An Improved Cross Talk Cancelling Digital Predistortion for MIMO Transmitters

Zhiliang Zhang,Ying Shen,Shihai Shao,Youxi Tang,Wensheng Pan

doi:10.1155/2016/5626495

Zhiliang Zhang, Ying Shen + Show 3 more

Open Access

https://doi.org/10.1155/2016/5626495

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Abstract

An improved cross talk cancelling digital predistortion (ICTC-DPD) with novel estimating technique and decoupling technique is proposed, which can be used to compensate the cross talk with possible delay and compensate the nonlinearity with memory effect in MIMO transmitting channels. The cross talk cancellation ability, which is defined as the cross talk power ratio before cancellation to after cancellation in decibel, is analyzed and its closed-form expression is derived. Simulation results prove that the ICTC-DPD can achieve higher cross talk estimation accuracy and higher cross talk cancellation ability than the original CTC-DPD. Experimental results show that the ICTC-DPD can achieve 20 dB cross talk cancellation for two channels transmitting 20 MHz LTE signals.

Highlights

Multiple-input multiple-output (MIMO) technology is one of the most promising solutions in improving the spectral efficiency of wireless systems [1,2,3,4,5] and has been used in several wireless communication standards, such as LTE and LTEAdvanced [6]
In CODPD, each direct path or coupling path uses a predistorter of memory polynomial model to compensate, where the possible delay of cross talk can be considered as memory effect and can be compensated
The second is cross talk cancelling DPD (CTC-DPD) [9,10,11], where an inversion of coupling matrix is introduced after predistorters for decoupling to make the channels between predistorters and power amplifiers (PAs) independent, and only M predistorters of memory polynomial model are needed by M outputs

Summary

Introduction

Multiple-input multiple-output (MIMO) technology is one of the most promising solutions in improving the spectral efficiency of wireless systems [1,2,3,4,5] and has been used in several wireless communication standards, such as LTE and LTEAdvanced [6]. In some proposed techniques in open literatures, the PAs’ nonlinearity and the distorted cross talk have been compensated concurrently. In CODPD, each direct path or coupling path uses a predistorter of memory polynomial model to compensate, where the possible delay of cross talk can be considered as memory effect and can be compensated It ignores the higherorder cross-terms, which results in a loss of performance, especially at high cross talk levels [9], and it has high complexity because too many predistorters are used. The second is cross talk cancelling DPD (CTC-DPD) [9,10,11], where an inversion of coupling matrix is introduced after predistorters for decoupling to make the channels between predistorters and PAs independent, and only M predistorters of memory polynomial model are needed by M outputs. Inconsistency of output channels can be compensated too

System Model

Analysis of Cross Talk Cancellation Ability

Results and Discussions

Conclusion