Implications of beamforming
In the TD-LTE environment, many service providers and equipment vendors have been considering beamforming in deployments. By focusing the transmission energy in beams:
• Higher range can be reached;
• Less energy can be used for the same range;
• Interference can be mitigated;
• Network capacity can be increased;
• Overall improvements in system performance.
Beamforming algorithms are distinguished on the basis of the algorithm used to select the “beamformer.” With regards to TD-LTE, one must consider that “air” is reciprocal in nature; i.e. the downlink wireless path looks exactly like the wireless path in the uplink. There may also be multipath reflections, wireless channel variations, phase changes etc. as the signal traverses the wireless environment. In general, beamforming algorithms utilize the characteristics of the air interface such as channel variations and reciprocity.
Channel emulation provides a methodology to reproduce over-the-air conditions in the lab for testing and benchmarking different devices. Channel emulation can be used to validate improvements and performance gains due to beamforming algorithms. However, robust test of a beamforming device in the lab will require the use of a channel emulator that is bidirectional and has reciprocal and balanced paths in a cabled lab environment (figure 2).