Filter Bank Based Multi-Carrier Systems for Future Broadband Wireless Communications

正交频分复用（OFDM）技术在有线和无线通信系统中越来越受欢迎，主要是因为它具有抗多径衰落的能力，可以显著提高传输速率。OFDM通过在每个长度大于信道长度的传输块前插入循环前缀（CP），有效地将频率选择信道转换为平行的平衰落信道。这大大简化了信道估计和接收机的数据恢复。然而，这些优点的代价是由于CP的插入而损失了10-25%的频谱效率，并且增加了对频率偏移和多普勒扩散的灵敏度，以及由OFDM信号的非恒定模量加剧的传输非线性。此外，由于无线信道的时变特性，需要周期性地传输训练序列以进行信道估计。对于快速衰落信道，训练序列和CP带来的开销可高达50%，造成显著的频谱效率损失。在本提案中，我们的目标是通过基于滤波器组的多载波系统来解决这些问题，该系统采用一种称为IOTA（各向同性正交变换算法）的特殊脉冲整形滤波器来产生良好的时间和频率定位特性，从而避免了符号间干扰（ISI）和载波间干扰（ICI），而无需使用cp。为了有效地解决当前基于正交频分多址（OFDMA）和单载波频分多址（SC-FDMA）上行通信中存在的载波频偏和高PAPR问题，提出了一种将IOTA与低密度签名（LDS）技术相结合的新型多址方案。我们的工作重点是研究和利用IOTA的一些被别人忽视的特性。我们的目标是在均衡、解码和信道估计设计中利用这些特性，以实现最优性能和最大容量，并具有可承受的计算复杂性。我们的目标是为未来无线通信的IOTA系统的成功实施提供理论参考和指导。

Orthogonal Frequency Division Multiplexing (OFDM) technique has gained increasing popularity in bothwired and wireless communication systems, mainly due to its immunity to multipath fading, which allows for a significantincrease in the transmission rate. By inserting a cyclic prefix (CP) before each transmitted block longer than the lengthof the channel, OFDM effectively transforms a frequency selective channel into a parallel of flat-fading channels. Thisgreatly simplifies both channel estimation and data recovery at receiver. However, these advantages come at the cost of aloss of 10-25% spectral efficiency due to the insertion of CP, and an increased sensitivity to frequency offset and Dopplerspread as well as transmission nonlinearity accentuated by non-constant modulus of OFDM signals. Additionally, dueto the time-varying nature of wireless channels, training sequence needs to be transmitted periodically for the purpose ofchannel estimation. The overhead imposed by training sequence and CP can be up to 50 percent for fast fading channels,causing significant loss of spectral efficiency.In this proposal we aim to tackle these problems with the filter bank based multi-carrier system employing a specialpulse shaping filter called IOTA (isotropic orthogonal transform algorithm) to yield good time and frequency localizationproperties so that inter-symbol interference (ISI) and inter-carrier interference (ICI) are avoided without the use of CP.We also investigate a linearly precoded IOTA system which facilitates blind channel estimation, resulting in a spectrallyefficient multi-carrier system without the transmission of training sequence in addition to the elimination of CP.In order to effectively combat carrier frequency offset and high PAPR problems in the current orthogonal frequency divisionmultiple access (OFDMA) and single carrier frequency division multiple access (SC-FDMA) based uplink communications,we propose a novel multiple access scheme which combines IOTA with low density signature (LDS) technique.The focus of our work will be on the study and utilization of some special properties of IOTA which have been overlookedby others. We aim to leverage these properties in the equalization, decoding and channel estimation design in order toachieve optimal performance and maximum capacity with affordable computational complexity. Our goal is to providetheoretical references and guidelines for successful implementation of IOTA systems for future wireless communications.