Martin Howard Meyers

Optimal space-time scheduling for block fading channels with partial power feedbacks

The multi-user multiple-input-multiple-output (MIMO) space-time scheduling problem is the prime focus of the paper. Using multiple transmit (nT) and receive antennas (nR), it is well known that the link-level throughput will be increased linearly with respect to min[nT, nR] without increasing the bandwidth and power budget. However, optimizing the link-level performance of the MIMO system does not always imply achieving scheduling-level optimization. Therefore, the design optimization across the link layer and the scheduling layer is very important to fully exploit the temporal and spatial dimensions of the communication channel. In this paper, we address the design of the optimal space-time scheduler for the multi-user MIMO system based on an information theoretical approach. Since full knowledge of channel matrix at the transmitter requires a feedback channel capacity not scalable with respect to nT (number of transmit antennas at mobiles) and nR (number of receive antennas at base station), we will assume two partial feedback models.

Neural network-based voice quality measurement technique

In this paper, we present a novel neural network-based predictor for subjective quality of speech signals. The output from the predictor is the estimated subjective quality or mean opinion score (MOS). The internal representation of signals is calculated using a model for the human auditory system. The perceptual distance between the reference speech and the speech sample under test is used as input to the neural network, which is then trained to model the underlying relationship between this perceptual distance and its subjective quality (MOS). Accurate MOS predictions have been demonstrated for speech coders used in common wireless applications including AMPS, TDMA, GSM and CDMA. MOS values predicted by the neural network MOS machine (NN-MM) were validated for clean and corrupted channels as well as for background noise conditions. Prediction accuracy is an order of magnitude better than anything previously reported, with worst case errors on the order of 0.05 MOS point.

Performance of Lucent cdma2000 3G1X packet data experimental system

The cdma2000 3G1X system is one of the first members of the IMT-2000 family of third generation wireless systems to reach field trial status. The cdma2000 3G1X system will provide service providers with increased voice capacity for their networks as well as high-speed packet data services. An experimental system based on the cdma2000 3G1X standard has been successfully developed by Lucent Technologies. In this paper, we will report the packet data performance results obtained from both lab and field tests of the experimental system. The measurements of packet data performance concentrate on high-speed packet data throughput. Peak user data rates of 144 kbps are demonstrated and the measured throughput performance is compared with simulation results. Good agreement was found between predicted/simulated performance and the empirically observed behavior of the trial system.

Iterative detection for BLAST systems with an arbitrary number of receive antennas

Turbo-coded Vertical Bell Labs Layered Space-Time Architecture (V-BLAST) is a multiple-antenna system employing turbo codes and bit-interleaving to offer flexible rates and high-speed wireless data communications. The conventional detection techniques based on one-shot demodulation and decoding algorithms may suffer poor performance or simply fail when there are fewer receive antennas than transmit antennas or when the multiple-input-multiple-output (MIMO) channel exhibits strong spatial correlations. We propose employing an iterative demodulation and decoding algorithm that solves these problems and greatly extends the applicability of V-BLAST. Simulations demonstrate that iterative V-BLAST offers the best-known performance in a wide range of settings. Through complexity analysis, we show that (a) the incremental computing complexity is small, although additional memory is required, compared with the conventional one-shot maximum likelihood (ML) decoding method, and (b) an iterative algorithm employing generalized sphere decoding will be a low-complexity, memory-reduced, and high-performance solution. We also give extensions to the technique beyond simple V-BLAST. In addition, when feedback from the receiver to the transmitter is available, we illustrate how to adapt code rate, modulation, and the power distribution to take advantage of the channel knowledge. With a combination of the “best in class” receiver performance and the ability to decode V-BLAST transmissions with fewer receive antennas than transmit antennas, the techniques described here can be viewed as key “technology enablers” for BLAST/MIMO in next-generation systems.

Dynamic effects of power control on third-generation system capacity

Dynamic simulations with mobility in multi-pilot environments have been developed to assess the capacity advantages of third-generation (3G) 800 Hz forward link power control. We show that the key component of 3G power control is not the higher inner loop power control speed but the creation of a bit energy-to-noise density (Eb/Nt) setpoint-based power control loop that provides a target for the inner loop power control. This allows fast tracking of the dynamic geometry variations, including the large instantaneous changes due to handoff as well as other-cell interference, and provides significant additional capacity gains even at vehicular speeds where Rayleigh fading cannot be tracked. Three different simulation tools, at the chip, symbol, and power control group (PCG) level, all confirm the excellent performance of 3G power control, as well as the existence of additional forward link capacity with 3G power control. Although our specific examples are based on CDMA2000∗, similar conclusions apply to the forward link power control algorithms used in wideband code division multiple access (W-CDMA).