Abstract
In a context of energy saving and operational cost reduction, energy efficiency (EE) has emerged as an important performance metric in cellular networks. According to the famous Shannon’s capacity theorem, maximising the EE while maximising the spectral efficiency (SE) are conflicting objectives, hence, both metrics can be jointly studied via their trade-off, i.e. the EE-SE trade-off. In this context, the aim of this thesis is to investigate the fundamental trade-off between EE and SE in futuristic cellular networks where distributed multiple-input multiple output (DMIMO) or coordinated multi-point (CoMP) scheme is utilised for meeting the high data rate of the next generation wireless communication networks. Focusing on the DMIMO system, a novel tight closed-form approximation of its EE-SE trade-off is derived and its accuracy verified for both the uplink and downlink channels and for both the idealistic and realistic power consumption models (PCMs). In addition, the low and high-SE regime approximations of the DMIMO EE-SE trade-off are derived in the uplink and downlink channels. Furthermore, these approximations are utilised for assessing both the EE gain of the DMIMO over the co-located MIMO (CMIMO) and the incremental EE gain of DMIMO in the downlink channel. It is observed that DMIMO is more energy efficient than CMIMO for cell edge users in both PCMs; whereas the results for realistic incremental EE gain indicate that the optimal approach in terms of EE is to connect the user terminal to only one radio access unit. Focusing on the uplink of the CoMP system, a generic closed-form approximation of the EE-SE trade-off is derived and its accuracy is demonstrated for both the idealistic and realistic PCMs. Asymptotic approximations of this trade-off in both the low and high SE regimes are also presented. Furthermore, these approximations are utilised to compare the EE of the CoMP system with the EE of the traditional non-cooperative system with orthogonal multiple access scheme. It is observed that in the idealistic PCM, CoMP is more energy efficient than the non-cooperative system due to a reduction in power consumption; whereas in the realistic PCM, CoMP can also be more energy efficient but due to an improvement in SE and mainly for cell-edge communication and small cell deployment.