Michael A. Temple

TDCS, OFDM, and MC-CDMA: a brief tutorial

This article gives a brief tutorial on transform-domain communication system (TDCS), OFDM, and MC-CDMA. The primary goal of this article is to give a detailed description of the TDCS transmitter and receiver systems and to highlight the fundamental differences relative to OFDM and MC-CDMA. The fundamental idea in TDCS is to synthesize a smart adaptive waveform to avoid interference at the transmitter instead of the more traditional mitigating of interference at the receiver. Unlike OFDM and MC-CDMA, TDCS has very little exposure in the current literature.

An operational and performance overview of the IRIDIUM low earth orbit satellite system

Today, both the military and commercial sectors are placing an increased emphasis on global communications. This has prompted the development of several low earth orbit satellite systems that promise worldwide connectivity and real-time voice communications. This article provides a tutorial overview of the IRIDIUM low earth orbit satellite system and performance results obtained via simulation. First, it presents an overview of key IRIDIUM design parameters and features. Then, it examines the issues associated with routing in a dynamic network topology, focusing on network management and routing algorithm selection. Finally, it presents the results of the simulation and demonstrates that the IRIDIUM system is a robust system capable of meeting published specifications.

Novel overlay/underlay cognitive radio waveforms using SD-SMSE framework to enhance spectrum efficiency- part i: theoretical framework and analysis in AWGN channel

Recent studies suggest that spectrum congestion is primarily due to inefficient spectrum usage rather than spectrum availability. Dynamic spectrum access (DSA) and cognitive radio (CR) are two techniques being considered to improve spectrum efficiency and utilization. The advent of CR has created a paradigm shift in wireless communications and instigated a change in FCC policy towards spectrum regulations. Within the hierarchical DSA model, spectrum overlay and underlay techniques are employed to enable primary and secondary users to coexist while improving overall spectrum efficiency. As employed here, spectrum overlay exploits unused (white) spectral regions while spectrum underlay exploits underused (gray) spectral regions. In general, underlay approaches use more spectrum than overlay approaches and operate below the noise floor of primary users. Spectrally modulated, spectrally encoded (SMSE) signals, to include orthogonal frequency domain multiplexing (OFDM) and multi-carrier code division multiple access (MC-CDMA), are candidate CR waveforms. The SMSE structure supports and is well suited for CR-based software defined radio (SDR) applications. This paper provides a general soft decision SMSE (SDSMSE) framework that extends the original SMSE framework to achieve synergistic CR benefits of overlay and underlay techniques. This extended framework provides considerable flexibility to design overlay, underlay and hybrid overlay/underlay waveforms that are scenario dependent. Overlay/underlay framework flexibility is demonstrated herein for a family of SMSE signals, including OFDM and MC-CDMA. Analytic derivation of CR error probability for overlay and underlay applications is presented. Simulated performance analysis of overlay, underlay and hybrid overlay/underlay waveforms is also presented and benefits discussed, to include improved spectrum efficiency and channel capacity maximization. Performance analysis of overlay/underlay CR waveform in fading channels will be discussed in Part II of the paper.

Cognitive radio - an adaptive waveform with spectral sharing capability

The growth of wireless applications and spectral limitations are serious concerns for both the military and civilian communities. Cognitive radio (CR) technologies expand spectrum efficiency using elements of space, time and frequency diversity that up to now have not been exploited. An adaptive waveform (AW) generation technique is presented which adapts to the changing electromagnetic environment and synthesizes waveform features in the frequency domain. Spectral coexistence with other applications is also addressed and can be accomplished in both static and dynamic environments. Bit error rate (BER) serves as the primary performance metric for evaluating and comparing AW processing with other waveforms and systems.

An overview of the IRIDIUM (R) low Earth orbit (LEO) satellite system

This paper provides a tutorial overview of the IRIDIUM(R) low earth orbit (LEO) satellite system. Section I contains an introduction to the IRIDIUM(R) network as well as the system specifications. Section II discusses the satellite constellation design, orbital parameters, and horizontal pointing angles between satellites. Section III introduces the idea of time dependent connectivity in a mobile network, and analyzes the cycle of network connectivity for IRIDIUM(R). Section IV discusses the IRIDIUM(R) Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) schemes and uses these to calculate the overall system capacity. Section V examines the call processing procedure to include user location and call set up. Finally, Section VI analyzes the network performance in terms of end-to-end delay and hop count.

Intrinsic Physical-Layer Authentication of Integrated Circuits

Radio-frequency distinct native attribute (RF-DNA) fingerprinting is adapted as a physical-layer technique to improve the security of integrated circuit (IC)-based multifactor authentication systems. Device recognition tasks (both identification and verification) are accomplished by passively monitoring and exploiting the intrinsic features of an ICs unintentional RF emissions without requiring any modification to the device being analyzed. Device discrimination is achieved using RF-DNA fingerprints comprised of higher order statistical features based on instantaneous amplitude, phase, and frequency responses as a device executes a sequence of operations. The recognition system is trained using multiple discriminant analysis to reduce data dimensionality while retaining class separability, and the resultant fingerprints are classified using a linear Bayesian classifier. Demonstrated identification and verification performance includes average identification accuracy of greater than 99.5% and equal error rates of less than 0.05% for 40 near-identical devices. Depending on the level of required classification accuracy, RF-DNA fingerprint-based authentication is well-suited for implementation as a countermeasure to device cloning, and is promising for use in a wide variety of related security problems.

Novel overlay/underlay cognitive radio waveforms using SD-SMSE framework to enhance spectrum efficiency-part II: analysis in fading channels

Interest in Cognitive Radio (CR) remains strong as the communications community strives to solve the spectrum congestion problem. In conventional CR implementations, interference to primary users is minimized using either overlay waveforms that exploit unused (white) spectrum holes or underlay waveforms that spread their power spectrum density over an ultra-wide bandwidth. In Part I, we proposed a novel hybrid overlay/underlay waveform that realizes benefits of both waveforms and demonstrated its performance in an AWGN channel. This was done by extending the original Spectrally Modulated Spectrally Encoded (SMSE) framework to enable soft decision CR implementations that exploit both unused (white) and underused (gray) spectral areas. In Part II, we analyze and evaluate performance of the proposed hybrid overlay/underlay waveform in frequency selective fading channels. A simulated performance analysis of overlay, underlay and hybrid overlay/ underlay waveforms in frequency selective fading channels is presented and benefits discussed.

Evolution of the air interface of cellular communications systems toward 4G realization

Early cellular networks used analog frequency modulation for voice communication and frequency division multiple access to accommodate multiple users. Despite their utility, these networks were often unstable and provided poor quality. Over the past 25 years, robust coding, modulation, and multiple access schemes have contributed greatly to improved, ubiquitous cellular service. This survey chronicles the coding, modulation, and multiple access developments within the evolutional framework of cellular communication systems which spans early first generation (1G) to future fourth generation (4G) systems. EVOLUTION OF THE AIR INTERFACE OF CELLULAR COMMUNICATIONS SYSTEMS TOWARD 4G REALIZATION 1ST QUARTER 2006, VOLUME 8, NO. 1 www.comsoc.org/pubs/surveys 1553-877X The views expressed in this article are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the U.S. Government.

Performance simulation of a transform domain communication system for multiple access applications

A previously proposed interference-avoiding transform domain communication system (TDCS) is shown capable of operating successfully in a multiple access environment (MAE). The TDCS uses phase coding (mapping) generated from a linear feedback shift register (LFSR) configured to output a maximal-length binary pseudorandom sequence (m-sequence). Quasi-orthogonal basis functions (BFs) are used in a code division multiple access (CDMA) scheme to provide private communication channels to independent user pairs in the MAE. An existing single channel TDCS model is augmented to simulate MAE interference effects on bit error performance (P/sub B/) The proposed TDCS system is simulated using MATLAB for system capacities up to eight channels and E/sub b//N/sub 0/ values ranging from 0 to 9 dB. Simulated MAE TDCS bit error performance closely approximates estimated results; the error for eight channels has a mean value less than 1.7/spl times/10/sup -3/ and a standard deviation less than 1.3/spl times/10/sup -3/. The analysis of acquisition-related performance metrics and bit error performance through computer simulation provides a good measure of TDCS operational capabilities in a MAE.

Application of wavelet-based RF fingerprinting to enhance wireless network security

This work continues a trend of developments aimed at exploiting the physical layer of the open systems interconnection (OSI) model to enhance wireless network security. The goal is to augment activity occurring across other OSI layers and provide improved safeguards against unauthorized access. Relative to intrusion detection and anti-spoofing, this paper provides details for a proof-of-concept investigation involving “air monitor” applications where physical equipment constraints are not overly restrictive. In this case, RF fingerprinting is emerging as a viable security measure for providing device-specific identification (manufacturer, model, and/or serial number). RF fingerprint features can be extracted from various regions of collected bursts, the detection of which has been extensively researched. Given reliable burst detection, the near-term challenge is to find robust fingerprint features to improve device distinguishability. This is addressed here using wavelet domain (WD) RF fingerprinting based on dual-tree complex wavelet transform (DT-CWT) features extracted from the non-transient preamble response of OFDM-based 802.11a signals. Intra-manufacturer classification performance is evaluated using four like-model Cisco devices with dissimilar serial numbers. WD fingerprinting effectiveness is demonstrated using Fisher-based multiple discriminant analysis (MDA) with maximum likelihood (ML) classification. The effects of varying channel SNR, burst detection error and dissimilar SNRs for MDA/ML training and classification are considered. Relative to time domain (TD) RF fingerprinting, WD fingerprinting with DT-CWT features emerged as the superior alternative for all scenarios at SNRs below 20 dB while achieving performance gains of up to 8 dB at 80% classification accuracy.