Waveform design for massive MISO downlink with energy-efficient receivers adopting 1-bit ADCs

Abstract

The self-archived postprint version of this conference article is available at Linköping University Institutional Repository (DiVA): http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-134225 N.B.: When citing this work, cite the original publication. Gokceoglu, A., Björnson, E., Larsson, E. G, Valkama, M., (2016) Abstract-In high-density low-bitrate Internet-of-Things (IoT) use case of 5G networks, the terminals and sensors are to be of extremely low-cost and low energy-consuming. Typically, the analog-to-digital converters (ADCs) dominate the power-budget of receiver chains, in particular if the quantization resolution is high. Hence, receiver architectures deploying 1-bit ADCs are of high interest towards realizing low-cost, high energy-efficiency device solutions. In this paper, we study the waveform design and optimization for a narrowband low-bitrate massive MISO downlink targeting to achieve rates higher than 1 bits/sec (per real-dimension) where the terminal receivers adopt only simple 1-bit quantization (per real-dimension ) with oversampling. In this respect, first we show that for a particular precoder structure, the overall link is equivalent to that of an AWGN SISO with controlled intersymbol interference (ISI). The filter design problem for generating the desired ISI in such SISO links has been studied in previous works, however, the only known method in literature is a computationally demanding brute force search method. As a novel contribution, we develop models and tools that elaborate on the conditions to be satisfied for unique detection and existence of solution for the filter coefficients. Then, as a concrete example, the developed models and tools are utilized to show that in the absence of noise, five-times oversampling is required for unique detection of 16-QAM input alphabet. Building on these findings, we then develop novel algorithms that can efficiently design the filter coefficients. Examples and simulations are provided to elaborate on filter coefficient design and optimization, and to illustrate good SER performance of the MISO link with 1-bit receiver even at SNRs down to 5 dB.

Spatio-Temporal Waveform Design for Multiuser Massive MIMO Downlink With 1-bit Receivers

“…In the same work, a linear temporal precoding scheme in the form of controlled inter-symbol-interference (ISI) is proposed where a brute force method is used to optimize the overall ISI in the considered single-user SISO case. Then, [1] extended the system model in [20] to frequency-flat block-fading MISO channels, and proposed well-structured and hence faster solutions to the ISI optimization problem compared to the approach in [20].…”

“…The main rationale is to include the information about the transmitted symbol into the controlled ISI of the oversampled signal such that the receiver can extract this information and can uniquely decode the transmitted symbol using the 1-bit quantized observation. In this respect, we substantially extend the works in [1] and [20] with several novel contributions which can be listed as follows: 1) In contrast to fairly simple single-user studies in [1] and [20], this paper focuses on multi-user massive MIMO scenario where multiple users, each equipped with a 1-bit receiver, are served simultaneously at the same time-frequency resource.…”

“…2) In [1] and [20], the search or optimization of the ISI sequence is done for a simplified system model where there are no constraints on the TX and/or RX filters. However, practical TX filters have transmission bandwidth constraints stemming from the spectral mask and emission requirements of the system whereas practical RX filters have bandwidth constraints determined by the desired suppression level of adjacent channel signals and other out-of-band noise and interference.…”

1-bit quantization and oversampling at the receiver: Sequence-based communication

“…For the high SNR regime, channel state information can be exploited at the transmitter for a channel inversion strategy for the construction of receive signals appropriate for 1-bit quantization. Moreover, the sequence design approach described in [11] for the singleinput single-output channel has been recently extended for the massive multiple-input single-output scenario in [15] and for the massive MIMO scenario in [16].…”

Zero-Crossing Precoding with Maximum Distance to the Decision Threshold for Channels with 1-Bit Quantization and Oversampling

“…A more practical approach was presented in [6], where filter coefficients are optimized for a 16-QAM transmission, in terms of the maximization of the minimum distance to the decision threshold, which is widely used also in other studies with quantization [7][8][9]. Later the approach in [6] was improved and extended for the multipleinput-single-output channel [10] and a more advanced waveform design was proposed for the multiuser multiple-input multiple-output (MIMO) downlink in [11], with a separate precoding for time and space.…”