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Superior spectral properties of Filter Bank Multi-Carrier (FBMC) techniques make them an interesting choice for future wireless systems. In order to directly apply well known pilot-symbol aided channel estimation in FBMC, however, the intrinsic imaginary interference has to be canceled. Such cancellation method is usually designed for a doubly-flat channel. In this paper, we investigate the effects...
In this paper, we analyze the performance of the fractional pilot reuse (FPR) scheme with pilot contamination mitigation in massive multiple-input multiple-output (MIMO) system. In FPR, users are classified into the cell- center and the cell-edge ones according to their signal-to- interference-plus-noise ratios (SINRs) at the receiver side. Then, the cell- edge users with low SINRs in different cells...
With the reuse of identical training sequences by users in different cells, massive MIMO is severely affected by pilot contamination due to residual error in channel estimation. In this paper, we consider the traditional structure of the training phase, where orthogonal pilot sequences are reused, and analyze a recently proposed group- blind detector in the uplink of an interference- limited network...
We propose a decentralized multi-cell aware opportunistic random access (MA-ORA) protocol that almost achieves the optimal throughput scaling in a K-cell random access network with one access point (AP) and N users in each cell. Under our MA-ORA protocol, users opportunistically transmit with a predefined physical layer data rate in a decentralized manner if the desired signal power to the serving...
This work1 analyzes the Generalized Degrees-of-Freedom (GDoF) of the 2-User Multiple-Input Single-Output (MISO) Broadcast Channel (BC) in the so-called Distributed CSIT regime, with application to decentralized wireless networks. This regime differs from the classical limited CSIT one in that the CSIT is not just noisy but also imperfectly shared across the transmitters (TXs). Hence, each TX precodes...
One of the orthogonal frequency division multiplexing (OFDM) schemes is the Time Domain Synchronous OFDM (TDS-OFDM) scheme, in which, the guard intervals between consecutive OFDM symbols contain Pseudo Noise (PN) sequences which are known to the receiver and are used for channel estimation and synchronization. In this paper, a joint channel estimation algorithm is proposed for TDS-OFDM scheme, the...
This work deals with beamforming for the MIMO Interfering Broadcast Channel (IBC), i.e. the Multi-Input MultiOutput (MIMO) Multi-User Multi-Cell downlink (DL). The novel beamformers are here optimized for the Expected Weighted Sum Rate (EWSR) for the case of Partial Channel State Information at the Transmitters (CSIT). Gaussian (Posterior) partial CSIT can optimally combine channel estimate and channel...
Pilot contamination limits the potential benefits of massive multiple input multiple output (MIMO) systems. To mitigate pilot contamination, in this paper, an efficient channel estimation approach is proposed for massive MIMO systems, using sparse Bayesian learning (SBL) namely coupled hierarchical Gaussian framework where the sparsity of each coefficient is controlled by its own hyperparameter and...
This paper characterizes the sources of distortion of offset-QAM based filter bank multicarrier systems when perfect channel state information at the receiver (CSIR) is not available. The statistical information of the distortion reveals that the mapping scheme, which determines how symbols are inserted in the frequency-time grid, can be optimized to reduce the impact of the estimation error. Moreover,...
Next generation (5G) mobile communication systems has a goal of ultra-high peak data rate. Ultra-Dense Network (UDN) is viewed as one of the key technologies to meet this challenge. The trend of network densification brings more complex interference. To solve this problem, a novel user-centric virtual cell design is proposed. Considering the changes of virtual cell load, we propose a load-aware virtual...
In this paper, we analyze the performance of multi-cell least-square (LS) channel estimation using pilot sequence hopping and pilot reuse strategy for pilot decontamination. We obtain achievable rates in uplink synchronous system in L-cell system using LS channel estimation and zero forcing (ZF) detection. Polynomial expansion approximation is performed to obtain a closed form bound of the asymptotic...
This paper optimizes the pilot assignment and pilot transmit powers to mitigate pilot contamination in Massive MIMO (multiple-input multiple-output) systems. While prior works have treated pilot assignment as a combinatorial problem, we achieve a more tractable problem formulation by directly optimizing the pilot sequences. To this end, we compute a lower bound on the uplink (UL) spectral efficiency...
Pilot contamination has been confirmed as a major bottleneck to performance improvement of time division duplexing (TDD) massive multiple-input-multiple-output (MIMO) systems. An asynchronous pilots scheduling (APS) scheme is proposed in this paper for pilot decontamination. According to interfering levels, users are divided into cell-center users, which are generally interfered slightly, and cell-edge...
How to improve system capacity and spectral efficiency is a key issue for next generation wireless communication. Heterogeneous network (HetNet) has been considered as a new promising technique for enhancing the quality of service and spectrum efficiency due to different radio access technology and network structures. However, conventional resource allocation algorithms in HetNets are achieved under...
The Interfering Broadcast Channel (IBC) applies to the downlink of (cellular and/or heterogeneous) multi-cell networks, which are limited by multi-user (MU) interference. The interference alignment (IA) concept has shown that interference does not need to be inevitable. In particular spatial IA in the MIMO IBC allows for low latency transmission. However, IA requires perfect and typically global Channel...
Superposed multicarrier transmission is a known method to improve frequency utilization efficiency when several wireless systems share the same spectrum. Obviously, an enhanced spectral efficiency comes at the expense of interference. To suppress the effect of interference, forward error correction (FEC) metric masking can be applied. In FEC, the corresponding log-likelihood (LLR) of the superposed...
Massive MIMO (multiple-input multiple-output) provides great improvements in spectral efficiency over legacy cellular networks, by coherent combining of the signals over a large antenna array and by spatial multiplexing of many users. Since its inception, the coherent interference caused by pilot contamination has been believed to be an impairment that does not vanish, even with an unlimited number...
Due to the difficulty of coordination in multi-cell random access, it is a practical challenge how to achieve the optimal throughput with decentralized transmission. In this paper, we propose a decentralized multi-cell aware opportunistic random access (MA-ORA) protocol that almost achieves the optimal throughput scaling in a multi-cell random access network with one access point (AP) and multiple...
Large-scale (a.k.a. Massive) Multiple-Input Multiple-Output (MIMO) systems are considered as a strong candidate to meet the exceptionally high spectral efficiency requirements for “beyond 4G” (or commonly termed 5G) wireless communications systems. For such systems, the availability of accurate uplink channel knowledge at the base station is critical to success, particularly in the time-division duplex...
This work deals with beamforming for the MaMISO Interfering Broadcast Channel (IBC), i.e. the Massive Multi-Input Single-Output (MaMISO) Multi-User Multi-Cell downlink (DL). The novel beamformers are here optimized for the Expected Weighted Sum Rate (EWSR) for the case of Partial Channel State Information at the Transmitters (CSIT). Gaussian partial CSIT can optimally combine channel estimate and...
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