摘要：This paper describes a Least Squares (LS) channel estimation scheme for MIMO ofdm systems based on time-domain training sequence. We first compute the minimum mean square error (MSE) of the LS channel estimation, and then derive the optimal criteria of the training sequence with respect to the minimum MSE. It is shown that optimal time-domain training sequence should satisfy two criteria. First, the autocorrelation of the sequence transmitted from the same antenna is an impulse function in a region longer than the channel maximum delay. Second, the cross-correlation between sequences transmitted from different antennas is zero in this region. Simulation results show that the estimator using optimal time-domain training sequences has better performance than that using optimal frequency training sequence at low signal-to-noise ratio (SNR). To reduce the training overhead, a suboptimal training sequence is also proposed. Comparing with optimal training sequence, it has low computation complexity and high transmission efficiency at the expense of little performance degradation.

摘要：An optimized channel estimation algorithm based on a time-spread structure in ofdm low-voltage power line communication（PLC） systems is proposed to achieve a lower bit error rate（BER）.This paper optimizes the best maximum multi-path delay of the linear minimum mean square error（LMMSE） algorithm in time-domain spread ofdm *** results indicate that the BER of the improved method is lower than that of conventional LMMSE algorithm,especially when the signal-to-noise ratio（SNR） is lower than 0 *** the LMMSE algorithm and the proposed algorithm are implemented and fabricated in CSMC 0.18μm technology. This paper analyzes and compares the hardware complexity and performance of the two *** indicate that the proposed channel estimator has better performance than the conventional estimator.

摘要：An SISO IEEE 802.11 baseband ofdm transceiver ASIC is implemented. The chip can support all of the SISO IEEE 802.11 work modes by optimizing the key module and sharing the module between the transmitter and receiver. The area and power are decreased greatly compared with other designs. The baseband prototype has been verified under the WLAN baseband test equipment and through transferring the video. The 0.18/zm 1P/6M CMOS technology layout is finished and the chip is fabricated in SMIC, which occupies a 2.6 × 2.6 mm^2 area and consumes 83 mW under typical work modes.

摘要：A set of integrated Orthogonal Frequency Division Multiplexing(ofdm) modulation and demodulation system is proposed and its performance is verified in reference to the standard of IEEE802.16a for *** design,combined with analogy front-end,adopts Texas Instrument(TI) Company's 6701 evaluation module(EVM) to construct digital Intermediate Frequency(IF) platform.A DSP-based baseband processing software module is embedded into the *** proposed scheme makes it possible for users to select various software modules to set up connections with different throughput *** into account the given hardware configuration,the design aims to optimize the algorithm modules to accomplish better system performance.

摘要：According to the quality of service （QoS） requirements of differentiated service （DiffServ）, a cross-layer resource allocation algorithm for multi-user orthogonal frequency division multiplexing （ofdm） systems is presented. The constant rate is maintained by adjusting the power dynamically for the voice traffics with high priority, whereas the fairness amongst the data traffics is guaranteed by weighted fairness queued （WFQ） algorithm. The two above-mentioned strategies are used for video traffics to realize variable data rate with the constraint of the minimum rate. Combing all these methods, both the throughput and the fairness are ensured when there are multiple users in the ofdm system. Simulation results indicate the validity of the proposed algorithm, which can work well even if the SNR is less than 0 dB.

摘要：The IEEE 802. 16 standard specifies the air interface of wireless metropolitan area network （WMAN）, and aims to provide wireless broadband access for integrated voice and video services. This paper presents the efficient design and implementation of fast Frouier transform （FFT） and inverse fast Frouier transform （IFFT） for the application in IEEE 802. 16d orthogoual frequency division multiplexing （ofdm） system. In this design, a novel pipeline structure for the branch of butterfly unit （BU） is proposed, which can improve the processing symbol rate by adding the number of branch flexibly. The symmetrical ping-pang structure of random access memory （RAM） is performed to increase the system throughput. Simulation results reveal that only with 1 branch of BU, the proposed FFF/IFFT design can almost achieve the maximum bandwidth requirement of IEEE 802. 16d ofdm system. And this design has been verified by FPGA and successfully implemented in the prototype of WiMAX transceiver.

摘要：Orthogonal Frequency Division Multiplexing(ofdm) is an effective technique to deal with a frequency selective channel since it can convert the channel into some flat fading ***,very different output SNR values of the subchannels will lead to poor bit error performance when a linear equalizer and Equal Bit Allocation(EBA) are adopted in ofdm ***,we proposed three novel nonlinear Joint Transceiver(JT) schemes based on Zero-Forcing(ZF) criterion and Minimum Mean Square Error(MMSE) criterion respectively,which can transform all subchannels of an ofdm system into subchannels with identical channel ***,EBA is equivalent to the Optimum Bit Allocation(OBA) for these *** analysis helps us to obtain the theoretical approximate BER values of the JT *** results verify the numerical analysis and confirm that the performance of our proposed JT scheme greatly outperforms the traditional linear equalizer with EBA at moderate and high SNR values.

摘要：针对设置有保护频带的ofdm系统,基于等间隔导频(UPPTS)设计方法,在保证最小二乘(LS)信道估计均方误差(MSE)最小的前提下,计算了系统允许存在的最大保护频带宽度,给出了初始导频位置的选择范围,通过调整导频序列的初始位置,使导频序列有效避开保护频带.仿真实验结果表明,当导频序列的初始导频落入本文所给出的导频位置选择范围之内时,系统给出了更高的信道估计精度和更低的误码率,进一步验证了算法的有效性和优越性.

摘要：提出了一种ofdm的推广形式,将复码元的实部和虚部分别采用不同的脉冲成形进行调制。把这种调制形式称为G-ofdm。讨论了G-ofdm的脉冲成形和星座图设计问题。数值仿真表明,G-ofdm在频率色散信道的性能优于传统ofdm,同时这一优势并未降低系统对抗AWGN及时间色散的性能。

摘要：针对时变信道下的ofdm系统的性能分析,通常采用信道在一个符号持续时间内保持不变的假设为前提。然而,这种假设在某些情况下并不合理。随着载波频率的提高,终端移动速度的加快以及符号长度的增加,由多普勒效应导致的载波间的串扰变得更加严重。本文分析了多普勒效应对最大可传送速率和信干比的影响,并且分别设计了使信干比和最大可传送速率最大化的符号长度。数值仿真结果进一步证实了作者的理论结果。