Intelligent reflecting surface (IRS) has emerged as a promising solution to enhance wireless information transmissions by adaptively controlling prorogation environment. Recently, the brand-new concept of utilizing IR...
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ISBN:
(纸本)9781728135557
Intelligent reflecting surface (IRS) has emerged as a promising solution to enhance wireless information transmissions by adaptively controlling prorogation environment. Recently, the brand-new concept of utilizing IRS to implement a passive transmitter attracts researchers' attention since it potentially realizes low-complexity and hardware-efficient transmitters of multiple-input single/multiple-output (MISO/MIMO) systems. In this paper we investigate the problem of precoder design for a low-resolution IRS-based transmitter to implement multi-user MISO/MIMO wireless communications. Particularly, the IRS modulates information symbols by varying the phases of its reflecting elements and transmits them to K single-antenna or multi-antenna users. We first aim to design the symbol-level precoder for IRS to realize the modulation and minimize the maximum symbol-error-rate (SER) of single-antenna receivers. In order to tackle this NP-hard problem, we first relax the low-resolution phase-shift constraint and solve this problem by Riemannian conjugate gradient (RCG) algorithm. Then, the low-resolution symbol-level precoding vector is obtained by direct quantization. Considering the large quantization error for 1-bit resolution case, the branch-and-bound method is utilized to solve the 1-bit resolution symbol-level precoding vector. For multiantenna receivers, we propose to iteratively design the symbol-level precoder and combiner by decomposing the original large-scale optimization problem into several sub-problems. Simulation results validate the effectiveness of our proposed algorithms.
constantenvelope (CE) precoding is a recently proposed technique for massive MIMO systems that decreases the hardware complexity of base station circuitry. In this letter, we build on this idea and propose a multi-en...
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constantenvelope (CE) precoding is a recently proposed technique for massive MIMO systems that decreases the hardware complexity of base station circuitry. In this letter, we build on this idea and propose a multi-envelopeprecoding method, which utilizes more than one (but only a few, e.g., 2 or 3) envelope levels and assigns higher levels on the antenna group(s) requiring more power in order to increase the achievable rates. The results demonstrate substantial gains with respect to the CE approach for both cases of discrete and continuous phase shifters with almost no increase in hardware complexity and a small increase in computational complexity.
Wireless communications is an important part of information and communication technologies. Particularly, with the introduction of 5G wireless systems, higher data rates, ultra-low latencies and improved power efficie...
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Wireless communications is an important part of information and communication technologies. Particularly, with the introduction of 5G wireless systems, higher data rates, ultra-low latencies and improved power efficiencies are demanded. It is un- derstood that multiple-input multiple-output (MIMO) systems constitute some of the promising technologies to meet these demands, however, currently used number of antennas at the base stations (BS) is not sufficient to reveal the full potential. As a result, massive MIMO systems which use a very large number of antennas at the BSs have recently been proposed as enabling solutions. While massive MIMO promises much for 5G and beyond wireless technologies, there are many problems to be solved including lowering of high built-in and operating costs of BSs to make this technology practical. constantenvelope (CE) precoding has recently been proposed as a way to reduce the hardware complexity of massive MIMO systems. CE precoding technique for downlink enables a BS structure with one (nonlinear) power amplifier (PA) coupled with continuous or discrete phase shifters in front of each antenna instead of separate highly linear PAs driving each. While CE precoding offers significant reductions in hardware costs, it results in some performance loss in terms of achievable data rates and power efficiencies compared to conventional zero forcing precoding based approaches. In this thesis, we build on the CE precoding idea and propose the use of a multi- envelopeprecoding technique for massive MIMO systems which utilizes more than one (but only a few, e. g., 2 or 3) PAs with the objective of recovering some of the performance loss due to the use of CE precoding. The proposed multi-envelope pre- coding method relies on the standard zero forcing algorithm to group the antennas, and then it utilizes an envelope with a higher level on the antenna group(s) requiring higher power. In other words, the number of power levels used equals to the nu
Optimal precoding for multiple-input single-output (MISO) systems with nonlinear power amplifiers (PAs) is proposed. The idea behind the precoding is to generate a set of transmitted signals s.t., after passing throug...
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Optimal precoding for multiple-input single-output (MISO) systems with nonlinear power amplifiers (PAs) is proposed. The idea behind the precoding is to generate a set of transmitted signals s.t., after passing through the nonlinear PAs and MISO channel, a desired signal will be obtained at the receiver's antenna. The channel is assumed to be frequency selective. It is assumed that the channel and noise power are known at the transmitter (TX). The specific aim of the proposed precoding is to maximize signal-to-interference and noise ratio (SINR) per symbol at the receiver. The proposed technique can be seen as a generalization of the constantenvelope (CE) precoding approach, based on the same concepts. However, in this work we assume a general PA nonlinearity and, therefore, the TX signals may have varying amplitude. Moreover, while in the CE only the nonlinear distortions (interference), seen at the receiver, are minimized, we propose to maximize the SINR. This approach shows better symbol error rate (SER) performance than CE precoding. For given SER requirement, the PSNR gap is clearly seen for a low number of TX antennas, although, as the number of TX antennas increases the PSNR gap decreases.
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