In this paper, we propose a multiple access technique using a simple interference canceller for common code transmission. In the proposed system, we adopt a common code for a receiver oriented system. All the transmit...
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In this paper, we propose a multiple access technique using a simple interference canceller for common code transmission. In the proposed system, we adopt a common code for a receiver oriented system. All the transmitters utilize the same pseudo noise (PN) code to communicate with a receiver. Here the receiver structure becomes very simple with only one matched filter (MF). The proposed system has two very important merits. One is to avoid packet collisions by means of an interference cancellation method based on a common code chip shift transmission technique. That is, in order to avoid interference, which occurs because all the received signals have the same PN code, the same data with different timing are transmitted in two channels. In this study, we define and evaluate three types of packet collision which can be reduced by the canceller. The other merit is to reduce the system degradation due to the correlation side-lobes by means of a side-lobe canceller. In spread spectrum (SS) communication systems with PN codes like M-sequences, the correlation side-lobes appear at the detector in the case of the polarity data changing from +/-1 to -/+ 1. The side-lobes degrade the system quality. Therefore in this system a interference canceller operates to cancel the correlation side-lobes and attempts to reduce the system degradation. Finally, by our cancellation method it becomes possible to realize a simple multiple access using only one PN code under the condition of a receiver oriented system without a base station.
An important step towards effective software maintenance is to locate the code relevant to a particular feature. In this paper Mie report a study applying an execution slice-based technique to a reliability and perfor...
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ISBN:
(纸本)0769501222
An important step towards effective software maintenance is to locate the code relevant to a particular feature. In this paper Mie report a study applying an execution slice-based technique to a reliability and performance evaluator to identify the code which is unique to a feature, or is common to a group of features. Supported by tools called ATAC and chi Vue, the program features in the source code can be tracked down to files, functions, lines of code, decisions, and then c- or p-uses. Our study suggests that the technique can provide software programmers and maintainers with a good starting point for quick program understanding.
A possible way to integrate variable bit rate (VBR) services into conventional synchronous direct-sequence, code-division multiple access (DS/CDMA) systems is to assign a number of unique codes (multiple codes) to a g...
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A possible way to integrate variable bit rate (VBR) services into conventional synchronous direct-sequence, code-division multiple access (DS/CDMA) systems is to assign a number of unique codes (multiple codes) to a given service which can be used whenever its bit-rate exceeds the available channel bandwidth. This has the disadvantage that the number of available spreading codes is reduced. Instead, an asynchronous system can be applied by assigning a common code to all users. However, occasional bit-synchronism in an asynchronous system will cause an unacceptable bit error rate (BER). In our proposed hybrid-code DS/CDMA system common codes are used only for mobile stations (MS) with VER services if the instantaneous required bandwidth exceeds the available channel bandwidth. A self-control mechanism is applied to guarantee bit-asynchronism between the bits spread by the same code. Simulation-based mobile network traffic models for integrated VER video, interactive PCM coded speech and bulk transfer of data have been examined to obtain the BER performance of the system. Various channel models have been applied to macrocellular mobile networks. (C) 1998 Elsevier Science B.V. All rights reserved.
This paper presents a random spreading code assignment scheme for enhancing channel efficiency in centralized DS-SS packet radio networks which employ a multiple-capture receiver for each code channel. Compared to the...
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This paper presents a random spreading code assignment scheme for enhancing channel efficiency in centralized DS-SS packet radio networks which employ a multiple-capture receiver for each code channel. Compared to the common code case, this approach requires modest increase in receiver complexity, but the number of distinct spreading codes being used is considerably less than the number of radios in the network. A general theoretical framework for evaluation of collision-free packet performance in each code channel is described, in which the possibility of collision-free transmission is conservatively estimated using a combinatorial method, and the effects of asynchronous multiple-access interference are characterized in terms of the primary and secondary user interferences. At the link level, the capture and throughput performances are evaluated for a proper set of codes, and compared with the results from the common code scheme. It is shown that the use of a random assignment scheme with more than one code results in a higher performance gain, and most of this gain can be achieved with just two distinct spreading codes.
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