This section is intended to provide a background to the various embodiments of the technology described in this disclosure. The description in this section may include concepts that could be pursued but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and/or claims of this disclosure and is not admitted to be prior art by the mere inclusion in this section.
Owing to the increasing demand to enhance wireless capacity and the lack of availability of spectrum in the lower frequency range (e.g., from 800 MHz to 3 GHz), the use of frequencies in tens of GHz is being investigated. Investigations explore the high frequency bands, for instance, in the frequencies of 6 GHz, 30 GHz, 60 GHz and 98 GHz for the future mobile networks, e.g., the 5th Generation (5G) networks. At such frequencies, a very large bandwidth of radio frequency band is available. This means both operating frequency and bandwidth for the 5G networks are much higher than those used in the legacy mobile network e.g., the 3rd Generation (3G) and the 4th Generation (4G) networks. However, due to the large signal attenuation with respect to path loss, a network operating over such high frequencies is supposed to cover small areas with densely deployed radio access nodes (ANs). Such a deployment may provide sufficient coverage for indoor/hot areas.
FIG. 1 schematically shows one example of the future mobile networks. As shown in FIG. 1, there is a network node or a control node called as Central Control Unit (CCU), which is responsible for parameter configurations and coordination among ANs or Access Points (APs), e.g., AN1, AN2, AN3, and AN4, or any other radio nodes that enable of covering a certain geographical area (similarly corresponds to a cell in the 3G or 4G). Each AN can serve one or more communication devices, such as User Equipments (UE), operating in the wireless communication networks or systems, also known as e.g., wireless terminals, mobile terminals and/or mobile stations and the like terminal devices. For example, AN1 serves UE1, and AN2 serves UE2, etc.
Spectrum sharing is an important characteristic of the future mobile networks. In order to improve the frequency resource utilization, spectrum sharing may be one important method in the future mobile networks compared to the mainly dedicated frequency resource allocation in the current 3G or 4G networks. Via spectrum sharing, each co-existing network can have the opportunity to use the whole shared spectrum when it has traffic and other co-existing network does not have traffic. Thereby, both the spectrum utilization efficiency and user experience can be clearly improved, compared to simply dividing the whole spectrum into multiple segments and assigning one spectrum segment to each individual network as dedicate frequency resource.
Considering the applicability of spectrum sharing in radio access for the future mobile networks and the inherited benefits of the contention-based radio resource allocation (e.g., higher flexibility and relative lower complexity), contention-based Medium Access Control (MAC) seems promising and may probably be used in the future mobile networks in combination with scheduling based method(s).
As one contention-based radio resource allocation scheme, the contention-based MAC works in a distributed way, where radio resource assignments are decided for each link pair separately. As a scheme similarly as IEEE 802.11, in order to avoid collision, a node which needs radio resource shall send a contention message to claim for resource according to predefined rules. The resource reservation is successful if a peer node accepts the reservation. The contention-based MAC works well when low coordination between cells is needed and is a low complexity solution to allow a diversity of link types. It is well known that contention based MACs are suffering high performance losses when heavy loads are in the system if certain coordination or situational parameter adjustment is not available
The Listen Before Talk (LTB) operating procedure in IEEE 802.11 is one most well-known contention-based MAC protocol. According to LBT, when there is data traffic for a link, the link's transmitter shall firstly listen to or sense corresponding radio resources (e.g., a radio frequency band corresponding to the link, also called as channel) to determine availability of the channel based on the received power over the channel. If the channel is determined to be available, the transmitter can take the channel by starting the data transmission over the channel directly or by using Request To Send (RTS)—Clear To Send (CTS) mechanism.
In the context of the 5G system, further enhancement of a contention-based method is necessary to boost its performance such as a superior and stable Quality of Service (QoS), spectrum efficiency. The Long-Term Evolution (LTE) network usually owns good network controllability by a good network dimension and well defined network controlling functionality, how to optimize the contention based radio resource allocation in 5G scenarios remains as an open issue.