## 1 Introduction
It should be noted that one of the main novelties of this work is the 4G signal characteristic parameters that have been used in the implementation of the Relay Nodes. This has made it possible to perform essential signal measurements in full compliance with the 3 GPP TS 38.104 standard using a high-performance spectrum analyzer. The integration of MIMO functionalities in an RN can improve its performance and allow for more reliable transmissions [22; 23]. However, MIMO A&F Relay Nodes present some problems which are yet to be solved, such as the degradation suffered by the signal between the eNB and the RN due to the propagation channel (an effect that will be transferred to the link between the Relay Node and the UE). In [24; 25; 26], various MIMO-RN schemes have been analyzed, based on knowing the Channel State Information (CSI), in order to determine the design of the optimal linear receiver. In real scenarios, the channel is unknown and, hence, needs to be estimated. Channel estimation and equalizer algorithms have been developed for MIMO-RN schemes in [27; 28; 29; 30; 31]. In this paper, we consider channel estimation using the pilot symbols and a Least Squares (LS) estimator. Besides, Minimum Mean Square Error (MMSE) and Zero-Forcing (ZF) pre-equalizations are adopted, prior to forwarding the signal by the MIMO A&F relay node. It should be noted that these equalization techniques have been standardized by the 3 GPP for the detection of LTEsignals. Furthermore, the A&F with ZF/MMSE pre-equalization have been deeply studied from a theoretical view without hardware implementation. Motivated by the related issues, in this paper, a MIMO Relay Node Co-operative System (RNCS) through a Software Defined Radio (SDR) platform has implemented. The LTE signal which fulfils the requirement of the 3 GPP has been considered. The major contribution of this paper are summarized as follows:  
1. A design and implementation of a completely functional testbed framework, based on a MIMO Software Defined Radio platform and Matlab(tm) tool have been presented, which employees the following LTE features [13]: * References Signals. * Primary Synchronization Signal (PSS). * Secondary Synchronization Signal (SSS). * Physical Broadcast Channel (PBCH). * Physical Format Indicator Channel (PCFIC). * Physical Downlink Control Channel (PDCCH). * Physical Downlink Shared Channel (PDSCH). In sense, the transmitted signal which is emulated by our eNodeB can be decoded by the MS2090A-Anritsu LTE /5G Commercial Equipment. 2. Three Amplify-&-Forward strategies have been implemented. The first A&F protocol implicates a MIMO conventional A&F scheme. Nevertheless, we focus on improving the conventional A&F relaying performance through stages of channel estimation and pre-equalization techniques. In fact, MIMO A&F protocol with Zero Forcing and Minimum Mean Square Error, have been developed, which the channel estimation has been performed by mean of Least Square (LS) estimator [32] and Bi-Cubic Interpolate (BCL) [33]. 3. A MIMO Decode-&-Forward strategy has been proposed, which decoding and encoding all channel emulated by the eNodeB and considers LS channel estimator and MMSE equalization stages. 4. The implemented relaying strategies have considered stages of frequency synchronization, as well as search Cell-ID, which allows adjusting the parameters of the CP-OFDM received signal. 5. 64-QAM modulation scheme and extensive experiments have taken into account in an indoor-to-indoor environment real-world, in order to analyze the performance of the implemented protocols. The rest of this paper is organized as follows: A brief summary of related works is given in Section 2. The system models of a two-hop MIMO, Amplify-&-Forward, and Decode-&-Forward Co-operative Communication Systems are presented in Section 3, and the mathematical models of the A&F pre-equalization schemes are described. Hardware Implementation of the RNCS through the A&F and D&F Relay Nodes is developed in Section 4. In Section 5, we present the measurement scenario.