Alexis Alfredo Dowhuszko

A decentralized cooperative Uplink/Downlink adaptation scheme for TDD Small Cell Networks

This paper presents a cooperative decentralized scheme for adjusting the Uplink (UL)-Downlink (DL) configuration of a Small Cell Network (SCN) with a TDD air interface. The goal of the cooperative decentralized scheme is to make a more efficient use of common wireless resources, selecting convenient TDD-frame configurations to maximize a sum utility function that takes into account both individual traffic demands and actual interference coupling situations. The cooperative decentralized scheme for UL/DL adaptation can be executed locally at each Base Station (BS), and relies solely on the exchange of low-rate signaling information among neighboring cells. Based on observed performance improvements, we conclude that cooperative decentralized schemes are a viable option for flexible-TDD implementation in SCN environments, particularly in presence of cells with strong interference coupling and low-rate signaling capabilities.

Coordination protocol for inter-operator spectrum sharing in co-primary 5G small cell networks

We consider spectrum sharing between a limited set of operators having similar rights for accessing spectrum. A coordination protocol acting on the level of the RAN is designed. The protocol is non-cooperative, but assumes an agreement to a set of negotiation rules. The signaling overhead is low, and knowledge of a competitors channel state information is not assumed. No monetary transactions are involved; instead, spectrum sharing is based on a RAN-internal virtual currency. The protocol is applicable both in a scenario of mutual renting and when the operators form a spectrum pool. The protocol reacts to variations in interference and load of operators, and shows gains in a simulated small cell scenario.

Interference management for LTE‐Advanced Het‐Nets: stochastic scheduling approach in frequency domain

Heterogeneous networks represent a practical way to face high traffic demands in densely populated areas. Nevertheless, to achieve these advertised data rates, advanced interference management techniques are required. Trying to tackle this problem, this paper presents a stochastic scheduling approach for two-layer LTE-Advanced networks. The proposed stochastic frequency-domain scheduling (SFDS) algorithm seeks the avoidance of cross-layer and colayer interference, and is based on allocating different portions of the transmission bandwidth probabilistically. The SFDS algorithm is first presented as an interference management solution for an orthogonal frequency-division multiple access system (i.e. LTE-Advanced downlink). Later on, the SFDS algorithm is extended to be compatible with single-carrier frequency-division multiple access transmissions, and its performance is evaluated when combined with open-loop power control techniques (i.e. LTE-Advanced uplink). Extensive system level simulations are carried out to evaluate the performance of SFDS algorithm in a predefined LTE-Advanced scenario that combines both macrolayer and femtolayer. Results show that the proposed algorithm allows to balance the cross-layer and colayer interferences, extending the performance trade-offs that well-known full-range spectrum allocation and orthogonal spectrum allocation approaches provide. Copyright

Distributed algorithm for downlink resource allocation in multicarrier small cell networks

In small cell networks (SCNs) co-channel interference is an important issue, and necessitates the use of interference mitigation strategies that allocate resources efficiently. This work discusses a distributed utility-based algorithm for downlink resource allocation (i.e., power and scheduling weights per carrier) in multicarrier SCNs. The proposed distributed downlink resource allocation (DDRA) algorithm aims to maximize the sum utility of the whole system. To achieve this goal, each base station (BS) selects the resource allocation strategy to maximize a surplus function comprising both, own cell utility and interference prices (that reflect the interference that is caused to neighboring cells). Two different utility functions are considered: max-rate and proportional fair-rate. For performance evaluation, a SCN deployed in a single story WINNER office building is considered. Simulation results show that the proposed algorithm is effective in enhancing not only the sum data rate of a SCN, but also the degree of fairness in resource sharing among users.

A unified protocol stack solution for LTE and WLAN in future mobile converged networks

The interworking of the LTE system and WLAN technologies has drawn much attention lately, due to the growing demands for various multimedia services and large data traffic in hotspot areas. Existing research studies have mostly investigated the coupling architectures for these two wireless communication standards at the network layer. However, in the current architectures, many important coordination functions and joint optimizations cannot be accomplished efficiently. To tackle this problem, a new CBS solution is proposed, which integrates different RATs at layer 2 in the true sense of convergence. We design a unified protocol stack that includes all the original functions of both LTE and WLAN systems. Then we propose a convergence architecture, the RMC sublayer, for joint management of these two RATs. The proposed CBS solution can support seamless offloading through soft handover, guaranteed QoS, forwarding management by a single IP address, and customized bandwidth aggregation service. Finally, our simulation and initial experiment results demonstrate the feasibility and efficiency of the CBS solution in future mobile converged networks.

Capacity of Generalized UTRA FDD Closed-Loop Transmit Diversity Modes

Transmit diversity techniques have received a lot of attention recently, and open-loop and closed-loop downlink transmit diversity modes for two transmit antennae have been included into universal terrestrial radio access (UTRA) frequency division duplex (FDD) specification. Closed-loop modes provide larger system capacity than open-loop modes, but they need additional side information of the downlink channel in the transmitter. In FDD systems this requires a separate feedback channel. Quantization of channel state information (CSI) in closed-loop transmit diversity schemes decreases the performance when compared to a closed-loop system where the transmitter has access to complete CSI. In this paper, we analyze the effect of quantization of CSI and deduce approximate capacity formulae for closed-loop transmit diversity schemes that are generalizations of the closed-loop schemes included in UTRA FDD specification. Moreover, we calculate approximation error and show by simulations that our approximation is tight for flat Rayleigh fading environments with and without fast transmit power control.

Closed-form solution for minimizing power consumption in coordinated transmissions

The growth in the demand of energy, and its consequent contribution to the greenhouse effect, gives rise to new challenges in the design of future wireless networks. Keeping in mind these requirements, in this article we study the power allocation problem in the downlink of an orthogonal frequency division multiple access (OFDMA) system, where two (or more) coordinated transmission points (CTPs) should find the best way to allocate their transmit power through the multiple orthogonal sub-channels of the system. The ultimate goal of the power allocation scheme is to minimize the joint power consumption of the system, but verifying at the same time the target throughput and the individual power constraint per CTP. The power allocation problem is formulated as a constrained optimization problem, and a group of closed-form power allocation solutions are derived. Based on the derived solutions (that take the form of the traditional water-filling but demanding cooperation among CTPs), a novel power allocation algorithm with joint minimization power consumption (JMPC-PA) is proposed. Numerical results are presented to verify the optimality of the results that were obtained by the JMPC-PA scheme. It is important to note that, due to the flexibility that exist in the definition of CTPs in this article, the derived power allocation scheme is valid for any kind of network that incorporates the coordinated multipoint transmission feature in its design.

On throughput-fairness tradeoff in virtual MIMO systems with limited feedback

We investigate the performance of channel-aware scheduling algorithms designed for the downlink of a wireless communication system. Our study focuses on a two-transmit antenna cellular system, where the base station can only rely on quantized versions of channel state information to carry out scheduling decisions. The motivation is to study the interaction between throughput and fairness of practical spatial multiplexing schemes when implemented using existing physical layer signaling, such as the one that exists in current wideband code division multiple access downlink. Virtual MIMO system selects at each time instant a pair of users that report orthogonal (quantized) channels. Closed-form expressions for the achievable sum-rate of three different channel-aware scheduling rules are presented using an analytical framework that is derived in this work. Our analysis reveals that simple scheduling procedures allow to reap a large fraction (in the order of 80%) of the sum-rate performance that greedy scheduling provides. This overall throughput performance is obtained without affecting considerably the optimal short-term fairness behavior that the end users would perceive.

Energy Efficiency Analysis of Two-Way DF Relay System With Non-Ideal Power Amplifiers

The energy efficiency (EE) problem of a two-way decode-and-forward relay system with three nodes is studied. The maximization of the EE is done by jointly optimizing the transmission time and power of each node, assuming non-ideal power amplifiers (PAs) and considering that data to be delivered is delay constrained. Theoretical analysis and numerical results show that the joint optimization of both parameters provides better EE than the equal allocation of time with independent optimization of transmission power. Moreover, it is observed that the use of non-ideal PAs and the increase in the downlink-to-uplink data ratio decrease the EE of the relay system under study.

Downlink multiuser scheduling algorithms with HSDPA closed-loop feedback information

System capacity can be increased if the base station (BS) is equipped with additional channel state information (CSI) of the downlink channel. In an FDD system, this means that mobiles have to provide CSI through some feedback mechanism. Although the two feedback modes included in the present WCDMA HSDPA standard have been designed for one-by-one transmission, a significant downlink throughput improvement can be achieved with multiuser scheduling (MS) [A. Dowhuszko et al., 2005]. In this paper we propose two practical MS algorithms compatible with the current HSDPA specification, that provide a significant performance gain at moderate power regimes, compared to the systems that transmit sequentially to the user with best channel.