It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel adaptive techniques have been deemed impractical in the past because of the problem of obtaining channel knowledge at the transmitter. The transmitter in many systems (such as those using frequency division duplexing) can not leverage techniques such as training to obtain channel state information. Over the last few years, research has repeatedly shown that allowing the receiver to send a small number of information bits about the channel conditions to the transmitter can allow near optimal channel adaptation. These practical systems, which are commonly referred to as limited or finite-rate feedback systems, supply benefits nearly identical to unrealizable perfect transmitter channel knowledge systems when they are judiciously designed. In this tutorial, we provide a broad look at the field of limited feedback wireless communications. We review work in systems using various combinations of single antenna, multiple antenna, narrowband, broadband, single-user, and multiuser technology. We also provide a synopsis of the role of limited feedback in the standardization of next generation wireless systems.

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An overview of limited feedback in wireless communication systems

Orthogonal frequency-division multiplexing (OFDM) effectively mitigates intersymbol interference (ISI) caused by the delay spread of wireless channels. Therefore, it has been used in many wireless systems and adopted by various standards. In this paper, we present a comprehensive survey on OFDM for wireless communications. We address basic OFDM and related modulations, as well as techniques to improve the performance of OFDM for wireless communications, including channel estimation and signal detection, time- and frequency-offset estimation and correction, peak-to-average power ratio reduction, and multiple-input-multiple-output (MIMO) techniques. We also describe the applications of OFDM in current systems and standards.

OFDM and Its Wireless Applications: A Survey

Space-Time Block Coding for Wireless Communications

A vehicle control system which can ensure high reliability, real-time processing, and expandability with a simplified ECU configuration and a low cost by backing up an error through coordination in the entire system without increasing a degree of redundancy of individual controllers beyond the least necessary level. The vehicle control system comprises a sensor controller for taking in sensor signals indicating a status variable of a vehicle and an operation amount applied from a driver, a command controller for generating a control target value based on the sensor signals taken in by the sensor controller, and an actuator controller for receiving the control target value from the command controller and operating an actuator to control the vehicle, those three controller being interconnected via a network. The actuator controller includes a control target value generating unit for generating a control target value based on the sensor signals taken in by the sensor controller and received by the actuator controller via the network when the control target value generated by the command controller is abnormal, and controls the actuator in accordance with the control target value generated by the control target value generating unit.

Vehicle Control System

Future smart grid systems will intelligently monitor and control energy flows to improve the efficiency and reliability of power delivery. This monitoring and control requires low-delay, highly reliable communication between customers, local utilities, and regional utilities. A vital part of future smart grids is the two way communication links between smart meters at the customer sites and a (decentralized) command and control center operated by the local utility. To enable these two-way communication links, narrowband power line communication (PLC) systems operating in the 3-500 kHz band are attractive because they can be deployed over existing outdoor power lines. Power lines, however, have traditionally been designed for one-directional power delivery and remain hostile environments for communication signal propagation. In this article, we review signal processing approaches to model channel impairments and impulsive noise and mitigate their effects in narrowband PLC systems. We examine ways to improve the communication performance based on current and emerging standards.

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Local Utility Power Line Communications in the 3–500 kHz Band: Channel Impairments, Noise, and Standards

A Smart Grid intelligently monitors and controls energy flows in an electric grid. Having up-to-date distributed readings of grid conditions helps utilities efficiently scale generation up or down to meet demand. Narrowband powerline communication (PLC) systems can provide these up-to-date readings from subscribers to the local utility over existing power lines. A key challenge in PLC systems is overcoming additive non-Gaussian noise. In this paper, we propose to use a cyclostationary model for the dominant component of additive non-Gaussian noise. The key contributions are (1) fitting measured data from outdoor narrowband PLC system field trials to a cyclostationary model, and (2) developing a cyclostationary noise generation model that fits measured data. We found that the period in the cyclostationary model matched half of the period of the main powerline frequency, which is consistent with previous work in indoor PLC additive noise modeling.

Cyclostationary noise modeling in narrowband powerline communication for Smart Grid applications

Transmitter precoding for multiple-input-multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) is an effective way of leveraging the diversity gains afforded by a multiple-transmit multiple-receive antenna system in a frequency selective environment. In the limited feedback scenario, optimal precoder representation for narrowband MIMO systems using moderately sized codebooks designed on the Grassmann manifold has been shown to perform remarkably well. In MIMO-OFDM systems, precoder matrices have to be designed for all subcarriers and the amount of feedback can get prohibitively large. This is especially true for next generation wireless local area networks and wireless metropolitan area networks which have a large number of subcarriers. In this paper, we present techniques to reduce this feedback requirement and the performance of these algorithms is numerically shown to provide improvement over existing schemes

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Reduced Feedback MIMO-OFDM Precoding and Antenna Selection

A coordinated multipoint transmitter is for use with a multiple antenna super-cell and includes primary and secondary base stations jointly connected via an X2 interface link, wherein the primary base station provides a transmission directive corresponding to an X2 interface protocol over the X2 interface link to the secondary base station for a joint transmission from the primary and secondary base stations.

Network multiple antenna transmission employing an x2 interface

A system and method for controlling a navigation receiver is disclosed. A current position is determined using the navigation receiver and then the navigation receiver is placed in a power-save mode. The current position is updated using information from position sensors. The navigation receiver is temporarily placed in an active mode at intervals to determine an intermediate position. The current position is also updated using the intermediate position. The navigation receiver may be a GNSS receiver, a cellular receiver, a WiFi receiver, or another position-fixing device. The position sensors may be accelerometers, gyroscopes, electronic compasses or mapping data. A power-save controller controls the power-save or active mode of the navigation receiver. A sensor conditioning circuit pre-processes the data from the position sensors before providing the data to the power-save controller. During the power-save mode, an RF subsystem and/or a baseband subsystem of the navigation receiver may be turned off.

Performance of a Navigation Receiver Operating in a Power-Save Mode with the Aid of Sensors

Systems and methods for building, transmitting, and receiving frame structures in power line communications (PLC) are described Various techniques described herein provide a preamble design using one or more symbols based on a chirp signal that yields a low peak-to-average power ratio (PAPR) According to some techniques, the preamble may be constructed with one or more different types and/or number of symbols configured to identify a PLC domain operating in close physical proximity to another PLC domain According to other techniques, one or more preamble symbols may be interspersed within a header portion of a PLC frame to facilitate estimation of a frame boundary and/or sampling frequency offset, for example, in the presence of impulsive noise According to yet other techniques, a PLC detector may be capable of receiving and decoding two or more types of PLC frames (eg, using different PLC standards)

Tarkesh Pande

Papers

Cyclostationary noise modeling in narrowband powerline communication for Smart Grid applications

Reduced Feedback MIMO-OFDM Precoding and Antenna Selection

Network multiple antenna transmission employing an x2 interface

Performance of a Navigation Receiver Operating in a Power-Save Mode with the Aid of Sensors

Building, Transmitting, and Receiving Frame Structures in Power Line Communications