Early TD-LTE deployments plan to combine MIMO and beamforming, offering the advantages of higher data rates as well as capacity and quality improvement. A typical MIMO beamforming configuration can be thought of as a 2x2 MIMO system, except that each of the two transmitted “layers” is actually a steered beam formed by four transmitting antenna elements. This has led to growth in the study of 8 × n systems, where each base station is equipped with eight antenna elements, as a cost-efficient, spectrally-efficient alternative to the addition of cell sites or additional carriers.
All of this creates an incredibly complex RF environment that must be tested before deployment, and the stakes are high. It is no secret that the world’s largest network operator, China Mobile, is currently deploying TD-LTE trial systems in six of China’s most populated cities. It’s also a safe bet that most if not all of the spectrum awarded in 2010’s Indian BWA auction will be used for TD-LTE as well, since that auction awarded single (“unpaired”) 20-MHz wide bands. It is true that this spectrum could also be used for WiMAX deployments, but Indian operators have made their intentions clear… in one case canceling a planned WiMAX deployment across two major cities. While it will be years before the majority of these Chinese and Indian subscribers use LTE service, it is worth noting that the operators involved represent billions (literally) of today’s mobile phone users.
There’s no question that the stakes are high, and there’s little doubt that combining antenna techniques creates an order-of-magnitude increase in the complexity of the radio link. It is difficult enough to optimize MIMO or beamforming when one of those techniques is deployed in isolation, but balancing the requirements of both adds new depth to both the design and testing processes.
Equipment being used to emulate the radio channel