The frequency and spatial characteristics of nonlin-ear distortion from a MIMO-OFDM (multiple-input multiple-output orthogonal frequency-division multiplexing) basestation with memoryful nonlinear amplifiers (modeled by a generalized memory polynomial) is studied herein. We prove a theorem about a linear representation of the amplified signal from which the nonlinear distortion is obtained. Our measurement results demonstrate that the generalized memory polynomial can provide better accuracy of the nonlinear distortion than the memoryless and memory polynomial models. Furthermore, it is shown that in contrast to the memoryless amplifier, the amplifier with memory can distort the useful linear signal and introduce interference in a wider range of sub carriers. The derived theory is useful to predict how the nonlinear distortion will behave, to analyze the in-band and out-of-band radiation, and to schedule users in the frequency plane to minimize the effect of nonlinear distortion.

In this paper, multiple-input multiple-output (MIMO) layer shifting with cubic metric (CM) preserving precoder and downlink control signal sharing is proposed as a uplink transmission scheme for 3GPP Long Term Evolution (LTE). The design criteria for CM preserving precoder are presented and uplink precoder is designed accordingly. By sharing MCS (modulation and coding scheme) and/or HARQ (hybrid automatic repeat request) among codewords, downlink control signal sharing reduces the control signal overhead at the expense of performance degradation, which motivates this paper. The proposed MIMO layer shifting on a per SC-FDMA (single-carrier frequency division multiple access) symbol basis eliminates the discrepancy of channel quality among codewords, and thus improves the performance in the presence of MCS and/or HARQ sharing. Simulation results show that layer shifting is beneficial to both minimum mean square error (MMSE) and successive interference cancellation (SIC) receivers.

Recently a MIMO-HSPA testbed based on the commercial release '99 products has been within Ericsson in order to demonstrate and evaluate enhanced data rates in the downlink for the evolution of HSPA. The testbed employs two antennas at both the base and mobile stations (2 times 2 MIMO) and is able to adapt between single- and dual-stream data transmission. An extensive outdoor measurement campaign has been carried out using dual-polarized antennas at both ends of the link. With such set-up, it is demonstrated that 2 times 2 MIMO double the peak rate compared to conventional HSDPA in areas of the cell experiencing line-of-sight (LOS) conditions with large SNR. More generally, the cell-wide result demonstrate gains in the 90th percentile Layer-1 throughput of 102% and 36% compared to conventional HSPDA with single- and dual-antenna receivers, respectively. Significant gains in the average throughput are also demonstrated.

We present a novel structure to efficiently exploit channel state information at the transmitter (CSIT) of a multiple-input multiple-output system. At the heart of our transmission scheme lies a mixing matrix that constructively combines the coded symbols before a CSIT-dependent weighting matrix is applied. A method to design the mixing matrix is presented. When combined with turbo-coded modulation, our system performs very close to the capacity limits. With only a few bits per channel use to feedback CSIT, we can achieve a substantial portion of the possible gain with perfect CSIT.

So far, the assumption of no channel knowledge at the transmitter has generally been inherent in the design of space-time codes. This paper, on the other hand, assumes that quantized channel information obtained from a feedback link is available at the transmitter and investigates how such channel information can be incorporated into the design of unstructured space-time block codes. Efficient codes are found by means of a gradient search over a continuous alphabet. Simulation results for an uncorrelated Rayleigh fading scenario using two and four transmit antennas and one receive antenna show the benefits of the code designs.

This work considers how the presence of quantized channel information obtained from a feedback link may be utilized for determining a transmit weighting matrix that improves the performance of a predetermined orthogonal space-time block (OSTB) code. To reduce the effects of feedback delay, quantization errors and feedback channel bit errors, methods based on vector quantization for noisy channels are used in the design of the feedback link. The resulting transmission scheme and feedback link take the imperfect nature of the channel information into account while combining the benefits of conventional beamforming with those provided by OSTB coding.

We investigate the capacity of a system with multiple transmit and receive antennas, assuming that the transmitter and receiver both have access to (possibly defective) channel-state information. Two different special cases of a general system are studied in detail. Our main results are capacity expressions for these cases and a general conclusion that the encoder can be split into separate "space-time coding" and "direction weighting" or "beamforming," without capacity loss. We also present numerical results illustrating the dependence of capacity on the parameters of a quantization scheme providing channel-state information to the transmitter from the receiver. These results have high practical value since the assumptions behind them are closely related to the ones of the closed-loop mode in the UMTS/WCDMA standard.

Multiple transmit and receive antennas can be used in wireless systems to achieve high data rate communication. Efficient space-time codes have been developed that utilize a large portion of the available capacity. These codes are designed under the assumption that the transmitter has no knowledge about the channel. In this work, on the other hand, we consider the case when the transmitter has partial, but not perfect, knowledge about the channel and how to improve a predetermined code so that this fact is taken into account. A performance criterion is derived for a frequency-nonselective fading channel and then utilized to optimize a linear transformation of the predetermined code. The resulting optimization problem turns out to be convex and can thus be efficiently solved using standard methods. In addition, a particularly efficient solution method is developed for the special case of independently fading channel coefficients. The proposed transmission scheme combines the benefits of conventional beamforming with those given by orthogonal space-time block coding. Simulation results for a narrow-band system with multiple transmit antennas and one or more receive antennas demonstrate significant gains over conventional methods in a scenario with nonperfect channel knowledge.

Previously, space-time codes have been developed that achieve a large portion of the capacity available in communication systems equipped with multiple transmit and receive antennas. These codes are designed under the assumption that the transmitter has no knowledge about the channel. In this work, on the other hand, we consider how the presence of vector quantized channel information obtained from a feedback link may be utilized for improving the performance of a space-time code. The transmission scheme we propose takes the non-perfect nature of the channel information into account while combining the benefits of conventional beamforming with those given by orthogonal space-time block codes. Simulation results demonstrate significant gains over conventional methods and also robustness to feedback channel errors.