1. How can we double the date rate of 802.11a
**Double the bandwidth**: 20MHz ---> 40MHz
**Double the number of carriers and double the data rate**:
64 ---> 128
**Use higher-order modulation**:
from 64 QAM(6 bits/carrier) to 4096( 12bits/carrier)
**MIMO** ( multiple antennas, transmit diversity & receive diversity)
**Channel bonding**:
simple concatenate two channels
**Combination of the above**
2. Four cadidates extending IEEE 802.11a
A: double clock rate
clock rate: 20MHz ---> 40MHz
instead of 250,000 OFDM symbols/s, send 500,000symbols/s
B: double sub-carrier numbers of and double clock rate
number of sub-carriers is twice as many as that of IEEE 802.11a
e.g. 52 subcarriers -------> 104 subcarriers
still 250,000symbols/s
C: 64QAM ----> 4096QAM
increasing the number of bits in M-ary QAM on each sub-carriers
e.g. 64QAM ----> 64QAM
D: OFDM/SDM (multi-carrier MIMO) system
using multiple transmit and receive antennas
each antenna transmit different data to increase transmit data rate
