共查询到20条相似文献,搜索用时 46 毫秒
1.
双向中继网络在提高频谱效率的同时会引入额外的自干扰,本文针对放大转发(AF)模式下双向多输入多输出(MIMO)中继网络中的自干扰抵消问题,从消除信道估计误差引入的剩余自干扰着手,提出一种采用信道独立预编码的盲干扰抵消(BIC)方案。新方案在源节点对信息进行行空间预编码,从而构建不依赖于MIMO信道矩阵的期望信号子空间和自干扰子空间,实现未知信道状态下自干扰抵消和期望信号分离,从而消除非理想信道估计带来的剩余自干扰信号。在此基础上,以最大化有效信噪比为目标设计最佳预编码,通过推导可达和速率的闭合表达式,分析不同方案下信道估计误差对可达和速率的影响。仿真结果表明,新方案在不同的信道估计误差下,能够实现完美自干扰消除,其检测性能和容量均优于基于信道估计的自干扰消除方案。 相似文献
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Xi Zhang Qinghe Du 《Communications Magazine, IEEE》2007,45(8):62-70
In this article we propose a cross-layer design model for multimedia multicast/broadcast services to efficiently support the diverse quality of service requirements over mobile wireless networks. Specifically, we aim at achieving high system throughput for multimedia multicast/broadcast while satisfying QoS requirements from different protocol layers. First, at the physical layer, we propose a dynamic rate adaptation scheme to optimize the average throughput subject to the loss rate QoS constraint specified from the upper-layer protocol users. We investigate scenarios with either independent and identically distributed (i.i.d.) or non-i.i.d. fading channels connecting to different multicast receivers. Then, applying the effective capacity theory at the data link layer, we study the impact of the delay QoS requirement (i.e., QoS exponent) on the multimedia data rate of mobile multicast/broadcast that our proposed scheme can support. Also presented are simulation results which show the trade-off among different QoS metrics and the performance superiority of our proposed scheme as compared to the other existing schemes. 相似文献
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In‐Taek Lim 《ETRI Journal》2001,23(2):52-60
In this paper, a medium access control protocol is proposed for integrated voice and data services in wireless local networks. Uplink channels for the proposed protocol are composed of time slots with multiple spreading codes per slot based on slotted code division multiple access (CDMA) systems. The proposed protocol uses spreading code sensing and reservation schemes. This protocol gives higher access priority to delay‐sensitive voice traffic than to data traffic. The voice terminal reserves an available spreading code to transmit multiple voice packets during a talkspurt. On the other hand, the data terminal transmits a packet without making a reservation over one of the available spreading codes that are not used by voice terminals. In this protocol, voice packets do not come into collision with data packets. The numerical results show that this protocol can increase the system capacity for voice service by applying the reservation scheme. The performance for data traffic will decrease in the case of high voice traffic load because of its low access priority. But it shows that the data traffic performance can be increased in proportion to the number of spreading codes. 相似文献
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Fairly adjusted multimode dynamic guard bandwidth admission control over CDMA systems 总被引:1,自引:0,他引:1
Guard-based call admission control schemes support admission priorities based on resources sharing with differentiated resource capacity limits. To minimize deviation from call blocking/dropping targets due to nonstationary call arrival condition, dynamic guard-based schemes with predictive adaptation control adjust differentiated capacity limits according to predicted future arrival rates based on specified estimation algorithms. Existing dynamic guard admission schemes are developed under the assumption of perfect estimation, which may not be possible in a highly nonstationary environment and, thus resulting in failures to maintain targeted blocking/dropping probabilities. This paper presents the fairly adjusted multimode-dynamic guard bandwidth scheme, which is a dynamic-guard-based scheme over code-division multiple-access systems with predictive adaptation control to adapt interference-based guard loading-limits under nonstationary call arrival condition; and reactive adaptation control to counteract arrival rate estimation errors. When the predictive adaptation control policy mode is not able to maintain long-term call blocking or dropping targets due to estimation error, this will trigger reactive adaptation control policy modes that include temporary blocking (preemption) of one or more lower priority classes subject to fairness constraints to ensure lower priority classes are not preempted at all costs during estimation error recovery. Analytical and simulation results show that proposed scheme is able to provide performance guarantees in terms of dropping probabilities under nonstationary traffic arrival and imperfect arrival rate estimation. 相似文献
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Cooperative relaying techniques can greatly improve the capacity of the multiple input and multiple output (MIMO) wireless system. The transmit power allocation (TPA) strategies for various relaying protocols have become very important for improving the energy efficiency. This article proposes novel TPA schemes in the MIMO cooperative relaying system. Two different scenarios are considered. One is the hybrid decode-and-forward (HDF) protocol in which the zero-forcing (ZF) process is operated on relays, and the other is the decode-and-forward (DF) protocol with relay node and antenna selection strategies. The simulation results indicate that the proposed schemes can bring about significant capacity gain by exploiting the nature of the relay link. Additionally, the proposed TPA scheme in the HDF system can achieve the same capacity as the equal TPA with fewer relay nodes used. Finally, the capacity gain with the proposed schemes increases when the distribution range of relay nodes expands. 相似文献
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Log-likelihood ratio (LLR) conversion schemes are proposed to mitigate the effect of collisions (or perforations) that occur in orthogonal code-hopping multiplexing (OCHM), which was previously proposed to accommodate more downlink channels than the number of orthogonal codewords. The proposed LLR conversion schemes greatly reduce the required SNR in channel decoding even when the perforation probability is high. The perforation probability in some LLR conversion schemes is estimated and several estimation methods are proposed. An LLR conversion scheme without estimation of the perforation probability is also proposed to avoid accurate estimation. The performance of the proposed schemes is evaluated by simulation in terms of the required E/sub b//N/sub 0/ for a 1% block error rate (BLER). 相似文献
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A spectrally efficient cooperative protocol for uplink wireless transmission in a centralised communication system is proposed, where each of the N users play the relaying and source roles simultaneously by using superposition (SP) modulation. The probability density function of the mutual information between SP-modulated transmitted and received signals of the cooperative uplink channels is derived. Using the high-signal-to-noise ratio (SNR) approximation of this density function, the outage probability formula of the system as well as its easily computable tight upper and lower bounds are obtained and these formulas are evaluated numerically. Numerical results show that the proposed strategy can achieve around 3 dB performance gain over comparable schemes. Furthermore, the multiplexing and diversity trade-off formula is derived to illustrate the optimal performance of the proposed protocol, which also confirms that the SP relaying transmission does not cause any loss of data rate. Moreover, performance characterisation in terms of ergodic and outage capacities are studied and numerical results show that the proposed scheme can achieve significantly larger outage capacity than direct transmission, which is similar to other cooperative schemes. The superiority of the proposed strategy is demonstrated by the fact that it can maintain almost the same ergodic capacity as the direct transmission, whereas the ergodic capacity of other cooperative schemes would be much worse. 相似文献
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This paper presents a distributed and adaptive fluctuation control scheme for many-to-one routing(FCM) in wireless sensor networks.Unlike well-known topology control schemes,the primary design objective is to reduce the fluctuation which happens due to overload of sensors in a data collection tree.More specifically,an estimation model of a sensor available capacity based on the number of its neighbors is proposed.In addition,this paper proposes a parent selection mechanism by three-way handshake.With such model and the selection mechanism,it is ensured that the load of a sensor does not exceed its available capacity.Finally,an adaptive maintenance mechanism is proposed to adjust the estimation of a sensor available capacity as the network environment changes.Simulation results demonstrate the effectiveness of the scheme. 相似文献
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Multiuser MIMO OFDM Based TDD/TDMA for Next Generation Wireless Communication Systems 总被引:1,自引:1,他引:0
Multiple-input multiple-output (MIMO) wireless technology in combination with orthogonal frequency division multiplexing (MIMO
OFDM) is an attractive air-interface solution for next-generation wireless local area networks (WLANs), wireless metropolitan
area networks (WMANs), and fourth-generation mobile cellular wireless systems. In this paper, one multiuser MIMO OFDM systems
with TDD/TDMA was proposed for next-generation wireless mobile communications, i.e., TDD/TDMA 4G, which can avoid or alleviate
the specific limitations of existing techniques designed for multiuser MIMO OFDM systems in broadband wireless mobile channel
scenarios, i.e., bad performance and extreme complexity of multiuser detectors for rank-deficient multiuser MIMO OFDM systems
with CDMA as access modes, extreme challenges of spatial MIMO channel estimators in rank-deficient MIMO OFDM systems, and
exponential growth complexity of optimal sub-carrier allocations for OFDMA-based MIMO OFDM systems. Furthermore, inspired
from the Steiner channel estimation method in multi-user CDMA uplink wireless channels, we proposed a new design scheme of
training sequence in time domain to conduct channel estimation. Training sequences of different transmit antennas can be simply
obtained by truncating the circular extension of one basic training sequence, and the pilot matrix assembled by these training
sequences is one circular matrix with good reversibility. A novel eigenmode transmission was also given in this paper, and
data symbols encoded by space–time codes can be steered to these eigenmodes similar to MIMO wireless communication systems
with single-carrier transmission. At the same time,, an improved water-filling scheme was also described for determining the
optimal transmit powers for orthogonal eigenmodes. The classical water-filling strategy is firstly adopted to determine the
optimal power allocation and correspondent bit numbers for every eigenmode, followed by a residual power reallocation to further
determine the additional bit numbers carried by every eigenmode. Compared with classical water-filling schemes, it can also
obtain larger throughputs via residual power allocation. At last, three typical implementation schemes of multiuser MIMO OFDM
with TDMA, CDMA and OFDMA, i.e., TDD/TDMA 4G, VSF-OFCDM and FuTURE B3G TDD, were tested by numerical simulations. Results
indicated that the proposed multiuser MIMO OFDM system schemes with TDD/TDMA, i.e., TDD/TDMA 4G, can achieve comparable system
performance and throughputs with low complexity and radio resource overhead to that of DoCoMo MIMO VSF-OFCDM and FuTURE B3G
TDD. 相似文献
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In this paper, a modified time‐of‐arrival (TOA) estimation error test and a hybrid time‐of‐arrival/angle‐of‐arrival (TOA/AOA) estimation error test for identification of line of sight (LOS) base stations (BSs) are proposed. The proposed schemes aim to improve the location accuracy of wireless location systems suffering from the non‐line of sight (NLOS) propagation errors. The modified TOA‐based estimation error test is considered a straightforward approach in identifying the LOS‐BS set when the number of LOS BSs is greater than or equal to three. When both TOA and AOA metrics are available, hybrid TOA/AOA squares of normalized estimation errors are formulated by adopting the approximate maximum likelihood (AML) estimation. The proposed hybrid estimation error test scheme is capable of identifying the LOS/NLOS status of each BS, and performing location estimation in the situation where only two LOS BSs exist. Simulation results show that the proposed schemes are capable of correctly identifying the LOS BSs and improving the overall location accuracy. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Many digital communication channels are affected by errors that tend to occur in bursts. A great deal of work has been devoted to finding good burst-error-correcting codes and developing burst-error-correcting schemes. However, burst-error-correcting codes are generally not effective for long bursts. Some burst-error-correcting schemes suffer long delay in decoding. Others are very sensitive to random errors in the guard space. Most of these schemes are not adaptive to channel conditions. A new adaptive scheme is proposed to overcome these drawbacks. The scheme employs a combination of two complementary punctured convolutional (CPC) codes. One of the codes is used for burst detection and for channel state estimation, and both codes are used for error correction. The proposed scheme is analyzed over a two state Markov chain channel model. Unlike existing burst-error-correcting schemes, it is shown that the proposed scheme is adaptive to channel conditions and less sensitive to errors in the guard space. For the same delay, the proposed scheme offers better performance than the interleaving schemes. When the channel is heavily corrupted by bursts, the improvement is even more pronounced 相似文献
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Blind and training-assisted subspace code-timing estimation for CDMA with bandlimited chip waveforms
In this paper, we present a group of subspace code-timing estimation algorithms for asynchronous code-division multiple-access (CDMA) systems with bandlimited chip waveforms. The proposed schemes are frequency-domain based techniques that exploit a unique structure of the received signal in the frequency domain. They can be implemented either blindly or in a training-assisted manner. The proposed blind code-timing estimators require only the spreading code of the desired user, whereas the training-assisted schemes assume the additional knowledge of the transmitted symbols of the desired user. Through a design parameter of user choice, the proposed schemes offer flexible tradeoffs between performance, user capacity, and complexity. They can deal with both time- and frequency-selective fading channels. Numerical simulations show that the proposed schemes are near-far resistant, and compare favorably to an earlier subspace code-timing estimation scheme that is implemented in the time domain. 相似文献
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Yih-Shen Chen Chung-Ju Chang Yi-Lin Hsieh 《Wireless Communications, IEEE Transactions on》2006,5(1):23-27
This paper proposes a channel effect prediction based power control scheme using pipeline recurrent neural network (PRNN)/extended recursive least squares (ERLS) for uplinks in direct sequence code division multiple access (DS-CDMA) cellular mobile systems. Conventional signal-to-interference (SIR) prediction-based power control schemes may incur prediction mistakes caused by the adjustment of transmission power. The proposed power control scheme purely tracks the variation of channel effect and, thus, can be immune to any power adjustment. Furthermore, it adopts the PRNN with ERLS for predicting the channel effect. Simulation results show that the channel effect prediction-based power control scheme using PRNN/ERLS achieves a 40% higher system capacity and a lower outage probability than the conventional SIR prediction-based power control scheme using grey prediction method (IEEE Trans. Veh. Technol., Vol. 49, No. 6, p. 2081, 2000). 相似文献
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This paper presents a hybrid-type TCAM architecture which can utilize the benefits of both NOR and NAND-type TCAM cells: high speed and low power. A hidden bank selection scheme is proposed to activate limited amount of cells during the search operation avoiding additional timing penalty. Match fine repeaters and sub-match fine scheme are used for fast NAND search operation. A test chip with 144-kb TCAM capacity is implemented using 0.1-/spl mu/m 1.2-V CMOS process to verify the proposed schemes. It shows 2.2 ns of match evaluation time on a 144-bit data search with 0.7 fJ/bit/search energy efficiency. 相似文献
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Data hiding is a technique for secret and secure data storing and transmission that embeds data into a media such as an image, audio, video and so on, with minimal quality degradation of the media. Some developed data hiding schemes are reversible. Reversibility property allows the media to be recovered completely after extraction of the embedded data. Vector Quantization (VQ)-based image data hiding is one of the most popular study areas in the literature. However, most VQ-based reversible data hiding schemes generate non-legitimate codes as output. In other words output codes generated by such schemes could not be decoded by the conventional VQ or VQ based decoders and may arouse the attention of interceptors. On the other hand, the existing VQ based reversible data hiding schemes that generate legitimate VQ codes as output, suffer from low capacity and poor quality of stego-image. In this paper a novel reversible data hiding scheme for VQ-compressed images based on locally adaptive data compression scheme (LAS) is proposed. Unlike other schemes, the proposed scheme doesn’t change the VQ indices; data is embedded by choosing one of the possible ways to encode each index. As a result, in comparison with the schemes that embed data by index replacement, in the proposed scheme no extra distortion is made by data embedding and the outputted codes are compatible with the conventional LAS decoder. These properties help to hide the existence of secret data and make the scheme suitable for steganography. Moreover, a framework to combine the proposed scheme with some other schemes to improve their capacity and embedding side information is proposed. Since LAS is a general data compression scheme, the proposed scheme could be used to embed data into any data formats. All existing LAS based data hiding schemes produce non-legitimate codes as their outputs and the proposed scheme is the first and only one that produces legitimate codes as output. Experimental results show that the proposed scheme outperforms the existing LAS based schemes and some other VQ based data hiding schemes. On average, the proposed scheme embeds 2.14 bits per index with almost the same bit-rate as the bit-rate of the VQ index table. 相似文献
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数据容量可以作为衡量自适应传输效率的标志,本文建立了TDMA/FDMA蜂窝小区内的数据容量解析模型,它采用空间自由损耗加平坦Rayleigh衰落的的信道模型,综合分析了信道估计误差,用户移动性,请求重传等因素对整体性能的影响,最后,作为实例,分析了两种自适应调制的数据容量。 相似文献