共查询到20条相似文献,搜索用时 31 毫秒
1.
Chia-Hsin Cheng Jen-Yung Lin Chao-Kai Wen Jyh-Horng Wen 《Wireless Personal Communications》2009,48(2):311-325
In this paper, a convenient signaling scheme, called orthogonal on–off BPSK (O3BPSK), along with a simple one-shot linear decorrelating detector (LDD) and a whitening Rake bank, is proposed for near–far
resistant detection in asynchronous DS/CDMA systems. Based on the maximum multi-path spreading delay, a minimum duration of
“off” is suggested, during which the temporally adjacent bits (TABs) that contain multi-user interference (MUI) and inter-symbol
interference (ISI) from different users at the receiver are decoupled. The O3BPSK signaling scheme is combined with the whitening Rake receiver to preserve multi-path diversity gain in multi-path fading
CDMA channels. The scheme offers low complexity, no detection delay, near–far resistance, and compensation for fading channels.
相似文献
Jyh-Horng Wen (Corresponding author)Email: |
2.
The non quantized nature of user rate wastes the code capacity in Orthogonal Variable Spreading Factor Codes (OVSF) based
Code Division Multiple Access (CDMA) systems. The code sharing scheme in multi code CDMA is proposed to minimize the code
rate wastage. The scheme combines the unused (wastage) capacity of already occupied codes to reduce the code blocking problem.
Simulation results are presented to show the superiority of the proposed code assignment scheme as compared to existing schemes.
相似文献
Sunil V. BhooshanEmail: |
3.
Chee Kyun Ng Nor Kamariah Noordin Sabira Khatun Borhanuddin Mohd Ali Sudhanshu Shekhar Jamuar Mahamod Ismail 《Wireless Personal Communications》2008,46(3):305-316
The performance of code division multiple access (CDMA) systems can be affected by small scale fading such as Rayleigh fading
channel. In this paper, the application of smart antenna and Large Area Synchronous CDMA (LAS CDMA) systems, which introduce
directional diversity channel, is presented. A novel interference cancellation scheme through dynamic space code (DSC) algorithm
is briefly described. The directional diversity can be realized from the directional gain of smart antenna system. It can
be found that when the number of elements in smart antenna is increase the directional gain of antenna system is much higher
than single antenna. The system performance analysis in term of error probability is compared between traditional and LAS
CDMA systems in both single and smart antenna systems. From the performance analysis it is found that CDMA system is more
susceptible to multipath fading channel than interferences from existing users.
相似文献
Mahamod IsmailEmail: |
4.
In this work the performance of a Fractional Fourier transform (FrFT) based Minimum Mean Squared Error receiver for MIMO systems
with space time processing over Rayleigh faded channels is presented. The proposed receiver called Optimum FrFT based MIMO
receiver (OFMR) shows improved performance outperforming the simple MMSE receiver in Rayleigh faded channel.
相似文献
Rajesh KhannaEmail: Email: |
5.
Channel Adaptive Power Control in the Uplink of CDMA Systems 总被引:2,自引:1,他引:1
In this paper, we propose an adaptive power control algorithm using optimal control theory for CDMA cellular systems. With
linear quadratic control, each mobile transmits to achieve a desired SIR under the fast varying environment of practical CDMA
cellular systems. We apply Kalman filter theory to estimate a channel variation which is vulnerable to nonconstant link gain,
mutual interference and uncertain noise. Through simulation comparison with DCPC algorithm, the suggested power control algorithm
shows an increased uplink channel capacity.
相似文献
Kwan-Ho You (Corresponding author)Email: |
6.
The throughput enhancement of Space-Time Spreading (STS)-based Code Division Multiple Access (CDMA) system is investigated
in this paper. Adaptive Modulation is utilized to improve the data throughput of the system in multipath Rayleigh fading channel.
In this contribution, an analytical approach is proposed to compute a new expression for the Bit Error Rate (BER) performance
and the output Signal-to-Interference-and-Noise Ratio (SINR) of the RAKE receiver-assisted STS-based CDMA system for QAM data,
considering multipath and multiuser interferences. The other contribution of the paper is deriving a new closed form expression
for computing the throughput enhancement and the BER performance of the adaptive modulated STS-based CDMA system over multipath
fading channel. Simulation and analytical results demonstrate that using adaptive modulation method in this system improves
the average throughput by keeping the BER performance at a target level. The novel expressions presented in this paper bring
out the facility of evaluation of the proposed system with no need to more calculations and simulations.
相似文献
Hassan AghaeiniaEmail: |
7.
In this paper, we present a robust adaptive channel estimator and a robust multiuser detector for wireless multicarrier code-division
multiple access (MC–CDMA) systems under narrowband interference (NBI). The conventional least-squares (LS) channel estimator
performs poorly when narrowband interfering signals contaminate the multicarrier systems. A new weighted recursive least M-estimate (WRLM) channel estimator is hence developed to estimate multipath fading channels in the presence of NBI. The new
robust channel estimator resorts to M-estimate and weighted least-squares (WLS) techniques. Simulations show that the WRLM channel estimator offers substantial
performance gain over conventional recursive least-squares (RLS), recursive least M-estimate (RLM) and weighted RLS (WRLS) channel estimators under NBI. With the estimated channel coefficients, a robust multiuser
detector is proposed to jointly suppress multiple access interference (MAI) and NBI. The performance of the linear decorrelator
will degrade substantially in the presence of NBI. A weighted least M-estimate (WLM) algorithm is therefore developed to combat the NBI. The WLM multiuser detector is also based on the weighted
M-estimate concept. Numerical results show that the proposed WLM multiuser detector significantly outperforms over the conventional
linear decorrelator, the robust decorrelator with M-estimate and the WLS detector under NBI.
相似文献
Z. G. ZhangEmail: |
8.
Stephan Sand Christian Mensing Carlo Mutti Armin Wittneben 《Wireless Personal Communications》2008,47(1):51-61
In this paper, we consider a transmission system employing orthogonal frequency division multiplexing with bit-interleaved
coded modulation and perfect channel state information at both transmitter and receiver. An adaptive bit loading scheme in
combination with cyclic delay diversity and discontinuous Doppler diversity is proposed at the transmitter and iterative demapping
and decoding at the receiver. The loading procedure minimizes the bit-error rate at the decoder output, and the transmit diversity
schemes mitigate channel correlations. We analyze the iterative receiver with extrinsic information transfer charts and present
the achievable gains.
相似文献
Armin WittnebenEmail: |
9.
The paper presents a new multiplexing scheme, called convolutional multiplexing (CM), to achieve high diversity gain and high
spectrum efficiency for OFDM-based systems. In this scheme, data symbols are spread onto several subcarriers by the convolutional
spreader. Spectrum efficiency can be improved by two approaches: high order modulation and multi-code multiplexing. With the
best spreading codes searched out, the multi-code multiplexing OFDM-CM system performs better in AWGN channel, but may lose
diversity gain in frequency selective fading channels. On the other hand, the single-code spreading OFDM-CM system with high
order modulation can achieve the maximum diversity order. Simulation results show that the multi-code convolutional multiplexing
perform better than code-division multiplexing (CDM) for OFDM-based systems.
相似文献
Wei JiangEmail: |
10.
Wei-Chiang Wu 《Wireless Personal Communications》2009,50(3):275-289
In this paper, we propose a two-stage linear multiuser detector (LMD) for ultra wideband (UWB) multiple single-input multi-output
(M-SIMO) system and multipath fading environment. Time-hopping (TH) and antipodal pulse amplitude modulation (PAM) are employed
for the multiple access system. The decorrelating detector is first employed at the front end of each receive antenna to eliminate
the multi-user interference (MUI), then a set of maximum-ratio-combiners (MRC) are proceeded to maximize the signal-to-noise
power ratio (SNR) for each user. Since the channel information is crucial for the Decorrelating-MRC (D-MRC) receiver, we develop
a subspace-based blind M-SIMO channel estimation method. The effect of channel estimation error on system performance is extensively
evaluated. It is also verified from the analytical and numerical results that by exploiting both spatial and temporal diversities,
the D-MRC receiver dramatically improves system performance even without additional coding. Moreover, we demonstrate that
both the D-MRC receiver and subspace-based blind channel estimator are computationally feasible and near-far resistant.
相似文献
Wei-Chiang WuEmail: |
11.
It is well known that adding more antennas at the transmitter or at the receiver offers larger channel capacity in the multiple-input
multiple-output communication systems. In this letter, a simple proof is presented for the fact that the channel capacity
increases with an increase in the number of receive antennas. The proof is based on the famous capacity formula of Foschini
and Gans and uses matrix theory.
相似文献
J. F. HayesEmail: |
12.
Modeling Channel Access Delay and Jitter of IEEE 802.11 DCF 总被引:1,自引:0,他引:1
Yun Li Chonggang Wang Keping Long Weiliang Zhao 《Wireless Personal Communications》2008,47(3):417-440
With the ever-increasing requirement of WLAN to support real-time services, it is becoming important to study the delay properties
of WLAN protocols. This paper constructs a new model to analyze the channel access delay and delay jitter of IEEE 802.11 DCF
in saturation traffic condition. Based on this analytical model, average channel access delay and delay jitter are derived
for both basic access and RTS/CTS-based access scheme. The accuracy of the analytical model is validated by simulations and
furthermore we discuss the impact of initial contention window, maximal backoff stage, and packet size on channel access delay
and delay jitter of 802.11 DCF using the proposed model.
相似文献
Chonggang WangEmail: |
13.
Quasisynchronous (QS) Code Division Multiple Access (CDMA) is currently being considered for a variety of wireless applications
and services because QS-CDMA enables information transmission with a good quality of service. In this paper, for M-ary signaling,
the Symbol Error Rate (SER) performance of QS-CDMA communication system with a maximal ratio combiner (MRC) over frequency-selective,
time-nonselective multipath Generalized Gamma (GG3) fading channels is derived not only for any deterministic spreading sequences
but also for any chip-limited chip waveforms, and it is investigated for Rectangular, Half-Sine, and Raised-Cosine chip waveforms
by means of numerical and simulation results. Numerical and simulation results show that the performance of QS-CDMA is as
good as or slightly better than synchronous CDMA (S-CDMA) when the maximum quasisynchronous delays do not need to be less
than some specific values depending on the path power scattering. With this flexibility of quasisynchronous delays, both the
transmitter and receiver complexities are reduced as quasisynchronous communication is a challenging task for researchers.
Additionally, since not only the spreading sequences but also the partial autocorrelation functions of the chip waveform are
influential on the performance of multipath QS-CDMA, a measure, Partial Power Ratio (PPR) is defined based on these partial
autocorrelation functions in order to select or design a chip waveform for quasisynchronous communication. Furthermore, results
show that QS-CDMA using the chip waveform whose PPR is greater has better performance.
相似文献
Oğuz Kucur (Corresponding author)Email: |
14.
Multi-user Detection of Nonlinearly Distorted MC-CDMA Symbols by Microstatistic Filtering 总被引:1,自引:1,他引:0
Jozef Krajňák Marc Deumal Pavol Pavelka Dušan Kocur Joan Lluís Pijoan Pavol Galajda 《Wireless Personal Communications》2008,47(1):149-160
Multi-carrier code division multiple access is a powerful modulation technique that is being considered in many emerging broadband
communication systems. In a downlink scenario orthogonal spreading sequences are used since they reduce multiple access interference
compared to non-orthogonal. However, the nonlinear amplification of the transmitted signal destroys the orthogonality and,
thus, reduces the system performance. In order to avoid performance degradation without requiring large back-offs in the transmitter
amplifier, it becomes necessary to use multi-user detection techniques at the receiver side. Conventional multi-user detectors
(MUD) are designed for linear environments and, as a result, might not exhibit enough performance improvement. In this paper
a new MUD based on microstatistic filtering is proposed. The presented MUD uses piece-wise linear filtering in conjunction
with threshold decomposition of the input signal, which introduces a nonlinear effect, to improve performance when a nonlinearity
is present. Maximum performance improvement compared to conventional MUD is achieved for low spreading factors and user loads
no greater than 50%.
相似文献
Marc DeumalEmail: |
15.
Ann-Chen Chang 《Wireless Personal Communications》2009,50(3):381-399
This paper deals with narrowband interference (NBI) and multiple access interference (MAI) suppression based on subspace-based
approaches for direct-sequence code-division multiple-access (DS-CDMA) systems. First, the signal subspace-based and the interference
subspace-based techniques are developed to estimate the noisy DS-CDMA signal and the interference signal, respectively. In
conjunction with a modified multiple constrained minimum variance multiuser detector, we develop two efficient schemes to
deal with the NBI and MAI that do not need any prior knowledge about the characteristics of the interference and specific
training sequence. Next, an adaptive implementation based on a signal subspace tracking algorithm and a recursive least mean
square algorithm is also developed. Several computer simulation examples in terms of bit error rate are provided for illustrating
the effectiveness of the proposed schemes.
相似文献
Ann-Chen ChangEmail: |
16.
Multimedia transport has stringent bandwidth, delay, and loss requirements. It is a great challenge to support such applications
in reconfigurable wireless networks (RWNs). Using multiple paths in parallel for multimedia transport provides a new degree
of freedom in designing robust multimedia transport systems. In this paper, we provide a multi-path extension to zone routing
protocol (ZRP) to support video transmission over RWNs. We compare ZRP and our multi-path routing scheme by using NS-2 simulator.
The experiments show that our method is effective in improving the robustness of video transport over RWNs.
相似文献
Shiwei YeEmail: |
17.
Chen Jie Vidhyacharan Bhaskar 《International Journal of Wireless Information Networks》2008,15(1):53-60
This paper analyzes the distribution and density functions of the probability of error for Rayleigh and Rician fading channels
with diversity. An expression for the signal-to-noise ratio is derived for an asynchronous CDMA (A-CDMA) system with diversity.
The error probability distribution and density functions are derived and plotted for different mean energy-to-noise ratios.
相似文献
Vidhyacharan BhaskarEmail: |
18.
Tai-Kuo Woo 《Wireless Personal Communications》2008,46(4):429-449
The delay elements of a conventional two-dimensional space–time receiver are fixed. The rather inflexible design is inappropriate
since the received signals among the antenna branches are correlated due to limited spacing, and the fading environment is
time-varying. In this paper we propose a dynamic finger assignment strategy for a space–time receiver, where the delay taps
are adjusted dynamically, based on the theory of finite projective planes, to improve the signal-to-noise ratio in correlated
antenna branches. The proposed finite projective plane (FPP) based finger assignment scheme maximizes the collected energy
by dynamically setting the tap delays depending on the correlation among antenna branches and the delay spread of the channel.
In the performance evaluation, we demonstrate that the FPP based finger assignment scheme can improve the signal-to-noise
ratio significantly in comparison to the conventional mesh-grid configuration when the correlation among antenna branches
is high and the channel dispersion is relatively long in comparison to the overall span of the fingers. However, the gain
is moderate if the channel dispersion ratio is short, where the gain of reduced correlation among antenna branches must compensate
for the reduced signal-to-noise ratio due to the missed signals.
相似文献
Tai-Kuo WooEmail: |
19.
This paper presents the evaluation of the average spectral efficiencies provided by the adaptive use of a set of LDPC-coded
QAM modulations in an OFDMA downlink scheme over mobile radio channels, considering a joint modeling of the channel and user-access
method. It discusses the selection of the set of coded modulations, briefly describes the joint modeling of the channel and
access method employed, and derives the average spectral efficiency provided by this approach in non-ARQ or H-ARQ environments.
Some comments about the effects of the system’s parameters upon its performances are also included.
相似文献
Vasile BotaEmail: |
20.
The performance of an optical code division multiplexing access (OCDMA) system employing the differential phase shift keying
(DPSK) data format and turbo code is investigated and simulated. A bandwidth-limited coherent time spreading (TS) OCDMA system
is considered. Theoretical results show that performance degradation due to bandwidth limitation could be effectively restrained
by the application of the DPSK data format in a coherent OCDMA system, and further performance improvement could be achieved
by incorporating turbo coding into the OCDMA system.
相似文献
Xiaogang ChenEmail: |