Subcarrier Level Research Articles

The performance analysis of a multi-carrier CDMA system in mobile environment

In this paper, several detection schemes are studied for a multi-carrier code division multiple access (MC-CDMA) system in the downlink case. Both analytical methods and system simulations are used to examine the performance of those detection schemes. The inter-symbol interference (ISI) can be absorbed by guard intervals, so the data in each subcarrier can be well equalized in slowly fading environment in case of coherent detection. Since each individual subcarrier of an MC-CDMA system is flat fading, it is possible to apply differential modulation schemes with non-coherent reception at subcarrier level. In the ideal case, the non-coherent reception provides worse performance than the coherent reception. However, the performance gap between coherent and differential reception reduces with increasing channel estimation and equalization errors. In the extreme cases, in fast-fading environment, the performance of differential detection may even exceed that of a coherent receiver with practical channel estimation methods. This is proved by the simulation results when a simple coherent detection scheme and a differential phase detection scheme are compared. It is also shown in this paper that with a simple equalizer, an MC-CDMA system can provide good performance in multi-user and multipath fading environments. Copyright © 2004 AEI.

直接変調方式を用いた１０，０００ｃｈ‐ＷＤＭ／ＳＣＭシステムにおける光デバイスのアナログ特性の検討と光伝送系の設計

Recently several new WDM/SCM optical transmission systems have been developed, to enable a higher transmission capacity of access networks such as CATV. Analog transmission performance of optical amplifiers and optical filters is important for these systems. Yet, there have been few studies that addressed this issue. In this paper, the required performance of optical devices and a system design method are investigated. In our study, we focused on the technical issues essential for 10, 000-channel WDM/SCM (32 WDM×310 ch SCM) systems using cost-effective direct modulation schemes. First, the mechanisms of sub-carrier level variation and distortion generation caused by FM-AM conversion on optical filters were examined both theoretically and experimentally. The required bandwidth of optical filters suitable for these systems was calculated. We then estimated the optical distribution number depending on the optical signal power input into EDFAs. We found that a configuration using three cascaded EDFAs enables developing 10, 000-channel WDM/SCM systems with 8, 000 distributions.

A differential phase-shift keying multicarrier code division multiple access system with an equal gain combining receiver

Multicarrier code division multiple access (MC-CDMA) is a spread-spectrum technique which allows simple implementation of multiuser detection techniques. Combining this with differential phase-shift keying (DPSK) allows a low complexity receiver design which achieves the channel estimation implicitly. If only downlink communication is considered, performing the DPSK at a subcarrier level allows significant performance gains and employing a joint phase estimation approach for all users signals allows the implementation of an effective equal gain combining receiver. Theoretical predictions and simulations of the performance in additive white Gaussian noise are demonstrated. Comparison with similar systems is shown through simulations in a fast fading typical mobile channel.

Analysis of polarization diversity at digital TV indoor receivers

The reduction of signal fading by using polarization diversity at a digital terrestrial TV receiver is evaluated. Two different diversity techniques, one operating at carrier (TV channel) level and the other at subcarrier level, are compared. A measurement campaign has been carried out in three different indoor environments using two antennas with orthogonal linear polarizations at the receiver. The polarization diversity gain has been calculated when the maximum selection technique is used. As expected, the level crossing rate and the average fade duration are considerably reduced by the diversity system.

Multichannel Coherent Subcarrier Multiplexed Lightwave System using Minimum Shift Keying

A multichannel coherent subcarrier multiplexed lightwave system is proposed for broadband distribution of digital data. The system uses minimum shift keying at the microwave subcarrier level. The overall performance of the system is compared to that of a similar system which uses frequency shift keying. It is demonstrated that the use of minimum shift keying significantly improves the overall performance of the distribution system.

VHF/FM receiver with ARI/RDS secondary services simulation models

On the basis of two simulation models, the authors evaluate the analysis of VHF-FM ARI/RDS receiver performance with two secondary services: analog auto-radio-information (ARI) and digital radio data services (RDS). The first approach involves processing at the 57-kHz subcarrier level. The second approach uses baseband modeling. Both simulation models are used to prove the compatibility of both secondary services, simultaneously used with the main program broadcasting. The accuracies of modeling and computing times needed for the evaluation in both cases are compared, giving clear insight into the mutual influence of the two secondary services. >

Compatibility of Video and Data Signals on the Same Satellite Television Channel

Satellite television systems may employ subcarriers for additional transmission of data via the same channel thus utilizing satellite transponders more efficiently. Data-rate and bit-error-rate of such systems are ultimately limited by maximal-permissible subcarrier levels which would not degrade the picture quality significantly.

Television Sound Subcarrier Transmission in Space Communication

In a nonideal transmission enviromnent, the transmission of video sound in the form of an FM subcarrier above the video baseband causes interactions between video and sound subcarrier which result in signal distortion. The degree of distortion depends on the type of channel impairments and the selection of transmission parameters. While the fidelity of the video signal can be preserved by mainly limiting the subcarrier level, the quality of the audio channel can be optimized by choosing the right subcarrier frequency. It can be shown that for a given video-carrier-to-noise ratio, subcarrier power below video signal power, and for given system impairments, there exists an optimum subcarrier location which provides a maxinum audio-signal-to-noise ratio.

Measurement of Nonlinear Distortions in Color Television Systems

NTSC color television tests for differential phase and gain in transmission facilities have shown the need for better measurement techniques. Two problems to be solved are the need to readjust the hue control between TV channels and distortion related to changes in average picture level. Dynamic gain may occur in the chrominance signal, the whole signal, or in the luminance and sync signals only. Dynamic phase affects the chrominance signal only. Present differential phase measurements are made with subcarrier levels smaller than the burst signal or chrominance signals of saturated parts of the picture. By adding a variable-amplitude subcarrier signal of constant phase to the variable luminance lines, we can probe the entire range of luminance signal values to detect the presence of distortions sensitive to chrominance amplitude.