## 1 Introduction  
During the last several decades, wireless sensor networks (WSNs) have been widely used in various areas, including environmental monitoring, home automation, healthcare, agriculture, unmanned battle fields, public space surveillance and intelligent traffic systems (ITSs) [1]. A WSN is usually deployed with static sensor nodes to perform monitoring missions in the region of interest. However, due to dynamic changes in events and hostile environment, a purely static WSN could face severe problems, such as scalability, coverage and unfair battery consumption. To overcome these problems, mobile wireless sensor networks (mobile WSNs) have been proposed [2]. Mobile WSNs are a particular class of WSN in which mobile sink or sensor nodes play a key role in the execution of the applications. Although it has been shown that mobile sensor nodes alleviate several issues related to fixed sensor network coverage and scalability, many technical issues remain [3; 4; 5; 6; 7; 8]. One of the most significant challenges for mobile WSNs is to form a reliable wireless channel among a mobile sink node and sensor nodes. Moreover, some mobile WSN applications, such as ITS, unmanned battle fields and public space surveillance, exploit rich sensing information, including video, audio or high definition images. To gather and use rich sensing information, wireless multimedia sensor networks (WMSNs) have been introduced and investigated to determine if sensor nodes are capable of producing different media streams [9; 10]. Multimedia information, such as video streams or high definition images, requires much higher data rates than those supported by current WSNs. It is essential to provide fast wireless links among a sink node and sensor nodes for efficient and fast data aggregation in WMSNs. Thus, a reliable and fast transmission technology for mobile sink and sensor nodes is one of the key technical issues to be tackled for mobile WMSNs. A multiple antenna technique may be an appropriate solution to provide reliable and high data rate channels in WMSNs. Multiple input and multiple output (MIMO) systems can support higher data rates than a single input and single output (SISO) system under the same transmit power budget and bit-error-rate (BER) performance requirements. MIMO communication exploits the spatial components of the wireless channel to improve the capacity and error rate performance of communication systems through spatial diversity or multiplexing. Diversity schemes, such as orthogonal space-time block codes (OSTBC) [11], are used to combat channel fading and provide increased link robustness. Spatial multiplexing (SM) enables the transmission of multiple parallel data streams as a means to enhance system throughput [12]. A MIMO system has been formerly studied as a promising technology for increasing the channel capacity and reliability in cellular or wireless local area network (LAN) systems [13; 14; 15; 16; 17; 18]. However, many research results have been proposed in the last few years to make use of MIMO technologies in WSNs [19; 20; 21; 22]. In conventional WSNs, the direct application of multi-antenna techniques to sensor networks is impractical, due to their limited physical size and the complexity of a sensor node, which typically can support only asingle antenna. For this reason, cooperative MIMO solutions have been proposed as an alternative solution, where SISO sensor nodes cooperate with each other to form a virtual MIMO [23, 24, 25, 26]. Recent advances in cost-effective wireless sensor node architectures on the millimeter level have led to designs of multiple antennas for WSNs [27, 28]. In these designs, a sensor node can be comprised of a two-element switched antenna array using a single radio frequency front-end. Based on these results, unlike the previous works, where MIMO has been considered for WSNs only in the cooperative virtual MIMO manner, non-cooperative MIMO techniques have been proposed [20, 21, 22]. In [21], and a space-time coded cooperative transmission has been proposed.