Parameterizing Enterprise WiFi Networks: The Use of Wide Channels

We investigate the joint channel, power, and carrier sensing threshold allocation problem in IEEE 802.11ac enterprise networks in a single 160 MHz band and show that the current practice, which is to use narrower channels at maximum power when the network is dense, yields much worse performance than a solution using the widest possible channel (i.e., 160 MHz) with a much lower power. This finding is consistent with cellular networks which use a reuse factor of one. Based on these insights, we propose and evaluate an algorithm that allocates the widest channel to all Access Points, and finds the appropriate transmission power and carrier sensing threshold for each of them to provide an efficient and fair solution to a managed IEEE 802.11ac enterprise network. The performance gains with respect to the best of the two benchmarks that we consider range from 60% in not too dense deployments to more than 200% in dense deployments

Channel Allocation and post-CCA based Bandwidth Adaptation in Wireless Local Area Networks with Heterogeneous Bandwidths

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 박세웅.The new prominent 802.11ac standard aims at achieving Gbps data throughput for individual users while at the same time guaranteeing backward compatibility. The approaches to achieving this goal use enhanced physical-layer features, such as higher modulation levels, MIMO (Multiple Input Multiple Output), and wider bandwidth. As for the bandwidth, the channel bonding technique that makes use of multiple 20MHz channels in 5GHz band is adopted. However, the heterogeneity of bandwidth in a network can cause asymmetric interferences in which some transmissions are not sensed by some nodes. As a result, the conventional CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) may not work well in 802.11ac networks and the Gbps throughput, which is attainable for a single link, is not achievable network-widely, which we call the Hidden Channel (HC) problem. In this dissertation, we illustrate the HC problem with a 802.11ac network as a reference system. Then we analyze the problem using Markov chain technique and show how the contention parameters and transmission time affect collision probability and fairness in some deployment scenarios. The validity of the analysis is verified through simulation in the same chapter. As a solution to the HC problem, a centralized and heuristic channel allocation algorithm, PCA (Primary Channel Allocation), in an enterprise local area network is proposed in the next part of this dissertation. The PCA algorithm, an extended version of well known ``University Timetabling'' algorithm for incorporating multi-channel purpose, is designed to avoid HC problem effectively. Through simulations, we demonstrate that our proposed channel allocation algorithm lowers the packet error rate (PER) compared to uncoordinated and RSSI (Received Signal Strength Indicator) based allocation schemes and increases the network-wide throughput as well as the throughput of a station that experiences poor performance. This implies improved fairness performance among transmission pairs with various channel bandwidths. Then, simple experiments are conducted with USRP and WARP boards to show that the problem is real and to prove that the validity of our next solution. Based on that, we argue for the need of bandwidth adaptation based on post-CCA, which is another clear channel assessment (CCA) procedure after finishing a transmission. The post-CCA helps mimic the CSMA/CD (CSMA with Collision Detection) mechanism in the wired Ethernet, thus enhancing channel assessment capability. Then, we propose PoBA (Post-CCA based Bandwidth Adaptation) that alters bandwidth and channel configuration dynamically. Using simulation, we confirm that the PoBA increases network-wide throughput, channel utilization and fairness, and decreases packet error probability.1 Introduction 1 1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Contributions and Outline . . . . . . . . . . . . . . . . 6 2 The HC (Hidden Channel) Problem 11 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2 Problem Description . . . . . . . . . . . . . . . . . . . 15 2.3 Numerical Analysis . . . . . . . . . . . . . . . . . . . . 20 2.4 Simulation Results . . . . . . . . . . . . . . . . . . . . 27 2.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 31 3 PCA (Primary Channel Allocation) 33 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 33 3.2 Channel Allocation for Alleviating HC . . . . . . . . . 39 3.2.1 Problem Formulation . . . . . . . . . . . . . . 43 3.2.2 A Heuristic Primary Channel Assignment Algo- rithm . . . . . . . . . . . . . . . . . . . . . . . 51 iv 3.3 Simulation Results . . . . . . . . . . . . . . . . . . . . 57 3.3.1 Case for a Network with Two APs . . . . . . . 58 3.3.2 Case for a Chain Topology with Six APs . . . . 60 3.3.3 Case for Various Sized Random Networks . . . 62 3.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 68 4 PoBA (Post-CCA based Bandwidth Adaptation) 69 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 69 4.2 Experimental Results . . . . . . . . . . . . . . . . . . . 72 4.3 Post-CCA & PoBA . . . . . . . . . . . . . . . . . . . . 78 4.3.1 Post-CCA Operation . . . . . . . . . . . . . . . 78 4.3.2 PoBA Algorithm . . . . . . . . . . . . . . . . . 81 4.4 Simulation Results . . . . . . . . . . . . . . . . . . . . 89 4.4.1 Case for a Chain Topology with Six APs . . . . 90 4.4.2 Case for Various Sized Random Networks . . . 92 4.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 96 5 Conclusion 97 5.1 Research Contributions . . . . . . . . . . . . . . . . . 97 5.2 Future Research Directions . . . . . . . . . . . . . . . 99Docto