Method and system for synchronizing time and frequency in orthogonal frequency division multiplex communication

Abstract

In the invention, at transmitting terminal, the original information treated with carrier modulation is serial-parallel converted into several branch data streams whose amounts are identical with the amounts of antennas; the branch data streams and frequency-domain pilot frequency sequence are commonly mapped into the data position corresponding to the preset frequency-domain pilot frequency pattern; generating each antenna data information which is processed with OFDM modulation and is transmitted by RF transmission. At receiving terminal, each antenna receives the RF signals and generates time-domain output sequence the time-domain output sequence is correlated with the reference sequence to construct synchronous objective function between each pair of antennas so as to implement the synchronization between time and frequency.

Description

technical field [0001] The present invention relates to multiplexing communication, more specifically, relates to a method and system for synchronizing time and frequency in Orthogonal Frequency Division Multiplexing (OFDM) communication. Background technique [0002] MIMO (Multi-Input Multi-Output, Multiple Input Multiple Output) and OFDM (Orthogonal Frequency Division Multiplexing, Orthogonal Frequency Division Multiplexing) technologies are two important contents of modern communication technologies. As an efficient multi-carrier transmission technology, OFDM technology has the advantages of high spectrum utilization rate and strong ability to resist frequency selective fading. The MIMO technology can provide a larger channel capacity than the SISO (Single-Input Single-Output) technology, and is a potential method for high-speed data transmission. The MIMO-OFDM method combining MIMO and OFDM can realize the purpose of providing high data transmission rate services in bro...

AI Technical Summary

Problems solved by technology

[0018] The main disadvantage of the method of superimposing the PN sequence is: the power of the PN sequence limits the minimum value of the bit error rate, usually the transmission signal requires a bit error rate as low as possible, and time and frequency synchronization require the PN sequence to have a certain power, both Contradictory; the PN sequence is superimposed on the random data and can only be used for synchronization. To achieve the correct demodulation of the signal, additional overhead is required for channel estimation, etc.; the method is originally aimed at the SISO system. If it is directly applied to In the MIMO-OFDM system, each antenna needs to superimpose the training sequence. Under the objective condition of a certain total transmission power, the ratio of data power to the total power will be further reduced, resulting in more serious interference of the data detection by the PN sequence.

[0048] It can be seen that the method for time synchronization of the pilot-assisted OFDM system has the following disadvantages: the adopted ML algorithm is derived based on the AWGN channel, and when used in a multipath fading channel, the autocorrelation characteristics of the received sequence r(k) will present complex changes, resulting in random changes in the likelihood function, and the performance of the algorithm is significantly reduced; the signal-to-noise ratio of the received signal needs to be estimated, and the estimation error will lead to a decrease in synchronization accuracy; although time synchronization and channel estimation can be completed at the same time, frequency synchronization still requires additional Complete, without substantially reducing system overhead; more difficult to use in more complex MIMO channel environments

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