Design And Implementation Of FDD-LTE Downlink MIMO Based On GNU Radio

With the rapid development of mobile communications and intelligent terminal, Now we have entered the era of “4G”. Compared with the last generation communication system, LTE uses a number of core technologies, including orthogonal frequency division multiplexing, multiple input multiple output,and so on.LTE system can short the delay of communication system, improve the system capacity, simplify the structure of the network and strengthen the ability to resist multipath interference. Relative to the “3G” era, wireless communication transmission rate has been greatly promoted.As a critical technology in LTE system,MIMO plays a vital role in improving wireless system transmission rate and combating multipath interference. In traditional single input single output system, it is greatly influenced by multipath interference, By setting more than one antenna in the sender and the receiver, the channel transfer matrix in MIMO technology is constructed to make full use of multipath information, so as to increase the purpose of the signal transmission rate and resistance to multipath interference.This paper designs and implements the LTE downlink MIMO system(2×2) based on GNU Radio as software platform and USRP B210 as hardware platform. On the e NB site, this thesis adopts the space frequency block coding(SFBC) as a transmission diversity way, in which the signal is coded in both the space domain and the frequency domain and then transmitted by different antennas. In the scheme, the hardware platform utilizes the USRP B210 instead of the USRP N210 because it is difficult for USRP N210 to realize the clock synchronization in MIMO system. Concerning the buffer deficiency of the USRP B210 and the complexity of the initial synchronization process, this scheme reset the output buffer size by means of the GNU Radio system scheduling mechanism. Meanwhile, as for the complicated resource mapping procedure of physical downlink shared channel on the e NB site,this paper adjust it to simplify this procedure, which can guarantee the validity of resource mapping. Finally, this paper proposes a new way to reduce the complexity of the synchronization process of the baseband signal wherein three orthogonal local PSS sequences are added to do the correlation detection with the received signal, which can reduce the complexity of estimation by two thirds.At last, in the RTP transmission mode, this paper uses the downlink MAC packet error rate to compare the performance of the LTE 1×1 system with the LTE 2×2 MIMO system using SFBC transmit diversity, respectively in 1.4MHz and 3MHz bandwidth.The result shows that the SFBC transmit diversity can efficiently improve the SNR and reduce the packet error rate. In the actual wireless channel, the average packet error rate of the 2×2 MIMO system is one fifth of the LTE 1×1 system,which declines by 80 percent. In the simulation channel, the packet error rate of LTE 2×2 MIMO system is one tenth of the LTE 1× 1 system, which declines by 90 percent.