Apostolos Papathanassiou

5G Network Capacity: Key Elements and Technologies

It has been projected that, in the next decade, a mobile traffic increase on the order of 1,000 times is expected compared to what we experience today. To meet that dramatic traffic growth, next-generation mobile networks are also expected to achieve a 1,000-fold capacity increase compared to the current generation of wireless network deployments. In this article, we discuss how such capacity growth could be achieved in a ten-year time frame. We discuss the techniques that we expect to have the highest opportunity for increasing the system capacity and estimate their gains based on analysis and simulation. We observe that the main driver of capacity growth is expected to come from network architecture advancements, with heterogeneous networks and convergence of information and communication technology being two of the key techniques. We also estimate that the air-interface evolution would focus not only on improving the link and system spectrum efficiency but also on facilitating the required network efficiency improvements. This article provides insights into the communication technology evolution and can be used as a guideline for technology development toward the fifth generation (5G).

Smart antennas for combined DOA and joint channel estimation in time-slotted CDMA mobile radio systems with joint detection

In cellular mobile radio systems, the directional inhomogeneity of the mobile radio channel can be exploited by smart antennas to increase the spectral efficiency. In this paper, a novel smart antenna concept applying receiver antenna diversity at the uplink receiver is investigated for a time-slotted code-division multiple-access (CDMA) mobile radio air interface termed time-division CDMA (TD-CDMA), which has been selected by the European Telecommunications Standards Institute (ETSI) in January 1998 to form part of the Universal Mobile Telecommunications System (UMTS) air interface standard. First, a combined direction-of-arrival (DOA) and joint channel estimation scheme is presented, which is based on DOA estimation using the Unitary ESPRIT algorithm and maximum likelihood estimation of the channel impulse responses associated with the estimated DOAs, which can also be used as an input for advanced mobile positioning schemes in UMTS. The performance of the combined DOA and joint channel estimation is compared with the conventional channel estimation through simulations in rural and urban propagation environments. Moreover, a novel joint data detection scheme is considered, which explicitly takes into account the signal DOAs and the associated channel impulse responses. The link level performance of a TD-CDMA mobile radio system using these novel schemes is evaluated by Monte Carlo simulations of data transmission, and average bit error rates (BERs) are determined for rural and urban propagation environments. The simulation results indicate that, depending on the propagation environment, the exploitation of the knowledge of the directional inhomogeneity of the mobile radio channel can lead to considerable system performance enhancements.

Video capacity and QoE enhancements over LTE

Quality of Experience (QoE) has taken a center stage in the performance evaluation of multimedia delivery technologies. The Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) system is the latest generation of wireless cellular technology expected to deliver higher data rates and meet the burgeoning data demand. With the projected dominant share of video services in mobile traffic, providing satisfactory QoE to video users is a key objective for LTE system design. In this paper, we present a QoE-based evaluation methodology to assess the LTE system video capacity in terms of the number of unicast video consumers that can be simultaneously supported for a given target QoE. We define and use the notion of rebuffering outage capacity to quantify the video service capacity. Our evaluation further incorporates adaptive streaming, a promising technology for video delivery over wireless, and presents its consequent QoE-capacity tradeoff. The impact of QoE-based outage criteria is also investigated on the downlink video capacity. Finally, we propose a QoE-aware radio resource management (RRM) framework which allows the network operator to further enhance the video capacity. Our results demonstrate that there is a significant potential to optimize video capacity through QoE awareness both at the application level and radio access network (RAN) level.

LTE in the unlicensed spectrum: Evaluating coexistence mechanisms

The Long Term Evolution (LTE) in unlicensed spectrum is an emerging topic in the 3rd Generation Partnership Project (3GPP), which is about an operation of the LTE system in the unlicensed spectrum via license-assisted carrier aggregation. The 5 GHz Unlicensed National Information Infrastructure (U-NII) bands are currently under consideration, but these bands are also occupied by Wireless Local Area Networks (WLAN), specifically those based on the IEEE 802.11a/n/ac technologies. Therefore, an appropriate coexistence mechanism must be augmented to guarantee a peaceful coexistence with the incumbent systems. With this regard, our focus lies on the evaluation of all the proposed coexistence mechanisms so far in a single framework and making a fair comparison of them. The coexistence mechanisms covered in this work includes static muting, listen-before-talk (LBT), and other sensing-based schemes that make a use of the existing WLAN channel reservation protocol.

LTE in the unlicensed spectrum: A novel coexistence analysis with WLAN systems

In this paper, we consider the operation of the Long Term Evolution (LTE) systems in the unlicensed spectrum. Given the lack of the exclusive use of the spectrum, the operation in the unlicensed band is fundamentally limited by interference from other technologies using the same frequency band. By noting that the unlicensed spectrum is heavily used by Wireless Local Area Networks (WLAN), here we focus on the mutual effect between LTE and WLAN when they coexist. For this, we developed a novel inter-system interference analysis technique based on the continuum field approximation and spiral representation, which improves the accuracy of the previous approaches and is applicable to both large-scale and small-scale networks. To this end, we quantify the effect of inter-system interference when the LTE and WLAN systems operate in the same unlicensed spectrum.

Evaluation of Joint Transmission CoMP in C-RAN based LTE-A HetNets with large coordination areas

Coordinated Multi-Point (CoMP) transmission is considered as one of the key technology enhancements for Rel-11 LTE-A systems. CoMP transmission is realized by exchanging coordination information between a set of transmission nodes, forming a so-called CoMP cluster. The size of the CoMP cluster is typically limited, which leads to cell-edge performance issues appearing at the CoMP cluster boundaries. However, in new radio access network (RAN) architectures such as Cloud RAN (C-RAN) the effect of cell-edge user performance degradation at the CoMP cluster boundaries can be minimized by considering larger CoMP coordination areas. In this paper, we investigate the Joint Transmission (JT) CoMP performance in a C-RAN implementation of LTE-A HetNet with large CoMP cluster sizes. Some approaches to minimize the CoMP processing requirements for this case are also discussed. As a baseline for comparison, the LTE-A time-domain enhanced Inter-Cell Interference Coordination (eICIC) scheme which has no coordination boundary issues is considered.

Downlink Spectral Efficiency of Mobile WiMAX

Mobile WiMAX is an OFDMA (orthogonal frequency division multiple access) mobile broadband air interface defined by the IEEE 802.16 family of standards and promoted by the WiMAX Forum as a solution to the requirements for mobile Internet services. Mobile WiMAX employs a number of radical enhancements, such as scalable OFDMA and advanced antenna techniques as basic features, compared to existing mobile technologies. This paper presents the results of extensive simulations to evaluate the downlink performance of mobile WiMAX employing MIMO. The results show that the use of OFDMA, large channel bandwidths, and MIMO techniques enables mobile WiMAX to provide a spectrally efficient cellular communications system suitable for broadband wireless services.

Medium access design for LTE in unlicensed band

In this paper, a medium access protocol suitably adapted for the operation of Long term evolution (LTE) in unlicensed band (LTE-U) is proposed. The MAC design considers the impact of LTE-U on the devices operating in unlicensed band, such as WiFi and legacy LTE. The LTE-U design differences from the legacy LTE system, an inherently a synchronized, tightly controlled system are explored. The performance of LTE-U is studied via a detailed system level simulator implementation and 3GPP simulation test scenarios. We show that our proposed MAC design enables high throughput in unlicensed band and achieves co-existence with the incumbent systems. Moreover, the use of channel reservation mechanisms is shown to improve LTE-U cell edge performance.

LTE with listen-before-talk in unlicensed spectrum

We consider the adoption of listen-before-talk (LBT) for Long Term Evolution (LTE) in unlicensed spectrum, which is currently under discussion in the 3rd Generation Partnership Project (3GPP). The first and foremost task to be done to allow LTE to use unlicensed spectrum is to study the coexistence with incumbent system, such as the Wireless Local Area Network (WLAN). In our study, we observe that a proper coexistence mechanism is imperative especially when both LTE Evolved Node Bs (eNBs) and WLANs are located outdoor. The outdoor deployment scenario is considered by the next generation WLAN, the IEEE 802.11ax, with high importance. The implementation of LBT in LTE plays an effective role in this scenario in balancing the performance between LTE and WLAN. In the conventional scenario where WLANs are located indoor and LTE eNBs are located outdoor, a plain coexistence without additional mechanism could be acceptable due to high penetration loss of outdoor walls.

RAN architecture options and performance for 5G network evolution

This paper discusses various RAN architecture design options, from fully centralized cloud-RAN to fully distributed edge cloud, as candidates for 5G network evolution. System-level performance is evaluated for each architecture option, while we also outline our vision for 5G network performance based on our extensive simulation studies. We further discuss the role of network virtualization, its challenges, and the expected technical and economic benefits for implementing the different RAN architecture options for 5G networks.