Pub Date : 2008-12-30DOI: 10.1109/ISWCS.2008.4726015
M. Biagi, E. Baccarelli, N. Cordeschi, C. Pelizzoni, Valentina Polli
Main goal of this work is to give insight on the possible performance improvement arising in the wireless local ad-hoc access from the synergic cooperation of two emerging paradigms, multi-antenna and cognitive radios. The target is the competitive maximization of each access rate in presence of multiple-access interference (MAI) induced by the other accessing terminals. Being the radios cognitive, they are capable to autonomously learn the ambient-context and, then, self-configure their access strategy via suitable power-allocation, that is, time-frequency-code-space signal-shaping. Furthermore, a generalized approach is developed to allow the node to access with a (possibly hybrid) scheme to the medium by combining different x-DMA strategies under QoS-guaranteed access policy.
{"title":"Collision erasure and generalized access in MIMO cognitive ad-hoc networks","authors":"M. Biagi, E. Baccarelli, N. Cordeschi, C. Pelizzoni, Valentina Polli","doi":"10.1109/ISWCS.2008.4726015","DOIUrl":"https://doi.org/10.1109/ISWCS.2008.4726015","url":null,"abstract":"Main goal of this work is to give insight on the possible performance improvement arising in the wireless local ad-hoc access from the synergic cooperation of two emerging paradigms, multi-antenna and cognitive radios. The target is the competitive maximization of each access rate in presence of multiple-access interference (MAI) induced by the other accessing terminals. Being the radios cognitive, they are capable to autonomously learn the ambient-context and, then, self-configure their access strategy via suitable power-allocation, that is, time-frequency-code-space signal-shaping. Furthermore, a generalized approach is developed to allow the node to access with a (possibly hybrid) scheme to the medium by combining different x-DMA strategies under QoS-guaranteed access policy.","PeriodicalId":158650,"journal":{"name":"2008 IEEE International Symposium on Wireless Communication Systems","volume":"129 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116204856","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 : 2008-12-30DOI: 10.1109/ISWCS.2008.4726127
G. Fabeck, D. Bielefeld, R. Mathar
Cross-layer design for wireless networks aims at optimizing system-wide performance measures by exploiting dependencies between different network layers. In this paper, an opportunistic power assignment algorithms for IR-UWB sensor networks is presented that is especially designed for distributed signal detection under resource constraints. Specifically, the objective is to minimize the global probability of error of distributed detection systems, given a fixed level of total transmission power. The cross-layer approach for the allocation of transmission power is based on individual sensor detection quality as well as location information. It leads to significant performance gains compared to uniform power assignment for both the parallel and the serial sensor network topology.
{"title":"Cross-Layer design of IR-UWB sensor networks for distributed detection applications","authors":"G. Fabeck, D. Bielefeld, R. Mathar","doi":"10.1109/ISWCS.2008.4726127","DOIUrl":"https://doi.org/10.1109/ISWCS.2008.4726127","url":null,"abstract":"Cross-layer design for wireless networks aims at optimizing system-wide performance measures by exploiting dependencies between different network layers. In this paper, an opportunistic power assignment algorithms for IR-UWB sensor networks is presented that is especially designed for distributed signal detection under resource constraints. Specifically, the objective is to minimize the global probability of error of distributed detection systems, given a fixed level of total transmission power. The cross-layer approach for the allocation of transmission power is based on individual sensor detection quality as well as location information. It leads to significant performance gains compared to uniform power assignment for both the parallel and the serial sensor network topology.","PeriodicalId":158650,"journal":{"name":"2008 IEEE International Symposium on Wireless Communication Systems","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123714799","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 : 2008-12-30DOI: 10.1109/ISWCS.2008.4726083
Hefdhallah Sakran, M. Shokair, A. A. Elazm
Peak to average power ratio (PAPR) is one of the serious problems in any wireless communication system using multicarrier modulation technique like OFDM, which reduces the efficiency of the transmit high power amplifier. In this paper, we suggest a new scheme based on μ-law compander where the optimum value of μ is calculated. With the newly proposed scheme, the simulation results show that, the PAPR is reduced by 5.8 dB. Moreover, Eb/N0 is decreased by 6 dB at bit error rate (BER)=10-3 in the presence of nonlinear power amplifier.
{"title":"A new peak-to-average power reduction technique in the OFDM system using μ-law compander","authors":"Hefdhallah Sakran, M. Shokair, A. A. Elazm","doi":"10.1109/ISWCS.2008.4726083","DOIUrl":"https://doi.org/10.1109/ISWCS.2008.4726083","url":null,"abstract":"Peak to average power ratio (PAPR) is one of the serious problems in any wireless communication system using multicarrier modulation technique like OFDM, which reduces the efficiency of the transmit high power amplifier. In this paper, we suggest a new scheme based on μ-law compander where the optimum value of μ is calculated. With the newly proposed scheme, the simulation results show that, the PAPR is reduced by 5.8 dB. Moreover, Eb/N0 is decreased by 6 dB at bit error rate (BER)=10-3 in the presence of nonlinear power amplifier.","PeriodicalId":158650,"journal":{"name":"2008 IEEE International Symposium on Wireless Communication Systems","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128661859","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 : 2008-12-30DOI: 10.1109/ISWCS.2008.4726112
K. Kusume, G. Bauch
We propose a parallel a posteriori probability (APP) decoding algorithm for increasing the decoding throughput of turbo codes. The parallel decoding algorithm divides a noisy codeword into multiple sub-blocks which are decoded in parallel. The authors in [1] proposed utilizing the forward and backward variables computed by neighbor sub-blocks in the previous iteration as the initial boundary conditions for each sub-block in the current iteration. We extend this algorithm by organizing sub-blocks into odd and even numbered groups, which perform recursions in unison but in the opposite directions. This enables more efficient utilization of the boundary conditions. We show by means of numerical simulations that our proposed algorithm further improves the decoding throughput of turbo codes in highly parallel decoding scenarios.
{"title":"A parallel APP decoding algorithm for accelerating decoding throughput of turbo codes","authors":"K. Kusume, G. Bauch","doi":"10.1109/ISWCS.2008.4726112","DOIUrl":"https://doi.org/10.1109/ISWCS.2008.4726112","url":null,"abstract":"We propose a parallel a posteriori probability (APP) decoding algorithm for increasing the decoding throughput of turbo codes. The parallel decoding algorithm divides a noisy codeword into multiple sub-blocks which are decoded in parallel. The authors in [1] proposed utilizing the forward and backward variables computed by neighbor sub-blocks in the previous iteration as the initial boundary conditions for each sub-block in the current iteration. We extend this algorithm by organizing sub-blocks into odd and even numbered groups, which perform recursions in unison but in the opposite directions. This enables more efficient utilization of the boundary conditions. We show by means of numerical simulations that our proposed algorithm further improves the decoding throughput of turbo codes in highly parallel decoding scenarios.","PeriodicalId":158650,"journal":{"name":"2008 IEEE International Symposium on Wireless Communication Systems","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128522492","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 : 2008-12-30DOI: 10.1109/ISWCS.2008.4726090
M. Karaca, Özgür Erçetin
In many cases, a mobile user has the option of connecting to one of several 802.11 access point (APs). We consider the case when users multihome, i.e., split their traffic among all available APs, based on the long-term channel characteristics such as burstiness and packet error rate. This type of operation requires a new multi-access control (MAC) protocol, where the user has to decide to which AP the packet is forwarded. In this paper we propose a new MAC protocol for multihomed users and the selection of the AP for each packet is performed in our proposed MAC protocol based on the most recent channel observation and the collected long-term statistics, where the aim is to maximize the probability of successful transmission of each packet. The proposed MAC protocol is analyzed using Qualnet network simulator, and it is shown that our proposed protocol can improve the efficiency of the system significantly compared to the standard 802.11 protocol where each user is associated with the AP that has the maximum received signal strength.
{"title":"A MAC protocol for multihomed WLANs","authors":"M. Karaca, Özgür Erçetin","doi":"10.1109/ISWCS.2008.4726090","DOIUrl":"https://doi.org/10.1109/ISWCS.2008.4726090","url":null,"abstract":"In many cases, a mobile user has the option of connecting to one of several 802.11 access point (APs). We consider the case when users multihome, i.e., split their traffic among all available APs, based on the long-term channel characteristics such as burstiness and packet error rate. This type of operation requires a new multi-access control (MAC) protocol, where the user has to decide to which AP the packet is forwarded. In this paper we propose a new MAC protocol for multihomed users and the selection of the AP for each packet is performed in our proposed MAC protocol based on the most recent channel observation and the collected long-term statistics, where the aim is to maximize the probability of successful transmission of each packet. The proposed MAC protocol is analyzed using Qualnet network simulator, and it is shown that our proposed protocol can improve the efficiency of the system significantly compared to the standard 802.11 protocol where each user is associated with the AP that has the maximum received signal strength.","PeriodicalId":158650,"journal":{"name":"2008 IEEE International Symposium on Wireless Communication Systems","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114832908","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 : 2008-12-30DOI: 10.1109/ISWCS.2008.4726072
T. Duong, Hans-Jürgen Zepernick
Performance of cooperative spatial multiplexing systems over composite channels is presented. In particular, we derive the closed-form average symbol error rate (SER) expression for cooperative spatial multiplexing systems with linear equalization receiver (e.g. Zero-Forcing) and M-ary modulation scheme in the composite channel of log-normal shadowing and Rayleigh fading. Using the Gauss-Hermite quadrature integration, the average SER is expressed in the form of the Appell hypergeometric function. Applying the series representation of the Appell hypergeometric function, we derive a very tight approximation for the average SER. We also perform Monte-Carlo simulations to validate our analysis. Subsequently, we apply the obtained analytical SER expression to evaluate some representative cooperative spatial multiplexing scenarios in composite channels.
{"title":"Average symbol error rate of cooperative spatial multiplexing in composite channels","authors":"T. Duong, Hans-Jürgen Zepernick","doi":"10.1109/ISWCS.2008.4726072","DOIUrl":"https://doi.org/10.1109/ISWCS.2008.4726072","url":null,"abstract":"Performance of cooperative spatial multiplexing systems over composite channels is presented. In particular, we derive the closed-form average symbol error rate (SER) expression for cooperative spatial multiplexing systems with linear equalization receiver (e.g. Zero-Forcing) and M-ary modulation scheme in the composite channel of log-normal shadowing and Rayleigh fading. Using the Gauss-Hermite quadrature integration, the average SER is expressed in the form of the Appell hypergeometric function. Applying the series representation of the Appell hypergeometric function, we derive a very tight approximation for the average SER. We also perform Monte-Carlo simulations to validate our analysis. Subsequently, we apply the obtained analytical SER expression to evaluate some representative cooperative spatial multiplexing scenarios in composite channels.","PeriodicalId":158650,"journal":{"name":"2008 IEEE International Symposium on Wireless Communication Systems","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114859635","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 : 2008-12-30DOI: 10.1109/ISWCS.2008.4726056
E. Baccarelli, M. Biagi, N. Cordeschi, C. Pelizzoni
Triggered by the Infostation system paradigm, next-generation wireless networks for personal communication services should be designed to transfer delay-sensitive bursty traffic flows over energy-limited buffer-equipped faded connections. In this application scenario, a still open basic question concerns the closed-form design of scheduling policies minimizing the average transfer-delay under constraints on both average and peak energies. The resulting optimal scheduler allocates step-by-step energy and rate on the basis of both current queue and channel states. We prove that, under the considered energy constraints, the scheduler retains two optimality properties. First, its stability region is the maximal admissible one. Second, the scheduler also minimizes the unconditional average queue-length (e.g., the queue-length averaged over both queue and channel state statistics).
{"title":"Minimum-delay optimal scheduling for delay-sensitive bursty-traffic connections","authors":"E. Baccarelli, M. Biagi, N. Cordeschi, C. Pelizzoni","doi":"10.1109/ISWCS.2008.4726056","DOIUrl":"https://doi.org/10.1109/ISWCS.2008.4726056","url":null,"abstract":"Triggered by the Infostation system paradigm, next-generation wireless networks for personal communication services should be designed to transfer delay-sensitive bursty traffic flows over energy-limited buffer-equipped faded connections. In this application scenario, a still open basic question concerns the closed-form design of scheduling policies minimizing the average transfer-delay under constraints on both average and peak energies. The resulting optimal scheduler allocates step-by-step energy and rate on the basis of both current queue and channel states. We prove that, under the considered energy constraints, the scheduler retains two optimality properties. First, its stability region is the maximal admissible one. Second, the scheduler also minimizes the unconditional average queue-length (e.g., the queue-length averaged over both queue and channel state statistics).","PeriodicalId":158650,"journal":{"name":"2008 IEEE International Symposium on Wireless Communication Systems","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114318267","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 : 2008-12-30DOI: 10.1109/ISWCS.2008.4726098
Jiang Hai, Wu Ye
A frequency offset estimation algorithm based on relativity of time-domain PN sequence is proposed in this paper. The form of this algorithm under multi-path fading channel is also given. The performance of the algorithm using different parameters is studied through theoretical analysis and simulation. The high performance of this algorithm using under both AWGN channel and multi-path fading channel is also verified by simulation.
{"title":"A frequency offset estimation algorithm for multi-path fading channel based on PN sequence","authors":"Jiang Hai, Wu Ye","doi":"10.1109/ISWCS.2008.4726098","DOIUrl":"https://doi.org/10.1109/ISWCS.2008.4726098","url":null,"abstract":"A frequency offset estimation algorithm based on relativity of time-domain PN sequence is proposed in this paper. The form of this algorithm under multi-path fading channel is also given. The performance of the algorithm using different parameters is studied through theoretical analysis and simulation. The high performance of this algorithm using under both AWGN channel and multi-path fading channel is also verified by simulation.","PeriodicalId":158650,"journal":{"name":"2008 IEEE International Symposium on Wireless Communication Systems","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131281105","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 : 2008-12-30DOI: 10.1109/ISWCS.2008.4726019
F. Weis, F. Allard, A. Luu, M. Tlais, Marie-Line Alberi-Morel, S. Kerboeuf
Mobile cellular networks are now largely deployed, and mobile customers are used to place and to receive calls at any location. The network coverage is continuous, but radio conditions met by users are not homogeneous. Thus, data rate is varying according to user mobility. In this paper, we propose to discriminate terminals by their radio conditions in order to select which data has to be sent. More precisely, terminals are supplied with data only when they are in zones of the cellular network offering good radio quality. With such an approach, continuous cellular networks are exploited in a logical discontinuous way. Our approach is based on a smart scheduling solution that favours data transfer when users have a good radio link. Simulation results highlights the improvements with a QoS policy guided by radio conditions for streaming services. Results are promising, a cache-based architecture contributes to a good service quality with no interruption. Furthermore, simulations show that this approach can increase significantly users density supported by the network.
{"title":"Improving wireless network capacity by logical discontinuous coverage","authors":"F. Weis, F. Allard, A. Luu, M. Tlais, Marie-Line Alberi-Morel, S. Kerboeuf","doi":"10.1109/ISWCS.2008.4726019","DOIUrl":"https://doi.org/10.1109/ISWCS.2008.4726019","url":null,"abstract":"Mobile cellular networks are now largely deployed, and mobile customers are used to place and to receive calls at any location. The network coverage is continuous, but radio conditions met by users are not homogeneous. Thus, data rate is varying according to user mobility. In this paper, we propose to discriminate terminals by their radio conditions in order to select which data has to be sent. More precisely, terminals are supplied with data only when they are in zones of the cellular network offering good radio quality. With such an approach, continuous cellular networks are exploited in a logical discontinuous way. Our approach is based on a smart scheduling solution that favours data transfer when users have a good radio link. Simulation results highlights the improvements with a QoS policy guided by radio conditions for streaming services. Results are promising, a cache-based architecture contributes to a good service quality with no interruption. Furthermore, simulations show that this approach can increase significantly users density supported by the network.","PeriodicalId":158650,"journal":{"name":"2008 IEEE International Symposium on Wireless Communication Systems","volume":"54 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122152452","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 : 2008-12-30DOI: 10.1109/ISWCS.2008.4726031
J. Sanguino, Filipe Tocha, A. Rodrigues
Location-based services rely on the accuracy of the user's position estimates. In WAW ("Where Are We?") location- based services, users want to be aware, not only, of their own position but also the position of the other elements on their group. If this information is available in real-time, this kind of service can be used to support coordinated positioning operations. This paper presents an algorithm for the estimation of a user's position, based on measurements from a group of mobile Global Positioning System (GPS) receivers. Receivers are assumed to have some common satellites in view, but measurements from all the satellites are used in the estimation process. Instead of estimating the user's position on an autonomous way, based only on the measurements of his own receiver, the proposed approach takes advantage from all the GPS measurements available in this kind of location-based service. None of the GPS receivers, used in the estimation process, is considered to be fixed or known. The approach leads to an improvement in the user's position accuracy and can particularly benefit those with a more restricted view of the satellite constellation. As such, the methodology, here presented, can be applied with advantage in the deployment of WAW location-based services in urban environments, more prone to the canyon effect. The paper describes in detail the positioning model and estimator used to achieve the accuracy improvements. Simulation results are presented based on real GPS satellite ephemeris, collected at the university campus.
{"title":"Improving positioning accuracy in WAW location-based services","authors":"J. Sanguino, Filipe Tocha, A. Rodrigues","doi":"10.1109/ISWCS.2008.4726031","DOIUrl":"https://doi.org/10.1109/ISWCS.2008.4726031","url":null,"abstract":"Location-based services rely on the accuracy of the user's position estimates. In WAW (\"Where Are We?\") location- based services, users want to be aware, not only, of their own position but also the position of the other elements on their group. If this information is available in real-time, this kind of service can be used to support coordinated positioning operations. This paper presents an algorithm for the estimation of a user's position, based on measurements from a group of mobile Global Positioning System (GPS) receivers. Receivers are assumed to have some common satellites in view, but measurements from all the satellites are used in the estimation process. Instead of estimating the user's position on an autonomous way, based only on the measurements of his own receiver, the proposed approach takes advantage from all the GPS measurements available in this kind of location-based service. None of the GPS receivers, used in the estimation process, is considered to be fixed or known. The approach leads to an improvement in the user's position accuracy and can particularly benefit those with a more restricted view of the satellite constellation. As such, the methodology, here presented, can be applied with advantage in the deployment of WAW location-based services in urban environments, more prone to the canyon effect. The paper describes in detail the positioning model and estimator used to achieve the accuracy improvements. Simulation results are presented based on real GPS satellite ephemeris, collected at the university campus.","PeriodicalId":158650,"journal":{"name":"2008 IEEE International Symposium on Wireless Communication Systems","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129129951","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：