We derive the outage capacity of a bursty version of the amplify-and-forward (BAF) protocol for s... more We derive the outage capacity of a bursty version of the amplify-and-forward (BAF) protocol for small signal-to-noise ratios when incremental relaying is used. We show that the ratio between the outage capacities of BAF and the cut-set bound is independent of the relay position and that BAF is outage optimal for certain conditions on the target rate R. This is in contrast to decode-and-forward with incremental relaying, where the relay location strongly determines the performance of the cooperative protocol. We further derive the outage capacity for a network consisting of an arbitrary number of relay nodes. In this case the relays transmit in subsequent partitions of the overall transmission block and the destination accumulates signal-to-noise ratio until it is able to decode.
We present a simple combining receiver for a dual-diversity wireless relay network. The main conc... more We present a simple combining receiver for a dual-diversity wireless relay network. The main concern of the paper is to face the trade-off between performance and complexity. The receiver focuses on signal-to-noise ratio (SNR) monitoring and selects dynamically between selection combining (SC) and equal gain combining (EGC) depending on the SNR ratio of the two received branches. It is shown that SC suffers no SNR degradation compared to a single branch communications system if the two receive branches are unbalanced, wheres EGC suffers a loss of 3 dB. Error performance with respect to branch unbalance is considered as well and limiting values for a high degree of branch unbalance are derived.
— Cooperative networking as a means of creating spatial diversity is used in order to mitigate th... more — Cooperative networking as a means of creating spatial diversity is used in order to mitigate the adverse effect of fading in a wireless channel and increase reliability of communications. We investigate signal-to-noise ratio (SNR) gain in wireless cooperative networks. We show that the differential SNR gain in the high data rate regime, which we refer to as SNR gain exponent ζ∞, is independent of the relaying strategy and only depends on the number of transmission phases used for communication. Furthermore, a straight-line upper and lower bound is derived based on geometric considerations. It is shown that the approximation error of the upper bound with respect to the exact SNR gain tends to zero for R → ∞. For the lower bound, the approximation error tends asymptotically to a constant factor δ for R → ∞. Both bounds are the best possible straight-line bounds with respect to absolute error.
We present a simple combining receiver for a dual-diversity wireless relay network. The main conc... more We present a simple combining receiver for a dual-diversity wireless relay network. The main concern of the paper is to face the trade-off between performance and complexity. The receiver focuses on signal-to-noise ratio (SNR) monitoring and selects dynamically between selection combining (SC) and equal gain combining (EGC) depending on the SNR ratio of the two received branches. It is shown that SC suffers no SNR degradation compared to a single branch communications sys-tem if the two receive branches are unbalanced, wheres EGC suffers a loss of 3 dB. Error performance with respect to branch unbalance is considered as well and limiting values for a high degree of branch unbalance are derived. I
We investigate the effect of imperfect feedback on the ǫ-outage capacity of incremental relaying ... more We investigate the effect of imperfect feedback on the ǫ-outage capacity of incremental relaying in the low signal-to-noise ratio (SNR) regime. We show that imperfect feedback leads to a rescaling of the pre-log factor (comparable to the multiplexing gain for networks operating in the high SNR regime) and thus reduces the ǫ-outage capacity considerably. Moreover, we investigate the effect of different degrees of feedback reliability on the system performance. We further derive a simple binary tree-based construction rule to analyze networks with an arbitrary number of relay nodes with respect to imperfect feedback. This rule can directly be mapped to a comprehensive matrix notation.
We present the e-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a... more We present the e-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a wireless cooperative network with slow Rayleigh fading channels. The relay performs decode-and-forward and repetition coding is employed in the network, which is optimal in the low SNR regime. We derive an expression on the optimal relay location that maximizes the e-outage capacity. It is shown
The specification of IEEE 802.22 defines the worldwide first cognitive radio (CR) standard. Withi... more The specification of IEEE 802.22 defines the worldwide first cognitive radio (CR) standard. Within a range of 40 MHz to 910 MHz CR systems are allowed to allocate spectrum besides the currently established radio services like radio and TV broadcasting. In order to fulfill the regulative guidelines of interference limitations, a capable spectral sensing and user detection has to be provided. Due to the wide frequency range specified in IEEE 802.22 and the high dynamic range of signals allocated in this band there are high demands on the CR receiver's front-end. Especially the performance requirements on analog-to-digital converters increase significantly compared to current wireless systems. Based on measurements taken in this frequency range requirements to CR's ADCs are figured out. Furthermore, the measurement results are analyzed regarding expectable allocation scenarios and their impacts to spectral sensing. Derived from this results and a comparison of general spectral sensing mechanisms an approach for a CR receiver supporting wide-band sensing is presented. Considering the apriori information resulting from scenario analysis and including adapted information processing in the terminal the ADC's performance requirements can be reduced.
2007 2nd IEEE International Symposium on New Frontiers in Dynamic Spectrum Access Networks, 2007
This contribution presents spectrum occupancy measurements which have been performed during the 2... more This contribution presents spectrum occupancy measurements which have been performed during the 2006 Football World Cup in Germany, in the cities of Kaiserslautern and Dortmund. The measurements investigate the time-variation of powers in 2G bands (900MHz and 1800MHz), a spectrum bandwidth including 3G bands and an ISM band (2000-2600MHz), and a global band (400-2600MHz), on the day prior to a match, the day of the match, and during the match. The first intention is to study changes in power levels and subsequently relate this to specific events, such as (i) the start of the match, (ii) half-time, and (iii) the end of the match. A next intention is to investigate the autocorrelation structure of changes in power levels, and relate this to the ease with which dynamic spectrum allocation might be performed. The results that ensue are used to inspire a discussion as to how dynamic spectrum allocation and short-range localized solutions such as IEEE 802.11 basestations might be leveraged to bolster capacity at large-scale events.
We present the e-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a... more We present the e-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a wireless cooperative network with slow Rayleigh fading channels. The relay performs decode-and-forward and repetition coding is employed in the network, which is optimal in the low SNR regime. We derive an expression on the optimal relay location that maximizes the e-outage capacity. It is shown
2009 43rd Annual Conference on Information Sciences and Systems, 2009
Cooperative networking as a means of creating spatial diversity is used in order to mitigate the ... more Cooperative networking as a means of creating spatial diversity is used in order to mitigate the adverse effect of fading in a wireless channel and increase reliability of communications. We investigate signal-to-noise ratio (SNR) gain in wireless cooperative networks. We show that the differential SNR gain in the high data rate regime, which we refer to as SNR gain exponent ζ ∞, is independent of the relaying strategy and only depends on the number of transmission phases used for communication. Furthermore, a straight-line upper and lower bound is derived based on geometric considerations. It is shown that the approximation error of the upper bound with respect to the exact SNR gain tends to zero for R → ∞. For the lower bound, the approximation error tends asymptotically to a constant factor δ for R → ∞. Both bounds are the best possible straight-line bounds with respect to absolute error.
International Symposium on Information Theory and Its Applications, 2010
We derive the outage capacity of a bursty version of the amplify-and-forward (BAF) protocol for s... more We derive the outage capacity of a bursty version of the amplify-and-forward (BAF) protocol for small signal-to-noise ratios when incremental relaying is used. We show that the ratio between the outage capacities of BAF and the cut-set bound is independent of the relay position and that BAF is outage optimal for certain conditions on the target rate R. This is
We present the ǫ-outage capacity in the low signal-to-noise ratio (SNR) regime of an incremental ... more We present the ǫ-outage capacity in the low signal-to-noise ratio (SNR) regime of an incremental relaying network. The network consists of one source, one destination, and two half-duplex relays. The one-bit feedback from the destination node is considered to be imperfect and is modeled as binary symmetric channel. The basic idea is that in each block only one terminal transmits depending on the feedback information in order to achieve a better use of the degrees of freedom of the channel. We derive a closed-form expression of the ǫ-outage capacity and show that the quality of the feedback link has a great influence on the ǫ-outage capacity of the network. We further examine an extension to the "usual" incremental relaying protocol by allowing the relays to overhear the transmissions of each other in order to increase their own decoding probability. This novel incremental relaying protocol performs close to the cut-set bound (within 0.5 bit/s/Hz).
We investigate the effect of imperfect feedback on the \epsilon-outage capacity of incremental re... more We investigate the effect of imperfect feedback on the \epsilon-outage capacity of incremental relaying in the low signal-to-noise ratio (SNR) regime. We show that imperfect feedback leads to a rescaling of the pre-log factor (comparable to the multiplexing gain for networks operating in the high SNR regime) and thus reduces the \epsilon-outage capacity considerably. Moreover, we investigate the effect of
2008 IEEE International Symposium on Wireless Communication Systems, 2008
We study signal-to-noise ratio (SNR) gains for two different cooperation strategies that are appl... more We study signal-to-noise ratio (SNR) gains for two different cooperation strategies that are applied to networks consisting of one source, one destination, and one or two relays, respectively. The first strategy is called orthogonal decode-and-forward where all transmit terminals transmit interference free in orthogonal time slots. The second strategy is called nonorthogonal decode-and-forward where all relays transmit simultaneously by applying
2010 4th International Symposium on Communications, Control and Signal Processing (ISCCSP), 2010
In this paper we present outage regions for two cooperation strategies, namely multi-routing and ... more In this paper we present outage regions for two cooperation strategies, namely multi-routing and adaptive multi-routing, if two different coding schemes are used. The first coding scheme is repetition coding and the second one is parallel channel coding. We show that for one cooperation strategy, the outage region for parallel channel coding is a strict subset of the outage probability
VTC Spring 2009 - IEEE 69th Vehicular Technology Conference, 2009
We consider a wireless relay network in a Rayleigh fading scenario where transmission power as we... more We consider a wireless relay network in a Rayleigh fading scenario where transmission power as well as transmission time per user are optimized. The criterion of optimization is the capacity. We apply an optimization algorithm based on Brent's method. Hence, we employ parabolic interpolation for finding the optimum whenever possible in order to achieve a faster convergence. If parabolic interpolation is not suitable, we use golden section search which is a robust root-finding method. Optimization takes place in two steps. First, we optimize power allocation and consider time as parameter. Second, time is optimized. We demonstrate that, depending on the cooperation strategy, remarkable capacity gains over direct transmission can be achieved by multi-routing. However, for a high overall transmission power, direct transmission outperforms multi-hopping. Generally, capacity gains increase with decreasing overall system power, which demonstrates that relaying is beneficial for low overall transmission powers.
We derive the outage capacity of a bursty version of the amplify-and-forward (BAF) protocol for s... more We derive the outage capacity of a bursty version of the amplify-and-forward (BAF) protocol for small signal-to-noise ratios when incremental relaying is used. We show that the ratio between the outage capacities of BAF and the cut-set bound is independent of the relay position and that BAF is outage optimal for certain conditions on the target rate R. This is in contrast to decode-and-forward with incremental relaying, where the relay location strongly determines the performance of the cooperative protocol. We further derive the outage capacity for a network consisting of an arbitrary number of relay nodes. In this case the relays transmit in subsequent partitions of the overall transmission block and the destination accumulates signal-to-noise ratio until it is able to decode.
We present a simple combining receiver for a dual-diversity wireless relay network. The main conc... more We present a simple combining receiver for a dual-diversity wireless relay network. The main concern of the paper is to face the trade-off between performance and complexity. The receiver focuses on signal-to-noise ratio (SNR) monitoring and selects dynamically between selection combining (SC) and equal gain combining (EGC) depending on the SNR ratio of the two received branches. It is shown that SC suffers no SNR degradation compared to a single branch communications system if the two receive branches are unbalanced, wheres EGC suffers a loss of 3 dB. Error performance with respect to branch unbalance is considered as well and limiting values for a high degree of branch unbalance are derived.
— Cooperative networking as a means of creating spatial diversity is used in order to mitigate th... more — Cooperative networking as a means of creating spatial diversity is used in order to mitigate the adverse effect of fading in a wireless channel and increase reliability of communications. We investigate signal-to-noise ratio (SNR) gain in wireless cooperative networks. We show that the differential SNR gain in the high data rate regime, which we refer to as SNR gain exponent ζ∞, is independent of the relaying strategy and only depends on the number of transmission phases used for communication. Furthermore, a straight-line upper and lower bound is derived based on geometric considerations. It is shown that the approximation error of the upper bound with respect to the exact SNR gain tends to zero for R → ∞. For the lower bound, the approximation error tends asymptotically to a constant factor δ for R → ∞. Both bounds are the best possible straight-line bounds with respect to absolute error.
We present a simple combining receiver for a dual-diversity wireless relay network. The main conc... more We present a simple combining receiver for a dual-diversity wireless relay network. The main concern of the paper is to face the trade-off between performance and complexity. The receiver focuses on signal-to-noise ratio (SNR) monitoring and selects dynamically between selection combining (SC) and equal gain combining (EGC) depending on the SNR ratio of the two received branches. It is shown that SC suffers no SNR degradation compared to a single branch communications sys-tem if the two receive branches are unbalanced, wheres EGC suffers a loss of 3 dB. Error performance with respect to branch unbalance is considered as well and limiting values for a high degree of branch unbalance are derived. I
We investigate the effect of imperfect feedback on the ǫ-outage capacity of incremental relaying ... more We investigate the effect of imperfect feedback on the ǫ-outage capacity of incremental relaying in the low signal-to-noise ratio (SNR) regime. We show that imperfect feedback leads to a rescaling of the pre-log factor (comparable to the multiplexing gain for networks operating in the high SNR regime) and thus reduces the ǫ-outage capacity considerably. Moreover, we investigate the effect of different degrees of feedback reliability on the system performance. We further derive a simple binary tree-based construction rule to analyze networks with an arbitrary number of relay nodes with respect to imperfect feedback. This rule can directly be mapped to a comprehensive matrix notation.
We present the e-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a... more We present the e-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a wireless cooperative network with slow Rayleigh fading channels. The relay performs decode-and-forward and repetition coding is employed in the network, which is optimal in the low SNR regime. We derive an expression on the optimal relay location that maximizes the e-outage capacity. It is shown
The specification of IEEE 802.22 defines the worldwide first cognitive radio (CR) standard. Withi... more The specification of IEEE 802.22 defines the worldwide first cognitive radio (CR) standard. Within a range of 40 MHz to 910 MHz CR systems are allowed to allocate spectrum besides the currently established radio services like radio and TV broadcasting. In order to fulfill the regulative guidelines of interference limitations, a capable spectral sensing and user detection has to be provided. Due to the wide frequency range specified in IEEE 802.22 and the high dynamic range of signals allocated in this band there are high demands on the CR receiver's front-end. Especially the performance requirements on analog-to-digital converters increase significantly compared to current wireless systems. Based on measurements taken in this frequency range requirements to CR's ADCs are figured out. Furthermore, the measurement results are analyzed regarding expectable allocation scenarios and their impacts to spectral sensing. Derived from this results and a comparison of general spectral sensing mechanisms an approach for a CR receiver supporting wide-band sensing is presented. Considering the apriori information resulting from scenario analysis and including adapted information processing in the terminal the ADC's performance requirements can be reduced.
2007 2nd IEEE International Symposium on New Frontiers in Dynamic Spectrum Access Networks, 2007
This contribution presents spectrum occupancy measurements which have been performed during the 2... more This contribution presents spectrum occupancy measurements which have been performed during the 2006 Football World Cup in Germany, in the cities of Kaiserslautern and Dortmund. The measurements investigate the time-variation of powers in 2G bands (900MHz and 1800MHz), a spectrum bandwidth including 3G bands and an ISM band (2000-2600MHz), and a global band (400-2600MHz), on the day prior to a match, the day of the match, and during the match. The first intention is to study changes in power levels and subsequently relate this to specific events, such as (i) the start of the match, (ii) half-time, and (iii) the end of the match. A next intention is to investigate the autocorrelation structure of changes in power levels, and relate this to the ease with which dynamic spectrum allocation might be performed. The results that ensue are used to inspire a discussion as to how dynamic spectrum allocation and short-range localized solutions such as IEEE 802.11 basestations might be leveraged to bolster capacity at large-scale events.
We present the e-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a... more We present the e-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a wireless cooperative network with slow Rayleigh fading channels. The relay performs decode-and-forward and repetition coding is employed in the network, which is optimal in the low SNR regime. We derive an expression on the optimal relay location that maximizes the e-outage capacity. It is shown
2009 43rd Annual Conference on Information Sciences and Systems, 2009
Cooperative networking as a means of creating spatial diversity is used in order to mitigate the ... more Cooperative networking as a means of creating spatial diversity is used in order to mitigate the adverse effect of fading in a wireless channel and increase reliability of communications. We investigate signal-to-noise ratio (SNR) gain in wireless cooperative networks. We show that the differential SNR gain in the high data rate regime, which we refer to as SNR gain exponent ζ ∞, is independent of the relaying strategy and only depends on the number of transmission phases used for communication. Furthermore, a straight-line upper and lower bound is derived based on geometric considerations. It is shown that the approximation error of the upper bound with respect to the exact SNR gain tends to zero for R → ∞. For the lower bound, the approximation error tends asymptotically to a constant factor δ for R → ∞. Both bounds are the best possible straight-line bounds with respect to absolute error.
International Symposium on Information Theory and Its Applications, 2010
We derive the outage capacity of a bursty version of the amplify-and-forward (BAF) protocol for s... more We derive the outage capacity of a bursty version of the amplify-and-forward (BAF) protocol for small signal-to-noise ratios when incremental relaying is used. We show that the ratio between the outage capacities of BAF and the cut-set bound is independent of the relay position and that BAF is outage optimal for certain conditions on the target rate R. This is
We present the ǫ-outage capacity in the low signal-to-noise ratio (SNR) regime of an incremental ... more We present the ǫ-outage capacity in the low signal-to-noise ratio (SNR) regime of an incremental relaying network. The network consists of one source, one destination, and two half-duplex relays. The one-bit feedback from the destination node is considered to be imperfect and is modeled as binary symmetric channel. The basic idea is that in each block only one terminal transmits depending on the feedback information in order to achieve a better use of the degrees of freedom of the channel. We derive a closed-form expression of the ǫ-outage capacity and show that the quality of the feedback link has a great influence on the ǫ-outage capacity of the network. We further examine an extension to the "usual" incremental relaying protocol by allowing the relays to overhear the transmissions of each other in order to increase their own decoding probability. This novel incremental relaying protocol performs close to the cut-set bound (within 0.5 bit/s/Hz).
We investigate the effect of imperfect feedback on the \epsilon-outage capacity of incremental re... more We investigate the effect of imperfect feedback on the \epsilon-outage capacity of incremental relaying in the low signal-to-noise ratio (SNR) regime. We show that imperfect feedback leads to a rescaling of the pre-log factor (comparable to the multiplexing gain for networks operating in the high SNR regime) and thus reduces the \epsilon-outage capacity considerably. Moreover, we investigate the effect of
2008 IEEE International Symposium on Wireless Communication Systems, 2008
We study signal-to-noise ratio (SNR) gains for two different cooperation strategies that are appl... more We study signal-to-noise ratio (SNR) gains for two different cooperation strategies that are applied to networks consisting of one source, one destination, and one or two relays, respectively. The first strategy is called orthogonal decode-and-forward where all transmit terminals transmit interference free in orthogonal time slots. The second strategy is called nonorthogonal decode-and-forward where all relays transmit simultaneously by applying
2010 4th International Symposium on Communications, Control and Signal Processing (ISCCSP), 2010
In this paper we present outage regions for two cooperation strategies, namely multi-routing and ... more In this paper we present outage regions for two cooperation strategies, namely multi-routing and adaptive multi-routing, if two different coding schemes are used. The first coding scheme is repetition coding and the second one is parallel channel coding. We show that for one cooperation strategy, the outage region for parallel channel coding is a strict subset of the outage probability
VTC Spring 2009 - IEEE 69th Vehicular Technology Conference, 2009
We consider a wireless relay network in a Rayleigh fading scenario where transmission power as we... more We consider a wireless relay network in a Rayleigh fading scenario where transmission power as well as transmission time per user are optimized. The criterion of optimization is the capacity. We apply an optimization algorithm based on Brent's method. Hence, we employ parabolic interpolation for finding the optimum whenever possible in order to achieve a faster convergence. If parabolic interpolation is not suitable, we use golden section search which is a robust root-finding method. Optimization takes place in two steps. First, we optimize power allocation and consider time as parameter. Second, time is optimized. We demonstrate that, depending on the cooperation strategy, remarkable capacity gains over direct transmission can be achieved by multi-routing. However, for a high overall transmission power, direct transmission outperforms multi-hopping. Generally, capacity gains increase with decreasing overall system power, which demonstrates that relaying is beneficial for low overall transmission powers.
Uploads
Papers by Tobias Renk