Time diversity is achieved in direct sequence spread spectrum by receiving different faded delayed copies of the transmitted symbols from different uncorrelated channel paths when the transmission signal bandwidth is greater than the coherence bandwidth of the channel. In this paper, a new time diversity scheme is proposed for spread spectrum systems. It is called code-time diversity. In this n...

Acquisition of the code timing in DS/SS systems is addressed for time-varying frequency-selective underwater acoustic channels. Acquisition algorithm based on adaptive channel estimation and fitlering is proposed. The algorithm employs feedback of pre-cursor and post-cursor inter-chip interference to provide a channel estimate from which the code timing is acquired. The channel estimate is also...

We consider interference suppression for direct-sequence spread-spectrum code-division multiple-access (CDMA) systems using the minimum mean squared error (MMSE) performance criterion. The conventional matched filter receiver suffers from the near-far problem, and requires strict power control (typically involving feedback from receiver to transmitter) for acceptable performance. Multiuser dete...

and Applied Analysis 3 1 1 2 2 Integrator Decision device

Spread-spectrum (SS) communications technology was first described on paper by an actress and a musician! In 1941, Hollywood actress Hedy Lamarr and pianist George Antheil described a secure radio link to control torpedos and received U.S. patent #2.292.387. It was not taken seriously at that time by the U.S. Army and was forgotten until the 1980s, when the came alive, and has become increasing...

In this paper, a residue number arithmetic is used in direct sequence spread spectrum system, this system is evaluated and the bit error probability of this system is compared to that of non residue number system. The effect of channel bandwidth, PN sequences, multipath effect and modulation scheme are studied. A Matlab program is developed to measure the signal-to-noise ratio (SNR), and the bi...

In this paper, it has considered Orthogonal Frequency Division Multiplexing (OFDM) as one of the most used technique in communications applied in a wide-band radio channel, it has been chosen as an air interface for the downlink in the framework of Long Term Evolution (LTE) standardization due to its flexibility and adaptively in the technical system design, also considered the use of undersea ...

Direct sequence spread spectrum transmissions (DSSS) are now widely used for secure communications, as well as for multiple access. Since the transmission uses a large bandwidth, the power spectral density of a DS-SS signal can be below the noise level. Hence, such a signal is difficult to detect. In this paper, we propose a method which is able to detect a spread spectrum signal hidden in the ...