Browsing by Author "Ribeiro, Lucas"
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- Channel Charting Aided Pilot Allocation in Multi-Cell Massive MIMO mMTC Networks
A4 Artikkeli konferenssijulkaisussa(2022) Ribeiro, Lucas; Leinonen, Markus; Rathnayaka, Isuru; Al-Tous, Hanan; Juntti, MarkkuServing a plethora of devices in massive machinetype communications (mMTC) can rely on spatial multiplexing enabled by massive multiple-input multiple-output (mMIMO) technology. To release the full potential, accurate channel estimation is needed. Due to the large numbers of devices it necessitates pilot reuse. We propose a pilot allocation algorithm based on multi-point channel charting (CC) to mitigate inevitable pilot contamination in a multi-cell multi-sector mMTC network with spatially correlated mMIMO channels. The generated CC represents an effective interference map from channel covariance matrices to capture the degree of pilot contamination caused by sharing the same pilot sequence among multiple users. The map is then fed into a greedy algorithm that aims at optimizing the reuse pattern of orthogonal pilot sequences to minimize the performance degradation caused by pilot contamination. The proposed CC-based method is empirically shown to obtain notable gains over a reuse-factor-aware random pilot allocation, yet leaving room for further improvements. - Channel Charting Aided Pilot Reuse for Massive MIMO Systems with Spatially Correlated Channels
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-12-01) Ribeiro, Lucas; Leinonen, Markus; Al-Tous, Hanan; Tirkkonen, Olav; Juntti, MarkkuMassive multiple-input multiple-output (mMIMO) technology is a way to increase spectral efficiency and provide access to the Internet of things (IoT) and machine-type communication (MTC) devices. To exploit the benefits of large antenna arrays, accurate channel estimation through pilot signals is needed. Massive IoT and MTC systems cannot avoid pilot reuse because of the enormous numbers of connected devices. We propose a pilot reuse algorithm based on channel charting (CC) to mitigate pilot contamination in a multi-sector single-cell mMIMO system having spatially correlated channels. We show that after creating an interference map via CC, a simple strategy to allocate the pilot sequences can be implemented. The simulation results show that the CC-based pilot reuse strategy improves channel estimation accuracy, which subsequently improves the symbol detection performance and increases the spectral efficiency compared to other existing schemes. Moreover, the performance of the CC pilot assignment method approaches that of exhaustive search pilot assignment for small network setups. - Exploiting Spatial Correlation for Pilot Reuse in Single-Cell mMTC
A4 Artikkeli konferenssijulkaisussa(2021-10-22) Ribeiro, Lucas; Leinonen, Markus; Al-Tous, Hanan; Tirkkonen, Olav; Juntti, MarkkuAs a key enabler for massive machine-type communications (mMTC), spatial multiplexing relies on massive multiple-input multiple-output (mMIMO) technology to serve the massive number of user equipments (UEs). To exploit spatial multiplexing, accurate channel estimation through pilot signals is needed. In mMTC systems, it is impractical to allocate a unique orthogonal pilot sequence to each UE as it would require too long pilot sequences, degrading the spectral efficiency. This work addresses the design of channel features from correlated fading channels to assist the pilot assignment in multi-sector mMTC systems under pilot reuse of orthogonal sequences. In order to reduce pilot collisions and to enable pilot reuse, we propose to extract features from the channel covariance matrices that reflect the level of orthogonality between the UEs channels. Two features are investigated: covariance matrix distance (CMD) feature and CMD-aided channel charting (CC) feature. In terms of symbol error rate and achievable rate, the CC-based feature shows superior performance than the CMD-based feature and baseline pilot assignment algorithms.