Practical network coding schemes for energy efficient long term evolution radio access network

Cellular mobile networks are facing the big challenge of delivering high data rates with high reliability everywhere and anytime in order to support the explosive demand for new applications and services. In their current design, however, this data delivery is being achieved by the corresponding increase of the consumed energy. This trend is clearly unsustainable and at some point in the future it will become a limiting factor of delivering the applications and services in the desired (quality. Moreover, the high energy consumption negatively affects the operational cost and significantly contribute to CO2 emission. The mobile operators are committed to overcome both of these issues. Motivated by the energy efficiency of wireless networks, we investigate the transmission protocols which are exploiting the concept of Network Coding (NC) in order to achieve throughput improvements with reduced energy consumption. NC is known to achieve the throughput improvements but its energy consumption savings have not been studied in cellular mobile networks. Hence, this thesis focuses on the implementation aspects and evaluation of benefits of the distributed coding, NC and fountain coding in the Long Term Evolution (LTE) and LTE-Advanced (LTE-A) cellular systems under realistic constraints and assumptions. This thesis presents two practical inter-flow and intra-flow NC transmission protocols that improve the throughput, reduce the energy consumption, save physical layer transmission resources and create distinctive energy-delay trade-offs characteristics in LTE and LTE-A networks. The contributions of this thesis are concerned with the energy metrics definitions, and with the implementations of inter-flow NC, intra-flow NC in the LTE networks with and without the relay nodes. First, the energy metrics are established for cellular mobile networks to evaluate their power and energy consumption. The specified energy metrics are applicable to network equipment, links, subsystems and to the overall radio access network. The energy metrics used are discussed in light of the relevant standardization activities of the wireless access networks. Second, a practical inter-flow NC protocol for the LTE network is introduced. The integration of the protocol within the LTE protocol Stack is examined. The implementation aspects and constraints of the NC protocol for the LTE relay network is considered in order to assess the usefulness of the NC under realistic assumptions. The usefulness of the NC protocol is evaluated for varying traffic load levels, varying geographical distances between the nodes, varying transmit powers, and different maximum numbers of retransmissions. Energy savings of 16 - 25% depending on the traffic in the network is achieved. Third, the scalability of the inter-flow NC protocol is investigated for multiple users and for various traffic loads. Energy savings are also attained when the number of users is increased and 25% savings is obtained for 4 users. The performance of this NC scheme is assessed in terms of the radio-frequency power as well as the radio overhead power, the throughput gain and the number of physical layer resources saved. Fourth, it is shown that the Medium Access Control (MAC) layer is well suited to incorporate the inter-flow NC and intra-flow NC schemes. The intra-flow NC implemented at the AIAC layer is found to have many benefits and to achieve good performance gains compared to its originally intended implementation at the application layer. Intra-flow NC schemes outperform, under certain conditions, the standardized Hybrid Automatic Repeat Request (HARQ) schemes in terms of the energy consumption, the amount of radio resources used, and the transmission latency. The main findings of our investigations are: the performance of network coding is affected by the ratio of transmit powers of the nodes involved in NC, MAC layer is well suited for implementing the intra-flow as well as inter-flow network coding schemes, and the intra-flow NC strongly effects the design and performance of adaptive transmission strategies including the adaptive modulation and coding schemes.