Reliable machine-to-machine multicast services with multi-radio cooperative retransmissions

The final publication is available at Springer via http://dx.doi.org/10.1007/s11036-015-0575-6The 3GPP is working towards the definition of service requirements and technical solutions to provide support for energy-efficient Machine Type Communications (MTC) in the forthcoming generations of cellular networks. One of the envisioned solutions consists in applying group management policies to clusters of devices in order to reduce control signaling and improve upon energy efficiency, e.g., multicast Over-The-Air (OTA) firmware updates. In this paper, a Multi-Radio Cooperative Retransmission Scheme is proposed to efficiently carry out multicast transmissions in MTC networks, reducing both control signaling and improving energy-efficiency. The proposal can be executed in networks composed by devices equipped with multiple radio interfaces which enable them to connect to both a cellular access network, e.g., LTE, and a short-range MTC area network, e.g., Low-Power Wi-Fi or ZigBee, as foreseen by the MTC architecture defined by ETSI. The main idea is to carry out retransmissions over the M2M area network upon error in the main cellular link. This yields a reduction in both the traffic load over the cellular link and the energy consumption of the devices. Computer-based simulations with ns-3 have been conducted to analyze the performance of the proposed scheme in terms of energy consumption and assess its superior performance compared to non-cooperative retransmission schemes, thus validating its suitability for energy-constrained MTC applications.Peer ReviewedPostprint (author's final draft

Improved scheduling techniques for efficient uplink communications with carrier aggregation

Transmitted power in Long Term Evolution - Advanced (LTE-A) uplink (UL) is strongly related to the number of physical resource blocks (PRBs) allocated. As the transmitted bandwidth increases power does so. However, this rise in power is also required to increase throughput. It is necessary to create efficient techniques that allows sending more information (bits) with the same power requirements. Against previous LTE releases, LTE-A allows the use of non-contiguous resource allocation in the UL together with the simultaneous transmission along multiple component carriers named, carrier aggregation. These features lead to an increase in spectral efficiency thanks to ling performance gains obtained from frequency diversity. This work studies the effect of scheduling techniques on the throughput performance and power consumption of users. Results show that cell edge performance is very sensitive to the scheduling decisions, therefore, limitations in bandwidth are introduced in order to reduce power consumption and improve throughput. Carrier Aggregation turns out to be more efficient as users can be classified and improve spectral and energy efficiency.Peer ReviewedPostprint (published version

THROUGHPUT OPTIMIZATION AND ENERGY EFFICIENCY OF THE DOWNLINK IN THE LTE SYSTEM

Nowadays, the usage of smart phones is very popular. More and more people access the Internet with their smart phones. This demands higher data rates from the mobile network operators. Every year the number of users and the amount of information is increasing dramatically. The wireless technology should ensure high data rates to be able to compete with the wire-based technology. The main advantage of the wireless system is the ability for user to be mobile. The 4G LTE system made it possible to gain very high peak data rates. The purpose of this thesis was to investigate the improvement of the system performance for the downlink based on different antenna configurations and different scheduling algorithms. Moreover, the fairness between the users using different schedulers has been analyzed and evaluated. Furthermore, the energy efficiency of the scheduling algorithms in the downlink of LTE systems has been considered. Some important parts of the LTE system are described in the theoretical part of this thesis.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Energy efficiency in cellular wireless networks

Energy efficiency of Long Term Evolution (LTE) cellular communication networks has become a major concern for network operators, not only to reduce the operational costs, but also to reduce their environmental effects. Within LTE cellular networks, base stations are responsible for most of the energy consumption, consuming 70-95% or more of the network power depending on the network topology, configuration, radio technology and data rates that are used. Power control is an important function in cellular wireless networks and refers to setting the output power levels of transmitters, termed eNodeB in the downlink and user equipment (UEs) in the uplink. LTE utilizes two different mechanisms for uplink power control: Open Loop Power Control (OLPC) and Closed Loop Power Control (CLPC). Uplink OLPC is performed by the UE following eNodeB configuration and can compensate for long term channel variation such as path loss and shadowing. The uplink CLPC mechanism attempts to improve power control performance by compensating fast channel variations due to multipath fading. In CLPC the eNodeB sends Transmit Power Control (TPC) commands to the UE to adjust the UE’s transmit power. This thesis focuses on an Open Loop Power Control (OLPC) scheme for LTE uplink by using the Okumura-Hata propagation path loss model to set the User Equipment (UE) uplink transmit power control parameters in order to reduce the UE energy consumption. In general, the UE requires more power to connect to distant base stations than closer base stations and therefore this thesis analyses the required power levels using the Okumura-Hata propagation path loss model. Estimation of path loss is very important in initial deployment of wireless network and cell planning. This thesis analyses the Okumura-Hata propagation path loss in different receiver antenna heights (

Spectrum and Energy Efficient Medium Access Control for Wireless Ad Hoc Networks

The increasingly growing number of mobile devices and volume of mobile data traffic necessitate establishing an effective self-organizing wireless ad hoc network to efficiently utilize radio spectrum and energy. The transmissions time and bandwidth should be dynamically coordinated based on instantaneous traffic load of the links in the network. Energy consumption in a mobile device can be reduced by putting the radio interface into a sleep mode. However, the mobile device cannot receive incoming data packets in the sleep mode. Thus, awake and sleep times of radio interfaces should be carefully planned to avoid missing incoming packets. In a wireless network, links that are far apart in distance can simultaneously transmit using the same bandwidth without interfering reception at destination nodes. Concurrent transmissions should be properly scheduled to maximize spatial spectrum utilization. Also, the transmission power level of each link should be optimized to enhance spectrum and energy efficiencies. First, we present a new energy-efficient medium access control (MAC) scheme for a fully connected wireless ad hoc network. Energy consumption is reduced by periodically putting radio interfaces in the sleep mode and by reducing transmission collisions. The network throughput and average packet transmission delay are also improved because of lower collision and contention overhead. The proposed MAC scheme can achieve energy saving for realtime traffic which requires a low packet transmission delay. An analytical model is established to evaluate the performance of the proposed MAC scheme. Analytical and simulation results demonstrate that the proposed scheme has a significantly lower energy consumption, achieves higher throughput, and has a lower packet transmission delay in comparison with existing power saving MAC protocols. Second, we present a novel distributed MAC scheme based on dynamic space-reservation to effectively coordinate transmissions in a wireless ad hoc network. A set of coordinator nodes distributed over the network area are employed to collect and exchange local network information and to periodically schedule links for transmission in a distributed manner. For each scheduled transmission, a proper space area around the receiver node is reserved to enhance spatial spectrum reuse. Also, the data transmission times are deterministic to minimize idle-listening radio interface energy consumption. Simulation results demonstrate that the proposed scheme achieves substantially higher throughput and has significantly lower energy consumption in comparison with existing schemes. We study joint scheduling and transmission power control in a wireless ad hoc network. We analyze the asymptotic joint optimal scheduling and transmission power control, and determine the maximum spectrum and energy efficiencies in a wireless network. Based on the asymptotic analysis, we propose a novel scheduling and transmission power control scheme to approach the maximum spectrum efficiency, subject to an energy consumption constraint. Simulation results show that the proposed distributed scheme achieves 40% higher throughput than existing schemes. Indeed, the scheduling efficiency of our proposed scheme is about 70% of the asymptotic optimal scheduling and transmission power control. Also, the energy consumption of the proposed scheme is about 20% of the energy consumed using existing MAC protocols. The proposed MAC, scheduling and transmission power control schemes provide effective spectrum sharing and energy management for future wireless hotspot and peer-to-peer communication networks. The presented asymptotic analysis determines the maximum spectrum and energy efficiencies in a wireless network and provides an effective means to efficiently utilize spectrum and energy resources based on network traffic load and energy consumption constrains

Cooperative Uplink Inter-Cell Interference (ICI) Mitigation in 5G Networks

In order to support the new paradigm shift in fifth generation (5G) mobile communication, radically different network architectures, associated technologies and network operation algorithms, need to be developed compared to existing fourth generation (4G) cellular solutions. The evolution toward 5G mobile networks will be characterized by an increasing number of wireless devices, increasing device and service complexity, and the requirement to access mobile services ubiquitously. To realise the dramatic increase in data rates in particular, research is focused on improving the capacity of current, Long Term Evolution (LTE)-based, 4G network standards, before radical changes are exploited which could include acquiring additional spectrum. The LTE network has a reuse factor of one; hence neighbouring cells/sectors use the same spectrum, therefore making the cell-edge users vulnerable to heavy inter cell interference in addition to the other factors such as fading and path-loss. In this direction, this thesis focuses on improving the performance of cell-edge users in LTE and LTE-Advanced networks by initially implementing a new Coordinated Multi-Point (CoMP) technique to support future 5G networks using smart antennas to mitigate cell-edge user interference in uplink. Successively a novel cooperative uplink inter-cell interference mitigation algorithm based on joint reception at the base station using receiver adaptive beamforming is investigated. Subsequently interference mitigation in a heterogeneous environment for inter Device-to-Device (D2D) communication underlaying cellular network is investigated as the enabling technology for maximising resource block (RB) utilisation in emerging 5G networks. The proximity of users in a network, achieving higher data rates with maximum RB utilisation (as the technology reuses the cellular RB simultaneously), while taking some load off the evolved Node B (eNodeB) i.e. by direct communication between User Equipment (UE), has been explored. Simulation results show that the proximity and transmission power of D2D transmission yields high performance gains for D2D receivers, which was demonstrated to be better than that of cellular UEs with better channel conditions or in close proximity to the eNodeB in the network. It is finally demonstrated that the application, as an extension to the above, of a novel receiver beamforming technique to reduce interference from D2D users, can further enhance network performance. To be able to develop the aforementioned technologies and evaluate the performance of new algorithms in emerging network scenarios, a beyond the-state-of-the-art LTE system-level-simulator (SLS) was implemented. The new simulator includes Multiple-Input Multiple-Output (MIMO) antenna functionalities, comprehensive channel models (such as Wireless World initiative New Radio II i.e. WINNER II) and adaptive modulation and coding schemes to accurately emulate the LTE and LTE-A network standards