It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

The authors present an overview of the characteristics of code division multiple access (CDMA) as it is currently being envisioned for use in wireless communications. There are many considerations in the design of such systems, and there are multiple designs being discussed. CDMA has been proposed for both terrestrial links and satellite links. However, there are key differences in the characteristics of the two types of links relative to the way they affect a CDMA system. The authors show how the ideas presented affect both terrestrial and satellite-based systems. >

Spread spectrum access methods for wireless communications

Wireless communications are transmitted from at least two radioterminals (110a, 110b) to a base station (120) co-channel over a return link using a return link alphabet. Wireless communications are also transmitted from the base station to the at least two radioterminals over a forward link using forward link alphabet that has more symbols than the return link alphabet. The co=channel signal are deciphered at the receiver, while the radio terminal can use a smaller return link alphabet, which can reduce the power dissipation at the radiotermials.

Co-channel wireless communication methods and systems using nonsymmetrical alphabets

A satellite is used to route push-to-send messages among terrestrial base stations. Reduced push-to-send delays thereby may be provided, when a source push-to-send radioterminal is widely separated from a destination push-to-send radioterminal. Satellite routing only may be used when the source push-to-send radioterminal and the destination push-to-send radioterminal are not communicating with a single terrestrial base station or with a group of terrestrial base stations that are proximate one another. A destination base station that is communicating with the destination push-to-send radioterminal may be determined at the satellite, at a satellite gateway and/or at a central server.

Satellite assisted push-to-send radioterminal systems and methods

In the paper various issues in personal satellite communications are addressed Basic geostationary and non-geostationary satellite constellations are considered The narrowband and wideband characterization of the mobile satellite channel and related system implications are discussed Satellite diversity is presented as a measure to overcome signal shadowing The capacity of TDMA and CDMA multiple access is estimated, taking into account co-channel interference Various network issues, such as mobility management, radio resource management, call control, routing, and network integration are addressed Finally, some regulatory and political issues are mentioned which may be most relevant for market development and financial success of satellite personal communication systems

Issues in satellite personal communication systems

The channel capacity of a satellite direct sequence CDMA system is analyzed including the effects of faded user interference, overlapping antenna beams, imperfect equalization of the antenna pattern across an antenna cell, and diversity reception. Simplified models are used to describe the impact of these effects on the channel capacity of single and multiple cofrequency CDMA systems. In a comparison of the uplink and downlink paths, the uplink of the CDMA system is shown to limit the channel capacity because the downlink can utilize code-orthogonality and coherent demodulation. In a multiple system comparison between band-shared CDMA and band-segmented FDMA/TDMA technologies, FDMA/TDMA is shown to provide about the same capacity for uniformly distributed traffic conditions over many cells and dramatically better capacity when traffic is concentrated in one cell. Due to the peak nature of telephony, this result supports the use of band-segmented systems in mobile user satellite systems. >

P. Monsen

Papers

Multiple-access capacity in mobile user satellite systems