共查询到20条相似文献,搜索用时 10 毫秒
1.
Two-Dimensional DPCM Image Transmission Over Fading Channels 总被引:1,自引:0,他引:1
A combined source-channel coding approach is described for the encoding, transmission, and remote reconstruction of image data. The transmission medium considered is that of a fading dispersive communications channel. Both the Rician fading and Rayleigh fading channel models are considered. The image source encoder employs two-dimensional (2-D) differential pulse code modulation (DPCM). This is a relatively efficient encoding scheme in the absence of channel errors. In the presence of fading, however, the performance degrades rapidly. By providing error control protection to those encoded bits which contribute most significantly to image reconstruction, it is possible to minimize this degradation without sacrificing transmission bandwidth. Several modulation techniques are employed in evaluation of system performance including noncoherent multiple frequency shift-keyed (MFSK) modulation. Analytical results are provided for assumed 2-D autoregressive image models, while simulation results are described for real-world images. 相似文献
2.
Tiziano Bianchi Fabrizio Argenti 《Signal Processing, IEEE Transactions on》2007,55(2):594-604
In this paper, the performance of filter bank transceivers in the presence of a dispersive time-variant channel is investigated. It is well known that filter bank transceivers can be adapted to the channel transfer function to yield intersymbol interference (ISI) cancellation. When the channel is time variant, several problems arise, since the transceiver should be changed whenever the channel evolves. In this paper, we will allow both the transmitter and the receiver to change and satisfy the interference-free condition, under the assumption of a zero-padded block transmission. In this case, the optimum transmitter-receiver pair can be computed by using a singular value decomposition (SVD) of the channel matrix. A fast receiver adaptation based on SVD tracking is presented. Simulation results show that minimum performance loss with respect to the optimum receiver can be achieved for our reduced complexity receiver 相似文献
3.
On SNR Estimation Techniques for Turbo Decoding Over Uncorrelated Rayleigh Fading Channels With Unknown Fading Parameters 总被引:1,自引:0,他引:1
《Vehicular Technology, IEEE Transactions on》2009,58(9):4955-4961
4.
This paper proposes a new switched MIMO system where the MIMO includes both diversity-based MIMO and spatial multiplexing MIMO (SM-MIMO). The proposed scheme is a closed-loop system where the feedback bits are sent back to the transmitter to indicate the channel quality. The switching operation is employed among groups of a certain number of transmit antennas. For diversity-based MIMO systems, the switching operation aims to improve the link performance, while the goal of the switching for the SM-MIMO systems is to increase the data rate. The authors analyze and optimize the proposed systems and show that there is considerable benefit in terms of performance and practical use 相似文献
5.
《IEEE transactions on information theory / Professional Technical Group on Information Theory》2009,55(3):944-951
6.
Since fading channels are characterized by frequent signal dropouts which are long compared to packet duration, substantial buffer space must be provided at both ends of the link. Systems which rely on selective, on/off transmission to achieve low bit error rates are seriously affected by the special conditions which must be imposed on them to prevent buffer overflow or underflow. This effect can be reduced by a method of buffer control developed and analyzed in this paper, in which the average transmission rate is varied as a function of queue length in an attempt to keep the queue away from the ends of the buffer. It is shown that buffer control provides the same improvement in average error probability as does doubling the buffer size, but without the associated doubled storage cost and doubled delay. In order to simplify the analysis and keep the discussion relevant, the system is oriented to transmission of fixed length blocks or packets. 相似文献
7.
Both adaptive modulation and diversity combining represent important enabling techniques for future generations of wireless communication systems. In this paper, capitalizing on recent developments in adaptive combining, we propose three joint adaptive modulation and diversity combining (AMDC) schemes. With these schemes, the modulation mode and diversity combiner structure are adaptively determined based on the fading channel condition and error-rate requirement. We accurately analyze these three AMDC schemes in terms of processing power consumption, spectral efficiency, and error-rate performance. Selected numerical examples show that the proposed AMDC systems meet the target error-rate requirement while achieving high spectral efficiency with low processing power consumption 相似文献
8.
Matthias Wetz Ivan Periša Werner G. Teich Jürgen Lindner 《Wireless Personal Communications》2008,47(1):113-123
We present an OFDM-based transmission scheme which is suitable for robust transmission in fast fading environments, where
a reliable channel estimate is impossible or very difficult to obtain. Our scheme is based on the combination of noncoherently
detected M-ary frequency shift keying (MFSK) and orthogonal frequency division multiplexing (OFDM). Noncoherent detection
of OFDM-MFSK allows an arbitrary phase choice for all subcarriers in the transmitter. One possibility to exploit this degree
of freedom is to choose the subcarrier phases such, that the peak-to-average power ratio (PARR) is reduced. A second possibility
is to use the subcarrier phases to transmit additional data. This can be done by differentially modulating the subcarriers
that are occupied by the OFDM-MFSK scheme. Both possibilities do not affect the robustness of the underlying noncoherently
detected OFDM-MFSK modulation.
相似文献
Jürgen LindnerEmail: |
9.
We consider layered transmission of a successively refinable source over a quasi-static fading channel. We establish a duality relationship between this problem and that of packet transmission over erasure channels and use it to share solution techniques in both domains. For a Gaussian source and the fading channel, a low-complexity, optimal algorithm is proposed, and it is shown that the corresponding dual for packet erasure channels has a linear complexity as opposed to the quadratic complexity of the best known optimal algorithms in the literature. For non-Gaussian sources, the optimal rate allocation problem for fading channels is solved using the dual solution for erasure channels. It is also shown that a single-layer system is optimal for fading channels if the goal is to maximize the rate. Numerical results for multiple antenna Rayleigh fading channels are presented for Gaussian sources and practical image coders. It is shown that a few number of layers significantly improves the performance. Finally, we numerically show that for practical operating conditions, optimizing the asymptotic measure of distortion exponent is not enough when there are more than one transmit or receive antennas. 相似文献
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11.
Mahmoud H. Ismail Hebat-Allah M. Mourad Magdi M. S. El-Soudani 《Wireless Personal Communications》2004,31(1):77-87
Link Adaptation (LA) has been proposed in the literature as a means of increasing the throughput obtained by each user in wireless communication systems. Due to its significant simplicity, LA has even been adopted as the standard adaptive coding technique for the next generation mobile communication system known as EDGE. In this paper, we present a novel link adaptation technique, valid for use in the case of Rayleigh fading wireless channels. The new technique is based on the blind channel estimation algorithm usually used for combating inter-symbol interference (ISI). The algorithm is presented and its efficiency in providing the maximum available throughput is illustrated by means of computer simulations. 相似文献
12.
Link Adaptation (LA) has been proposed in the literature as a means of increasing the throughput obtained by each user in wireless communication systems. Due to its significant simplicity, LA has even been adopted as the standard adaptive coding technique for the next generation mobile communication system known as EDGE. In this paper, we present a novel link adaptation technique, valid for use in the case of Rayleigh fading wireless channels. The new technique is based on the blind channel estimation algorithm usually used for combating inter-symbol interference (ISI). The algorithm is presented and its efficiency in providing the maximum available throughput is illustrated by means of computer simulations. 相似文献
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14.
This paper gives an evaluation of the performance of adaptive signaling techniques for jammed fading channels. These techniques perform remarkably well for fading channels with AWGN. The performance of both uncoded and coded systems is examined in the presence of jamming. Adaptive signaling schemes are shown to offer little improvement for uncoded antijam systems. However, for coded antijam systems, they provide improvements in the performance and, in some cases, simplify the receiver implementation. 相似文献
15.
In this letter, we address the end-to-end signal-to-noise ratio (SNR) gain achievable by dual-hop relaying over the single-hop transmission in single-input single-output (SISO) flat Rayleigh fading channels. We deal with both nonregenerative and regenerative relaying schemes. To quantify the SNR gain, a closed-form expression of the probability of SNR gain is developed. The probability of SNR gain results in an explicit function of an average power ratio of the per-hop channel in dual-hop relaying to the channel in the single-hop transmission. We investigate impacts of the average power ratio as well as the relaying location on the SNR gain. 相似文献
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17.
This paper investigates achievable rates for a wireless communication system when neither the transmitter nor the receiver has a priori knowledge of the channel state information (CSI). The dynamics of the flat fading channel are characterized by a known Doppler spectrum. Quantitative results are provided for independent and identically distributed (i.i.d.) Gaussian signals and long data blocks. Expressions for the achievable rates include a lower bound on mutual information, and the achievable rates of pilot-aided systems with optimized resource allocation. A simple, low-duty-cycle signaling scheme is proposed to improve the information rates in the low signal-to-noise ratio (SNR) regime, and the optimal duty cycle is expressed as a function of the fading rate and SNR. It is demonstrated that the resource allocation and duty cycle developed for Gaussian signals can also be applied to systems using other signaling formats. 相似文献
18.
Robust Packet Video Transport Over Wireless Fading Channels Using a Joint Source-channel Coding Approach 总被引:2,自引:2,他引:0
In this paper, we address the problem of robust video transmission over wireless networks. Specifically, we consider packet
video transmission over wireless IP networks based on the RTP/UDP/IP protocol stack. Digital video delivered over wireless
networks is expected to suffer quality degradation from both packet loss and bit errors in the payload. In this paper, both
packet loss and bit errors in the payload are considered and the performance of a joint source-channel coding (JSCC) approach
employing forward error-correction (FEC) coding schemes for H.263 + video transmission is studied. Results indicate that
with an appropriate JSCC approach, FEC-based error-control techniques can significantly improve the packetization efficiency
for a given end-to-end quality requirement and lead to more acceptable video delivery quality over time-varying wireless networks.
Another important observation is that with a JSCC approach the fading effects of wireless links upon end-to-end video quality
are substantially decreased compared to a system without using channel coding, resulting in attractive robust performance
characteristics.
相似文献
Yong PeiEmail: |
19.
Li-Chun Wang Jane-Hwa Huang Anderson Chen Chung-Ju Chang 《Wireless Personal Communications》2009,51(3):379-397
Adaptively adjusting transmit rate and power concurrently to enhance goodput and save energy is a challenging issue in a wireless local area network (WLAN) because goodput enhancement and energy saving are usually two contradictory goals. In this paper, we propose channel-driven rate and power adaptation (CDRPA) schemes and develop a physical (PHY)/medium access control (MAC) cross-layer analytical method incorporating the impacts of Nakagami fading channel and the carrier sense multiple access (CSMA) MAC protocol. The CDRPA scheme has much lower computation complexity than the energy-optimal complete-search scheme. In a multiuser contention scenario, we analyze the energy efficiency and the goodput of the power-first and rate-first CDRPA schemes as well as the energy-optimal complete-search adaptation scheme. At the cost of lower goodput, the power-first scheme has better energy efficiency than the rate-first CDRPA scheme, whereas if the goodput is the main concern, the rate-first CDRPA scheme shall be chosen due to better goodput performance. More interestingly, we find that the power-first CDRPA scheme can achieve about the same goodput and energy efficiency as the energy-optimal complete-search link adaptation scheme. 相似文献
20.
The objective of cooperative spectrum sensing is to collaboratively detect the presence of the primary user by the aid of multiple secondary users. It is known that the performance of such a framework substantially depends on the fading assumption. In this paper, we propose an advanced framework for linear cooperative spectrum sensing in cognitive radio networks over correlated log-normal shadow fading channels. Considering the realistic sensing and reporting channels which are not addressed in similar works, motivates us to propose a novel approximation for correlated log-normal sum based on moment generating function calculation and moment matching method. Furthermore, the linear cooperative spectrum sensing coefficients are computed based on the optimization of the deflection criterion. This results in a framework with reasonable complexity which is suitable for practical applications. Simulation results show the excellent agreement between the exact and approximated statistics and the superior performance compared with conventional equally gain combiner. 相似文献