Pub Date : 2010-04-29DOI: 10.1109/WSA.2010.5456419
M. Stefer, Martin Schneider
The influence of mutual coupling of antenna elements is usually not considered when dealing with MIMO (Multiple Input Multiple Output) communication systems. This is justifiable if mobile subscribers feature only one antenna and base station antenna elements are separated by a distance of several wavelengths. However, regarding pico-cell base stations that consist of multiple antenna elements, the coupling has to be taken into account due to the reduced antenna element spacing. In this paper, the influence of antenna coupling on adaptive MIMO-OFDM (Orthogonal Frequency Division Multiplex) systems is investigated in terms of the attainable signal-to-interference-plus-noise ratio (SINR). The mutual coupling of the antenna elements is calculated for different antenna models based on the ”infinitesimally thin” lambda/2 dipole and the Hertzian dipole. Additionally, a coupling model based on the isotropic radiator is considered. The different results for the SINR stemming from the antenna models when exploiting linear pre-equalization are presented. It is shown that using an isotropic radiator based model is not sufficient for describing the effect of mutual coupling for lambda/2 dipoles.
{"title":"On modeling antenna coupling for adaptive MIMO-OFDM systems","authors":"M. Stefer, Martin Schneider","doi":"10.1109/WSA.2010.5456419","DOIUrl":"https://doi.org/10.1109/WSA.2010.5456419","url":null,"abstract":"The influence of mutual coupling of antenna elements is usually not considered when dealing with MIMO (Multiple Input Multiple Output) communication systems. This is justifiable if mobile subscribers feature only one antenna and base station antenna elements are separated by a distance of several wavelengths. However, regarding pico-cell base stations that consist of multiple antenna elements, the coupling has to be taken into account due to the reduced antenna element spacing. In this paper, the influence of antenna coupling on adaptive MIMO-OFDM (Orthogonal Frequency Division Multiplex) systems is investigated in terms of the attainable signal-to-interference-plus-noise ratio (SINR). The mutual coupling of the antenna elements is calculated for different antenna models based on the ”infinitesimally thin” lambda/2 dipole and the Hertzian dipole. Additionally, a coupling model based on the isotropic radiator is considered. The different results for the SINR stemming from the antenna models when exploiting linear pre-equalization are presented. It is shown that using an isotropic radiator based model is not sufficient for describing the effect of mutual coupling for lambda/2 dipoles.","PeriodicalId":311394,"journal":{"name":"2010 International ITG Workshop on Smart Antennas (WSA)","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115920113","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 : 2010-04-29DOI: 10.1109/WSA.2010.5456450
Vincent Kotzsch, C. Jandura, W. Rave, G. Fettweis
It is well known that symbol timing offsets larger than the cyclic prefix between transmitter and receiver stations destroy the orthogonality among OFDM subcarriers inducing interblock interference by coupling subsequent OFDM symbols. In conjunction with MIMO transmission over frequency selective channels, this effect on top of multi-user interference strongly degrades performance. In this paper we analyze the timing constraints in cellular MIMO OFDM networks that necessarily occur due to time-of-arrival differences of signals from different locations. We investigate a simple hexagonal model, where three users transmit their data on the same time-frequency resource to three cooperating base stations. Based on a detailed analytical derivation of the transmission model we present results for the post detection SINR in systems with symmetric and uniform user distribution within one cooperative cell.
{"title":"On timing constraints and OFDM parameter design for cooperating basestations","authors":"Vincent Kotzsch, C. Jandura, W. Rave, G. Fettweis","doi":"10.1109/WSA.2010.5456450","DOIUrl":"https://doi.org/10.1109/WSA.2010.5456450","url":null,"abstract":"It is well known that symbol timing offsets larger than the cyclic prefix between transmitter and receiver stations destroy the orthogonality among OFDM subcarriers inducing interblock interference by coupling subsequent OFDM symbols. In conjunction with MIMO transmission over frequency selective channels, this effect on top of multi-user interference strongly degrades performance. In this paper we analyze the timing constraints in cellular MIMO OFDM networks that necessarily occur due to time-of-arrival differences of signals from different locations. We investigate a simple hexagonal model, where three users transmit their data on the same time-frequency resource to three cooperating base stations. Based on a detailed analytical derivation of the transmission model we present results for the post detection SINR in systems with symmetric and uniform user distribution within one cooperative cell.","PeriodicalId":311394,"journal":{"name":"2010 International ITG Workshop on Smart Antennas (WSA)","volume":"200 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116149849","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 : 2010-04-29DOI: 10.1109/WSA.2010.5456458
Aimal Khan, V. Kühn
Adaptive relaying schemes significantly improve the performance of relay networks by switching the forwarding technique according to the reliability of the received signal. In adaptive relaying without ARQ all the relays forward irrespective of the decoding status at the destination. This leads to inefficient resource utilization. In ARQ relay networks, the message is repeated upon the request from the destination. In this paper we incorporate ARQ into the adaptive relaying schemes to highlight the gains obtained by using adaptability in conjunction with ARQ. Furthermore, instead of all relays forwarding, only the minimum possible number of relays which ensure successful decoding at the destination participate in forwarding. Different adaptive relaying schemes are taken into consideration. The end-to-end performance and relay selection criteria are determined. Finally, outage probability and throughput of different adaptive schemes with and without ARQ are calculated numerically. The results show that due to the efficient resource allocation and ARQ, adaptive relaying delivers superb performance over the non-ARQ counterpart regarding outage as well as throughput.
{"title":"On the performance of adaptive relaying with ARQ","authors":"Aimal Khan, V. Kühn","doi":"10.1109/WSA.2010.5456458","DOIUrl":"https://doi.org/10.1109/WSA.2010.5456458","url":null,"abstract":"Adaptive relaying schemes significantly improve the performance of relay networks by switching the forwarding technique according to the reliability of the received signal. In adaptive relaying without ARQ all the relays forward irrespective of the decoding status at the destination. This leads to inefficient resource utilization. In ARQ relay networks, the message is repeated upon the request from the destination. In this paper we incorporate ARQ into the adaptive relaying schemes to highlight the gains obtained by using adaptability in conjunction with ARQ. Furthermore, instead of all relays forwarding, only the minimum possible number of relays which ensure successful decoding at the destination participate in forwarding. Different adaptive relaying schemes are taken into consideration. The end-to-end performance and relay selection criteria are determined. Finally, outage probability and throughput of different adaptive schemes with and without ARQ are calculated numerically. The results show that due to the efficient resource allocation and ARQ, adaptive relaying delivers superb performance over the non-ARQ counterpart regarding outage as well as throughput.","PeriodicalId":311394,"journal":{"name":"2010 International ITG Workshop on Smart Antennas (WSA)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131269097","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 : 2010-04-29DOI: 10.1109/WSA.2010.5456396
P. Gentner, W. Gartner, G. Hilton, M. Beach, C. Mecklenbräuker
This paper discusses and analyses the hardware implementation of an ultra-wideband (UWB) beamformer for UWB Impulse Radio data transmission. We use a Complex Programmable Logic Device (CPLD) acting as the binary baseband information source. The CPLD provides input to a pulse shaper and subsequently to a four-element array of UWB antennas. This smart antenna system comprises the digital baseband part, the radio-frequency frontend, and the antenna array. For this contribution, we discuss the design, implementation, and UWB measurement results obtained in an anechoic chamber.
{"title":"Towards a hardware implementation of ultra-wideband beamforming","authors":"P. Gentner, W. Gartner, G. Hilton, M. Beach, C. Mecklenbräuker","doi":"10.1109/WSA.2010.5456396","DOIUrl":"https://doi.org/10.1109/WSA.2010.5456396","url":null,"abstract":"This paper discusses and analyses the hardware implementation of an ultra-wideband (UWB) beamformer for UWB Impulse Radio data transmission. We use a Complex Programmable Logic Device (CPLD) acting as the binary baseband information source. The CPLD provides input to a pulse shaper and subsequently to a four-element array of UWB antennas. This smart antenna system comprises the digital baseband part, the radio-frequency frontend, and the antenna array. For this contribution, we discuss the design, implementation, and UWB measurement results obtained in an anechoic chamber.","PeriodicalId":311394,"journal":{"name":"2010 International ITG Workshop on Smart Antennas (WSA)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131153260","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 : 2010-04-29DOI: 10.1109/WSA.2010.5456443
M. Simko, C. Mehlführer, M. Wrulich, M. Rupp
In this paper, we present an Approximate Linear Minimum Mean Square Error (ALMMSE) fast fading channel estimator for Orthogonal Frequency Division Multiplexing (OFDM). The ALMMSE channel estimator utilizes the knowledge of the structure of the autocorrelation matrix given by the Kronecker product between the time correlation matrix and the frequency correlation matrix. We separate the Linear Minimum Mean Square Error (LMMSE) filtering matrix into two matrices corresponding to individual filtering in frequency and time. The eigenvalues of these two matrices are rank-one approximated by the eigenvalues of the LMMSE filtering matrix. The complexity of the ALMMSE estimator can be scaled by varying the number of the considered number of eigenvalues. Simulation results show that the proposed ALMMSE channel estimator looses only 0.1 dB compared to the LMMSE channel estimator in realistic scenarios.
{"title":"Doubly dispersive channel estimation with scalable complexity","authors":"M. Simko, C. Mehlführer, M. Wrulich, M. Rupp","doi":"10.1109/WSA.2010.5456443","DOIUrl":"https://doi.org/10.1109/WSA.2010.5456443","url":null,"abstract":"In this paper, we present an Approximate Linear Minimum Mean Square Error (ALMMSE) fast fading channel estimator for Orthogonal Frequency Division Multiplexing (OFDM). The ALMMSE channel estimator utilizes the knowledge of the structure of the autocorrelation matrix given by the Kronecker product between the time correlation matrix and the frequency correlation matrix. We separate the Linear Minimum Mean Square Error (LMMSE) filtering matrix into two matrices corresponding to individual filtering in frequency and time. The eigenvalues of these two matrices are rank-one approximated by the eigenvalues of the LMMSE filtering matrix. The complexity of the ALMMSE estimator can be scaled by varying the number of the considered number of eigenvalues. Simulation results show that the proposed ALMMSE channel estimator looses only 0.1 dB compared to the LMMSE channel estimator in realistic scenarios.","PeriodicalId":311394,"journal":{"name":"2010 International ITG Workshop on Smart Antennas (WSA)","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129319463","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 : 2010-02-02DOI: 10.1109/WSA.2010.5456453
Christoph Studer, M. Wenk, A. Burg
Physical transceiver implementations for multiple-input multiple-output (MIMO) wireless communication systems suffer from transmit-RF (Tx-RF) impairments. In this paper, we study the effect on channel capacity and error-rate performance of residual Tx-RF impairments that defy proper compensation. In particular, we demonstrate that such residual distortions severely degrade the performance of (near-)optimum MIMO detection algorithms. To mitigate this performance loss, we propose an efficient algorithm, which is based on an i.i.d. Gaussian model for the distortion caused by these impairments. In order to validate this model, we provide measurement results based on a 4-stream Tx-RF chain implementation for MIMO orthogonal frequency-division multiplexing (OFDM).
{"title":"MIMO transmission with residual transmit-RF impairments","authors":"Christoph Studer, M. Wenk, A. Burg","doi":"10.1109/WSA.2010.5456453","DOIUrl":"https://doi.org/10.1109/WSA.2010.5456453","url":null,"abstract":"Physical transceiver implementations for multiple-input multiple-output (MIMO) wireless communication systems suffer from transmit-RF (Tx-RF) impairments. In this paper, we study the effect on channel capacity and error-rate performance of residual Tx-RF impairments that defy proper compensation. In particular, we demonstrate that such residual distortions severely degrade the performance of (near-)optimum MIMO detection algorithms. To mitigate this performance loss, we propose an efficient algorithm, which is based on an i.i.d. Gaussian model for the distortion caused by these impairments. In order to validate this model, we provide measurement results based on a 4-stream Tx-RF chain implementation for MIMO orthogonal frequency-division multiplexing (OFDM).","PeriodicalId":311394,"journal":{"name":"2010 International ITG Workshop on Smart Antennas (WSA)","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126167942","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 : 2010-02-01DOI: 10.1109/WSA.2010.5456425
Hussein Al-Shatri, T. Weber
Multiuser OFDMA is a promising multiaccess technique for serving users with many non-interfering resources. In the present paper, the problem of the optimum power allocation for maximizing the sum rate with total fairness and total power constraints is tackled. If the sum rate would be a priori known, it could be simply distributed uniformly among the users. Then for each user, the minimum required power for obtaining the given rate can be easily found in a closed form using convex optimization techniques. The bisection method can be applied for finding the maximum sum rate that satisfies the total power constraint. The performance of the proposed method is investigated by simulations. The results show that there is an absolute loss in the sum rate independent of the number of resources per user as compared to waterfilling. Additionally, it is shown that our method is significantly better than waterfilling in typical scenarios in terms of the outage capacity.
{"title":"Fair power allocation for sum-rate maximization in multiuser OFDMA","authors":"Hussein Al-Shatri, T. Weber","doi":"10.1109/WSA.2010.5456425","DOIUrl":"https://doi.org/10.1109/WSA.2010.5456425","url":null,"abstract":"Multiuser OFDMA is a promising multiaccess technique for serving users with many non-interfering resources. In the present paper, the problem of the optimum power allocation for maximizing the sum rate with total fairness and total power constraints is tackled. If the sum rate would be a priori known, it could be simply distributed uniformly among the users. Then for each user, the minimum required power for obtaining the given rate can be easily found in a closed form using convex optimization techniques. The bisection method can be applied for finding the maximum sum rate that satisfies the total power constraint. The performance of the proposed method is investigated by simulations. The results show that there is an absolute loss in the sum rate independent of the number of resources per user as compared to waterfilling. Additionally, it is shown that our method is significantly better than waterfilling in typical scenarios in terms of the outage capacity.","PeriodicalId":311394,"journal":{"name":"2010 International ITG Workshop on Smart Antennas (WSA)","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132779314","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 : 2009-12-17DOI: 10.1109/WSA.2010.5456423
P. Marsch, P. Rost, G. Fettweis
This paper introduces a new mathematical framework which is used to derive joint uplink/downlink achievable rate regions for multi-user spatial multiplexing between one base station and multiple terminals. The framework consists of two models: the first one is a simple transmission model for uplink (UL) and downlink (DL), which is capable to give a lower bound on the capacity for the case that the transmission is subject to imperfect channel state information (CSI). A detailed model for concrete channel estimation and feedback schemes provides the parameter input to the former model and covers the most important aspects such as pilot design optimization, linear channel estimation, feedback delay, and feedback quantization. We apply this framework to determine optimal pilot densities and CSI feedback quantity, given that a weighted sum of UL and DL throughput is to be maximized for a certain user velocity. We show that for low speed, and if DL throughput is of particular importance, a significant portion of the UL should be invested into CSI feedback. At higher velocity, however, DL performance becomes mainly affected by CSI feedback delay, and hence CSI feedback brings little gain considering the inherent sacrifice of UL capacity. We further show that for high velocities, it becomes beneficial to use no CSI feedback at all, but apply random beamforming in the DL and operate in time-division multiplex.
{"title":"Application driven joint uplink-downlink optimization in wireless communications","authors":"P. Marsch, P. Rost, G. Fettweis","doi":"10.1109/WSA.2010.5456423","DOIUrl":"https://doi.org/10.1109/WSA.2010.5456423","url":null,"abstract":"This paper introduces a new mathematical framework which is used to derive joint uplink/downlink achievable rate regions for multi-user spatial multiplexing between one base station and multiple terminals. The framework consists of two models: the first one is a simple transmission model for uplink (UL) and downlink (DL), which is capable to give a lower bound on the capacity for the case that the transmission is subject to imperfect channel state information (CSI). A detailed model for concrete channel estimation and feedback schemes provides the parameter input to the former model and covers the most important aspects such as pilot design optimization, linear channel estimation, feedback delay, and feedback quantization. We apply this framework to determine optimal pilot densities and CSI feedback quantity, given that a weighted sum of UL and DL throughput is to be maximized for a certain user velocity. We show that for low speed, and if DL throughput is of particular importance, a significant portion of the UL should be invested into CSI feedback. At higher velocity, however, DL performance becomes mainly affected by CSI feedback delay, and hence CSI feedback brings little gain considering the inherent sacrifice of UL capacity. We further show that for high velocities, it becomes beneficial to use no CSI feedback at all, but apply random beamforming in the DL and operate in time-division multiplex.","PeriodicalId":311394,"journal":{"name":"2010 International ITG Workshop on Smart Antennas (WSA)","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116289851","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}
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