Transcript Introduction to Wireless: Voice and Data

Introduction to Wireless: Voice
and Data
CS480 Computer Science Seminar
Fall, 2002
Wireless Communication
• Communication without wires; invisible
electromagnetic waves are used to transmit
information (voice or data).
Brief History of Wireless technology
• 1876 Alexander Graham Bell demonstrated the
telephone (wired).
• 1880 Bell used reflected sunlight and photoelectric
selenium detector (receiver) to transmit without
wire intelligible speech over 700 feet.
• Heinrich Rudolf Hertz demonstrated the existence
of electromagnetic waves in the mid 19th century.
• 1886 Guglielmo Marconi received a patent for the
first practical wireless telegraph.
• 1890 Reginald Fessenden developed wireless
voice communication.
• 1920 the first commercial radio station KDKA
was established in Pittsburg, PA.
Brief History of Wireless technology
continued
• 1921first terrestrial mobile application, a one-way
system was used at the Detroit Police Department.
• 1926 John Logie Baier demonstrated B/W
television.
• 1927 color TV publicly demonstrated.
•
Over the last decade, wireless industry has experienced exponential growth
with cellular voice telephony accounts for the vast majority of the market. A
plethora of new technologies have emerged, including Truck Mobile Radio
(TMR), paging, cordless telephony, Wireless Office Communication Systems
(WOTS), celluar, wireless LANs, Wireless Local Loop (WLL), Low Earth
Orbiting Satellites (LEOs), Personal Communication Services (PCS), Personal
Digital Assistants (PDAs). Within each technology, there exist a number of
specific technologies for discussion.
Standard Organizations
• FCC, IEEE (US)
• CEPT/ETSI (Europe)
• ITU-R (international-radio communication
sector).
• …etc.
• Functions include frequency allocation
(spectrum management) and power level
regulation to avoid interference.
Advantages and disadvantages of
wireless
• Advantages
– Reduced cost of installation
– reconfiguration, improved speed of deployment and
reconfiguration
– Mobile
• Disadvantages
– Spectrum availability (radio operates between 3k to
30G Hz
– Multipath interference (MPI) leads to ghosting effect
The cell concept: frequency reuse
• Concepts date back in 1947 at Bell labs.
• Assuming 12 channels are available in a
metropolitan area of 60 miles radius.
– 1 macrocell supports 12 simultaneous conversations
– Divide a macrocell into 7 microcells, a reuse factor of
128 is realized, allowing 1,536 conversations.
– Divide a macrocell into 7 picocells, the system supports
in theory 6, 168 conversations.
Digital versus analog
• Advantages of digital
–
–
–
–
More efficient use of bandwidth thru compression.
Improved quality of transmission
Improved security thru encryption
Improved throughput (due to diminished error)
• Analog still in existence due to
– Incumbent technology
– Expensive and disruptive to completely rip it out
Multiplexing and access techniques:
FDMA
• Frequency division multiple access (FDMA):
divides a frequency range (channel) into multiple
carriers (sub channels) to support multiple
conversations; guard bands are often required.
• Analog cellular systems use FDMA exclusively,
e.g., U.S. AMPS (Advanced Mobile Phone
System): 40 MHz total allotted bandwidth is
divided into 666 frequency pairs, each pairs has a
bandwidth of 60 kHz (30 for forward channel,
another 30 kHz for reverse channel).
Multiplexing and access techniques:
TDMA
• Time division multiple access (TDMA): a digital
technique that divides each channel into fixed
number of time slots each of which supports a
conversation (similar to T-carriers).
• In GSM (Global System for Mobile
Communication), a channel of 200 kHz has a data
rate of approx. 200 kbps, which is divided into 8
time slots of 25 kbps, easily supports a low-bitrate digitized voice of 9.6 kbps. Each conversation
uses two time slots, one for the forward channel
and one for the reverse channel.
Multiplexing and access techniques:
CDMA
• Code division multiple access (CDMA) is based on spread
spectrum radio technology patented by Heddy Lamar in
1942. In spread spectrum radio, a narrow band signal is
spread and sent over a much wider spectrum of radio
frequencies. It may use either direct sequence (DS) or
frequency hopping (FH) techniques.
• Frequency hopping spread spectrum (FHSS) is generally
preferred today; it involves the transmission of short burst
of packets over a range of frequency channels within the
wideband carrier, with the transmitter and receiver hopping
from one frequency to another in a carefully
choreographed hop sequence, which is generally under the
control of the centralized base station antenna.
• CDMA improves BW utilization (20:1 theoretically,
around 4:1 in practice) because many users can share the
same wideband radio channel.
CDMA continued
• Qualcomm develops, manufactures,
markets, and licenses CDMA products. A
great number of manufacturers and
providers of cellular, PCS, wireless LANs
and other systems and networks have
licensed CDMA.
Switched mobile radio (SMR)
• 1921 Detroit Police Department first 2-way mobile radio
system (AM technology).
• Early 1930s Bayonne, NJ Police followed suit (still AM)
• Late 1930s, FM technology replaced the AM.
• 1949, FCC began to allocate spectrum and regulate it use.
• 1946 AT&T launched commercial application in St. Louis.
In addition to a 50-mile range centralized antenna, the
system was connected to PSTN.
• 1960s: SMR, also known as TMR (Trunk Mobile Radio),
marketed as improved mobile telephone service.
• SMR/TMR has been largely supplanted by cellular service.
Paging
• Introduced in the 1950s in New York.
• Standards
– 1981: international POCSAG (Post Office Code Standardization
Advisory Group); can support 2 millions individual addresses,
tone-only, numeric, and alphanumeric pagers are supported on a
one-way basis.
– ERMES (European Radio Message System): 1990, 16 European
countries endorsed it.
– Motorola recently developed FLEX with the hope that it will be
accepted as the new international standard. It supports
• 5 billion addresses
• FLEX: 1600 bps, 25 kHz channel, one-way
• ReFLEX: 1600, 3200, 6400, and 9600 bps, 25 or 50 kHz
channels downstream and 12.5 kHz upstream, two-way.
• InFLEX: up to 112 kbps, 50 kHz channels in the narrowband
PCS range; two-way, supported compressed voice
downstream
Paging equipment and applications:
contemporary and developing
• Opportunities for innovators to come up
with new applications.
Cordless telephone and wireless office
telecommunication systems (WOTS)
Cellular Radio
• Concepts date back in 1947 at Bell labs to meet the
increasing demand of SMR/TMR radio systems.
• Highly scalable: cell size can be flexibly changed.
• Cell diameter usually ranges from 1 to 5 miles, depending
on topography.
• Can switch from one cell to another thru hand-off, which is
handled by MTSO (mobile traffic switching office).
MTSOs are interconnected and are connected to PTSN.
• Soft hand-off (make and break) or hard hand-off (bread
and make); both are fine with voice communication, but
the latter has problem with data communication.
Cellular standards
• Analog cellular: G1 cellular systems
– AMPS: AT&T and Motorola; rapidly giving
way to digital technology worldwide.
– N-AMPS: narrow-band AMPS; Motorola.
– NMT (Nordic mobile telephone) in scandinavia
– TACS (Total access communication system)
developed in England.
Cellular standards continued
• Digital cellular: G2 cellular systems
– GSM (Global System for Mobile communication):
dominates worldwide; adopted in 1987 for pan-Europe
systems; operates in the 800 and 900 MHz ranges and
is ISDN compatible; 4-cell reuse plan and each cell is
divided into 12 sectors; used CDMA; supporting
roaming from country to country.
– D-AMPS (Digital AMPS): AKA US TDMA is the N.
Am. Standard; operates in the same 800 MHz band as
AMPS and uses the same 30 kHz bands as AMPS;
3:1improvement on band utilization over AMPS; coexists with AMPS; data rate up to 28.8 bps.
• Others: PDC (Japanese Digital Cellular), PCS
(Personal digital system).
The future of cellular radio: G3?
• Market increases quickly over the years
worldwide, often beyond projection.
• Cost continues to drop: $.45/minute in the
early 90s to 9.4 cents in 2000.
• G3 proposals are under consideration
– Calls for data rate from 144 kbps (fast moving)
to 384 kbps (pedestrian).
– Supports global roaming
Wireless data networks: packet radio
• Operating at various data rates (4.8 - 19.6 kbps; 77
kbps) and and bands (e.g., 800-900 MHz, 902-928
MHz, 2.3 and 2.4 GHz) from different companies
(BellSouth, Ardis, Metricom, etc.) data-specific
wireless networks have been deployed all over the
metropolitan areas in the US over the last few
years.
• Properiety packet protocols are used.
Wireless LANs or WLANs
• Based largely on spread-sprectrum technology.
• Operate in IR, radio range (e.g., 2.4-2.4834 GHz).
• Raw bandwidth 4 MHz with effective throughput
around 2 Mbps per hub. Infrared-based bridges
run at speed up to 622 Mbps.
• Standards were finalized in 1997 by IEEE (80211)
• Moderate success over the last few years.
Wireless local loop (WLL)
• Local loops were owned by ILECs (incumbent
local exchange carriers). The Telecommunication
Act of 1996 opened the local loops for
competition.
• Options:
– twisted pair (old and slow); not the way to go
– fiber: optimum choice, but too expensive now for low
capacity application (needs killer applications).
– So, Wireless local loops is a good choice. But it radio
frequency and other electromagnetc inteference can be
a problem.
Low-earth orbiting satellites (LEOs)