Steven D. Jones

Characterization of Spectrum Activities in the U.S. Public Safety Band for Opportunistic Spectrum Access

Dual site spectrum measurements have been made in the public safety band in Howard County, Maryland, USA. The public safety band is of interest because of its obvious importance and the increasing need to determine whether improved spectral utilization would accommodate increased usage for public safety. Two receiver suites were synchronized and used to measure concurrent spectra at separations between a few meters up to a few kilometers. These measurements prove useful in examining issues of spectrum sensing for dynamic spectrum access, including receiver sensitivity, primary user signal detection, adjacent channel interference, and policy performance with local and cooperative sensing. We analyze the collected data to characterize the usage of this public safety network and provide insights into how white space can be identified and utilized. We propose a class of opportunistic access strategies and demonstrate how collected data can be used to evaluate the performance of such schemes.

An experiment for sensing-based opportunistic spectrum access in CSMA/CA networks

Opportunistic access to spectrum and secondary allocation of spectrum are topics being studied by regulatory bodies and organizations with interest in spectrum utilization. The DARPA ATO neXt Generation (XG) Program is investigating opportunistic use of spectrum wherein users would dynamically access spectrum based on its availability. Such access may embody changes to regulatory policies governing access to the RF spectrum. Additionally, the methods studied by the XG program could be used for secondary access within a fixed portion of spectrum. Opportunistic access would open spectrum that is sparsely used (temporally and spatially) to users who otherwise would be confined to inadequate frequency bands. An XG-enabled radio would sense and characterize spectral activity, identify spectral opportunities for use, and coordinate access, with the goal of not interfering with the primary, non-XG, and users. This paper describes a sensor suite and media access control (MAC) concepts representative of XG. A prototypical experiment has been conducted with the XG MAC in an environment of 802.11b radios. Results are presented that illustrate the operation of the MAC concept and demonstrate performance parameterized by the load carried by both 802.11b and XG

Allocation of QoS connections in MF-TDMA satellite systems: a two-phase approach

We address the problem of providing guaranteed quality-of-service (QoS) connections over a multifrequency time-division multiple-access (MF-TDMA) system that employs differential phase-shift keying (DPSK) with various modulation modes. The problem can be divided into two parts-resource calculation and resource allocation. We present algorithms for performing these two tasks and evaluate their performance in the case of a Milstar extremely high frequency satellite communication (EHF-SATCOM) system. In the resource-calculation phase, we calculate the minimum number of timeslots required to provide the desired level of bit-error rate (BER) and data rate. The BER is directly affected by the disturbance in the link parameters. We use a Markov modeling technique to predict the worst case disturbance over the connection duration. The Markov model is trained offline to generate a transition-probability matrix, which is then used for predicting the worst case disturbance level. We provide simulation results to demonstrate that our scheme outperforms the scheme currently implemented in the EHF-SATCOM system. The resource-allocation phase addresses the problem of allocating actual timeslots in the MF-TDMA channel structure (MTCS). If we view the MTCS as a collection of bins, then the allocation of the timeslots can be considered as a variant of the dynamic bin-packing problem. Because the this problem is known to be NP-complete, obtaining an optimal packing scheme requires a prohibitive amount of computation. We propose a novel packing heuristic called reserve channel with priority (RCP) fit and show that it outperforms two common bin-packing heuristics.

A common lexicon and design issues surrounding cognitive radio networks operating in the presence of jamming

This paper discusses issues surrounding the design of cognitive radio (CR) networks that must operate in the presence of jamming and hostile Electronic Countermeasure (ECM) environments. Much of the research to date in the CR community has focused on spectrum-sensing techniques and multiple-access methods. Until recently, little work had been done in the general area of wireless network security and specifically the area of performance in the presence of jamming. Discussions on this topic have been inhibited in the greater CR community by a poorly defined lexicon, which makes addressing issues such as security and performance in jamming difficult. This paper attempts to provide a basic lexicon that can be used to clearly discuss the issues surrounding CR network security and performance in the presence of jamming. This paper then goes on to discuss the various jammer threats that might be encountered by a CR network and the ramifications of these threat types on CR network design.

Efficient resource allocation for QoS channels in MF-TDMA satellite systems

In this paper, we address the problem of providing guaranteed quality of service (QoS) channels over multi-frequency time division multiple access (MF-TDMA) systems that employ DPSK with multiple modulation modes. The two QoS measures that we consider are the bit error rate (BER) and the data rate. We treat the data rate as a deterministic QoS measure, and the BER as a statistical QoS measure. Our approach is divided into two phases: resource calculation and resource allocation. In the resource calculation phase, we calculate the number of timeslots required to provide the desired level of QoS. We treat this as a disturbance prediction problem and present a Markov model based scheme for solving it. We compare the performance of this scheme with that of the scheme implemented in the extremely high frequency satellite communication (EHF-SATCOM) systems, which are jointly used by the four military services. The resource allocation phase addresses the problem of allocating actual timeslots in the MF-TDMA channel structure (MTCS). The MTCS allows flexibility in capacity allocation, but suffers from inefficiencies caused by fragmentation. Here we propose a novel packing scheme called the Reserve Channel with Priority (RCP) fit, and show that it outperforms the first-fit and the best-fit algorithms in the cases considered.

Communications network architectures for the army future combat system and objective force

A key element of the USA armys transformation is the future combat system and objective force (FCS/OF). The FCS/OF will operate as a cohesive, mobile, lethal, survivable, and sustainable land combat force capable of rapid deployment and immediate employment upon arrival and able to defeat threats in the 2010-2025 timeframe. This is to be achieved through network-centric operations wherein the force is realized through the network. In this paper we consider three echelons of the objective force, the FCS at the lowest level, above which resides the unit of action and the unit of employment. A communications network architecture study has been conducted to determine how the mobile nodes of the FCS/OF network may be best configured to realize this force. The study has examined a number of potential architectural topologies and the performance that can be expected from each. Trade studies were conducted to assess the relative merit of various technologies to the FCS/OF network on the basis of measures of performance such as capacity, connectivity, coverage, protection, and scalability. The result is a recommended communications architecture that will most readily achieve the goals of the FCS/OF. A flat architecture at the lowest echelons exploits mobile ad hoc networking with directional antennas for terrestrial communications. Range extension is realized through relays of various forms including unmanned aerial vehicle and satellite communications. Unit of action communications are organized into subnetworks with relay to lower and higher echelons, as well as joint and coalition forces. The unit of employment network enables command and control on-the-move and reachback to continental USA and external forces.

Scalability of a class of wireless sensor networks

Recent advances in wireless communications and MEMS technology have led to the development of wireless sensor networks with a large number of small sensing devices. Most of these wireless sensor networks are motivated by the increases in sensing coverage and performance that can potentially be achieved through effective sensor data fusion. However, as the density of a wireless sensor network grows, the likelihood of transmission collisions among sensor nodes can increase simultaneously. In this paper, we consider a class of wireless sensor networks and show that there can exist fundamental limits on their performance based on recent results on the capacity of wireless networks. We study a simple distributed detection problem with wireless sensor networks and investigate the scalability of several common data fusion architecture under appropriate assumptions on the sensor models.

A dynamic spectrum access MAC appliqué for legacy military radios

There is interest in dynamically allocating spectrum due to the high degree of usage and interference in DoD wireless communications bands. While all bands may not always exhibit high usage, there are times and locations where radio usage is interrupted due to inability to access spectrum. With this in mind, the DoD has undertaken programs such as DARPA neXt Generation (XG) and Wireless Network After Next (WNAN) to develop methods for dynamic spectrum access (DSA). In DSA, a radio or set of radios may select to use a frequency channel at any given time on the basis of the sensed signal activity (or interference temperature) in that channel. Currently fielded military radios do not have such a DSA capability. The situation among DoD radios is such that there exist a variety of means of introducing DSA. Among these are: development of entirely new DoD radios, modification of the software load of current software-defined DoD radios to give them DSA capability, and finally the addition of a hardware and/or software applique to interface with existing DoD radios, particularly those not software-defined. Of course there will also be a class of DoD radios that are not suited for the addition of DSA capability. The DARPA WNAN Program is pursuing the first method above, by developing a new radio. The second method above is being pursued in the DARPA XG Program by modifying radio software to add DSA protocols and sensing. In this paper we consider a military radio set (the AN/PRC-117F and the like) which has the necessary features to allow a hardware/software sensing applique to be integrated with it resulting in a radio/sensor suite with cognitive features. This paper describes the design and implementation of such an applique, along with controlling software and its integration with the PRC-117F in a prototype fashion. The applique has been developed and tested in a laboratory environment.

A MetaNet architecture for end-to-end quality of service (QoS) over disparate networks

In this work we investigate an architecture for resource provisioning and route selection over multiple disparate networks. We have developed a layered hierarchy of internetworking and intranetworking levels of management called a MetaNet. Management at the internetwork level is conducted in a manner that models each network abstractly. At the intranetwork level management accounts for the detailed implementation and organizational characteristics of each network. The paper explores how to employ these layers to cooperatively satisfy end-to-end requests for connectivity with an associated QoS. In addition, we explore negotiation between the inter- and intranetwork levels of management and brokering of QoS by the internetwork level among the intranetwork level managers.