One method of implementing a wireless network in the home is to use products that adhere to the standards of the Home Radio Frequency Working Group. HomeRF is positioned as a global extension of Digitally Enhanced Cordless Telephony (DECT), the popular cordless phone standard that allows different brands to work together so that certified handsets from one vendor can communicate with base stations from another.
DECT has been largely confined to Europe because its native 1.9-GHz frequency band requires a license elsewhere, but HomeRF extends DECT to other regions by using the license-free 2.4-GHz frequency band. It also adds functionality by blending several industry standards, including IEEE 802.11 frequency hopping for data and DECT for voice. This convergence makes HomeRF useful for broadband households.
As more PCs, peripherals, and intelligent devices are installed in the home, and as network connections proliferate, users are faced with new opportunities for accessing information as well as challenges for sharing resources. For example, users want to;
- Access information delivered via the Internet from anywhere in the home.
- Share files between PCs and share access to peripherals no matter where they are located within the home.
- Control electrical systems and appliances whether in, around, or away from home.
- Effectively manage communications channels for phone, fax, and Internet usage.
Each of these capabilities requires a common connection between the various devices and networks found in the home. However, in order to truly be effective, any home network must meet certain criteria:
- It must not require additional home wiring. Most existing homes are not wired for networking, and retrofitting them would too labor-intensive and expensive. Awireless solution is a viable alternative.
- The wireless connections must be immune to interference, especially with the growing number of wireless devices and appliances emitting RF noise in the home.
- The range of the wireless connection must be adequate to allow devices to communicate from anywhere within and around a typical family home.
- The network must be safe and protected from unwanted security breaches.
- It must be easy to install, configure, and operate for nontechnical users. Most home users do not have the expertise to handle complex network installation and configuration procedures.
- The entire system must be easily and spontaneously accessible—anytime and from anywhere in or even away from the home.
These issues have been addressed by a consortium of vendors called the Home Radio Frequency Working Group (HomeRF WG), which has developed a platform for a broad range of interoperable consumer devices. Its specification, called the Shared Wireless Access Protocol (SWAP), is an open standard that allows PCs, peripherals, cordless telephones, and other consumer electronic devices to communicate and interoperate with one another without the complexity and expense associated with installing new wires.
The SWAP is designed to carry both voice and data traffic and to interoperate with the Public Switched Telephone Network (PSTN) and the Internet. It operates in the 2.4- GHz ISM (industrial, scientific, medical) band and uses frequency-hopping spread-spectrum radio for security and reliability.
The SWAP technology was derived from extensions of DECT and wireless local area network (LAN) technologies to enable a new class of home cordless services. It supports both a Time Division Multiple Access (TDMA) service to provide delivery of interactive voice and other time-critical services, and a Carrier Sense Multiple Access/Collision Avoidance (CSMA-CA) service for delivery of high-speed packet data.
Applications
The SWAP specification provides the basis for a broad range of new home networking applications, including:
- Shared access to the Internet from anywhere in the home, allowing a user to browse the Web from a laptop on the deck or have stock quotes delivered to a PC in the den.
- Automatic intelligent routing of incoming telephone calls to one or more cordless handsets, fax machines, or voicemail boxes of individual family members.
- Cordless handset access to an integrated message system to review stored voice mail, faxes, and electronic mail.
- Personal intelligent agents running on the PC for each family member, accessed by speaking into cordless handsets. This new voice interface would allow users to access and control their PCs and all the resources on the home wireless network spontaneously, from anywhere within the home, using natural language commands.
- Wireless LANs allowing users to share files and peripherals between one or more PCs, no matter where they are located within the home.
- Spontaneous control of security and electrical, heating, and air-conditioning systems from anywhere in or around the home.
- Multiuser computer games playable in the same room or in multiple rooms throughout the home.
Network Topology
The SWAP system can operate either as an ad-hoc network or as a managed network under the control of a connection point. In an ad-hoc network, where only data communication is supported, all stations are equal, and control of the network is distributed between the stations. For time-critical communications such as interactive voice, a connection point is required to coordinate the system.
The connection point, which provides the gateway to the public switched telephone network (PSTN), can be connected to a PC via a standard interface such as the Universal Serial Bus (USB) that will enable enhanced voice and data services. The SWAP system also can use the connection point to support power management for prolonged battery life by scheduling device wakeup and polling. The network can accommodate a maximum of 127 nodes. The nodes are of four basic types:
- Connection point that supports voice and data services.
- Voice terminal that only uses the TDMAservice to communicate with a base station.
- Data node that uses the CSMA-CA service to communicate with a base station and other data nodes.
- Integrated node thath can use both TDMAand CSMA/CA services
HomeRF uses intelligent hopping algorithms that detect wideband static interference from microwave ovens, cordless phones, baby monitors, and other wireless LAN systems. Once detected, the HomeRF hop set adapts so that no two consecutive hops occur within this interference range.
This means that, with very high probability, a packet lost due to interference will get through when it retries on the next hop. While these algorithms benefit data applications, they are especially important for voice, which requires extremely low bit error rates and low latency.
Future Plans
Work has already begun on the future HomeRF 2.1 specification, which will add features designed to reinforce its advantages for voice. Planned enhancements also will allow HomeRF to complement other wireless standards, including IEEE 802.11, also known as Wi-Fi. HomeRF 2.0 already supports up to eight phone lines, eight registered handsets, and four active handsets with voice quality and range comparable to leading 2.4-GHz phone systems.
With this many lines, each family member can have a personal phone number. HomeRF 2.1 plans to increase the number of active handsets with the same or better voice quality, thus supporting the needs of small businesses. The 150-foot range of HomeRF already covers most homes and into the yard. HomeRF 2.1 will extend this range for larger homes and businesses by using wireless repeaters that are similar to enterprise access points but without the need to connect each one to Ethernet.
HomeRF frequency hopping technology also avoids the complexity of assigning RF channels to multiple access points (or repeaters) and offers easy and effective security and interference immunity. This is especially important since households and small businesses do not usually have network administrators. To allow individuals to roam across very large homes and fairly large offices while talking on the phone and without loosing their voice connection, HomeRF 2.1 also will support voice roaming with soft handoff between repeaters.
HomeRF 2.0 supports Ethernet speeds up to 10 Mbps with fallback speeds and backward compatibility to earlier versions of HomeRF. Performance can be further enhanced to about 20 Mbps. The HomeRF WG is evaluating the need for such enhancements at 2.4 GHz in light of its planned support of 5 GHz. Aproposed change to Federal Communications Commission (FCC) Part 15 rules governing the 2.4-GHz ISM band will allow adaptive frequency hopping.
While not legal today, these proposed techniques allow hoppers such as Bluetooth and HomeRF to recognize and avoid interference from static frequency technologies such as Wi-Fi. Since HomeRF already adjusts its hopping pattern based on interference to ensure that two consecutive hops do not land on interference, supporting this FCC proposal seems trivial.
The HomeRF WG believes in the peaceful coexistence of 2.4 and 5 GHz since each frequency band and technology has specific strengths that complement each other. Rather than draft a specification for 5 GHz, the group simply endorses IEEE 802.11a (also known as Wi-Fi5) for high-bandwidth applications such as high-definition video streaming and MPEG2 compression.
It plans to write application briefs describing how to bridge between 2.4- and 5-GHz technologies, including how to handle differences in quality of service (QoS). This information, while written for IEEE 802.11a, also can apply to HiperLAN-2, IEEE 802.11h, and proprietary IEEE 802.11a extensions. Some analysts expect IEEE 802.11a to eventually take over as the wireless standard for enterprise offices, gain needed QoS support from IEEE 802.11e, and start a slow migration into homes.
It already supports 54 Mbps, and proprietary extensions increase performance to about 100 Mbps. But because of the higher frequencies used, IEEE 802.11a has disadvantages in cost, power consumption, range, and signal attenuation through materials. Acombination of HomeRF and IEEE 802.11a brings together the strengths of both technologies.
Home users have a need for a wireless network that is easy to use, cost-effective, spontaneously accessible, and can carry voice and data communications. Certified HomeRF products are available today from consumer brands such as Compaq, Intel, Motorola, Proxim, and Siemens through retail, online, and service provider channels. They come in a variety of form factors such as USB and PC card adapters, residential gateways, and a growing variety of devices that embed HomeRF.
