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In this paper, a novel pilot extension scheme is proposed for massive MIMO uplink transmission, and its performance is evaluated analytically. Specifically, we divide the cell users into two groups, namely near users and far users, according to their distances to the service base stations. The far users are more motivated to mitigate the inter-cell interference than the near users at the price of...
In this paper, we analyze uplink sum rate of multiple-input multiple-output (MIMO) systems with maximum-ratio combining (MRC) receivers. To be practical, receive correlation and different powers of users are assumed. Two novel approximate results on sum rate are derived in closed form. Based on the results, we also obtain the asymptotic results on sum rate when the number of base station antenna (M)...
In this paper, a multi-cell joint optimization scheme based on pilot allocation is proposed in order to mitigate pilot contamination for multi- cell massive MIMO systems. This method measures interference of each pilot sequence caused by users multiplexing from adjacent cells exploiting the massive MIMO characteristics of fading channels. The scheme takes jointly optimizing a plurality of cells into...
The pilot contamination problem is one of the major obstacles that limit the performance of time-division duplex (TDD) multi-cell massive multiple-input multiple-output (MIMO) systems. Pilot contamination results from the re-use of the same set of pilot sequences in the different cells of the system. In this paper, we compare between two different scenarios of pilot signals allocation with respect...
We consider a multi-user massive MIMO uplink system in which there are multiple users with each having a single antenna and one base station (BS) with a large number of antennas. It is assumed that each user and BS have neither small scale nor large scale channel state information. For such a noncoherent system, we systematically design a series of absolutely additively uniquely decomposable constellation...
In this paper, we investigates shadow fading impact on a multi-user massive multiple-input-multiple-output (MIMO) system. By deploying a large antenna array on the base station, the random channel vectors between users and base station antennas become pairwise orthogonal. This important property of massive MIMO makes small scale fading effect asymptotically vanish while large scale fading still remains...
In this paper, we consider the design of analogue beamformers for the downlink of multi-user massive multiple-input-multiple-output (MIMO) systems. We specifically investigate systems where both link ends are equipped with hybrid digital/analog (HDA) beamforming structures, where the analog beamformers are adapted based on second order channel statistics, reducing the training overhead as well as...
We consider a single-cell scenario involving a single base station (BS) with a massive array serving multi-antenna terminals in the downlink of a mmWave channel. We present a class of multiuser MIMO schemes, which rely on uplink training from the user terminals, and on uplink/downlink channel reciprocity. The BS employs virtual sector-based processing according to which, user-channel estimation and...
This paper studies the optimization of pilot training signals in Massive MIMO systems with insufficient pilot length. We aim at finding the optimal pilot design and pilot length that maximize the Spectral Efficiency (SE) of the system. To achieve that, we firstly derive an approximation of average achievable capacity, which is related to channel estimation error and pilot signals. Then some analysis...
Flat-fading channel models are usually invoked for analyzing the performance of massive spatial modulation multiple-input multiple-output (SM-MIMO) systems. However, in the context of broadband SM transmission, the severe inter-symbol-interference (ISI) caused by the frequency-selective fading channels can not be ignored, which leads to very detrimental effects on the achievable system performance,...
Cross-layer design is a suitable approach that can address some of throughput challenges for future multimedia applications. In this regard, effective capacity concept offers a suitable metric to assess the implications that physical layer design may have on link layer performance. However, most reported studies in this aspect consider the case of downlink scenario for convenience multiple input multiple...
This paper investigates the asymptotic behaviour (error and outage probabilities) of a single cell multiple-input multiple-output (MIMO) system aided by a large scale antenna array. Specifically, the uplink transmission over composite fading channel with power-scaling scheme is considered. Where, most reported studies in this respect discuss the case of downlink scenario for convenience MIMO systems...
Under the conditions where performance in a massive MIMO network is limited by pilot contamination, the uplink signal-to-interference ratio (SIR) exhibits different distributions when using different pilot allocation schemes. By utilising different sets of orthogonal pilot sequences, as opposed to reused sequences amongst adjacent cells, the resulting SIR distribution is more favourable with respect...
The maximal ratio combining (MRC) receiver has excellent performance in the uplink of massive multiple-input-multiple-output (MIMO) systems under favorable propagation, but the performance degrades very much in a harsh channel because of interference. Theoretical analysis showing this phenomenon is given for a particular class of fading channel. A novel receiver, exploiting preemphasis/deemphasis...
Massive multiple-input multiple-output (MIMO) is one of the promising technologies to be used in the future fifth generation (5G) wireless networks for its capability to increase the system throughput, improve spectral efficiency and energy efficiency. To achieve these benefits of the massive MIMO, there are many challenges that need to be handled. One of these challenges is the pilot contamination...
This paper introduces a simple and practical channel estimator for multipath multi-cell massive MIMO TDD systems with pilot contamination. Least squares (LS) channel estimators present low performance under moderate to strong pilot contamination, while minimum mean square error (MMSE) estimators perform much better than LS estimators in such conditions. However, MMSE estimators present an issue that...
Pilot contamination caused by non-orthogonal pilot sequences reuse in adjacent cells has become one of the main impairments for massive multiple-input multiple-output (MIMO) systems. A scheme named flexible pilot reuse is proposed in this paper to reduce the effect. The main idea is that users suffered from mild pilot contamination (PC) are allocated the same set of orthogonal pilots, while the users...
Massive MIMO (multiple-input multiple-output) has been identified as a key technology for next generation cellular systems. This paper considers a multi-cellular system with large antenna arrays at the base station (BS) and single antenna user terminals (UTs), operating in a time division duplex (TDD) mode, under a composite fading- shadowing environment. In the uplink transmission, the pilot contamination...
In this paper, we investigate the potential application of wireless power transfer (WPT) in heterogeneous networks (HetNets) with massive multiple-input multiple-output (MIMO) antennas. Users first harvest energy from the downlink WPT, and then use the harvested energy for uplink transmission. We adopt the downlink received signal power (DRSP) based user association to maximize the harvested energy,...
This paper is concerned with a multiuser uplink massive MIMO system in Ricean flat fading. To avoid the pilot contamination issue, we firstly propose a simple equal gain combining scheme based only on the line-of-sight (LOS) component for a Ricean link in the uplink scenario with a single cell or multiple cells. Then we investigate the power-scaling law for the Ricean link when the transmit power...
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