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TD-LTE 8-antenna dual-stream beamforming technology

With a view to enabling smooth evolution from TD-SCDMA to TD-LTE and to accomplishing a low-cost and rapid network upgrade, Datang Mobile worked with TD-LTE 8-antenna dual-stream beamforming technology for TD-LTE outdoor macro cell coverage.

Solution

8-antenna dual-stream beamforming technology, which can be used where there are sufficient signal scatterers, efficiently brings together smart antenna beamforming technology (i.e. single-stream beamforming technology) and MIMO spatial multiplexing technology. In a TD-LTE system, it uses the symmetry of TDD channels to simultaneously transmit two beamforming data streams for spatial multiplexing. In addition, it can retain the features of single-stream beamforming technology in order to expand coverage, increase cell capacity and minimize interference so as to improve the reliability of cell edge users as well as the throughput of cell center users.

Depending on user scheduling, this technology can be categorized into single-user and multi-user dual-stream beamforming technology.

In single-user dual-stream beamforming technology, the base station measures the upstream channels to glean their status information. It then calculates two beamforming vectors according to this upstream channel information, and uses the vectors for downlink beamforming of the two data streams to be transmitted. In single-user dual-stream beamforming technology, a single user can simultaneously transmit two data streams, and thereby benefit from beamforming gains and spatial multiplexing gains at the same time. In this way it can achieve a higher data rate than single-stream beamforming technology which increases the capacity of the system.

In multi-user dual-stream beamforming technology, the base station matches multiple users according to upstream channel information or UE feedback. It then, according to certain criteria, generates beamforming vectors, and uses the vectors for the beamforming of each UE and each stream. Multi-user dual-stream beamforming technology uses the smart antenna beam direction to enable multi-user spatial division multiple access (SDMA).

Solution performance analysis and validation

1. The system capacity is significantly increased in high-quality TD-LTE networks.

Dual-stream beamforming technology can effectively increase the TD-LTE system throughput. Compared with 2X2 MIMO TD-LTE antenna configuration, 8X2 dual-stream beamforming technology has much greater sector and edge throughput. According to the assessment of ITU, compared with 2-antenna MIMO technology, 8-antenna dual-stream beamforming technology can deliver both sector and edge throughput of 80% and 130% higher respectively.

TD-LTE theoretical analysis demonstrates that TD-LTE 2-antenna coverage is limited to the upstream traffic channel. A simulation evaluation concluded that an upstream traffic channel edge rate of up to 64Kbps is a precondition. The radius of TD-LTE 8-antenna cell coverage extends over an area about double that of TD-LTE 2-antenna cell coverage. Compared with TD-LTE 2-antenna technology, 8-antenna technology requires significantly fewer TD-LTE stations and lower TD-LTE CAPEX.

2. The cell radius is increased in order to lower CAPEX.

The radius of TD-LTE 8-antenna cell coverage is about the same as that of TD-SCDMA. Therefore, 8-antenna TD-LTE technology can cover the same area and share the same site as TD-SCDMA technology. During the smooth evolution from TD-SCDMA to TD-LTE, the existing sites, antenna feed systems and other resources can be reused to further cut the TD-LTE CAPEX.

The TD-SCDMA network construction experience has shown that the actual radius of single TD-LTE station coverage may be only 500m or even less.A comparison of the coverage of TD-LTE 2-antenna and 8-antenna technologies with TD-SCDMA technology.

The simulation evaluation demonstrated that TD-LTE 8-antenna technology can effectively solve the coverage limit problem by expanding coverage while increasing the edge rate.

The above figure shows the coverage of TD-LTE 2-antenna and 8-antenna technologies. When the coverage radius is 500m, the upstream edge rate of TD-LTE 8-antenna and 2-antenna technologies is 500Kbps and 64Kbps respectively. This shows that while having the same cell coverage as TD-SCDMA, the TD-LTE 8-antenna technology can significantly increase the edge rate, while the edge rate enabled by the 2-antenna technology is almost the same as that of TD-SCDMA. To provide an edge rate of 500Kbps, TD-LTE 2-antenna technology covers only a 280m radius. Therefore, it can't cover the same area or share the same site as TD-SCDMA technology.

According to the analysis, TD-LTE 8-antenna technology can significantly increase coverage and provide a high TD-LTE data rate while extending over the same area as that enabled by TD-SCDMA technology.

3. Performance validation

In December 2009 at the Datang Telecom head office in Beijing, Datang Mobile convened a TD-LTE new technology press conference themed "Innovation Empowers Dreams", launching the dual-stream beamforming technology, and demonstrating the features of the TD-LTE network and the performance of 8-antenna dual-stream beamforming technology.

The TD-LTE network being demonstrated covered the area between Xueyuan Bridge and Xuezhi Bridge on Xueyuan Road in Haidian District, Beijing. The demonstration vehicle showed that the throughput of TD-LTE 8-antenna dual-stream beamforming technology was higher than that of 2-antenna MIMO technology in a dynamic channel environment.

During the demonstration, the TD-LTE 8-antenna dual-stream beamforming technology attained better coverage than the 2-antenna technology. At both ends of the demonstration road section, i.e. the edge of the 2-antenna system coverage, the throughput of the 2-antenna technology diminished while the throughput of the 8-antenna technology remained stable. When the demonstration vehicle went under an overpass at the edge of the demonstration road section, the signal reception was affected due to the obstruction of the overpass. The throughput of the 2-antenna system dropped significantly. The throughput of the 8-antenna system was also affected, but it dropped only slightly and then remained stable.

A statistical analysis of the throughput during the demonstration showed that the spectral efficiency of 8-antenna dual-stream beamforming technology is 40%-50% higher than that of 2-antenna MIMO technology.

Typical scenario

Primary TD-LTE network technology, which is used for macro cell coverage in outdoor environments.

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