Implementation Issues for Multiuser DS-CDMA Receivers

Multiuser detection for CDMA has been an area ofconsiderable interest in the research community due tothe significant performance gains that can be obtainedthrough the use of sophisticated receivers that exploit the intrinsic structure of themultiple access interference. Recent advances inhigh-speed digital and mixed signal technologies arespawning practical implementations of real-timesuboptimal multiuser receivers. This paper focuses onimplementation issues for advanced DS-CDMA structuresbased on multiuser detection principles, reviewingseveral of the most interesting multiuser detectionschemes from a practical implementation point of view.The computational complexity of these algorithms, a keycriterion in the selection of a joint detection schemefor practical implementation, is evaluated in terms of the time complexity per bit (TCB)decision. Various approaches for multiuser parameterestimation are also reported in this paper, since ingeneral, accurate estimation of the received amplitudes, user delays, and carrier phases is central tomultiuser detection. Subsequently, two low-complexityasynchronous real-time multiuser detectors developed atVirginia Tech are presented along with experimental measurements. Finally, other importantdevelopments leading to practical implementation ofmultiuser receivers are described.     

Assay on FAQ''s on Total Lab Automation

The purpose of the introduction of an automated laboratory system in one format or another is reducing the costs of the laboratory by cutting staff. Also speeding up the performance often is a goal. At the same time it is planned to increase the quality of the work done by using automated labelling and reading of documents. The use of vacuum tubes and the handling of these by the apparatus are raising the safety of the labwork.

In this paper many aspects of the daily routines when using a TLA system are discussed. The aspects are collected during the discussions before and after the implementation of the Roche CLAS system in our laboratory. Some consequences were foreseen, and others came unexpectedly. But still the subjects form a point of discussion around the TLA systems. The most important message to be picked up is that one really has to consider all possible problems that could arise from the implementation of TLA.     

Design,Analysis, and DSP-Based Implementation of a Code-Phase-Shift Keying Receiver for Wireless Local Area Network Applications

This paper introduces code-phase-shift keying(CPSK), a novel M-ary direct-sequence spread-spectrum(DS-SS) signaling technique that is particularlysuitable for wireless local area network applications. In CPSK, each of the M signaling waveforms isobtained by a different code phase shift of a singlepseudonoise (PN) sequence. It increases the data ratewithout sacrificing spreading gain, and is more power efficient over additive white Gaussian noise(AWGN) than conventional DS-SS signaling methods. Thedesign, analysis, and implementation of a DSP-basedreceiver is presented to demonstrate the practicality of the signaling method. In our design, thereceived IF signal is downconverted into two quadraturebaseband components that are filtered and A/D convertedat 1 MHz into 8-bit samples for processing by three TMS320C40 processors. The tracking andacquisition schemes are adapted from conventional DS-SSreceivers, while the carrier-wave synchronizationproblem is solved by a novel technique calledphase-invariant reception. The design is tested in AWGN andsingle-tone interference environments. Implementationlosses and acquisition performances arequantified.