Spatial Transmission Mode Switching in Multiuser MIMO-OFDM Systems With User Fairness

Abstract

Multiantenna radio systems allow accessing the channel in diversity or spatial multiplexing (SMUX) mode. Adequate switching between these modes according to current channel conditions was shown to yield significant performance improvements while requiring little feedback from the receiving side. We present a transmission concept for the downlink of a multiuser multiple-input-multiple-output orthogonal frequencydivision-multiplexing (MU-MIMO-OFDM) system aiming at high user rates with limited feedback demands. An extended score-based scheduling (SB) approach ensures fair-resource allocation to the users, whereas transmission mode switching is used to guarantee high user rates. The degree of fairness of the scheduler can be adapted by adequately configuring a weighting function for the scores. Comparison with single-mode schemes reveals substantial throughput gains of the adaptive switching concept. Furthermore, targeting maximum throughput, we show that a considerable proportion of the capacity of the MIMO broadcast channel (BC) can be achieved with a comparatively low amount of required feedback.

Efficient MAC protocol for JT CoMP in small cells

“…Since ZF is optimal only if the user channels are orthogonal [6], we describe how to identify an appropriate user set maximizing the performance. For the identified set, finally we apply MIMO mode switching [7] and frequency-selective scheduling.…”

“…This is denoted as MIMO mode switching in the literature. Therefore, we consider the single-user case described in [7]. MIMO mode switching is considered here for zero forcing.…”

“…Mode switching stops typically after one or two discarded streams. Clearly, one could extend this idea for multiple users in each cell [7]. But gains are mainly due to user selection.…”

Multi-user chaos MIMO-OFDM scheme for physical layer multi-access security

“…To address this problem, multiuser MIMO (MU-MIMO), a type of advanced MIMO technique, has been proposed in which spatial multiple access can be achieved and in which the system capacity is increased even with a single antenna of a mobile terminal. As a result, many improved MU-MIMO systems have been studied [1][2][3][4]. In MU-MIMO, beamforming is conducted at the transmitter to avoid signals for multiple receivers interfering with each other.…”

Adaptive switching based on Markov model for multiuser MIMO-OFDM systems

“…In addition, orthogonal frequency division multiplexing (OFDM) [12] has been a key technique for transmission of signals over wireless channels in order to adapt with the multipath channel conditions. MIMO-OFDM technologies can be used to effectively reduce the bit error rate, improve quality of the system through spatial diversity (SD) or to have higher transmission data rates through spatial multiplexing (SM).…”