FDD MIMO test data"TDD (Time Division) Massive MIMO represents the only effective implementation of Massive MIMO at the frequency bands under consideration."!? So says Professor Erik Larssen, a leading researcher at Linkoping University in Sweden. Larsson blogged the controversial paper on April 4, the day after it was published at https://arxiv.org/pdf/1704.00623.pdf. The blog and the abstract of the paper is below. 

On the other hand, China Telecom, China Unicom, Huawei, and ZTE have announced successful trials of FDD (Frequency Division) Massive MIMO. A joint press release by China Telecom and ZTE asserts the opposite: "The FDD Massive MIMO solution is predictable to be deployed in China Telecom in 2017." Obviously, I'm not qualified to judge engineers of that quality when they disagree. I'll do my best to explain the issues and direct you back to the principals. 

The primary issue, as I understand it, is whether FDD overhead is inevitably too high for FDD to be practical. With line of sight (LOS), the two techniques appear to have similar results. Without decent Line of Sight. the new paper reports a significant difference.  

Massive MIMO requires constantly updated Customer State Information (CSI.) The transmitter needs constantly updated receiver location and capability to steer the many antennas. Larssen and colleagues have a theoretical model and now some test data that suggests FDD in many locations has too much overhead to be practical. 

In the new paper, Massive MIMO Performance—TDD Versus FDD: What Do Measurements Say?, five academics report tests of TDD and four examples of FDD. The lead is Jose Flordelis, a student at Lund University. Three other authors are at Lund, Fredrik Rusek, Fredrik Tufvesson, and Ove Edfors, as well as Larsson of Linkoping. The two Swedish Universities, 400 kilometers apart, are important EU wireless centers.

In a previous paper, Larsson joined Emil Bjornson and Tom Marzetta to offer a theoretical model that came to a similar conclusion. One of their examples show TDD requires about 12.5% for CSI and FDD would have overhead four times as high,

The Chinese have upended many assumptions over the last ten years so I'll wait for more data.

Here are the description of the testing, the abstract, and the conclusion of the paper. 

 Measurements

The measurements were acquired at a carrier frequency of 2.6 GHz, and a bandwidth of 50 MHz. A brief description of the two campaigns and the scenarios follows: • Campaign A. The UEs were located at the parking place outside the E-building of LTH, with the ULA mounted on top of the E-building, three floors above ground level. We consider five UE sites, denoted MS 1, . . . , MS 5. Sites MS 1 to MS 4 have mainly LOS propagation conditions to the BS, while site MS 5 experiences NLOS. At each site, several UE locations are measured. In this work, we consider three propagation scenarios, which are summarized in Table I as scenarios 1, 2, and 3. For further details on Campaign A, the reader is referred to [5]. • Campaign B. The UEs were located in a courtyard of the E-building. The ULA was on a roof two floors above ground, while the 16 UEs were spread out at various positions in the courtyard. In this environment, the UEs experience LOS propagation conditions to the array, along with a number of strong scattered components caused by interactions with the walls, outdoor furniture, and vegetation. (The Ricean K-factor [37], [38] is low compared to scenarios 1 and 3.) In this work, we consider three propagation scenarios, which are summarized in Table I as scenarios 4, 5, and 6. For further details on Campaign B, the reader is referred to [39].

 

HOW MUCH PERFORMANCE IS LOST BY FDD OPERATION?

There has been a long-standing debate on the relative performance between reciprocity-based (TDD) Massive MIMO and that of FDD solutions based on grid-of-beams, or hybrid beamforming architectures. The matter was, for example, the subject of a heated debate in the 2015 Globecom industry panel “Massive MIMO vs FD-MIMO: Defining the next generation of MIMO in 5G” where on the one hand, the commercial arguments for grid-of-beams solutions were clear, but on the other hand, their real potential for high-performance spatial multiplexing was strongly contested.

While it is known that grid-of-beams solutions perform poorly in isotropic scattering, no prior experimental results are known. This new paper: answers this performance question through the analysis of real Massive MIMO channel measurement data obtained at the 2.6 GHz band. Except for in certain line-of-sight (LOS) environments, theoriginal reciprocity-based TDD Massive MIMO represents the only effective implementation of Massive MIMO at the frequency bands under consideration.

Massive MIMO Performance—TDD Versus FDD: What Do Measurements Say?

Jose Flordelis, Student Member, IEEE, Fredrik Rusek, Member, IEEE, Fredrik Tufvesson, Fellow, IEEE, Erik G. Larsson, Fellow, IEEE, and Ove Edfors, Senior Member, IEEE Abstract—Downlink beamforming in Massive MIMO either relies on uplink pilot measurements—exploiting reciprocity and TDD operation, or on the use of a predetermined grid of beams with user equipments reporting their preferred beams, mostly in FDD operation. Massive MIMO in its originally conceived form uses the first strategy, with uplink pilots, whereas there is currently significant commercial interest in the second, grid-ofbeams. It has been analytically shown that in isotropic scattering (independent Rayleigh fading) the first approach outperforms the second. Nevertheless there remains controversy regarding their relative performance in practice. In this contribution, the performances of these two strategies are compared using measured channel data at 2.6 GHz. Index Terms—Massive MIMO, FDD, TDD, performance, channel measurements.

VI. CONCLUSIONS Using measured channels at 2.6 GHz, we have compared the performance of five techniques for DL beamforming in Massive MIMO, namely, fully-digital reciprocity-based (TDD) beamforming, and four flavors of FDD beamforming based on feedback of CSI (D-GOB, H-GOB, D-SUB, and H-SUB). The central result is that, while FDD beamforming with predetermined beams may achieve a hefty share of the DL sum-rate of TDD beamforming, performance depends critically on the existence of advantageous propagation conditions, namely, LOS with high Ricean factors. In other considered scenarios, the performance loss is significant for the non reciprocity-based beamforming solutions. Therefore, if robust operation across a wide variety of propagation conditions is required, reciprocity based TDD beam forming is the only feasible alternative.

dave ask

Newsfeed

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Verizon CEO Ronan Dunne: >1/2 VZ 5G "will approximate to a good 4G service" Midband in "low hundreds" Mbps

CFO John Stephens says AT&T is going to cut capex soon.

Bharti in India has lost 45M customers who did not want to pay the minimum USS2/month. It's shutting down 3G to free some spectrum for 4G. It is cutting capex, dangerous when the 12 gigabytes/month of use continues to rise.

Huawei in 16 days sold 1,000,000 5G Mate 20s.  

China has over 50,000 upgraded base stations and may have more than 200,000 by yearend 2019. The growth is astonishing and about to accelerate. China will have more 5G than North America and Europe combined for several years.

5G phone prices are down to $580 in China from Oppo. Headed under $300 in 2020 and driving demand.

No one believed me when I wrote in May, 90% of Huawei U.S. purchases can be rapidly replaced and that Huawei would survive and thrive. Financial results are in, with 23% growth and increased phone sales. It is spending $17B on research in 2019, up > 10%. 

5G phones spotted from Sharp and Sony

NTT DOCOMO will begin "pre-commercial service Sept 20 with over 100 live bases. Officially, the commercial start is 2020.

 More newsfeed

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Welcome  1,800,000 Koreans bought 5G in the first four months. The demand is there, and most of the technology works. Meanwhile, the hype is unreal. Time for reporting closer to the truth.

The estimates you hear about 5G costs are wildly exaggerated. Verizon is building the most advanced wireless network while reducing capex. Deutsche Telekom and Orange/France Telecom also confirm they won't raise capex.

Massive MIMO in either 4G or "5G" can increase capacity 3X to 7X, including putting 2.3 GHz to 4.2 GHz to use. Carrier Aggregation, 256 QAM, and other tools double and triple that. Verizon sees cost/bit dropping 40% per year.

Cisco & others see traffic growth slowing to 30%/year or less.  I infer overcapacity almost everywhere.  

Believe it or not, 80+% of 5G (mid-band) for several years will be slower than good 4G, which is more developed.