A novel analytical representation of bit error rate (BER) performance of an impulse-radio ultra-wideband energy detector on-off keying system using cooperative dual-hop amplify and forward relay technology, with various diversity combining schemes over IEEE 802.15.4a environment is presented in this paper. In particular, the approximate expressions based on energy detection principle are derived for various diversity combining cases, namely linear optimal combining, linear combining, and selective combining. Simulation results depict an improvement in BER performance, with increase in number of relay paths (L) and decrease in number of frames per symbol (N f ). Furthermore, the BER performance of the impulse-radio ultra-wideband energy detector on-off keying system improves substantially using dual-hop cooperative amplify and forward scheme, compared with that of non-cooperative or single link scenario. Among the diversity combining schemes, linear optimal diversity combining performs better when compared with linear diversity combining and selective combining. The analytical BER expressions are validated with the simulation results, which confirm the accuracy and precision in approximation used in the investigation of BER. energy detector (ED) receiver is introduced, which works by squaring the received signal followed by integration and detection through decision device [8][9][10].Owing to the strict guidelines issued by the Federal Communications Commission [1], UWB systems can operate at a maximum transmit power spectral density (PSD) of 41.3 dBm/MHz in order to avoid interference with other existing technologies. The low PSD of UWB signals not only limits it from achieving a wide coverage area but also makes its performance sensitive to distance [11,12]. Hence, to overcome such weaknesses, cooperative technology was introduced, which emerged as the perfect scheme to improve quality of service, coverage area, transmission reliability, and power efficiency [13,14].The simplest form of cooperative network, that is, a relay network, was first introduced by Meulen [15] and Gamal [16]. In cooperative technology, cooperative terminals or nodes share information and other resources through antennas, to create a virtual array through distributed transmission. Cooperative relay strategy protocols can be classified as amplify and forward (AF), detect and forward, and decode and forward (DF) [17,18]. The authors [19][20][21] have extended the use of AF and DF relay strategies in IR-UWB systems. Cho et al. [22] introduced the concept of cooperative dual-hop AF relaying scheme in IR-UWB system, whose results showed better performance than without using relay scheme. Among the previous contributions, Hamdi [23,24] analyzed the BER performance of IR-UWB differential transmitted reference system using dual-hop and multihop relay strategy. Maichalernnukul [25] discussed the BER performance of IR-UWB system using multi-antenna relay technology into dual-hop system, while Yazdi [11,26] investigated the BER performance of IR-UWB...