Research On Critical Issues Of Resource Optimization In Wireless Heterogeneous Network

The rapid growth of mobile data traffic in the past decades has led to the consequence of "the service-providing capability of the mobile networks becomes increasingly inadequate to satisfy the mobile users' demand".Since the existing communication networks are expected to deliver an ever-increasing volume data traffics.both the spectral efficiency(SE)and the throughput of the networks have to be substantially improved.Wireless heterogeneous networks(HetNets),which comprise architectures of both macro-and micro-cells,have been regarded as a promising solution for overcoming the above-mentioned challenges by providing efficient and seamless ubiquitous broadband wireless access for mobile users.Relying on HetNets,both the SE of the networks and the Quality of Service(QoS)of mobile users,particularly at specific areas(e.g.cell edge and hot spot areas),can be substantially improved.Furthermore,some new techniques such as device-to-device(D2D)have also been employed in HetNets.Despite all this,there still exist several challenges in operating and optimizing HetNets.First,the serious cross-tier interference residing in HetNets may significantly erode the SE of the whole network.Second,the tidal effect of mobile traffics observed in HetNets may inevitably degarde the energy efficiency(EE)of whole network.Last but not least,a significant load imbalance may exist between the D2D and cellular links,thus leading to a degarded resource utilization in HetNets.To address the above-mentioned issues,we mainly focus on investigating the resource optimization techniques in HetNets and giving full consideration to the the critical functionalities such as power control,spectrum sharing,base station sleeping and interference management,etc.The performance of HetNets in terms of SE,EE,capacity and throughput are analyzed and optimized in this dissertation.The main innovations of this dissertation are reflected as follows:(1)Unlike the existing "random-based user-pairing scheduling" schemes that has been widely employed in HetNets,a user-pairing based power control algorithm is proposed by taking both the user diversity and user-pairing scheduling into consideration.It is shown that the proposed scheme is capable of gaining the remarkable performance superiority over the traditional algorithm in terms of the SE.(2)The "base station sleeping" algorithm is proposed based on the partial-spectrum-reuse(PSR)scheme,followed by deriving the closed-form relationship between the optimal PSR factor and base station active probability ratio.After that,a joint scheme by combining the advantages of both the PSR and the base station sleeping is proposed for the purpose of improving the EE of HetNets.It is shown that the proposed joint scheme is capable of improving the network EE compared with the conventional scheme that employs an individual scheme(i.e.employing either PSR or base station sleeping),whilst without eroding the average ergodic rate of the HetNets.(3)Unlike the existing half-duplex(HD)mode D2D communications that has been widely employed in HetNets,the benefits brought about by implementing FD-D2D aided underlaying networks was analyzed,showing that the FD-D2D communication is capable of improving the sum throughput of the underlaying networks due to its essential capabilities of shortening the wireless link length and lowering the transmit power,despite of a much more severe interference than the HD-D2D mode imposed on the users.In addition,to guarantee the quality of cellular links,a Dynamic Cellular Link Protection(DCLP)mechanism is further proposed to prevent the D2D links from activation within the pre-set guard area.It is shown that the proposed DCLP mechanism is capable of improving the cellular links' throughput without significantly eroding the throughput of the D2D links.In conclusion,the main contributions of this dissertation are summarized as follows:?A user-pairing based non-cooperation power cotrol game is proposed for optimizing the SE of HetNets,with up to 30%SE improvement attained;?A PSR and base station sleeping based joint optimization scheme is proposed for optimizing the EE of HetNets,with up to 50%EE improvement obtained;?For optimizing the sum throughput of D2D based HetNets,a DCLP mechanism is proposed by addressing the critical problem of load imbalance that widely resides in D2D aided underlaying networks.