A novel scheduling algorithm to maximize the D2D spatial reuse in LTE networks

In order to offload base station (BS) traffic and to enhance efficiency of spectrum, operators can activate many Device-to-Device (D2D) pairs or links in LTE networks. This increases the overall spectral efficiency because the same Resource Blocks (RBs) are used across cellular UEs (CUEs) (i.e., all UEs connected to BS for both C-Plane and D-plane communication) and D2D links (i.e., where the UEs are connected to BS only for C-plane communication). However, significant interference problems can be caused by D2D communications as the same RBs are being shared. In our work, we address this problem by proposing a novel scheduling algorithm, Efficient Scheduling and Power control Algorithm for D2Ds (ESPAD), which reuses the same RBs and tries to maximize the overall network throughput without affecting the CUEs throughput. ESPAD algorithm also ensures that Signal to Noise plus Interference Ratio (SINR) for each of the D2D links is maintained above a certain predefined threshold. The aforementioned properties of ESPAD algorithm makes sure that the CUEs do not experience very high interference from the D2Ds. It is observed that even when the SINRdrop (i.e., maximum permissible drop in SINR of CUEs) is as high as 10 dB, there is no drastic decrease in CUEs throughput (only 3.78%). We also compare our algorithm against other algorithms and show that D2D throughput improves drastically without undermining CUEs throughput

무선통신망에서 처리율 개선을 위한 신호전달 부하의 저감에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2014. 2. 전화숙.무선통신망(wireless networks)은 무선 채널의 상태 변화에 따른 성능 저하를 줄이기 위해 링크 적응(link adaptation) 기술을 기본적으로 사용한다. 링크 적응 기술을 위해서는 채널 상태 정보를 추정하고 수집해야하기 때문에 이에 따른 신호전달 부하(signaling overhead)가 발생하게 된다. 본 논문에서는 무선통신망에서의 신호전달 부하를 줄이기 위한 두 가지 기법을 제안하였다. 먼저 협력 통신 네트워크(cooperative communication networks)에서의 적응적인 전송 기법을 제안하였다. 제안한 기법을 사용하는 협력 통신 네트워크는 ACK(positive acknowledgement)/NACK(negative ACK)와 같은 제한된 피드백 정보로부터 추정된 채널 상태에 기반을 두어 전송 속도를 조절하면서 릴레이(relay)의 사용여부도 함께 결정한다. 제한된 피드백 정보는 실제 채널 상태에 대한 부분적인 정보만을 제공하기 때문에 제안하는 기법을 불확실성 마코브 의사 결정(partially observable Markov decision process)에 따라 설계하였다. 다음으로, 셀룰러 네트워크에서의 기기 간(D2D, device-to-device) 통신을 위한 자원 관리 기법을 제안하였다. 제안한 기법은 두 단계로 구성되고 준 분산적(semi-distributed)으로 동작한다. 첫 번째 단계에서는 중앙 집중적(centralized)으로 기지국이 자원 블록을 B2D(BS-to-user device) 링크와 D2D 링크에게 할당한다. 두 번째 단계에서는 분산적(distributed)으로 기지국은 B2D 링크에 할당된 자원 블록들을 사용하여 전송 스케줄을 결정(scheduling)하고, 각 D2D 링크의 제 1 사용자 기기(primary user device)는 해당 D2D 링크에 할당된 자원 블록들에서의 링크 적응을 수행한다. 이러한 자원 관리 구조는 중앙 집중적 기법처럼 높은 네트워크 용량을 달성할 뿐 아니라 분산적 기법처럼 낮은 신호전달 및 계산(computational) 부하를 필요로 한다. 본 논문에서는 제안한 자원 관리 구조에서 주파수 자원 효율을 최대화하는 자원 블록 할당 문제들을 두 가지 서로 다른 자원 할당 정책에 대하여 만들고 이 문제들을 풀기 위해 탐욕(greedy) 알고리즘과 열 추가 기반(column generation-based) 알고리즘을 제안하였다. 또한 시뮬레이션을 통해 제안하는 기법들이 설계 목표를 달성하고 기존의 기법보다 높은 성능을 보이면서도 신호전달 부하를 줄일 수 있음을 보였다.Wireless networks usually adopt some link adaptation techniques to mitigate the performance degradation due to the time-varying characteristics of wireless channels. Since the link adaptation techniques require to estimate and collect channel state information, signaling overhead is inevitable in wireless networks. In this thesis, we propose two schemes to reduce the signaling overhead in wireless networks. First, we design an adaptive transmission scheme for cooperative communication networks. The cooperative network with the proposed scheme chooses the transmission rate and decides to involve the relay in transmission, adapting to the channel state estimated from limited feedback information (e.g., ACK/NACK feedback). Considering that the limited feedback information provides only partial knowledge about the actual channel states, we design a decision-making algorithm on cooperative transmission by using a partially observable Markov decision process (POMDP) framework. Next, we also propose a two-stage semi-distributed resource management framework for the device-to-device (D2D) communication in cellular networks. At the first stage of the framework, the base station (BS) allocates resource blocks (RBs) to BS-to-user device (B2D) links and D2D links, in a centralized manner. At the second stage, the BS schedules the transmission using the RBs allocated to B2D links, while the primary user device of each D2D link carries out link adaptation on the RBs allocated to the D2D link, in a distributed fashion. The proposed framework has the advantages of both centralized and distributed design approaches, i.e., high network capacity and low signaling/computational overhead, respectively. We formulate the problems of RB allocation to maximize the radio resources efficiency, taking account of two different policies on the spatial reuse of RBs. To solve these problems, we suggest a greedy algorithm and a column generation-based algorithm. By simulation, it is shown that the proposed schemes achieve their design goal properly and outperform existing schemes while reducing the signaling overhead.1 Introduction 1 1.1 Background and Motivation 1 1.2 Approaches to Reduce Signaling Overhead 5 1.3 Proposed Schemes 7 1.3.1 Adaptive Transmission Scheme for Cooperative Communication 7 1.3.2 Resource Management Scheme for D2D Communication in Cellular Networks 8 1.4 Organization 10 2 Adaptive Transmission Scheme for Cooperative Communication 11 2.1 System Model 11 2.2 Cooperative Networks with Limited Feedback 12 2.2.1 Operation of the Proposed Cooperative Network 12 2.2.2 Finite-State Markov Channel Model 15 2.2.3 Packet Error Probability 16 2.2.4 Channel Feedback Schemes 18 2.3 Adaptive Transmission Scheme for Cooperative Communication 19 2.3.1 POMDP Formulation 19 2.3.2 Solution to POMDP 22 3 Resource Management Scheme for D2D Communication in Cellular Networks 25 3.1 System Model 25 3.1.1 Network Model 25 3.1.2 Radio Resource Model 27 3.2 Proposed Resource Management Framework 28 3.2.1 Framework Overview 28 3.2.2 Two-Stage Resource Management 29 3.2.3 Advantages of the Proposed Framework 31 3.3 Conditions for Simultaneous Transmission of B2D and D2D Links 33 3.3.1 Analysis of Interference on B2D and D2D Links 33 3.3.2 Conditions for Simultaneous Transmission of B2D and D2D Links 36 3.4 Resource Block Allocation 38 3.4.1 Resource Block Allocation with Conservative Reuse Policy 39 3.4.2 Resource Block Allocation with Aggressive Reuse Policy 44 4 Performance Evaluation 52 4.1 Adaptive Transmission Scheme for Cooperative Communication 52 4.1.1 Simulation Model 52 4.1.2 Simulation Results 53 4.2 Resource Management Scheme for D2D Communication in Cellular Networks 62 4.2.1 Simulation Model 62 4.2.2 Simulation Results 64 5 Conclusion 75 Bibliography 77 Abstract 85Docto