My Paper Review ofHierarchical MAC Protocol with Multi-Channel Allocation

for Enhancing IEEE 802.11ah Relay Networks

YAN-TING LIN

A post-baccalaureate student at University of Taipei.

June 2016

Outline

• Abstract

• Introduction

• IEEE 802.11ah wireless LAN standard

• Proposed MAC Enhancement for 802.11ah

• Proposed Algorithm for Channel Assignment

• Simulation Parameters and Results

• Conclusions

Authors: Saurabh Kumar, HoChul Lim, HyungWon Kim [ IEEE Members ] School of Electronics Engineering, Chungbuk National University Cheongju, Chungbuk, South Korea

• With the introduction of IEEE 802.11ah wireless LAN standard, Internet of Things (IoT) is expected to develop more rapidly. IEEE 802.11ah introduces a relay node to extend wireless range with high energy efficiency for a large number of station nodes. This paper presents an efficient method of allocating multiple channels to multiple relay nodes of IEEE 802.11ah network. We propose a formulation for an optimal calculation of mutual exclusive segment angle using wireless link parameters. We present a hierarchical Medium Access Control (MAC) mechanism for efficient management and deployment of relays. It increases wireless range of network, improves the overall throughput by minimizing interference, and effectively conserves station node’s energy. We implemented IEEE 802.11ah relay protocol based the hierarchical MAC using ns-3 simulator. Experimental results show that the proposed scheme provides substantial improvement in throughput performance.

Analysis of Abstract - 1

• With the introduction of IEEE 802.11ah wireless LAN standard, Internet of Things (IoT) is expected to develop more rapidly. IEEE 802.11ah introduces a relay node to extend wireless range with high energy efficiency for a large number of station nodes.

• ↑ 背景說明、介紹 : Simple Introduction

• Abstract用字淺顯易懂，使用現在簡單式。

Analysis of Abstract - 2

• This paper presents an efficient method of allocating multiple channels to multiple relay nodes of IEEE 802.11ah network. We propose a formulation for an optimal calculation of mutual exclusive segment angle using wireless link parameters. We present a hierarchical Medium Access Control (MAC) mechanism for efficient management and deployment of relays.

• ↑ 這篇論文提出的方法 : Simple Methodology

• Abstract沒有使用任何 Reference符合規定

Analysis of Abstract - 3

• It increases wireless range of network, improves the overall throughput by minimizing interference, and effectively conserves station node’s energy. We implemented IEEE 802.11ah relay protocol based the hierarchical MAC using ns-3 simulator. Experimental results show that the proposed scheme provides substantial improvement in throughput performance.

• ↑ 簡單描述實驗跟結果 : Simple Results and Achievements

•唯一的問題是這裏後面實驗並沒有提到節省節點能耗

•這篇 Abstract沒有 Discussion

Introduction

• Internet of Things (IoT) or Machine to Machine (M2M) communications among various devices are enriching human to human communication for the next-generation communication systems. M2M communication is characterized by autonomous sensor data generation, exchange, processing and actuation among intelligent machines without human intervention. Recently, IEEE 802.11ah wireless LAN standard group targets a wireless communication standard to support use cases which include sensor networks and backhaul communication of sensor/meter data. In IEEE 802.11ah network [1], the network consists of devices called end stations, relay nodes, and root AP (See Fig. 1).

研究背景1. 背景基礎介紹2. 縮小研究範圍

Introduction - 2 研究背景簡單示意圖

Introduction - 3

• As shown in Fig. 1 some devices are out of the range of Root AP wireless area, so we can use relay nodes to extend the wireless range and connect those devices.

• This paper is organized as follows, in section II, some specifications of IEEE 802.11ah standard are discussed. Section III discusses hierarchical MAC enhancement in 802.11ah standard. Section IV describes proposed algorithm for channel allocation for relays and deployment of relays. Section V describes simulation parameters used in ns3 and simulation results and section VI presents conclusions from this paper.

1.背景介紹 (續)2.章節描述

IEEE 802.11ah wireless LAN standard

• IEEE 802.11ah [5][6][7][8] is an emerging wireless LAN (WLAN) standard that defines a WLAN system operation at sub 1 GHz license exempt bands.

• 802.11ah can be used for various purposes including large scale sensor networks, extended range hotspot, and outdoor Wi-Fi for cellular traffic offloading, whereas the available bandwidth is relatively narrow [2][3].

• To save bandwidth with reduced MAC and Physical layer overhead, 802.11ah root AP uses address identifier (AID) number to communicate with STAs assigned by root AP instead of lengthy MAC addresses and Null data packet(NDP) to save overhead of sending long control frames.

描述先前研究重點

IEEE 802.11ah wireless LAN standard - 2

• 802.11ah have many orthogonal channels with 1MHz, 2MHz and 4MHz bandwidth, which this paper utilizes for enhancement.

• A. IEEE 802.11ah Restricted Access Window (RAW)

• RAW is a medium access interval for a group of STAs during which a STA in the RAW group indicated by the RAW parameter set (RPS) element is allowed to contend for medium access. The RAW is divided into one or more RAW slots.

帶出論文方法所需的技術內容RAW是什麼

Source: http://slideplayer.com/slide/4529602/

IEEE 802.11ah wireless LAN standard - 3

• B. IEEE 802.11ah RelayA Relay is an entity that logically consists of a relay AP and a relay STA. A Relay STA is a non-AP STA with dot11RelaySTAOperation equal to true. An example of relay is illustrated in Fig. 3 (Relay Architecture), where relay 1 and relay 2 are relays, both of which consisting of a relay STA and a relay AP, whose relay STAs are associated with an AP that is a root AP. STA1 and STA2 are non-AP STAs associated with the relay AP of relay 1. STA3 and STA4 are non-AP STAs associated with the relay AP of relay 2. Frames from STA1 and STA2 are forwarded via the relay AP of relay 1 to the relay STA of relay 1 and then to the root AP. Similarly, frames from the root AP are forwarded to STA1 and to STA2 via relay STA and the relay AP of relay 1 [1].

補充 802.11 ah特徵Relay基本運作方式

Proposed MAC Enhancement for 802.11ah

• Hierarchical RAW (Restricted Window Access)

• In the proposed enhancement we use two different level of RAWs, one for root AP and another for relays, operation of hierarchical RAW is shown in Fig. 4. A Root AP broadcasts its RPS element with the beacon frame for relays and devices (STAs) connected with the root AP directly without relay. A relay is allowed to contend for medium access to communicate to the root AP only in its designated slot. During the rest of the time the relay will communicate with the stations connected to it by sending RPS for its RAW via beacon frame to STAs. A relay’s RAW time is equal to the root AP’s RAW time minus slot time for that relay. Each STAs communicates with its relay at only its slot that is specified in the RPS of Relay RAW, while the STA goes to sleep mode for the rest of the time. In this way, the hierarchical RAW scheme can enhance the battery life time of sensors and improve the network performance.

描述 RAW + Relay基本運作方式，以及如何讓網路省電。

Proposed Algorithm for Channel Assignment

A. Multi-channel Allocation for Relay If we use a single channel with the relay, only a single node in the network can transmit at a time to avoid collision. If multiple nodes in different relay transmit, they will cause interference [13] on each other or increase the chances of hidden node problems, leading to a loss of network performance. In our proposed algorithm we allocate different channels [4][9][10][11][12][13] to all the relays while communicating to STAs. In our proposed algorithm root AP is allocated with a dedicated channel for example, channel 1. Using this channel, all relays and all the stations connected to the root AP communicates with the root AP directly. Once a relay is done with its communication with the root AP, it switches its’ channel to a designated channel and communicates to STAs.

•時態都用現在簡單式

•紅色部分:說明單一 Channel效能的損失及無線傳輸封包互相傳輸干擾問題。

•綠色部分:提出想法，如果妥善分配 Channel讓它們不會互相干擾，便能增加空間重複使用率、同時許多節點進行傳輸。

Proposed Algorithm - 2

• C. Angle of Mutual Exclusive Segment

• In the proposed algorithm we calculate angle in the circular area of the root AP, in which all the relays will have mutually exclusive channels assigned to them to communicate with the STA’s. To calculate angle we first calculate wireless distance (range) of the relay,

Wireless Distance公式詳解

方法所需參數 1通訊距離方程式

Proposed Algorithm - 3

Angle of mutual exclusion is inversely proportional to number of relays presents in network, if we increase the number of relays by 2, angle will decrease by 2 because number of channels are constant and we cannot support unlimited channels, so interference will be more. If we have unlimited number of channels then this equation will not contain term for number of relays.

方法所需參數 2分配區域的角度

這裏有點問題，並沒有提及方程式的證明

Proposed Algorithm - 4

• D. Multi-Channel Allocation Algorithm

論文核心方法分配 Channel

實務經驗補充

If any segment has more than one relay then all the relays in that segment will be assigned with different channels to allow simultaneous communication with their STAs. While the proposed algorithm tends to generate more efficient usage of channels for networks with uniform distribution of relays, it works well for networks of any distribution of relays as shown in Fig. 6.

論文核心模型舉一個例子

Simulation Parameters and Results

To verify the performance of the proposed algorithm we have implemented key features of IEEE 802.11ah and relay operations with multi-channel support using ns-3 network simulator.

We have implemented sub 1 GHz frequency in the physical layer and defined MCSs needed for 1 MHz and 2 MHz bandwidth for 802.11ah. The data rate or MCS (Modulation and Coding Scheme) of each wireless link is determined by a link adaptive algorithm. We have also implemented the AID structure and the short frame format of 802.11ah to enhance the throughput for data communication between root AP and STAs. In addition, we have implemented key functions and protocol of relay nodes in ns-3. Parameters used in the simulation are specified in table 1.

跑系統模擬驗證模型1. 使用 NS-3模擬器

2. 說明參數、實作的細節

Simulation Parameters and Results - 2

The root AP evaluates the angle of mutual exclusion. Then with the beacon frame, it sends the channel ID allocated to the relay and the AP_RAW slot to communicate with the root AP via RPS. Each relay receives beacon frame from the root AP and broadcasts the channel ID assigned to it with Relay_RAW by calculating its’ RAW duration. In our simulation we have used 1 RAW interval in a beacon period in the Root AP. AP RAW is 400 ms long and has 4 RAW slots, so Relay RAW has 300 ms which is divided into 4 RAW slots for stations to communicate. In this experiment, we assume that channel switching in relay takes negligible time. All relays communicate with the root AP using channel 1 in its designated RAW slot and then switch to channel allocated to communicate with their STAs. 系統模擬流程說明

1. RAW模擬流程2. 使用亂數分佈節點

• STAs are connected to either a relay or the root AP based on the signal strength of the beacon frames received from Root AP and all relays.We have allocated the positions of relays and STAs using uniform random distribution. Fig. 7 illustrates an example 802.11ah network, where root AP is positioned in the middle and 4 relays are randomly positioned.

• In the case of 4 relays, with simulation parameter used we obtain θ of 90 degree using equation (3) with the simulation parameters, we allocate channel 2 and 3 to adjacent relays repeatedly, and use very less channels, which leads to least interference.

• We constructed three different 802.11ah networks with 4, 8, and 12 relays for experiment. Using these networks, we have conducted ns-3 simulations using 3 different channel allocation schemes: single channel case, random allocation, and the proposed allocation algorithm. See Fig. 8.

• From the simulation results shown in Fig 8 it is evident that the proposed algorithm provides throughput performance 18 times better than the single channel case. It also performs 10 % better than random allocation scheme even if we increase the number of relays in the network

系統模擬流程說明3.分配區域角度

4.分別以不同數量 Relay、不同分配Channel方法做實驗

結合圖表，開始描述系統模擬結果，說明這個方法效率

提升了多少。

使用圖表快速呈現並比較結果

• Fig 9 compares the ratio of successful packet delivery from the relays to the root AP. We can see that the proposed algorithm gives a ratio of successful packet delivery 9 times higher than the single channel case and 20 % higher than random allocation of multiple channels. With the higher successful delivery ratio, the proposed algorithm can ensure that the STAs have fewer retransmissions it can go to the sleep mode for most of the time and so save power which is a key requirement for most sensor networks in the case of sensor nodes are battery powered. The simulation time for each network was configured to 18 seconds for all the simulation results. We have used only 3 channels because in one segment only single relay is present.

整篇敘述實驗結果。強調此篇論文方法的好處，提升了多少

效能。

Conclusions

• In this paper we have proposed an efficient scheme of a hierarchical MAC for IEEE 802.11ah networks, with an enhancement using multiple channels for relay nodes. We have also introduced a formulation for the angle of mutual exclusive segments. It has been implemented into an algorithm that enables effective allocation of multiple channels to the relay nodes. The proposed scheme maximizes the throughput while reducing the energy consumption with the leverage of extending the wireless range of the network via multi-channel relays. The proposed algorithm allows many devices to transmit data simultaneously by optimally allocating channels to relays and so it can minimize the interference and increase the throughput. We have implemented the proposed multi-channel allocation scheme and the hierarchical MAC for relay protocols of IEEE 802.11ah MAC using ns-3 simulator. Simulation results proved that the proposed scheme provides a throughput 18 times higher than the current version of IEEE 802.11ah which uses only single channel. The proposed scheme also gives substantial improvement over a non-optimal multi-channel allocation scheme such as random channel allocation.

1. 重申此論文貢獻的方法2. 這個方法目標的功能3. 目標能帶來哪些好處

4. 這個方法簡單細節5. 實驗結果與結果討論