picking a cost function as well as algorithms that may improve the routing performance in terms of complexity, convergence and probability of finding a feasible path.
Meeting QoS requirements in Multi-Class Wireless Networks
S. Papavassilliou, NJIT
In this project we investigate the role of pricing as an additional dimension of the call admission control process in order to efficiently and effectively control the use of wireless network resources and meet the users’ Quality of Service (QoS) requirements. We will investigate and propose an integrated pricing and call admission control where the price is adjusted dynamically based on the current network conditions, in order to alleviate the problem of congestion. Our proposed integrated approach aims to implicitly implement a distributed user based prioritization mechanism by providing negative incentives according to network conditions, therefore, shaping the traffic in the network. We also plan to continue our previous efforts on using mobility information to improve the channel reservation process in cellular networks and thus offer better QoS to the various users, and develop efficient transmission scheduling techniques for wireless ad hoc networks.
Topology Establishment and Routing for Frequency Hopping Ad Hoc Networks
R. Yates, Rutgers
This project is a continuation of the year 2000 project on Bluetooth connection control. Motivated by Bluetooth, our research will address the issue of scheduling and topology construction in such point-to-point ad hoc networks. The objective is to define algorithms for topology construction such that performance objectives (maximum throughput, minimum delay) are met.
Power Control in Ad Hoc Networks Using Hello Packets
R. Yates, Rutgers
In this project, we propose a power control scheme in which each node dynamically adjusts its transmit power so as to maintain global connectivity over a minimum spanning tree. Each node adjusts its transmit power so that the probability a node remains connected to its MST neighbor is lower bounded. Computations are based on local information exchanged through periodic hello and acknowledgement packets. It is shown that the transmit power is a function of the hello timeout. We have optimized the hello timeout to minimize the average transmit power of a node over the channel life. For different mobility scenarios, we employ analysis and simulation to characterize the power usage of a node. Comparisons will be made with the case when no power control is used.
Using Mobility for Delay-Tolerant Data Transmission in Ad-Hoc Networks
R. Yates, Rutgers
We study delay and throughput in ad-hoc networks for applications with very loose delay constraints. Transmissions are constrained to nearest neighbors closer than some given distance. Thus, the network is not normally connected at any given instant and changes in network topology are essential for packet delivery. Mobile stations can keep copies of packets they receive and each packet to be delivered will almost certainly have many copies in the system at a given instant. We seek to understand average delay and throughput characteristics of such systems as functions of transmission range, mobile density and other parameters.
Forward Link Multicast Transmission
R. Yates, Rutgers
Multicast or broadcast signaling can be employed in a mobile wireless communication network to transmit a messages to multiple (two or more) receivers simultaneously. Radio communication links from a transmitter to a group of receivers have varying interference, fading, and attenuation. Since the radio link state is location-dependent, some radio links are better than others. To ensure that a broadcast transmission is received successfully by all users, the conventional approach limits the transmission rate to be acceptable to the worst-case receiver. However, this solution under-utilizes better radio links. Thus, we look to develop mechanisms for the broadcast of data and multimedia services that optimize the use of the available bandwidth.
Nash Games for Power Control in 3-G Wireless Networks
Gajic, Rutgers
The literature on the power control problem in 3-G wireless CDMA networks bases solutions on static Nash and/or Pareto games. The objective is to optimize a utility function along static constraints that represent the wireless network (channel). A more challenging, and more realistic approach is to study the power distribution for a dynamic wireless system Our approach will require the solution of a multiuser conflict situation using dynamic Nash games to follow the dynamics of channel variations. Hence, at each time instant, we will optimize a function of the mobile’s power and SIR error, subject to dynamic changes of the channel. The design of appropriate utility functions will be necessary.
Automated Information Triage for Mobile Alerting and Timely Decision Making
Hirsh, Rutgers
This project develops transparent software agents that can automatically decide which information to send to a mobile user. An ideal agent would work in a way much akin to a secretary, knowing where the user is and knowing which information to send to the user on a particular device. We call such an agent an Information Valet, or iValet, in that it provides “valet”-like functionality to help users manage their information. Currently, we have moved from one of our main domains where user context was central — email prioritization — to one in which effective information triage requires the exploitation of a range of dynamic information. Our current work focuses on the prioritization of information in a financial setting, integrating press releases, news stories, and stock data — in addition to observing users’ information handling behavior — to determine important financial events. Our goal is to develop server-side technology that monitors a range of inf! ormation sources, determining when information may be of interest to a user.