Nextivity Cel-Fi RS2 black - smart 3G amplifier

    Nextivity Cel-Fi RS2 black (single band)

    Surely each of us more than once faced with poor quality of communication - a low level of 3G-signal. For some, this problem is uncritical, but there are times when a stable connection is vital. If this is your case, I recommend reading this article.

    Coverage in Russia still leaves much to be desired. This is especially true for 3G networks. Even on the streets of the city, the phone doesn’t always catch 3G, not to mention offices in multi-storey business centers, all kinds of basement and garage rooms and other reinforced concrete structures. The central part of Russia is mostly flat, and outside the city the operator’s signal spreads without significant interference, the only question is the distance to the base station. However, in places with hilly or mountainous terrain or with dense urban development, even the proximity of the BS does not guarantee reliable reception.

    Many work remotely, resting from the city in the cottages and in country houses. And in this case, the necessary condition for smooth operation is the availability of high-quality coverage, as well as a stable and fast Internet channel.

    In this article I want to introduce you to the Nextivity Cel-Fi RS2 black subscriber terminal . This is a relatively new solution used by major international operators: Vodafone, AT&T, T-Mobile, Orange group, etc., as well as approved and certified in Russia. It serves to increase the area of ​​reliable reception and transmission of voice and data using 3G technology.

    There are not many options for improving coverage. First, consider common solutions, so that it becomes clear why there is a need for something new.

    Indoor 3G signal attenuation

    Standard Wired 3G Repeater / Amplifier

    When using it, firstly, it is necessary to understand the topic in great detail. The fact is that a bi-directional amplifier increases the network noise level (interference), making it difficult for other users to access the network. To minimize this effect, you have to read a lot, google, check. Secondly, you will need to buy the right accessories - an external and internal antenna, a suitable RF cable, connectors and adapters. Then mount all this, orient the antennas correctly, and achieve an acceptable signal level. Well, and thirdly, there are practically no ready-made kits on sale, nor are there certified solutions. The reason is that such systems spoil the signal to operators and change the coverage map. Due to the fact that such repeaters have a fixed gain, regardless of the required signal level and often exceeds the base station. In addition, the transmission of the signal up (towards the BS) is continuous.

    Standard Wired 3G Repeater / Amplifier

    As a result of such installations, even worse, the following sad situations arise: those. the operator’s department records the effect of unacceptable radio interference on the BS and initiates an appeal on the verification of the legality of the operation of radio electronic equipment (RES) to the Federal Service for Supervision in the Sphere of Communications, Information Technology and Mass Communications (Roskomnadzor). The Radio Frequency Center, in turn, conducts search and direction finding activities, analyzes the electromagnetic environment and reveals that the repeater is the source of the radiation. Next, the installation location and owner of the repeater is determined, and since the latter does not have permission to use radio frequency channels and there is no certificate of registration of such a repeater, Roskomnadzor issues a decision in the case of an administrative offense in the field of communications.

    Operators also have professional repeaters. They require a lot of settings and technical approvals. Their cost is lower than that of the base station, but all the same, these are amounts of the order of 100-300 thousand rubles. Therefore, they put such only on large facilities and key customers (who have high monthly charges).

    Dancing with a tambourine around a 3G modem

    Remote directional antenna, focusing antenna, transfer of the modem to the roof (in the country), etc. It may look something like this:

    Dancing with a tambourine around a 3G modem

    Here are DIY examples

    Judging by the reviews, focusing the signal “at random” is almost hopeless. Painstaking calculations are required here. And external antennas for the modem, again, are difficult to install and configure. In addition, we get only a limited version of the implementation of method No. 1 - exclusively for the Internet. The maximum that can be done is to install a 3G-roter and distribute the Internet via Wi-Fi. But talking on the phone is not talking, and if you have the same poor level of 2G and 3G - such a solution will be half-hearted.

    However, to whom it is interesting - following the links above the process is described in detail, and the authors are pleased with the result.

    Femtosota - “own” miniature base station

    It can be useful in a city where it is necessary to provide an office or any other premises with high-quality voice communications. For 3G Internet, the thing can be said to be useless, because the femtocell itself requires a stable Internet channel of 3-7 Mbit / s. Well, its installation must be coordinated with the operator, and for this you need to be a corporate client. It should be added that the femtocell has a strict geographic “link” to a specific address, and therefore there is no possibility of free movement. And if confidential information is stored in your local network, the channel to the operator potentially reduces data security. The advantage of femtocells is the complete absence of the need for a base station signal.


    On this, the common ways to improve the 3G signal, in general, end. And now, knowing the theory of the issue, we can see what kind of device the Nextivity company developed.

    Nextivity Cel-Fi RS2 black

    In short, this is a wireless system of two-way amplification of the 3G signal on the subscriber side, which does not require settings, does not interfere with other users and increases the capacity of the cellular network.

    Outwardly, it looks like two black boxes, although quite stylish, in the spirit of Apple. The kit consists of receiving and transmitting modules communicating with each other via Wi-Fi (hence, apparently, the name of the device is Cel-Fi). The receiver, the so-called Window Unit, is installed in the zone with the best level of 3G signal, most often closer to the window. The transmitter can be carried up to 25 meters (in open space) and positioned so as to cover the maximum, or simply problematic, area in the room. Moreover, the task of finding the optimal place is very simple and does not even require basic knowledge of the theory. Probably easier to see once.

    Now we will analyze in more detail the principle of operation of the device, the applied technologies, characteristics and features.


    The device comes in a weighty box. You cannot call it small and inconspicuous - the dimensions of the receiver are 20x15 cm, the transmitter is slightly smaller. I did not disassemble them, but the feeling that inside the cases of both modules is pretty empty. Alas, for all the technological effectiveness of the antennas, their size matters.

    Options Nextivity Cel-Fi RS2 black

    In the box are:

    • Window Unit Receiver
    • Coverage Unit Coating Device
    • Two identical power adapters
    • Installation and Connection Guide

    Everything is emphasized simply, nothing more.

    General view of Nextivity Cel-Fi RS2 black blocks

    On the front panel of the “receiver” is a power indicator and 5 LED indicators for signal strength in green. At first glance, a strange decision - it would be enough to do with one familiar, with 5 stripes. It is most likely explained by the fact that these blocks are at decent distances, and in case of changes, the user just needs to look from afar and fix the indication.

    Cel-Fi RS2 black receiving device - front view

    At the bottom there is a Micro SD slot (apparently, for tuning for the operator, as described below), an SMA port for an external antenna, a power connector, and a reset button.

    Cel-Fi RS2 black receiving device - bottom view

    The RS1 also had slots for hanging on the wall. RS2 does not have them. It was decided that this is not entirely correct in terms of the functionality of the built-in antennas. By attaching the device, for example, to a concrete wall, we completely closed the antenna.

    Cel-Fi RS2 black receiving device - rear view

    Cel-Fi RS2 black receiving device - top view

    On the front panel of the “transmitter” there is a numerical green LED that shows numbers from 0 to 9 and helps to determine the optimal location of the transmitter relative to the receiver. There is also a red indicator that signals a malfunction or improper installation of the module, as I will discuss below, and a power indicator.

    Cel-Fi RS2 black coating device - front view

    Cel-Fi RS2 black coating device - side view

    Cel-Fi RS2 black coating device - rear view

    At the bottom of the coverage device is a power input and a reset button. Plus micro-USB input - apparently for firmware and debugging.

    Cel-Fi RS2 black coating device - bottom view

    Cel-Fi RS2 black coating device - top view

    Both devices have passive cooling. Heat is dissipated through numerous slots in the housing. Probably, dust is perfectly accumulated in these slots.

    Power adapters are the same, so do not mix them up.

    Power adapter

    The principle of work, technology

    The window receiving module is installed in the zone of the most confident reception of the operator signal - usually on the windowsill. Because the case is half open, it will not be possible to install it on the street due to unacceptable temperatures and humidity. But there should not be much difference for the signal. In addition, you can optionally connect an external antenna, but, as I understand it, this is for completely neglected cases.

    SMA port for connecting an external antenna

    The received signal is transmitted to the coverage device via Wi-Fi. The blocks communicate with each other at a frequency of 5 GHz (frequency ranges U-NII-1 5.15-5.25 GHz or 5.25-5.35 GHz and U-NII-2 5.47-5.725 GHz). There is no such garbage in this range as in ordinary Wi-Fi, but the arrival of dual-band Wi-Fi here can affect the situation. However, the processor algorithm contains a 7-microsecond cycle of checking the frequency free in this range, in case of busy units "jump" to a clean one. if all ranges are occupied, the blocks, indeed, will not be able to communicate with each other.

    The distance between devices in an enclosed space can be up to 25 meters, depending on the possible signal loss when passing physical barriers (walls / partitions and their structural material). The experience of using people says that in areas where Wi-Fi does not penetrate, and this unit does not work and vice versa. For example, a person writes that he placed the transmitter through three walls and about 7.5 meters from the receiver, and the modules did not see each other (there is no Wi-Fi signal either). But having located it in the living room area, 10 meters, two walls, there is Wi-Fi coverage, we managed to achieve excellent Cel-Fi performance.

    The coverage device relays and amplifies the received 3G signal of the operator to an area of ​​up to 1235 sq.m.

    It is important that the signal is amplified in both directions - to the subscriber and to the base station.

    IntelliBoost Baseband Processor Installed in Cel-Fi. This is a specialized processor developed by Nextivity to optimize the reception and transmission of a 3G signal indoors. IntelliBoost has advanced filtering, signal equalization and echo cancellation capabilities. The processor is fast enough to provide a high data rate and widespread 3G signal in the building. Cel-Fi allows you to simultaneously support up to 30 voice and 6 date sessions. IntelliBoost controls real-time gain by automatically adjusting parameters without negatively affecting the macro network. Cel-Fi RS2 supports the Power control function on the up and down lines, as well as automatic shutdown of the transmitter when there is no activity of the subscriber equipment in the coverage area of ​​the subscriber terminal. Here, for clarity, measurements of the operation of this function from one of the Russian operators:

    Cel-Fi RS2 subscriber

    The subscriber has left the coverage area of ​​Cel-Fi RS2

    Built-in Cel-Fi software is protected by the manufacturer’s code and is pre-configured to work with one of the authorized networks of mobile operators in Russia: MTS, MegaFon, VimpelCom, Rostelecom. You can create Firmware for any operator "on the knee", but protection will not allow you to fill the firmware into the device’s memory. You can flash the device for another operator in an authorized center.

    The Cel-Fi device does not require activation and registration of the IMSI list of subscribers, as well as permissions from the mobile operator. Cel-Fi RS2 has all the necessary permissions for indoor installation and use.

    Specifications and Features

    • Processor: Nextivity's IntelliBoost Baseband II with unmodulated signal transmission, a high-tech algorithm for suppressing echo signals and frequency-selective filtering.
    • Supported cellular standard: UMTS 2100 MHz.
    • Operating band: 5 GHz, in accordance with ETSI EN301 893 V1.5.1.
    • Gain: up to 100 dB (up to 20 meters between the receiving device and the coating device).
    • Maximum EIRP : downlink - (14.7 dBm downlink and up to 25.7 dBm uplink).
    • Sensitivity WU: 104-106 dBm. If the signal is present in this value, then the WU will receive-process-amplify and transmit the signal to the CU. For a weaker signal, an external antenna can be installed. The antenna must be selected depending on the technical conditions: omnidirectional, directional: panel, parabolic.
    • Working height: from -60 to 3050 m. I don’t know what causes such restrictions, but the depth allows you to install the device also in the metro or in mountainous areas, not higher and not lower than people usually live. The ability to use is claimed more than 99.9%. For extreme conditions, I think there are other, specialized solutions.
    • Dimensions (width × depth × height): Receiver (Window Unit) 144 × 146 × 212 mm. Coverage Unit 146 × 59 × 158.5 mm.
    • Harm to health: complies with WEEE 2002/96 / EC). The maximum power of the studied signal is 295 mW. This is less than the peak power of a conventional mobile phone. Those. at a much more significant distance from a person there is no dangerous exposure at all.
    • Power consumption: less than 12 watts per device.
    • Operating temperature: 0-40 degrees, humidity 5-95% without condensation. This eliminates the installation of Cel-Fi on the street or even on the balcony.
    • Recommended retail price - 19990 p.

    Other technical specifications that are mainly of interest to specialized specialists (compliance with standards, noise immunity, certification, etc.) can be found in the documentation for the device.

    Algorithm Features

    • the automatic gain control (AGC) algorithm continuously monitors signal loss from the base station and transmits power to provide maximum gain.
    • optimization of the gain along the uplink in order to reduce the noise level at the input of the base station.
    • automatic shutdown of the transmitter in the absence of subscriber equipment activity in the coverage area of ​​the subscriber terminal.
    • the system shuts down at the command of the operator’s network or upon detection of a malfunction (the option is more priority for operators).

    Ability to use in:

    • apartments
    • offices
    • cottages
    • remote suburban cottage complexes
    • business centers
    • supermarkets
    • storage, basement and parking areas
    • industrial facilities
    • cafes and restaurants
    • other objects with unstable and weak 3G (UMTS) signal

    Switching on and setting up

    I plan to make a separate article with detailed testing of the device in different conditions, so I will now describe only a brief application experience.

    I put WU on the windowsill, where the phone shows 2-3 sticks.



    According to the instructions, CU and WU must be spaced in such a way as to achieve the maximum numerical value on the CU screen.



    Carrying the transmitter around the office is rather inconvenient due to the need to search for a power outlet each time or carry an extension cord. I would add a small backup battery, as is done in some electronic watches, so that you can turn off the power briefly and transfer to another place without turning off the device. But overall, this is not critical.


    I managed to find a place in the office where CU showed 8. The nearby phones immediately gave out all the “sticks” of the 3G signal. Before inclusion, in this place there were floating 1-2 divisions.

    Measurements made on the phone using Speedtest (download / upload / ping time):

    • Cel-Fi off: 820/45/311
    • Cel-Fi on, phone next to CU: 2455/823/132
    • Cel-Fi on, telephone approximately 7 meters from CU: 1617/729/61
    • Wi-Fi for comparison: 19020/15934/8

    Naturally, the quality of voice communication in this case also increases, echo, delays, noise, interference disappear.

    In our office, I was not able to connect WU and CU even on 2 neighboring floors. Apparently, the problem is in the materials of interfloor ceilings. There was also a place where the 3G signal was weak even with Cel-Fi running. But in order to check how and what affects the signal level and draw conclusions, I am going to conduct detailed tests. At the same time, I’ll check the problematic place I know, where a phone without a repeater constantly jumps between 2G and 3G, periodically skipping incoming calls.

    I have pictures with visualization of measurements for a 3-storey building.

    Standard 3G

    3G standard coverage

    coverage 3G coverage with Nextivity Cel-Fi RS2 black

    3G coverage with Nextivity Cel-Fi RS2 black


    It is not entirely correct to consider a Cel-Fi device in terms of “definitely helps / does not help”. Of course, you have to try.

    However, even what I saw during a quick test is impressive. The 3G signal reaches its maximum, the data transfer speed increases markedly.

    An important plus may be saving battery power in the phone: Cel-Fi controls the power level between the operator’s base station and user devices in order to extend the battery life of subscriber devices.

    There are significant advantages of using Cel-Fi for mobile operators: increasing network capacity, increasing traffic, reducing the number of disconnects and, as a result, increasing user loyalty and reducing the load on technical support.

    useful links

    1. Description and documentation on the website of the official representative in Russia
    2. Nextivity Coverage Tester (Android App)
    3. MDMA (Mobile Data Monitoring Application) monitoring software
    4. Review on Mobile Review (Cel-Fi RS2 white single band)
    5. Nextivity Corporate Website

    For reference, Nextivity was founded in 2006. The headquarters is in San Diego (California). Nextivity Inc. He is a designer and developer of carrier-class closed cellular systems, as well as the underlying software. The team’s experience includes participating in more than twenty start-up projects and collaborating with large companies such as Qualcomm, Broadcom, HP, Motorola and Intel. San Diego's headquarters maintains sales and technical support offices worldwide through partners. Since July 2009, shipments of Cel-Fi systems to operators in Europe, North America, Asia, the Middle East and Africa totaled tens of thousands of sets.

    Timeline of release and sales of Nextivity products Cel-Fi RS models Cel-

    Fi RS1 support for UMTS 2100 (discontinued):


    Cel-Fi RS2 white (single band) support for UMTS 2100 (sales in Russia until the end of 2012):


    Cel-Fi RS2 black (single band) support for UMTS 2100 (sold in Russia since 2013):


    Cel-Fi RS2 dual band support for UMTS 900/2100 (sold in Russia since 2013):


    Cel-Fi RS3 support for UMTS 900/2100, LTE (expected in Russia in 2014):


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