Precoding For MIMO In Mobile Communication

The precoding technology is to design a pre-processing with exploiting the channel state information at the transmitter, to remove the interference among the antennas or users in the receiving signals, and do adaptive processing to improve the system performance. One hand this method can simplify the processing at the receiver, the other hand the adaptive processing can improve the system performance. This paper main discuss how to realize the precoding to remove the interference at the transmitter.In the single user MIMO environment, the main task for precoding is to remove the interference among the antenna, and do self-adaptive processing according to the channel state information. There are two train of thought to realize the precoding. One is to apply the traditional user signal detection at the transmitter; the other is to decompose the MIMO channel to several independent parallel sub-channels by decomposing the channel matrix. The former is similar to the signal detection, which can effectively remove the interference according to the channel state information and simplify the information processing at the receiver. The latter needs a joint processing of the transmitter and receiver. This method relies on the decomposition of the matrix. The channel matrix is decomposed at the receiver, and then a unitary matrix is feedback to the transmitter. The data vector multiplies the unitary matrix to get the transmitted signals.Apply the equalization and interference cancellation to the received signals.The self-adaptive select the sub-channel and power allocation can be applied to decrease the bit error radio and increase the system capacity at the transmitter.Because the perfect channel state information feedback needs a lot of channel resource in practical application, how to reduce the quantity of feedback becomes an important research direction. A codebook based precoding is an effective method. At first a group of codebook is constructed and stored at the transmitter and the receiver. Then a codebook is selected with some performance criteria at the receiver, and the index of the codebook is feed backed to the transmitter. A properly designed codebook can reduce losses of the performance.In the cellular communication system, the multi-user MIMO is the most cases. Such as, the base station communicates with several users at the same time and frequency. Be different from the single user MIMO, there are interference among users for multi-user MIMO and no cooperation among users.The main task of the precoding is to remove the interference among the users and antennas. Most of the single user precoding methods can extended to multi-user precoding by properly modified.