Extensions to COST 2100 Channel Model for Extremely Large-Scale MIMO

Extremely large-scale multiple-input multiple-output (XL-MIMO) system providing more degrees of freedom and beamforming gain, can effectively increase the capacity and coverage of wireless networks, which has become one of the key technologies for 6G. However, the near-field and non-stationary effects will appear as the array aperture expands. Therefore, existing channel models such as COST 2100 are extended to model these propagation effects. Considering the actual deployment of extremely large-scale antennas, this paper further extends the COST 2100 channel, including a) extending BS VR to 3D modeling to support the non-stationary characteristics of large-scale arrays in vertical and horizontal dimensions; b) extending the distribution of MS VR in vertical height to support user equipments (UEs) which are distributed on floors at different heights; c) extending models to support spatially consistent propagation characteristics between multi-TRPs. Finally, we show that our modeling method is reasonable through parameter tuning and simulation, and it can be used to evaluate the system performance of large-scale MIMO with different deployment morphologies.

I. Introduction

Massive multiple-input multiple-output (MIMO), a key technology for increasing area spectral efficiency in cellular systems, has become a reality for the fifth-generation (5G) wireless networks [1]. Looking forward towards the sixth generation (6G), to meet the demands of a fully connected, intelligent digital world, further scaling up the antenna number/size significantly is proposed, known as extremely large-scale MIMO (XL-MIMO) [2]. Compared with traditional MIMO, as the antenna size further increases, XL-MIMO systems behave differently due to spatial non-stationarity and near-filed propagation. In the large-scale regime, non-stationarity occurs because the terminals/mobile stations (MSs) may only see a portion of array at base station (BS) [3]. And MS locates in the near-field region of BS array, in which the commonly used far-field assumption with uniform plane wave (UPW) model may become invalid, instead the near-field radiation with spherical wavefront need to be considered [4]. In order to evaluate the performance of XL-MIMO effectively, the channel model must model the characteristics of spatial non-stationary and spherical wavefront. There are some preliminary efforts on the channel modeling and validation of XL-MIMO channel models [5] –[7]. Among them, the channel model based on COST 2100 is widely investigated since it naturally supports spherical wave characteristics and even validated based on measurement by research team from Lund. For example, [5] [6] extended a concept of base station-side visibility region (BSVR) in COST 2100 channel model to model the appearance and disappearance of clusters in XL-MIMO systems and extracted the model parameters for the extensions using a 128 antenna elements uniform linear array (ULA) at 2.6 GHz. In addition to MS-side visibility region (MS-VR), a multipath component visibility region (MPC-VR) is proposed in [6] to model the birth-death processes of individual MPCs. However, with these extensions, COST 2100 channel model still has the following limitations: a) MS-VR is modeled as a circle that is evenly distributed on the horizontal plane and cannot support simulation of MSs distributed on different floors, which is a typical simulation scenario. b) BS-VRs are valid only for extremely large-scale ULA. But in practice, the array is mostly a uniformly planar array (UPA) with elements distributed both horizontally and vertically and can be deployed along the wall to form an extremely large-scale planar array. c) The model cannot support multiple arrays deployed in the same location but with different boresight.