Performance Study of an FFH/BFSK Self-Normalizing Receiver with Multitone Jamming's Frequency Offsets

This study investigates how frequency offsets of multitone jamming affect the fast frequency-hopped binary frequency shift keying (FFH/BFSK)self-normalizing (SNZ) receiver under additive white Gaussian noise (AWGN). The average bit-error-rate (BER) expressions of the FFH/BFSK SNZ receiver and the average BER expressions of an FFH/BFSK spread-spectrum (SS) communication system with frequency offsets of multitone jamming for the sake of understanding the simulation results better. Simulation results show that BER performance of the FFH/BFSK SNZ receiver with diversity under the worst casemultitone jamming (MTJ) and AWGN suffers from multitone jamming's frequency offsets when the jamming power is moderate, which is validated by several simulations with different frequency offsets configured in multitone jamming. Therefore, an FFH/BFSK SNZ receiver under multitone jamming can be combated with the help of frequency offsets of multitone jamming.     

OFDMA uplink frequency offset estimation via cooperative relaying

Frequency offset estimation for an orthogonal frequency-division multiple access (OFDMA) uplink for amplify-and-forward (AF) relays and a new type of relay (R) called decode-and-compensate-and-forward (DcF) relays are studied. Multiple relays are considered, and the relay with the best S rarr R channel is chosen to perform re-transmission, where S and R represent the source and relay nodes, respectively. Frequency offsets due to the mismatches between the transmitter and receiver oscillators are considered, and without considering the effect of Doppler shift, both S rarr D and S rarr R rarr D links have the same frequency offset, where D represents the destination. Thus, by using these two transmissions, D generates two frequency offset estimates, which are combined to minimize the mean square error (MSE). Power allocation between S and R can be adaptively adjusted to optimize the cooperative scheme in terms of frequency offset error variance. When channel state information (CSI) is available at each mobile node, a scheme where the relays adaptively switch between the cooperative and conventional (no relaying) transmissions is proposed to optimize the frequency offset estimation. Although the frequency offset estimation accuracy in the DcF mode is somewhat worse than the AF mode, both modes outperform the conventional transmission. However, DcF (or decode-and-forward (DF)) relays outperform AF relays in terms of channel capacity and bit error rate (BER).     

SIR analysis and interference cancellation in uplink OFDMA with large carrier frequency/timing offsets

In uplink orthogonal frequency division multiple access (OFDMA), large timing offsets (TO) and/or carrier frequency offsets (CFO) of other users with respect to a desired user can cause significant multiuser interference (MUI). In this letter, we analytically characterize the degradation in the average output signal-to-interference ratio (SIR) due to the combined effect of both TOs as well as CFOs in uplink OFDMA. Specifically, we derive closed-form expressions for the average SIR at the DFT output in the presence of large CFOs and TOs. The analytical expressions derived for the signal and various interference terms at the DFT output are used to devise an interference cancelling receiver to mitigate the effect of CFO/TOinduced interferences.     

The effect of carrier frequency offsets on downlink and uplinkMC-DS-CDMA

In this paper, we study the sensitivity of uplink and downlink MC-DS-CDMA to carrier frequency offsets, assuming orthogonal spreading sequences. For both uplink and downlink MC-DS-CDMA, we show that the performance rapidly degrades for an increasing ratio of maximum frequency offset to carrier spacing. We point out that the degradation in the uplink is larger than in the downlink because only the former is affected by multiuser interference. For a given (small) ratio of maximum frequency offset to carrier spacing, enlarging the spreading factor in a fully loaded system does not affect the downlink degradation but strongly increases the uplink degradation. Finally, we show that the downlink degradations of MC-DS-CDMA and fully loaded MC-CDMA are the same, provided that for both systems the ratio of frequency offset to carrier spacing is the same     

LTE上行信道的八天线干扰抑制合并技术

基于最小均方误差估计准则推导了LTE多天线上行信道的干扰 抑制合并和最大比合并的均衡公式。通过仿真比较,验证了八天线干扰抑制合并接收算法在 有同频干扰情况下的优越性：随着信噪比的增大,干扰抑制合并算法的误码率大幅降低,而 最大比合并算法则形成误码平台;八天线干扰抑制合并性能明显优于两天线性能。LTE在同 频组网时,基站可以采用八天线接收的干扰抑制合并技术以提高上行链路的抗干扰性能。     

Low Complexity Carrier Frequency Offset and Channel Estimation for Multiuser OFDMA Networks

Wireless Personal Communications - Multiple carrier frequency offsets exist in the orthogonal frequency-division multiple access (OFDMA) uplink receivers, and consequently induce inter-carrier...     

Joint Estimation of the Timing and Frequency Offset for Uplink OFDMA

Inheriting all the advantages of Orthogonal Frequency Division Multiplexing (OFDM), plus the ability to offer a fine level of bit granularity and dynamic subcarrier allocation for multiuser diversity, the Orthogonal Frequency Division Multiple Access (OFDMA) has emerged as a potential candidate for multiple access technique for future broadband wireless networks. However, the benefits of OFDMA come with stringent requirements on synchronization, especially in the uplink. Unless the timing offsets (TOs) and carrier frequency offsets (CFOs) among users in the uplink are kept under tolerable ranges, inter-symbol interference (ISI), inter-channel interference (ICI) and multi-user interference (MUI) will occur, which degrade the overall system performance severely. Accurate estimation of TOs and CFOs is required for each user, so that they can be accounted for at the user’s side or compesated for at the base station. This paper proposes a novel method to estimate jointly TOs and CFOs in the time-domain for multi-user in the OFDMA uplink. The method is shown to offer good accuracy, while maintaining a reasonable complexity compared to conventional estimation schemes.     

交织OFDMA上行系统CFO估计算法的研究

文中对OFDMA系统中的子载波分配方法进行了研究,介绍了两种子载波分配方法的原理,对两种子载波分配方法进行了仿真,结果显示在频率选择性衰落信道中交织分配的OFDMA系统要比块分配的OFDMA系统获得更多的频率分集.给出了交织OFDMA系统上行链路的信号结构,由于发射机和接收机之间存在的载波频率偏移(CFO)将会影响子载波间的正交性,对多用户的CFO估计提出了一种估计算法,仿真的结果显示所提出的算法具有较好的性能.     

空时分组码多音调制CDMA系统性能分析

提出了一种空时分组码（STBC,space-time block-code）多音调制CDMA（MT-CDMA）系统结构。对系统上行链路误码率（BER）性能进行了理论分析,推导出了在多径衰落信道下采用最大比合并时系统的BER表达式,并通过计算机仿真进行了验证。数值结果表明由于联合的空时与多径分集增益,使系统的BER性能、差错地板和容量都得到了显著地改善。     

Deterministic multiuser carrier-frequency offset estimation for interleaved OFDMA uplink

In orthogonal frequency-division multiple access (OFDMA), closely spaced multiple subcarriers are assigned to different users for parallel signal transmission. An interleaved subcarrier-assignment scheme is preferred because it provides maximum frequency diversity and increases the capacity in frequency-selective fading channels. The subcarriers are overlapping, but orthogonal to each other such that there is no intercarrier interference (ICI). Carrier-frequency offsets (CFOs) between the transmitter and the receiver destroy the orthogonality and introduces ICI, resulting in multiple-access interference. This paper exploits the inner structure of the signals for CFO estimation in the uplink of interleaved OFDMA systems. A new uplink signal model is presented, and an estimation algorithm based on the signal structure is proposed for estimating the CFOs of all users using only one OFDMA block. Diversity schemes are also presented to improve the estimation performance. Simulation results illustrate the high accuracy and efficiency of the proposed algorithm.     

一种改进的OFDM载波干扰自消除算法

OFDM系统因采用正交子载波技术使得对频率偏移非常敏感,尤其是当频率偏移较大时,误码率性能严重恶化.在分析由Zhao等提出的ICI自消除算法及其改进算法的基础上,提出一种收发端权重因子联合优化算法,该算法极大地提高了OFDM系统的载干比(CIR,carrier-to-interference power ratio)性能.仿真表明,该算法不仅实现简单,而且在频率偏移较大时仍然具有很好的性能.     

MAI and ICI of Asynchronous Uplink MC-CDMA With Frequency Offset

In this paper, we analyze the performance of random spreading code-division multiple-access (CDMA) systems with a multicarrier in asynchronous uplink channels. We first derive the probability density function (pdf) of the multiple-access interference (MAI) plus noise and then extend the results to orthogonal frequency division multiplexing (OFDM) with intercarrier interference (ICI) that is caused by a frequency offset. We obtain the pdf of the MAI and the ICI plus noise under Rayleigh and frequency-selective fading as a function of the number of users and the spreading factor, as well as the number of subcarriers and the frequency offset. The bit-error-rate (BER) analysis shows that the power penalty from the frequency offset increases with the system loading. We develop the Gaussian approximation that provides an accurate estimation of the BER with reduced computational complexity comparing to the direct calculations using the pdf.     

联合旋转平均周期图和解调软信息的载波同步方法

针对短突发信号的载波同步问题,该文提出联合旋转平均周期图和解调软信息的载波估计算法。该算法首先对导频信息旋转不同频偏,利用平均周期图法进行载波粗估计,然后以解调软信息的最大均方软输出为准则,采用分步式搜索进一步进行载波细估计。仿真结果表明该联合算法在导频开销较小的条件下,误码性能接近最佳相干解调性能,且复杂度较低,频偏估计范围可以达到50%的符号速率。当误比特率为10-2 ~ 10-4时,信噪比损失在0.3 dB内。     

Effects of multipath propagation delay on uplink performance of synchronous DS-CDMA systems communicating in dispersive Rayleigh fading channels

The effect of the maximum asynchronous arrival time difference (AATD) of the delayed multipath components on the uplink performance of synchronous DS-CDMA systems is investigated, when communicating in a frequency-selective Rayleigh fading channel. Numerical results demonstrate that the achievable user capacity gain may be as high as 64% at a bit error rate (BER) of 10/sup -2/, when the maximum AATD is sufficiently low.     

Edge sidelobe suppressor scheme for OFDMA uplink systems

We propose an edge sidelobe suppressor (ESS) for the uplink of orthogonal frequency-division multiple-access (OFDMA) systems, which mitigates the interference introduced by different frequency offsets between a desired user and the other users. The simulation results confirm that the proposed ESS scheme improves system performance by approximately 5-dB signal-to-interference ratio as compared to conventional OFDMA systems, and without increasing the level of transmitter and receiver complexity.     

自适应波束形成实现交织OFDMA上行链路的载波频偏补偿

在OFDMA系统中,采用交织子载波分配方法可以提高频率分集和系统容量,但是发射机和接收机之间的载波频率偏移会破坏子载波间的正交性,从而导致本用户的载波间干扰以及用户间干扰。该文分析了交织OFDMA上行链路的信号结构,提出了一种采用自适应波束形成器的载波频偏补偿方法,并给出了两种自适应波束形成器：匹配滤波器和MMSE方法。仿真结果验证了MMSE自适应波束形成器的误比特率性能优于匹配滤波器以及传统的循环卷积方法。     

Research on the low complexity adaptive power allocation algorithm in cooperative systems

Cooperative diversity is a new technology to improve bit error rate(BER)performance in wireless communications.A new power allocation algorithm to improve BER performance in cellular uplink has been proposed in this paper.Some existing power allocation schemes were proposed for the purpose of maximizing the channel capacity or minimizing the outage probability.Different from these schemes,the proposed algorithm aims at minimizing the BER of the systems under the constraint of total transmission power.Besides this characteristic,the proposed algorithm can realize a low complexity real-time power allocation according to the fluctuation of channels.Simulation results show that the proposed algorithm can decrease the BER performance of the systems effectively.     

Effects of carrier frequency offset on the average effective SNR and the average BER for asynchronous MC‐CDMA uplink systems with a guard period

This paper presents an analysis of asynchronous multicarrier‐code division multiple access (MC‐CDMA) systems over frequency‐selective multipath fading channels when the carrier frequency offsets (CFOs) of all users are random variables and the frequency offset for the desired user is compensated. The effect of residual CFO on the average bit error rate (BER) is evaluated by the semi‐analytical method, then the approximated BER performance is obtained as a closed‐form expression. Moreover, the signal‐to‐noise ratio (SNR) loss caused by residual CFO is evaluated. Derived results show that the performance degradation due to residual frequency offset is negligible if the estimation error of CFO for the desired user is less than the normalized value of 10^?1. Copyright © 2011 John Wiley & Sons, Ltd.     

Interleaved-OFDMA中基于子空间的上行链路载波频偏估计方法

在OFDMA系统中,通过为每个用户分配不同的子载波可以实现并行数据传输.采用Interleaved子载波分配方法可以提高频率分集和系统容量,但是发射机和接收机之间的载波频率偏移会破坏子载波间的正交性,从而导致本用户的载波间干扰(ICI)以及用户间干扰(MUI).本文提出了一种基于子空间的两阶段频偏搜索方法,该方法只采用一个OFDMA符号块就可以实现Interleaved-OFDMA上行链路多个用户频偏的联合估计,并且不需要知道接入的用户个数及用户所占用的子信道,因此适用于随机分配子信道的情况.仿真结果验证了算法的精确度和有效性.     

Effect of antenna array on the uplink orthogonal multicarrier DS‐CDMA system with imperfect power control

In this paper we analyze the effects of antenna array (AA) and imperfect power control on the performance of the uplink synchronous and/or asynchronous orthogonal multicarrier (MC) direct sequence‐code division multiple access (DS‐CDMA) system in multipath Rayleigh fading channels. Bit error rate (BER) performance is evaluated in terms of the number of antennas, the number of total subcarriers, power control error (PCE), and the number of users. Our numerical results show that the available user capacity of synchronous uplink is more than 1.5 times higher than that of asynchronous uplink, even though PCE increases. Copyright © 2009 John Wiley & Sons, Ltd.