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This forum contains 21 topics and 25 replies, and was last updated by  Presenter 1 year, 9 months ago.

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    • Coverage Distribution of Heterogeneous Cellular Networks Under Unsaturated Load
      Heterogeneous cellular networks have received considerable attention in the literature owing to increased data demands of cellular network users. Recently, Poisson Point processes (PPPs) are vastly used for modeling and analyzing cellular networks because of their accuracy and tractability. However, results in this area suffer from a big drawback. They considered a saturated load model in their analysis or used a base station (BS) activity factor independent of the network condition. In this work, we evaluate the performance of cellular networks under a more accurate definition of load. In cellular networks, a BS is active when it has at least one user associated and is inactive when it has no associated user. The load definition used in this paper is a user-based load model and denotes whether at least one user is associated with the BS or not. This paper provides a closed form relation for the probability of inactive BSs of each tier. Based on this value, the coverage probability of the network has been derived. Finally, the performance of analytical expressions has been validated with simulations.
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       Presenter

    • Dynamic Scheduling in System-Level Simulations for Multi-hop D2D Communications in LTE Networks
      Device-to-device (D2D) communication has attracted great attention and becomes a promising technology for future wireless networks. Besides two UEs communicating directly without going through the base station, D2D communication can be further broadened to multi-hop D2D communication, for example, a UE may serve as a relay for some D2D pair. In this work, we perform system-level simulation studies on multihop D2D communications overlay LTE networks with intra-cell and inter-cell interference from other D2D transmissions. We investigate dynamic scheduling for multi-hop D2D according to instantaneous channel and interference situation based on proportional fair metrics. Dynamic scheduling is a compromise between average and edge spectral efficiency, since using relays can increase edge performance but may decrease the average spectral efficiency as they consume more resources than direct D2D. In simulation studies, we can see that multi-hop D2D with dynamic scheduling outperforms direct D2D and multi-hop D2D with fixed scheduling for large D2D distance, and also increases edge spectral efficiency dramatically for small D2D distance with the expense of a little average spectral efficiency decrease.
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    • Efficient Multi-User MIMO Transmissions in the LTE-A Uplink
      Single-User Multiple-Input Multiple-Output (MIMO) transmissions are possible since Rel. 10 of 3GPP LTE-A. The Closed Loop Spatial Multiplexing (CLSM) transmission mode enables up to a four fold increase in spectral efficiency compared to Rel. 8, yet it requires complex User Equipment (UE) hardware supporting more than one transmit antenna. The closed loop spatial multiplexing transmission mode enables up to a four fold increase in spectral efficiency compared to Rel. 8, yet it requires complex UE hardware supporting more than one transmit antenna. As it is likely that the Base Station (BS) has more receive antennas than the UE transmit antennas, employing Multi-User (MU) MIMO transmissions in the uplink can lead to significant improvement in cell throughput. We formulate MU MIMO transmissions with linear receivers as a compact matrix system model. Based on our model we present a post-equalization SINR equation, allowing the calculation of a quantized feedback parameter, the Channel Quality Indicator (CQI) value. Within this framework we reveal possible MU gains through known scheduling algorithms although the frequency selective channel is approximated by its arithmetic mean.
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       Presenter

    • Filter Bank Multi Carrier Based MIMO System for 5G Wireless Communication
      Filter Bank Multicarrier (FBMC) transmission technique is a primary candidate for upcoming wireless communication standard 5G. It is also considered as an alternative to the famous Orthogonal Frequency Division Multiplexing (OFDM). To ensure interference free communication, OFDM utilizes Cyclic Prefix (CP) along with a rectangular pulse shaped filter. Which renders OFDM spectrally inefficient, when incorporated over large arrays of antennas. The FBMC can overcome this problem by using a different modulation scheme and a specialized prototype filter. We started this study by presenting a detailed analysis of an FBMC system. Furthermore, the FBMC system is interfaced with a Multiple Input Multiple Output (MIMO) antenna system with different antenna array sizes. We begin with a 22 antenna array and then we perform experiments with 8, 16 and 32 transmit and receive antennas. Signaling and channel specifications are different for each case. The performance of each system is measured using Zero forcing (ZF) and Minimum Mean Square Error (MMSE) equalizers. Bit Error Rate (BER) is measured against normalized Signal to Noise Ratio (SNR) or Eb=No for each system. The results of this study show that FBMC with MIMO depicts a satisfactory improvement in performance. For the 22 MIMO system MMSE outperforms the ZF equalizer. Moreover, a significant decrease in BER was observed as the array size was increased.
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    • Four-Dimensional Network Simulation of Direct Air to Ground LTE Networks
      In recent times in-flight Broadband Internet connection service is becoming more common. In Japan, most in-flight connectivity utilizes a satellite backhaul system. However, the satellite system tends to be very bulky and expensive for short-and medium-haul continental flights. The satellite system has limited capacity, especially serving a large number of continental aircraft in a limited geographical area. This, it produces a large transmission latency, that affects the real-time service quality. The solution is a Direct Air-to-Ground (DA2G) network based on Long Term Evolution (LTE) technology. The DA2G network deploys ground stations that are connected with aircraft flying overhead, thus providing an ultra-broadband backhaul infrastructure. The European Conference of Postal and Telecommunications Administrations (CEPT) has explored the potential of DA2G networks based on LTE with pencil beamforming in an attempt to improve the link performance. Here, based on the CEPT reports, this paper discusses the broadcasting and traffic channel coverage without pencil beamforming to keep the compatibility of conventional LTE. In addition, a hierarchical antenna architecture is proposed for covering all flight cruising altitudes of 4,000 - 12,000 m using conventional LTE. Moreover, a four-dimensional network simulation of DA2G LTE networks is introduced. The merits of the proposed antenna architecture are verified using a developed four-dimensional network simulator.
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    • Geometric Average Based Fast Converging Proportional Fair Scheduling for LTE Downlink Transmissions
      Long Term Evolution (LTE) wireless communication system has adopted Orthogonal  Frequency Division Multiple Access (OFDMA) technology to provide downlink transmissions to multiple User Equipment (UE) in a single transmission time interval. In OFDMA, UEs provide quantized channel quality information, called channel quality indicator (CQI), to the base station. CQI feedback is then used at the base station to choose which UE to be scheduled and which modulation and coding scheme (MCS) for the selected UE to be used in downlink transmissions. Each UE sends averaged CQI over all subcarriers instead of sending the CQI of each subcarrier to minimize feedback overhead. As a result, only one MCS is applied at the base station for multiple subcarriers intended for the same UE. This can cause significant throughput degradation, especially in low SNR regions in which the actual CQI of each subcarrier may vary significantly. Our experimental results show that the two well-known scheduling algorithms, namely Best CQI and Proportional Fair Scheduling (PFS), fail to provide spectrum efficiency and/or fairness among UEs. These algorithms tend to provide a large fraction of bandwidth to a single UE; hence, the UE fails to demodulate transmitted data to which only one modulation scheme was applied. In this paper, we propose a novel scheduling algorithm that achieves better throughput performance, while providing more fairness among UEs than existing solutions in both high and low SNR environments. The proposed algorithm improves cell throughput by 66% over the PFS when UEs experience various SNR values. When UEs undergo similar SNR values, the system throughput can be improved by more than 120% over BestCQI and by almost 60% over PFS. Extensive simulations validate that our proposed solution also significantly enhance Block Error ratio (BLER) in addition to network throughput and fairness.
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    • Link-Level Simulator for WLAN Networks
      Nowadays, interest for compatible simulators with high flexibility to explore the performance of Wireless Local Area Networks (WLANs) is definitely increasing. One of the main reasons of such interest is the upcoming 5G technology, related to the Internet-of-Things (IoT). In this paper, we present a MATLAB-based link-level simulator for WLAN with still used (IEEE 802.11g/n/ac) and upcoming (IEEE 802.11ah/af) technologies. Realization of the whole WLAN link-level simulator is highly inspired by the recognized Vienna LTE-simulator. As a result, it is possible to join together these simulators to explore the performance of WLAN and LTE, operating in the same radio frequency (RF) band. From the point of future 5G based cellular networks, such exploring is important because different coexistence scenarios can occur between wireless communications systems in the ISM and UHF bands.
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    • Modeling unicast device-to-device communications with SimuLTE
      In LTE-Advanced (LTE-A), device-to-device (D2D) transmissions allow two peering User Equipments to communicate directly without using the Evolved Node-B as relay. D2D is regarded as one of the enablers to bring LTE-A in the context of vehicular networks, smart cities, or M2M applications. Research on this topic is mostly carried out through link-level simulations. In this work, we describe instead the modeling of D2D into a system- level simulator, namely SimuLTE, which enables us to analyze the performance of applications and higher-layer protocols using D2D transmission. We first describe the modeling within the SimuLTE architecture, then we validate it and analyze the performance of D2D communications with frequency reuse.
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    • Modeling X2 backhauling for LTE-Advanced and assessing its effect on CoMP Coordinated Scheduling
      Many LTE-Advanced algorithms and protocols rely on node coordination and cooperation to reduce power consumption, increase spectral efficiency and improve cell-edge performance. Functions such as Coordinated Multi Point, Network Assisted Handover, etc., require a standard connection among nodes to support their operations. The LTE X2 interface meets the above requirements and allows operators to connect nodes for both rel-8 and more advanced (e.g rel-13) functionalities. In this work we describe the modeling of X2 within the SimuLTE system-level simulator. Most research works assume an ideal X2 connection, with null delay and infinite bandwidth. However, the X2 delay and bandwidth do affect the behavior and performance of the aforementioned algorithms. Thus, using CoMP Coordinated Scheduling as a case-study to test X2 functionalities, we show how X2 round-trip delay affects the performance of the CoMP scheduler.
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    • PHY Layer Abstraction for SU-MIMO LTE System Employing Parallel Interference-Aware Detection
      Maximum-likelihood (ML) receivers are optimum receivers for MIMO systems, but their complexity grows exponentially with the modulation order of the codeword and the number of spatial layers. The Reduced Complexity ML (R-ML) receivers based on low complexity adaptation of the max-log MAP detector and reduction of searching space are a good compromise to satisfy complexity-performance trade-off. In this paper we investigate physical layer abstraction for singleuser MIMO system with a R-ML receiver performing Parallel Interference Aware (PIA) detection. We develop a light-weight extended Mutual Information Effective SINR Mapping (MIESM) methodology based on look-up tables (LUT), which take the special non-linear nature of the PIA receiver into account. The results show that the proposed LUT-based MIESM abstraction method is as accurate as the direct MIESM abstraction, but at the same time has significantly less computational complexity. It can thus be easily used in performance prediction devices as well as system level simulators.
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    • The GTEC 5G Link-Level Simulator
      1570263742_presentation 1570263742_presentation_with_overlaysThe rapid evolution of nowadays wireless communication systems constitutes a challenge for the versatile and flexible evaluation of transmissions under different scenarios. In order to evaluate the current fourth generation (4G) and future fifth generation (5G) communication techniques, a modular link-level simulator was developed at the GTEC group of the University of A Coruña. In this paper, the structure of the simulator as well as how to use it are presented in detail. The simulator allows for performing link layer simulations both for Orthogonal Frequency-Division Multiplexing (OFDM) and Filter Bank Multicarrier (FBMC) signals. It includes fully-functional transmitter and receiver implementations, as well as different channel models and functions for processing the obtained results. Moreover, we show also that the simulator is fully integrated with the GTEC testbed, enabling not only for performing simulation-based evaluations, but also considering over-the-air measurements. Hence, the GTEC 5G Simulator constitutes a valuable tool for evaluating new communication systems in a versatile and flexible way. Some exemplary results obtained both by simulations and through measurements are included.
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    • Using System-Level Simulation to Evaluate Downlink Throughput Performance in LTE-A Networks with Clustered User Deployments
      Downlink throughput performance in Long Term Evolution - Advanced (LTE-A) networks has been widely investigated by many simulation studies. However, these studies generally assume that users are uniformly distributed in regularly arranged hexagonal cells. Analytical models and methods of stochastic geometry have been applied to wireless networks to consider the effects of spatial configuration of nodes and base stations on network performance by abstracting away many details of the systems. As such, comprehensive studies of the effects of spatial factors on throughput performance using standard-compliant, open-source software that simulates any details of LTE-A networks are still scarce. In this paper, we use the Vienna LTE-A Downlink System Level Simulator to re-evaluate the validity of usual throughput performance metrics under various spatial deployment scenarios and employ statistical methods to determine the significance of performance observations. Our primary aim is to show that clustered user deployments around a base station exhibit significantly different throughput performance compared to the case of uniformly distributed users throughout the cell. This is important since in practice, base stations are deployed in areas of high user density. In addition, we show that the most widely used scheduling scheme in cellular networks, namely the proportional fair scheduling, may lose its performance advantage over round robin scheduling when users are clustered around the base station. These findings are expected to have implications on the design and deployment of next generation cellular networks.
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