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The LOS components of the base station (BS) can provide a high SNR to mobile stations (MSs), but they cannot achieve a high spatial multiplexing gain in the MIMO-OFDMA system. The spatial multiplexing gain is obtained by degrees of freedom between MIMO antenna arrays. MIMO channels should be uncorrelated to achieve the maximum degrees of freedom, and it depends on rich scattering environments which...
The Physical Downlink Control Channel (PDCCH) is used to signal dynamic resource assignment information in the Long Term Evolution (LTE) system. In the presence of numerous active users, the system performance is likely to be hindered by shortage of control channel resource. In this paper, several simple algorithms are brought forward for making efficient PDCCH resource allocation. We first propose...
Relaying is generally considered as a method to ensure capacity improvement and coverage extension in cellular systems. The additional communication traffic between a mobile station and a relay intermediately inserted into a link between RUE and BS requires additional considerations on HARQ protocol. In this paper, we propose a method to jointly and dynamically balance the maximum number of transmissions...
In this paper, we analyze the interference distribution and gain of beamforming in closed access femtocells in downlink of a two-tier HSDPA cellular network. We show through simulations that indoor femtocell deployment leads to a dominant interferer scenario. According to results even simple null steering method based on the scarce codebook of HSDPA transmit diversity mode 1 can be beneficially applied...
We report on field trials using CoMP transmission in the downlink of a mobile radio network. Two new features enable over-the-air CoMP transmission from physically separated base stations and terminals. These are distributed synchronization and a fast virtual local area network. Using VLAN tags, terminals feed back the multi-cell channel state information to their serving bases where it is multiplexed...
In GERAN networks, Multiple Users Reusing One Single timeslot (MUROS) promises to enhance the cell capacity through pairing of two or more users onto a single timeslot. So far no work has been done on the basis on which the different users would be paired. The criteria used for the pairing decision to pair two or more users is critical for MUROS as this will eventually decide the actual gains due...
In this paper we investigate channel state information (CSI) feedback strategy for a basestation (BS) scheduling multiple users for data transmissions in the downlink. For the purpose of fair provisioning of service among users with possibly heterogeneous channel statistics, we adopt scheduling algorithms based on scores: specifically the maximum quantile (MQ) scheduling is used as one of such schedulers...
In a multiuser system, independent time-varying channels among different users can be exploited to provide multiuser diversity (MUD) gain and increase the system throughput. For the downlink channel, this requires the users to feedback their channel state information (CSI) to the base station (BS), which incurs a large aggregate feedback load, especially when the number of users is large. In this...
The 3GPP (Third Generation Partnership Project) LTE (Long Term Evolution) and LTE-Advanced activities work toward the evolved UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access (E-UTRA), and the solution of IMT-Advanced (International Mobile Telecommunications) and systems beyond. The combination of OFDM (orthogonal frequency division multiplexing) and MIMO (multiple-input...
Base station cooperation (BSC) has been identified as a key radio access technology for next-generation cellular networks such as LTE-Advanced. BSC maximizes its gains over non-cooperation (NC) in a network wherein interference from cooperating BSs is the main limitation. However, at locations where the signals from non-cooperating BSs are the dominant interference, the gains are minimal. Therefore,...
In this work we consider the allocation of buffer space to data streams sharing a common high-speed wireless transmitter. As an example, we focus on an OFDMA-based downlink system scenario. Scheduling for maximum throughput has been extensively studied in the literature. However, the practically interesting case of a finite buffer has not been sufficiently addressed before. Especially in the case...
In a downlink transmission, users can benefit from the high capacity gain achieved by transmitting independent data streams from multiple antennas to multiple users sharing the same physical time-frequency resources. This technique is known as multiuser MIMO (MU-MIMO). However, performance of MU-MIMO is sensitive towards propagation imperfections, such as time dispersion and inter-stream interference...
In two-tier networks consisting of a macrocell overlaid with femtocells in co-channel deployment and closed-access policy, spatial reuse is achieved at the price of severe cross-tier interference from concurrent transmissions. The lack of direct coordination between the macro and femtocells makes interference control as a challenging issue. Cognitive radio (CR) becomes a promising solution, where...
Decentralized base station (BS) assignment methods with limited backhaul information exchange are proposed to be combined with decentralized optimal multi-cell minimum power beamforming and Zero-Forcing (ZF) beamforming techniques. The aim of the combined BS assignment and downlink beamforming is to minimize sum power while guaranteeing a minimum SINR per user. A major finding is that a simple ZF...
In this paper we consider the Downlink Beamforming (DLBF) and resource allocation problem in MIMO-OFDMA systems. We consider the sum-power minimization or margin adaptive problem. This is a variable Signal to Interference and Noise Ratio (SINR), non-convex optimization problem and many aspects of this problem are not well understood. By using uplink downlink duality we first obtain the expression...
Coordinated multiple point transmission and reception (CoMP) has attracted a lot of attention recently because of its potential for multi-cell co-channel interference (CCI) mitigation and spectral efficiency increase. CoMP inevitably requires increased signaling overhead and inter-base communication. Therefore in practice, only a limited number of Base Stations (BS) can cooperate with acceptable overhead...
In this paper, three cooperative relaying schemes are proposed for relay networks comprised of two source terminals and multiple relays, each with single antenna. The new relaying schemes, corresponding to the maximum ratio combining of the downlink and uplink channels, phase rotation of the received signals at relays, and the channel gain equalization, are designed based on the maximization of the...
This paper examines linear beamforming methods for secure communications in a multiuser wiretap channel with a single transmitter, multiple legitimate receivers, and a single eavesdropper, where all nodes are equipped with multiple antennas. No information regarding the eavesdropper is presumed at the transmitter, and we examine both the broadcast MIMO downlink with independent information, and the...
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