Communications and Control Media. Bluetooth

Several media, individually or in combination, can be used in a home automation system. Power line carrier, twisted pair, coaxial cable, infrared, radio communications, Digital Subscriber Loop (DSL) technologies, cable modems, and fiber optics have been proposed and investigated. Each medium has a certain number of advantages and disadvantages. In this section, we will present some of the most profound features of the media.

The power line carrier (PLC) or mains has been proposed in several applications. It is the natural medium of choice in load management applications. No special cables need to be installed because the power line is the bus itself. From one side, the power line medium already has a large number of appliances connected to it, but on the other side it is not a very friendly medium for transmission of communication signals because there is a fluctuation of the power line impedance and a high noise level on the line. There is also interference with communication caused by other houses. Spread spectrum or ASK techniques have been proposed for efficient modulation of the signal in PLC.

Recent advances in twisted pair (TP) transmissions, especially in telecommunications and computer networking applications, make it very attractive for applications that use standard computer interfaces. TP can be the generic system for the home system datagram services; if new communication technologies reach the home, TP can be used for high-bandwidth applications as well. TP can be easily assembled and installed, and connectors can be easily attached to it.

Coaxial cables have not been extensively—except for the Japanese market—used in home automation systems. Their high bandwidth and the experience technical people have amassed through the cable systems make them a very attractive medium. Retrofitting them in existing houses is one of their major disadvantages.

Infrared (IR)—that is, electromagnetic radiation with frequencies between 10¹⁰ and 10²⁴ Hz—has been used extensively in remote control applications. Its use in home automation systems will require line-of-sight—that is, detectors in every single room so that there is a full coverage.

Radio waves—that is, electromagnetic signals whose frequency covers the range of 3 kHz to 300 MHz—do not need direct vision between the transmitter and the receiver, but there is a need for a license and problems with interference. Radio-frequency technology is being used for real-time data management in LANs in order to give free access to the host system from multiple mobile data input devices.

Wireless home networking technology will operate in the large-bandwidth radio-frequency ranges and will use proprietary compression techniques. In the future, consumers might receive e-mail messages wirelessly from a compliant handheld device or view enhanced Web content on their connected television sets. The use of a radio frequency of 2.4 GHz will cut down on noise within the home and provide some security.

Home networking opens up new opportunities for cost- effective phones that include Internet capabilities. By sharing resources, manufacturers should be able to reduce the cost of an Internet phone by using the processor and modem of a connected PC. Currently, a number of major manufacturers are developing their own wireless home networking products. Two major industry groups, the Home Phoneline Networking Alliance (HPNA) and the HomeRF, are attempting to develop standards for two different technology sets.

The HomeRF Working Group (HRFWG) was formed to provide the foundation for a broad range of interoperable consumer devices by establishing an open industry specification for wireless digital communication between PCs and consumer electronic devices anywhere in and around the home. HRFWG, which includes the leading companies from the PC, consumer electronics, peripherals, communications, software, and semiconductor industries, has developed a specification for wireless communications in the home called the Shared Wireless Access Protocol (SWAP).

The specification developed by the HRFWG operates in the 2.4-GHz band and uses relaxed IEEE 802.11 wireless LAN and digital European cordless telephone (DECT) protocols. It also describes wireless transmission devices and protocols for interconnecting computers, peripherals, and electronic appliances in a home environment.

Some examples of what users will be able to do with products that adhere to the SWAP specification include:
- Set up a wireless home network to share voice and data among peripherals, PCs, and new devices such as portable, remote display pads.

- Review incoming voice, fax, and e-mail messages from a small cordless telephone handset.
- Intelligently forward incoming telephone calls to multiple cordless handsets, fax machines, and voice mailboxes.
- Access the Internet from anywhere in and around the home from portable display devices.

- Activate other home electronic systems by simply speaking a command into a cordless handset.
- Share an ISP connection between PCs and other new devices.
- Share files, modems, and printers in multi-PC homes.
- Accommodate multiplayer games or toys based on PC or Internet resources.

Bluetooth. The Bluetooth program, backed by Ericsson, IBM, Intel, Nokia, and Toshiba, is already demonstrating prototype devices that use a two-chip baseband and RF module and hit data rates of 730 kbit/s at 2.4 GHz. Bluetooth uses a proprietary MAC that diverges from the IEEE 802.11 standard. Bluetooth has already managed to serve as a universal low-cost, user-friendly air interface that will replace the plethora of proprietary interconnect cables between a variety of personal devices and peripherals. Bluetooth is a short-range (10 cm to 10 m) frequency-hopping wireless system. There are efforts to extend the range of Bluetooth with higher-power devices.

Bluetooth supports both point-to-point and point-to- multipoint connections. Currently, up to 7 slave devices can communicate with a master radio in one device. It also provides for several piconets to be linked together in an ad hoc networking mode, which allows for extremely flexible configurations such as might be required for meetings and conferences.

The Bluetooth protocol stack architecture is a layered stack that supports physical separation between the Link Manager and the higher layers at the Host Interface, which is common in most Bluetooth implementations.

Bluetooth is ideal for both mobile office workers and small office/home office (SOHO) environment as a flexible cable replacement that covers the last meters. For example, once a voice over internet protocol (VoIP) call is established, a Bluetooth earphone may automatically switch between cellular and fixed telephone networks, when one enters his home or office. Of course, the low-bandwidth capability permits only limited and dedicated usage and inhibits Bluetooth from in-house multimedia networking.

IEEE 802.11. IEEE 802.11 is the most mature wireless protocol for wireless LAN communications, deployed for years in corporate, enterprise, private, and public environments (e.g., hot-spot areas). The IEEE 802.11 standards support several wireless LAN technologies in the unlicensed bands of 2.4 and 5 GHz, and share use of direct-sequence spread spectrum (DSSS) and frequency hopping spread spectrum (FHSS) physical layer RF technologies.

Initially, the IEEE 802.11 standard provided up to 2 Mbps at the 2.4-GHz band, without any inherent quality of service (QoS). The wide acceptance, however, initiated new versions and enhancements of the specification. The first and most important is the IEEE 802.11b specification, which achieves data rates of 5.5 and 11 Mbps. Recently, the IEEE 802.1lg task group has formed a draft standard that achieves data rates higher than 22 Mbps. In the 5-GHz band, the IEEE 802.1la technology supports data rates up to 54 Mbps using OFDM schemes.

OFDM is very efficient in time-varying environments, where the transmitted radio signals are reflected from many points, leading to different propagation times before they eventually reach the receiver. Other 802.11 task groups targeting specific areas of the protocol are 802.11d, 802.11e, 802.11f, and 802.11h.