Wireless Communications

1. Wireless Communications Mark Blunk Hassan Mirmotahari Wei Min, Cheng Wing Kai, Cheng Group 1 CIS 585, All rights reserved.

2. 1 - Wireless Spectrum http://et.nmsu.edu/~etti/spring97/techtips/spectrum.html Group 1 CIS 585, All rights reserved.

3. Physical Layer – Transmission Types • Infrared light spectrum • Radio wave spectrum • Microwave spectrum

4. Infrared Light - Positive Options • Inexpensive • Compatible with fiber-optic links • Not bandwidth limited • No licensing required (FCC) • Transmissions may be aimed (1 to 2 kilometers) • Transmissions may be omni-directional (30-60 feet) • Amplitude driven – little interference • Range of 1-2 kilometers (approximately ½ to 1 ½ miles) • Highest bandwidth and throughput • InfraLAN – product with infrared transmission

5. Infrared Light – Negative Aspects • Spectrum is shared with the sun and other lighting sources • LAN may become “useless” with enough interference • Signals will not permeate opaque objects (walls, dividers,etc)

6. Microwaves

7. Microwave - Positive Options • Higher throughput without spread spectrum • 5.8ghz band – using a narrow-band transmission • RadioLAN - product using microwave transmission

8. Microwave – Negative Aspects • Expensive to build infrastructure • Must operate at less than 500 milliwatts (strict FCC regulations) • Not commonly used – less available knowledge pool

9. Radio Waves - Spectrum Pure tone 500.00 Hz 1500.0 Hz http://www.heritage.org/library/categories/regulation/tp11c1.gif

10. Radio Waves - Positive Options • Commonly understood technology • Not subject to interference of light waves like infrared • Less expensive than microwave • Long-range medium – several architectures exist • Commonly used – larger knowledge pool • WaveLAN, BreezeNet pro, Proxim Rangelan2, & RadioLAN

11. Radio Waves – Negative Aspects • Spread spectrum technology – high overhead • Lower rates of data transmissions – due to overhead required • Subject to some interference – causing delays in transmission

12. Radio Waves – Spread Spectrum Methods • Direct Sequence Spread Spectrum (DSSS) • Transmission signal is spread over an allowed band • Frequency Hopping Spread Spectrum (FHSS) • Splits the band into subchannels – signal then hops to transmit

13. Radio Waves – Direct Sequence Spread Spectrum (DSSS) • Spreads signal over a band (Example, 50 MHz) • Random Binary String Modulates the Transmission Signal • String is known as a “Spreading Code” • Bits are mapped out as “chips” and mapped back as “bits” • Spreading Ratio – The number of “chips” per bit

14. DSSS Spreading Ratios • Higher Ratios Resist Interference Better • Lower ratios allow for use of more bandwidth • FCC dictates spreading ratios must be more than ten • IEEE 802.1 standard requires a spreading ratio of eleven • Sender & Receiver must synchronize to the spreading code • Orthogonal spreading codes allow sharing of the band between LANs • DSSS systems use wide subchannels, limiting LANs possible • Recovery is faster with DSSS due to ability to spread the signal over a wider band • Example Product = WaveLAN

15. Radio Waves – Frequency Hopping Spread Spectrum (FHSS) • Splits the band into many subchannels (1-2MHz) • Signal “hops” from subchannel to subchannel • Uses short bursts of data on each channel • Bursts are within a “dwell” time (very short time) • FCC requires at least 75 subchannels • FCC requires “dwell” time of no longer than 400ms • Less interference than DSSS due to hopping • Security is higher due to the hopping

16. Frequency Hopping Spread Spectrum (FHSS)(Continued) • Used by military and law enforcement • Jamming is very difficult as the whole band must be jammed • Orthogonal hopping sequence allows for co-location of multiple LANs • Allows for more co-located LANs than DSSS • Common new product method for wireless • Product Example = BreezeNet

17. Multipath Interference • Interference caused by signals bouncing off of physical objects and arriving at a receiver at differing times • Multipath is a problem for all wireless modes • DHSS resists the issue by hopping to other frequencies • Anti-Multipath algorithms exist to resist the problem • Rayleigh fading is a subset of Multipath and can completely cancel out the signal • Infrared resists Rayleigh fading due to small wavelengths

18. Wireless Types Information Sources Pinacor.com http://www.fcc.gov/oet/spectrum/ e http://www.ntia.doc.gov/

19. End Of Module

20. 2 -Examples of Wireless protocols and technologies The two main protocols and technologies discussed in this sections are: • Wireless ATM • Wireless Application protocol

21. Some background on ATM • ATM ( Asynchronous Transfer Mode) has been advocated as an important technology for the wide area interconnection of heterogeneous networks • In ATM networks, the data is divided into small, fixed length units called cells. The cell is 53 bytes. • Each cell contain a 5 byte header which comprises of identification, control priority and routing information. The rest 48 bytes are the actual data.

22. Background continued • ATM does not provide any error detection operations on the user payload inside the cell, and also provides no retransmission services, and only few operations are performed on the small header • ATM switches support two kinds of interfaces: user-network interface (UNI) and network-node interface (NNI). • UNI connects ATM end systems (hosts, routers etc.) to an ATM switch, while an NNI may be impreciselydefined as an interface connection of two ATM switches together

23. Why Wireless ATM? • ATM provides end-to-end communication in a WAN environment • Companies do not have to invest in extra equipment (i.e. routers, switches, etc.) • ATM reduces the complexity, improves flexibility, while providing end-to-end connectivity

24. Why ATM Cont... • Due to the recent advancement of fiber, next generation wireless networks should be designed so as to easily fit and co-exist with the Broadband ISDN (Integrated Services Digital Network). • In order to avoid a serious mismatch between wireline and wireless networks, it is now timely to begin consideration of broadband wireless networks with similar service capabilities

25. Wireless ATM Challenges • Both wireless networks technology, and ATM protocol are relatively new, and there are no fixed standards being defined for wireless ATM networks • Still in research stage and the technology is being developed • Some wireless LAN’s have lower speed and higher error rates

26. Modifications to ATM • The ATM cell size (53 bytes) may be too big for some wireless LANs ( due to lower speed and higher error rates), therefore wireless LANs may use 16 or 24 byte payload. • The ATM header can also be compressed and be expanded to standard ATM at the base station • An example of ATM header compression is to use 2 bytes containing 12-bit VCI (virtual channel identifier) and 4 bit control ( payload type, cell loss priority etc.)

27. WAP Defined • The Wireless Application Protocol (WAP) is simply a protocol—a standardized way that a mobile phone/unit communicates to a server installed in the mobile phone network • Many advertising agencies and “dot.coms” have announced WAP services • WAP takes a client-server approach. It incorporates a relatively simple microbrowser into the mobile phone, requiring only limited resources on the phone.

28. WAP Cont.. • This makes WAP suitable for thin clients and early smart phones • WAP puts the intelligence in the WAP Gateways while adding just a microbrowser to the phones themselves • Microbrowser-based services and applications reside temporarily on servers, not permanently in phones

29. WAP Cont.. • WAP is aimed at turning a mass-market mobile phone into a network-based smart phone • A person with a WAP-compliant phone uses the built-in microbrowser to: 1. Make a request in wireless markup language (WML), a language derived from HTML especially for wireless network characteristics 2. This request is passed to a WAP Gateway, which then retrieves the information from an Internet server either in standard HTML format or WML 3. The requested information is then sent from the WAP Gateway to the WAP client, using whatever mobile network bearer service is available and most appropriate

30. WAP Cont.. • WAP has also given a significant impetus for new players to add mobile as a new distribution channel for their existing products and services • For example, CNN and Nokia teamed up to offer CNN Mobile, and Reuters and Ericsson teamed up to provide Reuters Wireless Services

31. Business Applications Corporate applications that are being enhanced and enabled with a WAP interface include: • Job Dispatch • Remote Point Of Sale • Customer Service • Remote Monitoring Such As Meter Reading • Vehicle Positioning • Corporate Email

32. Business Applications Cont.. • Remote LAN Access • File Transfer • Web Browsing • Document Sharing/Collaborative Working • Audio • Still Images • Moving Images • Home Automation

33. Consumer Applications Consumer Applications that are being enhanced and enabled with a WAP interface include: • Simple Person to Person Messaging • Voice and Fax Mail Notifications • Unified Messaging • Internet Email • Prepayment • Mobile Commerce • Mobile Banking • Chat • Information Services

34. End Of Module

35. 3 -Wireless LAN Configurations • A Peer-to-Peer Network • Client and Access Point • Multiple Access Points and Roaming • Use of an Extension Point • The Use of Directional Antennas

36. A Wireless Peer-to-Peer Network

37. Client and Access Point

38. AP as Master

39. Multiple Access Points and Roaming

40. Use of an Extension Point

41. The Use of Directional Antennas

42. Factors to be Considered • Range and Coverage • Throughput • Integrity and Reliability • Compatibility with the Existing Network • Interoperability of Wireless Devices • Interference and Coexistence

43. Factors to be Considered • Licensing Issues • Simplicity/Ease of Use • Security • Cost • Scalability • Battery Life for Mobile Platforms • Safety

44. EP: EP Roles as AP

45. EP: Preferred Master List

46. EP Topology: Single EP

47. EP Topology: Tree

48. EP Topology: Multi-hop Linear

49. EP Topology: combination

50. Building Environment