Engineering topics

Rafferty, William

Publications and source records attributed to Rafferty, William.

13 records

NASA NTRS1993

Land-mobile satellite communication system

A satellite communications system includes an orbiting communications satellite for relaying communications to and from a plurality of ground stations, and a network management center for making connections via the satellite between the ground stations in response to connection requests received via the satellite from the ground stations, the network management center being configured to provide both open-end service and closed-end service. The network management center of one embodiment is configured to provides both types of service according to a predefined channel access protocol that enables the ground stations to request the type of service desired. The channel access protocol may be configured to adaptively allocate channels to open-end service and closed-end service according to changes in the traffic pattern and include a free-access tree algorithm that coordinates collision resolution among the ground stations.

Yan, Tsun-Yee↗

NASA NTRS1992

FD/DAMA Scheme For Mobile/Satellite Communications

Integrated-Adaptive Mobile Access Protocol (I-AMAP) proposed to allocate communication channels to subscribers in first-generation MSAT-X mobile/satellite communication network. Based on concept of frequency-division/demand-assigned multiple access (FD/DAMA) where partition of available spectrum adapted to subscribers' demands for service. Requests processed, and competing requests resolved according to channel-access protocol, or free-access tree algorithm described in "Connection Protocol for Mobile/Satellite Communications" (NPO-17735). Assigned spectrum utilized efficiently.

Yan, Tsun-Yee↗

NASA NTRS1990

A novel demodulator/detector for digital and analog signals on LMR channels

The design, implementation, and performance of an all-digital demodulator/detector suitable for differentially encoded phase-shift keying (DPSK), continuous-phase frequency-shift keying (CPFSK), frequency-shift keying (FSK), and analog FM are discussed. In this demodulator/detector, two detectors, one noncoherent and another differentially coherent, operate simultaneously to provide data detection and automatic frequency control (AFC). Test results indicate that the system provides improved performance over the conventional analog quadrature detector for two-period raised-cosine (2RC) CPFSK modulation in additive white Gaussian noise (AWGN) and Rayleigh fading channels. Being all-digital, the demodulator/detector is well suited for integrated circuit implementation. In addition, the system performs as well as the analog quadrature detector for analog FM voice transmissions, thereby maintaining full compatibility with analog land mobile radio (LMR) transmissions.

Saulnier, Gary J.↗

NASA NTRS1990

Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression.

Huck, R. W.↗

NASA NTRS1990

A satellite-based personal communication system for the 21st century

Interest in personal communications (PCOMM) has been stimulated by recent developments in satellite and terrestrial mobile communications. A personal access satellite system (PASS) concept was developed at the Jet Propulsion Laboratory (JPL) which has many attractive user features, including service diversity and a handheld terminal. Significant technical challenges addressed in formulating the PASS space and ground segments are discussed. PASS system concept and basic design features, high risk enabling technologies, an optimized multiple access scheme, alternative antenna coverage concepts, the use of non-geostationary orbits, user terminal radiation constraints, and user terminal frequency reference are covered.

Sue, Miles K.↗

NASA NTRS1989

A tone-aided dual vestigial sideband system for digital communications on fading channels

A spectrally efficient tone-aided dual vestigial sideband (TA/DVSB) system for digital data communications on fading channels is presented and described analytically. This PSK (phase-shift-keying) system incorporates a feed-forward, tone-aided demodulation technique to compensate for Doppler frequency shift and channel- induced, multipath fading. In contrast to other tone-in-band-type systems, receiver synchronization is derived from the complete data VSBs. Simulation results for the Rician fading channel are presented. These results demonstrate the receiver's ability to mitigate performance degradation due to fading and to obtain proper data carrier synchronization, suggesting that the proposed TA/DVSB system has promise for this application. Simulated BER (bit-error rate) data indicate that the TA/DVSB system effectively alleviates the channel distortions of the land mobile satellite application.

Hladik, Stephen M.↗

NASA NTRS1988

Proceedings of the Mobile Satellite Conference

A satellite-based mobile communications system provides voice and data communications to mobile users over a vast geographic area. The technical and service characteristics of mobile satellite systems (MSSs) are presented and form an in-depth view of the current MSS status at the system and subsystem levels. Major emphasis is placed on developments, current and future, in the following critical MSS technology areas: vehicle antennas, networking, modulation and coding, speech compression, channel characterization, space segment technology and MSS experiments. Also, the mobile satellite communications needs of government agencies are addressed, as is the MSS potential to fulfill them.

Rafferty, William↗

NASA NTRS1988

NASA's mobile satellite development program

A Mobile Satellite System (MSS) will provide data and voice communications over a vast geographical area to a large population of mobile users. A technical overview is given of the extensive research and development studies and development performed under NASA's mobile satellite program (MSAT-X) in support of the introduction of a U.S. MSS. The critical technologies necessary to enable such a system are emphasized: vehicle antennas, modulation and coding, speech coders, networking and propagation characterization. Also proposed is a first, and future generation MSS architecture based upon realized ground segment equipment and advanced space segment studies.

Rafferty, William↗

NASA NTRS1988

An 8-DPSK TCM modem for MSAT-X

This paper describes the real-time digital implementation of an 8-differentiated phase-shift keying (DPSK) trellis-coded modulation (TCM) modem for operation on an L-band, 5 kHz wide, land mobile satellite (LMS) channel. The modem architecture as well as some of the signal processing techniques employed in the modem to combat the LMS channel impairments are described, and the modem performance over the fading channel is presented.

Jedrey, Thomas C.↗

NASA NTRS1988

Pilot-aided modulation for narrow-band satellite communications

This paper discusses a number of tone-aided modulation techniques which have been studied as part of the Mobile Satellite Experiment (MSAT-X) Program. In all instances tone(s) are inserted into data-free portions of the transmit spectrum and used by the receiver to sense the amplitude and frequency/phase distortions introduced by the channel. The receiver then uses this information in a feedforward manner to lessen the effect of the distortions on the data detection performance. Particular techniques discussed are the Tone Calibration Technique (TCT), the Dual Tone Calibrated Technique (DTCT), Transparent Tone-In-Band (TTIB), and Dual-Tone Single Sideband (DTSSB).

Saulnier, Gary J.↗

NASA NTRS1988

A 20/30 GHz personal access satellite system study

JPL is exploring the potential and feasibility of a personal access satellite system which will offer the user freedom and mobility. This paper defines the system concept and applications, presents a strawman design, and identifies the enabling technologies. The system as currently conceived could provide voice and data services to users in the Contiguous United States (CONUS) in the late 1990s to the early 2000s using the 20/30 GHz bands.

Sue, Miles K.↗

NASA NTRS1987

Laboratory measurements and a theoretical analysis of the TCT fading channel radio system

This paper documents the laboratory and theoretical performance of a pilot-aided digital radio system. The technique considered transmits a midband pilot tone to improve the receiver data detection performance in a multipath fading channel and is referred to as the tone calibrated technique (TCT). The performance of a 860 MHz prototype system carrying 2.4 kbit/s data under Rician fading conditions is reported. Both experimental and analytical results show that the error floor experienced with nonpilot-aided transmission methods is effectively removed by the TCT scheme, resulting in significant performance gains at high signal-to-noise ratio values. The paper also examines the TCT system performance under typical operating conditions and presents a new analysis of the TCT theoretical error probability.

Rafferty, William↗

NASA NTRS1986

DSP-based non-coherent dual detector demodulator for land mobile radio channels

This paper outlines the development of a digital demodulator suitable for the non-coherent detection of various modulation formats including: Phase Shift Keying (PSK), Continuous Phase Frequency Shift Keying (CPFSK) and Frequency Modulation (FM). The demodulator design concept has been derived with a view towards a single integrated circuit (IC) implementation. Two detectors, one non-coherent and one differentially coherent, operate concurrently, providing data detection and automatic frequency control (AFC). Bit error rate results are provided which illustrate the receiver performance in white Gaussian noise.

Saulnier, Gary J.↗