Regular train students may have encountered this situation:
“
Li Lei: long-distance travel is too boring, you see what movie?
Han Meimei: I was watching "4 The Avengers" final battle, good read.
Li Lei: Well, I have not seen it, you can send me?
Han Meimei: This film has more than 1G it, I is not much traffic this month package, not to you, move the car is not how good signal to pass without Bluetooth.
Li Lei: Bluetooth is too slow, we arrived at the station travels are not necessarily finished. Wifi only back then pass. There is no way to transfer data directly to the phone for the phone yet?
”
Today we'll discuss this issue.
1. The communication range classification
Size classification according to a communication range, can be divided into near-field wireless communication network, a personal area network, LAN, MAN, WAN.
✔ a near field communication (NFC, Near Field Communication), as the name suggests, both the communication distance is very short, less than one meter, a non-contact type radio frequency identification (RFID) technology can be both point to point communications and inductive card reading function. Two NFC-enabled mobile phones to touch it, you can achieve file transfer; we have daily access card brush, brush with a bank card is RFID technology, which has been widely used in terms of things.
✔ area network range about 10 meters, to achieve a small amount of the main data communication, a Bluetooth personal area network is a kind of technology, we use the wireless headset, wireless mouse and keyboard, is employed selfie rod Bluetooth communication. There are often used in smart home of ZigBee technology, connecting nodes and data transfer rates than Bluetooth has increased.
✔ wireless local area network (WLAN, Wireless Local Area Network) is most familiar, covering communication within 100 meters range. Wifi is a kind of wireless LAN technology, wireless router installed at home, you can enjoy surfing the Internet fun. Wifi has become many people's most basic needs.
Range wireless metropolitan area network expanded to several kilometers to tens of kilometers, providing multipoint communication services. WiMax (Worldwide Interoperability for Microwave Access) 3G mobile communications technology as a standard road although ended, but as a broadband wireless metropolitan area network technology continues to development.
And our focus - mobile communication technology as a wide-area network technology exist, the purpose is to achieve long-range, wide range of communications functions, so that every corner of the globe can communicate freely. Pick up the phone, and we are separated by thousands of miles of family and friends face to face chat, you can query the data on the server on the other side of the globe, and learn to live and work brought great convenience.
But sometimes, we just give friends sitting beside send a picture, and the same quarters a good base of the Union to play a game machine, or transfer files between these two phones. Although the start and end of data in close proximity, but the network but equally, had from the phone to the base station, the core network after processing, to the external server, and then returned to the mobile core network, via the base station to the mobile phone. So if you're sitting in Beijing office next door micro letter to colleagues sent a picture, data may be sent to the server from Beijing Tencent data center in Guizhou and then back to Beijing, all the way around in a big circle.
Mobile communication technology enables long-distance communication, but we have to thrifty, for short-range communications, can not occupy channel resources to the base station, the mobile phone deal directly with their own, that too many resources to save ah.
2.D2D communication
D2D communication is such a technique. D2D (Device-to-Device, the device-to-device) refers to a way of direct communication between two peer user nodes. Bluetooth is a direct communication between two devices, pairing between the parties without third party intervention. D2D communication slightly different, is a cellular system based on short distance data transmission technology directly. Forwarding user data without going through the base station, each user node can send and receive signals, and has a function of forwarding a message, data transfer between terminals. But control of the series of operations, such as establishing a session, to maintain the radio resource allocation and billing, authentication, recognition, mobility management and the like still responsible for cellular networks, so the relevant data or control instructions via the base station needs to transmit. I.e. user plane using D2D transmission, or through the network control plane.
3.D2D application
In D2D communications network, the device at the same time play the role of server and client can be aware of each other's existence, self-organized to form a virtual or actual groups. This is much like social characteristics, it may be based on natural D2D social application features adjacent geographical perform such as content sharing, for transmitting data between adjacent interactive user games, users find function D2D adjacent area of interest to find a user. Local advertising service is also available near the target D2D precise user location, push merchandise discount promotions, new movie theater trailers and other information, to achieve maximum benefit.
With business growing high-volume multimedia features such as high-definition video, a huge data traffic brought great challenges to the core network and radio channels. In the crowded business district or university dormitory at night, often cell phone signal full but not on the network situation, this is the network overburdened and under-resourced situation. Use of local characteristics D2D communications to carry out local multimedia services, network resources can save money. For example, the operator or content provider can set up a server in a hot area, will be in the server, the server D2D mode provides services to people with business needs of current popular media content storage; users can also adjacent to the media business has obtained from at the user terminal to obtain the desired media content, without going through the base station to relieve the pressure transmission base station. Short-range communication between the user of the cell can also be switched to split D2D communication mode to enable network traffic. Thus, the communication can make a wireless channel used for normal, to enhance the utilization efficiency of the spectrum.
In addition to large data split outer, D2D large connector also has advantages. 5G mMTC mass of the machine type communication scenario a large number of things terminal to access the network. In these scenarios, many cases are close distribution equipment, such as smart factories, smart parking, a large number of communication devices, or networked car in V2X in the local area, and around the vehicle to vehicle, pedestrian facilities ,Telecommunication. If all transit via the base station, and a large amount of data transfer request command to make the network exhausted. By direct communication between the D2D, apparatus, after reducing the intermediate links, much shorter communication delay, reliability and safety has been improved.
Since the D2D with automatic network connection function, in emergency communications will have excellent performance, extreme natural disasters solve communication communications infrastructure damage caused by outages. When the rescue, the D2D communication mode, between adjacent base station without the mobile terminal can establish a wireless communication signal, disaster relief quickly set up a communication network for dispatching rescue. Further, the coverage hole in a wireless network, one or more hops through the user D2D communication may be connected to a cellular network user terminal within the coverage area, the subscriber terminal by means of normal traffic.
It is because of these advantages, D2D has been listed as a key technology 5G by multiplexing radio spectrum resources, increase spectral efficiency, ease the shortage of spectrum resources in a wireless communication system to some extent the problem.
4.D2D classification
As mentioned earlier, the biggest difference D2D and other short-range communication technology in the base station so controlled, using a licensed frequency band, so that it is controllable interference, data transmission with higher reliability. In the radio access level, according to differentiate cellular network coverage, the D2D communication is divided into three scenes.
D2D communication under the control of the base station 4.1
When both D2D communication device is within coverage of the base station, the base station will spectrum D2D scheduling and resource management control transmission power.
D2D communication by radio, to take up the same specific frequency band. The network may assign a dedicated piece of spectrum for D2D communication, so that, D2D and the general cellular network interference will not occur and to be the maximum transmit power signal. Under tension or not D2D spectrum resources needs, the dedicated spectrum is clearly not a good idea, and thus also D2D shared spectrum cellular network, using a mobile phone base station to a frequency band or a downlink channel to an uplink channel frequency band mobile phone base station. This inevitably interfere with each other and the cellular network communication.
Mobile figure above is between 1 and 2 the D2D communication, uses the uplink frequency band, a transmission signal, second receiving signal. A cellular network communication between the handset and the base station 4 3. 1 is transmitted to the base station 2 4 signal received, because the mobile phone 3, and sent to the base station an uplink signal of the same frequency band 4, the base station can cause interference to reception. Similarly, the signal sent to the mobile phone base station 3 of the mobile phone 2 is received, the mobile phone 2 also cause interference. It is necessary for the network to control and eliminate these disturbances.
Under management of the base station, the transmission power D2D device is strictly controlled and coordinated by the interfering base station, a frequency adjustment around equipment and power resources, the interference can be controlled within an acceptable range, ensure quality of service. Thus, in a limited spectrum resources, and a cellular network by multiplexing transmission D2D more data, increased cell throughput, improves spectrum efficiency.
D2D communication station under the assist control 4.2
Cellular network coverage boundary, only part of D2D communication apparatus is under control of the base station, then the base station is only involved in device discovery and session establishment, both the guide connection is established at the beginning, no subsequent resource scheduling, by the built-in apparatus according to the algorithm selection D2D resources, which have significantly lower network complexity than completely controlled D2D communication, but communication service experience and also will be affected.
4.3 D2D communication from the base station controller
In addition to the coverage of the cellular network, the D2D device independent device discovery, connection establishment, scheduling resources, which requires a higher capacity of the device, the device complexity is greater than the previous two ways. This approach is mainly used for emergency communications or blind zone, the cellular network can be ultimately connected to multi-hop transmission.
4.4 compare these three scenarios:
5G at high rate, low latency, large connection request to the base station as the center of the traditional business model felt great pressure, the D2D communication mode as a supplement for a new era of mobile terminal access to the mass, large-scale low-latency data transmission open up new avenues.
Having said that, summed up the D2D communication without operator's base station, it is not the money does not flow?
I think too much, do not forget to control D2D still base it on hand. We can expect is that this part of the flow has a more favorable course of.