Specifications

Radio Link Communications Model
Radio Frequency Channel Types
B-2 68P81095E55-E August 08, 2000
The RF signal consists of four independent side bands. The center frequencies of
these side bands are 4.5 KHz apart from each other (Figure B-2), and they are spaced
symmetrically about a suppressed RF carrier frequency.
Figure B-2 Logical RF Channel Sidebands
The iDEN system uses a combination of amplitude and phase modulation to identify
16 points in the radiated energy field. The Motorola 16-Quadrature Amplitude
Modulation (M16-QAM) method used is a standard that:
• reduces dependency on received signal strength
• increases the number of data bits transmitted in a given time
A digitally encoded signal is applied to each sideband sub-carriers. When the signal
is synchronously demodulated, a 16-point data symbol constellation is produced.
Each point in the constellation represents a 4 data-bits-per-symbol. These points
represent logical states (bit patterns) as shown in Figure B-3.
Figure B-3 Quadrature Amplitude Modulation Logic Points
The result is a digital signal that has a 64 kilo-bit-per-second (64 kps) gross radio
channel bit rate. This effectively forms a 64 kbs baseband signal that is the bitstream.
(4x4.5Mhz) + 0.6 ramp (actual carrier)
4.5KHz 4.5KHz4.5KHz
25KHz (FCC carrier size)
3.2Mhz3.2Mhz
Guard Bands and Doppler shift
Frequency Center
16 kilo-bit-per-second
16 kilo-bit-per-second
16 kilo-bit-per-second
16 kilo-bit-per-second
64 kilo-bit-per-second - Total
T. N. French
+
1000 1100 0100 0000
1001
1011
1010
1101
1111
1110
0101
0111
0110
0011
0010
0001
Phase and Amplitude
modulation of each signal
produces 16 possible offset
points
Each offset point represents a
4-bit pattern
Frequency
Center
+2
a
, -2
t
offset
-2
a
, -2
t
offset
+2
a
, +2
t
offset
-2
a
, +2
t
offset
Logical point in
time on carrier
(4x4.5Mhz) + 0.6 ramp (actual carrier)
4.5KHz 4.5KHz 4.5KHz4.5KHz
25KHz (FCC carrier size)
3.2Mhz3.2Mhz
Guard Bands and Doppler shift
One pattern every 1/4000th of a second is 16kbs (4X4)
One pattern each sideband is 64kbs (4X16)
T. N. French