| With the arrival of mobile Internet era, the demand for high-rate data transmission is becoming more and more urgent. At the same time, the crowded low frequency bands can hardly meet the requirements of high speed transmission, therefore the millimeter-wave bands attract more attention due to the abundant unused frequency bands. In 2012, IEEE (Institute of Electrical and Electronics Engineers) 802.11 standardization organization founded IEEE802.11aj working group to realize Gbps high-rate transmission on the 45GHz bands submitted by China. Compared to low frequency bands, the frequency of millimeter-wave is quite high and as a result, the wireless communication working on millimeter-wave bands suffered more from carrier frequency offsets, the influence of RF device nonlinearity is also more severe, and the impact of phase noise is worse as the restriction of device manufacturing. SC-FDE (Single Carrier-Frequency Domain Equalization) technique is less sensitive to carrier frequency offset and has lower PAPR than OFDM (Orthogonal Frequency Division Multiplexing), hence SC is a promising alternative to OFDM that can be used in a millimeter-wave wireless communication system. This paper mainly discusses the suppression of carrier frequency offset and phase noise in SC-FDE MIMO millimeter-wave communication systems, including the combining scheme of SC-FDE and MIMO, data frame structure design, carrier frequency and phase noise mitigation algorithm research.Firstly, the statistic models for carrier frequency offset and phase noise are given, especially the phase noise model for IEEE 802.11aj(45GHz) and its numerical simulation results, which shows the frequency-domain and time-domain characteristics. The high-order modulated constellations affected by phase noise are also simulated. The research of carrier frequency offset and phase noise lays the theoretical foundations for the following study on phase track algorithms.Secondly, this paper proposed one SC-MIMO system structure with CSD (Cyclic Shift Diversity) operation and a time domain multiplexed training sequences scheme adapted to this structure is also illustrated. Like frequency domain pilots in OFDM, time domain multiplexed training sequences provides receiver with prior information which can be utilized to suppress carrier frequency offset and phase noise. In this paper, one linear mitigation algorithm was proposed to track carrier frequency offset. Numerical simulation results show that the proposed algorithm can estimate and compensate carrier frequency offset effectively.Comparing to mitigation of carrier frequency offsets, the phase noise estimation and compensation are far more complicated. This paper also proposes one decision feedback LMS iterative algorithm to mitigate phase noise. This algorithm aims to estimate and eliminate phase noise in IEEE 802.11aj(45GHz) systems. Because adjacent samplings of phase noise are highly coherent, LMS estimator can be used and phase noise can be compensated.Finally, one feasible scheme that combines UW (Unique Word) and SC-FDE MIMO technique is discussed. UW is a classic approach to insert time domain multiplexed training sequences for SC-FDE systems. Not only can UW work as cyclic prefix, but also providing training information without introducing any extra overhead and complexities. Therefore, UW is widely used in SC-FDE systems. Unfortunately, UW based SC-FDE systems can hardly compatible with MIMO directly because of the CSD and spatial extending operations in MIMO. To solve this, this paper proposed a feasible scheme to combine UW based SC-FDE and MIMO, in which data blocks are arranged in orthogonal or Quasi-Orthogonal matrix to replace CSD and spatial extending operations. Following data-block rearrangement, UW is inserted and as UW is prior-known information to receiver, the damage UW caused to orthogonality can be removed. Simulation results show that the proposed scheme can improve the system performances by realizing MIMO spatial diversity. |
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