Radio resource allocation for wireless heterogeneous networks

By deploying small cells (i.e., femtocells) within the same service area of regular macrocells, a much higher area spectral efficiency, better indoor coverage, and significant mobile data offloading can be achieved at low cost.Because femtocells reuse the radio spectrum already assigned to macrocells in an uncoordinated fashion, new cell boundaries are created and the signal interference situation becomes far more unpredictable than in conventional networks.In this heterogeneous network setting, adaptive power allocation and dynamic spectrum access are needed to ensure a harmonized coexistence of network entities with diverse design specifications.Since femtocells are deployed by end users without any network planning, autonomous solutions are desirable to effectively control the severe intra-tier and cross-tier interferences.In this study, we develop and evaluate distributed radio resource allocation algorithms for wireless heterogeneous networks employing code-division multiple access (CDMA) and orthogonal frequency-division multiple access (OFDMA).Requiring no central coordination, the devised solutions robustly protect the ongoing operation of all existing macrocell users, while optimally exploiting the residual network capacity for femtocells.In CDMA-based networks, we propose a dynamic pricing scheme combined with femtocell user admission control to indirectly manage the cross-tier interference.The proposed joint power and admission control algorithms can be locally executed at each link to offer a maximum utility to individual users.For the total network utility maximization, we develop joint Pareto-optimal power control and signal-to-interference-plus-noise ratio (SINR) assignment algorithms that can fairly share radio resources among users.Upon applying convex optimization methods, the minimum SINRs prescribed by macrocell users are effectively enforced, whereas the sum network utility is globally maximized.In OFDMA-based networks, to resolve the highly nonconvex and combinatorial problem of joint power and subchannel allocation, we propose a dynamic spectrum management scheme that alternatively optimizes the powers and assigns the subchannels.With the adopted successive convex approximation approach, the total throughput of all femtocells is maximized whilst the macrocell network capacity is always protected.In cognitive femtocells where femtocell users opportunistically access the spectrum licensed to macrocells, we apply Lagrangian duality to devise jointly optimal power and subchannel allocation algorithms.The distributed solutions are shown to achieve their global optimality with low complexity.

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