MIMO (20141219) of LTE key technologies for wireless communication network learning

MIMO is called multi-input multi-output.

First, let's look at the concept of gain and how to calculate it:

There are two important concepts in spread spectrum communication systems: processing gain and anti-interference tolerance.

Processing gain is used to illustrate the improvement of signal-to-noise ratio of communication system, and is a performance index of system interference. Generally, the ratio of the spread spectrum signal bandwidth W to the information bandwidth F becomes the processing gain GP,

i.e. gp=w/F

For example: Full speed information bandwidth is 9.6kbit/s, spread spectrum bandwidth is 1.2288mbit/s, spread spectrum gain is 21dB. Algorithm: 10LG (1.2288*1024/9.6) =21db.

Let's talk about a few descriptive units of gain:

DB is used to characterize the relative ratio of power, this can be referred to the above example;

DBC is also a unit that characterizes relative power and is calculated in the same way as DB;

DBM is used to express the absolute value of power, the formula is 10LG (P power value/1MW);

Both DBI and dbm are used to express the power gain, both are a relative value, the reference datum is not the same, the DBI reference is the omni-directional antenna, the DBD reference datum is a dipole, the same gain is expressed in dbi with 2.15 larger than the DBD.

Here are a few concepts: transfer diversity, beamforming, Space Division Multiplexing, Space division multiple access, open loop, closed loop :

Data replication is sent multiple times to improve the quality of transmission, that is, the transfer diversity ;

Transferring multiple data together, increasing the data transfer quantity, which is the space Division multiplexing , and realizing the spatial multiplexing by transmitting each other's independent signals at different antennas.

The use of multiple terminals to receive data, that is, empty division multiple address ;

For closed-loop, we take a bus example, when we go to a strange city, take a bus, every stop, we have to look at, where, and then the next stop to where, and the platform confirmed after the decision to not get off, this is the closed loop, generally at low speed or static situation.

As for the closed loop, it was as if the bus was opening quickly, which led us to the station, but too late.

In the case of slow channel changes, such as indoor or nomadic access services in large cities, it is necessary to use the closed-loop MIMO to further improve the performance of the shampoo.

Closed-loop system is the receiving end of the information channel feedback to the transmitter, and then the transmission of data encoding, beamforming or antenna selection and other operations.

The feedback method is divided into full feedback or partial feedback . Full feedback is to feed the entire channel to the transmitter, because the feedback link to occupy the system overhead, in practical applications, the general use of partial feedback technology.

OK, this section focuses on several units of gain and their calculation methods, as well as six techniques for multi-input and multi-output.

Next time we continue our icic on key LTE technologies.

MIMO (20141219) of LTE key technologies for wireless communication network learning