Wireless Computing

• electronic data transmission
• radio frequency bands
• WAN Solutions
• LAN Solutions
• PAN Solutions
• see also:
  • Electromagnetic Radiation

Electronic data transmission:

• bandwidth and transmission rates of various media:
  •  

    Medium	Uses	Bandwidth (MHz)	Digital transmission rate (Mbps)
    Copper wire	Subscriber line	0.003-1	0.03-6
    Twisted pair	LAN	50	100
    Coaxial cable	Cable TV	750	3000
    Coaxial cable	Internet access	250	1000
    Optical fibre	Trunks	600-2500	2400
    Optical fibre	Undersea	150-2500	5000
    Optical fibre	Fiber to curb	150-620	50-600
    Radio	Cellular PCS	25	25
    Radio	Microwave	1
    Radio	Satellite	30	60
    Radio	Broadcast	6	20

• 2.4GHz Industrial Scientific Medical (ISM) band:
  • is an unlicensed band worldwide
  • shares airspace with:
    • microwave ovens
    • Home RF (max. 2Mbps)
    • IEEE802.11 wireless standard (max. 2Mbps)
    • IEEE802.11b wireless LAN standard (max. 11Mbps)
    • Bluetooth v1.0 (max. 1Mbps)
    • Bluetooth v2.0 (max. 10Mbps)
    • various commercial data-transmission systems
    • wireless telephones
    • wireless medical systems
    • Apple's AirPort wireless system
  • penetrates most walls unless there is substantial metal such as plumbing or heavy steel reinforced concrete
  • depending on power of transmitter, and wall structures, transmission is usually from 10-100m.
  • depending on the protocol, data transmission rates can reach 11Mbps?
• 2.5GHz:
  • data transmission rate up to 115Kbps
  • GPRS  is a packet-based network based on GSM. GPRS, like GSM will be pervasive in Europe and Asia Pacific.
• 3GHz:
  • data transmission rate up to 2000Kbps
  • 3G technologies include W-CDMA and CDMA 2000
• 5GHz:
  • HiperLAN (max. 54Mbps)

WAN solutions:

• Cellular mobile telephony:
  • a service area is broken into hexagonal geographic units called cells, typically with diameters of 1km & each with its own base station
  • frequency division multiple access (FDMA):
    • base station assigns a pair of frequencies (one for sending and one for receiving) to a user's phone & the phone automatically shifts to those frequencies
    • 1st generation of cellular phones
  • time division multiple access (TDMA):
    • base station assigns specific time slots to each calling phone in the cell; each phone synchronises itself with the base station so that the phone transmits & receives only when its assigned time slots occur; slots are repeated at high frequency so caller is not aware of any interruption
    • a freq. channel in use in one cell can be simultaneously used in many other cells without mutual interference, as long as the cells are not immediately adjacent
  • code division multiple access (CDMA):
    • uses a "spread spectrum" technique in which each phone in a cell uses a distinct code known to the base station to communicate
    • does not have the freq-resuse restrictions of TDMA
• Cellular Digital Packet Data (CDPD):
  • is a packet switched communications network that operates as an overlay on the AMPS cellular system.
  • Packet networks, including the internet break a stream of data into independent blocks of data, called packets. Each packet is transmitted independently and carries its own destination and error-correction information. Thus, packet networks perform extremely well in systems with variable traffic and channel quality - both of which are found in the wireless environment.
  • CDPD provides an advantage over circuit-switched (dial-up) data, in that you can connect to the network once and remain connected, similar to your LAN connection.
  • Speed:
    • CDPD transfers data over the cellular network at a rate of 19.2Kbps
  • Connectivity: via cellular phone
  • Availability:
    • CDPD is available in most metropolitan areas of the US, some parts of Mexico and Canada, Israel, New Zealand and parts of China
  • Security:
    • Wireless WAN's are inherently secure. Carriers provide wireless network authentication via a unique Electronic Serial Number (ESN) and Internet Protocol (IP) address assigned to each PC card. In addition, messages are broken into packets and then sent over multiple channels through an encrypted air link.
      The only point of susceptibility is from the cellular base station to the Enterprise LAN. Most IT managers do not want to open up the firewall to enable access in and out of the LAN. So, the solution is a Virtual Private Network (VPN), which provides an encrypted "tunnel" through the corporate firewall for user access to everything on the LAN.
• Future WAN technologies:
  • 2.5G (115Kbps) and 3G (2Mbps) will enable users to access their files, email and the internet up to 20 times faster than they do today over a dial-up modem connection.
  • GPRS is a 2.5G technology and is a packet-based network based on GSM. GPRS, like GSM will be pervasive in Europe and Asia Pacific.
  • 1XRTT is a packet-based version of the CDMA network. 1XRTT will be pervasive in the US.
  • 3G technologies include W-CDMA and CDMA 2000. Each will provide speeds up to 2Mbps.
•  

LAN solutions:

• Wireless LAN:
  • uses wireless PC cards which transmit radio to base station which is wired to the wired LAN
    • A wireless LAN consists of two main components: an access point and a WLAN card (PC card for notebook or PC card and a PCI adaptor or USB devices for desktops). The access point is a bridge between your "wired" network and your "wireless" network. The access point then allows WLAN card to communicate with your "wired" network, giving you the ability to walk around the office campus and access whatever is on your LAN (email, internet, files) as long as you are within proximity of the access point. In the case of a desktop PC, a wireless LAN enables you to get network access into conference rooms or hard to wire areas. To set up file and print share information within an office is as easy as a "wired" LAN. An alternative to the traditional access point for a small network is the PCI card. If you already have a desktop PC and adequate software, you can plug a PCI card into it and essentially use the PC as your access point.
    • Depending on how much noise is present in your environment and your contact speed, the range, with both access points, will cover 80 feet up to 1750 feet.
      
  • Standards:
    • 802.11b is the worldwide standard for wireless LAN's in the 2.4GHz spectrum developed by the Institute of Electrical and Electronic Engineering (IEEE).
      It specifies a higher rate physical layer that operates at 11Mbps, as opposed to previous technology standards such as 802.11 and Home RF which were limited to 2Mbps. Future technology standards such as 802.11a and HiperLAN provide for data rates up to 54 Mbps in the 5GHz spectrum. These technologies are expected to hit the market by 2002/3. As costs for these technologies continue to drop and data transmission speeds continue to approach those of wired Ethernet connections, wireless LAN solutions will become a viable alternative to the wired network.

PAN Solutions:

• Wireless PAN:
  • this refers to personal area network which is the short range communication within a room or cubicle
  • irDA:
    • infra-red is available on most notebooks and many printers
    • requires line of sight between transmitters
  • radio:
    • Bluetooth technology:
      • Bluetooth is the standard developed by the Bluetooth Special Interest Group (SIG) for PAN's. It specifies a communications standard for small-form factor, low-cost, short range radio links between notebooks, PDA's, peripherals (i.e. printers, scanners, digital cameras, mice, keyboards, projectors) and mobile phones. Bluetooth replaces the need for serial cables and IrDA that have been used in the past to link devices in a Personal Area Network. The Bluetooth SIG is an industry group consisting of leaders in the computing, telecommunications and networking industries that are driving development of the technology and helping bring it to market.
      • Bluetooth operates in the 2.4GHz Industrial Scientific Medical (ISM) band & uses frequency hop (FH) spread spectrum, which divides the frequency band into a number of hop channels which can be selected pseudorandonly during a connection.
      • supports up to 8 devices in a piconet (2 or more Bluetooth units sharing a channel)
      • Bluetooth operates at less than 1Mbps, whereas 802.11b wireless LAN solutions are now operating at 11Mbps.
      • Bluetooth 1.0 RF signals are solid to about 10m, but by increasing the transmit power, may be able to reach 100m & will pass through most walls unless there is a lot of metal in them such as plumbing or heavy steel reinforced concrete
      • Bluetooth 1.0 will operate at about 700Kbps. The next generation specification, Bluetooth 2.0 will operate at speeds up to 10Mbps. Bluetooth 2.0 products will likely lag Bluetooth 1.0 products by about one year.
      • Bluetooth is inherently secure. First, it is a Frequency Hopping Spread Spectrum technology, which simply means that data is sent via a random pattern that hops around from frequency to frequency within a particular band. This makes it very difficult for the average intruder to intercept. Secondly, Bluetooth users can set up their own levels of authentication. You can choose to set up your Bluetooth device to always communicate with another Bluetooth device or to only talk to certain Bluetooth devices. As the receiver of data, you can also choose to link with the device that is wishing to communicate with you or not.Lastly, once the communications link has been established, the data is all encrypted using a 40-bit or 64-bit algorithm.
      • Since Bluetooth and 802.11b wireless LAN solutions run at the same frequency, they do have some conflicts when they are within very close proximity of each other. As we believe the two solutions will co-exist, we are working with our partners to resolve these issues and driving towards solutions that will co-exist.
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