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.

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.

Military communications require the rapid deployment of mobile high-bandwidth systems. This work characterizes the electromagnetic interference (EMI) effects of ultra wideband (UWB) transmissions on an IEEE 802.11a ad-hoc network throughput performance. Radiated measurements in an anechoic chamber investigate interference performance for three binary modulation schemes including bi-phase shift keying (BPSK), pulse position modulation (PPM), and on-off keying (OOK) and four pulse repetition frequencies (PRF) transmitted over two unlicensed national information infrastructure (U-NII) channels. Results indicate that OOK and BPPM can degrade throughput performance by up to twenty percent at lower PRF and lower U-NII channels. Minimal performance degradation (less than one percent) due to interference is observed for BPSK at the lower PRF and higher U-NII channels.

Ultra Wideband (UWB) multiple access (MA) performance characterization is provided for Time Hopped-Biorthogonal Pulse Position Modulation (TH-BPPM). Network communication performance is provided for a UWB TH-BPPM synchronous system using both Gold sequence and random integer coding. The wireless multiple access environment considered contains up to 40 multipath replications from each of B network users. The proposed 4-Ary TH-BPPM technique provides results which are nearly identical to previously demonstrated binary TH-PPM performance. Although the Gold coded synchronous network maintains some advantage over the randomly coded network, its advantages rapidly diminish as multipath signals are introduced into the environment.

This paper reports the impact of digital signal processing on microwave receiver technology. The majority of modern receiver designs are based on digital technology. Wide-and narrow-band receivers are presented. The wide-band receivers cover approximately 1-GHz instantaneous bandwidth and are used to intercept radar pulses. Current narrow-band receivers cover up to 50-MHz instantaneous bandwidth and are primarily used for receiving communication signals. Two approaches for wide-band receiver design are discussed. One is the conventional digital receiver. The other one is called the monobit receiver, which has slightly inferior performance in some respects, but can be built on a single chip. Narrow-band receivers are best implemented in software because they can more adapt to changes. Two types of receivers are discussed. One is the software Global Positioning System receiver. The other one is called a transform-domain communication system. The object of this system is to avoid interference in a hostile communication environment.

This research characterizes the initial acquisition performance of a TDCS via modeling and simulation. As previously demonstrated, a TDCS provides an effective interference suppression capability and differs from traditional spread spectrum systems in two primary ways: 1) spectrally crowded regions are avoided via adaptive spectral notching, and 2) no carrier modulation is employed; rather; "noise-like" basis functions are data modulated. Relevant TDCS research has unrealistically assumed perfect synchronization conditions, a vitally important and complete element of most digital communication systems. This research investigated initial TDCS acquisition performance for various synchronization codewords and several acquisition methods, e.g., direct time correlation (DTC) and German's technique, using both peak and threshold detection techniques. Theoretical development and MATLAB(R) simulation results indicate a TDCS can achieve a high probability of detection (P-D > 0.9) for relatively low input Signal-to-Noise Ratios (SNRs), as low as -23 dB for peak detection and -21 dB far threshold detection. For peak detection, DTC provides the best acquisition performance, i.e., the highest P-D for a given input SNR and fixed probability of false alarm, P-FA. For threshold detection with fixed P-FA of 0.01, DTC provides the best acquisition performance for SNRs below -12 dB, and German's technique provides the best acquisition performance above -12 dB. DTC results are shown to approximate matched filter performance while providing reasonable improvement over radiometric processing. Extensive computer simulations and subsequent analysis indicate that a TDCS cart adequately acquire and accurately align a locally generated reference waveform with a received noise-like TDCS signal.