John Gu

Distributed scheduler design for multiuser detection enabled wireless mobile ad-hoc networks

There is a need for military and commercial wireless radio networks that can operate in dynamic environments while supporting high spectral efficiency with throughput guarantees and low latency. This is particularly challenging in wireless mobile ad-hoc networks (MANET). Multiuser detection (MUD) technology promises to address these needs. But most research in MUD technology to date has focused on the physical layer (PHY) challenges with little attention being paid to design of efficient MUD scheduler in medium access control layer (MAC). Our research described in this paper presents a distributed scheduler that addresses many challenging issues associated with a wireless MANET such as dynamic allocation of resources, handling of hidden and exposed nodes, QoS, and scalability. In particular, our research shows that the exposed node problem in MUD enabled radio systems is different from that in conventional interference avoidance systems. We provide guidelines to resolve this problem. Some simulation results are presented. The scheduler design is used in the DARPA Interference Multiple Access (DEVIA) communications program.

An Efficient Intranet Networking Solution for Airborne Networks

We illustrate a novel wireless intranet networking protocol providing the flexibility and efficiency needed to operate in airborne environments. A critical component of this protocol is an efficient mobile ad-hoc networking (MANET) design, known as adaptive hybrid domain routing (AHDR) protocol, devised primarily for airborne networking. We describe the driving networking requirements and tradeoffs, protocol architecture, and measured and simulated performance. The MANET element in this protocol is composed of a strategic combination of proactive and reactive algorithms. It provides updated route information for neighbor nodes and offers optimized route resolution for unknown routes in a fast-changing topology. The set of optimization parameters for making routing decisions is configurable via a network management module. The selection of the best route, data rate, transmission power, message format, frame length, and transmission time is distributed and depends on real-time optimization parameters

Multiuser detection enabled medium access control in mobile ad hoc networks

Increasing spectral efficiency has been a constant challenge in wireless communications. Many military and commercial applications require that wireless networks operate in dynamic environments and provide high data rates. Multiuser detection (MUD) has been demonstrated to increase spectral efficiency by increasing spectrum reuse. Most MUD research to date has focused on the physical layer (PHY) technology. Our research has focused on design of an efficient wireless media access controller (MAC) for MUD enabled mobile ad-hoc networks (MANET). Beyond MUD, other issues addressed in this design include overhead efficiency, optimization of dynamic resource allocation, and support for dense topologies, mobility, scalability, and Quality of Service (QoS). The MAC design is used in the DARPA Interference Multiple Access (DEVIA) communications program. In this paper, a frame structure and architecture of the MAC design are presented. Technical challenges are discussed and motivating factors behind the design are highlighted. The MAC described in this paper has been prototyped and demonstrated in laboratory environment and field trial. Some test results are presented.

Adaptive Management of Scalable Mobile Ad-Hoc Networks with Non-homogeneous Topology

In this paper, we discuss the management of scalable mobile ad-hoc networks (MANET) in which nodes are equipped with a range of adjustable capabilities (transmission range, data rate, and radio interface, etc.) and operate in quite diverse environment (in terms of channel condition and node density, etc.). To support communication in such a dynamic networking environment requires a MANET protocol that is adaptable to spatial and temporal changes. As such, it is crucial to optimize node/link controllability so that node/link resources can be best utilized and a good performance can be achieved. Moreover, it is also necessary to feature statistical measures when evaluating the performance, such as the variance of these metrics in addition to the average. As an extension of our previous research, we continue to study Adaptive Hybrid Domain Routing (AHDR) protocol in regard to the effectiveness of the flooding architecture. We also evaluate various topology control techniques that ensure guaranteed service to disadvantaged nodes and across critical links (sparse connectivity). These efforts serve as very first steps to comprehensively study the impact of network non-homogeneity and variance in topology management.

Flexible access secure transfer (FAST) tactical communications waveform for airborne networking

The military capabilities necessary to realize DODs vision on network centric operation depends upon achieving information and decision superiority through the implementation of an IP enabled jam resistant airborne networking waveform that extends the capabilities of the GIG into the tactical edge airborne and space environments. This paper describes a novel communication protocol called flexible access secure transfer (FAST) for airborne networking waveform that enables low latency communication for time sensitive tactical networking in addition to providing mobile ad-hoc networking in high mobility tactical edge operations. FAST is being developed to operate as a new mode for JTRS networking waveform primarily as an airborne Intranet. It can also be deployed in many of existing Air Force fighters equipped with multifunctional informational distribution system (MlDS) without integration impact to these platforms

Integrating Local Neighborhood Congestion and Path Stability into QoS Routing for Tactical Networks

Routing protocols for wireless Mobile Ad Hoc Networks (MANETs) have been explored extensively in recent years. However, most of the work thus far has focused on finding a feasible route from a source to a destination in a timely and efficient manner without considering the impact on the transport performance of existing application traffic or the newly added flows. As a result, parts of the network become saturated with no means of adaptively compensating for or routing traffic around the overloaded areas, thereby lowering network efficiency. While this limitation may be acceptable for best-effort or delay-tolerant data transfers, real-time applications often require a certain level of Quality-of-Service (QoS) from the network. A comprehensive QoS-enabled MANET solution benefits from a QoS-aware routing scheme that considers the applications transport requirements and the data transport conditions of available paths. We propose a distributed multi-path QoS-aware routing scheme that leverages common MANET characteristics (e.g., neighborhood congestion and path stability) to meet the transport service requirements of real-time applications. The QoS routing scheme implements a method of superimposing distributed neighborhood congestion, neighborhood density, link stability and delay information over multiple discovered paths when calculating the next hop decision. In addition, the solution increases overall network capacity by using otherwise idle network resources. In this paper, we discuss multi-path discovery, the associated QoS metric calculations, and the QoS-aware path selection process.

Network synchronization for distributed MANET

Mobile ad-hoc networks (MANET) are often characterized with rapidly changing topologies, presenting a constant challenge for time synchronization. This challenge holds especially true in tactical edge ground military networks, where topological instabilities are enhanced by hostile transmission environments. In the absence of GPS, time synchronization within the context of a tactical environment requires resilience and ease of deployment. Hardware requirements must be carefully controlled, while relying on distributed coordination techniques to avoid single points of failure. Current tactical ground networks are often deployed without high accuracy oscillators, but still require time synchronization on the order of 1us. Our work demonstrates a distributed synchronization approach with a resource efficient solution that handles these requirements. We introduce cross-layer ad-hoc network synchronization (CLANS), a low overhead time synchronization protocol designed for MANETs and enables coarse synchronization without relying on GPS data. CLANS leverages routing information, channel access schemes, and distributed scheduling protocols that typically exist in a MANET. This provides a resilient, distributed time synchronization solution with relaxed hardware requirements. Simulation results show that CLANS can achieve network synchronization within 1 us in lossy multi-hop networks with the presence of packet loss and measurement noise.

Power aware scheduling and power control techniques for multiuser detection enabled wireless mobile ad-hoc networks

Multiuser Detection (MUD) based receivers theoretically require no power control (PC) as they have the ability to separate signals regardless of their relative power levels as long as these signals achieve a suitable SNR. In practice, receiver designs have finite dynamic range. In this paper, power aware scheduling (PAS) and power control (PC) algorithms are investigated to address the finite MUD dynamic range and performance results are shown. The final PAS algorithm and motivating factors behind the design selections made on the DARPA Interference Multiple Access (DIMA) program are highlighted as well as different approaches involving both scheduling and PC. The techniques selected on the DIMA program are currently operating as part of the DEVIA mobile real-time experiments.