"Smartphones are now indispensable in our lives, but the Wi Fi performance of different brands of phones is uneven. How mobile phone manufacturers improve Wi Fi quality through complete testing in the production process
In recent years, with the strong rise of Chinese mobile phone brands in the Chinese market and the international market, the competition in the field of smart phones has become white hot. However, due to the maturity of chip and hardware technology, the functions of mobile phones are becoming more and more similar, and the performance parameters are becoming more and more similar, so it is more and more difficult to differentiate between mobile phone brands. At the same time, new features and running parameters are easy to cause aesthetic fatigue to consumers. Therefore, consumers pay more and more attention to the user experience, stability and durability of mobile phones. Therefore, whether we can continue to provide the best user experience and reliable quality has become the key to the success of mobile phone brands in the future.
Today's smart phone is no longer a simple communication tool, but a personal computing platform that enables people to connect to the Internet, work and entertainment anytime and anywhere - and Internet connection is the basis of work and entertainment. At present, there are two technologies that can provide network connection on mobile phones. One is the cellular mobile network with the birth of mobile phones, and the other is the IEEE 802.11 wireless local area network (WLAN), which appeared later but developed rapidly - which is more used under the name of Wi Fi. 802.11 technology works in unlicensed frequency band, which has the characteristics of low cost, high speed, simple deployment and wide coverage. It is the preferred way for users to access the Internet in homes, shopping malls, hotels, enterprises and public facilities. According to statistics, on mobile phones, the data traffic generated by users using Wi Fi is much greater than that generated by using cellular communication technology. Comparison of traffic share between mobile network and Wi Fi. Fixed / Wi Fi traffic has surpassed fixed / wired network traffic since 2018
Because Wi Fi components carry the most data traffic and use time of smartphone users, the performance and quality of Wi Fi components greatly affect the user experience. However, some mobile phone brands do not pay enough attention to the quality of Wi Fi components, resulting in the continuous decline of mobile phone user experience and brand recognition. Among them, several major problems such as weak Wi Fi signal, slow internet speed and high delay have received more user complaints, which has a negative impact on the image of these mobile phone brands. Therefore, how to improve the quality of mobile phone Wi Fi has become an urgent problem for manufacturers. From a technical point of view, this paper attempts to deeply explore the reasons and Countermeasures Affecting the quality of mobile phone Wi Fi, and reveal the importance of complete Wi Fi testing for smart phones.
Signal quality
By viewing the Wi Fi icon on the top of the mobile phone screen, users can directly understand the strength of the current Wi Fi signal. Sometimes two different brands of mobile phones are clearly in the same position, but the number of signal cells displayed is different, so users will complain about the poor Wi Fi signal of mobile phones with few signal cells. This is related to the performance of mobile phone Wi Fi receiver. When the Wi Fi component is connected to the router, the radio frequency (RF) receiver regularly measures the broadcast packets sent by the access point (AP), calculates the wireless received signal strength (RSSI), and then displays the signal strength on the operating system according to the RSSI value. Under normal circumstances, the closer the mobile phone is to the router, the higher the RSSI value, indicating that the stronger the Wi Fi signal received; The farther the mobile phone is from the router, the lower the RSSI, indicating that the Wi Fi signal is weaker.
For the calibrated and tested mobile phones, the measured RSSI value and signal lattice number are consistent with the real received signal strength, and the reception performance of downlink signals is also better. For the mobile phone without calibration test, the RSSI value and signal lattice number are inconsistent with the real received signal, and the reception performance of downlink signal is poor. Therefore, the mobile phone Wi Fi without receiver calibration test not only shows weak signal, but also the Internet speed and working range are worse than those of the calibrated mobile phone. It often shows no signal where the normal mobile phone can receive Wi Fi signal, resulting in poor user experience.
Another situation is that the user's mobile phone can sometimes clearly see more than one grid of Wi Fi signals, but the actual Internet speed is very slow, or even disconnected, and the user experience is seriously affected. The signal displayed on the mobile phone indicates that there is no problem with the receiver, so what is the problem? The answer lies in the transmitter power of the mobile phone. For mobile phones, transmitter power is very important - if the transmitter power is too high, the mobile phone will consume too much power and need to be charged frequently. If the transmission power is too low, the uplink signal cannot reach the receiving antenna of the router normally after path attenuation, which reduces the actual working range of the mobile phone. Therefore, in the process of mobile phone manufacturing, Wi Fi transmission power must be strictly calibrated and tested to ensure the accuracy of transmission power.
Since wireless communication is bidirectional, through strict calibration and testing of mobile phone Wi Fi transmission power and receiver sensitivity in the production process, it can ensure that the uplink and downlink of mobile phone match within the maximum working range without one of them being delayed. Smart phone transmitter and receiver are compared before and after calibration test
In the third case, because Wi Fi mainly works in the unauthorized frequency band and the spectrum is crowded, experienced users often choose to switch the router to a specific frequency with less interference. However, when the user's mobile phone uses different frequencies to access the router, sometimes it will be found that the signal strength and Internet speed will decrease significantly. This is because Wi Fi operates in two main frequency bands, 2.4GHz and 5GHz. Each frequency band is subdivided into multiple frequencies. For example, the 2.4GHz frequency band has 14 available frequencies from 2412mhz to 2484mhz, while the 5GHz frequency band has 24 frequencies distributed in the range of 5180mhz to 5825mhz due to its wider bandwidth. For mobile phone Wi Fi components, the RF performance of available frequencies in different frequency bands will be very different. Therefore, during the production test, multiple frequencies in these two frequency bands should be calibrated and tested in turn, so as to ensure that all frequencies at 2.4GHz and 5GHz can operate normally after the mobile phone leaves the factory.
Internet speed is not fast enough?
Next, let's talk about internet speed. As a wireless local area network technology, the coverage of Wi Fi is not as good as that of cellular mobile communication, and the terminal location is usually relatively fixed. Therefore, the frequency selectivity and spatial orthogonality of the wireless channel where the Wi Fi signal is located are better than those of the widely covered cellular network. Therefore, Wi Fi can make more effective use of the advantages of high bandwidth and multi antenna technology to greatly improve the rate. At present, the mainstream 802.11ac wave 2 products in the market can support up to 160MHz bandwidth and multi-user multiple input multiple output (MU-MIMO) technology. Take Qualcomm's snapdragon 835 / 836 mobile platform as an example. It can support 802.11ac 2x2 MU-MIMO, and the transmission rate is more than twice that of the previous generation. The future mobile platform will support higher bandwidth and more MIMO antennas.
However, if the testing of these new features is ignored in the manufacturing process, it is likely to lead to the problem of slow internet speed in the actual use of the product. For example, many early test instruments only support the generation and demodulation of bandwidth signals below 80MHz or 40MHz, resulting in the failure to test some high rate modes in production testing. Therefore, we cannot know whether the product has quality problems in the high rate mode, and there will be quality risks after the product is put on the market. Although some manufacturers use the spectrum splicing method to obtain the transmitter test results of mobile phone RF module, due to the use of non real-time sampling (multiple acquisition), such results can not accurately reflect the real characteristics of the signal, and there is a certain degree of error. Through the latest generation of wireless communication tester (such as LITEPOINT iqxel MW), it supports 160MHz signal demodulation and generation, and can fully test these high-speed modes.
There are similar problems in MIMO testing. Since most of the early instruments only had a set of vector signal analyzer / vector signal generator (VSA / VSG) combination, only one RF link can be verified at the same time. For mobile phones supporting MIMO, each RF link can only be verified in turn by time-sharing switching. Manufacturers adopting this method cannot know the real performance of DUT working in MIMO mode. Through new wireless communication testers such as iqxel MW, it can support up to 4 ~ 8 MIMO channel synchronization tests to realize mobile phone RF link performance tests in MIMO scenarios. Combination of different bandwidth and number of MIMO antennas
Achieve lower latency
There are some new popular applications on the Internet, such as online games. Due to its real-time and interactivity, the requirement for network waiting time is very high. The lower the delay, the better the game experience. The higher the delay, the worse the game experience, and even unable to play normally. Therefore, delay is an important indicator to evaluate the networking performance of smart phones. There are many reasons for the delay. Because IEEE 802.11 is a media access control (MAC) layer and physical layer (PHY) protocol working under TCP / IP protocol, it adopts the collision avoidance mechanism of "carrier sense multiple access / collision detection" (CSMA / CD). Therefore, the delay of Wi Fi wireless network is mainly caused by multiple retransmissions caused by poor signal quality of mobile phone or interference from other Wi Fi devices. However, the poor performance of the receiver of the mobile phone will also lead to the increase of downlink retransmission.
The main pointer to evaluate the quality of mobile phone Wi Fi transmission signal is error vector amplitude (EVM). EVM reflects the degree that the IQ modulation of mobile phone transmitter signal deviates from the ideal value. The higher the EVM, the worse the signal quality. After the attenuation of the wireless channel, it is difficult for the router receiver to demodulate the signal normally, resulting in packet loss and retransmission, thus prolonging the transmission delay. Therefore, we expect the signal quality at the transmitter of the mobile phone to be as good as possible in order to ensure the stability and low delay of transmission. In the process of mobile phone manufacturing, we use VSA instrument to demodulate and analyze the RF signal sent by mobile phone transmitter, and then we can calculate the EVM value.
Since the EVM value reflects the noise performance of the RF link, if the noise floor of the test instrument is too high, it will be superimposed on the signal to be measured and affect the accuracy of EVM measurement results. Generally speaking, the noise level of the instrument is about 10dB lower than that required by EVM specification. For example, the EVM of 11ac 256qam signal shall not be higher than - 32dB, and the noise layer of VSA shall be lower than - 42db to obtain relatively accurate EVM measurement results. The next generation 802.11ax standard requires 1024qam modulation, and EVM must reach - 35dB. The EVM of the above iqxel MW can reach below - 48dB, with a margin of more than 13dB compared with the requirements of 11ax. Therefore, the EVM value of these high-order modulation signals can be measured accurately. In addition to EVM, frequency error and symbol frequency error are also important indicators to measure the quality of mobile phone Wi Fi signal. Test instruments must be used to test these two indicators. EVM index requirements for different modulation orders
An important reason for the interference of Wi Fi signals between mobile phones is the interference between adjacent channels. This interference is mainly caused by leakage of adjacent channels; Adjacent channel leakage ratio (ACLR) reflects the energy ratio of mobile phone transmitter signal leakage to adjacent channels. The higher the ratio, the greater the interference to the mobile phone signal in other frequencies. If the adjacent channels of the mobile phone are not well suppressed, it will cause great interference to the environment, and the retransmission of the whole network will increase, resulting in increased delay and reduced transmission rate. 802.11 standard mainly evaluates the spectrum performance of mobile phone signals through transmission spectral mask. Through the test equipment supporting the transmission spectrum shielding test function, this index of the mobile phone can be evaluated to ensure that the product can reduce the interference to adjacent channels as much as possible in practical work.
The receiver performance of mobile phone is also very important for delay. A good receiver can correctly receive data packets sent remotely. If the reception fails, it will cause retransmission and data rate reduction, resulting in large delay. The main method to evaluate the performance of the receiver is to send Wi Fi standard signals of different modulation coding mechanisms (MCS) from the VSG of the test instrument, and judge the performance of the receiver by measuring the packet error rate (per) of the mobile phone receiver. For VSG, it is required to support a large dynamic range and have high requirements for noise layer.
epilogue
Today, smart phones are almost indispensable in our life, and major smart phone brands are still carrying out technological innovation. However, no matter what new features and functions are added to the smartphone, the Wi Fi component still carries the most network traffic. Therefore, the performance and quality of Wi Fi components affect the use experience of smartphone users and the brand identity of smartphones. This paper analyzes the common Wi Fi quality problems in smart phones from a technical point of view, such as the causes of signal strength, rate and delay; At the same time, from the perspective of testing, it provides mobile phone manufacturers with how to realize complete and accurate testing methods in the manufacturing process, so that mobile phone manufacturers can reduce these quality problems as much as possible.
Search aiban.com and pay more attention. You can master the latest development board, intelligent hardware, open source hardware, activities and other information every day.
Recommend attention“
Our other product:
