4G cascade system framework This technology has a faster data rate and greater system capacity. The target peak rate is: above 1Gbps in low-speed mobile and hotspot coverage scenarios, and 100Mbps in high-speed mobile and wide-area coverage scenarios. The above performance indexes are mainly achieved by two methods: improving the spectrum efficiency and expanding the system bandwidth.
In order to achieve a peak rate of 1Gbps, 4G systems require a system bandwidth of up to 100MHz, but it is almost impossible to allocate 100MHz continuous spectrum in the frequency band below 3GHz, and it is difficult to achieve seamless global coverage and high-speed mobile in high-frequency It is required to deploy a 4G system based on the existing site, so it is difficult to widely use relay and distributed antenna technology), so it is necessary to use part of the spectrum below 3GHz at the same time.
In other words, the 4G system will be a layered system, which requires the use of the above two discrete spectrums at the same time, which forms an important feature of the 4G system.
Cascading 4G system framework
The future 4G system may be composed of a broadband mobile communication (BMC) subsystem and a broadband hotspot access (BHA) subsystem. The BMC subsystem works in a lower frequency band (such as the IMT-2000 frequency band below 3GHz) to provide wide area coverage and high mobility. In order to achieve 4G performance indicators, it may be considered to use a slightly larger bandwidth than E3G, such as 20-40MHz.
The BHA subsystem works in higher frequency bands (such as 3GHz-5GHz may be allocated to the new frequency band of 4G). In order to achieve 4G performance indicators (fixed mobile peak rate 1Gbps), a large bandwidth (up to 100MHz) is required.
The two subsystems should be highly integrated (such as using a similar design) to enable users to flexibly access, schedule, and switch between the two systems. That is, when users are in fixed and low-speed mobile environments and are within the coverage of hot spots, they can access the BHA subsystem to obtain broadband access with high data rates. When the user is outside the coverage of the hotspot or high-speed mobile environment, you can switch to the BMC subsystem. Since the BHA subsystem has covered the center area of ​​the cell, the BMC subsystem can use limited frequency resources for the cell edge area to obtain higher performance.
The coverage of BHA is limited by the propagation characteristics of the frequency band in which it is located, which is about several hundred meters. In dense urban areas, the distance between base stations deployed by operators has dropped to hundreds of meters, and the BHA subsystem can also achieve continuous coverage to a certain extent, but high-speed mobile users in the coverage area should still be carried by BMC.
In general urban, suburban and rural areas, the distance between operator base stations may be extended to more than several kilometers. Without adding new sites, the BHA subsystem cannot provide continuous coverage. The BHA subsystem will only be used in specific areas Provide hotspot broadband access services.
The gap in the BHA coverage area is covered by the BMC. In general urban areas, suburbs, and villages, due to the relatively small restrictions on the construction of new sites, operators may consider installing BHA base stations or relay stations in necessary areas to expand the coverage of BHA subsystems.
Stacked system frame with relay system
Based on the basic system framework, relay technology or distributed antenna systems can be used to extend the coverage of the BHA subsystem. As an extension of the BHA subsystem, the Relay system is also only used for fixed and low-speed mobile users. High-speed mobile users are still provided access by the BMC subsystem.
Relay technology and distributed antenna technology still have many technical problems that need further study. Even if the technical problem is solved, it is difficult for operators to add a large number of new base stations and relay stations (RelayStaTIon, RS), and it is difficult to rely on relays and distributed antenna systems to provide global coverage. Some specific scenes as an effective supplement.
The newly developed 4G new air interface including BMC and BHA subsystems can focus 4G licensed frequency bands on wide-area and metropolitan scenarios covering more than 100 meters, while using existing WLAN and WPAN technical standards to achieve less than 100 meters The local and personal domains are covered, and the heterogeneous interface realizes the intercommunication and switching between the wide area / city area system and the local area / personal area system.
The cascading system framework based on discontinuous frequency bands is determined by the available spectrum characteristics of the 4G system and the actual deployment requirements of the operator (cannot add a large number of new sites). Based on this system framework, there are still a lot of problems to be studied, but it is expected that this will become a basic feature of the 4G system.
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