In the LTE mobile communication system, does the physical layer include a base station?

The uplink and downlink switching point is a special subframe, the protocol only talks about the layer, not specifically about the base station and UE, if you want to do a base station, obviously you also have to study 211 to 214, because most of this is an air port format, and the base station and UE must abide by it.

What is called a layer, do you know? The layer is a layer from one end of the communication to the other end and its equivalent, obviously the physical layer also includes the base station, and one end of the layer only interacts with the other end of this layer, not with the other end of the upper layer.

For example, the physical layer of the UE only interacts with the physical layer of the base station, while the MAC layer of the UE only interacts with the MAC layer of the base station, and the physical layer of the UE never interacts with the MAC layer of the base station.

Of course, the physical layer of the UE also interacts with the MAC layer of the UE, but that is only necessary for implementation, and is not part of the protocol.

Avoiding cross-cutting complex conversations, clearly dividing functions, and performing their own responsibilities to make the project achievable, this is the role of layers.

The base station in the mobile communication system includes the indoor base station main equipment and the outdoor antenna feeder system.

The base station is a form of radio station, which refers to the radio transceiver station that transmits information between the mobile communication exchange center and the mobile terminal in a certain radio coverage area. The construction of mobile communication base stations is an important part of the investment of China's mobile communication operators, and the construction of mobile communication base stations is carried out around the elements of coverage, call quality, investment efficiency, construction difficulty, and convenient maintenance. The UE physical layer will definitely not interact with the MAC layer of the base station?

A layer is the level from one end of the communication to the other end and its equivalent.

The base station BS is an important part of the TD-SCDMA RAN system, which is the main equipment unit for building wireless network coverage.

According to the hardware system composition, the node B device is divided into two parts: indoor base station main equipment and outdoor antenna feeder system. The main equipment of the indoor base station is the base band unit (BBU), and the main equipment of the outdoor antenna feeder system is the remote RF unit (RRU).

The so-called base station system is not a base station and a base station controller, but two different concepts.

This article will provide an overview of the main technical features of the 4G mobile communication system and discuss the key technologies that may be adopted in the 4G system.

The main features of the mobile communication system.

Compared with 3G, the technology of 4G mobile communication system has many transcendences, and its main characteristics are:

1) High rate. For high-speed mobile users in a large area (250km h), the data rate is 2mb s; For medium-speed mobile users (60km h), the data rate is 20mb s; For low-speed mobile users (indoor or walkers), the data rate is 100mb s.

2) Mainly digital broadband technology. In the 4G mobile communication system, the signal is mainly transmitted by millimeter wave, and the cell cell will be much smaller, which greatly improves the user capacity, but at the same time, it will also cause a series of technical problems.

3) Good compatibility. The 4G mobile communication system realizes a global unified standard, so that users of all mobile communication operators can enjoy common 4G services, and truly realize that a mobile phone can communicate anywhere in the world.

4) Strong flexibility. The 4G mobile communication system adopts intelligent technology to enable it to adaptively allocate resources, can process the changing size of the service flow in the communication process accordingly to meet the communication requirements, and uses intelligent signal processing technology to send and receive signals normally in various complex environments with different channel conditions, which has strong intelligence, adaptability and flexibility.

The process of physical layer cell search mainly involves two synchronization signals, namely the primary and auxiliary synchronization signals (PSS SSS). The process includes the synchronization of downlink time and frequency, the detection of the physical ID of the cell, and the detection of the CP length of the OFDM signal (Normal or ExtendedCP). Once these operations are completed, the terminal can start reading the system information in the broadcast channel (PBCH) of the service cell for further operations.

During this period, after the synchronization is obtained with the service cell through the detection of the synchronization signal, the terminal can use the downlink pilot signal (CRS) to synchronize the time and frequency more accurately and maintain the synchronization. Cell search process.

Through the adjustment of the uplink transmission time, the uplink signal time of the terminal and the service cell is synchronized, so that the uplink signals of different users can reach the base station synchronously. The process includes the adjustment of the transmission time during the asynchronous random access process and the uplink synchronization maintenance in the connection state.

In the process of asynchronous random access, as a response message for random access, the base station sends a timingadvance command with a length of 11 bits to the terminal, and the terminal adjusts the uplink sending time according to the information to achieve uplink synchronization.

In the connected state, the control information of the MAC layer carries a timing adjustment command with a length of 6 bits, and the terminal will adjust the sending time of the uplink according to this information to maintain the uplink synchronization.

The accuracy of the timing adjustment command is 15 (15000*2048)), and the delay between receiving the command and sending the uplink after adjustment is 6ms, that is, after the subframe receives the adjustment command, the information will be applied to the uplink transmission from the subframe.

According to the transmission characteristics of uplink and downlink signals, the LTE physical layer defines the corresponding power control mechanism.

For the uplink signal, the power control of the terminal is of great significance in saving power and suppressing the interference between users, so the mechanism of closed-loop power control is used accordingly to control the transmitted power of the terminal on the uplink single-carrier symbol.

For the downlink signal, the reasonable power distribution and mutual coordination of the base station can suppress the interference between cells and improve the system performance of the co-frequency network, so the open-loop power allocation mechanism is used accordingly to control the transmission power of the base station on each subcarrier of the downlink.