Shaomin Mo

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.

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.

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.

Distributed medium access control for multiple hop tactical networks

In mobile ad-hoc networks (MANET), traffic coordination is a constant challenge. Node topologies and transmission patterns are continuously changing, making wireless communications complicated and difficult to maintain. Adaptive transmission scheduling must be implemented in order to relieve the stresses placed upon a MANET by packet collisions. In this paper, we identify the impact of hidden nodes in a multiple hop network with reference to a new shift in warfare style. We introduce Distributed medium access control (DMAC), a distributed TDMA channel access protocol designed with low physical requirements (single-channel, half-duplex radio with clear channel assessment) that manages outgoing traffic based on traffic type. By selectively handling outbound packet types using transmission techniques suited to each type, DMAC reduces the overhead and complexity of coordinating channel access. DMAC strives to be portable and versatile while using distributed scheduling and traffic control to protect the network against hidden nodes. These techniques provide resilient collision avoidance with nodes beyond carrier sensing range. This allows DMAC to provide an adaptable solution for MAC access in a MANET. We compare DMAC performance to Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA) in relevant tactic1al scenarios. The scenarios model a realistic military field deployment with emphasis on the importance of multiple hop communications within a small network. In these scenarios, DMAC provides higher system throughput than CSMA/CA, by avoiding collisions and minimizing scheduling overhead. This provides compelling evidence for DMACs potential efficiency gains in MANET environments.

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.

Optimal platform placement and configuration in networked electronic warfare (EW)

In this work, we investigate dynamic resource allocation in a networked electronic warfare (EW) environment. In particular, we study the problem of placing EW capable nodes, including both electronic attack (EA) and electronic support (ES) nodes, to collaboratively carry out missions. We first provide a general formulation of the platform placement. The objective is to minimize the cost associated with the placement of both EA and ES nodes, while satisfying the requirement of jamming coverage and network connectivity. Since the placement problem is NP-hard, we next propose two heuristics that can provide good solutions with reasonable computational efficiency. Via several representative case studies, we evaluate the performance of the proposed heuristics.

Improving Network Reachability and Data Rate in Tactical Wireless Networks via Collaborative Communications

In this paper, we study simple collaborative communication schemes and evaluate how they can increase the reachability and data rate of a wireless network in a tactical environment. Often nodes employed in such an environment are constrained by transmitting power, range, and dead zones. As such, maintaining network connectivity in a tactical environment presents many challenges. Collaborative power combining schemes can overcome power and range constraints. This is done by exploiting the broadcast nature of signals - collaborating nodes first listen to the transmitted data packets and then constructively combine transmissions to increase radiated energy to the receiver. As a consequence, range and SNR increase. Using analysis and simulation, we demonstrate that, by utilizing such techniques, an increase in both network reachability and data rates is possible, even in the presence of detrimental environmental conditions. Our analysis shows that these schemes not only are useful in low SNR regimes and power constrained environments, but also can improve the variance of system performance.

A Novel Distributed Medium Access Control and Synchronization for Ad-Hoc Sensor Networks

In this paper, we provide a general framework of distributed medium access control (DMAC) and synchronization for ad-hoc sensor networks with omni-directional antennas. Compared to existing works that focus on minimizing the energy consumption, our design objectives aim to increase the throughput, to lower the latency, and to solve hidden and exposed nodes problem in a traffic-heavy and dynamic environment. DMAC uses different transmission techniques based on the type of outbound packets, to effectively reduce the overhead and complexity of channel access coordination. At its core, DMAC relies on node activate medium access (NAMA) scheduling to coordinate collision-free transmissions. As time synchronization plays a fundamental role in DMAC scheduling, we also design a synchronization scheme tailored to multi-hop networks with heavy traffic and packet loss. We evaluate the performances of the proposed framework via extensive simulations. Our results show that DMAC provides higher system throughput compared with carrier sense multiple access/collision avoidance (CSMA/CA) scheme. In addition, the proposed synchronization scheme can achieve synchronization error within 1 mus in the presence of packet loss and measurement noise, while incurring minimal increment of overheads.