User's Manual Chapter 13

Chapter 7: Operational Description
AT&T Wireless Services
7-95
FCC Type Acceptance Application
10991 Rev. 1.0 7/6/99
Figure 7.9— OFDM Time-Domain Waveform Generation
At the receiver, the incoming analog signal is converted to digital
samples, which are then transferred from the time-domain to the
frequency-domain using a Fast Fourier Transform (FFT). The resulting
OFDM tones are demodulated and their data passed on to the
appropriate physical layer entities.
7.2.2.1 PWAN Implementation of OFDM
The communications link between the Base and its RU population
takes place in a Frequency-Division Duplex (FDD) RF environment,
with 80 MHz of spacing between the Base downlink and the RU uplink
transmissions. The PWAN system is designed to operate in the United
States wideband PCS spectrum defined in Part 24 of the Federal
Communications Commission (FCC) regulations. Cells in the PWAN
are divided into four sectors, with each sector utilizing 1 MHz of
downlink and 1 MHz of uplink spectrum. The individual 1 MHz
segments associated with each sector are known as subbands. The
allocation of these subbands within a 5 MHz PCS frequency block is
depicted in Figure 7.10— below:
burst period
TB
1
TB
2
Σ
TB
n
OFDM Packet OFDM Packet OFDM Packet* * * *