Dense deployment which brings small base stations (BS) closer to mobile devices is considered as a promising solution to the booming traffic demand. Meanwhile, the utilization of new frequency bands and spectrum aggregation techniques provide more options for spectrum choice.Whether to increase BS density or to acquire more spectrum is a key strategic question for mobile operators. In this paper, we investigate the relationship between BS density and spectrum with regard to individual user throughput target. Our work takes into account load-dependent interference model and various traffic demands. Numerical results show that densification is more effective in sparse networks than in already dense networks. In sparse networks, doubling BS density results in almost twofold throughput increase. However, in dense networks where BSs outnumber users, more than 10 times of BS density is needed to double user throughput. Meanwhile, spectrum has a linear relationship with user throughput for a given BS density. The impact of traffic types is also discussed. Even with the same area throughput requirement, different combination of user density and individual traffic amount leads to different needs for BS density and spectrum.

Dense deployment of base stations (BSs) and multi-antenna techniques are considered as key enablers for future mobile networks. Meanwhile, spectrum sharing techniques and utilization of higher frequency bands make more bandwidth available. An important question for future system design is which element is more effective than others. In this paper, we introduce the concept of technical rate of substitution (TRS) from microeconomics and study the TRS of spectrum in terms of BS density and antenna number per BS. Numerical results show that TRS becomes higher with increasing user data rate requirement, suggesting that spectrum is the most effective means of provisioning extremely fast mobile broadband.

the continuing growth in the mobile data traffic magnifies the challenges for the design and deployment of scalable high-capacity mobile networks that can meet the future demand at reasonable cost levels. In order to meet the future traffic demand, an operator should invest on both infrastructure, i.e. densification of base stations, and more radio spectrum. Knowing the effectiveness of each element is thus of utmost importance for minimizing the investment cost. In this paper, we study the economic substitutability between spectrum and densification. For this, we measure the engineering value of spectrum, which refers to the potential saving in the total cost of ownership (TCO) as result of acquiring additional spectrum resources. Two countries are considered to represent different market situations: India with dense population and high spectrum price and Sweden with moderate population density and low spectrum fee. Numerical results indicate that additional amount of spectrum substantially relieves the need for densifying radio base stations, particularly for providing high user data rate in dense India. Nonetheless, the engineering value of spectrum is low in India (i.e. spectrum acquisition has less cost benefit) under the high spectrum price of today, whereas spectrum is instrumental in lowering the total cost of ownership in Sweden. Our finding highlights the importance of affordable and sufficient spectrum resources for future mobile broadband provisioning.

In this paper, we investigate the impact of networkdensification on the performance in terms of downlink signal-tointerference(SIR) coverage probability and network area spectralefficiency (ASE). A sophisticated bounded dual-slope path lossmodel and practical UE densities are incorporated in the analysis.By using stochastic geometry, we derive an integral expressionalong with closed-form bounds of the coverage probability andASE, validated by simulation results. Through these, we providethe asymptotic behavior of ultra-densification. The coverageprobability and ASE have non-zero convergence in asymptoticregions unless UE density goes to infinity (full load). Meanwhile,the effect of UE density on the coverage probability is analyzed.The coverage probability will suffer from decreasing with largeUE densities due to interference fall into the near-field, but it willkeep increasing with lower UE densites. Furthermore, we showthe performance is overestimated without applying the boundeddual-slope path loss model. Our study can give insights on efficientnetwork provisioning in the future.

In an Ultra-dense network (UDN) where there aremore base stations (BSs) than active users, it is possible thatmany BSs are instantaneously left idle. Thus, how to utilizethese dormant BSs by means of cooperative transmission is aninteresting question. In this paper, we investigate the performanceof a UDN with two types of cooperation schemes: non-coherentjoint transmission (JT) without channel state information (CSI)and coherent JT with full CSI knowledge. We consider a boundeddual-slope path loss model to describe UDN environments wherea user has several BSs in the near-field and the rest in thefar-field. Numerical results show that non-coherent JT cannotimprove the user spectral efficiency (SE) due to the simultaneousincrement in signal and interference powers. For coherent JT, theachievable SE gain depends on the range of near-field, the relativedensities of BSs and users, and the CSI accuracy. Finally, weassess the energy efficiency (EE) of cooperation in UDN. Despitecosting extra energy consumption, cooperation can still improveEE under certain conditions.