Complexity evaluation for the implementation of a pre-FFT equalizer in an OFDM receiver

Abstract

A Pre-FFT Equalizer (PFE) has been shown to offer a signifcant throughput efficiency improvement when applied to an OFDM receiver. Alternatively, the PFE can be used to increase the maximum delay spread conditions under which the OFDM system can operate effectively. Due to the manner of its operation, the PFE requires the use of modifed adaptation algorithms if iterative, decision directed, adaptation is required. In this paper, the computational complexity required to implement a PFE and a suitable adaptation strategy is evaluated. Initially, an LMS adaptation algorithm is investigated and evaluated in terms of its suitability for application in conjunction with the PFE to standards such as ETSI DVB-T and HIPERLAN/2 and IEEE 802.1 l a . The complexity requirements are found to be high, particularly in the case of DVB-T, The demand ,for a lower complexity adaptation algorithm is thus identified. As a result, a CSI-based adaptation method is subsequently considered, The complexity requirement of this algorithm is also analyzed and evaluated and is shown to be much lower than that of the LMS algorithm. Thus, it is shown that if the CSIbased adaptation method is used, the dominant complexity requirement is due to the implementation of the equalizingfilter and not the adaptation method. Reduced filter complexity requirement is thus shown to be the key to enabling effective application of the PFE. The ATSC 8-VSB standard is identified as a possible source of techniques to reduce or facilitate the high complexity demands for implementation of the PFE filter.

Testing different Channel Estimation Techniques in Real-Time Software Defined Radio Environment

“…Along the TA, the main determinant of transmission performance is channel estimation. Armour et al discussed the potential trade-offs between efficiency and complexity when using the decision directed Least Mean Square (LMS) algorithm with the Hiperlan E and IEEE P802.1la standards [6].…”

Comparação entre técnicas de transmissão e recepção em canais brasileiros de TV digital

“…Outra questão a ser considerada é a posic ¸ão das portadoras piloto que pode, eventualmente, ser otimizada para os canais utilizados. Esquemas de equalizac ¸ão para o OFDM também podem ser considerados [12], [21];…”

Equalização pré-FFT de sistemas baseados em orthogonal frequency-division multiplexing.

“…viço serão sempre bem-vindas. Optamos por estudar a equalização no domínio do tempo devido ao grande número de trabalhos que surgiram a esse respeito noś ultimos anos (veja, por exemplo: [3], [43], [44], [42] [46] baseado no algoritmo LMS [47] com o diagrama ilustrado na figura 39. Outras técnicas encontradas recentemente na literatura sugerem o uso da redundância presente no prefixo cíclico, o qualé adicionado no domínio do tempo, para uma estimação de canal mais precisa no domínio da freqüência 2 , como observado nos artigos [48] e [49].…”