Simeon Furrer

Multiple-Antenna Signaling Over Fading Channels With Estimated Channel State Information: Capacity Analysis

Multiple-antenna concepts for wireless communication systems promise high spectral efficiencies and improved error rate performance by proper exploitation of the randomness in multipath propagation. In this paper, we investigate the impact of channel uncertainty caused by channel estimation errors on the capacity of Rayleigh and Ricean block-fading channels. We consider a training-based multiple-antenna system that reserves a portion of time to sound the channel. The training symbols are used to estimate the channel state information (CSI) at the receiver by means of an arbitrary linear estimation filter. No CSI is assumed at the transmitter. Our analysis is based on an equivalent system model for training-based multiple-antenna systems which specifies the channel by the estimated (and hence, known) channel coefficients and an uncorrelated, data-dependent, multiplicative noise. This model includes the special cases of perfect CSI and no CSI. We present new upper and lower bounds on the maximum instantaneous mutual information to compute ergodic and outage capacities, and extend previous results to arbitrary (and possibly mismatched) linear channel estimators and to correlated Ricean fading. Several numerical results for single- and multiple-antenna systems with estimated CSI are included as illustration.

Simple ergodic and outage capacity expressions for correlated diversity ricean fading channels

Multiple-antenna systems have been shown to achieve very high spectral efficiencies. In this paper, we derive simple single-integral expressions for the ergodic and outage capacity of a diversity system in correlated Ricean fading channels, where the channel coefficients are assumed to be known to the receiver only. For illustration purpose, we present numerical results showing the effect of channel correlation, Ricean components, angular spread and multipath components in an orthogonal frequency-division multiplexing (OFDM) system

The IBM wireless sensor networking testbed

This paper describes the wireless sensor networking testbed built at the IBM Zurich Research Laboratory. The testbed has been used to address a wealth of exciting research challenges. Performance evaluations have been carried out with short-range wireless communication technologies, which are highly relevant for sensor networking such as IEEE 802.15.4/ZigBee networks, Bluetooth WPANs, and IEEE 802.11b WLANs. With the testbed, the merits of wireless mesh networking for range extension and reliability enhancement have been explored. New light-weight messaging protocols for communication between sensors and an application server have been tested which allow to bring messaging-oriented middleware down to very low-end sensors and actuators. In addition, the testbed has been used to develop sensor applications for remote metering and location-sensing

An opportunistic energy-efficient medium access scheme for wireless sensor networks

This paper introduces an opportunistic medium-access control (MAC) scheme for controlling the uplink message transfer from sensor nodes to a central controller in wireless sensor networks (WSN). By equipping the controller with multiple antennas to communicate with single-antenna sensors, we propose a scheme that benefits from diversity reception at the controller and leads to a considerable reduction of battery energy consumption in sensor nodes. The performance of the scheme is illustrated using a Rayleigh fading channel model.

Bounds on the ergodic capacity of training-based multiple-antenna systems

Multiple-antenna concepts for wireless communication systems promise high spectral efficiencies by proper exploitation of the randomness in multipath propagation. In this paper, we investigate the impact of channel uncertainty caused by channel estimation errors on the capacity of Rayleigh and Ricean block-fading channels. We consider a training-based multiple-antenna system that reserves a portion of time to sound the channel. The training symbols are used to estimate the channel state information (CSI) at the receiver by means of an arbitrary linear estimation filter. No CSI is assumed at the transmitter. We present an equivalent system model for training-based multiple-antenna systems, which specifies the channel by the estimated (and hence, known) channel coefficients and an uncorrelated, data-dependent noise. Based on this equivalent model, which includes the special cases of perfect CSI and no CSI, we derive upper and lower bounds on the maximum instantaneous mutual information and the ergodic capacity, and extend previous results to arbitrary (and possibly mismatched) linear channel estimators and to correlated Ricean fading

Analytical Expressions for the Readback Signal of Timing-Based Servo Schemes

Timing-based servo (TBS) is a powerful technology widely used in state-of-the-art tape systems for track following. To optimize TBS systems for future operating points with aggressive track-density scaling, an accurate model is needed to characterize how the servo read head geometry, servo format parameters, and magnetic media properties affect the readback signal. In this paper, we derive new analytical closed-form expressions for the readback signal of shielded magneto-resistive (MR) heads scanning over the magnetic transitions of TBS patterns. The expressions, derived via the reciprocity principle, are applicable to arctan-shaped transitions between arbitrarily magnetized areas of a thin-film magnetic medium and are given in the displacement and wavevector domain. We apply these new expressions to analyze isolated transitions as well as multi-transition TBS patterns on longitudinal, non-oriented or perpendicular media. Comparison between experimentally captured servo readback signals and the analytical expressions show an excellent match. By adding electronics and transition jitter noise, the readback signal expressions can be extended to a servo channel model suitable for TBS performance prediction by means of Monte Carlo simulations and/or bounds on the variance of the position-error signal.

Mean bit-error rates for OFDM transmission with robust channel estimation and space diversity reception

This paper investigates the performance of orthogonal frequency-division multiplexing (OFDM) systems applying linear minimum mean-square-error (LMMSE) based channel estimation for coherent detection. We analyze and discuss the robustness of the estimators mean-square error (MSE) performance under estimator-to-channel statistics mismatch and derive a closed form expression of the mean bit-error rate (BER) for coherent binary signaling. Different cases of single antenna and diversity reception over Rayleigh and Rician fading multipath channels are considered.

Flat-Profile Tape–Head Friction and Magnetic Spacing

The friction and magnetic spacing between magnetic tape and a recording head are measured as a function of the wrap angle at several tape speeds and tape tensions for two tape samples with different roughnesses. An increase in friction and a decrease in magnetic spacing are measured for: 1) increasing wrap angle; 2) decreasing tape speed; and 3) increasing tape tension. The relation between the magnetic spacing and friction is fixed when varying the tape tension or wrap angle. For the rougher tape sample, reducing the tape speed (and adjusting the tape tension and wrap angle accordingly) reduces the magnetic spacing without increasing the friction. Although the smoother tape experiences more friction for a fixed wrap angle and tape tension, a smaller magnetic spacing at a specified friction is measured for it than for the rougher tape.

Multiple-Antenna Signaling Over Fading Channels With Estimated Channel State Information: Performance Analysis

Multiple-antenna concepts for wireless communication systems promise high spectral efficiency and low error rates by proper exploitation of the randomness in multipath propagation. In this paper, we investigate the impact of channel uncertainty caused by channel estimation errors on the error rate performance. We consider a training-based multiple-antenna system that reserves a portion of time to sound the channel. Training symbols are used to estimate the channel by means of an arbitrary linear filter at the receiver. No channel state information (CSI) is assumed at the transmitter. We present a new framework to analyze training-based multiple-antenna systems by introducing an equivalent system model that specifies the channel by the estimated (and hence, known) channel coefficients and an uncorrelated, data-dependent, multiplicative noise. We derive the maximum-likelihood (ML) detector and highlight its behavior in the limiting cases of perfect CSI and no CSI, and its relation to several mismatched detectors. We deduce new exact expressions and Chernoff bounds of the pairwise error probability (PEP) used to assess word-error and bit-error rate bounds for ML and mismatched detection. Finally, we review the code design guidelines in terms of the deleterious effect of channel uncertainty for coherent and noncoherent signaling schemes, and present numerical results.

High-Performance Servo Channel for Nanometer Head Positioning and Longitudinal Position Symbol Detection in Tape Systems

In a tape system, the core of the reel-to-reel and track-following servomechanisms is the servo channel, which processes the servo signal generated by a servo reader reading a timing-based servo pattern. The servo channel estimates essential servo parameters, including tape velocity, head lateral position, and longitudinal tape position. The achievable precision of the various estimates determines how densely data can be placed on tape. In this paper, the architecture and the design of a high-performance synchronous servo channel (SSC) are presented. The channel performance is evaluated by means of analytical bounds on the estimation error, simulations, and experimental results, which demonstrate that the proposed servo channel is instrumental to achieve head positioning with nanometer accuracy and reliable detection of longitudinal position information in tape systems. Methods for the estimation of servo parameters with enhanced precision and of dynamic tape-to-head skew by dual SSCs operating on adjacent servo bands are also presented and their performance evaluated.