Hybrid Transmission Scheme Research Articles

Adaptive Hybrid Transmission Mechanism for On-Demand Mobile IPTV Over WiMAX

In this paper, we propose an Adaptive Hybrid Transmission (AHT) scheme for on-demand mobile IPTV service over broadband wireless access network (i.e. mobile WiMAX, 802.16e). Proposed algorithm utilizes hybrid mechanism which combines multi-channel multicasting and unicast scheme to enhance not only service blocking probability but also reduce overall bandwidth consumption of the wireless system which has very limited resources compared to wired networks. An adaptive resource allocation algorithm is also proposed, and is shown to achieve minimum blocking probability. In order to evaluate the performance, we compare proposed algorithm against traditional unicast and multicast schemes.

Hybrid zero-forcing beamforming/orthogonal beamforming with user selection for MIMO broadcast channels

This letter proposes a hybrid transmission scheme by combining zero-forcing beamforming (ZFBF) and orthogonal beamforming (OBF) for the multiple-input multiple-output broadcast channel. This method first utilizes ZFBF for only a part of the scheduled users with approximately orthogonal channels. By further constructing orthogonal beamformers in the null space of the ZFBF user channels, it then employs OBF for the rest of users to fully exploit the spatial dimension. Theoretical analysis, as well as simulation results, verify that our scheme outperforms the conventional ZFBF scheme and OBF scheme with user selection.

An Efficient Transmission Scheme for Minimizing User Waiting Time in Video-On-Demand Systems

To take the advantage of skewed popularity of videos, efficient video-on-demand (VOD) systems are more likely to deliver the most popular videos through periodic broadcasting and the least popular videos through on-demand multicasting. While videos delivered through multicasting usually share a pool of server channels, broadcasting of each video demands one or more channels dedicated to it. Given a total number of available channels, distributing them for individual broadcasting and the multicasting pool to achieve the optimal average user waiting time is a nonlinear optimization problem. This letter addresses this problem by proposing a hybrid transmission scheme, which uses dynamic programming approach to ensure optimally for any given number of channels and request arrival rate

Bandwidth allocation in B-ISDN

Abstract A channel group is a set of channels time-division-multiplexed onto the same transmission link, and a link group is a set of transmission links interconnecting two network nodes. This paper investigates a number of ways in which the transmission bandwidth of a link group can be shared by various telecommunication services based on the Asynchronous Transfer Mode (ATM). The prevailing unichannel transmission scheme requires cells belonging to the same call to follow the same channel along each section of the chosen route. Such a scheme is inefficient because the transmission bandwidth of a link group cannot be completely shared by all the calls supported by that link group at the cell level. Based on a bursty traffic analysis and other considerations, this paper concludes in favour of a multichannel and a hybrid transmission scheme. The former allows cells belonging to the same call to be transported over different channels of the chosen channel groups and the latter supports both unichannel and multichannel transmission. As call admission control is an important part of ATM networks, this paper also discusses how an admission control algorithm proposed for the prevailing unichannel transmission scheme can be adapted for the other two transmission schemes.

Acoustic Doppler measurement of internal waves: New techniques and observations

In the mid 1970s, acoustic Doppler techniques were first applied to the internal wave measurement problem. Since then, both pulse‐to‐pulse coherent (short‐range) and incoherent (long‐range) sonars have been developed. Recently, a 161‐kHz device that can operate in either mode, as well as a hybrid coded mode, has been created. In the hybrid mode, broadband pulses are transmitted. Doppler shift is estimated from the phase progression within individual returns. Incoherent averaging from pulse to pulse further improves the precision of the velocity estimate. Velocity error variance is reduced by a factor of 10 relative to uncoded pulses. The hybrid sonar was first operated in the Arctic, north of Svalbard, in conjunction with the 1989 ONR experiment, Cearex. While the under ice boundary layer was examined using a fully coherent operating mode, the large‐scale internal wave field was sampled to depths of 500 m using the hybrid transmission scheme. Strong baroclinic subinertial motions were seen at diurnal tidal frequency. These occasionally became unstable, producing borelike events with amplitudes in excess of 50 m. Toward the end of the experiment, an eddy drifted under the ice camp. The precision of the sonar was sufficient to resolve a “crown” of internal waves trapped to the dome of the eddy.

The Hybrid Transmission Scheme of a 900 MHz Digital Land Mobile Radio System

The hybrid transmission scheme of MATS-D uses different transmission principles on both directions of a duplex radio link. Based on the analysis of the radio transmission characteristics and of multiple-access methods, the two directions are designed independently from each other. In the downlink (from base station to mobile station) a combination of TDM and CDM is applied. In the uplink (from mobile station to base station) single channel per carrier FDMA with generalized tamed frequency modulation (GTFM) is employed. Both transmission schemes have been implemented. Measurements with fading generators as well as field tests were carried out. Experimental results are presented for the performance of both transmission schemes, expressed in terms of the bit error rate versus the signal-to-noise ratio and the signal-to-interference ratio.