In this paper we study spreading sequences for Code Division Multiplexing (CDM) generated from the AES algorithm in counter mode. These sequences are robust against jamming because they cannot be reconstructed from one of their segments. Additionally, they are flexible, have a large cardinality, and can be obtained from a small key. We show how their linear complexity profile, error probability, and acquisition performance are aligned with those of random sequences. To further enhance them, we introduce a new family of mixed AES/Gold sequences. First, we demonstrate how we can generate cosets of extended Gold sequences which are perfectly orthogonal for CDM. Then, we combine AES sequences and Gold cosets: the new sequences have better performance in terms of error probability and acquisition, while maintaining protection against jamming. All results are derived analytically and validated through simulation. As a case study, we consider an uplink scenario from a ground station to a constellation of Low Earth Orbit satellites. The proposed mixed sequences allow for a significant increase in the number of satellites that can be served in parallel, while maintaining the same level of performance and protection against jamming.

This paper investigates the performance of a satellite communication system which the onboard receiver regenerates the uplink pseudonoise (PN) ranging sequence. Using phase modulation, the PN ranging signal is transmitted together with the telecommand signal in the uplink and the telemetry signal in the downlink. Various ranging sequences are taken into consideration and tested prior to final international adoption. The reciprocal interference among telemetry, telecommand, and ranging signals is evaluated in terms of bit error rate and ranging phase acquisition time.

A technique is proposed to design a block demodulator for differential phase shift keying (DPSK) signals over a frequency flat correlated Rayleigh-fading channel. The technique allows one to drastically reduce the error floor typically present in the bit error rate (BER) curves at high signal to noise ratios (SNRs). The main idea is to use the Karhunen-Loeve expansion to have a more precise description of the fading process at the receiver end.

In this paper we discuss multidimensional signaling for transmission over the satellite channel, i.e., a bandlimited radio channel with nonlinearities. We derive a set of basis signals that are orthogonal and whose bandwidth occupancy is minimal, in the sense that they maximize the power inside a fixed frequency interval (/spl minus/B, B). Since we remove the assumption that the signals be confined in one symbol interval, the concept of orthogonality must be revisited. We design basis signals that satisfy the following requirements: (a) When passed through their matched filter, the sample sequence has no intersymbol interference; (b) when passed through the filter matched to another basis signal, the sample sequence has no interchannel interference, and (c) their bandwidth occupancy is minimum. The performance of four-dimensional signals designed according to this criterion is evaluated in terms of bandwidth occupancy and error probability over nonlinear satellite channels. Comparisons with two-dimensional modulation schemes (in particular QPSK) are also made.>

Using a new representation for continuous-phase modulated (CPM) signals, it is shown how a closed-form expression for the power spectral density of full-response M-ary CPM with modulation index J/M can be obtained by straightforward computations. This result is used to provide an explanation of the fact that this power spectral density depends only on J and not on M.>

The effects of imperfect carrier phase recovery on uncoded and trellis-encoded PSK (phase-shift keying) are compared. A recently proposed clock-aided carrier recovery scheme is analyzed and compared to the standard frequency multiplication circuit. Results obtained through a combination of analysis and computer simulation compare uncoded 4-PSK with trellis-encoded 8-PSK carrying two bits per channel symbol. The quality of the recovered carrier phase is evaluated using the ratio of tone power to background. The system error probability is evaluated and used to determine how accurate the time clock recovery must be in a clock-aided carrier recovery circuit in order to outperform classical recovery systems. It is shown that if the clock recovery system is accurate enough, clock-aided carrier recovery used with coded 8-PSK can compensate for the increased sensitivity of the latter to phase errors.>