Page 126 - From GMS to LTE

112 From GSM to LTE-Advanced Pro and 5G

technologies like cable and Asymmetric Digital Subscriber Line (ADSL) modems
reached the mass market and dramatically increased transmission speeds for end users.
With these technologies, transmission speeds of several megabits per second are easily
achieved. In many countries, fixed‐line network operators are now rolling out high‐
speed connections based on optical fibers that are either directly deployed into the
basements of buildings (fiber to the building) or to street‐side equipment cabinets (fiber
to the curb). The last few meters into buildings or apartments are then bridged with
copper technologies such as Ethernet or Very‐high‐bitrate Digital Subscriber Line
(VDSL). This way a shorter length of copper cable is used for the last leg of the connec-
tion, which helps to enable speeds of 25–100 Mbit/s per line and beyond. TV cable
operators are also upgrading their networks to achieve similar speeds.
In the mobile world, GPRS (see Chapter 2) with its packet‐oriented transmission
scheme was the first step toward the mobile Internet. With datarates of about 50 kbit/s
in the downlink direction for operational networks, similar speeds to those of contem-
porary fixed‐line modems were achieved. New air interface modulation schemes like
EDGE have since increased the speed to about 150–250 kbit/s per user in operational
networks. However, even with EDGE, some limitations of the radio network such as the
timeslot nature of a 200 kHz narrowband transmission channel, GSM medium access
schemes and longer transmission delays compared to fixed‐line data transmission could
not be overcome. Therefore, further increase in transmission speed was difficult to
achieve with the GSM air interface.
Since the first GSM networks went into service at the beginning of the 1990s, the
increase in computing power and memory capacity has not stopped. According to
Moore’s law, the number of transistors in integrated circuits grows exponentially.
Therefore, the processing power of today’s processors used in mobile networks is in
orders of magnitude more than that of the processors of the early GSM days. This in
turn enables the use of much more computing‐intensive air interface transmission
methods that utilize the scarce bandwidth on the air interface more effectively than the
comparatively simple GSM air interface.
For UMTS, these advances were consistently used. Although voice communication
was the most important application for a wireless communication system when GSM
was designed, it was evident at the end of the 1990s that data services would play an
increasingly important role in wireless networks. Therefore, the convergence of voice
and high‐speed data services into a single system has been a driving force in UMTS
standardization from the beginning.
As will be shown in this chapter, UMTS is as much an evolution as it is a revolution.
While the UMTS radio access network (UTRAN) was a completely new development,
many components of the GSM core network were reused, with only a few changes, for
the first step of UMTS. New core and radio network enhancements were then specified
in subsequent steps. Today, this process continues with the LTE and 5G radio access
and core network architectures that are discussed in Chapter 4.
The Third Generation Partnership Project (3GPP) is responsible for evolving the
GSM, UMTS, LTE and 5G wireless standards and refers to the different versions as
‘Releases’. Within a certain time frame all enhancements and changes to the standards
documents are collected, and once frozen, a new version is officially released. Each
3GPP release of the specifications includes many new features for each of the radio
access technologies mentioned, some large and some small. As it is impossible to