MM depends on receiving back from the phone information on the channel. That uplink information has practical limitations on many cases, including from interference. In this paper, Bjornson, Hoydis, and Sanguinetti take on the assumption that there is a theoretical limit of spectral efficiency. Beginning with Marzetta, potential problems have been recognized.

"The pilot resources are limited by the channel coherence time, the same pilots must be reused in multiple cells. This leads to pilot contamination. ... it appears that pilot contamination is a fundamental issue that manifests a finite SE limit, except in some impractical special cases."

In 30 page dense with mathematics, the authors claim, "We will show in this paper that this is basically a misunderstanding, 

spurred by the popularity of analyzing independent Rayleigh fading channels and suboptimal combining schemes, such as MR and S-MMSE. We prove that the SE increases without bound in the presence of pilot contamination when using M-MMSE combining/precoding, if a simple condition on asymptotically linearly independent covariance matrices is satisfied."

In other words, in most cases you can in theory keep adding antennas to get any performance levels you like. Nominally that means you could cram nearly infinite data into a limited amount of spectrum. 

Practical considerations of course limit capacity. Antennas need space and power. They have substantial costs. Heat often becomes a design limit.

Spectrum policy is obsolete in 2017 that doesn't recognize high capacity from MIMO as well as frequency agile systems. For example, a reasonable proposal at the U.S. FCC would allow WI-Fi like radios from 3.7 GHz to 4.2 GHz. But exclusive use should be minimized to a control channel of perhaps 20 MHz. Capacity can be added, at modest cost, with more antennas. Beyond that, a provider can find open spectrum in the hundreds of megabits available. That works. Wi-Fi was the first to prove sharing is possible, and Verizon/Qualcomm testing for LAA is convincing that sharing can be used in almost all bands. The request for 160 MHz of spectrum is absurd; most of the band should remain a lightly regulated commons.

Sharing spectrum allows 200% to 500% more capacity so is almost always the right choice today.  

 

Massive MIMO has Unlimited Capacity

Emil Bjornson, ¨ Member, IEEE, Jakob Hoydis, Member, IEEE, Luca Sanguinetti, Senior Member, IEEE

Abstract The spectral efficiency (SE) of cellular networks can be improved by the unprecedented array gain and spatial multiplexing offered by Massive MIMO. Since its inception, the coherent interference caused by pilot contamination has been believed to create a finite SE limit, as the number of antennas goes to infinity. In this paper, we prove that this is incorrect and an artifact from using simplistic channel models and suboptimal precoding/combining schemes. We show that with multicell MMSE precoding/combining and a tiny amount of spatial channel correlation or large-scale fading variations over the array, the SE increases without bound as the number of antennas increases, even under pilot contamination. More precisely, the result holds when the channel covariance matrices of the contaminating users are asymptotically linearly independent, which is generally the case. If also the diagonals of the covariance matrices are linearly independent, it is sufficient to know these diagonals (and not the full covariance matrices) to achieve an unlimited asymptotic capacity.

dave ask

Newsfeed

Lei Jun Xiaomi "5G to have explosive growth starting from Q2 2020"5G to have explosive growth starting from Q2 2020" I say sooner

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.