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Traditional GFDM has many advantages such as excellent adaptability and low out-of-band (OOB) radiation. However, because of intrinsic inter carrier interference (ICI) and low signal-to-noise ratio (SNR), the multiple access performance is degraded. In this paper, we introduced CDMA technology into GFDM. Two different spread spectrum modes, Cyclic Code Shift Keying (CCSK) soft spread spectrum and Direct Sequence Spread Spectrum (DSSS), are considered and compared in this paper to illustrate the benefits of GFDM-CDMA in low SNR scenario. The simulation and analysis results show that the proposed GFDM-CDMA scheme reduce the performance degradation caused by interference.
????????? In recent years, with the rapid development of ground mobile communication system, the necessity to support global coverage and mass connectivity is growing. The communication with 5G/6G may be a potential and effective solution because satellite communication and terrestrial mobile communication complement each other in coverage, capacity, speed and many other aspects. In the future, communication system will be a major information infrastructure that expands human activities into the sky, the open sea and even the deep space. So, this topic attracts more and more attention and research. Code Division Multiple Access (CDMA) has been used for 2G/3G physical layer access technology for a long time. CDMA has many advantages such as robustness in the case of low signal to-noise ratio (SNR), high capacity, good confidentiality and so on. Because of these outstanding advantages CDMA is also widely used in 5G communication. As technology develops, cyclic prefix orthogonal frequency division multiplex (CP-OFDM), which is much more flexible, is adopted in 4G/LTE systems due to its ability to resist multipath interference and low complexity. 5G new radio (NR) will continue to use OFDM. More than that, we consider to employ improved OFDM technology, Generalized Frequency Division Multiplexing (GFDM). GFDM divides time and frequency resource into independent blocks, where each subcarrier contains a number of sub symbols. The good adaptability and high spectral efficiency of GFDM make it more compatible for massive Machine Type of Communication (mMTC) scenario, which will promote the integration of 5G/6G with the satellite wide-area Internet of things . In a word, GFDM is suitable for 5G communication system.
- Cyclic prefix orthogonal frequency division multiplex (CP-OFDM)
- Code Division Multiple Access (CDMA)
- Traditional GFDM has many advantages such as excellent adaptability and low out-of-band (OOB) radiation. However, because of intrinsic inter carrier interference (ICI) and low signal-to-noise ratio (SNR), the multiple access performance is degraded.
- cyclic prefix orthogonal frequency division multiplex (CP-OFDM), which is much more flexible, is adopted in 4G/LTE systems due to its ability to resist multipath interference and low complexity. 5G new radio (NR) will continue to use OFDM. However, its high peak average- power ratio (PAPR).
- CDMA Modulator
- GFDMA Modulator
- match filtering (MF) receiver
- zero-forcing (ZF) receiver
- minimum mean square error (MMSE) receiver
- MF successive interference cancellation (MF-SIC) receiver
- The PAPR performance of proposed GFDM-CCSK waveform is obviously improved compared with traditional OFDM and GFDM.
- Meanwhile the multi-code GFDMCCSK can effectively increase the access success ratio and reduce the average delay of system
The millimeter-wave supports wide bandwidth, and the short wavelength of it enables the miniaturization of antennas. Therefore, millimeter-wave based mobile communication systems can be equipped with more antennas in the same space as long-term evolution (LTE) base stations. However, short wavelengths can cause high path loss and low signal to noise radio (SNR).? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
BLOCK DIAGRAM EXPLANATION
The block diagram of the SS-GFDM transceiver system is shown above. On the sending side, the original binary data is encoded by channel code firstly. Through serial to parallel conversion, the coded binary data is grouped and mapped into multibit symbols. These symbols are modulated into spread spectrum signals and transmitted as sub symbols of GFDM. After CDMA signal is generated, it needs to be modulated to the corresponding GFDM sub symbols. The UE can randomly select any subcarriers and sub symbols for data transmission. Owing to the duality between time and frequency, GFDM modulation and demodulation operations can be implemented in time domain or in frequency domain
MATLAB 2018 and above
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