The continuous development of wireless networks and mobile devices has motivated an intense research in mobile data services. Some of these services provide the user with context-aware information. Specifically, location-based services and location-dependent queries have attracted a lot of interest.In this article, the existing literature in the field of location-dependent query processing is reviewed. The technological context (mobile computing) and support middleware (such as moving object databases and data stream technology) are described, location-based services and location-dependent queries are defined and classified, and different query processing approaches are reviewed and compared.

https://webdiis.unizar.es/~silarri/PUBLICATIONS/acmSurvLDQP09.pdf

Location-dependent query processing: Where we are and where we are heading

This paper investigates flexible spectrum usages for LTE network that consists of overlaying macrocell and femtocell. In such a networking environment, shared spectrum usage and partitioned spectrum usage are two options to be employed between two radio tiers. After recognizing the pros and cons of these two usages, we propose hybrid spectrum usage to take advantage of their merits. In our proposal, the femtocells embedded in macrocell are differentiated to inner and outer femtocells, which operate in partitioned spectrum usage and shared spectrum usage, respectively. Analysis and performance evaluation are given to illustrate and justify our proposed method on improving spectrum utilization for wireless overlay network.

Hybrid Spectrum Usage for Overlaying LTE Macrocell and Femtocell

In split spectrum macrocell-femtocell networks, certain portion of the available spectrum resources are dedicated to each tier in order to avoid interference problems among the tiers. In such a setting, effective partitioning of the spectrum resources carries critical importance for maximizing the total capacity and satisfying quality of service (QoS) requirements of the users within each tier. This paper proposes spectrum splitting methods for a macrocell-femtocell network considering factors other than the capacity maximization. First, a capacity maximizing spectrum splitting solution is derived based on certain simplifying assumptions. Then, a modified QoS-oriented fairness metric is introduced which captures important characteristics of tiered network structures that are not captured by the Jain''s fairness index. Finally, a spectrum splitting strategy that simultaneously considers capacity maximization, fairness constraints, and QoS constraints is proposed. Example numerical results show that while only considering total capacity maximization may yield unfair spectrum splitting, a more balanced spectrum allocation can be achieved by also considering fairness and QoS constraints.

Fair and QoS-Oriented Spectrum Splitting in Macrocell-Femtocell Networks

Wireless communications systems enable the end users to be mobile. The majority of the wireless communications networks are cellular networks. Several methods are developed to increase the performance of the cellular networks, which depends on the correct determination of the design parameters as well as the architecture of the system and the traffic requirements. In this study, we introduce a Simulated Annealing (SA) based method to determine the design parameters of a multi-tier cellular network, for which the implementation cost is minimized. The cellular system employs guard channels and allows calls to overflow to upper tiers. We conducted experiments with the SA-based technique on different example problems in two-tier cellular networks and obtained promising results.

Multi-Tier Cellular Network Dimensioning

This paper investigates spectrum resource coordination for the mixed macrocell and femtocell deployment. Though sharing spectrum provides larger bandwidth for both macrocell and femtocell, cross-tier interferences exist and become drawbacks for them to achieve higher capacities. After analyzing the interferences when using shared spectrum, we propose to employ hybrid spectrum sharing with respect to different femtocells such that the merit of sharing spectrum can be kept and the major interferences can be reduced. Then, we present a method to mitigate the remaining interference when employing hybrid spectrum sharing. Performance evaluation is given to justify our proposed approach on improving overall spectrum utilization.

Resource coordination and interference mitigation between macrocell and femtocell

The performance in terms of signal-to-interference ratio (SIR), teletraffic, and spectral efficiency of a combined macrocellular and microcellular network is investigated when either both types of cells share the same channel set, or when the channel set is partitioned between the macrocells and the microcells. The analysis is for time-division multiple access (TDMA) with frequency hopping, power control, and discontinuous transmission, and the radio channel is composed of an inverse fourth-power path loss law with log-normal fading. We commence by introducing a single microcell into a hexagonal cluster of macrocells before considering clustered microcells. Both omnidirectional and sectorized cells are examined. We find that high reuse factors are required when channel sharing is employed. When channel partitioning is used, no co-channel interference occurs between the microcells and the macrocells allowing them to be planned independently. The reuse factors in the microcells and macrocells therefore do not need to be increased beyond conventional values. The outcome is that by opting for channel partitioning, the improvement in spectral efficiency compared to channel sharing is two to three times greater.

/pdf/introducing-microcells-into-macrocellular-networks-a-case-1q72tfxmr6.pdf

R. Coombs

Papers

Introducing microcells into macrocellular networks: a case study