共查询到20条相似文献,搜索用时 15 毫秒
1.
Hyung-Kun Park 《Wireless Personal Communications》2006,39(2):253-264
One of the principal disadvantages of multicarrier modulation technique is the sensitivity to the frequency offset introduced by Doppler shift. This frequency offset introduces inter-carrier interference (ICI) among the multiplicity of carriers in the multicarrier modulated signal. However, Doppler spread induced by temporal channel variations can provides another means for diversity. In this paper, we propose a modified multicarrier code division multiple access (CDMA) system to exploit Doppler diversity as well as multipath diversity. The key work of our framework is a canonical time-frequency-based decomposition of the mobile wireless channel into series of independent fading channel. The decomposition naturally leads to a time-frequency generalization of the Rake receiver that exploits both multipath and Doppler diversity. 相似文献
2.
多载波CDMA具有更高的灵活性 ,更高的频谱效率 ,简单的检测技术 ,窄带干扰抑制能力等一系列优点 ,引起了研究者的广泛兴趣。文中介绍了三种多载波CDMA技术 ,即MC CDMA (多载波CDMA) ,多载波DS CD MA (直接序列CDMA)和多音CDMA并简单介绍了它们的发射和接收技术。最后还指出多载波CDMA技术所固有的缺陷。 相似文献
3.
Jenn‐Kaie Lain Shang‐Yi Yang Chih‐Wei Lin 《International Journal of Communication Systems》2013,26(8):964-973
This paper presents a joint carrier frequency offset estimation and multiuser detection based on a maximum likelihood approach in multicarrier code division multiple access systems. With the definition of a score function based on the log‐likelihood, the joint carrier frequency offset estimation and multiuser detection can be formulated as a nonlinear optimization problem over the joint of a multidimensional real space and a multidimensional discrete space. To reduce the computational complexity required by the joint decision statistic, while still obtaining a desirable performance, a new method using cross‐entropy optimization is proposed to solve the nonlinear optimization problem. Because of the robustness of the cross‐entropy optimization, the joint decision statistic can be efficiently solved, and, as shown by the furnished simulation results, the proposed approach can achieve satisfactory performance in various scenarios. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
4.
In this letter, the performance of multicarrier code-division multiple-access (CDMA) systems is studied in the presence of narrowband interference for future ultra-wideband (UWB) communications. A Nakagami fading channel is assumed, and notch filters along with diversity techniques are used in the multicarrier CDMA receiver. A complete performance analysis of error probability is given. It is shown that when the number of subcarriers jammed by narrowband interference is small, the multicarrier receiver without notch filters can work well, due to the gain of frequency diversity from nonjammed subcarriers. On the other hand, when the number of subcarriers jammed by the narrowband interference is large, using notch filters can improve the multicarrier system performance significantly. 相似文献
5.
MAI and ICI of Asynchronous Uplink MC-CDMA With Frequency Offset 总被引:1,自引:0,他引:1
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. 相似文献
6.
7.
瑞利衰落信道中MC-CDMA系统的载波频率偏移性能 总被引:1,自引:0,他引:1
多载波CDMA(MC-CDMA)技术结合了OFDM和CDMA技术的优点,在无线衰落信道中传输高速数据时具有突出的性能。但由于MC-CDMA采用了多载波技术,载波频率偏移对系统性能的影响非常大。本文对瑞利衰落信道下存在载波频率偏移的MC-CDMA系统性能进行了理论分析并对误码率进行了详细讨论。 相似文献
8.
Phase noise and fading effects on system performance in MT-DS-SS 总被引:1,自引:0,他引:1
《Vehicular Technology, IEEE Transactions on》2005,54(5):1759-1767
Multicarrier (MC) modulation and code division multiple access (CDMA) schemes have seen much recent attention for the high capacities and flexibility they can provide. A potential difficulty with these systems is their sensitivity to the effects of imperfect frequency up/down conversion due to local oscillator phase noise and frequency offset. In this paper, we provide a general method to upper bound and/or approximate system performance in multitone direct-sequence spread spectrum (MT-DS-SS) signaling in the presence of imperfect synchronization. We model phase noise as a slow random processes with small variance. In particular, we assume coherent detection with binary phase-shift keying (BPSK) modulation and use a phase noise model based upon one for a practical phase-locked loop (PLL). Comparisons between simulations and analysis show excellent agreement, and also show that system degradation is dominated by the common phase noise, and that the intersubcarrier-same-user interference (IS-SUI) contribution is very small. The approach we employ provides an effective analytical/numerical method for performance evaluation for low target error probability values, on the order of 10/sup -6/ or lower. In addition, our method can also be easily applied to any multicarrier system with other frequency offset/phase noise models. 相似文献
9.
The performance of a multicarrier direct sequence code-division multiple-access (CDMA) system employed in the forward link of a cellular system operating over a Rayleigh fading channel is analyzed and compared to the performance of both single-carrier CDMA and hybrid multicarrier CDMA/frequency division multiplexing systems. A RAKE receiver is provided for each subcarrier. We compare the performance of all three systems for various multipath intensity profiles. It is found that for a service requiring high quality and a small number of users, the multicarrier system is the best, but for a service requiring low quality and a large number of users, the hybrid system can support more users than the others. Also, for the case when nonorthogonal codes are used, the multiple-access interference in different resolvable paths are correlated. In that case, to maximize the signal-to-noise ratio in a correlated interference environment; maximal-ratio combining (MRC) is not optimal. However, we found that there is not much difference between the optimum combining and the conventional MRC 相似文献
10.
Multicarrier code-division multiple access (CDMA) with time and frequency spreading has been recently considered as a candidate for fourth-generation (4G) wireless systems. This signaling scheme simultaneously utilizes code spreading in the time and frequency domains to simultaneously improve frequency diversity and minimize multiuser access interference. As a result, it is capable of outperforming multicarrier CDMA systems that employ 1-D spreading. In this paper, a novel adaptive subcarrier allocation algorithm is developed for multicarrier CDMA with time and frequency spreading to improve the overall bit error rate (BER) performance for all spreading configurations. This algorithm assigns users to subcarrier groups that provide favorable fading characteristics while simultaneously reducing the amount of interference caused to other users. The proposed algorithm is shown to provide a performance improvement, ranging from 1.5 dB with 2times16 (time times frequency) and spreading to 7 dB with 16times2 (time times frequency) spreading. The algorithm is also shown to maintain or improve the BER floor for each spreading configuration. It is concluded that at higher and lower levels of Eb/No, a higher frequency- and time-domain spreading should be, respectively, employed to improve BER performance. Furthermore, the Eb/No threshold level to switch between time and frequency spreading for the analyzed system is found to be 2.5 dB. 相似文献
11.
Yang Wei Chen Junshi Tan Zhenhui Cheng Shixin 《电子科学学刊(英文版)》2007,24(5):607-612
Code-Division Multiple-Access (CDMA) systems are interference limited,and therefore efficient interference management is necessary to enhance the performance of a CDMA system.In this paper,a successive beamforming (spatial filtering),linear decorrelating MultiUser Detection (MUD, temporal filtering) and diversity reception structure for uplink multicarrier Direct Sequence CDMA (DS-CDMA) system with antenna array are proposed.By beamforming,the antenna array suppresses interference according to the distinct array signature.Subsequently,linear decorrelating MUD is ap- plied to separate the signals of different users and eliminate Multiple Access Interference (MAI).Finally, the decorrelated signals at different subcarriers that belong to the same user are combined to achieve frequency diversity.Simulation results show that the proposed structure offers significant Bit Error Rate (BER) performance improvement by successively exploiting the space-time-frequency processing. 相似文献
12.
A novel fuzzy minimum output energy (MOE) detector is proposed for uplink multicarrier CDMA (MC-CDMA) systems with carrier frequency offset (CFO) over multipath fading channels. The proposed receiver involves the following stages. First, the fuzzy CFO constrained MOE detector after coarse CFO estimation is proposed to suppress multiple access interference and combat the degradation problem of the conventional MOE detector caused by the CFO effect. Next, using the signal subspace projection technique, the proposed detector can further reduce the enhanced noise due to the fuzzy CFO constrained detector. Finally, the output data obtained from these detectors are coherently combined to offer multipath diversity gain in accordance with the maximum ratio combining criterion. Furthermore, the proposed single input single output (SISO) robust detector can be easily extended for a multiple input multiple output (MIMO) MC-CDMA system with a high rate of performance. Simulation results show that the proposed SISO detector, which offers a similar performance as the optimal detector, can provide robustness against CFO and outperform the conventional detectors. The proposed MIMO detector with spatial multiplexing gain also exhibits excellent performance. 相似文献
13.
This paper suggests that multicarrier modulation reduces the complexity and the delay caused by the multiuser interference cancellation process utilizing convolutional codes. For spread spectrum multiple access, multiuser interference (interference due to signals from other users) limits the performance of the communication link. To remove this interference, a multiuser interference cancellation technique which utilizes orthogonal convolutional codes has been proposed for the uplink (mobiles to a base station) of the cellular code-division multiple-access (CDMA) systems. However, this technique requires large interleavers and huge memory, or artificial multipath diversity and a RAKE system to achieve sufficient coding gain if it is applied to wireless indoor communications and fading is slow compared to the data rate. To reduce the complexity of the canceller, multicarrier modulation is employed as it provides frequency diversity gain and coding gain without the interleavers or a RAKE system. This paper shows that multicarrier modulation reduces the complexity of the canceller and still provides sufficient coding gain in order to cancel the multiuser interference. A canceller with decoding in the initial decision and multicarrier modulation improves the capacity by a factor of 1.4 as compared with a canceller without decoding 相似文献
14.
Future generations of wireless communication systems will be designed with the aim of making the best possible use of the limited radio spectrum in order to further increase throughput as well as user-capacity. In this paper, the application of multicarrier CDMA (code division multiple access) within mobile communication systems is discussed. An overview of the main types of multicarrier spread-spectrum systems is given. The multicarrier CDMA system is described in detail, including its relationship with OFDM (orthogonal frequency division multiplexing), its general performance in comparison with direct sequence CDMA and some specific implementation problems. The paper also presents some results comparing the performance of a selection of algorithms that can be used to isolate the individual signal of each user. Potential capacity increases achievable with adaptive loading in time and frequency slots is briefly demonstrated. By allocating users multiple codes, very high data rates can be achieved, and the paper gives a comparison of multicode, multicarrier CDMA with OFDM-based wireless LAN systems 相似文献
15.
16.
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. 相似文献
17.
Jiangzhou Wang Hu Huang 《Wireless Communications, IEEE Transactions on》2002,1(3):448-455
We introduce the slow frequency hopping (SFH) technique to the multicarrier (MC) code-division multiple-access (CDMA) systems for overlay situations. Using lower chip rate, which results in a narrower spectrum for each carrier and hopping the signal in frequency, the MC direct sequence (DS)/SFH system achieves better performance than the MC DS CDMA system in most cases, especially when the bandwidth of the narrowband interference (NBI) is narrower than one subchannel. It also exhibits a stable performance against the variations of the NBI location and bandwidth. When there is no NBI, the two systems perform approximately the same. The evaluation is performed over a frequency selective Rayleigh fading channel, with both Gaussian approximation and Monte Carlo simulation 相似文献
18.
This article is a review of our ongoing research effort to construct a new multicarrier CDMA architecture based on orthogonal complete complementary codes, characterized by its innovative spreading modulation scheme, uplink and downlink signaling design, and digital receiver implementation for multipath signal detection. There are several advantages of the proposed CDMA architecture compared to conventional CDMA systems pertinent to current 2G and 3G standards. First of all, it can achieve a spreading efficiency (SE) very close to one (the SE is defined as the amount of information bit(s) conveyed by each chip); whereas SEs of conventional CDMA systems equal 1/N, where N denotes the length of spreading codes. Second, it offers MAI-free operation in both upand downlink transmissions in an MAI-AWGN channel, which can significantly reduce the co-channel interference responsible for capacity decline of a CDMA system. Third, the proposed CDMA architecture is able to offer a high bandwidth efficiency due to the use of its unique spreading modulation scheme and orthogonal carriers. Lastly, the proposed CDMA architecture is particularly suited to multirate signal transmission due to the use of an offset stacked spreading modulation scheme, which simplifies the rate-matching algorithm relevant to multimedia services and facilitates asymmetric traffic in up- and downlink transmissions for IP-based applications. Based on the above characteristics and the obtained results, it is concluded that the proposed CDMA architecture has a great potential for applications in future wideband mobile communications beyond 3G, which is expected to offer a very high data rate in hostile mobile channels 相似文献
19.
Lingyun Cai Youyun Xu Haibin Zhang Wentao Song 《Wireless Communications and Mobile Computing》2006,6(4):475-482
In this paper, we present a novel group space‐time block coding slow frequency‐hopping multicarrier direct‐sequence code division multiple access (GSTBC SFH/MC DS‐CDMA) system over frequency selective fading channels. The proposed scheme greatly improves the bandwidth‐efficient through assigning the users employing the same frequency‐hopping (FH) pattern. Moreover, the users employing the same FH pattern are assigned into different virtual groups, in which the users are assigned to the different spreading codes, while the users are assigned to the same spreading code in the same virtual group. Then, a novel group detection scheme that we denote by group ordered successive interference cancellation (GOSIC) is presented to suppress the interference between the different virtual groups. Our proposed scheme consists of ordering group at the receiver side in order to maximize the overall system performance, and carrying BLAST‐STBC (LSTBC) detection for the users in the same virtual group. We define and derive the optimal group order based on the post group signal to interference plus noise ratio (PGSINR). We also propose another suboptimal group order in order to overcome the complexity issues. Finally, we compare the performance of our proposed GOSIC with conventional group successive interference cancellation (GSIC), conventional STBC multiuser detection (MUD), and LSTBC‐MUD, and show that significant improvement is introduced. Finally, it is shown that the proposed scheme is robust to the imperfect channel estimation. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
20.
Lanke Lakshmi Prasanna Kumar Kamavaram Ellore Srinivasa Murthy Mahendhra Nanjappa Giri Prasad 《International Journal of Communication Systems》2020,33(13)
From the past decade, the multicarrier code division multiple access (MC‐CDMA) transmission schemes have placed major role in wireless communications. It is providing a secured wireless communication to the users with guaranteed performance. In many situations, the performance of the MC‐CDMA is restricted due to the interference caused by multiple access interference (MAI), which also influences the frameworks of CDMA. To overcome this issue, we concentrated on developing the efficient technique for data transmission with interference cancellation for downlink MC‐CDMA. In the proposed method, the interference cancellation procedure is done by using the regeneration and subtraction of MAI from the signal. The simulation results are evaluated using the MC‐CDMA system with different decision functions. Results proved that the proposed system is efficient in reducing the MAI along with an improved bit error rate (BER). 相似文献