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Abstract
This paper proposes a new channel estimation scheme based on implicit pilots, optimized for a simplified massive multiple input, multiple output (MIMO), implemented with precoding, combined with Single-Carrier with Frequency-Domain Equalization (SC-FDE) modulations. We propose an iterative receiver that considers an iterative detection with interference cancellation and channel estimation. The channel estimates are usually obtained with the help of pilot symbols and/or training sequences multiplexed with data symbols. Since the required overheads in massive MIMO schemes can be too high, leading to spectral degradation, the use of superimposed pilots (i.e., pilots added to data) is an efficient alternative. Three different types of preprocessing algorithms are considered in this paper: Zero-Forcing Transmitter (ZFT), Maximum Ratio Transmitter (MRT), and Equal Gain Transmitter (EGT). The main advantage of MRT and EGT is that they do not require matrix inversions. Nevertheless, some level of interference is generated in the decoding process. Such interference is mitigated by employing an optimized iterative receiver. By employing the proposed implicit pilots, the performance of MRT and EGT is very close to the Matched Filter Bound just after a few iterations, even when the number of transmit or receiver antennas is not much higher than the number of data streams.
Highlights
Massive MIMO (m-MIMO) schemes are a key technique employed in emergent wireless communications that tends to achieve higher network capacity and spectral efficiency [1, 2]. m-MIMO is expected to be utilized in 5G (Fifth Generation) systems, alongside with Millimeter Wave communications, due to its increased channel coherence bandwidth, as compared to centimeter wave
This section studies the Bit Error Rate (BER) performance obtained with m-MIMO using precoding, after the estimation of the channel parameters, using implicit pilots
The BER is evaluated as a function of Eb/N0, where N0 is the one-sided power spectral density of the noise and Eb is the Matched Filter Bound (MFB) Zero-Forcing Transmitter (ZFT) Maximum Ratio Transmitter (MRT): without interf. cancel Equal Gain Transmitter (EGT): without interf. cancel
Summary
Massive MIMO (m-MIMO) schemes are a key technique employed in emergent wireless communications that tends to achieve higher network capacity and spectral efficiency [1, 2]. m-MIMO is expected to be utilized in 5G (Fifth Generation) systems, alongside with Millimeter Wave (mm-Wave) communications, due to its increased channel coherence bandwidth, as compared to centimeter wave. The inherent use of OFDM signals, composed of a sum of many independent and parallel subcarriers, tends to present high requirements in terms of PAPR This can be mitigated by using SC-FDE schemes, instead of OFDM signals, which present lower envelope fluctuations of the signals, translating into low complexity and more efficient power amplification [9]. A very efficient receiver commonly associated with SC-FDE schemes is the Iterative Block-Decision Feedback Equalization (IB-DFE) technique [15,16,17] Such an iterative receiver makes use of feedforward and feedback coefficients to process the signals in the frequency domain, reaching a performance typically much better than that of a noniterative receiver. This paper is organized as follows: Section 2 describes the system characterization associated with generic SC-FDE signals; Section 3 considers the transmitter structure for the proposed m-MIMO using precoding; Section 4 describes the channel estimation using multiplexed or implicit pilots; Section 5 deals with the receiver design for MIMO detection and channel estimation; Section 6 analyzes the performance results; and Section 7 concludes the paper
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