Analysis of wireless communication systems in the presence of Nakagami fading.

摘要

Nakagami model (also known as the Nakagami-m model) has been one of the most important statistical fading channel model in wireless communications due to its wide versatility, experimental validity, and analytical tractability. Extensive research work has been focused on narrowband systems.; Orthogonal frequency division multiplexing (OFDM) has proven to be the preferred modulation for broadband wireless communications. System design and performance evaluations of OFDM-based systems in the presence of frequency selective Nakagami-m fading have been attracting lots of attentions recently. Unfortunately, all previously published results were based on an incorrect frequency domain fading model. We shall propose in this dissertation a correct model in terms of the statistics of the corresponding frequency-selective Nakagami- m fading model. This new model has great values in both theoretical analysis and practical design especially for wideband systems. Based on this model, we shall show that a multiple input multiple output (MIMO) OFDM system can be accurately evaluated.; Multicarrier code division multiple access (MC-CDMA), which is a combination of OFDM and CDMA, is also a candidate for the next generation mobile radio systems. In the literature independency among all subcarriers was often assumed in MC-CDMA performance analysis in the presence of Nakagami-m fading. We shall show, however, that a frequency-selective Nakagami- m fading channel model may have been overemphasized for MC-CDMA compared to a frequency-selective Rayleigh fading model when, this independency is addressed.; Channel capacity is a crucial criterion in wireless communications. Ergodic capacity of MC-CDMA (OFDM) system in frequency-selective Nakagami- m fading has not been studied. We shall show that when the channel knowledge is only available at the receiver, the ergodic capacity is generally a function of the number of multipaths. One extreme case is that ergodic capacity is not a function of the number of multipaths if, the fading is frequency-selective Rayleigh.; Channel statistics can be used not only for performance analysis, but also for system design if this knowledge is available at the transmitter side. We shall present a new and simple precoder design approach for MIMO-OFDM system where frequency-selective Rician fading is assumed. The precoder can easily be constructed in terms of Rice factor. We shall also show that great ergodic capacity improvement can be achieved when such a precoder is applied at transmitters.; Level-crossing rate (LCR) and average fade duration (AFD) are two important characteristic parameters describing fading. The LCR's and AFD's for diversity combining in the presence of correlated Nakagami- m fading have not well been studied. We shall derive either closed-form or approximate expressions for three combining techniques: selection combining (SC), maximum ratio combining (MRC), and equal gain combining (EGC). These expressions are quite helpful in evaluating the diversity systems in correlated fading channels.