developed since 1990s – most of today’s n/w use 2g technology. the most popular 2g stds. include...

• Developed since 1990s – Most of today’s n/w use 2G technology.

• The most popular 2G stds. include three TDMA and one CDMA std.:

1. Global System for Mobile (GSM) – supports eight time slotted users (TDMA) for each 200kHz radio channel and has been deployed widely in the cellular and PCS bands by various service providers in Europe, Asia, Australia, South America and some parts of US (in the PCS band only)

2. Interim Standard 136 (IS 136) also known as North American Digital Cellular (NADC) or US digital cellular (USDC) – supports three time slotted users (TDMA) for each 30kHz radio channel and is widely used in North America, South America and Australia.

3. Pacific Digital Cellular (PDC) – a Japanese TDMA std. similar to IS-136

2G CELLULAR NETWORKS

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4. Interim Standard 95 (IS 95) – a popular 2G CDMA standard, also known as CDMAone – supports upto 64 users that are orthogonally coded and simultaneously transmitted on each 1.25MHz channel. Widely used in North America, Asia and Australia.

These 2G stds. represent the first set of wireless air interface std. to rely on digital modulation and sophisticated digital signal processing in the handset and the base stn.

Specs. of 2G systems: - uplink and downlink freqs., multiple access technology, modulation technique, carrier separation, channel data rate and speech coding.

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The 2G stds. Were designed before the widespread use of Internet. They use circuit switched data modems that limit data users to a single circuit switched voice channel.

2G supports single user data rates of the order of 10kbps, - too slow for Internet browsing applications.

2G supports limited Internet browsing and sophisticated SMS (short message services).

The 2G technology is now upgraded by so many paths as shown in fig. 3.1. Most requires change in network infrastructure and handset.

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EVOLUTION OF 2.5G CELLULAR NETWORKS

New 2.5G technology allows existing 2G equipments to be modified and supplemented with new base stn. add ons and subscriber unit software upgrades to support higher data rate transmission for web browsing, E-mail, M-commerce etc.

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The 2.5G technologies support a popular new web browsing format language called Wireless Application Protocol (WAP), that allows std. web pages to be viewed in a compressed format specifically designed for small and portable handsets.

The appropriate 2.5G upgrade path for a particular wireless operator (service provider) must match the original 2G technology choice made earlier by the same service provider as shown in fig. 3.1.

The 2.5G improves Internet access speed and provides us Internet ready cell phones.

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The three TDMA upgrade options include:

1. HSCSD – High speed circuit switched Data Circuit switched technique that allows a single mobile

subscriber to use consecutive user time slots in the GSM std. Instead of limiting each user to only one specific time slot in

frame, it allows individual data users to commandeer consecutive time slots.

Relaxes the error control coding algorithms originally specified in GSM std. for data transmissions and increases the data rate to 14.4kbps compared to 9.6kbps original and using up to four consecutive time sots, HSCSD is able to provide transmission rate up to 57.6kbps.

Ideal for dedicated streaming Internet access or real time interactive web sessions and only requires a service provider to change software at existing base stns.

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2. GPRS – General Packet Radio Service Packet switching network well suited for non real time

Internet usage – E mail, faxes and asymmetric web browsing (more downloads than uploads)

Supports multi user network sharing of individual radio channels and time slots – supports many more users than HSCSD.

Retains the original 2G TDMA modulation formats, but uses a completely redefined air interface in order to better handle packet data access.

It requires the GSM operator to install new routers and Internet gateways at the base stns along with new software that redefines the base stn air interface std for GPRS channels and time slots, but no new base stn. RF network is required.

It provides services to both GSM and IS 136 operators and packet data rate up to 21.4kbps. 7

3. EDGE – Enhanced Data rates for GSM Evolution More advanced upgrade to GSM (Enhanced

GPRS) and requires the addition of new hardware and software at existing base stns.

New digital modulation formats – 8 PSK, which is used in addition to GMSK original.

Allows for nine different air interface formats, known as multiple modulation and coding schemes, with varying degrees of error control protection.

Data rate up to several Mbps.

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The CDMA 2.5G upgrade includes:

1. IS- 95B IS 95 CDMA has a single upgrade path for eventual 3G

operation. Provides high speed packet and circuit switched data

access on a common CDMA radio channel by dedicating multiple orthogonal user channels (Walsh functions) for specific users and specific purposes.

Provides data rate of 115.2kbps compared to 14.4kbps original.

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3G CELLULAR MOBILE NETWORKS 3G systems provide voice quality comparable to PSTN,

high data transfer rate (2Mbps), video conferencing, voice over Internet protocol (VoIP), voice activated calls, unparalled network capacity, Internet ready phone etc.

Users can receive live music, conduct interactive web sessions and have simultaneous voice and data access with multiple users at the same time using a single handset.

Supports both symmetric and asymmetric traffic (ADSL), full roaming, reprogramming or modification in platform by downloading software over the air.

Also supports LEO (low earth orbit) satellite networks and GPS (Global Positioning System). 10

The plan for 3G formulated in 2000MHz band for all countries and have single std called IMT 2000 (International/Improved Mobile Telephone).

But the single std has not still realized due to two divisions of technology throughout the world; i.e. GSM/IS 136/PDC and IS 95 CDMA.

So, 3G technologies has two parallel paths for development. GSM/IS 136/PDC system leads to wideband CMDA (W

CDMA), also called UMTS (Universal Mobile Telecom Service)- based on the network fundaments of GSM and EDGE.

IS 95 CDMA evolves to CDMA 2000 with several variants. Two groups of ITU IMT 2000 working in two parallel directions:

(i) 3GPP – 3 G partnership Project for W-CDMA and (ii) 3GPP2 – for CDMA 2000.

ITU recommended 2500-2690MHz, 1710-1885MHz and 806-960MHz bands for 3G. 11

(A) W- CDMA (UMTS):

Backward compatibility with 2G GSM/IS 136/PDC TDMA as well as 2.5G TDMA technologies.

The n/w structure and bit level packaging of GSM data is retained, additional capacity and BW is provided by a new CDMA air interface.

The air interface std. for 3G had been designed for “always on” packet based wireless service, so that computers, entertainment devices and telephones may all share the same wireless network and be connected to Internet any time, any where.

Support packet data rates upto 2.048Mbps per user and allow high quality data, multimedia, streaming audio, video and broadcast type services to consumers. Future versions give upto 8Mbps data rate. 12

W- CDMA provides virtual private network (VPN) features, video conferencing, M-commerce and virtual home entertainment.

It requires a min. 5MHz spectrum allocation. Complete change out of RF equipment at base stn. A single 5MHz radio channel support 100 to 350

simultaneous voice calls depends on antenna sectoring, propagation conditions, user velocity and antenna polarizations.

W-CDMA employs variable/selectable direct sequence spread spectrum (DSSS) chip rates that can exceed 16 Megachips per second per user.

Six times spectral efficiency over GSM. Fully implemented by year 2010. 13

One more variant of GSM TDMA compatible 3G std is called TD-SCDMA – Time division synchronous CDMA.

It relies on existing GSM infrastructure and allows a 3G network to evolve through the addition of high data rate equipment at each GSM base stn.

TD-SCDMA combines TDMA and TDD (same ch. gives forward and reverse link in different time slots) technique to provide a data only overlay on existing GSM n/w.

Upto 384kbps of packet data rate is provided to data users. The radio channels are 1.6MHz in BW and rely on smart

antennas, spatial fading and joint detection techniques to yield several times more spectrum efficiency than GSM.

For asymmetric traffic (higher download than upload), it provides more time slots to forward link (download) than reverse link (upload).

Easily and inexpensively added to existing GSM n/w and widely used in China.

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(B) CDMA 2000: Upgrade to CDMA technology by using a building

block approach that uses original 1.25MHz channel BW per radio channel.

Does not require change entire base stns or reallocation of spectrum.

The first 3G CDMA air interface, CDMA 2000 1xRTT, implies that a single 1.25MHz radio ch. is used.

RTT stands for radio transmission technology, language suggested by IMT 2000 body.

No additional RF equipment is needed to enhance the performance, the changes are all made in software or in baseband hardware.

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CDMA 2000 1xEV is an evolutionary advancement for CDMA and provides option of installing radio channels with data only (CDMA 2000 1xEV –DO) or with data and voice (CDMA 20001xEV –DV).

The performance is twice as compared to IS 95B. The CDMA 2000 3xRTT std uses three adjacent

1.25MHz radio channels that are used together to provide instantaneous packet data throughput speeds in excess of 2MBps per user.

It is comparable to W-CDMA since CDMA 2000 allows the same spectrum, BW, RF equipment and air interface framework to be used at each base stn.

But it gives more seamless and less expensive upgrade paths when compared to W-CDMA.

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4G CMS FEATURES:

Expected in near future. The main requirement from this system is transmission

data rate of 1Gbps at a standstill condition and 100Mbps at a moving condition.

Concepts of OFDM (Orthogonal FDM) is exploited to achieve higher data rate compared to CDMA.

Also, it requires unification of various mobile and wireless networks.

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CONCEPT OF WLL (WIRELESS IN LOCAL LOOP) :

The basic telephony services are not available everywhere even today; for e.g.; rural and isolated areas, regions subjected to severe conditions such as earthquakes and floods.

WLL provides solution to these problems better than wired loop access technology.

Also it reduces cost of operation and maintenance since there is no wire to maintain.

Conceptually, WLL implies to the use of radio and wireless technologies in the local loop instead of copper wire technologies to provide access to PSTN.

The WLL application must provide the same or greater quality of service (QoS) compared to PSTN. 18

In many cases WLL performs better than the wired line in terms of economics and as such provides a direct substitute for today’s wired line local loop.

Unlike CMS, WLL is fixed wireless commu. System and able to take advantage of well defined, time invariant nature of propagation channel between fixed transmitter and receiver.

Modern fixed wireless systems are usually assigned microwave or millimeter radio freqs. in the 28GHz band and higher; which is greater than ten times the carrier freq. of 3G terrestrial cellular telephone n/ws.

At these freqs., wavelengths are extremely small, which in turn allows very high gain directional antennas to be fabricated in small physical form.

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High gain antennas have spatial filter properties that can reject multipath signals that arrive from directions other than line of sight (LOS) and supports the transmission of very wide BW signals without distortion.

WLL supports broadband Internet connection as well as VoIP.

Most WLL systems are based on W-CDMA technology. It provides ISDN like services, facsimile services and

high data rates to subscribers.

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WIRELESS LOCAL AREA NETWORK (WLAN)

In 1977 the FCC allocated 300 MHz of unlicensed spectrum in the Industrial, Scientific & Medical (ISM) bands of 5.150-5.350 GHz and 5.725-5.825 GHz for the express purpose of supporting low power license free spread spectrum data communication. This allocation is called the Unlicensed National Information Infrastructure (UNII) band.

The IEEE 802.11 Wireless LAN working group was founded in 1987 to begin standardization of spread spectrum WLANs for use in the ISM bands.

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WIRELESS LOCAL AREA NETWORK (WLAN)

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WIRELESS LOCAL AREA NETWORK (WLAN)

•Above shown WLAN standard also include infrared communications

•Both Frequency Hopping spread spectrum (FH-SS) and Direct Sequence spread spectrum (DS-SS) approaches were used.

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WIRELESS LOCAL AREA NETWORK (WLAN)

Unique WLAN channels for 802.11b for the 2400-2483.5 MHz band

BLUETOOTH & PERSONAL AREA NETWORKS (PANS)

Bluetooth is an open standard, which provides an ad-hoc approach for enabling various devices to communicate with one another within a nominal 10 meter range.

Named after King Harald Bluetooth, the 10th century Viking who united Denmark & Norway, the Bluetooth standard aims to unify the connectivity chores of appliances within the personal workspace of an individual.

Bluetooth operates in the 2.4 GHz ISM Band and uses a frequency hopping TDD scheme for each radio channel has a 1 MHz bandwidth and hops at a rate of approx. 1600 hops/sec.

Transmission are performed in 625 msec slots with a single packet transmitted over a single slot.

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BLUETOOTH & PERSONAL AREA NETWORKS (PANS)

The IEEE 802.15 standards committee has been formed to provide an international forum for developing Bluetooth and other PANs that interconnect pocket PCs, personal digital assistants (PDAs), cell phones, light projectors and other appliances.

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THANKS

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