Annonce

Starting date : September or October 2023

 

Full Time, 1 year Contract : funded by the POSEIDON ANR Project « Power-efficient and lOw complexity approacheS for cEll-free massIve MIMO Network «. Possibility of one year renewal through another grant.

 

Salary (2770 euros/month).

 

Laboratory : CEDRIC/Laetitia, at CNAM, located in Paris.

 

Requirements : We seek international candidates with a strong academic background, ideally with expertise in physical layer of radiocommunications networks.

 

One of the 5G, B5G and 6G network service is the massive Machine-Type Communications (mMTC), which offers low bandwidth connectivity with deep coverage. It helps collect large volume of small data packets from a huge number of devices simultaneously. Most mMTC applications are characterized by the transmission of sporadic burst of short data packets over a relatively long distance (up to 10 Km), low bandwidth, low-power devices and long-life battery or power supply requirements. Among the multiple use cases concerned by mMTC, we may cite the smart city application, which is the one retained in the Poseidon project. In a smart city, sensors can be placed everywhere to collect data, with streets, buildings, public and personal devices all being interconnected, and the huge amount of data generated by these sensors then being communicated, analysed and fed back to the infrastructure to affect changes in operation. This use case uses sensors and IOT-based subsystems.

 

IoT is an emerging paradigm for future communication systems, which has been investigated for co-located massive MIMO systems as massive MIMO can support massive connectivity due to its high capacity, reliability, and energy efficiency. Recently, cell-free massive MIMO [1] was investigated as a way to support IoT systems. By leveraging the macro-diversity gain and better coverage resulting from distributed antennas, cell-free massive MIMO can outperform the IoT network supported by co-located massive MIMO systems. Therefore, it is interesting to consider and further study the use of cell-free massive MIMO to support IoT.

 

The smart city application of mMTC considered in Poseidon has the objective to enable massive connectivity, for the uplink, from limited time-frequency resources. The uplink represents a primary challenge due to the massive number of uncoordinated connections in mMTC and is the focused of this study. Current solutions to enable massive connectivity mainly fall into two categories: medium access control (MAC) and physical (PHY) layer solutions.

 

The MAC-layer solutions aim to redesign the access protocols such that the limited time-frequency resource can be shared by more devices. For example, the narrow-band IoT (NB-IoT) standard [2] enables subcarrier-level resource allocation and supports single-tone transmissions with a subcarrier spacing as low as 3.75 Khz, allowing more devices to be served simultaneously. Another example is the grant-free transmission [3] which requires only very low control overhead, but often suffers from collisions and low efficiency. However, with an appropriate collision resolution mechanism, grant-free access can be made highly efficient. Consequently, grant-free access control seems favorable for mMTC. The outcome of collisions, though, is strongly dependent on the specific physical layer technologies. The PHY- layer solutions are mostly based on advanced receivers based on non-orthogonal multiple access (NOMA) [4].

 

For the poseidon project, we consider a NB-IoT waveform jointly with a grant-free random access protocol such that users are randomly active in the resulting contention period. Due to the random activity in each slot, only a subset of users is actively sending data. From a PHY perspective, this leads to estimation problems with sparsity, as the subset

of active users is unknown and has to be estimated jointly with the user data. To further enhance the connectivity capability of mMTC networks, we propose to consider, solely or in addition to NOMA techniques exploiting sparsity, widely linear processing at reception, with its interesting capability to create virtual antennas [5], provided improper

modulations are considered. For this reason, we consider pi/2-BPSK modulation, which is permitted by the NB-IoT uplink, and we aim to design mechanisms that can further improve the performance of NB-IoT networks, especially in terms of the number of devices supported per sector. Such a study has been done recently in [6], with very promising

results, but for mMTC cellular networks and without exploiting the sparsity of the observations.

 

We propose to evaluate the applicability of the existing grant-free random access scheme, developed for co- located massive MIMO cellular networks, to cell free networks, jointly with the potential associated constraints. Furthermore, we propose to investigate more particularly the use of widely linear (WL) receivers, jointly with 1-D constellation, for cell-free MTC networks grant free access based on NB-IoT, potentially combined or not with NOMA schemes.

 

 

The work will begin by a state of art of grant-free access techniques for cell-free networks. A simulation chain, integrating a typical mMTC scenario, some reference processing of the literature and the new processing developed

during the study will then be developed. A performance evaluation and comparison with the state of art will be done. A behavioural simulation will then be developed to evaluate the impact of the developed processing on the network

connectivity. A report synthetising the results will then be written at the end of the study.

 

 

[1] E. Bjornson and L. Sanguinetti, “Scalable cell-free massive MIMO systems,” IEEE Trans. Commun., vol. 68, no. 7, pp. 4247-4261, Jul. 2020

[2] J. Xu, J. Yao, L. Wang, Z. Ming, K. Wu, L. Chen, « Narrowband Internet of Things : Evolutions, Technologies, and Open Issues», IEEE Internet of Things Journal, Vol. 5, N°3, pp. 1449-1462, June 2018.

[3] G. Berardinelli and al, « Reliability analysis of grant-free transmission over shared resources », IEEE Access, Vol. 6,pp. 23602-23611, 2018.

[4] Z. Ding, X. Lei, G.K. Karagiannidis, R. Schoeber, J. Yuan, V.K. Bhargava, « A survey of non-orthogonal multiple access for 5G networks : Reserach challenges and future trends», IEEE J. Select. Areas Commun, Vol. 35, N°10, pp. 2181-2195,Oct. 2017.

[5] P. Chevalier, F. Pipon, "New insights into optimal widely linear array receivers for the demodulation of BPSK, MSK and GMSK signals corrupted by non circular interferences – Application to SAIC", IEEE Trans. Signal Processing, Vol 54, N°3, pp. 870-883, March 2006.

[6] R. Gui, N.M. Balasubramanya, L. Lampe, « Connectivity Performance Evaluation for Grant-Free Narrowband IoT With Widely Linear Receivers », IEEE Internet of Things Journal, Vol. 7, N°10, pp. 10562-10572, October 2020.

 

Contact : Pascal Chevalier – CNAM Professor (pascal.chevalier@cnam.fr)

 

CEDRIC laboratory, HESAM university, 292 rue Saint-Martin, 75141 Paris Cedex 03