In this contribution we investigate the performance of the UMTS Long Term Evolution (LTE) physical layer using turbo coding and 64QAM with Gray mapping. We show how the mapping of systematic and parity bits to the six different bit positions defining one complex 64QAM symbol influences the convergence of the turbo decoder and thereby the bit error rate (BER) performance as well as number of necessary decoding iterations. Exploiting the unequal error protection (UEP) property of Gray mapped 64QAM results in an SNR performance gain of approximately 2 dB for the non-iterative system and in addition leads to a significant reduction of the necessary decoding iterations when iterative decoding is performed.
Recently, MIMO detectors which are based on Markov Chain Monte Carlo (MCMC) simulation techniques have been proposed as alternatives to, e.g., the well-known sphere detector. In this paper, we present a systematic analysis of the performance of MCMC detectors. We study the impact of several parameters such as the list size and the number of independently running chains. As a performance criterion, our analysis is based on the mutual information over an equivalent modulation channel, rather than on coded bit error rates, because this metric is independent of the outer channel code and provides valuable insights over the whole SNR range of interest. Furthermore, we show that combining the MCMC detector with a hard-output sphere detector removes the error floor at high SNR, which is a well-known problem of the MCMC principle.
SUMMARYIn this contribution we investigate the performance of the universal mobile telecommunications system (UMTS) long-term evolution (LTE) physical layer using turbo coding and 64QAM with Gray mapping. We show how the mapping of systematic and parity bits to the six different bit positions defining one complex 64QAM symbol influences the convergence of the turbo decoder and thereby the bit error rate (BER) performance as well as number of necessary decoding iterations. Exploiting the unequal error protection (UEP) property of Gray mapped 64QAM results in an signal-to-noise ratio (SNR) performance gain of approximately 2 dB for the non-iterative system and leads to goodput gains especially in regions of low SNR.
The performance of direct sequence code division multiple access (DS-CDMA) systems depends on the autocorrelation and cross-correlation properties of the deployed spreading sequences. Since good auto-correlation characteristics come at the expense of the cross-correlation properties and vice vena, a combmation of these two measures needs to be optimized when designing a DS-CDMA system. In this paper, we consider the design of complex-valued spreading sequences with optimized correlation characteristics. In particular, the maximum nontrivial aperiodic correlation values are used to specify the cost or fitness function for the optimization problems. A genetic algorithm is presented for the design of polyphase sequences, namely, Oppermann sequences and modified Walsh-Hadamard sequences. It can be seen from these applications that the genetic algorithm is well suited to efficiently design polyphase sequences especially when the number of parameters for the optimization problem is large.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.