Digital Cordless Telephone Interface Summary
Frequency band (MHz)
1850 1910/1930 1990
Carrier spacing (kHz)
Number of carriers
16 pairs/10 MHz
Channel bit rate (kbps)
transmit power (mW)
Peak handset transmit
Frame duration (msec)
General allocation to PCS; licensees may use PACS.
Source: Ref. 18, Table 2.
is 10 mW (80-mW peak power) and no greater than 500 mW (4-W peak power) for the
cell site. The PHS frame duration is 5 msec. Its voice coding technique is 32-kbps ADPCM
In the United States, digital PCS was based on the wireless access communication
system (WACS), which has been modified to an industry standard called PACS (personal
access communications services). It is intended for the licensed portion of the new 2-
GHz spectrum. Its modulation is
/4 QPSK with coherent detection. Base stations are
envisioned as shoebox-size enclosures mounted on telephone poles, separated by some
600 m. WACS/PACS has an air interface similar to other digital cordless interfaces, except
it uses frequency division duplex (FDD) rather than time division duplex (TDD) and more
effort has gone into optimizing frequency reuse and the link budget. It has two-branch
polarization diversity at both the handset and base station with feedback. This gives it an
advantage approaching four-branch receiver diversity. The PACS version has eight time
slots and a corresponding reduction in channel bit rate and a slight increase in frame
duration over its predecessor, WACS. Table 18.1 summarizes the characteristics of these
several types of digital cordless telephones and their interfaces.
Wireless LANs (WLANs), much like their wired counterparts, operate in excess of
1 Mbps. Signal coverage runs from 50 ft to less than 1000 ft. The transmission medium
can be radiated light (around 800 nm to 900 nm) or radio frequency, unlicensed. Several
of these latter systems use spread spectrum with transmitter outputs of 1 W or less.
WLANs using radiated light do not require FCC licensing, a distinct advantage. They
are immune to RF interference but are limited in range by office open spaces because
their light signals cannot penetrate walls. Shadowing can also be a problem.
One type of radiated light WLAN uses a directed light beam. These are best suited for
fixed terminal installations because the transmitter beams and receivers must be carefully
aligned. The advantages for directed beam systems is improved S/N and fewer problems
with multipath. One such system is fully compliant with IEEE 802.5 token ring operation
offering 4- and 16-Mbps transmission rates.