Cloud Radio Building Industry-Best 4G Networks

  • The CoMP Lite technology is used to lower the requirements for bandwidth and delay, and makes the advanced technologies available in popular PTN, IP-RAN, and microwave bearer networks, significantly reducing mobile operators' investment in 4G networks.
  • Cloud Radio Overview

    Cloud Radio is a performance enhancement solution for LTE network. This solution could effectively mitigate the inter-cell interference and significantly improve the performance of LTE networks, especially for the cell-edge performance which has a great influence on user experience. This solution provides high-speed and seamless mobile broadband access experience for users.

    The key technology of Cloud Radio solution is cloud coordination, which introduces differentiated innovative technologies, such as Coordinated Multi-Point (CoMP) Lite and dynamic CoMP, on the basis of CoMP solution. Therefore, this solution can overcome the application limitations of standard CoMP technologies, and can implement inter-site, physical-layer coordination based on the existing PTN, microwave, and other bearer networks.

    Source of Innovation
    Serious Inter-Cell Interference in LTE Networks and Restrictions on CoMP Solutions

    Compared with 2G and 3G networks, the inter-cell interference in LTE network becomes more severe. The reasons are:

    • Co-frequency networking: Compared with the Frequency Division Multiplexing (FDM) GSM technologies and Code Division Multiplexing (CDM) WCDMA technologies, the OFDMA-based LTE technologies have no inborn mechanisms for inter-cell interference mitigation. In addition, due to scarce and expensive spectrum, normally LTE uses co-frequency networking, which makes the interference problem worse.
    • Dense cells: LTE networks aims for high-speed data access, it should give more consideration to satisfied bandwidth than signal coverage. Therefore, LTE sites will become much denser than 3G (only several hundred meters or even less in dense urban areas), which increases inter-cell interference and lowers cell performance.
    • Heterogeneous networking: The heterogeneous network has become a major solution for LTE capacity enhancement. Small cells often use the same frequencies as macro base stations, it does improve capacity while introduce interference at the same time. LTE network performance, especially the cell-edge performance, depends greatly on interference mitigation and elimination technologies.
     
    • The interference in large-scale commercial LTE networks is more serious than expected, while standard CoMP solutions are limited by mobile backhaul conditions.
    • Insufficient attentions on interference: The interference in LTE network is not obvious when the traffic is light. With the scale application of LTE service, the rapid growth of LTE traffic will dramatically increase the interference and worsen system performance, and the Inter-Cell Interference Coordination (ICIC) technology is not enough to solve the complicated interference problems.
    • Limitation of standard CoMP applications: The commercial LTE Networks use diversity bearer networks, transmission bandwidth start from tens of Mbps and end with fiber-to-the-site (tens of Gbps). Standard CoMP solutions can achieve the best coordination performance in fiber-to-site scenario, but this requirement is much higher than the performance of existing bearer networks. Therefore, Stand CoMP solutions can only be used in very limited scenarios.
     Inter-Site Coordination Is More Important for Improving User Experience
    • Intra-site coordination is not enough for seamless moving user experience.

    Standard CoMP solutions have high requirements on the bandwidth and delay performance of bearer network, normally is only implemented inside a site. Intra-site coordination mainly improves the performance of a single base station; there are still lots of performance troughs among multiple sites, so user experience fluctuates greatly when users move across the network.

    •  Inter-site coordination is more important than intra-site coordination.

    Cell-edge performance has obvious affects on network KPIs, such as the access success rate and the Dropped-Call Rate (DCR) during handover. Therefore we should focus on inter-site (cell-edge) coordination. A small improvement of the cell-edge performance will bring significant changes in user experience, while further improvement of cell-center performance cannot evidently enhance user experience.

    Highlights and Benefits of Cloud Radio

    As a leading vendor of wireless network solution, ZTE launched the innovative Cloud Radio solution at the Mobile World Congress held in Barcelona in February 2013.

    Cloud Radio solution breaks the limitations of standard CoMP technologies on mobile bearer networks. For example, the CoMP Lite technology is used to lower the requirements for bandwidth and delay, and makes the advanced technologies available in popular PTN, IP-RAN, and microwave bearer networks, significantly reducing mobile operators' investment in 4G networks.

    With ZTE's innovative Cloud Radio solution, operators can solve LTE network interference problems with lower costs and provide users with beyond 4G access performance.

     

    Flexible Adaptation to Existing Mobile Bearer Networks, Lowering LTE Network Deployment Costs

    • Popularization of advanced coordination technologies: By using the innovative CoMP Lite, scheduling in advance, Joint Transmission (JT), and Coordinated Scheduling (CT) technologies, Cloud Radio solution can significantly reduce the requirements for bandwidth and delay of mobile bearer networks, and frees CoMP from intra-site and intra-BBU-pool scenarios. I.e. Cloud Radio technologies will no longer depend on dark fibers, and are adaptable to multiple existing IP bearer networks.
    • Dynamic adaptation to mobile bearer conditions: Cloud Radio solution supports IP-based coordination data exchanging, and is adaptable to mobile network conditions through multi-level cloud coordination mechanisms. Cloud Radio solution can help carriers deploy the most suitable coordination solutions according to the available bandwidth of microwave, MPLS, and PTN bearer networks. In addition, the elastic bandwidth mechanism allows for reliable operation of cloud coordination technologies even in case of sharp fluctuations of bearer network performance. Therefore, Cloud Radio solution has a higher environmental adaptability compared with standard solutions.
    • The highest coordination profit with Lowest bearer cost: ZTE's adaptable cloud coordination technologies make possible independent LTE access network construction and bearer network upgrade, and can achieve the best wireless coordination performance with available bearer resources in any stage. Therefore, operators do not need to invest heavily in bearer network construction in the initial stage of LTE deployment but can use the existing bearer networks to make more profit from performance improvement. With ZTE's Cloud Radio solution, operators can achieve the coordination performance in PTN bearer networks similar to that achieved in dark fiber bearer conditions.  

     

    Dynamic Coordination for High-Speed and Seamless User Experience

    Static coordination clusters are required for standard CoMP technologies, and the coordination cluster size is limited. Although fairly good coordination performance can be achieved inside a coordination cluster, user experience decreases sharply when users go across the borders of coordination clusters.

    Cloud Radio solution uses dynamic coordination scheme, which implements seamless coordination in both macro-macro scenario and macro-micro scenario. This solution provides high-speed wireless access and the best static and mobile user experience.

    Innovative Applications of Cloud Radio

    Cloud Radio solution is applicable to both popular distributed base station construction scenario and the C-RAN deployment scenario (centralized baseband pool). The main highlight of this solution is rapid deployment based on the existing mobile bearer networks.

    Here are the field test results of Cloud Radio solution in commercial LTE networks.

     
    Tianhe Business District of Guangzhou: the First Show of Cloud Coordination

    During the Cloud Radio test in the Tianhe Business District of Guangzhou, ZTE easily achieved the network-level inter-site cloud coordination function without making any modifications in third-party PTN transmission networks, which is the first in the industry. Take joint reception for example, the bearer bandwidth required by standard LTE-A solutions is several Gbps, and the delay must be less than several hundred microseconds.

    ZTE's innovative Cloud Radio technology requires a bandwidth of only several hundred or tens of Mbps, and the delay can vary from several hundred microseconds to several milliseconds. Therefore, ZTE's solution does not need dark fiber transmission resources or bearer network upgrade/reconstruction but uses the spare bandwidth in exiting IP bearer networks to bring considerable performance profit for operators.

    The test result shows that, after using ZTE's inter-site cloud coordination technologies, the probability of the throughput being lower than 2 Mbps decreased from 8% to 1%, and that of the throughput being lower than 4 Mbps decreased from 20% to 8%. The throughput of the 5% users with the lowest access rate increased by 300%, and that of the 10% users with the lowest access rate increased by 100%. This solution reduces inter-site interference and improves user performance significantly in JT, CS, and JT/CS adaptation situations.

    The experts and leaders from the China Mobile Research Institute were satisfied with the test result of the Cloud Radio solution, and relevant coordination functions have been written into the technical bid specifications of China Mobile.

    Huaqiao University in Quanzhou: Practice of Multi-User Test in Commercial Networks

    If the field test in Guangzhou is a good start, the test in Huaqiao University in Quanzhou is really a practice of the large-scale commercial use of the Cloud Radio solution. The field test in Quanzhou involving more than 10 TD-LTE base stations and 20 users tested the uplink and downlink performance on specific spots, and verified the mobile access performance.

    In the field test in Huaqiao University, the cloud coordination had extremely low requirements (for example, a maximum bandwidth of 5 Mbps and a delay of less than 4 ms) for bearer networks, and did not need reconstruction or upgrade of transmission networks. Therefore, this solution can achieve inter-site cloud coordination and make significant profit from performance improvement at the lowest network expenses.

    In a scenario with 100% load of serving cell and 50% load of neighboring cell, which is similar to the commercial scenario, when CoMP is enabled, the UE throughput increased by a maximum of 237.4%, the average edge UE throughput increased by 92.7%, and the average cell throughput increased by 19.5%.

    During the downlink driver test with 100% load, the throughput of 5% of the mobile users at the edge increased by 161.5% on average.

    During the uplink mobile test with 100% load, the throughput of 5% of the mobile users at the edge increased by 146.7% on average, and the average cell throughput increased by 2.8%.

    In addition, Cloud Radio solution is completely compatible with commercial R8 terminals, and allows users to enjoy the performance of LTE-A in the initial stage of commercial LTE use, seizing the technical advantages and market opportunities of commercial 4G use.

     
    Dense Urban in Tianjin: Large-Scale Commercial Use of Cloud Radio Coming Soon

    The field test in Tianjin involved over 30 base stations and 100 cells, and covered the most densely populated area of Tianjin, including skyscrapers, residential buildings, roads, pedestrian zones, plazas, shopping malls, and CBDs. In this area, wireless environment is very complicated, for example, the antennas are at different heights, the inter-cell interference is severe, and the cell overage is highly overlapped. In addition, Tianjin Mobile started to issue TD-LTE numbers half a year ago, and has nearly 20,000 active users, providing favorable conditions for verifying the Cloud Radio performance.

    During the outdoor test, after the cloud coordination function was enabled, the throughput of edge users increased by 20% to 80%. Because indoor signals are weaker than outdoor signals, after the cloud coordination function was enabled during the indoor test, the throughput of edge users increased by 40% to 150%. In both outdoor and indoor environments, the higher the neighboring cell interference, the more obvious the coordination gains of edge UEs.

    During the outdoor driving test, the CDF of mobile UE indicated that the Spectrum Efficiency lower than 1 decreased from 70–80% in a normal environment to 10–15% in a 70% load environment. Namely, after the cloud coordination and ICIC functions were enabled, the proportion of UEs with low throughput decreased by 4–5 times.

    In addition, the field test in Tianjin also tested the driving performance in different network load conditions, providing valuable experience for large-scale commercial use of the Cloud Radio solution.

    Summary

    • Cloud Radio solution, which helps operators obtain better access performance than that of 4G networks at the lowest bearer expenses, makes ZTE occupy a favorable position in the market competition of 4G networks, and is the best choice for mobile operators in the 4G era.
    • The innovative Cloud Radio solution is by far the most advanced 4G network enhancement solution, which makes ZTE rank as one of the top providers again in the industry in wireless product competitiveness.

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