## 1 Introduction
Furthermore, Non-Orthogonal Multiple Access (NOMA) has been recently proposed for VLC systems, aiming at increasing the bandwidth in multiple access schemes by providing the entire channel bandwidth to all users. Power-Domain-NOMA (PD-NOMA) is the most common variant used in VLC, and it uses power allocation for each user: the greater the user distance is, the higher the transmitted power is. The decoding process is performed by applying successive interference cancellation, the data being recovered iteratively by the users closer to the emitter. However, both OFDMA and NOMA require a high processing power for signal demodulation in IoT devices, thus increasing the price and power consumption, which would not fit the IoT requirements [38; 39; 40]. Alternatively, multi band-Carrierless Amplitude and Phase (m-CAP) modulation has been proposed for VLC systems as it presents high spectral efficiency and easy implementation [41]. In an IoT context, m-CAP can be used to allow multiple access from different devices at the same time, assigning a set of bands per user. The concept was recently proposed, where m-CAP and Subcarrier Multiplexing (SCM) were combined, allowing up to 20 users in a single VLC system, with a total data rate of 162.5 Mb/s [42]. However, aiming at IoT scenarios, the node devices would require a digital implementation of an m-CAP demodulator, which could negatively impact the IoT device's requirements. This paper proposes an m-CAP modulated system, where the demodulation is performed resorting to analog circuitry. As opposed to a digital m-CAP demodulator, using an analog demodulation architecture could potentially demodulate m-CAP signals with minimal hardware, allowing low-cost, low-power, and small-sized devices [43]. A full analog implementation of CAP for optical systems was previously proposed in [44], making use of analog transversal filters for optical communications. Analog demodulation of a digitally generated m-CAP signal for visible light communications was first presented in [45]. Commonly found in the literature, the digital m-CAP modulation frequency spectrum lacks guard bands; although the continuous frequency spectrum presents higher spectral bandwidth, it poses severe requirements at the receiver. Typical m-CAP systems use a raised cosine filter as a pulse shaping filter. However, such filters are not feasible in the analog domain. Moreover, abrupt frequency response decay with analog filters is usually difficult to achieve due the components' tolerances. Therefore, easy-to-implement analog filters, such as Bessel and Butterworth filters, should be considered at the receiver side. This paper studies the system's performance regarding two parameters: filter choice and guard bands. The filter choice analysis evaluates the system's performance regarding the analog filter at the receiver side, as well as the impact of substituting the raised cosine filter by one that matches the receiver filter. Concerning the guard band analysis, it evaluates the performance when guard bands are considered, either created by the suppression of the even bands, modulating only the odd bands, or alternatively, by varying the raised cosine filter roll-off factor, compressing the bandwidth of each band. The paper is structured as follows: Section 2 describes the theoretical model for the proposed system. Section 3 describes the simulation setup. Section 4 presents the achieved results, and lastly, Section 4 states the conclusions of the paper.