Communication channel

About: Communication channel is a research topic. Over the lifetime, 137411 publications have been published within this topic receiving 1715077 citations. The topic is also known as: communication channel & communications channel.

Logical channel prioritization procedure for generating multiple uplink transport blocks

Abstract: The invention relates to methods for scheduling of uplink transmission and generating transport blocks according to multiple received uplink assignments. Furthermore, the invention is also related to the implementation of these methods in hardware and software. To propose strategies for generating plural transport blocks within a given time constraint, the invention introduces prioritization of the uplink assignments, so that multiple uplink assignments can be ranked in the mobile terminal in a priority order. The prioritization of the uplink assignments is used to determine the order in which the individual transport blocks corresponding to the uplink assignments are filled, respectively how the data of different logical channels is multiplexed to the transport blocks for transmission in the uplink. Another aspect of the invention is to suggest joint logical channel procedures that operate on virtual transport blocks accumulated from the received uplink assignments. One or more such joint logical channel procedure can be performed in parallel.

An efficient resource-allocation scheme for spatial multiuser access in MIMO/OFDM systems

Abstract: Fast adaptive transmission has been recently identified as a key technology for exploiting potential system diversity and improving power-spectral efficiency in wireless communication systems. An adaptive resource-allocation approach, which jointly adapts subcarrier allocation, power distribution, and bit distribution according to instantaneous channel conditions, is proposed for multiuser multiple-input multiple-output (MIMO)/orthogonal frequency-division multiplexing systems. The resultant scheme is able to: 1) optimize the power efficiency; 2) guarantee each user's quality of service requirements, including bit-error rate and data rate; 3) ensure fairness to all the active users; and 4) be applied to systems with various types of multiuser-detection schemes at the receiver. For practical implementation, a reduced-complexity allocation algorithm is developed. This algorithm decouples the complex multiuser joint resource-allocation problem into simple single-user optimization problems by controlling the subcarrier sharing according to the users' spatial separability. Numerical results show that significant power and diversity gains are achievable, compared with nonadaptive systems. It is also demonstrated that the MIMO system is able to multiplex several users without sacrificing antenna diversity by using the proposed algorithm.

On the transport and modification of Antarctic Bottom Water in the Vema Channel

Abstract: The Verna Channel is a deep passage across the Rio Grande Rise in the South Atlantic through which Antarctic Bottom _Water (AABW) must flow · on its way northward from the Argentine Basin to the Brazil Basin and eventuafly into the North Atlantic. Both dynamic computation and direct current measurement based on recently acquired data indicate that the volume transport of AABW is about 4 X 10° m/sec northward with a standard deviation of about 1.2 X 10° m/sec. There are no known_·exits for AABW below 1 •c out of the Brazil Basin and it is estimated by heat flux balance that if AABW leaves this basin across isopycnals, a diffusion rate of 3-4 cm/sec so directed is required. There is a sharp water mass transition between the two basins across the Rio Grande Rise with J\\ABW in . the Argentine Basin being distinctively fresher and_ colder in the potential temperature range from 0.2 •c to 2.0°C at the. same density. Cold tongues of fresh. water · iidvected into the Verna Channel may be thoroughly ·mixed by lateral eddy diffusion at a rate estimated to be 4 X 10° cm/sec. This process demands a supply of Brazil Basin AABW. from the north consistent with an observed weak southward flow to the east of the much more intense northward jet. Isopycnals show a reversal in slope with·depth within the channel (but not outside) such that the coldest water is in the west at shallow AABW depths but in the. east near the bottom. East of the channel axis there are thick bottom boundary layers which are nearly homogeneous in the vertical but horizontally stratified. We suggest a dynamical, nonmixing, mechanism for producing these features. Dissolved silicate measurements reveal a filament of low concentration, presumably North Atlantic Deep Water, which is located over the channel axis at 2500 m depth. This is some 1000 m above the Rio Grande Rise and 2000 m above the Channel floor.

Enhancing VANET Performance by Joint Adaptation of Transmission Power and Contention Window Size

Abstract: In this paper, we present a new scheme for dynamic adaptation of transmission power and contention window (CW) size to enhance performance of information dissemination in Vehicular Ad-hoc Networks (VANETs). The proposed scheme incorporates the Enhanced Distributed Channel Access (EDCA) mechanism of 802.11e and uses a joint approach to adapt transmission power at the physical (PHY) layer and quality-of-service (QoS) parameters at the medium access control (MAC) layer. In our scheme, transmission power is adapted based on the estimated local vehicle density to change the transmission range dynamically, while the CW size is adapted according to the instantaneous collision rate to enable service differentiation. In the interest of promoting timely propagation of information, VANET advisories are prioritized according to their urgency and the EDCA mechanism is employed for their dissemination. The performance of the proposed joint adaptation scheme was evaluated using the ns-2 simulator with added EDCA support. Extensive simulations have demonstrated that our scheme features significantly better throughput and lower average end-to-end delay compared with a similar scheme with static parameters.

Communication method and apparatus using analog and digital hybrid beamforming

Abstract: A communication method and apparatus using analog and digital hybrid beamforming are provided. The method includes receiving a first message including a measurement and selection condition for hybrid beamforming from a Base Station (BS), measuring channels of a plurality of BS transmission beams, selecting at least one BS transmission beam based on channel measurements, transmitting report information about the selected at least one BS transmission beam to the BS, receiving from the BS a second message, estimating an effective channel matrix for the selected final BS transmission beam according to the measurement and report condition, determining feedback information for digital beamforming of the BS based on the effective channel matrix, transmitting the determined feedback information to the BS, and receiving a data burst from the BS according to a Multiple Input Multiple Output (MIMO) mode and/or a configuration scheduled based on the feedback information.