Cloud radio - a new chapter for wireless

Chen Zhiping and Duan Xiaowei
15 Jul 2013

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History review: SDR led Multimode Network Convergence
In 2008, ZTE took the lead in releasing the Software Defined Radio (SDR) base station system in the mobile communications field. The biggest difference between an SDR base station and a traditional base station is that the baseband unit of an SDR base station has flexible multimode capability, and the function of RF unit is re-definable via software reload. Thus, one hardware set could support multiple wireless standards, or supports smooth evolution from 2G to 3G/4G standard, allowing the coexistence of multiple standards and multiple bands. As a result, the network structure is obviously simplified and the network Total Cost of Ownership (TCO) is greatly reduced.

The SDR base station system was like a shining star, attracting great attention in the mobile communications field. It was intensely reported by news media in the world, and highly praised by third-party analysts, and operators were deeply impressed by ZTE’s technical strength. SDR brought ZTE’s wireless access network into an era of advanced competitiveness. Undoubtedly, the release of SDR had an unprecedented impact on the competitors’ market, arousing criticisms and debates, such as “what is the real SDR?”, and “what is the better choice? SDR, Multiple Standard Radio (MSR), or Multiple Band Radio (MBR)?” We could understand the reasons behind these questions, but the honors and the delivery data have proven that SDR is invincible.

In contrast, ZTE’s competitors including Ericsson, the leading vendor in mobile communications industry, launched dual-mode baseband modules or RF products after SDR, and multimode and multi-band products began to appear in their market roadmaps. Today, multimode capability and smooth evolution have become the basic technical requirements of operators. A series of successful stories have proved that the SDR technology fully met operators’ demands with a forward-looking perspective; nowadays it’s still an attractive solution in multimode convergence.

Since SDR was put into large-scale commercial use, ZTE has never stopped the pace of wireless innovation. C-RAN, Active Antenna System, TD-LTE and FD-LTE converged network solutions are walking in the forefront of the industry.

Look into the future: Cloud radio is writing a new chapter in wireless innovation
With the step-by-step commercial use of LTE networks in Europe, America, and Asia Pacific, ZTE predicts that mobile operators will soon face the following problems:

Same-frequency networking, dense sites, and heterogeneous networking will make the interference problem in LTE networks more complicated. With large subscriber base, the interference problem in LTE networks will be much worse than what we have expected. Dealing with the problem by just relying on standard Inter-Cell Interference Cancellation (ICIC) and enhanced Inter-Cell Interference Cancellation (eICIC) becomes powerless.

From the perspective of user experience improvement, inter-site users suffer much severe interference problems than the intra site-uses, so they should be put in the first priority when we do the coordination. However, the biggest problem of existing collaboration technologies (such as 3GPP Joint Reception) is that they demand very high transport bandwidth and low latency while this is not always available in the real deployment scenario, so the standard coordination technologies apply only in the intra-site case or centralized baseband deployment scenario, not the more common distributed site case. Thus most of the interference cancelation technologies are “seemed”, while UE is naturally “seamless” roaming.

Is there an innovative solution that can efficiently solve the interference problem of LTE networks, and break through the limitation of the existing collaboration technology, to improve network performance significantly, especially the cell edge performance with little increase in bearer network investments?

In February 2013, Mobile World Congress, ZTE officially released its 4G-oriented wireless innovation, Cloud Radio solution. This solution can implement cloud scheduling and cloud collaboration based on any existing IP bearer network, to effectively suppress network interference, improve network performance, especially cell-edge performance, and achieve seamless user experience with existing transmission resource.

The Cloud Radio solution has two major innovations: cloud collaboration and cloud scheduling.

Cloud collaboration, through the multi-level collaboration mechanism, and the boundlessness collaboration concept, can intelligently select the best collaborative mode, dynamically adapt to transmission conditions of the bearer network, and “translate” the wire line bearing bandwidth to the wireless coordination performance to the maximum extent. In this way, the overall network performance is enhanced, and the cell-edge user performance is nearly doubled, allowing users to enjoy smooth experience in the LTE network, very similar to the softer-handoff experience in 3G network.

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