There are four broad wireless technology categories:
Wireless personal area network.
A wireless personal area network (WPAN) is designed for hand-held and portable devices at slow to moderate transmission speeds. The maximum distance range between devices is generally 33 feet (10 meters) transmitted at 1 Mbps.
There are two types of Bluetooth network topologies. The first is known as a Bluetooth piconet.
In this topology, when two Bluetooth devices come within range of each other, they automatically connect to each another. One device is the master, and controls all of the wireless traffic.
The other device is known as a slave, which takes commands from the master. Slave devices that are connected to the piconet and are sending transmissions are known as active slaves; devices that are connected but are not actively participating are called parked slaves .
Devices in a Bluetooth piconet can be in one of five different modes:
● Standby. A device in standby mode is waiting to join a piconet.
● Inquire. In inquire mode another device is looking for other devices with which to connect.
● Page. Page mode is when a master device is asking to connect to a specific slave.
● Connected. When a device is either an active slave or a master it is in connected mode.
● Park/Hold. A device in park/hold mode is part of the piconet but is in a low-power state
If multiple piconets cover the same area, a Bluetooth device can be a member in two or more overlaying piconets. A group of piconets in which connections exist between different piconets makes up the second type of Bluetooth network topology and is called a Bluetooth
A Bluetooth device can be a slave in several piconets but can be a master in only one piconet.
Bluetooth uses frequency hopping spread spectrum (FHSS) so that all devices in a Bluetooth network must change frequencies at the same time and in the same sequence in order for communications to take place. The timing in the hopping sequence is determined by the master’s clock, to which each active slave is synchronized.
attacks on wireless:
Bluetooth technology are not uncommon. Two Bluetooth attacks are bluejacking and bluesnarfing.
- Bluejacking is an attack that sends unsolicited messages to Bluetooth-enabled devices. Usually bluejacking involves sending text messages, but images and sounds can also be transmitted. Bluejacking is usually considered more annoying than harmful because no data is stolen. However, many Bluetooth users resent receiving unsolicited messages.
- Bluesnarfing is an attack that accesses unauthorized information from a wireless device through a Bluetooth connection, often between cell phones and laptop computers. In a bluesnarfing attack the attacker copies e-mails, calendars, contact lists, cell phone
pictures, or videos by connecting to the Bluetooth device without the owner’s knowledge or permission.
The first is video and audio distribution for home entertainment systems, which includes high-speed digital video transfer from a digital camcorder to a screen and interactive video gaming.
The second application is higher-speed data transferintended for MP3 players, personal home storage devices, printers, scanners, and transfers to and from digital still cameras and kiosks.
UWB has not been widely implemented. Because it distributes a signal across a wide range of spectrum (sometimes several gigahertz), widespread interference on other transmissions is a concern.
As an alternative to using UWB for wireless home entertainment systems, a new technology known as Wireless Display (WiDi) is
gaining popularity. WiDi enables a user to project a display from a WiDi-enabled portable device like a notebook or tablet to a
WiDi adapter connected to a television using 802.11n. A user can share documents or stream movies on the portable device and display them onto the TV screen. WiDi does not even require that the image on the device’s screen be the same as that that being projected, so that a user can stream a movie while checking e-mail at the same time.
Low Rate technologies (802.15.4)
Some times low speed and low power are more desirable. A WPAN device using low power can be much smaller in size, even down to the size of a penny. Applications using low rate technologies include motion sensors that control lights or alarms, light wall switches, meter reader devices, game controllers.
Two popular low rate 802.15.4 technologies are ZigBee and radio frequency ID(802.15.4f).
ZigBee is a low-power, short-range, and low-data rate specification. It is based on 802.15.4 but includes standards for network configuration, security and other higher-level features that are not covered by the IEEE standard. ZigBee’s data rate is 250 kbps and is
best designed for occasional data or signal transmission from a sensor or input device.
ZigBee is typically found in the following applications:
● Smart lighting
● Advanced temperature control
● Medical data collection
● Smoke and intruder detection
Radio Frequency Identification (RFID)
Although currently not governed by an established IEEE standard, the 802.15.4f group is working on standards that relate to radio
frequency identification (RFID). RFID can be active or passive:
- Passive RFID tags do not have their own power supply.
- Active RFID tags must have their own power source. Although this makes the tags larger (about the size of a coin), the tags have longer ranges and larger memories than passive tags, as well as the ability to store additional information sent by the transceiver.
Many active tags have a range of 98 feet (30 meters) or more and a battery life of several years.
- Automobile toll booths
- Asset tracking
- Tire manufacturer
- Card , hotel chain.
- Smart key
A similar technology based on RFID standards is near field communication (NFC). NFC is a set of standards primarily for smartphones and smart cards that is used to establish communication between devices. Once the devices are either tapped together or brought into close
proximity (several centimeters) to each other a two-way communication is established. NFC devices are used in contactless payment systems where a consumer can pay for a purchase by simply tapping a store’s payment terminal with their phone.
Body area networks (802.15.6)
A BAN is formally defined by the IEEE as “a communication standard optimized for low power devices and operation on, in or around the human body (but not limited to humans) to serve a variety of applications including medical, consumer electronics/personal entertainment and other.” A BAN is essentially a network system of devices in close proximity to a person’s body that cooperate for the benefit of the user.
BANs are commonly used for sports and fitness monitoring. These are then transmitted via computer or smartphone to a third party physician who can make a decision regarding any medications to prescribe or lifestyle changes to recommend. Known as a managed body sensor network (MBSN) .
A more robust approach is the autonomous body sensor network (ABSN). Instead of only reading and transmitting information, an ABSN introduces actuators in addition to the sensors so that immediate effects can be made on the human body. One type of ABSN has already been approved for use.
Visible Light Communications (802.15.7)
Advantages over RF.
- First, sources of interference that impact RF transmissions have no impact on transmissions that are based on light.
- Second, unlike RF devices that decrease the throughput as the transmission distance increases, devices that rely on light do not vary the transmission speed.
One of the original WPAN technologies using light is based on a standard known as IrDA. IrDA is an acronym for the Infrared Data Association, which is a nonprofit consortium. Infrared data ports conforming to the IrDA specifications were installed on notebook computers, computers, printers, desktop adapters, cameras, phones, watches, pagers, storage devices, and kiosks. These IrDA devices can transmit from 9.6 Kbps to 16 Mbps.
Popularity significantly diminished due to its drawbacks:
● IrDA technology was designed to work like the standard serial port on a personal computer. These ports are seldom used today.
● IrDA devices cannot send and receive at the same time because the transmitter and receiver are not optically isolated.
● Strong ambient light can negatively impact the transmissions.
● The angle at which the sending and receiving IrDA devices align or face each other is very important. When the two devices have a deflection angle of no more than 15 degrees, the distance between devices can be up to 3 feet (1 meter).
Visible light communications (VLC)
Anew type of WPAN based not on infrared light but on visible light (which is adjacent to infrared on the frequency spectrum) is gaining popularity. It is known as visible light communications (VLC) .
Because this modulation is faster than the human eye can detect, humans cannot perceive a transmission taking place. A comparison of VLC to the frequency and wavelength of other wireless technologies is shown in Figure bellow,
while a comparison of different data rates and distances is provided in Figure bellow:
In a star topology, all of the devices communicate with a single central controller, called the coordinator. Each VLC star network operates independently from all other star networks. In a broadcast topology the device in a broadcast mode can transmit a signal to other devices without actually forming a network. This communication is unidirectional and the destination address of the receiving devices is not required.
VLC has several advantages:
● Visible light is harmless to the human body.
● VLC networks can be created to transmit data by adding optical communication devices to the sockets of existing light fixtures.
● No electromagnetic interference (EMI) impacts VLC.
● There are no regulations regarding the use of light.
● The signals cannot be intercepted because the transmission range is narrowly confined so transmissions are secure.
Wireless local area network.
WLANs such as IEEE 802.11a/b/g/n are for portable or stationary devices that are within a few hundred feet of each other or a centrally located access point (AP) (the maximum distance is usually 350 feet or 107 meters). Depending upon the standard, transmission speeds may range up to 600 Mbps.
Wireless metropolitan area network.
A wireless metropolitan area network (WMAN) is designed for devices in a range of up to 35 miles (56 kilometers) using radio frequency (RF) or infrared transmission technology at different speeds.
Wireless metropolitan area networks (WMANs) cover an area of up to about 35 miles (56 kilometers) as the distance between devices.
Free Space Optics (FSO)
Whereas VLC is used for indoor communications, free space optics (FSO) is an optical, wireless, point-to-point, line-of-sight wireless technology for outdoor transmissions.
It was originally developed over 30 years ago by the military and today serves as an alternative to high-speed fiber optic cable. Currently FSO can transmit at speeds comparable to fiber optic transmissions of up to 1.25 Gbps at a distance of 2.5 miles (4 kilometers). FSO uses infrared transmission instead of RF, sending low-powered infrared beams through the open air.
Because FSO is a line-of-sight technology, the link heads must be mounted high in office buildings to provide a clear transmission path. However, unlike other technologies that require the units to be located on an open roof (which sometimes requires leasing roof space from the building’s owner), FSO link heads can be mounted behind a window in an existing office.
Under ideal conditions, FSO could transmit up to 6.2 miles (10 kilometers).
There are several advantages of FSO:
● Lower installation costs. FSO installations cost significantly less than installing new fiber optic cables or even leasing lines from a local carrier. One project compared the costs of installing fiber optic cables to FSO in three buildings and found the cost of the former was almost $400,000 whereas the cost of FSO was less than $60,000.
● Faster installation. FSO can be installed in days or weeks compared to months and sometimes years for fiber optic cables. In some instances, FSO systems have been installed over a weekend in major office buildings with no disruption of service to the users.
● Scaling transmission speed. The transmission speed can be scaled to meet the user’s needs, anywhere from 10 Mbps to 1.25 Gbps. If high speeds are not required, the user does not have to pay a premium for unused capacity as when leasing a line from a carrier but instead can design the FSO system to match needs.
● Good security. Security is a key advantage in an FSO system. IR transmissions cannot be intercepted and decoded as with some RF transmissions.
The primary disadvantage of FSO is that atmospheric conditions can affect FSO transmissions.
Broadband Radio Service (BRS)
Broadband Radio Service (BRS) is a wireless technology that uses microwave frequencies.
Formerly known as Multichannel Multipoint Distribution Service (MMDS), BRS is commonly used as a wireless alternative to cable television reception.
BRS hubs are typically located on top of mountains, towers, buildings, or other high points.
The hub uses a point-to-multipoint architecture that multiplexes communications to multiple users. The tower has a backhaul connection to the carrier’s network, and the carrier network connects with the Internet. Because they operate at a lower frequency, BRS signals can travel longer distances.
The advantages to BRS are its long range of transmission, its large cell size, and the fact that it is less vulnerable to poor weather conditions. However, it still requires a direct line of sight and the wireless transmissions are generally not encrypted.
Wireless wide area network.
Wireless facilities that connect networks in different parts of a country or of the world are known as wireless wide area networks (WWANs). The transmission speeds again vary, although often are slower than those for a WMAN.
The primary technologies for WWAN are WiMAX and long term evolution (LTE).
WiMAX (Worldwide Interoperability for Microwave Access) is based on the IEEE 802.16 standards. The MAC layer of WiMAX is different than that used in IEEE 802.11a/b/g (CSMA/CA) or Ethernet (CSMA/CD). Instead, WiMAX uses a scheduling system and the device only has to compete once for initial entry into the network. Once the device has been accepted it is allocated a time slot. Although this time slot can expand and shrink, it remains assigned to that device and other devices must take their turn. This type of scheduling algorithm is more stable under heavy loads and is more efficient with bandwidth. The scheduling algorithm also allows the base station to control Quality of Service (QoS) by balancing the assignments among the needs of the subscriber stations.
WiMAX has counterparts in other nations as well. The WiMAX equivalent in Europe is HIPERMAN. Korea’s standard, WiBro, has already agreed upon interoperability with WiMAX.
WiMAX can be broken down into two categories:
Fixed WiMAX, based on IEEE 802.16-2004, can serve as a substitute for fiber optic connections between buildings similar to FSO and BRS. It provides up to 31 miles (50 kilometers) of linear service area range and does not require line-of-sight. WiMAX also provides shared data rates up to 70 Mbps.
Mobile WiMAX, which is based on IEEE 802.16e-2005, can connect mobile devices over a wide area. One mobile WiMAX base station can cover an area of 6 miles (9.6 kilometers). It can also support users traveling at vehicular speeds of 70 miles per hour (112.6 kilometers per hour). Mobile WiMax is often promoted as a solution to the last mile connection.
Long Term Evolution (LTE)
Cellular telephones work in a manner that is unlike wired telephones. The coverage area for cellular telephony is divided into cells. In a typical city the cells, which are hexagon-shaped, measure 10 square miles (26 square kilometers). At the center of each cell is a cell transmitter to which the mobile devices in that cell send and receive RF signals. These transmitters are connected to a base station, and each base station is connected to a mobile telecommunications switching office (MTSO). The MTSO is the link between the cellular network and the wired telephone world and controls all of transmitters and base stations in the cellular network. All of the transmitters and cell phones operate at a low power level that enables the signal to stay confined to the cell and not interfere with other cells. Because the signal at a specific frequency does not go outside of the cell area, that same frequency can be used in other cells at the same time.
Because of frequency reuse, a typical cellular telephone network in one city uses only 830 frequencies to handle all callers.
As cellular telephony has evolved from analog to more advanced packet-switching digital systems, digital WWAN technologies can be used to replace these older analog systems.
Although LTE is commonly referred to as a fourth generation (4G) technology, technically the current version of LTE does not meet all the requirements for 4G. It is anticipated that the next generation of LTE, known as LTE Advanced, will meet these requirements.
In January 2011, the IEEE Task Group for 802.11ac published its first draft of IEEE 802.11ac, known as Very High Throughput <6Ghz, to support higher data rates, in part to address the demand for wireless video delivery. Building upon many of the enhancements introduced in 802.11n, this new standard has advertised data rates over 1 Gbps. Some of 802.11ac’s technologies include:
● Spectrum. 802.11ac will operate in the less-crowded 5 GHz spectrum. It will not support the 2.4 GHz spectrum.
● Increased channel bandwidth. Whereas 802.11n uses channels up to 40-MHz-wide channels, the 802.11ac standard uses channel bandwidths up to 80 MHz. To achieve this, it was necessary to adapt automatic radio tuning capabilities so that higherbandwidth channels are only used when necessary in order to conserve spectrum use.
● MU-MIMO. A variation of MIMO known as Multi-User MIMO (MU MIMO) is implemented in 802.11ac. MU-MIMO enables the simultaneous transmission of different data frames to different clients. This requires that equipment is able to utilize the spatial awareness of the different remote users.
● Error correction coding. Advances in chip manufacturing technology have enabled designers to take advantage of additional levels of processing power so that more sensitive coding techniques that depend on finer distinctions in the received signal can be used. This reduces the number of error correction check bits needed.
● Beam forming. Under 802.11n, transmit beam forming (TxBF) was available, but many products did not take advantage of it.
● Improved battery life. Because of its increased speed in file transfers and similar activities, mobile users may find that by using 802.11ac they can increase their battery life (because it takes less time for activities that require the device to draw significant battery power)