mmWave in smartphones: how Qualcomm made the impossible possible

    Qualcomm recently unveiled the world's first fully integrated 5G NR (mmWave) and sub-6 GHz RF modules for mobile devices. Up to now, mmWave signals have not been used for mobile communication due to numerous technical difficulties. Therefore, many in the industry were convinced that this is simply impossible. How the difficulties were overcome and what effect the millimeter range will have on 5G - in our review below.

    By 2020, mobile data transmission traffic around the world will increase by 30 times compared to 2014 and amount to 8 billion gigabytes per day . 75% of this traffic will fall on streaming of multimedia data, follows from the forecast of Nokia Bell Labs, published in 2016 and which is still coming true. At the same time, more than 86% of smartphone users, according to polls, would like the next smartphone that they buy, the Internet would work faster, and 50% are ready to buy a smartphone with 5G when it is available.

    The network of the fifth generation is on its way. They will provide 10 times higher data transfer rates compared to LTE and 10 times faster response (in response to reports understand less pings), but so far many mobile device manufacturers expected 5G to be used for the Internet of things, for remote control applications, for virtual reality - in general, for anything, but not for ordinary consumer devices that we carry with us every day: smartphones and tablets. There are two fundamental reasons for this.

    What are the problems?

    All the advantages of 5G in the form of huge user data transfer rates and low pings and a fundamentally larger network capacity, allowing this level of service to be provided to a huge number of subscribers at the same time, are realized not with the help of some sort of magic, but primarily through the use of wider bandwidth frequencies compared to the same LTE. Where to get these frequencies, in general, is also clear: it is necessary to use more and higher ranges. So we got to millimeter waves (the higher the frequency, the shorter the wavelength, we remember that from the school physics course) or mmWave: this is the range from about 24 to 300 GHz. For 5G, the “low-frequency” part of this band will be used, in particular, specific frequency bands have already been allocated, for example, 26.50–29.50 GHz (n257), 24.25–27.50 GHz (n258).

    Along with the “high” frequencies of mmWave in 5G, frequencies below 6 GHz will also be used, they are also Sub-6 (for example, in Europe and, we hope, in Russia it is 3.4–3.8 GHz) - they are intended primarily for providing a wider than in the case of the millimeter range, coverage, that is, for the construction of macro networks; about speeds of several tens of gigabits per second, as in mmWave, there is no question here. Both bands will be used to transmit 5G NR radio waves; NR in this case is New Radio, that is, the new exchange protocol between the base station and the end device.

    So what is the difficulty with the millimeter range? The laws of physics mmWave does not contradict, but it was really difficult to implement in a compact device such as a smartphone. The fact is that modems that support both Sub-6 and mmWave are not a complete ready-made device, as a man in the street sees it, but only a modulator / demodulator in the classical sense. And there are still radio modules - that is, amplifiers, bandpass filters, etc., which were just considered impossible to implement in the form factor of a smartphone due to its size, weight and power consumption.

    In general, frequencies above 24 GHz have been used in radio communications for quite some time, for example, for radio relay lines operating at a distance of direct visibility, satellite channels, and similar fixed solutions. The key word is fixed, since stationary equipment has no restrictions on size and weight, as well as energy consumption and, of course, can be set so that this direct visibility is ensured.

    Such high frequencies are characterized by a significant attenuation of the signal with increasing distance, as well as greater sensitivity to obstacles: the human body, head, and even the arm can become an insurmountable obstacle to wave propagation, and there is nothing to say about the ability to penetrate inside buildings. Therefore, for mobile communication millimeter waves have never been used. It was believed that in the dimensions of the phone, any solution would either not provide a stable connection, or would instantly eat up the battery, and most likely, both.

    A mmWave modem research prototype (left) 5G and a reference smartphone in which you can embed a commercial 5G modem with mmWave support

    The second barrier to the introduction of mmWave in smartphones was that this technology implies extremely tight installation of base stations: many believe that almost every room in the building, and in the city - on each lamppost with an interval of 150-200 meters is different there must be a base station from a friend so that the use of the millimeter-wave range makes at least some sense. And since operators do not realize this very soon, then it is not necessary to build support for these ranges into smartphones.

    However, Qualcomm engineers believe that mmWave base stations are needed, by and large, only to provide indoor coverage: you don’t have to hang the 5G BS under each bush; for early carpet coverage, LTE BS will be enough for the “carpet” coverage, and later - Sub-6 requiring a much lower installation density (and here it’s a sin not to recall the statistics of cellular operators, which says that up to 80% of data traffic is generated from premises).

    Who is the problem, and who is the task

    In 2017, at MWC in Barcelona, ​​Qualcomm showed a working prototype of a data transmission system operating in mmWave at 28 GHz in the dimensions of a mobile device.

    Thanks to the use of adaptive bimforming and bimtracking (forming a directional signal beam between the client device and the base station and tracking its movement relative to the BS), a stable connection was achieved inside a moving car, in an office building (with a signal passing through noncapital walls) with instant beam switching "To another base station and protected from blocking the" beam "by the body or hand, which the subscriber holds the smartphone. For beam forming in three-dimensional space, both at the base station and on the mobile device, antenna arrays with high gain factors are used: from 128 to 256 or more elements at the BS and from 4 to 32 at the subscriber terminal. In this case, the beam may be indirect: the antenna arrays control it taking into account the reflection of waves from surrounding objects.

    The solution for the millimeter range is implemented on the basis of the 5G-modem Snapdragon X50, which supports the installation of several antenna arrays under the front and rear panels of the smartphone, which create almost spherical coverage and thereby eliminate the problem of shading by hand holding a smartphone

    The modules are equipped with a built-in transceiver, an integrated power supply control circuit, radio components of the input stages and support for phased antenna arrays. The QTM052 module supports aggregation up to 800 MHz (8x100) in the frequency ranges 26.5-29.5 GHz (n257), 27.5-28.35 GHz (n261), and 37-40 GHz (n260). The QPM5650, QPM5651, QDM5650 and QDM5652 modules support integrated SRS switching required to optimize Massive MIMO technology applications. They operate in the 3.4–4.2 GHz (n77), 3.3–3.8 GHz (n78) and 4.4–5.0 GHz (n79) frequency bands and can use 100 MHz of spectrum. The QPM series differs from the QDM series in the presence of an integrated power amplifier (PA). Samples of QTM052 mmWave antenna modules and QPM56xx radio modules are currently being sent to customers.

    Ready for commercialization solution

    Old-timers remember that thirty years ago, the same thing was said about CDMA: they say it will be too difficult or will not work at all, let's make simple and clumsy GSM. However, Qualcomm then managed to implement CDMA in mobile devices and the same CDMA-800 in the nineties (spread in the United States, Korea and several other countries) was superior in all respects to GSM. When it came time to turn off analog networks, for example, NMT-450, CDMA also came to replace them - by the way, Sky Link in Russia in CDMA-450 became the first mobile broadband operator: at the beginning of the zero, there were already speeds in a couple of megabits per second while the GSM operators were barely starting EDGE. And in the same zero, when they developed 3G (UMTS), they took the technology implemented by Qualcomm back in 1989: WCDMA (Wideband CDMA) is essentially the same CDMA,

    Now the situation is repeated. This summer, prototypes with wwWave support took shape into a ready-made commercial solution for 5G-smartphones, thanks to which the first production devices will be released next year. These are the first fully integrated 5G NR QTM052 modules for mmWave and radio modules supporting frequencies up to 6 GHz QPM56xx. They are compatible with Qualcomm Snapdragon X50 5G modems and are essentially the only thing that needs to be established between the modem and the antenna, and the modem supports up to four of these modules simultaneously, which will allow using different frequency ranges.

    In general, we are looking forward to the year 2019, which promises to be bright on the events in the world of 5G.

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