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This paper reviews the concepts of spectrum efficiency, the parameters for assessing system performance, and the techniques for improving spectrum utilization. The rationale of possible bandwidth reduction and power savings by combined modulation techniques is discussed and special attention is given to combined amplitude and phase modulation (APSK)(More)
This paper reviews the factors affecting the gen­ eration of intermodulation interference in crystal mixers and suggests a new approach of determining an optimum set of parameters for effective intermodula­ tion rejection. Intermodulation products may result from various mixing processes in the mixer, but all these undesired responses are attributed to the(More)
This paper reviews the concept of spectrum efficiency and discusses the factors affecting the spectrum efficiency of communication systems. However, major effort is devoted to the evaluation of the spectrum efficiency of direct sequence systems and to investigate the possibility of operating such systems over some existing frequency bands already assigned(More)
This paper discusses the possible sources of narrowband interference and their effects on the operations of direct sequence systems. We analyze the effects of narrowband interference on the performance of the systems under perfect synchronization condition and compare the analytical results with those of experimental observations. Techniques for suppressing(More)
Reviews strategies of suppressing interference and noise under various circumstances in order to justify the applications of spread spectrum systems. The basic principles of spread spectrum systems are discussed to demonstrate their capabilities of suppressing noise and interference, and other significant advantages of using such systems. The paper is also(More)
  • C. P. Tou
  • Digest on Antennas and Propagation Society…
  • 1989
The author introduces an adaptive modeling scheme for characterizing radio propagation channels and shows its application to problems caused by adverse propagation conditions. The proposed scheme is based on a similar adaptive modeling scheme for an unknown system using an LMS (least-mean-square) adaptive filter. An identical and synchronized signal must be(More)
  • C. P. Tou
  • Conference Proceeding IEEE Pacific Rim Conference…
  • 1989
An inverse adaptive modeling scheme for characterizing and equalizing satellite communication channels is presented. Major atmospheric effects on satellite signals and the difference between propagation and channel models are discussed. The concept of inverse adaptive modeling of an unknown system is presented to help explain the proposed modeling of(More)
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