除此之外，我們提出了一個用於使用前導序列的同調大量多輸入多輸出系統的方法，此方法利用傳送過的資料訊號作為前導序列，並設計相互正交的前導序列，可使傳送前導序列的時間縮短。 ;Massive MIMO systems are popular studies in recent years. Differential encoding scheme is not required to transmit pilot sequence for channel estimation, so it does not cause pilot contamination. A differentially encoded QAM (quadrature amplitude modulation) scheme for uplink massive MIMO was proposed recently which outperforms conventional differential APSK (amplitude-phase shift keying) scheme for 1000 receiver antennas.
In this letter, we raise and try to resolve some questions about this differential QAM scheme. We construct new tables for differentially encoded 16-QAM. We compare differential 16-QAM with differential 16-APSK for the same detector, and compare the detector with a conventional detector for the same transmitter. Simulation results show that differential 16-APSK has the best error performance for any number of receiver antennas.
Besides, we propose a new scheme for uplink coherent massive MIMO. This scheme uses transmitted data signal as pilot sequences, and we also design the pilot sequences to make it orthogonal to each other, which can shorten the time of transmission of the pilot sequence.
