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UMTS (Towards 3G) - 1

Towards 3G [Under UMTS]

1992-2000 period mainly belonged to (digital) 2G(eneration) systems - GSM/GPRS, IS-95, PDC.

GSM came into commercial existence in 92, followed by GPRS in 2nd half of 90s. This was TDMA/FDMA based systems with GMSK modulation and FDD as duplexing technique (UL/DL in separate frequencies). The standard was set by ETSI. The region was Europe.

CDMA (with FDMA) based IS-95 (cdmaOne) systems were launched in USA in '95. This used QPSK and FDD.

In '93, PDC standard based 2G systems were launched in Japan. This was TDMA/FDMA based systems using DQPSK modulation technique and FDD operation.

2G systems provided standardised digital wireless communication for general public use. Though well designed, the systems were meant for wireless telephony services and so they provided lesser data rates (compared to their landline counterparts) and/or were inefficient in using radio resources.

Even before these 2G systems were being launched, standard organisations from various countries had already started looking for (radio) technologies that would provide higher data rates to support high end applications like multimedia and be more efficient compared to 2G systems.

By '97, ETSI formed groups to decide 3G technologie s (mainly radio) out of various alternatives based on CDMA, TDMA, OFDMA, and combinations of it. Both TDD and FDD operations were considered.

In '98- '00 period, ITU-R (International Telecommunications Union for Radio communications) introduced IMT-2000 framework which set the requirements for 3G systems.. This was meant for ETSI's UMTS solution, but regional standard organisations which were members of ITU also submitted their proposals for 3G access technologies.

At around same time, ETSI introduced EDGE/EGPRS which used 8-QPSK (retaining GMSK) modulation giving higher data rates. In CDMA world, cdma200 and cdma/EV-DO was introduced giving comparable data rates (in fact better) to EGPRS. These systems are known as 2.5G (some people may even consider these as part of 3G).

Various regional standard organisations worked on deciding 3G radio technologies and most of them preferred CDMA based systems. This resulted in formation of new standardisation body called 3GPP in '99 by ATIS & T1 from USA, ETSI from Europe, TTA from Korea and ARIB & TTC from Japan. Later CCSA from China joined the project. ETSI had chosen WCDMA (FDD operation); the standardisation work was handed over to 3GPP. Looking at it, a decade was taken from year '88 till '99 in deciding access technology for UMTS i.e. UTRA !

First UMTS standard came in 1999-2000 as 3GPP release 99. 3GPP2 was formed to maintain wireless technologies based on IS-95 CDMA standards.

3GPP later introduced HSDPA in Rel 5, year '04 (rate = 10 Mbps), HSUPA in Rel 6, year '05 (rate = 5.5 Mbps, and HSPA in Rel 7 & 8. This can be considered as 3G evolution or 3.5G. 3GPP2 introduced EV-DO Rev A and B in parallel lines.

4G technology using OFDMA, called LTE is also being worked out by 3GPP in Rel 8, continued by Rel 9. LTE advanced is also in pipeline. 3GPP2 working on UMB for 4G.

There is another player working in wireless access field: IEEE, popular for WiFi/WLAN (802.11) standards. IEEE maintain 802 group of standards which provide specifications for layers below network layer (IP). 802 stack structure is: (from top to bottom) Logical Link Control layer, MAC (Medium Access Contention) layer, and then Phy layer. IEEE came out with 802.16 standards for fixed radio access in '04, later amended for mobile radio access as 802.16e. The radio access is based on OFDMA, so it may be considered as 3.5/4G technology. Currently IEEE is working on 802.16m which is possibly parallel to LTE advanced.

So what is the range of bit rates we are talking about ?

Roughly, 2G systems provide maximum bit rates in the range of tens of kbps, 2.5G to provide couple hundreds of kpbs, 3G should provide maximum data rates in the range of Mbps, 3.5G to provide few Mbps, and 4G systems are targeted for hundreds of Mbps. These are mainly downlink data rates, uplink rates are typically lower (may be half or 1/3rd of downlink data rates) as traffic density is higher in downlink than in uplink for typical data traffic (e.g. Internet traffic).

Diagram below shows the history in brief:

1992 1995 2000 2004 2010
2G systems - GSM/GPRS, IS-95, PDC launched.
Various standard organisations had already started looking for 3G (radio) technologies.
By '97, ETSI formed groups to decide 3G technologies (mainly radio) out of various alternatives based on CDMA, TDMA, OFDMA, and combinations of it.
In '98-'00 period, ITU-R (International Telecommunications Union for Radio communications) introduced IMT-2000 framework which set the requirements for 3G systems.
ETSI selected WCDMA (FDD operation) for UMTS in '98
New standardisation body called 3GPP formed in '99 by leading regional standard organisations to continue UMTS standardisation work from ETSI.
During later period of 90s, EDGE/EGPRS, cdma2000, cdma2000/EV-DO were introduced.
UMTS standards released as Release 99 by 3GPP at around year 2000.
3GPP2 was formed to maintain wireless technologies based on IS-95 CDMA standards.
3GPP later introduced HSDPA in Rel 5, year '02 (rate = 10 Mbps), HSUPA in Rel 6, year '05 (rate = 5.5 Mbps), and HSPA in Rel 7 & 8. This can be considered as 3G evolution or 3.5G.
3GPP2 introduced EV-DO Rev A and B in parallel lines.
4G technology using OFDMA, called LTE is also being worked out by 3GPP in Rel 8, continued by Rel 9.
3GPP2 working on UMB for 4G.
IEEE introduced OFDMA based radio access standards 802.16d (for fixed access) and 802.16e corrigendum (for mobile access).
Next is LTE advanced from 3GPP and 802.16m by IEEE.

References: UMTS by Sanchez and Thioune, WCDMA for UMTS by Holma and Toskala, LTE - Theory to practice by Sesia, Toufik, and Baker, WiMAX handbook by Ahson and Ilyas.

Copyright © Samir Amberkar 2010§

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