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In this paper, the problem of Downlink Multi-User MIMO (DL MU-MIMO) transmission from two interfering transmitters, each equipped with M antennas to multiple users each equipped with K antennas is considered. It is assumed that all users receive a single data stream of rank one from only one of the transmitters. A novel transmission/reception scheme is proposed based on the idea of Interference Alignment...
In this paper we consider two alternate packet structures for estimating the multi-input multi-output (MIMO) powerline channel and their impact on achievable application throughputs. In the first packet structure, an orthogonal pair of OFDM symbols is used to estimate the channel. When compared to single-input single-output (SISO) transmissions that use one OFDM symbol to estimate the channel, there...
In this paper, we consider user selection algorithms for Multi-user MIMO systems with perfect or partial channel state information at the transmitter (CSIT). A novel user selection algorithm based on chordal distance is proposed. The basic principle is to serve the user subset in which one is approximately orthogonal to the others. Since the chordal distance relies only on the channel direction information,...
In this paper we analyze the performance of advanced OFDM packet scheduling techniques based on 3GPP UTRAN Long Term Evolution (LTE) framework for high velocity scenarios. Based on our previous investigations in system performance analysis, we demonstrate that packet scheduler being part of the whole radio resource management (RRM) process has a major impact on it. On the other hand high user velocities...
Multiple-Input Multiple-Output (MIMO) communications have shown great promise in providing high spectral efficiency for wireless ad hoc networks. In this paper we study the problem of joint routing, scheduling, power control and bit rate selection in MIMO-based ad hoc network with the goal of maximizing the system throughput that satisfies a given end-to-end traffic demand. We formulate this cross-layer...
Hierarchical femtocell architectures have become popular recently because of their potential to provide increased coverage and capacity in cellular systems. However, introduction of femtocells might reduce the overlay macrocell system performance due to increased interference caused to macrocel-lular users. With MIMO precoding, the Least Interference (LI) technique can be employed at the femtocellular...
This paper presents results from a novel OFDMA multi-cell mobile broadband system level simulator. The tool is used to statistically characterize uplink and downlink inter-cell interference. Without suitable interference management, multi-billion dollar networks can collapse under the strain of heavy traffic loads. Fully loaded interference studies cannot be performed on the network until it has been...
Channel reciprocity is regarded as one of the most important advantages of TDD systems. However, the RF front-ends contribute to the channel experienced, and their TX/RX mismatches might cause reciprocity error, and thus degrade system throughput. Therefore, channel reciprocity calibration is a crucial issue. Among the existing calibration methods, Over-the-air (OTA) calibration is a promising approach...
MIMO, OFDMA and cooperative relaying are the key technologies in future wireless communication systems. However, under the usage of these technologies, resource allocation becomes a more crucial and challenging task. In multi-user MIMO-OFDMA relay-enhanced cellular networks, we formulate the optimal instantaneous resource allocation problem including user group selection, path selection, power allocation,...
Multi-cell MIMO technique theoretically promises large improvement in spectral efficiency and fairness in cellular networks and is regarded as the key enabling technique for solving the troublesome issue of inter-cell interference. To evaluate its practical performance in the cellular network, we have implemented the real-time downlink multi-cell MIMO trial system operating over bandwidth of 20 MHz...
Multi-user MIMO is a promising technology to enhance the performance of WLANs. However, the MAC protocol of the IEEE 802.11 standard (the DCF MAC protocol) is not able to solve the new coordination and synchronization issues that are needed to enable multiple simultaneous transmissions. This paper presents an enhanced MAC protocol for Downlink SDMA in WLANs where only the Access Point is equipped...
In this paper we focus on finding a suitable Link Adaptation (LA) algorithm which is implemented as Channel Quality Indicator (CQI) selection technique in the 3GPP Long Term Evolution (LTE) system. The potential of Link Adaptation in the LTE system is not fully exploited. Therefore in our study, we compare the performances from different LA algorithms in the LTE system. The presented LA algorithms...
Significant throughput gains can be achieved in a multi-user MIMO (MU-MIMO) wireless system by exploiting the combination of multi-user scheduling and multi-user diversity. Open-loop MU-MIMO (OL-MU-MIMO) is a codebook based precoding technique where precoders are fixed a priori at the base station (BS) in a known fashion and the user needs to feedback which precoding vector is to be chosen referred...
In Multi-user MIMO (MU-MIMO), the Base Station (BS) schedules multiple users simultaneously on the same resources. Closed loop MU-MIMO uses explicit feedback from each of these users for scheduling and allocation of resources. In this scheme, an estimate of the SINR experienced is fed back by each user and is known as the CQI (Channel Quality Information). This CQI is used by the BS for link adaptation...
Multiple-Input Multiple-Output (MIMO) technology has great potential for improving the throughput of Wireless Mesh Networks (WMNs). In this paper, we investigate the joint stream allocation and scheduling problem for single-user MIMO communication in WMNs with the objective of maximizing the demand satisfaction for a set of flows. The notion of transmission configuration (TC) is introduced and a heuristic...
Long Term Evolution (LTE) is an emerging 4G wireless access technology. Multiple-Input Multiple-Output (MIMO) systems are a primary enabler of the high data rate sought to be achieved by LTE. Closed-Loop-Spatial-Multiplexing and Open-Loop-Spatial-Multiplexing are the two primary MIMO transmission modes used in the LTE downlink. An LTE Base Station (eNodeB) is expected to select and switch transmission...
The performance evaluation of the MIMO transmission schemes based on the IEEE 802.16m technology by the system level simulation is conducted in this paper. IEEE 802.16m technology supports various MIMO transmission schemes. We perform the evaluation of the system by applying various MIMO transmission schemes and compare the results. The evaluation results for each channel can be indicator to select...
For the first time in the WLAN technology, multi-user downlink transmission will be made possible by the upcoming IEEE standard, 802.11ac. In this paper, we will report its current status, focusing on the MAC modifications and enhancements that are necessary to support the unique feature of downlink multi-user MIMO transmission. Specifically, the technique of TXOP sharing and its related issues and...
A power/area aware design is mandatory for the MIMO (Multi-Input Multi-Output) detectors used in LTE and WiMAX standards. The 64-QAM modulation used in the MIMO detector requires more detection effort compared to the smaller constellation sizes widely implemented in the literature. In this work we propose a new architecture for the K-best detector, which unlike the popular multi-stage architecture...
This paper presents a proposed measurement method utilizing the reverberation chamber to measure MAC layer throughput for LTE enabled wireless devices. By using the reverberation chamber a statistically isotropic environment is produced, which is a suitable reference environment for terminal antenna testing.
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