Showing papers on "Direct-sequence spread spectrum published in 1971"

Variable bandwidth apparatus for transmission system

Abstract: A variable bandwidth apparatus for a signal transmission system having a circuit for changing the bandwidth in response to the spectrum of a signal to be transmitted.

Spread spectrum communication link using surface wave devices

Abstract: A fast lock-up, 8-MHz bandwidth 8,000 bit per second data rate spread spectrum communication link breadboard is described that is implemented using surface wave devices as the primary signal generators and signal processing elements. It uses surface wave tapped delay lines in the transmitter to generate the signals and in the receiver to detect them. The breadboard provides a measured processing gain for Gaussian noise of 31.5 dB which is within one dB of the theoretical optimum. This development demonstrates that spread spectrum receivers implemented with surface wave devices have sensitivities and complexities comparable to those of serial correlation receivers, but synchronization search times which are two to three orders of magnitude smaller.

Optimum Bandwidth of a Low-Pass Filter for Detection of a Pulse in Nonstationary Noise

Abstract: The two-dimensional spectrum is used to compute the optimum low-pass filter bandwidth for the detection of a pulse in noise having an exponential variation of the spectrum level. A simple equation for the two dimensional spectrum of the input is derived. The resulting equations are used to compute curves showing the time variation of the optimum filter bandwidth and the variation of the output signal-to-noise ratio.

High process gain opto-electronic matched filters for communications applications

Abstract: This paper is concerned with the application of opto-electronic signal processing to a certain class of interference-resistant communications techniques. The processing techniques are applicable to spread spectrum digital transmissions which are processed by a matched filter at the receiver. The analysis of optical delay line matched filters of the diffraction type is discussed. The analysis considers the basic ultrasonic light modulator, that is, the modulation of a light source by a sonic wave. The sonic wave may represent a received spread spectrum signal or received noise or a combination of both. Two ultrasonic modulators in cascade perform the desired correlation or matched filter function. The analysis considers the effects of intermodulation of signal and noise and also the effects of the beamspreading and attenuation of the sonic signal in the delay lines. Finally, the design of a matched filter having 40 dB process gain is presented together with an estimate of its communications performance.