Delay-Differentiated Scheduling in a Fading Channel

This paper studies scheduling in a time-varying wireless channel where different users may have different delay-requirements. The scheduling problem is formulated as a dynamic programming problem, taking into account both user-specific delay penalties and the time-varying channel state. A scheduling rule similar to the exponential rule is derived, applying dynamic delay-penalized optimization. Threshold-based scheduling optimizes the throughput-delay trade-off in a single-user memoryless channel. Modifications of the optimal single-user scheduling rule to a multiuser channel are studied both in a time-correlated and in a memoryless environment. Numerical experiments suggest that a simplified threshold derived for a memoryless setting performs well in a time-correlated channel. The applicability of the scheduling model to a virtual fading channel with relay nodes is discussed.     

Square-matrix embeddable space-time block codes for complex signalconstellations

Space-time block codes for providing transmit diversity in wireless communication systems are considered. Based on the principles of linearity and unitarity, a complete classification of linear codes is given in the case when the symbol constellations are complex, and the code is based on a square matrix or restriction of such by deleting columns (antennas). Maximal rate delay optimal codes are constructed within this category. The maximal rates allowed by linearity and unitarity fall off exponentially with the number of transmit antennas     

Transmit Diversity in the WCDMA System

This document presents the transmit diversityconcept adopted for the FDD mode of the thirdgenerationWCDMA system in ETSI in 1998. The open-loop mode isbased on the space-time block code attaining full diversity order with two transmit antennas.Different feedback modes are specified. They all utilizeterminal measurements in controlling the transmitweighting in the transmit antennas. The concept is described in detail for two transmit antennas.It is shown that very limited feedback from the terminalto the base, as defined for the FDD mode, can increasedownlink performance significantly when compared to single-antenna transmission.     

Industrial embrace of smart antennas and MIMO

In this article we provide a practical standardization related viewpoint on beamforming and MIMO technologies. In particular, we address the status in different industry-driven standardization for a (3GPP and IEEE 802) and discuss the rationale for possible adoption or use of such technologies in current or future wireless systems. We draw attention to some practical system-level and implementation aspects that need to be resolved before a successful application of beamforming or MIMO in real systems.     

Design Criteria for Non-Orthogonal Space–Time Block Codes in Multipath Channels

We consider the problem of designing high rate space–time block codes in multipath fading channels. For this, both minimizing the effect of the self-interference induced by the code itself, and mitigating the inter-symbol-interference induced by the channel have to be addressed. We translate the problem into an equivalent problem of designing a constrained code in a single-path channel with more antennas, and argue that design criteria derived in single-path apply when optimizing this constrained code. Here we concentrate on an analytic measure pertinent to mutual information maximization and BER-performance optimization. The design program is successfully applied to rate one linear space–time transmissions from four transmit antennas. A family of discrete permutations of the transmitted sequences are considered. Performance is optimized within this family, and the results are seen to effect directly both mutual information and error performance.