2,242 research outputs found

    System level modeling and evaluation of advanced linear interference aware receivers

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    To cope with the growth of data traffic through mobile networks, efficient utilization of the available radio spectrum is needed. In densely deployed radio networks, User Equipments (UE) will experience high levels of interference which limits the achievable spectral efficiency. In this case, a way to improve the achievable performance is by mitigating interference at the UE side. Advanced linear interference aware receivers are linear receivers able to mitigate external co-channel interference. Optimum linear interference rejection is obtained with the Interference Rejection Combining (IRC) receiver which relies on the ideal knowledge of the interference covariance matrix. The IRC interference covariance matrix is the sum of all interference channel covariance matrices. In practical radio networks, like LTE-Advanced, the knowledge of interference channel covariance matrices might not always be available. However, the IRC interference covariance matrix estimation can be done with a data-based or reference-symbol-based interference covariance matrix estimation algorithm. In this thesis, the modeling and evaluation of advanced linear interference aware receivers for LTE-Advanced downlink are studied. In particular, the data-based and reference-symbol-based covariance matrix estimation algorithms are modeled by using the Wishart distribution. This modeling allows the evaluation of advanced linear receivers without explicit need for baseband signals. The evaluation is done with a system level simulator. Later, a comparison of performance between advanced linear interference aware receivers and 3GPP baseline linear receivers for multiple homogeneous and heterogeneous deployment scenarios is presented. Finally, it is shown that advanced linear interference aware receivers can provide spectral efficiency improvements specially to UEs located at cell borders

    Advanced Coordinated Beamforming for the Downlink of Future LTE Cellular Networks

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    Modern cellular networks in traditional frequency bands are notoriously interference-limited especially in urban areas, where base stations are deployed in close proximity to one another. The latest releases of Long Term Evolution (LTE) incorporate features for coordinating downlink transmissions as an efficient means of managing interference. Recent field trial results and theoretical studies of the performance of joint transmission (JT) coordinated multi-point (CoMP) schemes revealed, however, that their gains are not as high as initially expected, despite the large coordination overhead. These schemes are known to be very sensitive to defects in synchronization or information exchange between coordinating bases stations as well as uncoordinated interference. In this article, we review recent advanced coordinated beamforming (CB) schemes as alternatives, requiring less overhead than JT CoMP while achieving good performance in realistic conditions. By stipulating that, in certain LTE scenarios of increasing interest, uncoordinated interference constitutes a major factor in the performance of CoMP techniques at large, we hereby assess the resilience of the state-of-the-art CB to uncoordinated interference. We also describe how these techniques can leverage the latest specifications of current cellular networks, and how they may perform when we consider standardized feedback and coordination. This allows us to identify some key roadblocks and research directions to address as LTE evolves towards the future of mobile communications.Comment: 16 pages, 6 figures, accepted to IEEE Communications Magazin

    Advanced Radio Resource Management for Multi Antenna Packet Radio Systems

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    In this paper, we propose fairness-oriented packet scheduling (PS) schemes with power-efficient control mechanism for future packet radio systems. In general, the radio resource management functionality plays an important role in new OFDMA based networks. The control of the network resource division among the users is performed by packet scheduling functionality based on maximizing cell coverage and capacity satisfying, and certain quality of service requirements. Moreover, multiantenna transmit-receive schemes provide additional flexibility to packet scheduler functionality. In order to mitigate inter-cell and co-channel interference problems in OFDMA cellular networks soft frequency reuse with different power masks patterns is used. Stemming from the earlier enhanced proportional fair scheduler studies for single-input multiple-output (SIMO) and multiple-input multipleoutput (MIMO) systems, we extend the development of efficient packet scheduling algorithms by adding transmit power considerations in the overall priority metrics calculations and scheduling decisions. Furthermore, we evaluate the proposed scheduling schemes by simulating practical orthogonal frequency division multiple access (OFDMA) based packet radio system in terms of throughput, coverage and fairness distribution among users. As a concrete example, under reduced overall transmit power constraint and unequal power distribution for different sub-bands, we demonstrate that by using the proposed power-aware multi-user scheduling schemes, significant coverage and fairness improvements in the order of 70% and 20%, respectively, can be obtained, at the expense of average throughput loss of only 15%.Comment: 14 Pages, IJWM
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