## 1 Introduction  
Ways and means to improve the quality of communication and to reduce its cost have become popular research topics in the field of wireless personal networks. It is expected that a combination of ultra-wideband (UWB) systems and multi-antenna systems will increase the transmission data rate. The UWB technology has the advantages of high-speed transmission, low-transmit power, low duty cycle, low-cost and simple transceiver structures, and less interference as compared to other applications. UWB is a valuable technology for future wireless applications such as indoor communication [1; 2; 3] and the intra-vehicular wireless sensor network (IVWSN) [4; 5; 6]. Indoor communication is limited to short distances and subjected to severe attenuation and multipath effect. In an IVWSN, the vehicle control systems and energy budgets of the sensor nodes in an in-car channel contain a large number of metal reflectors because of the short distance. Specifically, the distance between the transmitter and the receiver in an in-car channel is less than 10 m.  
Smart antenna technology allows the device to collect more energy to improve the signal-to-noise ratio (SNR) at the receiver, while the multiple-input and multiple-output (MIMO) system has the advantage of high capacity gain [7; 8; 9; 10; 11]. MIMO systems are well-suited for working in diverse systems. In rich multipath channels, the probability of having more than one independent path increases. The properties of an MIMO channel, especially its capacity, are highly dependent on the spatial structure of the channel. Different diversity techniques have been applied to communication systems to improve their quality of communication [12; 13; 14; 15]. UWB is mainly applied to indoor environments characterized by the multipath effect. The UWB technique has a plurality of diversity techniques and has almost exclusively been applied to MIMO to improve its quality of communication. The MIMO-UWB system has the potential for short-range, high-speed transmission requirements, and is especially suitable for complex indoor environments. It is a wireless solution that performs better in the current system design. MIMO-UWB has become a compelling candidate for extremely high data-rate communications [16; 17; 18; 19]. This paper applies the real orthogonal design (ROD) [20; 21], a diversity technique, in an MIMO-UWB system. Using an ROD to increase the transmit diversity scheme, the transmitter does not require any feedback from receivers. The computation complexity of the ROD is equal to maximal ratio receive combining. Applying an ROD in an MIMO-UWB system addresses the market demands for quality and efficiency without requiring a significant redesign of existing UWB systems. The bit error rate (BER) performance is better when applying a high-order ROD. However, the intersymbol interference (ISI) effect is proportional to the size of the ROD. The multipath effect of the ISI, which increases the BER and outage probability, degrades the performance of an MIMO-UWB system. The rake receiver combines signals arriving on multiple propagation paths, and the tapped delay line (TDL) is used in this matched filter [22; 23; 24]. Therefore, a rake receiver is deployed to not only suppress the ISI multipath effect, but also utilize the energy present in multiple propagation paths. Ray-tracing techniques are used to calculate the channel state information for different antenna radiation patterns [25]. The process can be carried out through simulation to overcome these drawbacks as long as the accuracy of the simulation tools can be proven. It conceptually assumes that a pincushion of rays is sent out from the transmitter, and is traced over the environments until either the ray has reached the receiver or the ray has lost enough power and its contribution to the received signal is negligible. The transmitting ray will be transmitted, reflected, or diffracted to the receiver.