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This paper presents indoor experimental results on an implemented real-time downlink multiuser multiple-input multiple-output (DL-MU-MIMO) transceiver for next generation wireless LAN systems. In the transceiver, channel state information (CSI) is estimated at each station (STA) and fed back to an access point (AP) on a real-time basis. At the AP, transmit beamforming weight for DL-MU-MIMO transmission...
In this paper, a resource allocation problem for downlink multiple input-single output orthogonal frequency division multiple access (MISO-OFDMA) systems is investigated. The problem is defined as maximizing the minimum user rate with the constraints of total power and bit error rate (BER). Since it is difficult to obtain the optimal solution to this problem, a suboptimal but efficient solution is...
In this paper, we investigate efficient beamforming schemes for downlink broadcast channels of MIMO systems. Optimal solution to this problem is known to be infeasible due to the prohibitive complexity and recent research focuses on suboptimal approaches with reduced complexity. We first present a progressive beamforming method that maximizes the net gain in sum throughput for newly added users and...
Because of its simplicity, amplify-and-forward (AF) is one of the most popular cooperative relaying technique. Relays are used in cooperative communication to improve reliability, coverage or spectral efficiency of cell-edge users. However, relays tend to increase the interferences seen by users of adjacent cells, particularly by the cell-edge users, when used in multi-cell systems. In this paper,...
Base station cooperation in the downlink of cellular systems has been recently suggested as a promising concept towards a better exploitation of the communication system's physical resources. It may offer a high gain in capacity through interference mitigation. This however, comes at a cost of high information exchange between cooperating entities and a high computational burden. Clustering of base...
When the joint processing technique is applied in the coordinated multipoint (CoMP) transmission downlink, the user data for each mobile station (MS) needs to be distributed among multiple base stations (BSs), which incurs the exchange of user data via the backhaul. In order to alleviate the requirement on the backhaul capacity, we propose to minimize the exchange of user data among the BSs, subject...
This paper studies robust transmission strategies for downlink time division duplex coordinated multi-point (CoMP) systems with non-ideal uplink-downlink channel reciprocity due to imperfect antenna calibration. By exploiting the statistics of antenna calibration errors, we first characterize the optimal parametric precoder structure that maximizes the weighted sum rate, based on which a closed-form...
The quality of channel state information (CSI) has large impact on the performance of coordinated multi-point (CoMP) systems. In this paper we study the impact of channel prediction on the performance of coherent CoMP transmission in time-varying channels with large backhaul latency. We resort to large system analysis to derive an explicit expression of the average user rate of the CoMP system when...
Coordinated multi-point transmission (CoMP) has been widely recognized as a promising technique for improving spectral efficiency in future cellular systems. However, it may require high-capacity backhaul links, which can increase expense. In this paper, we study the cooperative transmission method with limited-capacity backhaul. Downlink CoMP transmission requires the exchange of information between...
The explosively increasing demand of high-data-rate multimedia wireless services and ubiquitous access has triggered rapidly booming energy consumption at the wireless network operator side. Therefore, energy-efficient design is becoming a mainstream for future wireless networks. In this paper, we study energy-efficient resource allocation in downlink OFDMA networks with partial channel state information...
In 3GPP LTE-Advanced, relay is considered as an important means for extending cell coverage and improving capacity. Backhaul resource allocation needs to be carefully designed to achieve the performance advantage of relay. In this paper, we propose a two-step backhaul resource allocation scheme for an inband relaying system based on relay buffer level. The resource assignment to relays meets the actual...
The paper investigates the use of Radio Environment Maps (REMs) as a tool for Interference Management (IM) in two-tier cellular networks comprising macro- and femto-cells. The REMs are databases that provide, through different instances distributed over network elements, a variety of network- and user-related context information for improving IM and Radio Resource Management (RRM) procedures. In this...
This paper studies QoE (Quality of Experience) enhancement of audio-video IP transmission over the uplink channel, i.e., from subscriber stations (SSs) to the base station (BS), in the IEEE 802.16 BE service. We assume two types of capacity allocation schemes for uplink and downlink burst durations: static and adaptive. Furthermore, we introduce a piggyback request mechanism for uplink bandwidth requests...
We propose an optimal and a suboptimal resource allocation algorithms for sum rate maximization in an MISO-OFDMA based cognitive radio network subject to a primary user outage constraint. By converting the outage constraint into user and subcarrier dependent peak power constraints, we obtain the optimal joint subcarrier assignment and power allocation solution by applying Lagrange dual-decomposition...
This paper studies the joint resource allocation problem of antenna, subchannel, transmission power, and phase duration for the relay-enhanced bidirectional multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) networks. The goal of resource allocation is to minimize the transmission energy in the networks with multiple relay stations (RSs) under the data rate constraints...
In IEEE 802.16m networks, each frame is divided into eight advanced air interface (AAI) subframes, composed of Logical Resource Units (LRUs). According to stations' requirements, advanced base stations (ABSs) allocate bursts constructed by contiguous LRUs to stations. If ABSs can not efficiently schedule and allocate bursts, bandwidth resource will be wasted in or among bursts. Such these problems...
LTE standard defines strict requirements for service classes in order to provide end users with exceptional QoS characteristics including fast connectivity and high data rates. However there is no standard scheduling algorithm defined for LTE and the task of protecting end user satisfaction while maintaining service class restrictions is left upon the service provider and currently is an open issue...
IEEE 802.11ac standard has newly adopted a downlink multi-user multiple-input and multiple-output (DL-MU-MIMO) scheme. For user multiplexing in downlink WLAN, we can also use a frame aggregation scheme for multiplexing multiple users' data with space-time block coding (STBC) for achieving spatial diversity. We compare the performance of the two downlink user multiplexing schemes: multi-user MIMO and...
Heterogeneous networks (HetNets) are expected to be one of the major performance enhancement enablers of LTE-Advanced. Due to significantly challenging interference scenarios, enhanced inter-cell interference coordination (eICIC) based on almost blank subframes (ABS) is the key technology enabler that makes HetNets a reality. The key factor determining the gain of ABS-based eICIC is the configured...
A novel decomposed transceiver design scheme is developed for multiuser non-regenerative MIMO relay downlink systems. With a decomposed relay structure, the whole system can be decomposed into a point-to-point and a point-to-multipoint systems, thus the transceiver design can be individually proceeded for the first and second hop. In the first hop, the transceiver is derived to minimize the mean square...
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