Kilian Roth

Achievable Rate and Energy Efficiency of Hybrid and Digital Beamforming Receivers With Low Resolution ADC

For 5G, it will be important to leverage the available millimeter wave spectrum. To achieve an approximately omnidirectional coverage with a similar effective antenna aperture compared with the state-of-the-art cellular systems, an antenna array is required at both the mobile and base stations. Due to the large bandwidth, the analog front-end of the receiver with a large number of antennas becomes especially power hungry. Two main solutions exist to reduce the power consumption: Hybrid BeamForming (HBF) and Digital BeamForming (DBF) with low resolution Analog to Digital Converters (ADCs). An HBF system can also be combined with low resolution ADCs. This paper compares the spectral and energy efficiency based on the RF-frontend configuration. A channel with multipath propagation is used. In contrast to previous publication, we take the spatial correlation of the quantization noise into account. We show that the low resolution ADC DBF is robust to small Automatic Gain Control (AGC) imperfections. We showed that in the low SNR regime, the performance of DBF even with 1–2 bit resolution outperforms HBF. If we consider the relationship of spectral and energy efficiency, DBF with 3–5 bit resolution achieves the best ratio of spectral efficiency per power consumption of the RF receiver frontend over a wide SNR range. The power consumption model is based on components reported in the literature.

Covariance based signal parameter estimation of coarse quantized signals

The use of low resolution analog-to-digital converters is an effective solution to reduce the complexity and the power consumption of the analog front-end, especially in the context of massive multiple-antenna and large system bandwidth. However, most well-known signal parameter estimation algorithms assume that the receiver has access to the observations data with infinite precision. In this paper, we investigate a method to improve the performance of covariance based algorithms that operate on quantized signals. To this end, we use a particular transformation between the input and output second order statistics when affected by non-linear processing. By applying this transformation, we could then utilize standard algorithms with almost no additional complexity. The introduced method is also of particular interest in the context of adaptive signal processing, since many adaptive processing algorithms are based on estimating the received signal covariance matrices. Through simulations, we show that the method is capable of improving the estimation performance especially in the extreme case of one-bit quantization.

MAC rate region of low resolution ADC digital and hybrid beamforming massive MIMO UL

For 5G it will be important to leverage the available millimeter wave spectrum. To achieve an approximately omnidirectional coverage with a similar effective antenna aperture, an antenna array is required at both the mobile and basestation. Due to the large bandwidth and inefficient amplifiers available in CMOS for mmWave, the analog front-end of the transceiver with a large number of antennas is especially power hungry. Two main solutions exist to reduce the power consumption: Hybrid BeamForming (HBF) and Digital BeamForming (DBF) with low resolution ADC. This work compares the uplink rate region for both systems assuming a basestation with a large number of antennas. We show, that in the low SNR regime, the performance of DBF even with about 1–2 bits of resolution outperforms the one of HBF in terms of the achievable sum rate. The higher the SNR, the higher also the required resolution of the ADC to achieve a similar performance compared to HBF. If there is a large spread in receive power of the signal from different users, systems with very low resolution (1–3 bit) suffer from a performance loss.

Performance analysis of FBMC and CP-OFDM in the presence of phase noise

Multi-Carrier (MC) modulation schemes like Orthogonal Frequency Division Multiplexing (OFDM) are highly sensitive to Phase Noise (PN). In the case of air interfaces operating in higher frequencies, e.g. the range between 6 and 100 GHz frequently called millimeter wave (mmWave), the PN generated by the local oscillators is even more accentuated. Alternative MC systems are being considered for future mmWave wireless communications. In this contribution, we analytically derive expressions for an upper bound for the interference power generated by the PN in OFDM, DFT-Spread-OFDM and Filter Bank Multi-Carrier (FBMC). Then, we evaluate the performance degradation due to that imperfection in terms of coded and uncoded BER.

Cell Search for a Millimeter Wave Cellular System with 1-Bit Quantization at the Receiver

For 5G it will be important to leverage the available millimeter wave spectrum. Communication at high carrier frequencies requires antenna arrays at both the base and mobile station. A 1-bit analog to digital converter can effectively reduce the complexity and power consumption of the analog frontend. This is especially interesting in the context of large antenna arrays with a sizable signal bandwidth. In this paper we investigate the cell search capabilities of a mobile station with an antenna array and an analog frontend with 1-bit quantization behind each antenna. We derive the Likelihood Ratio Test (LRT) for this problem with full channel knowledge. We also show the generalized Likelihood Ratio Test (GLRT) for a case without channel knowledge, and compare the performance to practical algorithm based on correlation. We show that the practical correlation achieves a similar performance compared to the theoretical optimal GLRT. Compared to a system with high resolution analog to digital conversion our results show the theoretical derived SNR gap of 2 dB.

A Leaner Carrier for the New 5G Air Interface

This paper studies the physical layer performance of a lean carrier with reduced reference symbols and reduced control channel overhead as a possible candidate for a new 5G air interface. Specifically, we will show that, with minor modifications and optimizations, competitive link level performance can be achieved even in extreme use case scenarios using synchronization and channel estimation algorithms already employed in LTE-A. Further, we propose a set of enhancements to the broadcast channel and to the common search space configurations to fully dispense with cell specific reference symbols and legacy control channels.