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2-TX<br />
antennas<br />
Figure 8.5. Uplink Dual Antenna beamforming and MIMO.<br />
With uplink 2X2 (and 2X4) MIMO the uplink peak rate reaches 23 Mbps per 5 MHz carrier with 16 QAM<br />
modulation. As an additional evolutionary step, the introduction of 64 QAM modulation can be considered,<br />
which would bring the uplink peak rate with MIMO to 35 Mbps per 5 MHz carrier or to 69 Mbps if it were to<br />
be supported in combination with Dual Carrier HSUPA configuration.<br />
8.3.3 DOWNLINK MULTIPOINT TRANSMISSION<br />
The downlink Multipoint Transmission concept is improving the achievable HSDPA cell edge data rates<br />
by both reducing the inter-cell interference and increasing the energy of the desired signal. By<br />
transmitting identical data from two cells on the same frequency to the cell edge UE, the cell edge signalto-noise<br />
ratio can be increased. This operation is analogous to the soft handover used in downlink DCH<br />
channels since Rel-99. Alternatively if the two cells transmit independent data to the UE, the peak and<br />
average data rate can be increased. This gain stems from spatial multiplexing and it would be similar to<br />
the Dual-Cell HSDPA operation standardized in Rel-8.<br />
Current HSDPA<br />
HSDPA<br />
Multipoint<br />
Transmission<br />
1 or 2<br />
streams<br />
Interference<br />
2 or 4 RX<br />
antennas<br />
Signal<br />
High inter-cell interference<br />
Signal<br />
Signal<br />
Improved cell edge data rates +50%<br />
Figure 8.6. Downlink Multipoint Transmission.<br />
www.4gamericas.org February 2011 Page 87
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