Background [Under LTE]
Below is a simplified presentation of achievable data rate pattern in a cross section of a cell in 2G. Darker color indicate better data rates compared to lighter color. Data rates are likely to be better (and consistent) near to source of transmission. As we move towards cell edges and as more n more geographical changes are encountered, data rates are likely to be lesser and more inconsistent.
Technological efforts will be in a direction to achieve better and better data rates with consistency as shown in picture below, sort of making above picture "more perfect or balanced" !
2.5G/GPRS introduced packet based data transmission, which were later enhanced with EDGE/EGPRS. With the success of 2G (both commercial and technological), an effort was made in 3G/UMTS to achieve better data rates by adopting WCDMA PHY and taking an optimised approach between circuit switched and packet switched wireless transmission approaches.
Even though 3G allowed us to think of advanced services on wireless network like video call, streaming etc., its wireless access (WCDMA based) was "just not perfect". We needed "better/efficient" data rates and "more balanced or perfect" data rate pattern as shown above.
So how do we do it ?
Shall we again look for different phy as we did for 2G to 3G or shall we first evolve 3G as we did in EDGE/EGPRS or we do this in parallel ? Which techniques will give us optimised results in field ?
This is what currently being done !
On one side, 3G/WCDMA is being evolved with HSDPA, HSUPA, HSPA+ and in parallel, LTE solution is being worked out with different PHY OFDMA (already made popular by 802.16/WiMAX) !! In both PHY solutions, various techniques like HARQ, MIMO are being adopted in stages or otherwise .
Again idea for 3G to LTE/3G+ migration is similar to that for 2G to 3G: selectively or phase wise add LTE/3G+ capabilities to existing 2G/3G cells.
Not all network operators would be happy with these changing PHY, network configurations etc., considering 3G itself not fully absorbed yet in networks. But they will agree in principle that sooner or later, LTE (or may be OFDMA PHY) will play pivotal role in wireless networks. In fact, in developing countries, some of the big network operators may put LTE capability in few cells in their 2.5G (3G absent) networks, sort of direct 2.5G to 3.99G transition (by passing 3G/3G+), at least for trial purposes, !!
Direct 2.5G to 3.99G transition may be best thing to do if trials work out well !! Anyone taking this approach may well jump to the first place in the race !! :-)
With this background, let us begin our journey towards LTE, starting at 3G.
References: 3G Evolution: HSPA and LTE by Dahlman, Parkvall, Sköld, and Beming, LTE - From Theory to Practice, Edited by Sesia, Toufik, and Baker, and UMTS by Sanchez and Thioune.
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