Reconsidering Linear Transmit Signal Processing in 1-Bit Quantized Multi-User MISO Systems

In this contribution, we investigate a coarsely quantized Multi-User (MU)-Multiple Input Single Output (MISO) downlink communication system, where we assume 1-Bit Digital-to-Analog Converters (DACs) at the Base Station (BS) antennas. First, we analyze the achievable sum rate lower-bound using the Bussgang decomposition. In the presence of the non-linear quanization, our analysis indicates the potential merit of reconsidering traditional signal processing techniques in coarsely quantized systems, i.e., reconsidering transmit covariance matrices whose rank is equal to the rank of the channel. Furthermore, in the second part of this paper, we propose a linear precoder design which achieves the predicted increase in performance compared with a state of the art linear precoder design. Moreover, our linear signal processing algorithm allows for higher-order modulation schemes to be employed

On OSTBC Codes for LTE-A Systems-Design and Performance Evaluation

Long Term Evolution-Advanced (LTE-A) is a Fourth Generation (4G) standard of wireless communications that introduces high data rate, high performance, and low delay. These features of LTE-A resulted from the new techniques developed for wireless communications such as Multiple-Input Multiple-Output (MIMO) technique. At the heart of this technique is the Space Time Codes, which were developed by the researchers in recent decades to achieve the mentioned features. The designs of OSTBC codes for MIMO systems having any number of transmit antennas and any number of receive antennas have attracted the attention of many researchers. Based on the theory of real and complex orthogonal designs, this paper deals with the design of real and complex OSTBC codes to be used with real signal set constellation such PAM and complex signal constellation such as PSK and QAM. Real and complex OSTBC codes for MIMO systems with two, three, four, five, six, seven and eight transmit antennas and any number of receive antennas, are presented. Simple linear processing ML decoders are derived and presented. The used channel is Rayleigh fading channel MIMO and assumed to behave in a “quasi-static” fashion. Finally, the performances of OSTBC schemes were evaluated and compared in terms of the Bit Error Rate (BER) and Signal to Noise Ratio (SNR). The environment of simulation is MATLAB which is a powerful tool for mathematical calculation and system simulation. The methods of modulations chosen are QPSK, 16QAM, 64QAM, and 128QAM with gray scale mapping

Single-Carrier Modulation versus OFDM for Millimeter-Wave Wireless MIMO

This paper presents results on the achievable spectral efficiency and on the energy efficiency for a wireless multiple-input-multiple-output (MIMO) link operating at millimeter wave frequencies (mmWave) in a typical 5G scenario. Two different single-carrier modem schemes are considered, i.e., a traditional modulation scheme with linear equalization at the receiver, and a single-carrier modulation with cyclic prefix, frequency-domain equalization and FFT-based processing at the receiver; these two schemes are compared with a conventional MIMO-OFDM transceiver structure. Our analysis jointly takes into account the peculiar characteristics of MIMO channels at mmWave frequencies, the use of hybrid (analog-digital) pre-coding and post-coding beamformers, the finite cardinality of the modulation structure, and the non-linear behavior of the transmitter power amplifiers. Our results show that the best performance is achieved by single-carrier modulation with time-domain equalization, which exhibits the smallest loss due to the non-linear distortion, and whose performance can be further improved by using advanced equalization schemes. Results also confirm that performance gets severely degraded when the link length exceeds 90-100 meters and the transmit power falls below 0 dBW.Comment: accepted for publication on IEEE Transactions on Communication