1

Overview of Wireless Communications

Chapter 1

2

Brief History of Wireless Communications

Basic Terminology

Examples of Wireless Communication Systems

• Paging Systems

• Cellular Radio Communications

• Wireless Metropolitan Area Networks (WMANs)

• Wireless Local Area Networks (WLANs)

• Wireless Personal Area Networks (WPANs)

Outline of Chapter 1

3

1888 - Heinrich Hertz generates and detects electromagnetic radiation (radio waves)

1890-1900 – A number of radio-related inventions. It is difficult to attribute the invention of radio

(wireless telegraph) to any single individual.

1890 (approx) - Édouard Branly invents a coherer (a detector used in early radio communication)

1893 – Nikola Tesla gives a public demonstration of wireless communication in St. Louis, Missouri;

he describes in detail the principles of radio communication in his address to the Franklin Institute in

Philadelphia. Tesla filed the first US radio patent in 1897.

1894 – Oliver Lodge demonstrates transmission of radio signals at Oxford University

1895 – Alexander Popov demonstrates transmission and reception of radio waves for communication

at the Russian Physical and Chemical Society

1895 – Guglielmo Marconi demonstrates transmission of radio signals over a hill at Villa Griffone in

Pontecchio (presently Sasso Marconi) near Bologna, Italy

1896 - Marconi demonstrates “wireless telegraph” to the British post and telegraph office

1899 - The first wireless telegraph transmission demonstrated by Marconi between England and

France

1900 – Radio equipment designed by Popov installed on ships of the Russian Navy, allowing two-way

communications with land stations (birth of mobile radio)

1901 - Marconi claims to have successfully transmitted radio signal (Morse code letter S sent

repeatedly) across the Atlantic Ocean from Cornwall to Newfoundland; the claim is still disputed

1902 - First radio transmission of audio signals by Reginald Fessenden (father of radio broadcasting)

using hot wire barretter and later electrolytic detectors

1909 - Guglielmo Marconi and Karl Ferdinand Braun share a Nobel prize in physics for “their

contributions to the development of wireless telegraphy”. Around 1898 Braun invented a crystal diode

rectifier (aka cat’s whisker detector), used by Marconi in his experiments and tuning patents.

Brief History of Wireless Communications Early Days

4

1920/30s - Mobile communication adopted for police vehicles in the USA 1934 – Edwin Armstrong proves advantages of frequency modulation (FM). FM was the primary modulation technique for mobile radio until late 80s. 1946 - Connection of mobile users to public switched telephone network (PSTN) introduced in 25 major American cities

• A single, high-powered transmitter is used in order to cover distances over 50 km. • The entire spectrum is allocated on a frequency division multiplexing basis, where each user is assigned a dedicated frequency. If the number of channels (i.e. available carrier frequencies) is given by C, only C users per geographic area can be served.• Half-duplex mode of operation, i.e. only one person on the phone call can talk at a time.• Each channel occupies 120 kHz bandwidth (although the actual telephone-grade speech requires only 3kHz) due to inefficient RF filter designs.

Brief History of Wireless Communications (cont.)Birth of Mobile Telephony

5

1960s - Improved Mobile Telephone Service (IMTS) introduced in the US.

• IMTS supports full-duplex, i.e. both parties can talk simultaneously. • IMTS supports auto-dial, i.e. no operator’s assistance.• IMTS supports auto-trunking, i.e. no dedicated frequency. Therefore, it is possible to sell mobile equipment to more than C users by assigning channels on a demand basis assuming a certain probability of blocking.

1970s - IMTS quickly became saturated in major markets. For example, in 1976, Bell Mobile Phone service for the New York City area had only 12 channels and could serve only 543 customers; service was poor due to call blocking due to the few available channels and too many subscribers.

1970s - Cellular concept introduced: This involves breaking a coverage area into small cells (sub-areas), each of which reuses portions of the spectrum to improve efficiency of spectrum usage (more details to follow later in this chapter).

1979 - NTT (Japan) deploys the first commercial cellular telephone system.

Brief History of Wireless Communications (cont.)Birth of Mobile Telephony (cont.)

6

Basic Terminology- I

Simplex (SX) transmission: One way communication from one point to another, e.g. radio/TV broadcasting stations, paging systems.

Half-duplex (HDX) transmission: Information can flow in both directions, but the flow is only one-way at any given time, e.g. dispatch radio systems (push-to-talk), walkie-talkie.

Full-duplex (FDX) transmission: Simultaneous communication in both directions, e.g. telephone. There are two ways to implement FDX transmission:

• Frequency Division Duplex (FDD) uses two separate frequency channels (two separate carrier frequencies).• Time Division Duplex (TDD) uses adjacent time slots on a single radio frequency channel (one carrier frequency).

Downlink (Forward) channel: Base station Mobile station

Uplink (Reverse) channel: Mobile station Base station

7

Basic Terminology- II

Frequency Division Duplex (FDD)

1.05F Rf f

RfFf

BS MS MS BS

frequency

• At the base station, separate transmit and receive antennas can be used

to accommodate two separate channels.

• At the mobile station, a single antenna (through the use of a duplexer)

is used for both transmission to and reception from the base station.

• To provide sufficient isolation, roughly ; 45 MHz

separation is often used in cellular systems to enable sufficient signal

isolation.

Usually, fF > fR

8

Time Division Duplex (TDD)

time FC RC FC RC FC RC

• TDD is only feasible with digital transmission.

• If the data transmission rate in the channel is much higher than the

end-user’s data rate, it is possible to store information bursts and

provide the “appearance” of full duplex operation to a user, although

two simultaneous radio transmissions are not present at any instant.

• Guard times must be used to account for variable propagation

delays and other timing imperfections.

Basic Terminology- III

FC – forward channel

RC – reverse channel

9

Basic Terminology- IV

Multiple Access Methods

In the reverse link (uplink), multiple MSs transmit to the BS, i.e. many-to-one

transmission occurs. This mode of transmission is referred to as multiple

access. If two or more user signals arrive at the BS at the same time, there will

be interference unless the signals are orthogonal.

The question is how to maintain orthogonality among the transmitted signals

from different users: FDMA, TDMA and CDMA.

• Frequency Division Multiple Access (FDMA): Each user is allocated a

portion of the system bandwidth to be used over the entire duration of his call.

• Time Division Multiple Access (TDMA): Each user is allowed to use the entire

system bandwidth in time slots occupying a fraction of the duration of his call.

• Code Division Multiple Access (CDMA): Each user is allowed to use the

entire system bandwidth over the entire duration of his call. Each user’s signal is

distinguished from others through the use of unique signature codes. CDMA

scheme in its usual implementation provides non-orthogonal channelization on

the uplink.

More details to come in Chapter 6.

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Examples of Wireless Communication Systems

Base Station (Access Point) Mobile Station

In the following, we will take a closer look at some examples of wireless

communication systems. These are:

Paging Systems

Cellular Radio Communications

Wireless Metropolitan Area Networks (WMANs), Wireless Local Area

Networks (WLANs) and Wireless Personal Area Networks (WPANs)

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Paging Systems Paging systems are simplex communication systems that send brief messages (numeric, alphanumeric or voice) to a subscriber.

System does not need to know the location of a pager. Same message is simultaneously transmitted from each base station, i.e. simulcasting occurs. Each user listens to all transmissions, but only decodes its intended message associated with its unique subscription number. Paging systems are designed to provide very reliable coverage, even inside buildings. Please see http://en.wikipedia.org/wiki/Pager for more information on current status of paging systems.

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Paging Systems (cont’d)

Simulcasting can often cause multiple versions of the same message to be received at a pager with propagation delays that differ by as much as 100 μs (30 km difference in propagation distance). This results in so-called intersymbol interference (ISI).

Rule of thumb: To avoid the need for equalization (mitigation of ISI; more details in Chapter 4), it is necessary to make the pulse duration greater than at least about 5 times the delay spread.

6

5 100 500 s1 1 2 kb/s

500 10

s

ss

T

RT

µ

−

= × =

⇒ = = =⋅

Hence, simple binary modulation formats are limited to data rates of a couple of kb/s.

13

A cell is a geographical area served by a single base station.

Each cell is allocated a group of k channels.

N cells form a cluster, in which all C = kNdifferent channels available in the system are used.

M clusters (each of which includes N cells) cover the entire geographical area,

Each channel is re-used M times. Each channel is re-used once every N cells.

Cellular systems employ frequency re-use, which allows efficient use of scarce and expensive radio spectrum.

Channels can be re-used when there is sufficient distance between the transmitters to attenuate interference. Careful planning of carrier frequency and time slot allocation is usually necessary.

Basics of Cellular Radio Communications

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Before Cellular Mobile Telephony(e.g. IMTS)

Cellular Mobile Telephony

Example: Mobile radio coverage for New York City

Basics of Cellular Radio Communications (cont’d)

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A cellular system consists of mobile stations (MS), base stations (BS) and a

mobile switching center (MSC). MSC is connected to broadband backbone

network. MSC is known as a base station controller (BSC) in GSM and as a

radio network controller (RNC) in UMTS (3G WCDMA system).

The only wireless communication link in the above configuration is the link

between the MS and BS, but it is also the most vulnerable link of the whole

system.

The communication system engineer should be able to design a reliable

link over the wireless channel, which is much more challenging than a wireline

channel. This course will attempt to show how to do it.

Basics of Cellular Radio Communications (cont’d)

A typical MSC handles 100 base stations, 100, 000 subscribers and

10,000 simultaneous conversations at a time. In large cities, several

MSCs are used by a single company.

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A number of channels are assigned as control channels for communication

between MS and BS to carry control signals (signalling channels).

When a MS is turned on (not yet engaged in a call), it first scans downlink

control channels to determine the BS with the strongest signal and monitors that

control channel until it drops below a useable level. It also registers itself with the

location area (a subset of BSs) this BS belongs to. Location areas are identified by

specific location area codes periodically broadcast by their BSs.

When a phone call (from a wireline phone) is placed to a MS, the MSC sends the

request (page) to the BSs in the MS’s location area. The mobile identification

number (MIN, 10 digits) is broadcast in the paging message over the control

channels of these BSs.

The MS receives the paging message sent by the BS it monitors and responds by

identifying itself over the control channel (Reverse Control Channel, RCC).

The BS relays the acknowledgment sent by the MS and informs the MSC of the

handshake. The BS assigns an unused voice channel within the cell to that particular

MS and instructs the MS to tune itself to the assigned voice channel.

Basics of Cellular Radio Communications (cont’d)

Once a call is in progress, the BS adjusts the transmitted power of the mobile

(if required) in order to maintain the call quality.

17

Figure: Timing diagram illustrating how a call to a mobile user initiated by a landline subscriber is established.

ESN – Electronic serial number (32 bits) stored in the phone (AMPS, IS-54 and IS-95); GSM equivalents: IMEI –International Mobile Equipment Identity (stored in the phone), and IMSI - International Mobile Subscriber Identity (stored in the SIM – Subscriber Identity Module card); CDMA2000 addition: UIMID – User Identity Module Identifier stored in an R-UIM – Removable User Identity Module.

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When an MS originates a call, a call initiation request is sent on the control

channel (RCC) to the BS. The BS receives the request and sends it to the MSC.

The MSC validates the request and makes the connection to the called party

through the PSTN. At the same time, it instructs the BS to ask MS to move to an

unused voice channel, allowing the conversation to begin.

If the MS moves from one cell to another, a handoff (handover) process (i.e.

switching to another BS) enables the call to proceed uninterrupted.

Roaming allows subscribers to operate in service areas other than the one from

which service is subscribed. Each MSC keeps track of the users through home

location register (HLR) and visitor location register (VLR). If a roaming

subscriber is identified, its information is sent to its home MSC, which updates

the location of its subscriber in its HLR.

If a call is made to a roaming subscriber from any phone in the world, the call

is routed directly to its home MSC. The home MSC checks the HLR to determine

the location of the subscriber and routes the call to the visited network.

Basics of Cellular Radio Communications (cont’d)

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Figure: Timing diagram illustrating how a call from a mobile user is established.

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The number of cellular subscribers exceeded 6.8 billion (about 97% of the

world’s population) in 2013. Approximate geographical distribution of ~6.8 B users:

• North America (US 327.5 M (104%) + Canada 26.5 M (74%)): 354 M

•Latin America (incl. Mexico): 680 M (~115%)

• Europe (including Russia): 1100 M (~150%)

• Asia: 3825 M (~85%)

• Africa: 800 M (~77%)

• Australia & New Zealand: 35 M (129%)

Trends in Cellular Radio Communications

Smartphones: ~ 2 B sold

since 2007

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1980s - First Generation (1G): Analog modulation (FM), FDD/FDMA

1990s and early 2000s - Second Generation (2G): Digital modulation, FDD/TDMA or CDMA

From the actual advertisement

Briefcase model: “You can carry it wherever you go!”

Handheld phones…

For voice communication

For voice and low-rate data communication

Trends in Cellular Radio Communications (cont’d)

Early 2000s - 2.5G : Improved data rates over those of 2G. Based on 2G infrastructure.

22

2000s - Third Generation (3G):

For voice and higher rate data communication supporting internet and various multimedia services such as video telephony, video streaming, on-line gaming etc.

Trends in Cellular Radio Communications (cont’d)

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Second Generation (2G) Cellular Systems

24

2.5G Cellular Systems

2G systems were originally designed for voice communication and low-rate

data communication. They used circuit-switched data modems that limited users to

data rate of a single voice channel (~9.6 kb/s). Example of 2G data communication

application: SMS (Short Message Service) of GSM.

In an effort to upgrade 2G standards to enable increased data rates to support

Internet applications (e.g. Wireless Applications Protocol, WAP, and i-mode on

PDC in Japan) and multimedia services, 2.5G standards were introduced.

2.5G allows existing 2G equipment to be used with some software/hardware/

add-ons at the base station and software upgrades on the mobile station.

TDMA (GSM) -based upgrades:

HSCSD: High Speed Circuit Switched Data

(14.4 – 57.7 kb/s) on aggregated slots

GPRS: General Packet Radio Service

(56 – 140.8 kb/s)

EDGE: Enhanced Data Rates for GSM Evolution

(200 – 384 kb/s)

CDMA-based upgrades: IS-95B

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Third Generation (3G) Cellular Systems 3G standards were developed to support demanding data rate requirements of Internet/multimedia services. Target peak data rates were 2 Mb/sec for indoor nomadic, 384 kb/s for pedestrian and 144 kb/sec for vehicular environments.

International Telecommunication Union (ITU) initiated International Mobile Telephone (IMT-2000) plan with a vision for a single, ubiquitous wireless communication standard throughout the world.

The following table illustrates the primary worldwide proposals that were approved by ITU as IMT-2000 standards in 1999. Currently, two of these proposals, i.e. CDMA2000 and W-CDMA (UMTS), have taken the lead. With major political and economic backing behind both camps, it is now apparent that the hope for a single 3G worldwide standard will not materialize.

The world’s first 3G commercial system was launched by SK Telecom (Korea) in October 2000. It is based on CDMA2000 (1x RTT, which is not a true 3G system). W-CDMA was launched in Japan in 2001.

It is expected that CDMA2000 and W-CDMA based technologies will dominate the worldwide market. One exception is China who has developed and supports deployment of its own wireless standard TD-SCDMA.

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Third Generation (3G) Cellular Systems (cont’d)

For updated information and latest statistics on 3G subscribers, check

http://www.3gpp.org http://www.gsmworld.com/

http://www.3gpp2.org http://www.cdg.org

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Beyond 3G Cellular: LTE (Long-Term Evolution of 3G)

and LTE-Advanced (4G) Standards

The basic technology driver: Higher and higher data rates to support ever-increasing

data/video service demands of nomadic/mobile users. MIMO (multiple-input multiple-

output) antenna techniques and OFDM (orthogonal frequency division multiplexing) as

enabling techniques at the physical layer. Target peak data rates: 1 Gb/s nomadic and

100 Mb/s mobile at much reduced cost per bit.

Seamless service provisioning across multilayer networks containing macro, pico

and femto nodes, as well as relays Heterogeneous cellular networks (HetNets)

4G systems use packet switching and IP. No circuit-switched voice channels (VoIP).

ITU (International Telecommunications Union) in the fall of 2010 announced that

the LTE-Advanced (Release 10 LTE) and the 802.16m (advanced WiMAX) meet its

IMT-Advanced requirements and hence can be called 4th generation (4G) cellular

systems.

Technology supporting 4G (multi-user MIMO, MIMO-OFDM, coordinated

multipoint transmission/reception, infrastructure-based relaying) is still under intensive

research by industrial and academic research centres around the world.

28

29

ITU – the source of the G in cellular systems

International Telecommunications Union

ITU-Radio Working Party 8F (now 5D)

International Mobile Telephony

IMT-2000: 3G IMT-Advanced: 4G

All IMT systems have access to designated IMT spectrum.

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Spectral Efficiency Requirements and Targets

Item Sub category LTE (3.9G)

target

LTE-

Advanced

(4G) target

IMT-

Advanced

(4G)

requirement

Peak spectral efficiency (b/s/Hz)

Downlink 16.3(4x4 MIMO)

30(up to 8x8 MIMO)

15(4x4 MIMO)

Uplink 4.32(64QAM SISO)

15(up to 4x4 MIMO)

6.75(2x4 MIMO)

Downlink cell spectral efficiency

in b/s/Hz at 3 km/h,500m ISD

2x2 MIMO 1.69 2.4

4x2 MIMO 1.87 2.6 2.6

4x4 MIMO 2.67 3.7

Downlink cell-edge user spectral

efficiency in b/s/Hz, 5 percentile, 500m ISD

2x2 MIMO 0.05 0.07

4x2 MIMO 0.06 0.09 0.075

4x4 MIMO 0.08 0.12

ISD is inter-site (inter-BS) distance. The performance figures have been obtained from system-level simulations

involving calculation of throughput by repeatedly dropping ten users randomly into the cell.

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LTE-Advanced Enabling Technical Solutions

• Bandwidth aggregation (up to 100 MHz bandwidth)• Enhanced uplink multiple access

– Clustered SC-FDMA (single-carrier FDMA, aka DFT-S-OFDM)– Simultaneous control and data

• Higher order MIMO

– Downlink up to 8x8– Uplink up to 4x4

• Coordinated multipoint (CoMP) Tx/Rx

• Infrastructure-based relaying

• Heterogeneous network support

32

Bandwidth Aggregation

• Lack of sufficient contiguous spectrum up to 100 MHz forces use of bandwidth aggregation to meet peak data rate targets

• Able to be implemented with a mix of terminals• Backward compatibility with legacy system (LTE)• System scheduler operating across multiple bands• Component carriers (CC) – Max 110 RB (radio resource blocks)• May be able to mix different CC types• Contiguous and non-contiguous CC allowed

PUSCH

PUCCH

Contiguous aggregation of two

uplink component carriers

33

PUCCH – physical uplink control channel

PUSCH – physical uplink shared channel

(packet data traffic channel)

Higher Order MIMO Transmission

• Up to 8x8 downlink (from 4x2 for LTE)– Baseline being 4x4 with 4UE receive antennas– Peak data rate reached with 8x8 SU-MIMO

• Up to 4x4 uplink (from 1x2 for LTE)– Baseline being 2x2 with 2 UE transmit antennas– Peak data rate reached with 4x4 SU-MIMO

• Use of beamforming with spatial multiplexing to increase data rate, coverage and capacity

• Challenges of higher order MIMO– Need for tower-mounted radio heads– Increased power consumption– Increased product costs– Physical space for the antennas at both eNB and UE

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Coordinated Multi-Point (CoMP) Tx/RxTraditional MIMO – co-located transmission Coordinated Multipoint

Downlink

• Coordinated scheduling / beamforming

- payload data is required only at the serving cell

• Joint transmission or fast transmission point selection

- payload data is required at all transmitting eNB

- requires high speed symbol-level backhaul between eNB

Uplink

• Simultaneous reception requires coordinated scheduling

35

36

Beyond 4G: A Vision of 5G Cellular

In about a decade the amount of data handled by wireless networks will have

increased by more than a factor of 100: < 3 EB (exabytes) in 2010, > 180 EB in 2018, >

500 EB in 2020. Also, roundtrip latency, energy consumption and cost per bit will have

to be reduced by about 10x and 100x, respectively.

Expected requirements:

• Area capacity (b/s/km2) increase by 1000 over 4G

• Cell edge rate (5% rate) increase to > 100 Mb/s (1 Mb/s for 4G)

• Roundtrip latency reduced to 1 ms (15 ms in 4G)

Some possible technical solutions:

• Extreme densification (dense HetNets with multi-RAT association; RAT – radio

access technology)

• mmWave systems

• Massive MIMO

• Non-orthogonal multi-carrier signalling

• Cloud radio access networks (C-RANs) with centralized baseband processing

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Wireless Metropolitan Area Networks (WMANs)

Last-mile broadband access

WiMAX (Worldwide Interoperability for Microwave Access -

IEEE 802.16 family), WiBro (Korea), HIPERMAN (Europe)

Wireless Local Area Networks (WLANs)

License-free, low-power, short-range data communications

Wi-Fi (IEEE 802.11 a/b/g/n/ac/ad)

Wireless Personal Area Networks (WPANs)

Very short range inter-device connection: Bluetooth, Zigbee

(IEEE 802.15)

Other Wireless Access Systems

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Wireless Metropolitan Area Networks (WMANs)

Fixed wireless access provides a reliable and inexpensive alternative to

optical fibre access for the “last mile”; operates in licensed RF bands.

Unlike mobile cellular phone systems, fixed wireless access systems are

able to take the advantage of almost time-invariant channel between the

fixed transmitter and the fixed receiver.

Standardization efforts are centered around IEEE802.16 and ETSI-HiperMAN,

which also include later mobile versions (e.g. 802.16e).

For updated information, check http://www.wimaxforum.org/

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Wireless Local Area Networks (WLANs)

WLANs provide license-free, low-power short-range (20-70 m indoor) data

communication, which facilitates Internet connection and private computer

communications at the workplace and other designated areas such as coffee

shops, airports, libraries, etc., as well as for home networking.

Although the IEEE 802.11 WLAN standards body was established in 1997,

WLANs did not get popular until mid-2000s. The wide-scale acceptance of

Internet combined with increasing use of laptops and other mobile computing

devices such as PDAs has caused WLANs to gain momentum.

WLANs operate in the 2.4-2.5 GHz or 4.915-5.825 GHz ISM (Industrial,

Scientific and Medical) bands. These are the same unlicensed bands where

cordless phones, baby monitors and Bluetooth (WPAN) devices operate.

Current WLAN standards are based on IEEE 802.11a/b/g/n/ac. Although

the term “Wi-Fi” has been originally introduced to denote 802.11b, it is

currently used as a generic term. 802.11ad (60 GHz mmWave system) is

known as WiGig (peak bit rate of 7 Gb/s).

802.11ac was finalized in Dec 2013: 80 or 160 MHz channels in 5 GHz

band, OFDM with up to 256 QAM, up to 8 MIMO spatial streams; currently

offered peak rate 1.3 Gb/s with 3 spatial steams in 80 MHz channel.

Check http://www.wi-fi.org/ for latest updates.

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Wireless Personal Area Networks (WPANs)Bluetooth

Named after king Harald Bluetooth

(the 10th century Viking who briefly

united Denmark and Norway), the

Bluetooth standard aims to unify the

connectivity chores of appliances

within the personal workspace of an

individual.

Bluetooth is an open standard that has

been embraced by over 1000 manufacturers

of electronic appliances. It provides an ad-

hoc approach for enabling various devices

to communicate with one another within a

typical < 10 m range.

It operates in the unlicensed 2.4 GHz ISM band, and uses FH-CDMA

(frequency-hopped CDMA: 79 hop carriers spaced by 1 MHz, 1600 hops/s, dwell

time = 625µs, GMSK). A single FH channel supports 1 Mb/s.

For further information, check http://www.bluetooth.com/