Qualcomm HSPA+ Uplink Beamforming Demonstration
In this demonstration, we present the closed-loop (CL) beamforming (BF) scheme and its performance improvement over non-beamforming in the HSPA Uplink (UL). The CL BF scheme employs two transmit antennas at the UE to improve the uplink transmission performance. The Node B dynamically selects the UL transmit BF vector which has equal weights on both TX antennas and introduces a phase offset of 0, 90, 180, or 270 degrees. The BF vector is chosen to maximize the UL received SNR. The Node B then sends the selected BF vector to the UE. The UE applies the BF vector at its transmitter. We have two UEs – one non-beamforming UE and one CL BF UE – in active calls with a Node B sharing the same cabled RF channel. Both UEs run User Datagram Protocol (UDP) data in the UL. We switch between two demo modes to show different types of benefits:
- TX power gain mode: both UE’s transmit at the same data rate (e.g., ~550kbps). Given the time-varying RF channel used, the TX power gain is between 2-2.5 dB. TX power gain can be translated into coverage gain. For example, 2.5 dB TX power gain can be translated into a coverage extension of about 17% in radius or 37% in area.
- Throughput gain mode: both UE’s transmit at the same power where the CL BF UE transmits at higher data rate (e.g., 900kbps vs. 550kbps).
- Smooth switching between these 2 demo modes can be done automatically or manually.
In the animation, we have a car driving back-and-forth through 5 regions (chosen from 3 different region types below)
- Region type 1: Rural area where the UE has complete line-of-sight channel to the Node B, the driving speed is 30km/h
- Region type 2: Suburban area where the UE may have some reflection/diffraction in the propagation environment, the driving speed
- Region type 3: Urban area where the UE often have significant reflection/scattering in the propagation, the driving speed is 3km/h.
The non-beamforming UE and the CL BF UE are co-located on the car. An important aspect of the demonstration is to illustrate the beamforming effect where the CL BF UE can steer the main lobe of the radiation pattern of the two TX antennas towards the Node B. As the car passes through different regions, the CL BF UE decodes the BF vector from DL and applies at the two transmit antennas which is intended to maximize the UL SINR. This results in the transmit antenna pattern of the CL BF UE consistently pointing its main lobe towards the serving Node B. This enables the UE to focus its TX power in the desired direction and reduce inteference caused to the neighbor cells.
The antenna beam pattern is computed real-time based on the BF vector applied at the UE side. As a reference, the onmi antenna pattern of the non-beamforming UE is shown as well.
The CL BF UE is a prototype UE consisting of 2 SURFs (each containing one MSM7201A and the associated RF transmission chain) plus new functional blocks to support the CL BF feature.
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