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Local Multipoint Distribution System (LMDS)
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PDF of this tutorial4. Modulation
Modulation methods for broadband wireless LMDS systems are generally separated into phase shift keying (PSK) and amplitude modulation (AM) approaches. The modulation options for TDMA and FDMA access methods are almost the same.The TDMA link modulation methods typically do not include the 64–quadrature amplitude modulation (QAM), although this might become available in the future. The FDMA access modulation methods are listed in Table 2 and are rated on an estimated scale as to the amount of bandwidth they require for a 2–Mbps constant bit rate (CBR) connection (without accounting for overhead due to ATM and FEC). Values are approximate, as there are issues involving channel filter mask roll-off factors, which can be important when providing the relationship between microwave bandwidth and data rates.
| Name | Modulation Method | MHz for 2 Mbps CBR Connection |
| BPSK | binary phase shift keying | 2.8 MHz |
| DQPSK | differential QPSK | 1.4 MHz |
| QPSK | quaternary phase shift keying | 1.4 MHz |
| 8PSK | octal phase shift keying | 0.8 MHz |
| 4–QAM | quadrature amplitude modulation, 4 states | 1.4 MHz |
| 16–QAM | quadrature amplitude modulation, 16 states | 0.6 MHz |
| 64–QAM | quadrature amplitude modulation, 64 states | 0.4 MHz |
Table 2. FDMA Access Modulation Methods
