MSA: Key Technology for future evolution of Wireless Networks

With the continuous development of wireless networks, multi-Stream Aggregation (MSA, Multiple Stream Aggregation) can improve the edge throughput by 500% through deep fusion of Multi-standard, multi-carrier and multi-layer networks, realizing the concept of borderless networks enables users to enjoy high-speed and stable data access services wherever they are on the network. It will become a key technology for network evolution in the future.

The popularity of smart terminals and the rapid development of mobile broadband have led to explosive growth of mobile data services. The industry predicts that the global mobile data business volume will grow exponentially over the next decade, which will bring an unprecedented impact to the current network.

Challenges facing the current network

The current network is usually deployed in a single layer, that is, different wireless Access technologies (RAT, Radio Access Technology), such as GSM, UMTS, LTE, and Wi-Fi, independent deployment and management, and network access through different core network devices. At the same time, users can only transmit data with a single node in one type of RAT, which leads to problems such as insufficient wireless resource utilization, repeated investment in network infrastructure, and further improvement of network capacity.

Although HetNet is currently a typical application scenario for improving network capacity, as the number of small sites increases, more and more "community edges" will emerge in the future ", frequent switching, increased failure rate, and reduced throughput of edge users are becoming more and more prominent, all of which have an impact on user experience. Therefore, problems such as mobility, interference, and resource utilization are the main challenges facing the network.

Mobility

With the intensive deployment of HetNet, the number of small sites is gradually increasing, and frequent switching and ping-pong switching will continue to emerge. Generally, the signal transmission characteristics of the station and the macro station are different due to the low deployment location of the station antenna. As the distance increases, the signal attenuation of macro stations is slow. After the deployment of the station, although the signal strength in the vicinity of the station is significantly improved, as the distance from the station increases, the signal will quickly decline, and in severe cases, the user will drop the call.

In short, the Failover failure rate in the HetNet scenario is generally higher than that in the traditional homogeneous scenario (only macro stations are deployed) due to the fast-fading feature of small station channels and the interference caused by the introduction of small stations) the failover failure rate in the scenario, especially when the user switches from the station to the macro station.

Interference

If a small station is deployed within the coverage range of the macro station, because of the same frequency interference of the macro station, the coverage of the small station will obviously contract, that is, the closer the small station is to the macro station, the smaller the coverage range is. For example, if a small station is deployed on the edge of the macro station, its coverage can reach more than MB. If a small station is deployed on the center of the macro station, then its coverage can only reach dozens of meters or even dozens of meters. In addition, due to the presence of co-frequency interference, user throughput will also be significantly reduced.

Resource Utilization

Generally, there are always different business requirements between macro stations and small stations at different times and geographic locations. In the traditional HetNet scenario, resources cannot be shared among different sites, resulting in insufficient resource utilization and different user experience on different sites.

Macro stations have a large coverage and can absorb more users. Therefore, the load of macro stations may be heavier, which leads to a low throughput of macro Station users, especially for the edge users of macro stations, their user throughput is lower because they are far away from the macro station and are also affected by the interference of small stations with the same frequency. For a small station, because of the constraints of coverage, the number of users it absorbs is small, and the load is light, so the throughput of users in the small station is high. Therefore, the user experience of the macro site is obviously different from that of the small site.

Key Technology for future wireless network evolution-MSA

With the continuous development of wireless networks, MSA uses multi-standard, multi-carrier, and multi-layer networks for in-depth integration, it can effectively solve the problems of mobility support to be improved, prominent interference problems, and low resource utilization in the current network, thus greatly improving the edge throughput and realizing the concept of borderless network.

In the future, wireless networks will combine network layering with MSA to enable users to enjoy high-speed and stable data access services no matter where they are on the network, ultra-broadband, zero-wait, and ubiquitous connections bring high speed, high quality, and simple and free sharing business experience. Network layering refers to a multi-Layer network architecture, including Host Layer and Boosting Layer, as shown in 1. The Host Layer is mainly used to ensure network coverage. It establishes a Host link to provide signaling and data transmission, and provides ubiquitous connections to ensure reliable basic user experience; boosting Layer is mainly used to increase network capacity. It establishes a Boosting link to provide users with data transmission for the best user experience. The MSA is a key technology for organically aggregating Host Layer and Boosting Layer. It provides multi-stream aggregation through multiple nodes, further enhancing user experience and network capacity, this technology has been widely recognized by the industry and is gradually supported by 3GPP R10 and has become a hot topic in the current standard discussion.

Network entities on the RAN side, such as the BBU pool or SRC (Single Radio Controller), can be used as the central control node of the MSA to implement unified control functions, in this way, network layers, data delivery, and coordination and scheduling are better implemented.

Host Layer: ensures reliable basic user experience

The Host Layer can effectively solve the mobility and interference problems faced by the current network.

In the same-frequency scenario, the Host Layer can adopt the network deployment mode with the same Cell ID. Different Nodes use the same Physical Cell ID (PCI, Physical Cell Identifier) to avoid the same-frequency switching; in scenarios with different frequencies, such as multi-carrier or multi-standard scenarios, the Host Layer enables users to always attach to the macro station, that is, no matter how the user moves within the coverage of the macro station, always maintain the Host link between the user and the macro station to avoid abnormal frequency switching.

After network layering, interference can be further divided into intra-layer interference and inter-layer interference. Coordinated scheduling can be used to solve intra-Layer interference. For example, for sensitive users, the Host Layer can coordinate neighboring area scheduling to reduce interference. Time-Frequency resource separation can be used to solve inter-Layer interference. For example, a part of time-Frequency resources are reserved for SFN (Single Frequency Network) transmission between different nodes of the Host Layer to achieve optimal coverage, other Time-frequency resources are reused across nodes to achieve optimal efficiency. In other words, different layers reduce inter-layer interference by ensuring resource independence.

The Host Layer ensures the continuity of user services by avoiding switching. It reduces interference and increases user throughput, thus ensuring a reliable basic user experience.

Boosting Layer: provides the best user experience

MSA is a key technology for organic aggregation of Host Layer and Boosting Layer. It further covers Intra-frequency MSA, Inter-frequency MSA, and Inter-rat msa for different application scenarios.

Intra-frequency MSA: uses multiple same-frequency nodes to provide multi-stream convergence for users

In traditional HetNet scenarios, users can only transmit data with a single attached node, and system resources cannot be fully utilized. In the future, the network can use the Intra-frequency MSA technology to enable users to dynamically transmit data with one or more optimal nodes to achieve multi-stream convergence between nodes at the same frequency, achieve the best user experience. In the same-frequency MSA, data transmission nodes are transparent to users. Even in scenarios with different cell IDs, no signaling overhead is required to maximize the use of system resources, it can better solve the problem of insufficient resource utilization in the current network and achieve consistent user experience.

In addition, Intra-frequency MSA uses some advanced algorithms to improve edge throughput by 200%, including: CS-PC (Coordination Scheduling Power Control ), implement interference management through Coordinated scheduling power control; CLB (Coordination Load Balance); improve spectrum efficiency through adaptive Coordination of Load balancing; CoMP (Coordinated Multi-Point ), dynamic node selection or joint Transmission Based on Real-Time Channel Changes to achieve service load balancing.

Inter-frequency MSA: uses multiple different frequency nodes to provide multi-stream convergence for users

In traditional HetNet scenarios, when a user moves between a macro station and a small station, the abnormal frequency switching is triggered, which may affect the user experience. In the future, the network can use Inter-frequency MSA technology to ensure that users are always attached to the macro station, that is, the Host link is always maintained between the user and the macro station, and the best small station can be dynamically selected, use the Boosting link between the user and the best small site to distribute macro station data. For users, multi-stream convergence between different carriers is formed, which further improves user experience and network capacity.

According to the delay characteristics of backhaul link between the macro station and the small station, Inter-frequency MSA is divided into two scenarios: Ideal backhaul and non-ideal backhaul. The ideal backhaul indicates that the transmission latency between the macro station and the small station is negligible. The unsatisfactory backhaul indicates that the transmission latency between the macro station and the small station cannot be ignored. It is worth mentioning that, in the non-ideal backhaul scenario, data streams on different carriers of different nodes can be flexibly aggregated, which is one of the core hotspots of 3GPP Rel-12 standard and has been widely concerned in the industry.

Inter-rat msa: provides multi-stream aggregation for users using multiple nodes of different standards

Multi-stream convergence (Inter-rat msa) of different standards is a key technology to achieve the integration of different standards. The Host Layer can be UMTS or LTE, And the Boosting Layer can be LTE or Wi-Fi.

Take the scenario of LTE and Wi-Fi integration as an example. LTE, as the Host Layer, is used to provide coverage, ensure that the Host link between the user and the macro station always exists, and ensure reliable basic user connections. Wi-Fi is used as the Boosting Layer for capacity improvement, the Boosting link between the user and the Wi-Fi improves the transmission rate to achieve the best user experience.

During network deployment, the downstream traffic of most data services far exceeds the upstream traffic. However, the transmission resources of the cellular network are basically symmetric between the upstream and downstream traffic. Therefore, the downstream data transmission of the cellular network needs to be enhanced. In addition, due to problems such as access conflicts, hidden terminals, and QoS in the uplink of the Wi-Fi network, these problems will deteriorate sharply as the number of users increases. Based on the above considerations, Huawei believes that the most efficient transmission solution is to use Wi-Fi for downstream data transmission, that is, based on factors such as channel, network load, and interference conditions, by using the newly defined control entity src on the ran side, the downlink data on the Host link of the honeycomb can be flexibly distributed to the Boosting link of Wi-Fi, which improves the user's peak experience exponentially, in addition, the network capacity can be greatly increased.

Currently, based on the above solutions and technologies, Huawei has implemented the MSA technology using the existing product platform, and successfully verified the User Experience Improvement brought about by the integration of network layering and MSA technology in the field, it truly realizes the concept of borderless networks in the future.

Figure 1 network layering and MSA convergence in wireless networks in the future