Wireless Networking Technologies Chapter 16 Wireless Networking Technologies © Bobby Hoggard, Department of Computer Science, East Carolina University These slides may not be used or duplicated without permission

Wireless Network Classification Wireless networks come in a wide variety of sizes and types – part of which comes from government regulations on ranges of the electromagnetic spectrum available for communication Communication in some parts of the spectrum requires a license, while other parts of the spectrum is unlicensed (in the US, a required license would come from the FCC) Wireless Networks Personal Area Networks (PAN) Local Area Networks (LAN) Metropolitan Area Networks (MAN) Wide Area Networks (WAN)

Personal Area Networks (PANs) Intended for short distance communication with devices owned & operated by a single user Bluetooth Intended as a wireless replacement for cables (i.e. headphones, mouse, etc.) Devices are masters or slaves, where the master grants permissions to the slave device Ultra Wideband (UWB) Originally designed for commercial radar systems Spreads data across several frequencies; requires less power to reach the same distance Consumes very low power Signal can go through obstacles, such as walls ZigBee Used in low data rate applications requiring a long battery life Home automation, wireless sensors, smoke/intruder alarms, medical data collection Typically for short distances, but can transmit longer distances through a mesh network Infrared (IrDA) Often used in remote controls, and as a cable replacement (i.e. wireless mouse) RFID Radio Frequency Identification / Used for inventory control, sensors, passports, etc. Small tags contain identification information that a receiver can pull/extract from the tag Passive tags draw power from the receiver's signal / active tags contain batteries Limited distance, but active tags extend further

Wireless Bands Used by PANs and LANs Uses areas of the electromagnetic spectrum reserved by governments for Industrial, Scientific and Medical use These are unlicensed frequencies 26 MHz bandwidth 83.6 MHz bandwidth 125 MHz bandwidth 902 928 2.4 2.484 5.725 1200 MHz MHz GHz GHz GHz KHz

Wireless LAN Technologies Popular standards for wireless LAN technologies: Standard Frequency Band Data Rate Notes 802.11 2.4 GHz 2 Mbps Equipment no longer manufactured / too slow Unregulated frequency means interference from microwaves, cordless phones, etc. 802.11a 5 GHz 54 Mbps Higher frequency = shorter range Regulated frequency prevents interference from other devices 802.11b 11 Mbps Not compatable with 802.11a equipment 802.11g Attempt to combine the better range of b with the faster speed of a Supported by practically all network equipment in use today Backward compatable with b so it works with b equipment – however, if any b equipment is used, the entire network slows to 11 Mbps 802.11n 300 Mbps Uses several wireless signals and antennas (MIMO technology) Increased signal intensity = better range Backward compatable with b and g equipment Use of multiple signals may interfere with nearby 802.11b/g networks

Wireless LAN Technologies Current popular standard: Standard Frequency Band Data Rate Notes 802.11ac 2.4 GHz and 5 GHz Up to 5300 Mbps Supports simultaneous connections on both the 2.4 and 5 GHz bands Vendors advertise AC1300 / AC1750 / AC1900 etc. to indicate the maximum possible speed of the equipment 40 MHz bandwidth for 2.4 GHz stations / 80 MHz for 5.0 GHz stations with support for 160 MHz channels Supports up to 8 MIMO streams (several wireless signals and antennas) Supports beamforming (target signal in direction of station for better/stronger signal) Uses 256-QAM (8 bits per signal change), with some vendors using 1024-QAM (10 bits per signal change) Next Step: 802.11ax with support for up to 10,000 Mbps and range of over 500 ft

Spread Spectrum Technologies Uses multiple frequencies to send data Increased data rate (send multiple bits in parallel) Increased immunity to noise (send multiple copies of the data) These techniques help wireless LANs function in noisy enviroments Major spread spectrum technologies used in wireless LANS include: Name Expansion Description DSSS Direct Sequence Spread Spectrum Similar to CDMA where a "chip sequence" is used to divide the data into blocks to send over multiple frequencies. Receiver uses the same sequence to decode the data FHSS Frequency Hopping Spread Spectrum Data is spread over a pseudorandom sequence of frequencies, which is known in advance by both sender and receiver OFDM Orthogonal Frequency Division Multiplexing FDM where the band is divided into multiple carriers such a way as to minimize interference from the other channels

Wireless LAN Architecture Ad-hoc – wireless hosts communicate among themselves without a base station Also called peer-to-peer networks Used for technologies such as Wi-Fi Direct Infrastructure – wireless hosts communicate only with a base station, which relays packets Access points are deployed throughout buildings, and devices (hosts) communicate with the access point to gain access to a network

Wireless LAN Architecture hub or switch Basic Service Set (BSS) The set of devices serviced by an access point range of access point access point

Wireless LAN Architecture Internet hub or switch router modem

Wireless LAN Architecture Dead zones exist when access points are too far apart Hosts in this area have no wireless connectivity Overlap occurs when access points are too close together Hosts in this area can reach multiple access points dead zone overlap

successful transmission Wireless Frame Format Overlap is handled by requiring the host to associate with only one access point 802.11 frame format requires the address of an access point 2 bytes 2 bytes 6 bytes 6 bytes 6 bytes 2 bytes 0 – 2312 bytes 4 bytes control duration AP address source address destination address sequencecontrol payload CRC frame type connection ID or time in ms the channel is allocated for successful transmission access point's MAC address sender's MAC address receiver's MAC address cyclic redundency check used to help reassemble multiple packets in the correct order

Access Point Coordination Complex access points coordinate with each other to ensure a smooth handoff as a device moves from one BSS (basic service set) into another This is often attempted by measuring signal strength connected strength=10 strength=2

Access Point Coordination Complex access points coordinate with each other to ensure a smooth handoff as a device moves from one BSS (basic service set) into another This is often attempted by measuring signal strength strength=5 strength=4 connected

Access Point Coordination Complex access points coordinate with each other to ensure a smooth handoff as a device moves from one BSS (basic service set) into another This is often attempted by measuring signal strength hand off strength=4 strength=5 connected

Access Point Coordination Complex access points coordinate with each other to ensure a smooth handoff as a device moves from one BSS (basic service set) into another This is often attempted by measuring signal strength Simpler, lower cost, access points leave it to the hosts to handle changing from one access point to another An argument for this is that signal strength isn't a good measure point

Multi-Access Coordination Although 802.11 defines two approaches for channel access, only DCF is actually used Point Coordinated Function (PCF) requires the access point to ensure that station transmissions do not interfere with each other For example, by assigning each station a different frequency to use Distributed Coordinated Function (DCF) requires each station in a BSS to run a random access protocol. 802.11 networks use CSMA/CA Before sending a packet of data, CSMA/CA requires: sending station to transmit a Ready To Send message receiving station to transmit a Clear To Send message

Multi-Access Coordination The standard also defines how long stations must wait Short Inter-Frame Space of 10 μs Amount of time receiver waits before sending response Distributed Inter-Frame Space of 50 μs (SIFS + 2*slot time) Amount of time channel must be free before a station attempts a transmission Slot Time of 20 μs Twice the time it takes for a pulse to travel the theoretical distance between two stations DIFS Ready To Send SIFS Clear To Send SIFS Data SIFS Acknowledgement

Wireless MAN Technology WiMAX (World-wide Interoperability for Microwave Access) is a specific MAN technology with potential for commercial success Uses licensed spectrum Standard Description Fixed WiMAX Does not provide for handoff among access points Designed for fixed/stationary connections between user and service provider (such as a provider to an office building or residence) Mobile WiMAX Technology offers handoffs as users move between access points Designed for moving connections (such as laptops or cell phones)

Wireless MAN Technology Potential Uses Speed Requires Use High Data Rates Line-of-Sight Backhaul from access points to a service provider Private connections among sites in a company Connections between small and large ISPs Lower Data Rates Non Line-of-Sight Last-mile Internet access (instead of DSL, cable, satellite, cellular) High speed connection for mobile users (instead of cellular) Backup for a site's normal Internet connection

WiMAX Deployment Non Line-Of-Sight Backhaul Line-of-Sight Access wired connection Wi-Fi Non Line-of-Sight Access

Wireless WAN Technology WAN technologies consist of: Cellular Satellite

Cellular Communications Originally designed for voice services to mobile customers, and so was designed to interconnect to the public telephone network Now, cellular services provide data connectivity and Internet access and so the technologies have evolved over time to adapt to this

Cellular Architecture Towers provide cellular service to an area, called a cell Mobile Switching Center tracks a mobile user and manages handoff as user moves from cell to cell public switched telephone network + Internet connection mobile switching center mobile switching center wired connections cell

Cellular Coverage In theory, perfect coverage occurs if each cell forms a hexagon, because they can be arranged into a honeycomb pattern In reality, cell towers use omnidirectional antennas and transmit in a circular pattern. In addition, interference and obstructions distort signal patterns and create overlap and dead zones.

Micro Cells In rural areas, density of cell phones is low and cell size is large One tower may be enough to cover a large geographic area In cities, many cell phones are concentrated in a given area A region may be broken into several cells, in order to handle more cell phones Cells can even be broken so small that a few floors of a building could be a cell Micro cells are used to create these extremely small cell sizes, and use much less power so as to avoid interference They can also be used to provide cellular service to a customer in a rural area where cellular service is not available

public switched telephone network + Internet connection Micro Cells Micro cells connect to a wired Internet connection and are configured to recognize a specific set of cell phones public switched telephone network + Internet connection switching center micro cell

Frequency Reuse A I B A A F B J C A C H K G C B E C L D B D G E D F To avoid interference, adjacent pairs of cells should not use the same frequency A cluster approach is used so that Clusters are cells arranged in a pattern that can be replicated Each cell in the pattern is assigned a different frequency Cluster Size 12 Cluster Size 7 A Cluster Size 4 Cluster Size 3 I B A A F B J C A C H K G C B E C L D B D G E D F

Frequency Reuse A G D B C F E A G D B C F E A G D B C F E A G D B C F

Cellular Generations Generation Description 1G First generation used analog signals to carry voice telephone calls 2G Second generation used digital signals to carry voice calls 3G Focused on addition of higher-speed data services of up to 2 Mbps Example supported applications include web browsing and photo sharing Allows a single phone to roam across North America, Japan, and Europe 4G Focused on support for real-time multimedia Example supported applications include television programs and high-speed video Includes multiple connection technologies, such as Wi-Fi and Satellite

Standards At creation of 2G, many groups attempted to choose an approach and create a standard Standard Description GSM Uses TDMA technology and was intended to be a world-wide standard Created in Europe iDEN Uses TDMA technology Created for use in the United States by Motorola IS-95A Uses CDMA technology Adopted by most US and Asian carriers

Standards 3G systems were designed using voice standards, with data as an added feature 4G systems were designed to use the Internet Protocol and packet switching Voice transmission is just another application Standard Description HSPA+ HTC Evo 4G LTE WiMAX Although marketed as 4G technologies, these do not technically meet the standards defined for 4G LTE Advanced WiMAX Advanced Meets the specifications for 4G and thus is referred to as "True 4G"