Planning, Designing, and Implementing the Simulation

Chapter 4

Planning, Designing, and Implementing the Simulation

4.1Introductionto Smart Grid Wireless Infrastructure Planing (SG-WIP) Tool

The SG-WIP is a Wireless Network Topology Planning Application. We has developed this planning tool to assist the planning, and desginning phase of the AMI wireless network infrastructure. Figure 4.1 shows the GUI of SG-WIP.

The SG-WIP is a Google Maps mashup [29, 30]. It can provide the information about the geographical location of the network topologies, network devices, or the residental housing units in the service areas of the utility.

Figure 4. 1 SG-WIP tool for planning AMI wireless infrastructure network in Colorado Springs

In the network planning phase, we has conducted some researches that use the SGWIP tool.

• The research for antenna placement of the WiMAX/WiFi networks has employed the SG-WIP platform as a tool to extract information of the geographical network topologies such as housing unit locations, or street light poles.

Figure 4.2 shows the planning antennae placement for the smart meters and the WiMAX/Wi-Wi-Fi gateway on the Google Maps.

Figure 4. 2 Using SG-WIP tool for planning the antennae position. The WiMAX/Wi-Fi gateway was place on streetlight pole.

• The research about housing unit density of the designing wireless networks has also used the SGWIP platform to gather the distribution of the housing units.

Table 5.1 shows the range of number housing units in the LAN, NAN, WAN topologies. The dimensioning information is helpful for the designning of smart grid network simulation. For example, Table 5.1 shows the number of housing units in the LAN, NAN, MAN topologies for the conducted simulation.

Table 5. 1 The range of housing units in the LAN, NAN, MAN topologies in Colorado Springs.

Figure 4.3 shows the WLAN topology size 100x100 square meters that has fifty housing units.

Figure 4. 3ThisWLAN topology (100x100 square meters) has a high density of resident housing units.

The exported information about the network topologies from SG-WIP platform, as well as the research results about the housing unit density, and the antenna locations can help the AMI network infrastructure researchers and designers in the simulation and analysis of the wireless network infrastructure of the AMI.

4.2Planning the Network Simulation

• The following network topologies will be simulated:

• Wireless Local Area Network (WLAN)
• Wireless Neighborhood Area Network (WNAN)
• Wireless Metropolitan Area Network (WMAN)
• Wide Area Network (WAN)

• The main purpose is for evaluating the network throughput of the Hybrid WiMax/WiFi Infrastructure that will be employed for the AMI meter reading reporting application
• Network topologies
• WiMax, WiFi technologies
• Grid Topology: with pre-defined distance between wireless nodes
• Adequate bandwidth data link connection
• Applications
• Traffic pattern: Up-link data flows from the Smart Meter nodes to the Utilities Data Center node
• Each Smart Meter sends one meter reading message to the Data Center in every second. The network throughput is calculated based on the number of arrived messages in every one second at the Data center.
• The network throughput is measured from many simulation experiments that have the inputs as following:
• Number of Smart Meter nodes
• Number of Wireless Mesh Hops, and Access Points
• Number of Wimax/WiFi Gateways
• Number of WiMAX Base Stations

• The transmission delay (Tx Delay) of a meter data message is designed to measure the average delay of the transmission of a meter data message throughout the network infrastructure.

4.3Designing the Network Simulation

4.3.1Physical Network Model

4.3.1.1HybridWMN Architecture

There are three types of WMNs: Flat WMN, Hierarchical WMN, and Hybrid WMN [21]. The brief description for these WMN categories are as following:

4.3.1.1.1Flat Wireless Mesh Network

The flat WMN includes nodes that have roles as both client and router. The nodes can perform the networking functionalities such as routing, network configuration, services, and other applications. This architecture is similar to the Ad-hoc wireless network and it is the simplest type among the three WMN architecture types. Its disadvantages are lack of network scalability and high resource constraints.

4.3.1.1.2Hierarchical Wireless Mesh Network

The hierarchical WMN has multiple tiers or levels. The client nodes form the lowest tier in the hierarchy. The client nodes communicate together through the backbone network formed by WMN routers. The WMN routers are the dedicated nodes for routing functions. They are not source or destination of data traffic like the client nodes. In the backbone network, there are some router nodes that may have an external connections to the other resources such as the Internet, and other servers in a wired networks, then such nodes are called gateway nodes.

4.3.1.1.3Hybrid Wireless Mesh Network

Hybrid WMN is a special case of the hierarchical WMN where the WMN utilizes other wireless networks for communication. For example, the hierarchical WMN that has the client and router nodes used the Wi-Fi technology, can employ the infrastructure-based networks such as cellular, WiMAX, or satetlite networks to connect to the Internet.

The hybrid WMNs can utilize multiple technologies for both WMN backbone and backhaul. Since the growth of the WMNs depend heavily on the ability to work with other existing wireless networking solutions, this architecture type is very important in the future.

In the figure 4.4, the WiMAX has been use directly as part of Wi-Fi mesh network. The WiMAX Subscriber Terminal put on the Wi-Fi Mesh Access Point. So the Wi-Fi Networks automatically are more reliable in wider coverage area, and reduce cost of connections that are caused by cable drawing in the gateway installation.

Figure 4. 4 WiMAX as backhaul inter Wi-Fi mesh networks (source: Intel)

4.3.1.2WiMAX/WiFi Network Infrastructure

Basically, the WM Communication Network component provides the data transportation services. The requests and responses from Meter Data Center component and Wi-Fi Smart Meter component will be delivered by the using to the transportation services of WM Communication Network component.

The WM Communication Network component has three layers of network services like the first three layers of the OSI model [22]:

Figure 4. 5 Logical view of the WM Communication Network includes the first three layers of the OSI model

The WM Communication Network is an integrated Wireless Mesh Network (WMN), which uses Wi-Fi and WiMAX technologies [17]. The WM Communication Network has the WiMAX Base Station, the WiMAX/Wi-Fi Gateway, and Wi-Fi Dual Band Mesh Routers.

The figure 4.6 shows the physical model of the wireless mesh communication network. The WiMAX Base Stations are connected to the Meter Data Center through wired network. The Wi-Fi mesh routers are at the bottom level of the network hierarchy and can connect with the Wi-Fi smart meters. Wi-Fi smart meters connect to the meter data center via the hybrid WiMAX/Wi-Fi Communication Network.

Figure 4. 6Physical model of the WM Communication Network. The network hierarchy includes the Wi-Fi Mesh Routers, the WiMAX/Wi-Fi Gateways, and the WiMAX BS.

4.3.1.3Overview of NS-3 WiMAXModule

The NS-3 WiMAX model attempts to provide an accurate MAC and PHY level implementation of the IEEE 802.16 specification with the Point-to-multipoint (PMP) mode and the Wireless MAN-OFDM PHY layer. The WiMAX model composed of three layers:

• The MAC Convergence Sublayer (MAC-CS)
• The MAC Common Part Sublayer (MAC-CPS)
• The Physical (PHY) layer

The MAC Convergence Sublayer (CS)

The MAC-CS in this module implements the Packet CS, designed to work with the packet-based protocols at higher layers. The CS is responsible of receiving packet from the higher layer and from peer stations, classifying packets to appropriate connections (or service flows) and processing packets. It keeps a mapping of transport connections to service flows. This enables the MAC CPS identifying the Quality of Service (QoS) parameters associated to a transport connection and ensuring the QoS requirements.

The MAC Common Part Sublayer (MAC-CPS)

The MAC Common Part Sublayer (CPS) is the main sublayer of the IEEE 802.16 MAC and performs the fundamental functions of the MAC. The module implements the Point-Multi-Point (PMP) mode. In PMP mode BS is responsible of managing communication among multiple SSs. The key functionalities of the MAC-CPS include framing and addressing, generation of MAC management messages, SS initialization and registration, service flow management, bandwidth management and scheduling services.

• Framing and Management Messages

The module implements a frame as a fixed duration of time, i.e., frame boundaries are defined with respect to time. Each frame is further subdivided into downlink (DL) and uplink (UL) subframes. The module implements the Time Division Duplex (TDD) mode where DL and UL operate on same frequency but are separated in time. A number of DL and UL bursts are then allocated in DL and UL subframes, respectively. Since the standard allows sending and receiving bursts of packets in a given DL or UL burst, the unit of transmission at the MAC layer is a packet burst. The module implements a special PacketBurst data structure for this purpose. A packet burst is essentially a list of packets. In the case of DL, the subframe is simulated by transmitting consecutive bursts (instances PacketBurst). In case of UL, the subframe is divided, with respect to time, into a number of slots. The bursts transmitted by the SSs in these slots are then aligned to slot boundaries. The frame is divided into integer number of symbols and Physical Slots (PS) which helps in managing bandwidth more effectively. The number of symbols per frame depends on the underlying implementation of the PHY layer. The size of a DL or UL burst is specified in units of symbols.

• Network Entry and Initialization

The network entry and initialization phase is basically divided into two sub-phases, (1) Scanning and synchronization and (2) Initial ranging. The entire phase is performed by the LinkManager component of SS and BS.

• Connections and Addressing

All communication at the MAC layer is carried in terms of connections. The standard defines a connection as a unidirectional mapping between the SS and BS's MAC entities for the transmission of traffic. The standard defines two types of connections: the Management Connections for transmitting control messages and the Transport Connections for data transmission. Note that each connection maintains its own transmission queue where packets to transmit on that connection are queued. The ConnectionManager component of BS is responsible of creating and managing connections for all SSs.

• Scheduling Services

The module supports the four scheduling services defined by the IEEE 802.16-2004 standard:

Unsolicited Grant Service (UGS)

Real-Time Polling Services (rtPS)

Non Real-Time Polling Services (nrtPS)

Best Effort (BE)

These scheduling services behave differently with respect to how they request bandwidth as well as how the it is granted. Each service flow is associated to exactly one scheduling service, and the QoS parameter set associated to a service flow actually defines the scheduling service it belongs to. When a service flow is created the UplinkScheduler calculates necessary parameters such as grant size and grant interval based on QoS parameters associated to it.

WiMAX PHY Model

The Wireless MAN OFDM PHY specifications is implemented. This specification is designed for non-light-of-sight (NLOS) including fixed and mobile broadband wireless access. The proposed model uses a 256 FFT processor, with 192 data subcarriers. It supports all the seven modulation and coding schemes specified by Wireless MAN-OFDM. It is composed of two parts: the channel model and the physical model.

• Channel model

When a physical device sends a packet (FEC Block) to the channel, the channel handles the packet, and then for each physical device connected to it, it calculates the propagation delay, the path loss according to a given propagation model and eventually forwards the packet to the receiver device.

• Physical model

The physical layer performs two main operations: (i) It receives a burst from a channel and forwards it to the MAC layer, (ii) it receives a burst from the MAC layer and transmits it on the channel.

Transmission Process: A burst is a set of WiMAX MAC PDUs. At the sending process, a burst is converted into bit-streams and then splitted into smaller FEC blocks which are then sent to the channel with a power equal P_tx.

Reception Process: The reception process includes the following operations:

1- Receive a FEC block from the channel. 2- Calculate the noise level. 3- Estimate the signal to noise ratio (SNR) with the following formula. 4- Determine if a FEC block can be correctly decoded. 5- Concatenate received FEC blocks to reconstruct the original burst. 6- Forward the burst to the upper layer.

The below figure 4.3 shows an overview of the WiMAX sublayers traversed for transmitting and receiving a packet. More detailed information about the NS-3 WiMAX model is preseneted in [ref-paper].

Figure 4. 7 NS-3 WiMAX protocol stack overview

4.3.1.4Overview of NS-3 Wi-Fi Module

The NS-3 802.11 model provides an accurate MAC-level implementation of the 802.11 specification and the PHY-level model of the 802.11a and 802.11b specifications.

There are four levels that were implemented in the current implementation:

• The PHY layer model
• The so-called MAC low models
• The so-called MAC high models
• A set of Rate control algorithms used by the MAC low models

The PHY layer implements a single 802.11a model in the ns3::WifiPhy class, and recently extended to cover 802.11b physical layers.

The MAC low layer is split in 3 components:

• ns3::MacLow takes care of RTS/CTS/DATA/ACK transactions
• ns3::DcfManager and ns3::DcfState implement the DCF functions
• ns3::DcaTxop and ns3::EdcaTxopN handle the packet queue, packet fragmentation, and packet retransmissions.

The MAC high models contain the implementations for three Wi-Fi topological elements – Access Point (AP) implemented in ns3::ApWifiMac, non-AP Station (STA) implemented in ns3::StaWifiMac, and STA in an Independent Basic Service Set (IBSS) implemented in ns3::AdhocWifiMac.

Rate control Algorithms include:

• ns3::ArfWifiManager
• ns3::AarfWifiManager
• ns3::IdealWifiManager
• ns3::CrWifiManager
• ns3::OnoeWifiManager
• ns3::AmrrWifiManager
• ns3::CaraWifiManager
• ns3::AarfcdWifiManager

The below figure 4.4 shows the overview of the Wi-Fi L2 sublayers traversed for transmitting and receiving a packet. More detailed information about the NS-3 Wi-Fi model is preseneted in [ref-paper].

Figure 4. 8NS-3 Wi-Fi layer 2 stack overview

4.3.2Application Model

4.3.2.1Client-Server architecture

The AMI metering data collection processincludes three components that are Meter Data Center, Wireless Mesh (WM) Communication Network, and Wi-Fi (WF) Smart Meter. The Meter Data Center component accesses the WF Smart Meter’s reading via the WM Communication Network as in the Figure 4.9.

Figure 4. 9 Smart meters access the Meter data center through the Wireless mesh communication network

4.3.2.2Meter data traffic generation

Our current software simulates constant bit rate traffic. We allow users specifyingthe starting time of packet streams. This allows for better network performance since the packets from different nodes will not collide. It also helps debug the end to end transmission and ensures that the network properly delivers the packets.

4.3.2.3NS-3 Server application

An UDP protocol Server. It receives the meter messages.

4.3.2.4NS-3 Client application

An UDP protocol Client. It sends the meter messages to the Server.

4.3.3WLAN Simulation Design

4.3.3.1Topology Configuration

• Standard: WiFi IEEE 802.11b
• Connection mode: Infrastructure
• Smart Meter (SM) at random position within the coverage area of the corresponding AP
• The WiFi AP has the coverage range of 100 meters
• Number of SMs: [1 – 100]
• WiFi link capacity: 11Mbps
• Application Configuration

• Server application is installed on the AP.
• Client application is installed on SM.
• Each Client application will send onemeter message with 20 bytes length to the Server application by using the Internet protocol UDP.
• The Client application’s Data-Rate property is set to 20 bytes x 8 bits = 160bps = 0.160kbps
• Simulation Planning

• Repeatedly running the simulation scenarios with the different number of SMs
• Output: the network throughput, Tx Delay
• Results Analysis and Conclusion

• Calculate the average network throughput, Tx delay
• Conclusion: Do the AP receive all of the messages from the SMs in 1 second?

4.3.4WNAN Simulation Design

4.3.4.1Topology Configuration

• Standard: WiFi IEEE 802.11a
• Connection mode: Mesh
• The Mesh Routers (MR) /Access Points (AP) are installed in the Grid topology
• Distance between adjacent nodes (horizontal and vertical): 200 meters
• Number of MRs/APs: [1 – 9]
• WiFi link capacity: 54Mbps
• Application Configuration

• Server application is installed on the Gateway (GW).
• Client application is installed on APs.
• Each Client application will send 100 messages, which have 20 bytes length, to the Server application by using the Internet protocol UDP.
• The Client application’s Data-Rate property is set to 100 x 20 bytes x 8 bits = 16000bps = 16kbps
• Simulation Planning

• Repeatedly running the simulation scenarios with the different number of MRs and APs
• Output: the network throughput, Tx delay
• Results Analysis and Conclusion

• Calculate the average network throughput, Tx delay
• Conclusion: Do the GW receive all of the messages from the APs in 1 second?

4.3.5WMAN Simulation Design