Upgrade of the CMS Muon Spectrometer in the forward region with the GEM technology

The Large Hadron Collider (LHC) will be upgraded in several phases that will allow significant expansion of its physics program. The final luminosity of the accelerator is expected to exceed 5~$\times$~10$^{34}$~cm$^{-2} $s$^{-1}$, five times the original design value. The CMS muon system must be able to sustain a physics program after the increase of luminosity and maintain sensitivity for electroweak physics for TeV scale searches similar to what was achieved up to now. To cope with the corresponding increase in background rates and trigger requirements, the installation of additional sets of muon detectors based on Gas Electron Multiplier (GEM) technology, referred to as GE1/1, GE2/1 and ME0, has been planned. The installation and commissioning of the GE1/1 chambers is scheduled by 2019/20, while the GE2/1 and ME0 detectors are expected to be installed between 2023 and 2027. We present an overview of the Muon Spectrometer upgrade using GEM technology, a description of the ongoing GE1/1 project: production, qualification, installation and details of the GE2/1 and ME0 upgrade. We will focus on the novel solutions adopted for realization of the latter project, both from detectors and electronics side, with a summary of the ongoing R$\&$D activities.