Resource Management for Heterogeneous Networks in LTE Systems

Mobile communications, which enable anytime and anywhere ubiquitous connectivity, have been an integrated part of our daily life. With the widespread adoption of smart mobile devices such as smart phones, tablets and ultra-portable laptops and the subsequent explosive expansion of bandwidth-hungry mobile applications, wireless communication traffic continues to grow rapidly. As voice traffic grows at a steady rate, the major traffic explosion comes from data communications. According to Cisco’s Visual Networking Index, data traffic has been more than doubled in both 2011 and 2012. Projection through 2018 expects a compound annual growth rate (CAGR) of around 50 % [1]. To sustain such a traffic growth and in the meantime to improve user experience and network coverage, continuous innovations on wireless data communication technologies are required.

A two-tier heterogeneous network model in LTE is studied throughout this book. As shown in Fig. 2.1, consider downlink communications in a heterogeneous cellular network with high transmit power macro evolved Node Bs (MeNB) and low transmit power small evolved Node Bs (SeNB) or relay nodes (RN). Each macro cell is divided into several sectors served by directional antennas. Within each macro cell sector, there are several SeNBs or RNs uniformly distributed.

Traditional way of mobile association is based on a best-power approach where each UE associates with the eNB that it receives the highest power from. In heterogeneous networks, however, due to the disparity in transmit power of the macro and small cell eNBs, if best-power based mobile association is again used, most of the UEs will associate with the macro eNBs leaving the small cell eNBs largely under-utilized.

As illustrated in Fig. 4.1, in an FFR scheme, the total sub-bands F is divide d into two parts, f ₁ and f ₂ with size F ₁ and F ₂, respectively.

Intra-cell coordinated multiple point (CoMP) transmission is discussed in Chap. 2. Downlink intra-cell cooperative transmission and optimal intra-cell CoMP resource allocation schemes are investigated in heterogeneous networks with cooperative relays in [1–3]. In this chapter, radio resource allocation schemes for two-tier heterogeneous networks in LTE are further discussed. Radio resource allocation schemes with intra-cell CoMP and in-band wireless backhaul are studied, and an optimal framework with resource allocation strategy is presented that is asymptotically optimal on the proportional fairness metric.

Global mobile traffic increases 66 times with an annual growth rate of 131 % between 2009 and 2014. On the contrary, the peak data rate from 3G to 4G wireless technology only increases 55 % annually. Clearly there is a huge gap between the capacity growth of new wireless access technologies and the growth of wireless data traffic demand. As wireless channel efficiency is approaching its fundamental limit, future improvements on the wireless capacity are more likely achieved by infrastructure technologies such as node density increase, cooperative and collaborative radio resource management techniques. Moreover, the fast growing data traffic volume and dramatic expansion of network infrastructures will inevitably trigger tremendous escalation of energy consumption in mobile wireless networks, the growing energy consumption becomes one of the major challenges in meeting the cost reduction and green environment targets. To meet those goals, heterogeneous network deployment has emerged as a new trend to enhance the capacity/coverage and to save energy consumption for the next generation wireless networks. A heterogeneous network, or HetNet, is a wireless network containing nodes with different transmission powers and coverage sizes. High power nodes with large coverage areas are deployed in a planned way for blanket coverage of urban, suburban, or rural areas. Low power nodes with small coverage areas aim to complement the high power nodes for coverage extension and throughput enhancement. Furthermore, the infrastructure featuring a high density deployment of low power nodes can also greatly improve energy efficiency compared to the one with a low density deployment of fewer high power nodes, owing to the high path loss exponent in a wireless environment.