Spectrum resources are the most precious resources in wireless communication. Due to stratospheric traffic increases, spectrum utilization encounters technical bottlenecks with current wireless technologies. Improving spectrum efficiency has become a problem to be settled urgently.

Upgrading communication technology is like upgrading the highway (communication pipeline), in both cases you seek traffic improvement, that is more vehicles (data) within the unit time. To achieve this, the following methods can be used:

1. Expand highways, for example, expand two-lane highways to eight-lane highways.
2. Change the original two-lane highways to elevated highways with the upper and lower decks.
In telecommunications, expansion means a new device and network deployment, which requires high investment.

If you reduce the car size or improve the top speed of cars, you can ensure that more cars can pass through within a time unit. In the communication field, this method means mobile phone modification to ensure that mobile phones can receive more data. However, the basic architecture of existing mobile phones is fixed and hard to be changed. In addition, once sold, a mobile phone will be used for several years and so won’t conform to 5G standards and won’t contain compliant mobile phone chips. Therefore, this solution is also not feasible.

ZTE put forward the Space Division Multiple Access (SDMA) technology first, which enables traffic improvement without highway (communication network) expansion or car (mobile terminal) modification.

SDMA: The Only Technology to Multiply Spectrum Efficiency
To solve the spectrum problem, the common view in the industry is to explore technologies that can improve spectrum efficiency. The 3G and 4G communication systems have already reached the noise limit and single-link Shannon capacity. In theory, the spectrum efficiency cannot be dramatically improved. The Code Division Multiple Access (CDMA) technology of 3G networks ensures multi-channel communication at the same time, frequency, and space. However, the CDMA technology uses orthogonal codes to distinguish users.

Multiple orthogonal codes form a self-interference system. To meet orthogonal requirements, all users need to cut down their transmission rates. That is, if N users communicate at the same time, each user can use 1 transmission rate at most for communication. Therefore, the CDMA technology cannot maximize spectrum efficiency. Its theoretical spectrum efficiency is the same as that of Time Division Multiple Access (TDMA). However, the SDMA technology ensures that users do not need to cut down their transmission rates when multiple users communicate at the same time. In this case, the spectrum efficiency is improved by multiple times.

The SDMA technology divides the space to form different beams in different directions through the adaptive antenna array. Each beam provides a unique channel without other user interference. In this case, the same frequency band can be multiplexed in different space. This is similar to the cars running on the same carraigeway at the same time without affecting each other.

"SDMA is the only technology to multiply spectrum efficiency. Because it ensures multi-channel communication at the same time, using the same frequency band, and in the same macro physical space without interference, which maximizes limited spectrum resources." said Doctor Xiang Jiying, ZTE chief scientist. "The SDMA technology divides the space to form different beams in different directions through the adaptive antenna array. Each beam provides a unique channel without other user interference. In this case, the same frequency band can be multiplexed in different space. This is similar to the cars running on the same driveway at the same time without affecting each other. In this case, traffic can be improved without highway (communication network) expansion or car (mobile terminal) modification."

Currently, SDMA is widely recognized by the industry as a trend for spectrum efficiency improvement.
ZTE started to study this SDMA technology in 2013, making them the first company to do so. Currently, ZTE has successfully applied this technology to TDD and FDD networks and has leveraged their first-mover advantage.

ZTE 5G Technologies: Leading in the Industry and Solving Industry Problems
According to the planning of international communication organizations and government agencies, 5G communication technology will be commercially used in about 2020. However, 4G networks are still being deployed in many areas and the deployment may be just completed in 2020. This brings a new challenges for communication equipment vendors.

5G networks cannot be deployed at one moment in time. Due to high-speed traffic increases, operators will upgrade their live networks continuously to ensure gradual network evolution.

Massive MIMO is one of the SDMA technologies and was first introduced by ZTE in pre-5G and key 5G technologies. Based on its leadership in SDMA technologies, ZTE developed TDD Massive MIMO and FDD Massive MIMO and tried to put them into commercial use.

In June 2014, ZTE was the first to put forward the pre-5G concept. By heavy optimization on the base station side, pre-5G ensures that users enjoy 5G network experience without changing their terminals, improving network competitiveness of operators. To operators, pre-5G can be smoothly upgraded to 5G on the base station side without investment waste.

In 2015, TDD-based pre-5G Massive MIMO completed product development and field tests. Commercial products are selected by multiple well-known operators for commercial use testing and deployment. This solution was first applied to commercial use by SoftBank. Sun Zhengyi, CEO of SoftBank, said "TD-LTE enables us to obtain major success" at the GTI conference held in February 2017 and pointed that Massive MIMO is an important method for evolving TD-LTE to 5G.

In February 2016, ZTE pre-5G Massive MIMO was awarded Best Mobile Technology Breakthrough and Outstanding overall Mobile Technology—The CTO’s Choice 2016 at MWC 2016 in Barcelona. It is the first time in the GSMA award history that 5G core technologies obtained these awards. In this case, a large number of FDD LTE operators are looking forward to utilizing FDD Massive MIMO.

Breakthrough: Bringing Massive MIMO to FDD Networks
About 85% of mobile network operators around the world have adopted FDD technology. However, multi-antenna space division on FDD networks faces tremendous difficulties. In FDD-LTE mode, different spectrum resources are used in the uplink and downlink and channels are not reciprocal. That is, signal change viewed in the uplink is inconsistent with that viewed in the downlink. This is because the uplink and downlink phases change randomly. The traditional view is that mobile phones need to proactively measure downlink signals sent by base stations on FDD networks and then send messages to base stations to form closed-loop MIMO on the base station side.

However, a Massive MIMO base station has dozens of antennas. If base stations send the antenna information to mobile phones and the mobile phones report information to the base stations after measurement, more than 100% of the resources need to be occupied according to the existing 4G mechanism. Therefore, bringing Massive MIMO to FDD networks becomes one of the core challenges.

Based on accumulation in TDD Massive MIMO, ZTE broke down a large number of technical barriers after one year of effort. ZTE developed the FDD-based patent channel algorithm. With strong processing capabilities of self-developed baseband processing chips, software algorithm breakthrough, and hardware capability improvement, ZTE successfully applied Massive MIMO technology to FDD-LTE networks. The traffic is increased by multiple times, and users did not need to change terminals. FDD Massive MIMO provides a comfortable way for hundreds of global FDD operators to deliver 5G and a new evolutionary path and development space for existing 4G networks. Its value and significance are impossible to evaluate.

Constructing the Bridge from 4G to 5G
Even though the final 5G standard has not been determined, the general direction is clear. High and low frequency combinations and gradual commercial adoption are widely accepted in the industry. In low frequency bands, only the SDMA technology can be used to improve the spectrum efficiency. The coverage area of high frequency bands is small, and the SDMA technology also needs to be used to improve coverage, which is actually a degenerated version of SDMA. Therefore, for 5G networks, both high and low frequency bands greatly depend on the SDMA technology.

Currently, more than 60 pre-5G networks are deployed in 40 countries around the world, including leading multinational operators, such as SoftBank, Telefonica, Hutchison, VEON, Telenor, Singtel and three major national operators (China Mobile, China Telecom, and China Unicom).

Application of key 5G technologies, such as ZTE’s Massive MIMO in existing mobile network 5G scenarios is enabling ZTE to obtain commercial use experience and actual test data in multiple network scenarios. In this case, ZTE can solve technical and application problems during commercial use in advance, accelerate maturity and optimization of 5G core technologies, and shorten the period for product verification and scale commercial use. In this process, ZTE has applied for hundreds of technical patents and provides multiple valuable solutions to standards organizations based on massive data in actual scenarios. Pre-5G brings benefits to 4G networks and existing users and provides commercial use reference for future 5G developments, constructing the bridge from 4G to 5G. Pioneer advantages in scale commercial use of pre-5G Massive MIMO positions ZTE in a strong position for 5G.

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