PERFORMANCE ANALYSIS OF NON-COHERENT IR-UWB COOPERATIVE COMMUNICATION SYSTEM

Abstract

Impulse Radio􀀀Ultra􀀀WideBand (IR􀀀UWB) communication systems of late has attracted strong attention from the researchers, for its high speed and short range applications in the field of wireless communication. According to Federal Communications Commission (FCC), signals that possess a bandwidth larger than 500MHz or a fractional bandwidth of more than 20% are said to be UWB. IR􀀀UWB is a single band carrierless communication technology, transmitting information onto a sequence of impulse like waveforms (nanosecond duration pulses), thereby occupying the entire bandwidth of 7:5 GHz. The enormous bandwidth occupancy of UWB signal, makes it robust to multipath fading and intersymbol-interference (ISI) effects. It also makes the channel frequency selective, resulting in a large number of resolvable multipath components, which offer the potential of multipath energy combining at the receiver end by coherent or non􀀀coherent means. While a coherent Rake receiver gives better bit error rate (BER) performance, it requires accurate channel estimation and synchronization for extracting multipath energy from multipath components that results in high complexity. Hence, simple and less complex non􀀀coherent IR􀀀UWB autocorrelation (AC) systems such as transmitted reference (TR), transmitted reference pulse cluster (TRPC), and differential transmitted reference (DTR) are preferred. But, AC systems require long analog delay lines for performing correlation during detection, thereby leading to hardware complexity issues. Hence, low complexity energy detector (ED) system is preferred, which works by squaring the received signal, followed by integration and detection through decision device. Owing to the strict guidelines issued by the FCC, 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. So, to overcome such weaknesses, cooperative technology was introduced, which emerged as the perfect scheme to improve quality of service (QoS), coverage area, transmission reliability, and power efficiency. ix Abstract The two relaying strategies that can be applied to a cooperative domain are regenerative and non􀀀regenerative relaying. In case of Detect and Forward (DTF), a classification of regenerative relaying, the relay node detects the received signal at the relay node in 1st time slot, and then forwards the extracted information to the destination node in the next time slot. However in case of Amplify and Forward (AF), a classification of regenerative relaying, the received signal is forwarded to the destination node after being amplified at the relay node. The research for cooperative transmission in multipath scenario using non􀀀coherent IR􀀀UWB system is largely unexplored. AC systems such as TR and DTR use long analog delay taps for storing past samples of the received signal that is required for correlation during detection process. This leads to an increase in storage requirement, which increases the hardware complexity and cost of receiver. Due to its less complexity and sensitivity to synchronizing errors, ED system that works by squaring the received signal followed by integration and detection through decision device, is preferred. If complexity is preferred over performance in the trade􀀀off between complexity and performance, then ED receiver acts as the best choice because of its simplicity and less hardware complexity. Taking inference from the existing study and knowing the research gaps, we firstly present an analytical approach to determine the BER performance of non􀀀coherent IR􀀀UWB system namely AC and ED, in single􀀀link scenario, over IEEE 802.15.4a UWB environment. The analytical approach for evaluating the BER of AC systems such as TR and DTR, is based on autocorrelation principle while, ED systems such as ED􀀀OOK, ED􀀀PPM, use energy detection principle for performance analysis. The analytical results are also validated with simulations for (Nf = 1; 2), where Nf signifies the number of frames. Furthermore, computer simulations are used to compare the BER performance of various non􀀀coherent IR􀀀UWB systems namely, TR, DTR, ATR, RTR, RATR, ED􀀀OOK and ED􀀀PPM, in single􀀀link environment. We then analyse the BER performance of non􀀀coherent IR􀀀UWB AC (TR,DTR) systems using cooperative dual􀀀hop AF and DTF relay strategy for various diversity combining schemes namely, linear combining, selective combining and optimum linear combining, over 802.15.4a UWB environment. The analytical approach used for BER evaluation is based on autocorrelation principle and is validated with the simulation results. In the 1st time slot, UWB signal modulated by the information bit is transmitted from the source node to relay as well as destination node. The received signal at relay node is either amplified or detected, depending on the relay strategy used, and then forwarded to the destination x Abstract node in the next time slot. The decision statistics obtained at the destination node in the two time slots are combined using various combining techniques to form the final decision statistic, which is compared to the decision threshold to recover the original bit. A novel analytical representation of BER performance of non􀀀coherent IR􀀀UWBED􀀀OOK and ED􀀀PPM systems using cooperative dual􀀀hop AF and DTF relay strategy for various combining techniques, over IEEE 802.15.4a environment, is illustrated. In particular, the approximate expression based on energy detection principle are derived for various diversity combining schemes namely, linear combining, selective combining and optimal linear combining. The analytical BER expressions are also validated with the simulations for Nf = 1; 2. Computer simulations are also used to compare the BER performance of non􀀀coherent IR􀀀UWB systems based on increase in number of relay paths L, decrease in number of frames Nf , channel used (CM1,CM2), relaying strategies, diversity combining schemes and type of system used.