The Wireless Internet is not just wireless communications across town or the country. It is also local—sometimes in a home or office building. Wireless LANs are just becoming popular with economically  priced  wireless  Ethernet  equipment.  Standards such as IEEE 802.11, HiperLAN2, and Home RF are leading the way to untethered communications in-building or outside over small areas. Another important development is the Personal Area Network, also known as Bluetooth. Let’s take a look at each of these to see how they further promote Wireless Internet sessions.

BLUETOOTH

Bluetooth is a low-cost, low-power, short-range radio link for mobile devices and for WAN/LAN access points. It operates in the ISM band. The Bluetooth standard was created primarily to replace serial cables between computers and printers or other peripherals. Speed and reliability were key considerations. Bluetooth is capable of both voice and data communications at speeds up to about 70 Kbps.

Bluetooth technology is an enabling technology for the Wireless Internet and the mobile user. It can be an Internet bridge between a mobile device and a wireless access point in an ad-hoc network, as are other WLAN technologies such as 802.11 or Home RF. However, some features of Bluetooth are unique to it and not available in other WLAN technologies. Bluetooth actually creates a Personal Area Network. It is small enough to be embedded in everyday devices such as headsets or microphones. It can be embedded in a PDA and automatically synchronize a computer to a PDA. Bluetooth can also download a file or picture received on a Wireless Internet phone to a printer or a PDA or computer.

Applications for Bluetooth wireless technology come from no only the telecom industry but also from the computer, home entertainment, automotive, health care, automation, and toys industries. What good is a wireless Internet session if you must constantly connect to wired network to print? Bluetooth uses a low-cost short-range radio link or bridge between Bluetooth enabled devices. Computers, phones, printers, wireless headsets, and microphones can all communicate with each other without wires being dragged about. Bluetooth started as an idea in  1994 at Ericsson. Today, the Bluetooth SIG boasts almost 2,500 members with nearly every major communications company represented.

Bluetooth computer and telecom consumer products will appear in late 2001 or early 2002. Products in other industry sectors will become available later in 2002.

The Bluetooth Specification addresses two ranges: short (around 10 m) and medium (around 100 m). The radio link is capable of voice or data transmission to a maximum capacity of 720 Kbps per channel. The radio spectrum used is in the unlicensed  ISM band at 2.4  GHz.  Modulation  is  Frequency Hopping Spread Spectrum (FHSS).

Because Bluetooth encompasses many applications, there is no single competitive technology. Infrared is a competitor in some cases but it requires line of sight, whereas wireless LANs have much greater range. Perhaps the closest competitor is Home RF but it too is more a wireless LAN than a personal area network.

IEEE 802.11

Ethernet is IEEE 802.11b today, the IEEE standard for wireless LAN’s. IEEE 802.11b operates in the ISM band at 11 Mbps. However, several new versions of the standard is being developed, 802.11a, which supports data rates of up to 54 Mbps, and operates  in  the 5-GHz UNII  (Unlicensed National Information Infrastructure) band. Another version 802.11g is currently being developed which will support up to 20+ Mbps. Table 2-1 summarizes the different versions of 802.11 and includes HiperLAN2 for comparison. It should also be noted that the IEEE is working on 802.11e, a standard that spans home and business environments with QoS and multimedia support while maintaining full backward compatibility  with 802.11b and 802.11a. This version will support voice and include a higher level of security than 802.11b. The release date for the standard is unclear at this time.

The IEEE802.11b specification was finalized in 1999 and quickly adopted by many companies. However, it was just as quickly discovered that there are two problems: the security is weak and the theoretical transmission speeds of 11 Mbps falls short—real world speed is only about 7 Mbps.

FEATURES.   IEEE802.11  also  supports  infrastructure  networks and ad hoc networks. One very important characteristic of 802.11 is that the data rate will be automatically decreased as signal deteriorates between the access point and the stations. While 802.11b does include a security mechanism, it has been discovered to be weak. It also supports station roaming between access points.

UNLICENSED SPECTRUM USAGE FOR WLAN. 

The Federal Communications Commission (FCC) specifies the rules for operating in the unlicensed 2.4 GHz spectrum. The largest governing concern is harmful interference with authorized services and must work around any interference that may be received from phones, microwaves or other RF devices.

The FCC mandates that a device must operate in one of two ways in the 2.4 GHz ISM band:

•   Frequency  Hopping  Spread  Spectrum (FHSS).  The frequency changes in a pseudo-random manner based on a predefined code.

•   Direct Sequence Spread Spectrum (DSSS).   The data signal is broken up into sequences and transmitted to the receiver, which reassembles the sequences into the data signal.

Future versions such as 802.11g may adopt OFDM if the FCC decides to support it and the industry can agree to rally behind it. However, at the time of writing this article, these are two very big “ifs.”

It  is  estimated that more than 7.8 million wireless LAN chipsets were produced in 2000. A similar number is expected in 2001. Sales are growing from almost $400 million in 2000 to $1.2 billion by 2005. Costs have dropped during 2001, causing  widespread  usage  in  homes  and  enterprise  systems. However, 2002 will see the release of more Home RF and 802.11g products also. Parks Associates estimates that, while 5 percent of U.S. households currently have a PC network in place, as many as 15 percent will have one in five years. Of that, wireless networking will account for 40 percent of all those home networks.

HIPERLAN AND HIPERLAN2

HiperLAN or  more  recently,  HiperLAN2  are  standards approved  by  the  European  Telecommunications  Standards Institute (ETSI). HiperLAN2 is the most recent version. It is an interoperable  standard  providing  high-speed,  broadband connectivity  for  wireless  LANs  in  corporate  environments, public “hot spots” and home environments

HiperLAN2 provides a 54 Mbps data rate on the globally allocated  5.15-5.3 GHz band. It also may be used in the 17.1-17.3 GHz band in certain geographic locations. It surpasses the IEEE 802.11a standard with both greater security and  traffic  prioritization  capabilities.  HiperLAN2  also includes mechanisms for handoffs between WLANs and 3G mobile systems.

Currently several European manufacturers are implementing solutions that provide a wireless Virtual Private Network (VPN) solution for HiperLAN 2 which includes authentication and encryption. This will enable wireless mobile users to have a secure connection to their corporate networks when traveling through so called “hot spots,” such as airports, hotels and conference centers.

HiperLAN2 achieves its high data rate by using a frequency multiplexing method called Orthogonal Frequency Digital Multiplexing (OFDM) with various physical layer modulation schemes as shown below:

OFDM is particularly efficient in time-dispersive environments, i.e. where the radio signals are reflected from many points such as in offices. The basic idea of OFDM is to transmit broadband, high data rate information by dividing the data into several  interleaved,  parallel  bit  streams,  and  let  each  bit  stream modulate a separate subcarrier. HiperLAN2 is time-division multiplexed and connection-oriented. It can be used for point-topoint or point-to-multipoint connections. A dedicated broadcast channel is also included. Each connection can be assigned either a simple relative priority level or a specific QoS in terms of bandwidth, delay, jitter, bit error rate, etc. Hiperlan2 uses an approach for the Access Channel that differs from the OSI model but is very similar to the IEEE 802-11 standard.

HiperLAN2 was designed for short range communications, about 150 feet maximum. It is primarily meant to be used in a stationary environment but does support mobility up to 4.3 feet/second. It may be used on networks with or without infrastructure to support isochronous traffic such as audio or video with minimum latency. It can support asynchronous traffic data of 10Mbps with   immediate access. HiperLAN2 is also compatible with ATM.

Radio-based wireless  LANs tend to exhibit  randomized “bursty”  traffic  patterns  which  can  result  in  performance issues. Many factors have to be taken into consideration, when quality of service is to be measured. Among these are:

•   Landscape topography

•   Elevations that might cause shadows

•   Multi-path from signal-reflection surfaces

•   Signal loss through absorbing surfaces

•   Quality and placement of the wireless equipment

•   Number of stations

•   Interference

•   Etc.

HIPERLAN2 FEATURES. 

Other than the high data rate and QoS features, HiperLAN2 includes including the following:

•   Automatic frequency allocation

•   Security support

•   Mobility support

•   Network and application independent

•   Power save mode

Automatic  frequency  allocation  is  especially  important because this allows for easy installation without the need for complicated frequency planning such as that required for cellular. The access points use a built-in support for automatic transmission frequency allocation.

HiperLAN2 networks also supports  authentication  and encryption. A handoff mechanism is managed by the mobile terminal based on received signals from each access point. Connections are maintained just in cellular (hopefully maybe even better). The HiperLAN2 network may also integrated with a variety of fixed networks.

A power save mechanism is based on mobile terminal-initiated negotiation of sleep periods. A request is made to the access point for a low power state and a specific sleep period. At the end of the sleep period, the mobile terminal searches for a wake up indicator from the access point, and in the absence of that, sleeps the next period, etc.

HOME RF

Another industry group, the Home Radio Frequency Working Group (HRFWG)—made up of members of industry leading companies  such  as  Compaq,  Ericsson,  HP,  IBM,  Intel, Microsoft,  Motorola,  and  others—created  the  Home  RF Standard  Specification.  Home  RF  combines  elements  of 802.11 and Digital Enhanced Cordless Telecommunications (DECT) but supports only up to 2 Mbps. It is aimed at homes and small businesses.

The price of Home RF is generally less expensive than 802.11 but performance is considerably less. The devices operate in the 2.4 Ghz ISM band just as 802.11 devices do. In actuality Home RF competes more with Bluetooth than 802.11. It was designed for embedded applications in appliances and computing equipment such as printers. Only time will tell if this standard prospers.