共查询到18条相似文献,搜索用时 125 毫秒
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本文对正交码扩频多址系统在相干接收和非相干接收时的性能进行了分析。当采用前向纠错编码时,扩频系统多址容量会明显提高。在保证相同的扩频倍数的情况下,选择适当长度的扩频码和适当的FEC码可以在不降低系统性能的同时减少了正交码译码所需的运算量。 相似文献
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根据飞行器测控技术发展特点,提出多址正交码扩频体制,分析了系统的发射、接收模型及其误码率性能;仿真了多址正交码扩频系统的噪声性能、多址性能和抗干扰性能;讨论了对正交码同步捕获与跟踪、正交扩频体制下的伪码测距等关键技术问题。 相似文献
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TCM正交序列扩频多址通信系统性能分析 总被引:2,自引:0,他引:2
将纠错技术与扩频相结合,是进一步提高扩频多址通信系统性能的重要手段之一。本文研究了在正交码扩频通信系统中,应用TCM(网格编码调制)的原理,通过对信号集的扩展和分割,使发送信号序列间的最小欧氏距离得以增加,性能分析和计算机模拟表明,在存在加性高斯白噪声和多址干扰的信道环境中,扩频通信系统的性能得到了显著的提高。 相似文献
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基于扩频与跳频的多带OFDM-UWB多址技术 总被引:1,自引:0,他引:1
根据多带OFDM-UWB通信系统的特点,提出一种基于扩频与跳频的多址技术。该多址技术将多载波码分多址和跳频多址相结合,构成一种新颖的多址技术-正交频分多址(OFDMA),实现多载波码分多址技术和跳频多址技术的优势互补,此接收机的复杂性明显小于常规时频码的多用户接收机。仿真结果表明,基于OFDMA多址技术方案的UWB系统在系统误比特率性能上优于常规时频码方案约5dB。 相似文献
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直接序列扩频码分多址系统是目前应用最广泛的扩频系统,影响系统容量的主要因素是系统内多址信号的干扰。分析了采用Gold码的码速率异步直扩系统多址干扰,对扩展积分周期和单一积分周期均进行了数值仿真。仿真结果表明,码速率异步的Gold序列互相关函数不再具有三值特性;随着积分长度的扩展,互相关函数的统计值逐渐递减,即多址干扰减小;多址干扰与码偏移量大小有关,在某些特定码偏移量,积分长度为最小公倍数周期时,互相关函数接近为单值,而这些码偏移量正负对称出现;积分长度为单一周期时,多址干扰随码偏移量的变化趋势与扩频码长度无关;在相同码偏移量的情况下,随着扩频码的长度增加而减小。 相似文献
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一种新颖的超宽带无线通信多址接入方式的研究 总被引:2,自引:0,他引:2
多址干扰是限制超宽带(UWB)系统容量的主要原因。本文介绍了一种混合式多址接入方案:即采用直接序列扩频与固定跳时扩频相结合的多址接入机制,称之为DS-BPSK/固定THMA)。由于固定跳时码的存在,不同用户脉冲的碰撞概率被有效地减小。同时,即使发生脉冲碰撞,利用代表数据符号的直接序列PN码良好的自相关和互相关特性,将进一步抑制多址干扰影响。性能分析和仿真结果表明DS-BPSK/固定TH的UWB系统比传统的通过脉冲调制实现的跳时多址接入UWB系统具有更大用户容量。 相似文献
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本文将多重TCM技术应用于室内慢衰落信道下的直接序列扩频多址(DS/SSMA)系统中,提出了一种发射端和接收端分别采用多重伪码扩频和多重相关接收的DS/SSMA系统模型及其理论分析方法。在系统用户数、用户信源比特速率和伪码周期相同的条件下,模拟结果表明采用多重TCM的DS/SSMA系统性能显著优于一重TCMDS/SSMA系统的性能 相似文献
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本文讨论了混合DS-SFH扩频多址SSMA通信系统在瑞利衰落信道中多径分集接收的性能,基于多径干扰、多址干扰和信道噪声之和为一个高斯随机变量的分析,推导了在等增益组合和选择最大多径分集接收算法下,扩频系统的平均差错概率,理论分析和数值模拟指出:扩频多径分集接收可以明显地改善DS-SFH SSMA系统的性能,在提高系统性能方面,等增益组合算法优于选择最大分集算法。 相似文献
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Three multirate access schemes, multicode, variable spreading gain (VSG), and spectral overlaid multiple‐symbol‐rate (MSR), for asynchronous space‐time block coded (STBC) multicarrier code division multiple access (MC‐CDMA) systems are proposed. The three possible spectral overlaid configurations for MSR systems are also investigated. The expressions to evaluate the multiple access interferences, bit error rate (BER) performances, and system capacities of a antenna STBC MC‐CDMA using the three multirate access schemes are obtained. Transmit power allocation is adjusted according to the service rates and the number of active users in each service class to maintain the link quality and to improve the system capacity. Our numerical results show that systems with multicode access scheme using orthogonal Gold spreading codes and with VSG access scheme have similar system performance and capacity, and both perform in general better than systems with MSR access scheme of any spectrum configurations. In case when non‐orthogonal Gold codes are used, multicode access scheme shows degradation in the system capacity as compared to VSG, due to the presence of larger self‐interference (SI) among the codes used by each user. The achievable capacities for the three spectral overlaid configurations of MSR multirate systems are also compared. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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In this paper a turbo receiver for multicarrier spread spectrum systems employing parity bit selected spreading code (MC-SS-PB) is proposed where detection and decoding are performed iteratively for each detected bit in the receiver. In MC-SS-PB systems, the parity bits generated by a linear block encoder are used to select a spreading code from a set of orthogonal spreading sequences. The selected spreading code is then used to spread the signals in all subcarriers. In the proposed receiver, soft information passes between the detector and the decoder on multiple iterations. Detection is performed by using the received signal in combination with the extrinsic likelihood provided by a soft input soft output decoder. The turbo receiver is further extended to a multiple user system where the multiple access interference is estimated in each iteration and subtracted out from the received signal. Simulations show a significant reduction in bit error rates when a turbo receiver is used in these systems. 相似文献
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The next generation wireless access technology highly relies on nonorthogonal multiple access (NOMA) technique. This paper proposes a novel power domain cyclic spread multiple access (PDCSMA) scheme for the design of NOMA system with power domain superposition coding (SC) and cyclic spreading at the transmitter concurrent with symbol level successive interference cancellation (SL‐SIC) at the receiver. Based on acceptable difference in channel gain, the users are grouped together to form PDCSMA clusters, and the unique power is allotted to each user in a cluster. The user with good channel condition is allotted less power, and the user with poor channel condition is allotted more power. Each PDCSMA cluster has its own spreading code, and the data of every user in a cluster are cyclic spread with the same code. Each cluster supports the number of multipath components equivalent to the length of the spreading code. The use of cyclic spreading makes the signal suffered by multipath fading less prone to intra cluster interference. The user signal is decoded by minimum mean square error‐frequency domain equalization (MMSE‐FDE) or maximal ratio combining (MRC)–based receiver in which weak user is detected with hard decision, and strong user is detected with SIC. Compared with conventional power domain NOMA (PDNOMA) and interleaved NOMA, the proposed PDCSMA achieves better bit error rate (BER) performance and assures guaranteed detection. 相似文献
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本文分析室内无线多径衰落信道中网络编码调制的直扩多址通信系统的性能,系统采用网络编码多相调制技术以改善系统性能,本文讨论了网格编码技术与系统性能之间的关系及载波恢复相位误差对系统性能的影响,本文给出了误码率的理论分析结果和计算机模拟结果,并与常规的未编码直扩系统性能对比。 相似文献
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Qiyue Yu Weixiao Meng Fumiyuki Adachi 《Wireless Communications and Mobile Computing》2014,14(13):1314-1328
The two‐dimensional (2D) block spread code division multiple access (CDMA) can avoid the uplink multiple‐access interference with low‐complexity single‐user detection in a slow fading channel and, therefore, is very attractive. In the 2D spreading, orthogonal variable spreading factor (OVSF) is used for spreading; an important problem is how to efficiently assign the limited resource of OVSF codes to users with different data rates, while meeting the requirement of quality of service in a multi‐cell environment. In this paper, it is shown that the code reuse can improve the code reuse efficiency and the proposed code reuse scheme combined with code assignment algorithm can allow flexible multi‐rate uplink transmission. The computer simulation confirms that the proposed code assignment algorithm improves the code reuse efficiency while achieving lower blocking probability than traditional CDMA. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献