With the rapid development of mobile broadband, wireless operators' demand for spectrum resources has increased accordingly. However, the paired new LTE FDD spectrum will become increasingly difficult to obtain and expensive, and the operation of the two networks TD-LTE and LTE FDD will gradually become an important networking method for increasing network capacity in the future. The gradual listing of terminals that simultaneously support TD-LTE and LTE FDD also provides a powerful guarantee for the operation of the two networks.
However, in actual operation, we also need to consider the priority of TD-LTE and LTE FDD when switching between different frequencies, so as to flexibly control the priority of the terminal to switch to the TD-LTE network or LTE FDD network, to achieve interoperability between the two networks Complement each other ’s advantages and improve resource utilization.
Introduction to TD-LTE FDD Interoperability Technology
Since the handover signaling and flow defined in TD-LTE and LTE FDD are the same, the corresponding interoperation between TD-LTE and LTE FDD, such as handover or reselection, is basically equivalent to that in LTE FDD or TD-LTE system. To switch or re-select.
The main process of TD-LTE and LTE FDD network handover operation is that when the handover has a trigger condition, the end user performs handover related measurements and reports to eNodeB (Evolved NodeB, Evolved Network Base Station). The eNodeB judges whether the handover conditions are met based on the measurement results If it is satisfied, a handover instruction is issued to enable the user to make handover selection between the TD-LTE and LTE FDD networks.
Huawei is the first to implement flexible interoperable solutions
According to operators' different positioning and network deployment strategies for TD-LTE and LTE FDD networks, Huawei provides a wealth of interoperable solutions. User interoperability scenarios between standards are mainly classified according to terminal working status, business requirements, load status, and coverage.
(1) When the user is in the idle state, there are the following solutions for different scenarios:
Priority-based camping: Operators can choose which network users prefer to camp on based on the two-standard network deployment strategy. For example, LTE FDD is a macro coverage network, and hot spots use TD-LTE to absorb traffic. Then the dual-mode terminal preferentially resides in the LTE FDD network in the network. When the LTE FDD network load is higher than a certain limit, the eNodeB can camp the terminal on the TD-LTE network according to the preset system parameter configuration.
LTE FDD coverage-based bidirectional reselection: Assuming that the terminal is idle in the TD-LTE network, when leaving the TD-LTE coverage area and entering the LTE FDD Only coverage area, the terminal will reselect and camp on the LTE FDD network on. Otherwise, the terminal moves from the LTE FDD area to the TD-LTE FDD overlapping coverage area, and the terminal will reselect and camp on the TD-LTE network.
Based on user type SPID (Subscriber Profile ID: user profile code) residency: TD-LTE FDD dual-mode terminal configures an SPID when signing up. When the terminal user performs cell reselection, the eNodeB can configure the user's default residency according to its SPID information Stay on the network.
(2) When the user is in the activated state, according to different network coverage conditions, load conditions, service types, etc., there are the following corresponding schemes:
Coverage-based active state switching: When the terminal active state leaves the TD-LTE coverage area and enters the LTE FDD coverage area, the eNodeB terminal switches from the TD-LTE to the LTE FDD network, and vice versa.
Load-based active state switching: In overlapping coverage areas, there may be a situation where one network load is high and another network load is low. At this time, load-based switching is required to achieve the most efficient TD-LTE and LTE FDD network utilization good. The system will dynamically schedule user switching between TD-LTE / LTE FDD networks to maintain load balance between the two networks.
Service-based active state switching: Select a network with higher priority according to the type of service. For example, only data services will select the TD-LTE network first, and voice services will switch to the LTE FDD network first.
Operators can flexibly combine various strategies according to different scenario requirements to effectively improve the utilization rate of the TD-LTE and LTE FDD networks, and make full use of the TD-LTE and LTE FDD network resources to coordinate the load, enhance coverage, and improve user access to the network Experience, realize the smooth transition of switching between different networks.
The TD-LTE FDD interoperability solution has an interruption delay of less than 100ms at the service level, and users are basically unaware of PS (Packet Service, packet service) domain services. There is no difference between TD-LTE and LTE FDD switching delay analysis from the standard level. Compared with LTE FDD inter-frequency switching delay, the delay increases by about 10ms.
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