Introduction to Wireless Networking ECE 401WN Spring 2009

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1 I. Overview of Bluetooth Introduction to Wireless Networking ECE 401WN Spring 2009 Lecture 6: Bluetooth and IEEE Chapter 15 Bluetooth and IEEE What is Bluetooth? An always-on, short-range radio hookup that resides on a microchip. First developed by Swedish mobile-phone maker Ericsson in Now several thousand companies produce Bluetooth products. Through an industry consortium known at the Bluetooth Special Interest Group (Bluetooth SIG). IEEE standardized Bluetooth as IEEE Other related standards are IEEE and Name comes from King Harald Blaatand (Bluetooth) of Denmark. Lived in the 10 th century. Credited with unifying Denmark and Norway. Hence, Bluetooth unifies communication between many devices. The Bluetooth logo comes from his initials. Goals Provides universal short-range wireless capabilities. Using 2.4 GHz band. Within 10 meters. Up to 720 kbps. Lecture 7, Page 1 of 16

2 Why is a short-range wireless network like this useful, instead of just using ? Smaller devices, no need to connect to the Internet, more automatic configuration. Lower power. Intended to support an open-ended list of applications. Data, audio, graphics, even video. What are possible example applications? Audio headsets, cordless phones, home stereos, MP3 players. Wireless headset for a cell phone. Eliminate cables from computers to printers, keyboards, and the mouse. Wireless connections for MP3 players to download music. Home networks to integrate air conditioning, oven, entertainment, children s Internet surfing, etc. And control home networks remotely. Lecture 7, Page 2 of 16

3 Many products are being sold, with lots of marketing push. Cell phones with Bluetooth. Bluetooth computer peripherals. Bluetooth enabled cameras. Bluetooth Application Areas Bluetooth has defined three general application areas. Data and voice access points Real-time voice and data transmissions. Cable replacement Eliminates need for numerous cable connections. - Non-Bluetooth wireless devices use an unlicensed frequency band at 27 MHz. - Range of 2 meters instead of 10 meters MHz is more affected by obstructions. - Less security. - Or use infrared. Ad hoc networking Instant connections with other Bluetooth radios. - As soon as they come into range of each other. - Examples: Instant synchronization of PDA and host computer, instant downloading of images from a camera. Table 15.1 in the text gives some examples of Bluetooth uses. Bluetooth Standards Well over 1500 pages of documents. Divided into two groups: Core and Profile specifications. Core Specifications Details of layers of the Bluetooth protocol architecture. Also interoperability with related technologies, testing requirements, definition of Bluetooth timers, etc. Profile Specifications Describe support for various applications. For each profile, defines which technologies in the core specifications are mandatory, optional, or not applicable. Allows vendors to interoperate based on a profile, not the whole Bluetooth standard For example, wireless cellphone headsets. Two categories of profile specifications - Cable Replacement - Wireless Audio Short range voice connections. Lecture 7, Page 3 of 16

4 Bluetooth Architecture Consists of core protocols, cable replacement and wireless audio protocols, and adopted protocols. See Figure Core protocols Bluetooth radio frequencies, use of frequency hopping, modulation schemes, transmit powers. Baseband Connection establishment within a cluster of Bluetooth devices, addressing, packet format, timing, power control. Link manager protocol (LMP) Ongoing link management between devices, authentication and encryption, packet sizes. Logical link control and adaptation protocol (L2CAP) Adapts upper layer protocols to the baseband layer. Provides connectionless and connection-oriented services. Service discovery protocol (SDP) Supports queries of the capabilities of other devices (device information, services, characteristics of the services). Lecture 7, Page 4 of 16

5 Profile-based Protocols the cable replacement protocol. - Provides a virtual serial port. - Designed to make replacement of cables as transparent as possible. - Binary data transport - Emulates EIA-232 control signals (formerly called RS-232). the telephony control protocol. - Defines call control for the establishment of speech and data calls. Adopted Protocols Specifications from other standards bodies that are incorporated into the Bluetooth architecture. Usage Models Define the protocols to be used for a particular application. Here are the usage models that are the highest priority. File transfer file transfer and the ability to browse files on a remote device. Internet bridge connect through a mobile phone for a modem-like connection. LAN access devices can connect and function as if directly connected to a wired LAN. Synchronization device-to-device synchronization of personal information (phone book, calendar, messages). Three-in-one phone can act as a cordless phone connecting to a voice base station, or as an intercom device for connecting to other telephones. Headset can act as an audio input and output interface for a remote device. Lecture 7, Page 5 of 16

6 As an example, Figure 15.2 (a) shows the protocols used for file transfer. Clustering Up to 8 devices create a small network called a. Consists of a master and up to seven slave devices. The Master makes the determination of the frequency hopping sequence and timing for all 8 devices. A slave may only communicate with the master, not other slaves. - And only when granted permission from the master. A slave in one piconet can be a master or slave in another (node M/S below). - A node can be a master in only one piconet, however. Lecture 7, Page 6 of 16

7 Up to ten piconets can coexist in the same coverage area. And will overlap at devices which are members in multiple piconets. This is called a. Figure 15.4 shows how this is different than other wireless configurations. Lecture 7, Page 7 of 16

8 What is the advantage of the piconet/scatternet scheme compared with the other configurations above? Allows many devices to share the bandwidth, but not have to associate with all of the other devices. Frequency Hopping According to a pseudorandom sequence. Bluetooth uses a carrier spacing of 1 MHz. Typically up to 80 frequencies are used for a total bandwidth of 80 MHz. At any one time, only one carrier is used by a piconet. Shared on a time slot basis with the 8 devices, as dictated by the Master. Lecture 7, Page 8 of 16

9 Other piconets can share this same bandwidth. Collisions can occur if more than one piconet uses the same frequency out of the 80 in a time slot. More piconets, more chances of collisions. - This is why there is a limit of 10 piconets in a scatternet. But collisions will be brief. Error control detection, correction, and retransmission mechanisms are used in case there are collisions. What two purposes do you suppose frequency hopping accomplishes? 1. Resistance to interference. 2. Allows multiple access. How it works Total bandwidth is divided into 79 channels (due to regulations in almost all countries, France and Spain use 23) of 1 MHz each. Hop rate is 1600 hops per second. - So each channel is occupied for milliseconds. Packets begin transmission at the beginning of a time slot. Packets can take 1, 3, or 5 time slots. - The frequency stays constant during the packet, even if it takes more than one slot. - Once completed, the radio jumps back to get back onto what would have been its original sequence. - This may mean skipping 2 or 4 frequencies. The frequency hopping sequence is a function of the master s Bluetooth address and other factors. Different masters have different addresses, and, therefore, different hopping sequences. Lecture 7, Page 9 of 16

10 Radio Specification Three classes of transmitters Class 1 - Max 100 mw (+20 dbm) for maximum range. - Power control must be used the node must dynamically adjust its power levels to only what is really needed. Class mw - Power control is optional. Class 3 - Lowest power. 1 mw. Physical Links two types between master and slave. 1. Synchronous connection oriented (SCO) Allocates a fixed bandwidth A point-to-point connection between a master and a single slave. Uses reserved time slots Two consecutive slots are reserved, one for each direction. Provides guaranteed data rates and time-bounded delays. A master can support up to three simultaneous SCO links. Lecture 7, Page 10 of 16

11 SCO packets are never retransmitted. But errors may be detected and corrected by error control codes that come along with the packet. Or a few lost packets might not cause a problem. - Example: Thousands of packets per second of audio, one would certainly not be missed. 2. Asynchronous connectionless (ACL) Point-to-multipoint link. Between master and all slaves. Used in slots not reserved for SCO links. Only a single ACL link can exist. Retransmission is usually used for ACL packets. Packets can be 1, 3, or 5 slots A 5-slot unprotected (no error control) packet achieves a data rate of 721 kbps in the forward direction (master to slave) and 57.6 kbps in the reverse direction. Packet formats, error correction, logical channels See textbook for details. Beyond the scope of this class (pp ), so will not be on exams. Channel Control (p. 485) Operation of a piconet two major states. Standby default state, low power, only the clock is running. Connection device is connected to the piconet as master or slave. There are seven other interim substates used to add new slaves to the piconet. Masters page slaves; devices inquire about other devices in range, responses. Lecture 7, Page 11 of 16

12 Inquiry Procedure First, potential masters identify devices in range that wish to participate in the piconet. The potential master broadcasts an inquiry access code over 32 of the 79 carriers. - These 32 are called. - Devices in standby periodically wake-up and scan the wake-up carriers for inquiries. They save power by only scanning 32 of the 79 carriers. Once responses to inquiries have been received, the master pages devices to set up the piconet. - These are indicated by the paging states in the figure above. - Sets up the frequency hopping sequence. - Sets up timing. Lecture 7, Page 12 of 16

13 Bluetooth audio, link manager specifications, logical link control, quality of service are in the textbook on pp See textbook for details. Beyond the scope of this class. II. IEEE Working Group for Wireless Personal Area Networks (PANs) Personal Area Networks Short range Small area All of the devices on the network are typically owned by one person or a very small group. Devices PCs Personal Digital Assistants (PDAs) Peripherals Cell phones Pagers Consumer electronic devices First effort for Formal standard for Bluetooth Approved in is used unlicensed bands Same as created recommended practices for coexistence of the two. Lecture 7, Page 13 of 16

14 Status of Different physical layers, different MAC requirements. Different scope of application Lecture 7, Page 14 of 16

15 Two main directions after , plus others. 1. Low cost, low power, faster than Low cost and low power compared to Goal is high data rates over 20 Mbps Connecting digital cameras to printers or kiosks Laptops to projectors PDAs to cameras or printers Surround-sound speakers Video distribution from a set-top box or cable modem. Sending music to headphones or speakers Video camera display on a television Called by some Wireless USB An draft standard has been issued. Operates in unlicensed 2.4 GHz band. Up to 55 Mbps is possible. Other faster technologies were under consideration for a while, but efforts were disbanded because agreements could not be reached. 2. Low cost, low power, slower than Very low cost, very low power. Standard issued in 2003 and extended in Solution Low data rate Multimonth to multiyear battery life. Low complexity. Two physical layers 868/915 MHz - 20 kbps and 40 kbps 2.4 GHz kbps Lecture 7, Page 15 of 16

16 These types of applications have gained a lot of interest. Now the idea of small, low-power sensors is popular. What are possible uses? Security monitoring Weather, earthquake. Chemical sensing defines physical and MAC layers. The Alliance is producing specifications for network, security, and application layers. We will study sensor networks in detail in a later lecture. Other interesting directions of the Working Group can be seen at Mesh networking Body area networks Radio Frequency Identification Tags (RFIDs) Lecture 7, Page 16 of 16