## 1 Introduction  
The application space of continuous wave (CW) radar systems is continuing to expand due to the small size, resolution, penetration depth, and low operation overhead of these systems. With this growth, a variety of techniques have been implemented to improve performance, gleam additional target information, and reduce interference while maintaining a low monetary and integration cost [1; 2]. Of these methods, the most prominent approach that has emerged is the modulation of the carrier frequency of the radar, which allows for the range and speed of a target to be recovered. Frequency-modulated continuous wave (FMCW) radar systems are used predominantly in the automotive industry [3] and are still being explored for use in activity monitoring [4; 5; 6], gesture recognition [7; 8; 9], and vital sign detection [10; 11; 12; 13]. In addition, improvements are still being made to CW Doppler systems used to perform vital sign monitoring and gesture detection through the in-depth analysis of processing methods [14] and gesture frame detection [15]. With the potential for radar-to-radar interference growing, investigations have been conducted into potential strategies that can reduce the spectral load values of modulated radar systems while maintaining target detection [16], the feasibility of passively measuring vital signs and gesture motion [17], and the way in which radar systems interfere with one another [18; 19]. An alternative to using FMCW radar systems in ultra-wideband (UWB) radar systems has also attracted scholarly interest. These radar systems also implement frequency modulation but cover much wider bandwidths by pulsing the transmitter signal, rather than being continuous in nature. This process introduces less interference into nearby systems and can generate a higher transmission power. UWB radar systems have shown promise in performing vital sign detection [20; 21], as well as short-range in-vehicle [22] and in-cabin [23] gesture detection. In looking to expand the vital sign detection capabilities of FMCW radar systems further, multiple-input multiple-output (MIMO) radar systems have been and continue to be explored [24]. These systems take advantage of the information scaling that comes from having multiple radar systems (bistatic) [25] or a radar system with multiple coherent transmitters and receivers (monostatic) [26], thereby creating an array of virtual transmitter-receiver channels. Both MIMO variations can perform noncontact vital sign sensing and rely on orthogonal waveforms for proper operation. This orthogonality can be achieved through various methods, each with advantages and drawbacks [27]. The most common and straightforward to implement is time-division multiple access (TDMA) using alternative transmissions. This approach ensures that the transmitted waveforms do not interfere with one another as they occupy separate time windows. Digital beam forming can help improve vital sign detection [28], and alternating the transmission channels enables the full frequency bandwidth for each channel. However, this benefit comes at the cost of more time being required to build the data cube, as well as the potential loss of information as transmitters are cycled. Another digital approach to orthogonal MIMO radar systems is through code-division multiple access (CDMA), in which the phase of each transmitter is encoded with a unique pseudorandom binary sequence (PRBS) that has high autocorrelation and low cross-correlation with other codes in the same family. By using these phase codes, all transmitters can operate at the same time as opposed to those in TDMA MIMO systems, increasing the data rate by the number of transmitters being simultaneously used.