Increasing bandwidth
with carrier aggregation is the first and most robust technique to achieve
higher 4G data rates. The next option to achieve higher 4G data rates in the DL
is to upgrade to 256QAM DL Modulation. Then, increase the number of spatial
streams overlaying 4X4 MIMO on one or more of the CCs that have been
aggregated.
4x4 MIMO effectively reuses the same 20MHz CC four times
over to transmit more data. Thus, it is a more efficient use of spectrum. Some
important considerations in 4x4 MIMO deployments include the following
- · Only applies in the DL.
- · Data rates increase by a factor of two for each CC it is applied compared to 2X2.
- · Requires four unique data streams transmitted from a minimum of four unique antennas at the base station.
- · Needs four corresponding unique receiver chains in the mobile device.
·
Effectiveness is gated by the ability to
de-correlate the four separate antennas in the handset — if the antennas can
talkbto each other (interference), then the benefit drops.
All this means more receiver components — such as filters,
switches, low noise amplifiers (LNAs), and antenna control devices — are needed
in the mobile front end. Because DL is onlyvassociated to the receiver side of
the RF chain, transmit power amplifiers are not affected. 256QAM DL modulation
has a 1.33x multiplier on the data rate of each CC. It requires no change to
the RF front end in the mobile device.
The 4G “baby” is now approaching maturity. For example, an
FDD network and mobile device can achieve a theoretical peak 4G DL data rate of
1Gbps using:
- · 3CC aggregating 3 x 20 MHz to create a 60 MHz “fat pipe”and achieve 450 Mbps
- · 4x4 DL MIMO applied to just two out of the three CCs, to achieve 750 Mbps
- · 256QAM DL modulation on all three CCs to achieve 1Gbps
- · A modem that supports ten spatial layers
The path to achieve even higher 4G DL peak data rates (in
the 1.6Gbps range) is gated by the availability of transceiver/modem chipsets
that support additional spatial layers (2017 chipsets can typically support up
to 12 spatial layers), and the ability of hand-sets to accommodate the RF front
end for more than two bands with four
receivers.
