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Post-CCA and Reinforcement Learning Based Bandwidth Adaptation in 802.11ac Networks
Jang, Seowoo,Shin, Kang G.,Bahk, Saewoong IEEE Computer Society 2018 IEEE TRANSACTIONS ON MOBILE COMPUTING Vol.17 No.2
<P>The new 802.11ac standard aims at achieving Gbps data throughput for individual users by exploiting enhanced physical-layer features, such as higher modulation levels, Multiple Input Multiple Output (MIMO), and wider bandwidths. However, the heterogeneity of bandwidth in a network can cause asymmetric interferences in which certain transmissions cannot be sensed by some other nodes. As a result, the conventional Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) may not work well in 802.11ac networks. We call this the <I>Hidden Channel</I> (HC) problem, which is shown to be <I>real</I> via experiments with USRP and WARP boards. To solve this problem, we propose bandwidth adaptation based on <I>post-CCA</I>, which is a clear channel assessment (CCA) procedure performed <I>after</I> completing a transmission. Post-CCA in wireless networks helps mimic the CSMA with Collision Detection (CSMA/CD) mechanism in the wired Ethernet, thus enhancing channel assessment capability. Using post-CCA, we propose Post-CCA based Bandwidth Adaptation (PoBA) that alters bandwidth and channel configuration dynamically by applying a reinforcement learning mechanism. Post-CCA and PoBA do not require any hardware modification and are also compliant with the 802.11 standards. PoBA is shown via simulation to increase network-wide throughput, channel utilization and fairness, and also lower packet error probability.</P>
Seowoo Jang,Saewoong Bahk IEEE 2015 IEEE transactions on mobile computing Vol.14 No.3
<P>The major goal of IEEE 802.11ac is to provide very high throughput (VHT) performance while at the same time guaranteeing backward compatibility. To achieve this goal, 802.11ac adopts the channel bonding technique that makes use of multiple 20 MHz channels in 5 GHz band. Due to the heterogeneity of bandwidth that each device exploits, and the fixed total transmission power in the standards, a problem called `Hidden Channel' arises. In this paper, we first analyze the problem and show how the contention parameters and transmission time affect collision probability and fairness in some deployment scenarios. Then, we propose a heuristic channel allocation algorithm that aims to avoid such problematic situations effectively. Through simulations, we demonstrate that our proposed channel allocation algorithm lowers the packet error rate (PER) compared to uncoordinated and received signal strength indicator(RSSI) 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.</P>
( Seowoo Jang ),( Jin-ghoo Choi ),( Sung-guk Yoon ) 한국인터넷정보학회 2016 KSII Transactions on Internet and Information Syst Vol.10 No.9
With the increased popularity of IEEE 802.11 WLAN, the density of the WLAN devices per access point has also increased, resulting in throughput performance degradation. One of the solutions to the problem is improving the protocol efficiency by a using multi-round contention scheme. This paper first discusses how to estimate the number of contending stations in a WLAN network by using minimum elapsed backoff counter values that can be easily monitored by each station. An approximate closed form expression is derived for the number of active contending stations using the smallest backoff counter value in the network. We then apply this result to adapt the number of contending rounds according to the network loading level to enhance the throughput performance of a multi-round contention scheme. Through simulation, we show that the accuracy of the estimation algorithm depends on the contention parameters of and the number of backoff counter observing samples, and found a reasonable value for each parameter. We clearly show that our adaptive multi-round contention scheme outperforms the standard contention scheme that uses a fixed number of rounds.
CAMR: Congestion-Aware Multi-Path Routing Protocol for Wireless Mesh Networks
Jang, Seowoo,Kang, Seok-Gu,Yoon, Sung-Guk The Korean Institute of Electrical Engineers 2017 Journal of Electrical Engineering & Technology Vol.12 No.1
The Wireless Mesh Network (WMN) is a multi-hop wireless network consisting of mesh routers and clients, where the mesh routers have minimal mobility and form the backbone. The WMN is primarily designed to access outer network to mesh clients through backhaul gateways. As traffic converges on the gateways, traffic hotspots are likely to form in the neighborhood of the gateways. In this paper, we propose Congestion Aware Multi-path Routing (CAMR) protocol to tackle this problem. Upon congestion, CAMR divides the clients under a mesh STA into two groups and returns a different path for each group. The CAMR protocol triggers multi-path routing in such a manner that the packet reordering problem is avoided. Through simulations, we show that CAMR improves the performance of the WMN in terms of throughput, delay and packet drop ratio.
CAMR: Congestion-Aware Multi-Path Routing Protocol for Wireless Mesh Networks
Seowoo Jang,Seok-Gu Kang,Sung-Guk Yoon 대한전기학회 2017 Journal of Electrical Engineering & Technology Vol.12 No.1
The Wireless Mesh Network (WMN) is a multi-hop wireless network consisting of mesh routers and clients, where the mesh routers have minimal mobility and form the backbone. The WMN is primarily designed to access outer network to mesh clients through backhaul gateways. As traffic converges on the gateways, traffic hotspots are likely to form in the neighborhood of the gateways. In this paper, we propose Congestion Aware Multi-path Routing (CAMR) protocol to tackle this problem. Upon congestion, CAMR divides the clients under a mesh STA into two groups and returns a different path for each group. The CAMR protocol triggers multi-path routing in such a manner that the packet reordering problem is avoided. Through simulations, we show that CAMR improves the performance of the WMN in terms of throughput, delay and packet drop ratio.
Energy Efficient SWIPT Systems in Multi-Cell MISO Networks
Jang, Seokju,Lee, Hoon,Kang, Seowoo,Oh, Taeseok,Lee, Inkyu INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS 2018 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.17 No.12
<P>This paper studies beamforming design problems for multi-cell multi-user downlink networks with simultaneous wireless information and power transfer (SWIPT). In this system, multi-antenna base stations (BSs) concurrently transfer information and energy to multiple single-antenna information decoding (ID) and energy-harvesting (EH) users. We aim to maximize EH efficiency (EHE) that is defined as the ratio of the harvested energy at the EH users to the amount of energy consumption at the BSs while guaranteeing the quality-of-service constraint for each ID user. The EHE metric quantifies the efficiency of the power transfer capability of the SWIPT network. For the EH operation, both an ideal linear model and a practical non-linear model are individually investigated. We optimally solve this non-convex problem in two different scenarios according to the cooperation level among the BSs. First, for the centralized case, where global channel state information (CSI) is available at all BSs, we propose a centralized beamforming method based on the semi-definite relaxation and the successive convex approximation techniques. Next, in order to reduce the backhaul signaling overhead, decentralized algorithms are presented where each BS computes its beamforming vector by only using local CSI. The simulation results show that the proposed SWIPT beamforming algorithms offer a significant EHE performance gain over conventional schemes.</P>