Wireless Personal Area Networks
Darrin Vallis, Senior Field Applications Engineer, Cypress Semiconductor
The Information Age Begins
At the end of the 20th century, a few key technologies changed our world. Personal Computers evolved and proliferated at an incredible rate. These millions of PCs, coupled with HTML and the web browser, drove an Internet explosion. Communications equipment business soared to dizzy heights, as companies raced to meet demand for network bandwidth. In the meantime, modern cell phones let people change the way they work and live. This was the first era of a digital communications revolution.
The Second Era of Digital Communications
The next few years of this 21st century will start a second era in digital communications. Personal electronics are evolving into highly portable or wearable devices. Digital cell phones, ultra-light notebook computers and Personal Digital Assistants (PDAs) are leading the trend. They provide instant access to information, computing and communications. The next great leap will come as these devices are integrated by Wireless Personal Area Networks. (PANs)
Figure 1 : PAN Enabled Cellular Handset
The concept is simple: Enable personal consumer electronics with an inexpensive, common wireless network protocol. This will allow devices to communicate and share data real-time as a background process, invisible to the user.
Personal Area Network Applications
The implications of this technology are astounding. Existing applications can be combined in completely new ways. Here are just a few examples:
Synchronizing PDA, PC or cell phone
Wireless PC or PDA Internet via cell phone
Wireless Internet portal at hotels and airports
PC to cable modem wireless access
Wireless PAN hands-free car kit
Inexpensive wireless PC peripherals
PC to Set-Top box PAN interface
Point-of-sale payment with PDA or cell phone
Wearable wireless PCs with Internet access
Automatic vehicle keyless entry (recognizes owners laptop, cell phone or PDA)
The list of consumer applications is huge, limited only by an entrepreneur's imagination. However, there is one key which must be in place for the PAN market to explode: a wireless standard.
Competing Wireless PAN Standards
There are three wireless protocols competing for the PAN market; Bluetooth, IEEE 802.11b and HomeRF. Though each has a different set of feature extensions, they share a common 2.4 GHz operating frequency with spread spectrum RF transmission.
IEEE 802.11 was proposed 1997 as the standard for wireless business LANs. It was designed for 1-2 Mbps data rates, over a 2.4 GHz radio link. In 1999, the protocol was extended with two new variants. 801.11a was proposed for fixed, infrastructure applications, with 6-54 Mbps bandwidth on a 5 GHz RF link. The mobile WAN and PAN segment was addressed with 802.11b. It operates at 2.4GHz and delivers11 Mbps of bandwidth up to 300 feet. It is 802.11b that competes squarely with Bluetooth and HomeRF.
HomeRF follows a different vision of wireless networking. Its goal is to implement a low cost, wireless voice and data network in the home. The standard is officially known as Shared Wireless Access Protocol, SWAP. It combines features of 802.11 and European Digital-Enhanced-Cordless Telephony (DECT). The original protocol was designed for 1-2 Mbits/s data rates, with 2.4 GHz, FHSS over a 150 foot range. It has recently been extended to 10Mbps with SWAP 2.0. HomeRF architecture uses the PC as a wired gateway to your home, via cable, DSL or standard modem. The PC then acts as a host for other HomeRF enabled devices.
Figure 2 : HomeRF Network
Bluetooth was originally designed for cell phone applications, such a wireless headsets. The standard has since been modified to allow multiple device interconnected networks. Its 2.4 GHz signal uses FHSS, and can deliver data at 723 Kbps over 30 feet. The range can be increased to 300 feet, but currently violates FCC regulations. There are several large semiconductor companies investing heavily in Bluetooth development. Their goal is a $5 single chip solution.
Figure 3 : BlueTooth Network Topology
Pros & Cons
Glancing at the table below, each standard has a clear advantage in certain applications. However, there is a lot more to each standard than just the bandwidth and range. For example, 802.11b delivers the highest throughput, but it does not allow peer to peer traffic. This makes it attractive as a wireless Internet gateway, but not the right choice for networking personal electronics.
Table 1 : Wireless PAN Summary
The system architecture of each standard makes a difference. An 802.11b network is designed to provide 11 Mbps per access point. However, if you have several notebook computers with wireless 802.11b LAN cards, they share this bandwidth. You can add multiple access points, and up to three of eleven RF channels, but the bandwidth is still shared. With this in mind, current 802.11b implementations can actually deliver 14Mbps aggregate system throughput. 802.11 has the largest installed hardware base of the three protocols, is the most widely supported, and is the definitely the current choice for wireless office LANs.
With its SWAP 2.0 upgrade, HomeRF offers near the maximum bandwidth of 802.11b, and some additional unique features. Unlike wireless Ethernet, HomeRF allows direct peer to peer communications, without the need for an access point. This is very convenient for applications such as file or printer sharing on a small ad-hoc network. HomeRF also incorporates an isochronous transfer mode, intended for streaming audio and video. Some hot applications that stand to benefit from this are wireless Voice Over IP telephony, TV to set-top-box streaming video, and even wireless integrated home multimedia systems.
Though Bluetooth may appear similar to HomeRF, simply operating at a lower frequency, it was designed with a very different architecture. Bluetooth networks can be used in a multiple access configuration, as in 802.11 and HomeRF, but its strength lies in Piconets. Any eight Bluetooth devices within range of each other may form a piconet, with one unit acting as the master. Multiple piconets are permitted to overlap, forming a scatternet. Traffic on this network can travel in isochronous voice, or asynchronous data channels. This interactive, flexible architecture has the support of major consumer electronics suppliers. The obvious advantages of having your PC, PDA and cell phone link via Bluetooth are driving this technology development. Multi-chip modules are already available in the $20 range. However, for Bluetooth to explode into consumer electronics, a single chip $5 device must be developed.
Cypress Semiconductor joined the Bluetooth race in Q2 of 2000, acquiring RadioCom and Alation. This venture brought single chip RF technology, Bluetooth baseband expertise and Bluetooth software experience immediately into Cypress Interface Products Division. Recognized as the world's dominant supplier of USB microcontrollers, Cypress has been granted Associate membership in the Bluetooth SIG, and a significant H.I.D. Workgroup member status.
Cypress has three Bluetooth products in development. The CY7C6961 is a low-cost single chip Bluetooth radio, with exceptional signal-to-noise ratio and interference immunity. The CY7C6971 is a single chip Bluetooth Host Controller, including radio and base-band logic in a 100 ball FBGA package. Finally, the CY6972 is a single chip Bluetooth Peripheral Controller, also incorporating a transceiver and base band logic in one 100 ball FBGA device. Preliminary data sheets are available, with first samples scheduled for April of 2001.
Figure 4 : Cypress Bluetooth Devices
Its Getting Crowded Out There
Interoperability of 802.11b, HomeRF and Bluetooth is becoming a major concern. A HomeRF cable modem gateway will not communicate with the wireless LAN 802.11b card in your laptop. That new Bluetooth cell phone won't talk to either of them. Wireless is definitely going to require bridge devices between the three protocols.
To make matters worse, each standard competes for bandwidth over the same 2.4 GHz range. HomeRF and Bluetooth use Frequency Hopping Spread Spectrum for channel allocation, hopping at 50 Hz and 1600 Hz respectively. These devices will often interfere with each other. Fortunately, 802.11b relies on Direct Sequence Spread Spectrum for channel allocation. This is much more immune to interference, and less likely to be disrupted by Bluetooth and HomeRF devices. However, testing has shown significant problems with all three devices operating in close proximity. Standards committees are still working on this problem.
State of the Market
At the moment, 802.11 is dominant in the wireless business LAN segment. Dell, Compaq and IBM all offer 802.11 solutions for mobiles and desktop computers. After all, 802.11 was designed for wireless LAN. However, it remains a fairly expensive solution in comparison with the other standards.
HomeRF is competing with 802.11 for the consumer home network. HomeRF probably has the edge here, since it is much more cost effective and has adequate bandwidth for the home user. Compaq is headlining HomeRF as its home networking solution, which may generate critical mass for the standard.
Bluetooth is currently the wild card. Though offering the lowest bandwidth, it is far less expensive than 802.11 or HomeRF. Based on its price point and features, Bluetooth has the opportunity to become a de-facto standard for wireless mobile networking.
For the near term at least, Bluetooth, HomeRF and 802.11 will remain in specialized applications. Each target a different wireless market, and have their own advantages in that segment. More importantly, they share the same 2.4 GHz spectrum, and it is currently unclear how well the standards will coexist. The next year will see interesting times for the wireless networking market.