To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
In a high speed wireless communication system, the problem of inter-symbol interface occurs. Accordingly, recent systems prefer Code Division Multiple Access (CDMA) or Orthogonal Frequency Division Multiplexing (OFDM) which does not generate the inter-symbol interference problem.
In general, a mobile communication system was developed to provide voice services while guaranteeing user activity. However, currently mobile communication systems have gradually expanded their service area to include data service as well as voice service and have been developed to provide high speed data service. Though, since resources are lacking and users demand higher speed services in the mobile communication system providing a current service, a more improved mobile communication system is needed.
To meet these demands, standardization of Long Term Evolution (LTE) is being progressed by the 3rd Generation Partnership Project (3GPP) as one of the next generation mobile communication systems that are being developed. LTE is a technology implementing high speed packet-based communication having a transmission rate of a maximum of 100 Mbps with the goal being to commercialize LTE in 2010. To this end, several methods are being discussed, including a method of reducing the number of nodes located on a communication channel by simplifying network architecture, and a method of making wireless protocols maximally close to wireless channels, and the like.
A Multiple Input Multiple Output (MIMO) wireless communication system supports a MULTI USER (MU)-MIMO mode to increase a system yield. Particularly, Long Term Evolution-Advanced (LTE-A) considers a transmission mode of up to a maximum of 8 layers.
Data streams corresponding to a maximum of 8 layers are properly allocated to users according to channel states and scheduling schemes of the users, and support from a Single User (SU)-MIMO mode to the MU-MIMO mode.
CDMA or OFDM is required to perform channel estimation to compensate for distortion of a signal due to a channel. Channel estimation methods may be classified into a pilot symbol aided channel estimation method of transmitting an appointed signal called a pilot and estimating a channel by using the pilot and a decision directed channel estimation method of estimating a channel by using both the pilot symbol and general data.
Further, in connection with this, technologies such as full dimensional MIMO or massive MIMO which uses many more input/output antennas based on LTE-A or the next generation communication standard. In this case, a communication method and system considering the accuracy of channel estimation and signal overhead according to transmission/reception of pilot signals is required. More specifically, when signals are transmitted or received through more antennas, transmission of more pilot signals is required to acquire the same channel estimation as the number of antennas increases. However, full dimensional MIMO or massive MIMO uses a larger number of antennas in comparison with previous MIMO. Accordingly, when the number of pilot signals increase, radio resources for transmission/reception of the pilot signals have overhead and transfer volume of the pilot signals may deteriorate.
The decision directed channel estimation method uses not only pilots, but also general data for the channel estimation, and uses determined data as if the data is the pilot based on an assumption that the decision is accurate. When a decision error is not generated, the decision directed channel estimation method may use larger amounts of information to acquire a better result compared to the pilot symbol aided channel estimation.
In contrast, when a large number of decision errors are generated, the conventional decision directed channel estimation method may directly use a hard decision value of the data channel. Accordingly, if an operation signal to noise ratio is low, the symbol of the data channel having the error rather acts as interference. Particularly, when a bit error rate is high, the decision directed channel estimation method may have the lower performance compared to the channel estimation method using only the pilot channel. Further, the conventional channel estimation method does not consider a communication method including eight or more transmission/reception antennas or suggests only estimating the channel through MIMO communication using the number of antennas used in the convention communication system.