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

Spatial antenna diversity has been important in improving the radio link between wireless users. Historically, microscopic antenna diversity has been used to reduce the fading seen by a radio receiver, whereas macroscopic diversity provides multiple listening posts to ensure that mobile communication links remain intact over a wide geographic area. In later years, the concepts of spatial diversity have been expanded to build foundations for emerging technologies, such as smart (adaptive) antennas and position location systems. Smart antennas hold great promise for increasing the capacity of wireless communications because they radiate and receive energy only in the intended directions, thereby greatly reducing interference. To properly design, analyze, and implement smart antennas and to exploit spatial processing in emerging wireless systems, accurate radio channel models that incorporate spatial characteristics are necessary. In this tutorial, we review the key concepts in spatial channel modeling and present emerging approaches. We also review the research issues in developing and using spatial channel models for adaptive antennas.

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Overview of spatial channel models for antenna array communication systems

This paper and its companion are devoted to the evaluation of the impact of chaos-based techniques on communications systems with asynchronous code division multiple access. Sequences obtained by repeating a truncated and quantized chaotic time series are compared with classical m-sequences and Gold sequences by means of a performance index taken from communication theory which is here defined and thoroughly discussed. This analysis reveals that, unlike conventional sequences, chaotic spreading codes can be generated for any number of users and allocated bandwidth. Numerical simulations are reported, showing that systems based on chaotic spreading sequences perform generally better than the conventional ones. Some analytical tools easing the comprehension of these advantages are summarized.

Chaotic complex spreading sequences for asynchronous DS-CDMA. I. System modeling and results

A digital radio frequency transport system that performs bi-directional simultaneous digital radio frequency distribution is provided. The transport system includes a digital host unit and at least two digital remote units coupled to the digital host unit. The bi-directional simultaneous digital radio frequency distribution is performed between the digital host unit and the at least two digital remote units.

Point-to-multipoint digital radio frequency transport

For pt.I see G. Mazzini et al., vol.44, pp.937-47 (Oct. 1997). This paper and its companion (Part I) are devoted to the evaluation of the impact of chaos-based techniques on communications systems with asynchronous Code Division Multiple Access. In Part I, a performance index was introduced and exploited to a priori estimate the performance of DS-CDMA communications systems based on chaotic spreading sequences, and to compare it to that of conventional systems. Here, tools from nonlinear dynamical system theory are employed to give a formal ground for those results. Analytical bounds on the expected partial cross correlation between spreading sequences obtained by quantizing and repeating a chaotic time series are derived, ensuring general applicability of such a technique in a real environment. Further analytical arguments guarantee that, when particular chaotic generators are used, expected performance is not worse than that of a well-behaving communications system. This analysis ensures also that, unlike conventional sequences, chaotic spreading codes can be generated for any number of users and allocated bandwidth.

Chaotic complex spreading sequences for asynchronous DS-CDMA. Part II. Some theoretical performance bounds

In this paper, the use of antenna arrays at a base station for cellular CDMA is studied. We present a performance analysis for a multicell network with an antenna arrays at the base station. A recursive least squares (RLS) algorithm is used to adjust the weight coefficients of the array. We show that by using antenna arrays at the base station we can increase system capacity several fold. Results of simulation studies are also presented.

Capacity improvement with base station antenna arrays in cellular CDMA

A synchronous chaotic spread-spectrum CDMA system is presented. In the system, we use an open flow coupled-chaotic sequence as the signature sequence. This coupled map lattices has a long chaotic transient and can be recovered easily. The autocorrelation and cross-correlation properties of the chaotic sequences are investigated and compared to m and Gold sequences. Finally, the error probabilities of the proposed system are analyzed.

A synchronous CDMA system using discrete coupled-chaotic sequence

A new procedure is proposed for resolving multipaths for the wireless channel. This method uses antenna arrays at the base station to estimate the direction of arrival (DOA) of the multipaths. Beams are formed in the specific DOAs. Thus the significant paths can be separated from one another and then fed into the fingers of a RAKE type receiver. Each finger is adaptively adjusted for delay to achieve optimum combining. We show that such enhancement greatly improves the system performance. Results of preliminary simulation studies are also presented.

http://ieeexplore.ieee.org/iel3/3816/11158/00542252.pdf

A RAKE type receiver structure for CDMA mobile communication systems using antenna arrays

In this paper, a multi-channel MAC protocol that supports multiple traffics will be presented. The dynamic channel selection scheme by receiver decision is implemented and the number of the data channel is independent of the network topology. An adaptive back off algorithm is employed to provide service differentiation for delay sensitive and best-effort traffic. The simulation results have shown that it can support multiple traffics and provide a certain QoS guarantee.

A MAC protocol supporting multiple traffic over mobile Ad Hoc networks

A new approach to calculate fault detection probabilities is presented. Fault-free simulation is used in the approach. The quantities of controllability and observability are defined as probabilities of controlling and observing the nodes in the circuit. The probability distribution of random signals on the circuit nodes is analyzed, and it is proved that controllability is in normal distribution. Thus the unbiasing estimation of the fault detection probability can be obtained. According to the concept of observability, we deal with the fan-out nodes. The fault coverages for actual circuits obtained from this approach agree favorably with the fault simulation results.

Hu Jiandong

Papers

Capacity improvement with base station antenna arrays in cellular CDMA

A synchronous CDMA system using discrete coupled-chaotic sequence

A RAKE type receiver structure for CDMA mobile communication systems using antenna arrays

A MAC protocol supporting multiple traffic over mobile Ad Hoc networks

A new probabilistic approach for estimating fault detection probability