A new approach to PN code acquisition is presented and analyzed. A recirculation loop is used to improve probability of synchro cell detection P/sub D/ in each retrace of the code uncertainty region. To further improve P/sub D/ and probability of false alarm P/sub fa/ simultaneously, code diversity (a number of synchro channels in parallel) is used. This is especially effective in the channel with multiple access interference and near-far effect. Typical applications are networks with very low signal-to-noise ratio. Examples are code division multiple access (CDMA) LEO satellite systems experiencing high Doppler or any CDMA network where the number of users is approaching capacity limits. Even if the carrier Doppler is compensated, in any asynchronous LEO satellite network, compensation of code Doppler is not feasible. For this reason, in order to cope with code Doppler (D) and delay (/spl tau/), a modification based on transforming the two-dimensional uncertainty region (D, /spl tau/) into a new uncertainty region (T/sub c/, /spl tau/) will be introduced. Parameter T/sub c/ is the period of the correlation pulses at the output of a sliding correlator. When Doppler rate is present, the three-dimensional uncertainty region (D, R/sub d/, /spl tau/) is transformed into a new one (T/sub c/, R/sub t/, /spl tau/) where R/sub d/ and R/sub t/ are Doppler rate and correlation pulse period change rate, respectively. The main motivation for this work is to find new algorithms suitable for all digital receiver implementation and operation at low signal-to-noise ratios. These algorithms make CDMA techniques feasible for direct communication between LEO satellite and small ground-based user terminals (handsets). A comprehensive performance study of the new PN code acquisition system is presented and discussed. The results obtained demonstrate that, for low signal-to noise ratios, the acquisition time achieved with the new algorithm is one order of magnitude shorter compared with standard techniques known so far.

This paper provides an introduction to the classic paper "Transoceanic Communication by Means of Satellites," which was written by J.R. Pierce and R. Kompfner and appeared in the March 1959 issue of the Proceedings of the IRE. This paper also provides a periscopic view of satellite communications development since then. Surprisingly, in some aspect, the fundamental ideas have not changed much after 40 years. Conceptually, most technical development falls within these ideas. Practically, however, technological advances and significant progress has been made in all areas of space segment, ground segment, and launch vehicles. Today, due to its impact and usefulness, satellite communications is no longer the domain of the technologists alone. Instead, it has created industries, established relevant institutions, coordinated regulations and standards, provided employment, and financially benefitted many persons. This paper addresses these issues, which have been indirectly created by the scientists and engineers who developed satellite communications.

The paper presents an up-to-date overview as well as new results on mobile satellite communications. Specifically, the following subjects are addressed: worldwide activities; satellite orbits; multiple access techniques; Novstar global positioning system; economic and regulatory issues; future trends. Some of these technical and nontechnical subjects appeal disjoint, but they are unique and significant among the many facets, which effect the development and operation of mobile satellite communication systems.>

A snapshot of the present status of ISDN (integrated services digital network) is presented in terms of standardization efforts, field trials and demonstrations, implementations and services, and equipment and devices. A review of opinions and controversies as well as future trends is also given. The authors emphasize the importance of the worldwide standardization effort and discuss the organizations that are responsible for establishing such standards. It is pointed out that, with the limitation and inflexibility of the narrowband ISDN and the broadband ISDN, issues for higher-rate services have become prominent. For broadband services, the problem is not merely increasing the speed of the operation. It affects the compatibility of switching technology, the workability of the local loop arrangement, the availability of rate adaption, and the efficiency of bandwidth utilization. Although some basic principles of narrowband ISDN can be carried to broadband ISDN, the technology is quite different. For example, the interconnection and transmission problems of video, HDTV, (high-definition television), and high-speed data are different from those of voice. Thus, the standard 64-kb/s B channel itself, the fundamental rate of ISDN transmission, appears inadequate for wideband services. At present, the solution is to establish the multiples of 64 kb/s for accommodation of broadband or higher rates.>

The simple automatic repeat request (ARQ) scheme, error concealment by command refreshment, appropriate queuing discipline and priority switching design, layered source coding schemes, and other signal processing techniques are summarized with emphasis on different layered source coding schemes. Four types of signal priority classification schemes are identified: bit-plane separation (BPS), frequency-domain separation (FDS), combined bit-plane-frequency separation (CBFS) and feature plane separation (FPS). CBFS is shown to offer a good alternative to the FDS for possible cell dropping compensations in the ATM network. Different layered source coding schemes are described and compared, and a CBFS-based combined-transform coding (CTC) scheme is highlighted.>

This paper addresses the issues concerning the future of satellite communication, which will be influenced by the advancement of fiber optical cables, the proliferation ofC- andKu-band satellites, the standardization of ISDN, the requirements for new and low cost services, the economic disparity among countries, the extent of institutional policy changes, as well as technological breakthroughs. The factors will dictate and shape, both internationally and domestically, the directions of future satellite communications. In addition, the following subjects are discussed:\bulletservice and traffic projections\bulletaccess strategies\bulletmodulation alternatives\bulletsatellite switching and on-board processing\bulletphase array antennas\bulletlow-altitude orbit options\bulletsatellite lifetime extension.

This paper discusses a number of coding techniques for future satellite communication; they include Reed-Solomon error decoding for message blocks, probabilistic decoding techniques for punctured convolutional codes, and planar Euclidean geometry difference set codes for random multiple access applications. The provision of code concatenation, helical interleaving, and simulation results of new punctured convolutional codes are included. A number of coded satellite systems that demonstrate the usefulness of coding in satellite communications are described.

Part II presents a unified code-generation algorithm which contains new codes with rates from 14/15 to 49/50. For use with this class of codes, some simplifications of the weighted maximum likelihood decoding are suggested. An approximated error probability expression is set forth for using these codes in communications satellite channels, The measured results are remarkably close to the error rate calculations.

This paper is the last part of a three-part series on threshold decoding new convolutional codes. The first part of this paper concludes the list with new rate 1/2 codes. For these codes a characteristic equation, in terms of the number of correctable errors and code constraint length, is derived by least square approximations. The second part of the paper is concerned with the usefulness of the codes derived including those in Parts I and II. Based upon the uncorrectable error statistics of the decoder, the concatenation of such codes is suggested. The characteristic of this class of codes with the property of not producing additional and bursty errors at the output of the decoder when the capability of the decoder is exceeded, is not shared by most powerful decoders such as Reed-Solomon, BCH, and Viterbi.

New convolutional self-orthogonal codes (CSOC's) are generated by extending the work of Massey and Robinson. These classes of high-rate or low-redundancy codes are known to be threshold decodable. Actual applications have demonstrated the usefulness of these codes for satellite communications. Part I of this paper contains codes from rates 2/3 to 13/14, with code minimum distances varying from 4 to 51.