Pub Date : 2011-06-26DOI: 10.1109/SPAWC.2011.5990433
B. Godana, T. Ekman
MIMO systems require eigenmode information at the transmitter to exploit the multiplexing gain of the channel. In practice, the eigenmode information available at the transmitter after feedback is noisy and outdated. One of the efficient feedback methods used in MIMO systems involves the decomposition of unitary matrices into Givens rotations. This entails the possibility to update the eigenmodes by predicting the Givens rotations. In this paper, two MIMO precoder prediction schemes based on channel prediction at the mobile station (MS) and Givens parameters prediction at the base station (BS) are proposed. The system capacity of the two schemes is evaluated and compared by using a simulation on a time-varying MIMO channel. Simulations show that both prediction schemes improve the system performance; however, channel prediction at the MS has better performance than Givens prediction at the BS. Despite a lower performance, Givens prediction at the BS reduces the number of parameters to be tracked and is suitable for variable delay systems.
{"title":"Linear prediction of time-varying MIMO systems using Givens rotations","authors":"B. Godana, T. Ekman","doi":"10.1109/SPAWC.2011.5990433","DOIUrl":"https://doi.org/10.1109/SPAWC.2011.5990433","url":null,"abstract":"MIMO systems require eigenmode information at the transmitter to exploit the multiplexing gain of the channel. In practice, the eigenmode information available at the transmitter after feedback is noisy and outdated. One of the efficient feedback methods used in MIMO systems involves the decomposition of unitary matrices into Givens rotations. This entails the possibility to update the eigenmodes by predicting the Givens rotations. In this paper, two MIMO precoder prediction schemes based on channel prediction at the mobile station (MS) and Givens parameters prediction at the base station (BS) are proposed. The system capacity of the two schemes is evaluated and compared by using a simulation on a time-varying MIMO channel. Simulations show that both prediction schemes improve the system performance; however, channel prediction at the MS has better performance than Givens prediction at the BS. Despite a lower performance, Givens prediction at the BS reduces the number of parameters to be tracked and is suitable for variable delay systems.","PeriodicalId":102244,"journal":{"name":"2011 IEEE 12th International Workshop on Signal Processing Advances in Wireless Communications","volume":"158 12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128844878","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-06-26DOI: 10.1109/SPAWC.2011.5990439
M. Nahas, A. Saadani, R. Hatoum
In previous works, delay tolerant codes were proposed with variable length ensuring a full transmit diversity for a certain interval of delay profiles. The code performances are enhanced when the code length is incremented; however, this causes an increasing complexity at the receiver which motivates our research for low complexity decoding methods. First, it is shown that optimal decoding methods cannot be used for large code lengths. Moreover, new decoding schemes with reasonable complexity and good performance are proposed for any code length and any tolerated delay.
{"title":"Asynchronous Space Time Block Codes: Low complexity decoding methods","authors":"M. Nahas, A. Saadani, R. Hatoum","doi":"10.1109/SPAWC.2011.5990439","DOIUrl":"https://doi.org/10.1109/SPAWC.2011.5990439","url":null,"abstract":"In previous works, delay tolerant codes were proposed with variable length ensuring a full transmit diversity for a certain interval of delay profiles. The code performances are enhanced when the code length is incremented; however, this causes an increasing complexity at the receiver which motivates our research for low complexity decoding methods. First, it is shown that optimal decoding methods cannot be used for large code lengths. Moreover, new decoding schemes with reasonable complexity and good performance are proposed for any code length and any tolerated delay.","PeriodicalId":102244,"journal":{"name":"2011 IEEE 12th International Workshop on Signal Processing Advances in Wireless Communications","volume":"55 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127466702","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-06-26DOI: 10.1109/SPAWC.2011.5990475
A. Rueetschi, A. Scaglione
In randomized cooperative transmission, relay nodes transmit a random linear combination of a space-time code (STC), to realize MISO gains at the end receiver without prior coordination of relays. Unlike selective cooperative combining schemes, the channel estimation and tracking becomes inherently much more challenging, due the fact that each radio has its own local oscillator, clock, propagation and processing delay, and multiple of them will be normally cooperating at unison. In this paper we show that the new class of channel estimators, that are based on compressed sensing models, can retain much of the diversity gain that the codes are theoretically designed to harvest when the channel is ideally known. This is in contrast with standard schemes for linear equalization, which fail to compensate for the channel distortion in the presence of realistic amounts of asynchrony and channel dispersion. The contribution of this paper is a semi-analytical performance evaluation that leads to the insightful comparison of the receiver architectures.
{"title":"Can we cope with the distortion of decentralized cooperative schemes?","authors":"A. Rueetschi, A. Scaglione","doi":"10.1109/SPAWC.2011.5990475","DOIUrl":"https://doi.org/10.1109/SPAWC.2011.5990475","url":null,"abstract":"In randomized cooperative transmission, relay nodes transmit a random linear combination of a space-time code (STC), to realize MISO gains at the end receiver without prior coordination of relays. Unlike selective cooperative combining schemes, the channel estimation and tracking becomes inherently much more challenging, due the fact that each radio has its own local oscillator, clock, propagation and processing delay, and multiple of them will be normally cooperating at unison. In this paper we show that the new class of channel estimators, that are based on compressed sensing models, can retain much of the diversity gain that the codes are theoretically designed to harvest when the channel is ideally known. This is in contrast with standard schemes for linear equalization, which fail to compensate for the channel distortion in the presence of realistic amounts of asynchrony and channel dispersion. The contribution of this paper is a semi-analytical performance evaluation that leads to the insightful comparison of the receiver architectures.","PeriodicalId":102244,"journal":{"name":"2011 IEEE 12th International Workshop on Signal Processing Advances in Wireless Communications","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127497703","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-06-26DOI: 10.1109/SPAWC.2011.5990428
Yunlong Cai, D. Le Ruyet, R. D. de Lamare, D. Roviras
In this work, we propose a linear base station (BS) precoding strategy based on switched relaying (SR) processing for downlink multiuser multiple-input multiple-output (MIMO) relay systems. The BS and the MIMO relay station (RS) are both equipped with a codebook of interleaving matrices. For a given channel state information (CSI) the selection function at the BS chooses the optimum interleaving matrix from the codebook based on the maximum sum received signal-to-interference-plus-noise ratio (SINR) or sum rate to design the linear BS precoder. Prior to the payload transmission the BS sends the index corresponding to the selected interleaving matrix to the RS, where the optimum interleaving matrix is selected as the optimum relay processing matrix. The entries of the codebook are randomly generated unitary matrices. Simulation results show that the performance of the proposed techniques is significantly better than prior art in the case of perfect CSI.1
{"title":"Linear precoding based on switched relaying processing for multiuser MIMO relay systems","authors":"Yunlong Cai, D. Le Ruyet, R. D. de Lamare, D. Roviras","doi":"10.1109/SPAWC.2011.5990428","DOIUrl":"https://doi.org/10.1109/SPAWC.2011.5990428","url":null,"abstract":"In this work, we propose a linear base station (BS) precoding strategy based on switched relaying (SR) processing for downlink multiuser multiple-input multiple-output (MIMO) relay systems. The BS and the MIMO relay station (RS) are both equipped with a codebook of interleaving matrices. For a given channel state information (CSI) the selection function at the BS chooses the optimum interleaving matrix from the codebook based on the maximum sum received signal-to-interference-plus-noise ratio (SINR) or sum rate to design the linear BS precoder. Prior to the payload transmission the BS sends the index corresponding to the selected interleaving matrix to the RS, where the optimum interleaving matrix is selected as the optimum relay processing matrix. The entries of the codebook are randomly generated unitary matrices. Simulation results show that the performance of the proposed techniques is significantly better than prior art in the case of perfect CSI.1","PeriodicalId":102244,"journal":{"name":"2011 IEEE 12th International Workshop on Signal Processing Advances in Wireless Communications","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128167399","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-06-26DOI: 10.1109/SPAWC.2011.5990374
Jitendra Tugnait
Recently several time-domain approaches relying on the generalized likelihood ratio test (GLRT) paradigm have been proposed for multiple antenna spectrum sensing in cognitive radios. These approaches are suitable for flat-fading channels in white noise with equal noise variances across antennas; knowledge of the noise variance is not required, unlike the energy detector. In this paper we investigate a method based on analysis of the multivariate power spectral density (PSD) of the received multiantenna signal. Our proposed approach is also based on GLRT, but exploits the noisy signal PSD which is allowed to be colored with unknown PSD but must be uncorrelated across sensors under the null hypothesis (PU signal absent). An analytical method for calculation of the test threshold is provided and illustrated via simulations.
{"title":"Multichannel spectrum sensing via multivariate power spectrum analysis","authors":"Jitendra Tugnait","doi":"10.1109/SPAWC.2011.5990374","DOIUrl":"https://doi.org/10.1109/SPAWC.2011.5990374","url":null,"abstract":"Recently several time-domain approaches relying on the generalized likelihood ratio test (GLRT) paradigm have been proposed for multiple antenna spectrum sensing in cognitive radios. These approaches are suitable for flat-fading channels in white noise with equal noise variances across antennas; knowledge of the noise variance is not required, unlike the energy detector. In this paper we investigate a method based on analysis of the multivariate power spectral density (PSD) of the received multiantenna signal. Our proposed approach is also based on GLRT, but exploits the noisy signal PSD which is allowed to be colored with unknown PSD but must be uncorrelated across sensors under the null hypothesis (PU signal absent). An analytical method for calculation of the test threshold is provided and illustrated via simulations.","PeriodicalId":102244,"journal":{"name":"2011 IEEE 12th International Workshop on Signal Processing Advances in Wireless Communications","volume":"1 8","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133322370","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-06-26DOI: 10.1109/SPAWC.2011.5990398
G. Haßlinger, O. Hohlfeld
50 years ago, Gilbert and Elliott introduced 2-state Markov channels to characterize bursty error processes in data transmission. The focus of this work is on the analysis of the effect of bit errors on higher layer blocks or packets. Starting from 2-state bit error channels in an extended Gilbert-Elliott format, packet errors again result in a 2-state process of the same type. The parameters of the packet error process are explicitly derived from those of the underlying bit error process. The solution for main performance measures is based on a superposition of two geometrical functions for the distributions of packet error bursts and gaps and the second order statistics.
{"title":"Analysis of packet errors in Gilbert-Elliott channels","authors":"G. Haßlinger, O. Hohlfeld","doi":"10.1109/SPAWC.2011.5990398","DOIUrl":"https://doi.org/10.1109/SPAWC.2011.5990398","url":null,"abstract":"50 years ago, Gilbert and Elliott introduced 2-state Markov channels to characterize bursty error processes in data transmission. The focus of this work is on the analysis of the effect of bit errors on higher layer blocks or packets. Starting from 2-state bit error channels in an extended Gilbert-Elliott format, packet errors again result in a 2-state process of the same type. The parameters of the packet error process are explicitly derived from those of the underlying bit error process. The solution for main performance measures is based on a superposition of two geometrical functions for the distributions of packet error bursts and gaps and the second order statistics.","PeriodicalId":102244,"journal":{"name":"2011 IEEE 12th International Workshop on Signal Processing Advances in Wireless Communications","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129643619","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-06-26DOI: 10.1109/SPAWC.2011.5990469
Yaniv George, I. Bergel, Ephi Zehavi
The performance of wireless ad hoc network are mostly limited by the self interference caused by the network members. Smart antennas and carrier sensing multiple access (CSMA) have been considered separately as efficient methods for self-interference reduction. In this paper we analyze the effect of directional antennas on the transmission capacity of slotted CSMA networks. The analysis is based on a Poisson point process shot noise model for the aggregate interference. The effect of directional antennas is shown to be equivalent to network density scaling. This scaling is expressed through a single parameter, which depends only on the antenna and the channel exponential decay factor. The paper also presents a useful bound on rate ratio of a pair of slotted CSMA networks. This bound is used to demonstrate the transmission capacity gain of slotted CSMA over slotted ALOHA networks. In particular it is shown that if the antennas have very narrow beams then the advantage of CSMA over ALOHA is negligible.
{"title":"The effect of directional antennas on slotted CSMA ad hoc networks","authors":"Yaniv George, I. Bergel, Ephi Zehavi","doi":"10.1109/SPAWC.2011.5990469","DOIUrl":"https://doi.org/10.1109/SPAWC.2011.5990469","url":null,"abstract":"The performance of wireless ad hoc network are mostly limited by the self interference caused by the network members. Smart antennas and carrier sensing multiple access (CSMA) have been considered separately as efficient methods for self-interference reduction. In this paper we analyze the effect of directional antennas on the transmission capacity of slotted CSMA networks. The analysis is based on a Poisson point process shot noise model for the aggregate interference. The effect of directional antennas is shown to be equivalent to network density scaling. This scaling is expressed through a single parameter, which depends only on the antenna and the channel exponential decay factor. The paper also presents a useful bound on rate ratio of a pair of slotted CSMA networks. This bound is used to demonstrate the transmission capacity gain of slotted CSMA over slotted ALOHA networks. In particular it is shown that if the antennas have very narrow beams then the advantage of CSMA over ALOHA is negligible.","PeriodicalId":102244,"journal":{"name":"2011 IEEE 12th International Workshop on Signal Processing Advances in Wireless Communications","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134647505","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-06-26DOI: 10.1109/SPAWC.2011.5990487
E. Dall’Anese, J. Bazerque, Hao Zhu, G. Giannakis
The present paper develops a collaborative scheme whereby cognitive radios cooperate to localize active primary transmitters and reconstruct the power spectral density (PSD) maps (one per frequency band) portraying the power distribution across space. The sensing scheme relies on a parsimonious linear system model that accounts for the narrow-band nature of transmit-PSDs compared to the large swath of sensed frequencies, and for the group sparsity emerging when adopting a spatial grid of candidate primary user locations. Combining the merits of Lasso, group Lasso, and total least-squares (TLS), the proposed group sparse (GS) TLS approach yields hierarchically-sparse PSD estimates, and copes with model uncertainty induced by channel randomness and grid mismatch effects. Taking advantage of a novel low-complexity solver for the GS-Lasso, a block coordinate descent scheme is developed to solve the formulated GS-TLS problem. Simulations demonstrate the superior localization and PSD-estimation performance of GS-TLS compared to approaches that do not account for model uncertainties.
{"title":"Group sparse total least-squares for cognitive spectrum sensing","authors":"E. Dall’Anese, J. Bazerque, Hao Zhu, G. Giannakis","doi":"10.1109/SPAWC.2011.5990487","DOIUrl":"https://doi.org/10.1109/SPAWC.2011.5990487","url":null,"abstract":"The present paper develops a collaborative scheme whereby cognitive radios cooperate to localize active primary transmitters and reconstruct the power spectral density (PSD) maps (one per frequency band) portraying the power distribution across space. The sensing scheme relies on a parsimonious linear system model that accounts for the narrow-band nature of transmit-PSDs compared to the large swath of sensed frequencies, and for the group sparsity emerging when adopting a spatial grid of candidate primary user locations. Combining the merits of Lasso, group Lasso, and total least-squares (TLS), the proposed group sparse (GS) TLS approach yields hierarchically-sparse PSD estimates, and copes with model uncertainty induced by channel randomness and grid mismatch effects. Taking advantage of a novel low-complexity solver for the GS-Lasso, a block coordinate descent scheme is developed to solve the formulated GS-TLS problem. Simulations demonstrate the superior localization and PSD-estimation performance of GS-TLS compared to approaches that do not account for model uncertainties.","PeriodicalId":102244,"journal":{"name":"2011 IEEE 12th International Workshop on Signal Processing Advances in Wireless Communications","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121968138","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-06-26DOI: 10.1109/SPAWC.2011.5990470
J. Richter, A. Wolf, Eduard Axel Jorswieck
In this paper, the combination of linear network coding over a finite field and beamforming for a multiple-antenna network is studied. Assuming a multicast transmission scheme and a decode-and-forward protocol, optimal beamforming strategies for the network nodes are derived for a certain class of interference networks. An efficient algorithm is presented to calculate the achievable rate region of these networks. The sum power for the transmission of the multicast information is minimized under rate requirements. The proposed approach is illustrated by one important scenario.
{"title":"Achievable rate regions in multiple-antenna networks with linear network coding","authors":"J. Richter, A. Wolf, Eduard Axel Jorswieck","doi":"10.1109/SPAWC.2011.5990470","DOIUrl":"https://doi.org/10.1109/SPAWC.2011.5990470","url":null,"abstract":"In this paper, the combination of linear network coding over a finite field and beamforming for a multiple-antenna network is studied. Assuming a multicast transmission scheme and a decode-and-forward protocol, optimal beamforming strategies for the network nodes are derived for a certain class of interference networks. An efficient algorithm is presented to calculate the achievable rate region of these networks. The sum power for the transmission of the multicast information is minimized under rate requirements. The proposed approach is illustrated by one important scenario.","PeriodicalId":102244,"journal":{"name":"2011 IEEE 12th International Workshop on Signal Processing Advances in Wireless Communications","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116543442","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-06-26DOI: 10.1109/SPAWC.2011.5990474
K. L. Law, A. Gershman, S. Shahbazpanahi
We consider the problem of distributed beamforming in a relay network, which consists of a single-antenna transmitter, a multi-antenna receiver, and multiple single-antenna relays. Assuming that the channel state information (CSI) is available, our goal is to maximize the destination quality-of-service (QoS) under the total relay transmitted power constraint. Using the semi-definite relaxation (SDR) technique, the problem is turned into a convex semi-definite programming (SDP) problem, which can be solved efficiently using interior point methods. Simulation results show that the proposed relay network beamforming approach offers considerable performance improvements as compared to the single-antenna receiver case.
{"title":"Distributed network beamforming with a multi-antenna receiver","authors":"K. L. Law, A. Gershman, S. Shahbazpanahi","doi":"10.1109/SPAWC.2011.5990474","DOIUrl":"https://doi.org/10.1109/SPAWC.2011.5990474","url":null,"abstract":"We consider the problem of distributed beamforming in a relay network, which consists of a single-antenna transmitter, a multi-antenna receiver, and multiple single-antenna relays. Assuming that the channel state information (CSI) is available, our goal is to maximize the destination quality-of-service (QoS) under the total relay transmitted power constraint. Using the semi-definite relaxation (SDR) technique, the problem is turned into a convex semi-definite programming (SDP) problem, which can be solved efficiently using interior point methods. Simulation results show that the proposed relay network beamforming approach offers considerable performance improvements as compared to the single-antenna receiver case.","PeriodicalId":102244,"journal":{"name":"2011 IEEE 12th International Workshop on Signal Processing Advances in Wireless Communications","volume":"70 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125515379","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：