A recent 4G throughput test campaign from PC World in the US, produced the graph above. The whole report can be found here but the interesting point to note is that essentially it is a comparisson between the efficiency of LTE Vs HSPA+ using the same bandwidth. Allow me to explain..
Both AT&T and Verizon are currently operating LTE networks using 10MHz of spectrum in the 700MHz band. T-Mobile on the other hand is operating an HSPA+ network using the Dual Cell/Carrier feature which it labels 4G (or fauxG if you are a purist). As the Dual Cell/Carrier feature essentially aggregates two 5MHz carriers the total amount of spectrum is the same (i.e. 10MHz).
Looking at the results it is clear that LTE performs better than HSPA+ but the difference is not that big. Both technologies are using 10MHz of spectrum and capable of 64QAM. LTE has the advantage of MIMO which in certain radio conditions can double the data rate.
The difference between T-Mobile and AT&T is 3.6Mbps and the difference between T-Mobile and Verizon is 1.8Mbps.
But what about the difference between the theoretical peak and the actual average rate? LTE @ 10MHz should deliver 73Mbps. In the tests the best network delivered 9.12Mbps. That is 12.5% of the max.
HSPA+ Dual Cell/Carrier should deliver a theoretical peak of 42Mbps. In the tests T-Mobile achieved 5.53Mbps. That is 13.2% of the max, which is a little bit better than LTE. We also need to remember that T-Mobile's HSPA+ network is a mature network with a lot of existing traffic. As LTE devices become more popular we can expect the LTE networks to slow down due to resource sharing.
One last point to mention, is that it is possible to combine Dual Cell/Carrier with MIMO. Although T-Mobile doesn't offer this capability it would have been interesting to see how close the results would have been. Maybe even HSPA+ would out-perform LTE?!