Increasing terminal antennas is one of important means for improving spectral efficiency to further enhance a network capacity, and currently increasing terminal antennas is mainly limited to the following several aspects:
1. Terminal volume: a device that currently accesses a cellular network is mainly a handheld device, for example, a mobile phone, and limited by a size of the device that currently accesses the cellular network, an application of a multiple-antenna technology is limited on a terminal side.
2. Antenna coupling and channel relevancy: Within a limited volume, arranging multiple antennas that work in a same frequency band may result in coupling enhancement between the antennas and channel relevancy enhancement, which degrades system performance. On the other hand, the channel relevancy enhancement may reduce a quantity of layers for spatial multiplexing, and therefore, improving of the spectral efficiency is limited.
3. Because of an application of carrier aggregation, a cellular frequency band presents a polarized development. On one hand, a high frequency band is applied to a cellular frequency band to improve the spectral efficiency. On the other hand, an application of a low frequency band (for example, a frequency band released by an analog television) enlarges an antenna size, and further reduces a quantity of antennas in a single device.
4. Another limitation of multiple antennas on the terminal side is costs of a radio-frequency channel.
A terminal coordinated communication solution is a solution in which increasing a quantity of (virtual) antennas is implemented by a terminal by means of antenna sharing and coordinated communication. The terminal coordinated communication solution can break the foregoing several limitations, and can improve and enhance the system performance. In a communication process, a terminal with a service is referred to as a benefited terminal, and a terminal that assists the benefited terminal in performing communication is referred to as a supporting terminal, where the supporting terminal shares an antenna of the supporting terminal with the benefited terminal.
On one hand of the terminal coordinated communication solution, by means of collaboration between terminals, a spatial dimension that can be used on the terminal side can be effectively enhanced, and a system capacity is enhanced. On the other hand, by means of collaboration between terminals, interference from an adjacent terminal can be effectively suppressed, and transmission quality is improved. What is different from coordinated transmission on a network side is that there is no high-speed optical fiber or another dedicated transmission link between terminal nodes for completing interaction of shared information. Generally, for information sharing between the terminal nodes, information transmission needs to be completed by using an air interface link. Currently, main standardization organizations including 3GPP (Third Generation Partnership Project) have already started research and standardization work of D2D (device-to-device) direct communication. A continuous development of a near field communication technology such as WiFi (Wireless Fidelity) has brought near field transmission into a G-bit era. These provide a reliable transmission solution for direct information interaction between terminals.
In addition, a product based on wireless communication is increasingly popularized, each user concurrently has multiple terminals (single-user multi-terminal) that can access the cellular network, and when an antenna of each terminal is idle, the antenna may be used to collaborate with another terminal in communication.
In an implementation process of the foregoing terminal collaboration solution, when each UE (terminal device) sends an uplink signal to a base station, because positions of all UE and the base station are different and multipath paths that all the UE passes through are different, when different UE sends uplink signals at a same moment, the signals received by the base station cannot be aligned (that is, signals from all the UE arrive at the base station at different moments), and this phenomenon may cause interference between terminals. To avoid occurrence of this phenomenon, TA (time advance) is introduced in 3GPP for uplink time synchronization.
In the terminal coordinated communication technology, different internal delays and different external multipaths that are of the supporting terminal and the benefited terminal result in different TA between UE. Because there is no service in the supporting terminal, the supporting terminal does not need to perform network access in principle. However, in some scenarios, the supporting terminal needs to send an uplink signal. For example, in a TDD (time division duplex) system, the supporting terminal sends uplink sounding according to a configuration of the benefited terminal, and the base station schedules a best resource for the benefited terminal according to an uplink aggregate channel of the supporting terminal and the benefited terminal. Another application scenario is that in a system of uplink terminal coordinated communication, the supporting terminal collaborates with the benefited terminal in sending data to the base station.
In the terminal coordinated communication technology, the supporting terminal needs to completely access the network and complete uplink synchronization, and then can send the uplink signal; otherwise, interference to another terminal is caused.