Spectrum Leasing as an Incentive towards Uplink Macrocell and Femtocell Cooperation

The concept of femtocell access points underlaying existing communication infrastructure has recently emerged as a key technology that can significantly improve the coverage and performance of next-generation wireless networks. In this paper, we propose a framework for macrocell-femtocell cooperation under a closed access policy, in which a femtocell user may act as a relay for macrocell users. In return, each cooperative macrocell user grants the femtocell user a fraction of its superframe. We formulate a coalitional game with macrocell and femtocell users being the players, which can take individual and distributed decisions on whether to cooperate or not, while maximizing a utility function that captures the cooperative gains, in terms of throughput and delay.We show that the network can selforganize into a partition composed of disjoint coalitions which constitutes the recursive core of the game representing a key solution concept for coalition formation games in partition form. Simulation results show that the proposed coalition formation algorithm yields significant gains in terms of average rate per macrocell user, reaching up to 239%, relative to the non-cooperative case. Moreover, the proposed approach shows an improvement in terms of femtocell users' rate of up to 21% when compared to the traditional closed access policy.Comment: 29 pages, 11 figures, accepted at the IEEE JSAC on Femtocell Network

Interference management in femtocell communication system

[no abstract

INTERFERENCE MITIGATION PADA JARINGAN FEMTOCELL DENGAN PENYESUAIAN DAYA DAN BANDWIDTH MELALUI SKEMA SELF-CONFIGURATION

Seiring berkembangnya teknologi, komunikasi jarak jauh bukan lagi suatu hal yang eksklusif, kebutuhan akan komunikasi semakin tinggi, termasuk untuk di area indoor building. Permasalahan cukup besar yang dialami saat ini adalah sinyal dari BTS menurun drastis karena terhalang dinding dan beton, sehingga diperlukan adanya femtocell untuk menjaga kualitas sinyal. Salah satu permasalahan yang ditemui dalam penggunaan femtocell itu sendiri adalah munculnya interferensi yang dialami oleh pengguna yang berada pada jangkauan langsung BTS macro, yang dikenal dengan interferensi cross-tier. Permasalahan berikutnya yang muncul dari interferensi tersebut adalah tidak meratanya throughput yang diterima oleh pengguna femtocell. Salah satu skema untuk memaksimalkan kembali kualitas sinyal yang diterima oleh pengguna indoor building atas permasalahan interferensi jenis tersebut adalah dengan skema self-configuration. Siterapkannya sistem reward dan penalty pada skema tersebut, throughput yang didapatkan oleh setiap pengguna akan terus dipantau, sehingga pada akhirnya mendapat throughput diatas nilai yang diinginkan dengan tidak terlalu berlebih. Hasil yang didapatkan pada Tugas Akhir ini, skema self-configuration berhasil menaikkan throughput pengguna yang diobservasi pada saat dibawah nilai yang diinginkan, dan menurunkan throughput yang terlalu berlebih pada seluruh skenario bandwidth yang diujikan. Skema self-configuration dengan bandwidth 10MHz menjadi yang paling efektif jika dibandingkan dengan penggunaan dua bandwidth lainnya, dengan hasil saat throughput awal kurang dari 2Mbps, throughput meningkat 6.364 kali. Sedangkan ketika throughput awal lebih dari 2Mbps+Uf, throughput diturunkan 1.136 kali

5G uplink interference simulations, analysis and solutions: The case of pico cells dense deployment

The launch of the new mobile network technology has paved the way for advanced and more productive industrial applications based on high-speed and low latency services offered by 5G. One of the key success points of the 5G network is the available diversity of cell deployment modes and the flexibility in radio resources allocation based on user’s needs. The concept of Pico cells will become the future of 5G as they increase the capacity and improve the network coverage at a low deployment cost. In addition, the short-range wireless transmission of this type of cells uses little energy and will allow dense applications for the internet of things. In this contribution, we present the advantages of using Pico cells and the characteristics of this type of cells in 5G networks. Then, we will do a simulation study of the interferences impact in uplink transmission in the case of PICO cells densified deployment. Finally, we will propose a solution for interference avoidance between pico cells that also allows flexible management of bands allocated to the users in uplink according to user’s density and bandwidth demand

펨토셀 네트워크에서 자원 관리에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2014. 8. 전화숙.모바일 트래픽 수요가 폭발적으로 증가함에 따라 실내 사용자들에게 낮은 비용으로 고품질의 데이터 서비스를 제공할 수 있는 펨토셀이 주목을 받고 있다. 본 논문에서는 펨토셀이 기존의 매크로셀 위에 구축된 two-tier 펨토셀 네트워크에서 주파수 효율과 에너지 효율 향상을 위한 두 가지 자원 관리 기법을 제안하였다. 먼저, 주파수 효율을 향상시키기 위한 펨토셀들과 중첩 매크로셀 사이의 하향 링크 무선 자원 분할(radio resource partitioning) 기법을 설계하였다. 제안하는 무선 자원 분할 기법에서는 모바일 데이터 폭증 문제에 대한 또 다른 해결 방안인 분할 주파수 재사용(fractional frequency reuse, FFR) 기술이 적용된 매크로셀 네트워크를 고려하였다. FFR 구조에서 매크로셀의 주파수 대역은 다수의 주파수 분할들(frequency partitions, FPs)로 나누어지고, FP마다 다른 전송 전력이 할당된다. 제안한 기법에서 각 FP는 다시 매크로 전용 부분(macro-dedicated portion), 공용 부분(shared portion), 그리고 펨토 전용 부분(femto-dedicated portion)으로 구성되고, 이 세 부분의 비율은 FP마다 다르게 설정된다. 제안하는 기법은 최적화 방식을 이용하여 주파수 효율을 최대화하도록 각 FP 내 자원 분할 비율을 결정한다. 다음으로, 공항 및 쇼핑몰과 같이 사용자들이 밀집된 공공장소에 많은 수의 펨토 기지국들이 설치된 개방형 펨토셀 네트워크에서 에너지 효율을 향상시키기 위한 자원 관리 기법을 제안하였다. 고려하는 펨토셀 네트워크에서는 펨토 기지국들이 최대 트래픽 부하를 지원하기 위해 높은 밀도로 설치되기 때문에 대부분의 동작 시간 동안 펨토셀들은 무선 자원을 충분히 활용하지 않는다. 따라서 사용자들의 셀 접속을 적절히 조정하여 가능한 적은 펨토 기지국들을 활성화시키고 그 이외의 펨토 기지국들을 수면 모드(sleep mode)로 동작시킨다면 해당 펨토셀 설치 지역에서의 네트워크 에너지 효율을 크게 향상시킬 수 있을 것이다. 따라서 본 논문에서는 에너지 효율을 향상시키기 위해 펨토 기지국의 동작 모드(active 또는 sleep)와 사용자들의 셀 접속을 동시에 결정하는 펨토 기지국 동작 모드 결정 및 사용자 접속 (femto BS sleep decision and user association, SDUA) 기법을 설계하였다. 제안하는 기법에서 SDUA 문제는 사용자들에게 만족할 만한 서비스를 제공하면서 전체 에너지 소모를 최소로 하는 것을 목표로 하는 최적화 문제로 정식화되었다. SDUA 문제는 기지국의 동작 모드와 사용자의 셀 접속이 상호 영향을 주어서 계산 복잡도가 높으므로 본 논문에서는 먼저 활성화 펨토 기지국들의 집합이 주어진 상태에서 최적의 사용자 접속(user association, UA) 문제를 풀고, 각기 다른 집합들에 대해서 최적화 UA를 반복적으로 수행함으로써 최선의 활성화 펨토 기지국 집합을 찾는 휴리스틱 알고리즘을 설계하였다. 제안하는 두 자원 관리 기법들이 각각 주파수 효율과 에너지 효율에 대해서 기존의 기법들보다 우수한 성능을 보임을 시뮬레이션을 통해 확인하였다.Femtocell has received wide attention as a promising solution to meet explosively increasing traffic demand in cellular networks, since it can provide high quality data services to indoor users at low cost. In this thesis, we study resource management in two-tier femtocell networks where the femtocells are underlaid by macrocells, from two different aspects: spectral effciency and energy eciency. First, we design a downlink radio resource partitioning scheme between femtocells and their overlaid macrocell to enhance the spectral eciency. We consider that the overlaid macrocell network adopts the fractional frequency reuse (FFR) techniques, which is also one of solutions to the mobile data surge problem. With FFR, the frequency band of a macrocell is divided into several frequency partitions (FPs) and the transmission power levels assigned to FPs differ from each other. With the proposed scheme, every FP is divided into the macro-dedicated, the shared, and the femto-dedicated portions. The ratio of these three portions is different for each FP. We suggest a method to determine a proper ratio of portions in each FP, by using optimization approach. Next, we propose a scheme to enhance the energy efficiency in open access femtocell networks where many femto base stations (BSs) are deployed in a large public area such as office building, shopping mall, etc. In those areas, the femtocells are overlapped and underutilized during most of the operation time because femto BSs are densely deployed to support the peak traffic load. So, if we properly coordinate the user association with cells and put the femto BSs having no associated users to sleep, the network energy efficiency in the femtocell deployment area can be greatly enhanced. Therefore, we propose a femto BS sleep decision and user association (SDUA) scheme that jointly determines the operation modes (i.e., active or sleep) of femto BSs and the association between users and the active BSs. The SDUA problem is formulated as an optimization problem that aims at minimizing the total energy consumption while providing the satisfied service to users. Since the SDUA problem is too complicated to be solved, we first solve the optimal user association (UA) problem for given set of active femto BSs and then design a heuristic algorithm that finds the best set of active femto BSs by iteratively performing the optimal UA with each different set. By simulation, it is shown that the proposed schemes achieve their design goals properly and outperform existing schemes.1 Introduction 1.1 Background and Motivation 1.2 Proposed Resource Management Schemes 1.2.1 Radio Resource Partitioning Scheme for Spectral Efficiency Enhancement 1.2.2 Base Station Sleep Management Scheme for Energy Efficiency Enhancement 1.3 Organization 2 Radio Resource Partitioning Scheme for Spectral Efficiency Enhancement 2.1 System Model 2.1.1 Heterogeneous Network 2.1.2 Capacity Model 2.2 Proposed Downlink Radio Resource Partitioning Scheme 2.2.1 Macrocell Protection Mechanism 2.2.2 Determination of Dedicated Portion for Macrocell/Femtocell Users 2.3 Capacity Estimation 2.3.1 Achievable Macrosector Capacity 2.3.2 Achievable Femtocell Capacities 2.3.3 SHG Availability of Femtocell 3 Base Station Sleep Management Scheme for Energy Efficiency Enhancement 3.1 System Model 3.1.1 Open Access Femtocell Network 3.1.2 Operation Modes and Power Consumption of a BS 3.1.3 Energy Efficiency 3.2 Analysis on Energy Efficiency 3.2.1 Mathematical Model 3.2.2 Derivation of Energy Efficiency 3.2.3 Numerical Results and Discussion 3.3 Proposed Femto BS Sleep Decision and User Association (SDUA)Scheme 3.3.1 Problem Formulation 3.3.2 Solution Approach 3.3.3 Implementation Example of SIR Estimation 4 Performance Evaluation 4.1 Radio Resource Partitioning Scheme 4.1.1 Simulation Model 4.1.2 Simulation Results 4.2 Base Station Sleep Management Scheme 4.2.1 Simulation Model 4.2.2 Simulation Results 5 Conclusion Bibliography AbstractDocto