Recently there has been a lot of buzz on a new LTE mode called TM9 and how it is related to User Specific (UE) 3D beamforming. 3D beamforming is the ability to form and direct antenna patterns in both vertical and horizontal directions to each UE or device. Let us first explore what TM9 is, and why people often mistaken it as a prerequisite for 3D beamforming, a prelude to Massive MIMO deployment.
What is TM9?
TM9 (Transmission Mode 9) is a standard transmission mode defined by 3GPP. This transmission mode can greatly improve the data transmission to mobile phones by creating beams specific to each UE. This is accomplished by high resolution channel sounding and feedback enabled by TM9 transmission mode. TM9-capable UEs report high resolution channel status to the network which is then used to form dedicated beams for data transmission to the targeted UE. Typical deployment with passive antennas can only form beams in the Azimuth plane called 2D-beamforming. Active antenna systems implemented as a planar array allows beams to be shaped in both Azimuth and Elevation plane. This is called 3D-beamforming. 3D-beamforming allows UEs to be better targeted thus improving the reliability of the link with higher Signal to Noise Ratio (SNR).
A Massive MIMO or more specifically Full Dimension MIMO (FD-MIMO) system increases capacity of a network by taking advantage of 3D-beamforming capability of large active antenna system along with Multi-User MIMO (MU-MIMO). Simultaneous transmission to multiple UEs reusing the same time- frequency resource is called MU-MIMO. TM9 scheme helps shape 3D-beams more precisely to avoid inter-beam interference for MU-MIMO. In theory, each mobile phone’s exclusive use of an independent beam should significantly increase the user throughput and cell capacity. Referenced in many industry articles, the increasing number of antennas and TM9 capable phones allow more UEs to have exclusive beams, which greatly improves the data throughput of cellular networks.
How does TM9 enable user specific beamforming?
As a new transmission mode specified in 3GPP Release 10, TM9 introduces a channel state information -specific reference signal (CSI-RS) for channel state information (CSI) measurement and feedback. This is a high-resolution channel sounding mechanism transmitting CSI-RS from many active antenna elements. TM9-capable UEs detect these reference signals and report higher resolution radio channel status to the network which is then used by the network to form UE specific beams. Additionally, the network capacity is also increased by MU-MIMO which schedules multiple users simultaneously using the same time-frequency resources by spatially multiplexing these UEs on their respective UE specific beams.
Now the real question is how many of today’s handsets are TM9 enabled and therefore be able to benefit from FD-MIMO.
Which handsets are TM9 capable?
For the handsets to be TM9 capable, their modems must be capable of doing all the TM9 specific functionality mentioned above. A few chipset vendors (Qualcomm, HiSilicon) announced support of TM9 in Q4 2017. Given that the chipset vendors are just coming out with the initial rollout of TM9, the proliferation of TM9 capable devices to the masses would most likely take at least 18 to 24 months. Furthermore, to enable those functionalities via software, it will take another 12-18 months to fully enjoy the benefit of TM9 enabled handsets.
Aggregating the Mobile Refresh Rate data from the top four US operators with the number of wireless subscribers and their projected growth, we see that less than 60% of the US mobile users will have a TM9 handset by the end of 2020.
Slow adoption of TM9 is a significant barrier to FD-MIMO
Because TM9 is a pre-requisite for FD-MIMO, operators today cannot widely deploy Massive MIMO without incurring significant investment by replacing subscribers with new handsets.
However, there is another elegant approach to improving capacity in current networks and devices with 3D-beamforming using active antennas.
Blue Danube’s hybrid Massive MIMO solution does not need TM9 handset’s CSI-RS information
Blue Danube’s hybrid Massive MIMO solutions delivers cell shaping with 3D beamforming that does not require CSI-RS based channel sounding and feedback. Blue Danube’s solution shapes beams (up to 8 distinct beams) to targeted hotspots and reduce intercell interference. In addition, the beams can also be dynamically updated as fast as a millisecond.
It is well known that most of the mobile traffic distribution is very predictable. It’s like driving a car to work every day and you know where the typical hotspots and congestions are. People leave home around the same time every day, and drop off kids, and go to work, creating common hotspots in specific areas in the city, at a common predictable time.
Blue Danube’s hybrid Massive MIMO solution can create distinct, configurable and programmable antenna beams to focus RF energy at these hotspots to maximize signals and minimize interference to adjacent cell sites resulting in the overall increase of network capacity or improving the quality of service to users. These benefits can be realized independently of the proliferation of newer TM9 handsets.
Operators can deploy Blue Danube’s hybrid Massive MIMO solution today and seamlessly software upgrade to fully realize the additional functionality of FD-MIMO once TM9 handsets are widely available.
4 In conjunction of integration with Base Band Unit (BBU) schedulers (i.e, BBU scheduler determines when and where to move the beams and instructs BeamCraft™ to change antenna pattern to the targeted area. BeamCraft can move antenna beams every millisecond – within a single LTE subframe time – after receiving request from BBU)