Page 221 - From GMS to LTE

Universal Mobile Telecommunications System (UMTS) and High-Speed Packet Access (HSPA) 207

had no such restriction due to the completely new implementation of the air interface
and availability of a dedicated frequency band for the new technology.
UMTS uses a chip rate of 3.84 MChip/s while CDMA2000 uses a chip rate of 1.2288
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MChip/s. To increase capacity, a base station can use several 1.25 MHz carriers. Up to
the latest revision of the standard described in this book (1xEV‐DO; see below), a
subscriber is limited to a single carrier.
UMTS uses a power control frequency of 1500 Hz compared to CDMA2000’s 800 Hz cycle.
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UMTS uses unsynchronized base stations, while in CDMA2000 all base stations are
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synchronized using the Global Positioning System (GPS) clock.
As UMTS uses unsynchronized base stations, a three‐step synchronization process is
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used between the mobile device and the network, as described in Section 3.4.4.
CDMA2000 achieves synchronization on the basis of a time shift process that adapts
the clock of the mobile device to the network.
While UMTS has a minimal frame length of 10 milliseconds, CDMA2000 uses
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20‐millisecond frames for user data and signaling and 5‐millisecond frames if only
signaling has to be sent.

As discussed earlier, UMTS has evolved to higher datarates with HSDPA. The corre-
sponding upgrade path of CDMA2000 is referred to as 1xEV‐DO (Evolution‐Data
Only) Revision 0 and uses one or more 1.25 MHz carriers exclusively for high‐speed
packet data transmission. Datarates in practice range between several hundred kilobits
and a few megabits. As only 1.25 MHz carriers are used, top speeds are not as high as
for HSDPA or HSPA+.
In a further evolution of the standards, referred to as Revision A, uplink performance
is improved to a level similar to UMTS HSUPA. Additional QoS features enabling the
use of VoIP and other real‐time applications over packet‐switched networks further
extend the functionality.
Further enhancements of the CDMA standard were initially foreseen but at some
point it was decided by network vendors and network operators that the 3GPP LTE
system should become the common successor to UMTS and EV‐DO. For this purpose,
extensions in the LTE specifications were defined to have a standardized interface to the
EV‐DO core network. These enable dual‐mode devices to access both systems and to
handover ongoing sessions between the two radio network technologies in a similar
way to handover between UMTS and LTE.

Questions

1. What are the main differences between the GSM and UMTS radio network?

2. What advantages does the UMTS radio network have compared to previous
technologies for users and network operators?

3. What datarates for a packet‐switched connection were offered by early Release 99
UMTS networks?

4. What does OVSF mean?