Mobility testing for beamforming base stations.(WIRELESS TEST)

The continuing goal in today's data-centric wireless technology is to improve data rates and fidelity in the most cost-efficient way. Recent advances in antenna technology have introduced wide-scale deployment of antenna arrays used in multiple-in, multiple-out (MIMO) configurations.

Next-generation wireless technologies such as WiMAX. Long-Term Evolution (LTE) and Ultra Mobile Broadband (UMB) all make use of multiple-antenna-array technologies. Now they also can utilize beamforming, a more advanced technique.

Beamforming is a signal-processing technique that requires estimating channel information and adaptively shaping beams to enhance some signals and suppress others. To implement beamforming, three basic techniques are used: adaptive beam steering, maximum ratio transmission (MRT), and Eigen beamforming (EBF).

Adaptive beam steering can be implemented when the mobile device has a single antenna; MRT and EBT are MIMO beamforming techniques. All three methods can dynamically adjust the relative amplitude and phase, the antenna weights, on each element of the base-station antenna array. Table 1 compares and contrasts the three approaches.

 
Table 1. Beamforming Techniques 
 
Beamforming Technique   Channel Characteristics       Notes 
 
Adaptive Beam Steering  LOS or small angular     High gain for single 
                        spread, very high        user but ineffective 
                        correlation              in environments that 
                                                 cause high 
                                                 angular spread 
 
Maximum Ratio           High SNR, low velocity,  Maximum SNR but 
Transmission            large angular spread,    requires frequent 
                        high correlation         channel measurements 
                                                 and is 
                                                 computationally 
                                                 intensive 
 
Eigen Beamforming       Low SNR or high          Robust in high-speed 
                        velocity,                mobility but offers 
                        high correlation         less beamforming 
                                                 gain than MRT 

The result is that lobes of constructive interference or beams can be created and steered on the transmitted link. On the received link, beams can be created and aimed toward desired users while nulls can be steered toward sources of unwanted interference. Figure 1 shows the basic concept of a beamforming system.

[FIGURE 1 OMITTED]

Adaptive Beam Steering

In single-user-antenna beamforming, the mobile device periodically sends a channel sounding signal. Each base-station antenna element receives this signal at a slightly different phase offset and amplitude so that algorithms can estimate direction-of-arrival (DoA) for each user based on a unique spatial signature. …

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