## 2 Related Work  
Previous research indicates that the performance of CC networks in real time wireless systems has been analyzed and evaluated on the basis of various testbeds. The testbed comprised of various kind of hardware design and functionalities. Regarding the performance of testbed, the BER approach was commonly adopted. For example, author et al. [8] exploited CoopMAC protocol on 802.11 standard devices in connection with open source platform. They performed a number of experiments on relays ranging from 3 to 10 in a single testbed. Similarly, in [12], commodity hardware multiple relays were utilized for implementing testbed, where the selection of strong signal was either from sender or relay without taking into account the signal combining technique. However, the drawback of this approach is that the actual cooperative diversity gain cannot be achieved at the destination. Furthermore, this hardware is not easy to modify at MAC layer and almost impossible to alter at physical layer, where actually CC technology is applied.  
To overcome the limitations of commodity hardware, later on, fast processors and boards like DSP and FPGA based testbeds were used to analyze CC system. For example, [PERSON] et al. [11] developed a testbed using a DSP kit with laptop or PC, and commonly used relaying schemes, such as amplify and forward (AF), Decode and forward (DF) and Compress and forward (CF). Furthermore, at the destination for getting the actual diversity gain of CC network, MRC technique was applied. The benefit of these testbeds, on the one hand, is that they provide hardware and software flexibility, and on the other hand they are cost effective. Similarly [16; 17] developed a Wireless Open Access Research Platform (WARP) that uses amplify and forward relaying scheme and is based on the orthogonal frequency division multiplexing (OFDM) technique and distributed Alamouti transmit diversity scheme. However, the drawback of this approach on the one hand is that due the absence of external clock interface in hardware platform, the multi-relay synchronization becomes difficult. On the other hand, it is very expensive.  
The platform of USRP and GNU Radio is becoming very popular because of the implementation of all signals processing in CC testbed on it. The open source availability of GNU radio software made it possible to add new functionality and modifications. Due to its flexibility and popularity, a lot of novel ideas have been proposed and implemented on GNU Radio based testbed, including efficient analog network coding [18; 19; 20].  
Distributed asynchronous cooperation (DAC) is introduced in [21], and the tradeoff between the diversity gain and the reduction in multiplexing opportunities is analyzed. Novel cross layer techniques are also proposed to verify the real time environment effect. To analyze the performance of multi-antenna system GNU radio based testbed is also used. In [22], GNU Radio based testbed to build hydra prototype and analyze the performance of MIMO system, and on basis of the experimental results, rate adaptation protocol is proposed. In [23], range extension is observed by comparing multiple relay network with single relay network. While [24] analyzed the performance of DF and selective DF without signal combining technique with GNU Radio based testbed. In [25], signal combining of CC was evaluated but optimal position of the relay and channel capacity have not been evaluated on this platform. These are most important facts to evaluate the performance of the system. In this research channel capacity analysis is evaluated for the cooperative network using USRP and LabVIEW.