Joshua D. Niedzwiecki

Recent advances in cognitive communications

This article describes recent advances in cognitive communications. We combine the concepts of signal processing, communications, pattern classification, and machine learning to make dynamic use of the spectrum, such that the emanated signals do not interfere with the existing ones. Unlike other programs such as neXt Generation communications of the Defense Advanced Research Projects Agency, where radio scene analysis is performed to find the spectrum holes or the white space, we make use of the white, as well as the gray space for non- interfering signal transmission. We examine the possibility of employing machine perception and autonomous machine learning technologies to the autonomous design and analysis of air interfaces. The underlying premise is that a learning module will facilitate adaptation in the standard classification process so that the presence of new types of waveforms can be detected, features that best facilitate classification of the previously and newly identified signals can be determined, and waveforms can be generated by using the basis-set orthogonal to the ones present in the environment. Incremental learning and prediction allows knowledge enhancement as more snapshots of data are processed, resulting in improved decisions. Some of the contributions of this project include technological advances in signal detection, feature identification, signal classification, sub-space tracking, adaptive waveform design, machine learning, and prediction.

Machine Learning based Cognitive Communications in White as Well as the Gray Space

This paper describes new ideas and results on machine learning based cognitive communications in White as well as the Gray space. We combine the concepts of signal processing, communications, pattern classification and machine learning to make a dynamic use of the spectrum such that the emanated signals do not interfere with the existing ones. Unlike other programs such as the neXt Generation (XG) communications program of the Defense Advanced Research Projects Agency (DARPA), where radio scene analysis is carried out to find the spectrum holes also known as the White space, we make use of the White as well as the Gray space for non-interfering signal transmission. Our assumption is that a learning module will facilitate adaptation in the signal classification process, so that the presence of new types of waveforms can be detected, features that best facilitate classification of the previously and newly identified signals can be determined, and waveforms can be generated by using the basis-set orthogonal to the ones present in the environment. Incremental learning and prediction allow knowledge enhancement as more snap-shots of data are processed, resulting in improved decisions. Use of non-competitive policy set results in zero interference with the already existing signals with a modest increase in the White and Gray space utilization. On the other hand competitive policy set utilizes machine learning to predict the future behavior of the signals which results in more than 90% utilization of spectrum at an expense of some interference due to errors in prediction.

MUD Enabled Media Access Control for High Capacity, Low-Latency Spread Spectrum Communications

Unlike conventional wireless communication systems that operate under an interference avoidance paradigm, the DARPA Interference Division Multiple Access (IDMA) program exploits multi-access interference to enable high-capacity, low-latency spread spectrum communication that requires no infrastructure or coordination. The enabling technology behind IDMA is Multi-User Detection (MUD) at the Physical Layer, which enables a receiver to simultaneously demodulate multiple interfering users. To fully exploit this new Physical Layer capability, novel Media Access Control (MAC) protocols are required that control and encourage users to collide rather than avoid interference all together. This paper discusses the motivating factors behind the IDMA MAC design and highlights the technical challenges in developing a MAC that both facilitates and exploits MUD at the Physical Layer. Particular attention is given to key decentralized MAC mechanisms, including distributed synchronization and scheduling. Analysis is presented highlighting the performance gains of IDMA over conventional adhoc communication systems, such as 802.11. Looking to the future, insight is provided into military applications and concepts of operations where IDMA technology is expected to dramatically improve performance and provide novel capabilities to the warfighter.

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.

Real time implementation of a multiuser detection enabled ad-hoc network

In contrast to the interference avoidance paradigm that conventional wireless communication systems follow, the DARPA Interference Multiple Access (DIMA) Communications program intentionally structures multiple-access interference to enable high-capacity, low-latency, spread spectrum communications. The systempsilas adaptive multi-user detection (MUD) receiver algorithms enable the transmission of multiple data streams in the same time and frequency channel without need for centralized control of synchronization or power levels. This paper focuses on the DIMA system level implementation of the prototype radio network, along with the results from both non-real-time testing and real-time performance characterization efforts. Extensive simulations and non-real-time over-the-air testing helped to drive the design of a real-time MUD receiver implemented on a single FPGA. The Media Access Control Layer, implemented on a General Purpose Processor (GPP), facilitates intentional interference through a defined frame structure that also enables distributed synchronization and scheduling. During the real-time performance characterization period, the DIMA prototype network demonstrated 3.5 times the spectral efficiency of comparable 802.11 ad-hoc systems at low signal to noise ratios (SNRs). DIMA demonstrated up to 11x reductions in latency jitter in the same comparison. These gains can be leveraged in future military applications to provide increased capabilities and improved performance to the war fighter.

Multiple-access capacity gains using multiuser detection under uniform linear power spacing

This paper reviews the driving factors that affect performance gains in wireless networks when receivers are enabled by multiuser detection (MUD). Assuming the many-to-one, Gaussian multiple-access channel, we compare the capacity of a jointly optimal MUD receiver with the single user match filter using TDMA, FDMA and orthogonal CDMA access schemes. Comparisons are made under both equal power and unequal power conditions. Unequal power cases are constrained to uniform linear power spacing where the received powers are equally spaced over a given power spread. Motivation for this analysis is to better understand what multiple-access schemes will realize the highest potential improvements by incorporating MUD technology and under what system constraints those gains are maximized.

Application of multiuser detection to the common data link waveform

The growing use of small form factor unmanned aerial systems (UAS) in theater presents severe co-channel interference issues with todaypsilas radio technology. This paper addresses this concern by describing multiuser detection receiver technology and its application to the Common Data Link (CDL) ISR waveform protocol. By equipping CDL radios with MUD receiver technology developed under the DARPA Interference Multiple Access Communications Program, we show a significant reduction in spectrum pre planning requirements and increases in spectral efficiency. This technique enables multiple UASs to occupy the same channel at the same time without centralized coordination or power control.

Interference multiple access communications

The implementation of network centric warfare on the battlefield has driven the growing demand for high capacity warfighter communication systems. Although new high capacity SATCOM systems such as WGS are being introduced in the near term, these systems use the interference avoidance paradigm, which fundamentally limits overall network performance. This paper introduces a new wireless networking paradigm called Interference Multiple Access (IMA), developed under the auspices of DARPA. The interference multiple access paradigm exploits multi-access interference to enable revolutionary improvements in wireless communication capacity and latency without the need for infrastructure, coordination, or spectrum preplanning. Simulation and over-the-air test results suggest that greater than 3X increases in network throughput (especially in low SNR scenarios) can be achieved over traditional contention and scheduled-based spectrum access approaches when applied to WIN-T NCW terminals communicating in a mesh topology over the WGS constellation.