I. Introduction
The modeling of multiplicative fading channels, which are also called cascaded propagation channels, refers to the modeling of multipath fading as the product of classical fading processes, e.g., Rayleigh, Rice, and Nakagami- processes. In recent years, multiplicative fading models have gained recognition due to their potential of capturing the multipath effects encountered in new wireless applications such as mobile-to-mobile (M2M) communications like mobile ad hoc networks and wireless sensors networks, vehicle-to-vehicle (V2V) communications, and cooperative relaying systems. Existing investigations on multiplicative channels have mainly dealt with the double Rayleigh fading model. Based on measurement data in [1] and [2], Honcharenko et al. and Erceg et al., respectively, demonstrated that the double Rayleigh fading model well describes the multipath fading effects encountered in indoor and urban microcellular propagation environments where both the transmitter and the receiver are moving. Moreover, Kovacs et al. [3] showed that the cascaded Rayleigh model provides a perfect fit to measurement data collected in different suburban outdoor-to-indoor M2M propagation environments. The underlying fading model has also been used for the modeling of multiple-input multiple-output (MIMO) keyhole channels [4]– [6]. Recently, Matolak and Frolik showed in [7] that double Rayleigh processes are also suitable for modeling V2V propagation environments where the multipath fading effects are found to be more severe than those described by the classical Rayleigh [8]. More recently, measurement-based studies reported in [9] and [10], where measurement campaigns have been conducted under non-line-of-sight (NLOS) conditions, showed that radio-frequency identification channels can be statistically described by the double Rayleigh model.