LTE Air Interface Research Articles

Coexistence of Cognitive Small Cell and WiFi System: A Traffic Balancing Dual‐Access Resource Allocation Scheme

We consider a holistic approach for dual‐access cognitive small cell (DACS) networks, which uses the LTE air interface in both licensed and unlicensed bands. In the licensed band, we consider a sensing‐based power allocation scheme to maximize the sum data rate of DACSs by jointly optimizing the cell selection, the sensing operation, and the power allocation under the interference constraint to macrocell users. Due to intercell interference and the integer nature of the cell selection, the resulting optimization problems lead to a nonconvex integer programming. We reformulate the problem to a nonconvex power allocation game and find the relaxed equilibria, quasi‐Nash equilibrium. Furthermore, in order to guarantee the fairness of the whole system, we propose a dynamic satisfaction‐based dual‐band traffic balancing (SDTB) algorithm over licensed and unlicensed bands for DACSs which aims at maximizing the overall satisfaction of the system. We obtain the optimal transmission time in the unlicensed band to ensure the proportional fair coexistence with WiFi while guaranteeing the traffic balancing of DACSs. Simulation results demonstrate that the SDTB algorithm could achieve a considerable performance improvement relative to the schemes in literature, while providing a tradeoff between maximizing the total data rate and achieving better fairness among networks.

Physical Downlink Control Channel for Beyond LTE-Advanced

With the rapid deployment of LTE, the standardization activities of releases beyond LTE-Advanced (LTE-A) are recently being actively progressed in 3GPP. The emerging services and key enhancements such as Further Enhancement of Downlink Multiple-Input Multiple-Output (MIMO), Heterogeneous Networks, and Carrier Aggregation (CA) in LTE-A has revealed and motivated the standardization of an enhanced physical control channel(s) for the LTE air interface. The advanced Physical Downlink Control Channel (PDCCH) design shall be able to support increased control channel capacity, to support frequency domain Inter Cell Interference Coordination (ICIC), to achieve improved spatial reuse of control channel resource, to support beamforming and/or diversity and at the same time able to support flexible resource allocation of control channel. In this paper, we analyzed the features and capacity of enhanced control channels considered in LTE, starting with the motivations and the standardized Enhanced PDCCH (EPDCCH). The paper proceeds to consider the PDCCH design for 5G New Radio (NR) with the advantages of both PDCCH and EPDCCH while mitigating the limitations of them. Moreover, simulation results are presented to exhibit clear performance benefits of EPDCCH and NR-PDCCH.

LTE/Wi-Fi Coexistence in 5 GHz ISM Spectrum: Issues, Solutions and Perspectives

The introduction of a high number of small cells in cellular networks and the complementary adoption of WLAN technologies in unlicensed spectrum are interesting options to attend the increasing demand for Internet traffic in wireless broadband access networks. One alternative for integrating both solutions is the aggregation of ISM unlicensed spectrum to licensed bands, using wireless networks defined by IEEE and 3GPP. While Wi-Fi networks are aggregated to LTE small cells via LTE/WLAN Aggregation (LWA), in proposals like LTE-U and LAA-LTE, the LTE air interface itself is used for transmission on the unlicensed band. Wi-Fi technology is widespread and also operates in the 5 GHz ISM spectrum bands, which may bring performance issues due to the coexistence of both technologies in the same spectrum band. This work is dedicated to the study of coexistence between LTE and Wi-Fi access systems operating in 5 GHz ISM Spectrum. A distributed coordination mechanism is proposed and evaluated via system-level simulations, and results indicate that the proposed solutions provide significant gains when compare to the situation without distributed coordination.

Comprehensive Spectrum Management for Heterogeneous Networks in LTE-U

Recent interesting activities in spectrum analysis have introduced an additional band, the 5 GHz unlicensed spectrum, which has been primarily used for Wi-Fi. There are many challenges related to the coexistence of two different networks, a Wi-Fi network and an LTE network, sharing unlicensed bands but causing interference with each other. In this article, to solve the coexistence challenges, we propose a new protocol for carrier sensing and interference avoidance for heterogeneous networks: carrier sense LTE unlicensed access (CASLUA). The key idea of this protocol is that it listens to the channel by using a Wi-Fi air interface, but actually transmits data via an LTE air interface. This is achieved by using a proposed dual frame aggregation scheme where two frames (an L-frame and a U-frame) are allocated to licensed and unlicensed bands, respectively. Two implementations of CASLUA are carried out, one based on standalone operation (S-CASLUA)and the other operating with assistance from a software-defined network controller (SDN-CASLUA). SDN assistance lies in the monitoring of multiple network parameters, which are then used to make a decision on effective spectrum allocation with awareness of interference and capacity demands. Simulation results show that the CASLUA protocol helps to avoid interference and increases the average throughput by up to 40 percent for both Wi-Fi and LTE users in LTE-Unlicensed.

Wireless Communication for Factory Automation: an opportunity for LTE and 5G systems

The evolution of wireless communication from 4G toward 5G is driven by application demands and business models envisioned for 2020 and beyond. This requires network support for novel use cases in addition to classical mobile broadband services. Wireless factory automation is an application area with highly demanding communication requirements. We classify these requirements and identify the opportunities for the current LTE air interface for factory automation applications. Moreover, we give an outlook on the relevant design considerations to be addressed by 5G communication systems.

Performance Evaluation of Multi Antenna Techniques in LTE

High data rate requirements of the Long Term Evolution - Advanced (LTE-A) systems can be achieved by adopting advanced Multiple Input Multiple Output (MIMO) antenna techniques on both uplink and downlink. The LTE air-interface supports multiple-antenna transmit arrays and different modes of multiple antenna transmissions. In this paper, performance of different MIMO techniques is evaluated using QualNet network simulator. The MIMO techniques considered for performance evaluation are SingleInput/Multiple-Output (SIMO), Open Loop Spatial Multiplexing (OLSM) and Space-Frequency Block Coding (SFBC). The performance metrics considered are throughput, delay and jitter.

A survey on 3GPP heterogeneous networks

As the spectral efficiency of a point-to-point link in cellular networks approaches its theoretical limits, with the forecasted explosion of data traffic, there is a need for an increase in the node density to further improve network capacity. However, in already dense deployments in today's networks, cell splitting gains can be severely limited by high inter-cell interference. Moreover, high capital expenditure cost associated with high power macro nodes further limits viability of such an approach. This article discusses the need for an alternative strategy, where low power nodes are overlaid within a macro network, creating what is referred to as a heterogeneous network. We survey current state of the art in heterogeneous deployments and focus on 3GPP LTE air interface to describe future trends. A high-level overview of the 3GPP LTE air interface, network nodes, and spectrum allocation options is provided, along with the enabling mechanisms for heterogeneous deployments. Interference management techniques that are critical for LTE heterogeneous deployments are discussed in greater detail. Cell range expansion, enabled through cell biasing and adaptive resource partitioning, is seen as an effective method to balance the load among the nodes in the network and improve overall trunking efficiency. An interference cancellation receiver plays a crucial role in ensuring acquisition of weak cells and reliability of control and data reception in the presence of legacy signals.