1G Systems and Networks

1G Systems and Networks
Table 2.4 summarizes the worldwide 1G analog cellular systems. All these systems use
two separate frequency bands for forward (from base station to mobile) and reverse
(from mobile to base) channels, a scheme referred to as frequency-division duplex
(FDD) transmission. The typical allocated overall band in each direction (e.g., for
AMPS, TACS, and NMT-900) was 25 MHz in each direction. The dominant frequencies
of operation for these systems were in the 800- and 900-MHz bands. In an ideal
situation, all countries would use the same cellular standard and the same frequency
bands, ensuring compatibility and interoperability among all mobile devices and base
stations. However, in practice, as shown in Table 2.4, a variety of frequencies and
standards were adopted in various countries and regions of the world. The reason for
the differences in frequencies of operation was that the frequency administration agencies
in the various countries had to abide by earlier frequency allocation rulings that
restricted the assignment choices. The reason for adopting different standards was that
cellular providers then assumed that services would be used solely within one country
and did not envision an eventual universal service. The channel spacing or bandwidth
allocated to each user was either 30 or 25 kHz or a fraction of either. The 25-kHz channel
spacing was used previously for mobile satellite services, but the 30-kHz channel
spacing was a new allocation for cellular telephone application.
All of the 1G cellular systems used analog frequency modulation (FM), for which
the transmission power requirement depends on the transmission bandwidth. On the
other hand, power is also related to signal coverage and to the size of mobile radios. TABLE 2.4 Worldwide First-Generation Cellular Systems
Standard
Forward
Band (MHz)
Reverse
Band (MHz)
Channel
Spacing
(kHz) Region Comments
AMPS 824–849 869–894 30 United States Also in
Australia, SE
Asia, Africa
TACS 890–915 935–960 25 EC Later, bands
were
allocated to
GSM
ETACS 872–905 917–950 25 UK
NMT 450 453–457.5 463–467.5 25 EC
NMT 900 890–915 935–960 12.5 EC Frequency
overlapping,
also in
Africa and
SE Asia
C-450 450–455.74 460–465.74 10 Germany,
Portugal
RTMS 450–455 460–465 25 Italy
Radiocom 192.5–199.5 200.5–207.5 12.5 France
2000 215.5–233.5 207.5–215.5
165.2–168.4 169.8–173
414.8–418 424.8–428
NTT 925–940 870–885 25/6.25 Japan First band is
nationwide,
others
regional
915–918.5 860–863.5 6.25
922–925 867–870 6.25
JTACS/NT
ACS
915–925 860–870 25/12.5 Japan All are regional
898–901 843–846 25/12.5
918.5–922 863.5–867 12.5
Therefore, one can compensate for the reduction in transmission bandwidth per user
by reducing the size of a cell in a cellular network. Reduction in cell size increases the
number of cells and the cost of installation of the infrastructure. By way of example,
the AMPS system in North America uses 30-kHz channel spacing, whereas C-450 in
Germany uses 10-kHz spacing, one-third the AMPS channel spacing. Therefore, one
expects a denser infrastructure for deployment of C-450. As another example, Japan
has several systems using full- and split-band operation, with 25 and 12.5 kHz being
used in different systems. The cell sizes for split-band operation are smaller than for
full-band operation.
A technique called band splitting can be utilized to support increased traffic capacity
in a service network without having to increase the number of base stations.
However, this technique incurs the need for increased investment in network infrastructure In the wireless industry, 1G often refers only to analog cellular technology because
it is the only system implemented based on popular standards such as AMPS or NMT.
However, we can generalize the designation 1G systems to include other types of
wireless services and products. The analog cordless telephone, which appeared in the
market in the 1980s, can be considered as a 1G cordless telephone product. Paging
services, which were deployed at around the same time as analog cellular systems
and cordless telephones, can be referred to as 1G mobile data services providing oneway
transmission of short data messages. In the early 1980s, before release of the
ISM bands and the start of the WLAN industry, a few small companies in Canada and
the United States developed low-speed connectionless wireless local area networks
using voiceband modem chip sets and commercially available walkie-talkies. These
products operated at the speed of voiceband modems (<9600 bits/s) but used the
medium access control techniques then found in data-oriented LANs. Although because
of their low data rates, they do not comply with the IEEE 802 community definition
for LANs, one may refer to them as 1G wireless LAN products.