4x4 Downlink MIMO and 256QAM

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.

The 4G and 5G HetNet

Remember all the talk about the HetNet, the heterogeneous network? I show it below is the HetNet using all licensed components, However, for the HetNet you can have unlicensed connections like Wi-Fi and LTE-U. It is the combination of many different types of BTS, from macro to mini to small cell to a hotspot.

The way that LTE is going to migrate into 5G is by using more and more different types of RF units and technologies. Many RF bands will be working together to give the end user a great quality of experience. The end user will not know that all of this is going on if it all works well. They will notice problems. The Quality of Service, QOS, will matter to some customer depending on what application they are running.

When the customer starts seeing problems, it is a Quality of Experience, QOE, issue. You want every user to have a great QOE because they will switch service if they don’t get it. However, it does matter what they are doing with their device.

Most users are very forgiving with data problems. They expect to have some downloading issues.

I bring this up here because switching of services will greatly affect the user experience. In an unlicensed spectrum, there is the potential for interference which will cause problems with the QOE because it won’t have a clear signal. For example, if you use your Wi-Fi at home, chances are good it works well in your house, right? How about when you use it in a public area where there are many hotspots? Then you see a serious degradation in service. They interfere with each other while the UE equipment will jump across hotspots.

So, the HetNet will be a bigger part of the future networks, but the carriers will need to smart about the handoff. They shouldn’t hand it off outside of the licensed network unless they have no choice. Today, there is a problem with overloading, so the carrier welcomes the unlicensed network. They want to see LTE-U because of the format and the improved efficiencies.

Will 5G replace LTE?

No, LTE will be the foundation for the 5G network. LTE will get new terms, like 
LTE-Advanced, just like 4G will become 4.5G and 4.9G before 5G is released. You 
will see great increases in speed and LTE will become more and more advanced. It 
is quite impressive what the OEMs are doing. 

The HetNet will be an applicable term. Networks will handoff between so many 
different types of systems. However, I do believe that the 5G systems may be a type 
of LTE to hand off to each other properly. Remember that there will be multiple 
systems running simultaneously. They would need to have a seamless handoff for 
the best user experience. 

I will use an example. The carriers have truly adopted wi-fi because of the 
complexity of the shift from LTE to Wi-Fi, that is why the carriers are so excited 
about LTE-U. The see a viable way to make the best use of unlicensed spectrum. 
The Wi-Fi carriers don’t like it because they invested a lot of money into their 
license free Wi-Fi networks. 

The 5G systems will need to have a way to such seamless handoffs without 
dropping a call or a session.