Communication baseband is closely related to mobile phone network speed and call quality

Since we entered the 4G era, we have heard a series of terms related to communication networks, such as support for full network access, x-mode x-frequency, etc., at the new product launches of processors from various mobile phone manufacturers. These technologies mainly come from a chip called baseband in the mobile phone. So what is a baseband chip?

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What is baseband?

Many netizens must be familiar with the term baseband. After all, in the "ancient" era of Android, the baseband can be rewritten at will, just like updating the ROM. After the new baseband is flashed, the signal and call quality of the mobile phone may be improved to a certain extent. However, here, the baseband we refer to is the baseband chip on the hardware.

The baseband chip is the communication module in the mobile phone. Its main function is to communicate with the base station of the mobile communication network and modulate, demodulate, encode and decode the uplink and downlink wireless signals. Without its support, your mobile phone can only be a decoration and cannot play the communication function that the mobile phone should have, including a series of interconnection functions such as calling, texting and surfing the Internet. The role of the baseband is very similar to that of the optical modem and ADSL modem in our daily life, except that the signal processing object is changed from light and electricity to electromagnetic waves.

The core part of the baseband chip is mainly divided into two parts: the RF part and the baseband part. The RF part modulates the electrical signal into electromagnetic waves and sends it out or demodulates the received electromagnetic waves, and realizes the up-conversion and down-conversion of the baseband modulated signal. The baseband part is generally for signal processing, and is generally provided with powerful processing capabilities by a fixed-function DSP. In modern communication equipment, DSP is generally used for voice signal processing, channel encoding and decoding, image processing, etc.

Therefore, the network and frequency band supported by your mobile phone, the quality of calls, the speed of the network, and the strength of the signal are all determined by this baseband chip. The parameters, performance, and experience of different baseband chips are very different. Therefore, the quality of the baseband has basically determined the user experience of your mobile phone. No matter how beautiful and exquisite the mobile phone is, without a powerful baseband chip silently supporting it, it is just a vase thing that looks good but is not practical. The baseband chip is the core part of the mobile phone and also the part with the highest technical content. Only a very small number of manufacturers in the world have this technology.

What does the baseband look like?

Integrated in SoC:

Currently, mobile basebands tend to be integrated on SoC (System on a Chip, which is a chip that integrates many functions). Take Qualcomm Snapdragon 835 as an example. The entire SoC chip integrates CPU, GPU, DSP, ISP, security module and X16 LTE Modem, which is the mobile baseband.

Generally speaking, a built-in communication baseband in SoC often means that the manufacturer has strong baseband design capabilities and holds the most important basic communication technology patents. In addition, the power consumption requirements of mobile phone basebands are very strict, and it is not easy to accurately control the changes in power consumption. Currently, manufacturers that can integrate baseband functions on SoC include: Qualcomm, MTK, Huawei, etc.

Therefore, it is very convenient to sell a large number of Qualcomm and MTK SoC solutions. They have already debugged the CPU, GPU, baseband, etc., which is very attractive to mobile phone manufacturers who need a large number of new phones to maintain sales and profits. The disadvantage of integrated baseband is that it has a certain impact on RF performance, and it is necessary to examine the mobile phone manufacturer's ability to design RF antennas.

SoC integrated baseband will be the mainstream in the future. Qualcomm, MTK, and Huawei are all working on integrated baseband. The benefits are obvious. The cost has been reduced. This is easy to understand. Things that used to require two or more chips can now be done with just one chip.

External baseband:

Due to the high technical threshold, long R&D cycle and large capital investment of baseband chips, it is not cost-effective for general manufacturers to develop baseband chips by themselves, and they all achieve communication functions by plugging in basebands from other manufacturers. In addition, some manufacturers have a slow pace in baseband R&D and cannot keep up with the speed of CPU upgrades, so external basebands are obviously cheaper.

It is not shameful to use an external baseband. Even Samsung is still using the external baseband strategy as a mobile phone communication module. This is purely a helpless move. After all, the basic communication technology has an insurmountable patent barrier. You have to purchase technology licenses from other companies. It is rumored that Samsung's next-generation Shannon 359 baseband will be fully integrated into the SoC.

And there is another very important reason, that is, Qualcomm is the inventor of Code Divsion Multi Access (CDMA), owns the most CDMA basic patents, and has designed a huge and intricate patent barrier. GSM, WCDMA, CDMA, and TD-SCDMA networks have made extensive use of CDMA's technical principles and patents, which are unavoidable now and in the foreseeable future. It is difficult for outsiders to integrate these technologies into their own baseband designs unless they pay a considerable amount of patent "protection fees."

Apple iPhone 7 uses A10 Fusion SoC + Samsung RAM, with external Qualcomm MDM9645M Cat.12 baseband solution

Signal processing

When we use mobile phones to make calls or surf the Internet, the electrical signals must first be processed by the baseband, and then a logical channel is established between the mobile phone and the base station. The voice and network data are sent to the base station through the logical channel to achieve information interconnection and communication.

A simplified digital communication system model is shown below:

Voice source coding methods under different network standards

Source Coding - Simplifying the Complexity

The main thing at present is to filter the source data that needs to be transmitted in the early stage, remove all useless and redundant data, and use a certain algorithm to compress the information. The benefits are self-evident, saving channel resources and improving system effectiveness.

Voice source coding methods under different network standards

Channel coding - adding redundancy to error detection

In contrast to source coding, the main purpose of channel coding is to add redundant information. When electromagnetic wave signals propagate in free space, there are often interference, noise and multipath fading problems in the channel, which may cause errors in signal reception and transmission. Therefore, channel coding was invented to introduce redundant information so that the received information can also correct and detect errors by itself.

Channel coding methods under different network standards

Digital modulation – spectrum shifting

The transmitter moves the modulated signal from the low-frequency end to the high-frequency end (the digital baseband signal is multiplied by the sine wave and modulated into a digital bandpass signal), which facilitates antenna transmission or the realization of different signal sources, and can multiplex the spectrum to improve utilization.

Source decoding, channel decoding, and digital demodulation are all reverse processes, and also require dedicated hardware support. Currently, with the development of digital signal processing technology, ARM microprocessors, DSPs, and FPGA architectures have become the main methods for implementing mobile terminal chips.

Who are the “players” in the baseband field?

Downlink Cat Explanation

Uplink Cat Explanation

Qualcomm:

With its years of accumulation in CDMA technology, Qualcomm has become the largest player in the baseband market. According to the latest report from Strategy Analytics, a foreign market research organization, the global cellular baseband processor market size reached $10.5 billion in the first half of 2016, with more than 50% of the revenue share going to Qualcomm, and the shipment share also reaching 54%.

In order to maintain its leading edge in technology, Qualcomm has invested a lot of money in baseband research and development. Therefore, Qualcomm has a large number of high-performance, integrated full-network, and fully-supported communication basebands, which can be used externally or internally. Qualcomm has also released the world's first 5G network communication baseband, the X50. Qualcomm has always adhered to the style of technology first, and the standards are set by "me".

MediaTek:

Thanks to the promotion of low-end and mid-range smartphones in China and emerging markets, MTK MediaTek's communication baseband shipment share climbed to 23%, ranking second. With lower prices, MediaTek has aggressively entered the low-end and mid-range market. In the early stage, it has supported a large number of "five-mode" dual 4G basebands, successfully avoided Qualcomm's patents in CDMA, and gained a large number of market users. Since then, it has achieved full network access integrated on SoC.

Samsung:

Samsung has always been in the self-developed and self-used mode in the baseband market, but it is the king of the Android market, ranking third with a 12% share. And all of them are in the form of plug-ins. It is reported that Samsung's next-generation Shannon 359 baseband will be integrated into the SoC.

Exhibition News:

As one of the few Chinese players, Spreadtrum's name may not seem very well-known, but its external baseband is well-known in the industry. In the past few years, it has received large investments from Intel, so its baseband performance is very good. It has even developed a dual-SIM dual-standby dual-channel solution that even Qualcomm has not yet developed.

Intel:

Intel was also unknown in the baseband market before. However, as Intel no longer sticks to the X86 processor market and comprehensively diversifies its businesses, driven by the global 4G wave, LTE baseband suppliers have gained a market share that exceeds their previous market share. In addition, the Intel XMM series baseband was integrated into the iPhone 7 for the first time. In addition, the iPhone is a hot seller every year, and Intel's baseband market share will be further increased.

What is Multimode Multifrequency?

We often see at mobile phone launch conferences that this phone supports five modes and thirteen bands, full network access, etc., so what exactly is it?

Multi-mode refers to the types of mobile communication standards supported. In China, mobile communication standards include China Mobile TD-LTE, China Telecom/China Unicom LTE FDD, China Mobile TD SCDMA, China Unicom WCDMA, China Mobile/China Unicom GSM, China Telecom CDMA2000, China Telecom CDMA 1x, and EVDO.

Multi-band means that the mobile phone can support working frequencies in various modes. Since each country in the world has inconsistent network standards and frequency band divisions, and to avoid frequency band interference, there will be differences in frequency bands even if they are running on the same network standard.

For example, the five-mode thirteen-frequency proposed by China Mobile simultaneously supports five mobile communication standards: TD-LTE, LTE FDD, TD-SCDMA, WCDMA, and GSM; supports TD-LTE Band38/39/40, TD-SCDMA Band34/39, WCDMA Band1/2/5, LTE FDD Band7/3, GSM Band2/3/8, the 10 most commonly used frequency bands in China. In addition, it also supports TD-LTE Band41, LTE FDD Band1/17, and GSM Band5, which enables global roaming of mobile phones.

In fact, you don’t have to worry too much about the quality of your mobile phone communication, because the telecommunications network is a public network, and a problem with one device may affect the operation of the entire network. Therefore, China has long adopted a network access license system for telecommunications equipment. All equipment entering the public telecommunications network must pass the inspection, and only those that meet the relevant requirements are allowed to access the network.