Page 38 - From GMS to LTE

24 From GSM to LTE-Advanced Pro and 5G

As the message waiting flag is also set in the HLR, the SMS also reaches a subscriber
who has switched off the mobile device in London, for example, and switches it on again
after a flight to Los Angeles. When the mobile device is switched on in Los Angeles, the
visited MSC reports the location to the subscriber’s home HLR (location update). The
HLR then sends a copy of the user’s subscription information to the MSC/VLR in Los
Angeles including the message waiting flag and thus the SMSC can also be notified that
the user is reachable again.
The SMS delivery mechanism does not include a delivery report for the sender of the
SMS by default. The sender is only notified that the SMS has been correctly received by
the SMSC. However, if supported by a device, it is also possible to request an end‐to‐end
delivery notification from the SMSC. In practice, there are a number of different ways
this is implemented in mobile devices. In some mobile operating systems, delivery
reports can be activated in the SMS settings. Confirmations are then shown with a
symbol next to the message or are displayed in the status bar. Other operating systems
include a separate list of received or pending confirmations.

1.7 The Base Station Subsystem (BSS) and Voice
Processing

While most functionality required in the NSS for GSM could be added via additional
software, the BSS had to be developed from scratch. This was mainly necessary as
earlier generation systems were based on analog transmission over the air interface and
thus did not have much in common with the GSM BSS.

1.7.1 Frequency Bands
In Europe, GSM was initially specified only for operation in the 900 MHz band between
890 and 915 MHz in the uplink direction and between 935 and 960 MHz in the downlink
direction, as shown in Figure 1.18. ‘Uplink’ refers to the transmission from the mobile
device to the network and ‘downlink’ to the transmission from the network to the
mobile device. The bandwidth of 25 MHz is split into 125 channels with a bandwidth of
200 kHz each.
It soon became apparent that the number of available channels was not sufficient to
cope with the growing demand in many European countries. Therefore, the regulating
bodies assigned an additional frequency range for GSM, which uses the frequency band
from 1710 to 1785 MHz for the uplink and from 1805 to 1880 for the downlink. Instead
of a total bandwidth of 25 MHz as in the 900 MHz range, the 1800 MHz band offers
75 MHz of bandwidth, which corresponds to 375 additional channels. The functionality

Uplink Downlink Figure 1.18 GSM uplink and downlink in
the 900 MHz frequency band.
890 MHz 915 MHz 935 MHz 960 MHz

125 Channels of 200 kHz each Frequency