排序方式: 共有46条查询结果,搜索用时 343 毫秒
1.
This paper presents the theoretical analysis of adaptive multiuser RAKE receiver scheme in frequency selective fading channel for direct-sequence code division multiple access (DS-CDMA) system. Least mean square (LMS) algorithm is used to estimate the channel coefficients. Chaotic sequences are used as spreading sequence and corresponding bit error rate (BER) in closed form is derived for imperfect channel estimation conditions. Performances of chaotic sequences are compared with pseudorandom noise (PN) sequences. Under perfect synchronization assumption, various simulation results are shown to investigate the performance of the proposed system. 相似文献
2.
This paper presents an algorithm to minimize the performance loss (PL) of minimum mean square error (MMSE) in code division multiple access (CDMA) based optical multiple input multiple output orthogonal frequency division multiplexing (O-MIMO-OFDM) systems over 1200 km of standard single mode fiber (SSMF). The performance of the system using proposed algorithm scheme is compared to MMSE scheme by simulation results. It shows the superior performance of proposed algorithm. 相似文献
3.
Hai Huyen Dam Hans-Jürgen Zepernick Sven Nordholm Jörgen Nordberg 《Annals of Operations Research》2005,133(1-4):249-264
The performance of a code division multiple access system depends on the correlation properties of the employed spreading
code. Low cross-correlation values between spreading sequences are desired to suppress multiple access interference and to
improve bit error performance. An auto-correlation function with a distinct peak enables proper synchronization and suppresses
intersymbol interference. However, these requirements contradict each other and a trade-off needs to be established. In this
paper, a global two dimensional optimization method is proposed to minimize the out-of-phase average mean-square aperiodic
auto-correlation with average mean-square aperiodic cross-correlation being allowed to lie within a fixed region. This approach
is applied to design sets of complex spreading sequences. A design example is presented to illustrate the relation between
various correlation characteristics. The correlations of the obtained sets are compared with correlations of other known sequences. 相似文献
4.
姜波 《新疆大学学报(理工版)》2004,21(3):325-328
无线资源管理是CDMA蜂窝移动通信系统保证业务质量(QoS)和提高频谱利用率的关键技术,本文提出了CDMA系统中无线资源管理算法的一般模型,阐述了三种重要的无线资源管理算法,即功率控制算法、呼叫接纳控制算法和分组调度算法的主要研究情况,并分析了目前研究中仍然存在和需要解决的问题。 相似文献
5.
Eshima Nobuoki; Kohda Tohru; Tabata Minoru 《IMA Journal of Mathematical Control and Information》2007,24(3):289-298
6.
In this paper we have proposed a novel prime spreading sequence family hereby referred to as “new-Modified Prime Code (n-MPC)”
for direct-detection synchronous optical code-division multiple-access (OCDMA) networks. The new code has been applied to
Overlapping Pulse-Position Modulation (OPPM) CDMA system and the performance of system is evaluated. In addition, we have
analyzed the system throughput and also introduced a new interference cancellation technique which significantly improves
the bit error probability (BEP) of OPPM-OCDMA systems. 相似文献
7.
A new interference cancellation technique for direct-detection optical code- division multiple-access (OCDMA) network employing
pulse-position modulation (PPM) is proposed in this paper. The multiple access interference (MAI) estimation is achieved by
pre-reserving one of optical spreading code sequences at the receiver based on the correlation property of padded modified
prime codes (PMPC). The estimated interference is then cancelled out after photo-detection process. Additionally, the transmitted
signal is Manchester-coded to further improve the system performance. Based on this proposed interference canceller in a shot-noise
limited regime, we have obtained an expression for the upper bound of the bit-error probability (BEP) taking into account
effects of both MAI and shot-noise. This BEP is compared with that of a PPM-OCDMA without cancellation. Finally, the receiver
structure of the proposed optical network unit (ONU) is fairly simple to compare with the conventional cancellation schemes. 相似文献
8.
A mixture of reservation plus contention data slots is now widely implemented in TDMA/ CDMA systems to make a system flexible enough to suit various kinds of packets but preserve the good nature of frame-based protocols. We conducted performance analysis for an arbitrary connection in such a system under the assumption of MMPP (Markov-modulated Poisson process) arrivals. Accessible slot locations of this connection in a frame are made general. Success probability in accessing a contention slot is also made general. We have obtained the system size distribution which can be used to evaluate the performance of various frame-based MAC protocols. The MMPP arrival pattern can be generalized to the BMAP (batch Markovian arrival process) family to further accommodate a broader set of traffic sources.Part of the work was performed when the authors were with Graduate Institute of Communication Engineering, National Taiwan University, Taipei, Taiwan 106.This revised version was published online in June 2005 with corrected coverdate 相似文献
9.
DAVID CHAPMAN 《Fiber and Integrated Optics》2013,32(5):375-385
The coupling of light from a number of few or single-moded fibers into a single multi-mode fiber is analyzed using geometric optics, and simple results demonstrating mode conservation are derived. Coupling from multiple single-mode fibers into a multi-mode fiber is investigated in detail using the overlap integral to determine coupling into each mode of the output fiber as a function of the light phase in the inputs. As well as results with practical relevance to fiber tapped delay-line filters and optical CDMA, the analysis provides pedagogic insight into light propagation and the light-gathering properties of fiber. 相似文献
10.
Free space optics (FSO) link at high transmission rate is delimited due to its perceptivity to diversified surroundings especially in hilly regions. A demonstration of CDMA-FSO coherent detection system is reported in this work to achieve a prolonged 10 Gbps-FSO link with acceptable SNR under the impact profound haze, rain and fog environment. Further, the work is extended to weigh the proposed CO-CDMA-OSSB-FSO transmission system against OFDM-OSSB-FSO direct detection system 0045 and 0050. 相似文献