Specifications

Interface Protocols
Operating Characteristics
3-6 68P81095E55-E August 08, 2000
Carrier Characteristics
The iDEN system does not use the entire 25 Mhz range allocated for each carrier.
The iDEN system sub-divides the carrier into four sidebands. This helps reduce
interference to the data. Data is transmitted on each of the four sidebands. Using
four sidebands allows more data to be transmitted because it increases the data rate.
The iDEN RF signal consists of four independent side bands. The center frequencies
of these side bands are 4.5 KHz apart from each other, and they are spaced
symmetrically about a suppressed RF carrier frequency (Figure 3-2). Each sideband
is a logical 16 kbps data carrier. The resulting signal produces a
64 kilo-bit-per-second (64 kps) gross-radio-channel-bit-rate.
Figure 3-2 Logical RF Channel Sidebands
Carrier Modulation
The method used to modulate digital voice and data on the RF carrier is Motorola 16-
Quadrature Amplitude Modulation (M16-QAM). This implementation of the data
transfer standard uses phase and amplitude modulation to create 16 offset points
around the carrier waveform. Each point represents a bit pattern (Figure 3-3).
Figure 3-3 Quadrature Amplitude Modulation on 4 carrier sidebands
(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