Wireless Personal Area Networks (WPAN)

Definition

The main characteristic of a Wireless Personal Area Network (WPAN) is that its communication systems concentrate on a typical 10-meter area surrounding the location of an individual or device, whether or not in motion.  “Unlike a wireless local area network (WLAN), a connection made through a WPAN involves little or no infrastructure or direct connectivity to the world outside the link.”  This type of technology also aims at efficient resource use, so that simple protocols optimal for each communication need and application have been designed.

Interconnection of personal devices differs from connection of computer devices.  Typical connection solutions for computer devices (such as a WLAN connection for a notebook computer) associate the user of the device with available data services.  This contrasts with the intimate and personal nature of a wireless connection for devices associated with particular users.  The user is associated with the electronic devices in his possession or vicinity rather than to any exact place or network location.  The term “personal area network” (PAN) was developed to describe this different type of network connection.  A WPAN may be viewed as a personal communications bubble around a person.  Within this bubble, which moves as the person moves around, personal devices can connect with one another.

Working groups

There are mainly four WPAN technology task groups, each with specific characteristics and interests, which are generating standards to meet specific communication needs.

• The 802.15.1 Task Group has derived a standard based on Bluetooth Foundation Specifications.  The group published the IEEE 802.15.1 standard on June 14, 2002.

• The 802.15.2 Task Group is developing models to facilitate coexistence of WLANs and WPANs, and of their surrounding devices.

• The 802.15.3 Task Group works to determine statuses and publish a new standard for high-rate (20 Mbits/s or greater) WPANs (published in June 2003).  Besides a high data rate, the new standard will provide for low power, low cost solutions addressing the needs of multimedia applications.

• Task Group 4 to derive IEEE 802.15.4 is researching and developing low data rate solutions with multi-month to multi-year battery life and very low complexity. This task group has published the standard bearing its name:  IEEE 802.15.4.

Types of WPAN

The IEEE 802.15 Task Group has defined three types of WPANs, distinguished by their data rate, energy consumption, and quality of service (QoS):

• High-rate WPANs (802.15.3) designed for multimedia applications requiring high QoS levels

• Mid-rate WPANs (802.15.1/Bluetooth) that can handle tasks ranging from cell phones to communication between Personal Digital Assistants (PDA).  Their QoS is appropriate for voice applications

• For the final type of application, WPAN-LRs (802.15.4) (low speed, low-rate).

WPAN components

The ultimate aim of communication protocols is permit applications on different devices so that they can interact.  For this, devices require compatible communication stacks.  This means both that the stack communication protocols running in the devices must be compatible and functional and that applications running on such stacks must be compatible.

Bluetooth

Bluetooth is a technology that enables several electronic devices, such as mobile phones, computers, or PDAs, to connect with one another utilizing a short-range connection, without the need for cable.  Such cableless connection is established via a low frequency radio link.  The main benefit of this technology is that it eliminates the need for the cables now required for information transfer.

Bluetooth works using a device with a special installed microchip, which essentially serves as a short-range walkie-talkie. This 9 x 9 mm microchip enables the device to send short-range radio signals that seek other devices with Bluetooth technology.  When another device is located, the two devices begin to communicate and information can be exchanged.  Bluetooth is fighting to use electromagnetic spectrum in the 2.4 GHz band, specifically between 2,402 and 2,480 GHz.

Coverage cannot exceed 10 meters, which is why devices interconnected using this technology are called Wireless Personal Area Networks (WPAN).  This wireless connection’s maximum rate is 1 Mbps, but in practice, it is about 725 kbps. The chip is manufactured using 0.25-micron CMOS technology and modulates the device’s signal.  As a protocol is required for more effective transmission, each device has an MAC address identifying each component of the wireless network.

Although neither IrDA nor Bluetooth requires cable for communication and information exchange, with IrDA, to maintain communication, the devices must be in line of sight.  As Bluetooth is based on radio transmission, devices need not be in line of sight.  Instruments using Bluetooth technology can communicate at greater distances than those using IrDA, even if there are objects in the way that obstruct communication.

Bluetooth topologies

Piconet:

Some Bluetooth units may be within the range of others, so that point-to-point, point-to-multipoint, or ad hoc connections may be configured.  Units are connected to and disconnected from the network dynamically. Two or more Bluetooth units sharing a single channel form a piconet.  A piconet will always have one master and the other devices will be slaves (See Figure 1).

Figure 1:  Piconets with p-t-p and p-t-mp operation

Piconet characteristics:

• Star topology

  • One master and up to seven active slaves sharing one asynchronous channel
     

  • Unlimited number of parked slaves, up to 255 virtually-connected slaves (one device can participate every 2 ms)
     

  • A device may serve without distinction as master or slave

• The master is a device in a piconet that marks the frequency that will be used to synchronize all slave units of the piconet

  • Determines the frequency hopping scheme and timing
     

  • Administers the piconet (polling)

• Logic channels

  • Asynchronous, packet oriented (ACL)
     

  • Synchronous, connection oriented (voice, reserve of slot) (SCO)

·      Rate

• 1 Mbits/s total capacity

Scatternet:

Slave devices may participate in different piconets and the master of one piconet may be the slave of another, resulting in a scatternet.  A scatternet can have no more than 10 piconets (See Figure 2).

Some piconets may be formed and linked together in ad-hoc scatternet networks to make it possible to communicate and exchange data in flexible configurations.  If other piconets are within range, they will operate independently and will have access to the total bandwidth.  Each piconet has a different frequency-hopping scheme.  All users participating in one piconet will be synchronized to its frequency-hopping scheme.

Figure 2:  A scatternet

 Working document taken from:
 

1. Valle Islas, L.F.: Coexistencia de Redes WLAN & WPAN (thesis, B.S. in Electronic and Communications Engineering, Department of Electronic Engineering, University of the Americas, Puebla, Mexico). Web page: http://140.148.3.250/u_dl_a/servlet/mx.udlap.ict.tales.html.Block?Thesis=lem103582&Type=T
2. MundoGPS:  “Bluetooth:  un nuevo aliado en la transmisión de datos”

Web page:  http://www.mundogps.com/formacion/articulos.asp?id_articulo=274

Adapted for the international course: “Comunicaciones Fijas Inalámbricas” by Alex José Chávez Ramírez:  ajchavez@pucp.edu.pe