User's Manual Chapter 13

Chapter 7: Operational Description
AT&T Wireless Services
7-97
FCC Type Acceptance Application
10991 Rev. 1.0 7/6/99
Dividing the 1 MHz subband into 16 FDMA slots is an effective means
of providing multiple access in the frequency domain. However, the
capacity of the PWAN would be insufficient if this were the only
multiple access method utilized. Consequently, Time Division Multiple
Access (TDMA) is utilized as well, where each of the 16 FDMA slots
are divided into eight TDMA slots (refer to Figure 7.12—).
Figure 7.12—PWAN TDMA Framing Structure
The airlink resources derived from this process are most easily
visualized in terms of a matrix, with 16 FDMA slots along the x-axis
and eight TDMA slots along the y-axis, resulting in a total of 128
Frequency-Time Resources (FTRs) for allocation in each airlink
subband.
In an OFDM system, the modulation format for any given tone is
entirely independent of that used by its neighbor(s). The PWAN airlink
takes advantage of this and will utilize either Quadrature Phase Shift
Keying (QPSK) or 16 Quadrature Amplitude Modulation (16-QAM)
within individual FTRs on an as-needed basis.
The basic PWAN parameter values are summarized in Table 7.2—.
Table 7.2— Basic PWAN OFDM Parameters
PWAN OFDM Parameter Value
Burst Period 340-
µ
s
Guard Time 35-
µ
s
TDMA Time Slot Period 375-
µ
s
TDMA Frame Period 3-ms (Eight 375-
µ
s
TDMA time slots)
TDMA Frame = 8 TDMA Slots
3 ms
0 1 72 63 54
TDMA Slot
375
µ
s