International Conference on Electrical, Electronic and Computer Engineering, 2004. ICEEC '04., 2004
A programmable/reconfigurable baseband chain with filter and amplifier sections that can be share... more A programmable/reconfigurable baseband chain with filter and amplifier sections that can be shared by two different wireless standards, GSM and DECT, is presented in this paper. This results in a simplified, low power and cost-effective design solution. Filters and amplifiers of the baseband chain were implemented using a fully balanced differential difference amplifier (FBDDA). A new approach is used to implement an analog to digital converter using the FBDDA in order to enhance the design regularity. The noise and linearity performance of individual stages was investigated, and simulations of the overall system showed that it complies with both standards under consideration. Using a suitable algorithm implemented by the digital signal processor (DSP) of the receiver, the chain could be configured to operate efficiently in different environments.
Femtocells randomly deployed in a given macrocell coverage area share the wireless spectrum avail... more Femtocells randomly deployed in a given macrocell coverage area share the wireless spectrum available to the macrocell. The unplanned and ad hoc nature of the femtocell deployment in the macrocell environment renders centralized frequency planning inapplicable. Furthermore, the femtocells are unable to apriori know neither the channel assignment of their neighbours nor the impact of their transmissions on nearby macrocell users due to the lack of explicit coordination. In this paper, we present the distributed Autonomous Opportunistic Channel Access (AOCA) framework that allows the femtocells to share the available spectrum with the overlaying macrocell without any kind of coordination neither between the macrocell and femtocells nor amongst the femtocells. Furthermore, it provides statistical guarantees on the performance of the macrocell users. We formulate the AOCA constrained spectrum access problem as non-linear program to find its optimized parameters' settings. Simulation results show that AOCA achieves multiple folds improvement in the average femtocell network rate due to its probabilistic and non-greedy access that enables multiple neighbouring femtocells to simultaneously use a given channel.
The Cognitive Radio (CR) technology is envisioned as a primary solution to the spectrum scarcity ... more The Cognitive Radio (CR) technology is envisioned as a primary solution to the spectrum scarcity problem in future wireless communication networks. Cognitive radio networking allows the exploitation of unutilized spectrum in an opportunistic manner, and thereby, improves the efficiency of the spectrum utilization. Cognitive radio Networks (CRNs) provide wireless connectivity via heterogeneous wireless architectures and dynamic spectrum access techniques. The enabling technologies and the benefits of CR and CRNs have received significant research and industry interest. However, the energy efficiency of such technologies has received far less interest. In this paper, we shed the light on the move towards energy-efficient CRN that fits the global vision of green communication networks.
IPv6 Neighbor Discovery (ND) based on RFC 4861 is not designed for non-transitive wireless links.... more IPv6 Neighbor Discovery (ND) based on RFC 4861 is not designed for non-transitive wireless links. Its heavy use of multicast transmission makes it inefficient and sometimes impractical for IPv6 over Low power Wireless Personal Area Networks (6LoWPAN). Recently, further optimizations have been proposed by Internet Engineering Task Force (IETF) to make ND more suitable for 6LoWPAN. In this paper, we provide an implementation of the most prominent features of the new optimized ND protocol based on RFC 6775 over the Contiki operating system (OS). First, we evaluate the performance of the basic non-optimized IPv6 ND protocol, and analyze its originally implemented functions to set up a good foundation for our implementation and to maintain compatibility. Then, we implement the new optimized Router Solicitation (RS) and Router Advertisement (RA) messaging scheme that reduces the effect of multicasting and unfavorable periodic RA messages. Our results show that the optimized RFC 6775 ND protocol reduces the number of the exchange radio messages in the network by 60-80%. Such optimization alleviates network congestion and saves more power. Index Terms-neighbor discovery; Contiki OS; performance evaluation; RFC 6775. I. * This work is part of the ITEA2 Web of Objects Project funded in Egypt by the Egyptian Ministry of Communication and Information Technology.
The Routing Protocol for Low power and Lossy Networks (RPL) has recently been considered as the s... more The Routing Protocol for Low power and Lossy Networks (RPL) has recently been considered as the standard routing protocol for wireless sensor networks (WSN). RPL builds routes between nodes based on specific metrics that reflect arbitrary optimization objectives through the RPL Objective Functions (OFs). In this paper, we propose a Context-Aware Objective Function (CAOF) that takes into account the limited resources of the sensor nodes and their temporal changes. The proposed CAOF optimizes the power exploitation as a critical resource by taking the battery level into consideration in the routing decision. Simulation results show that our CAOF increases the network lifetime by up to 44% compared to noncontext-aware OFs of RPL. Furthermore, CAOF ensures more fairness in the exploitation of batteries of the different nodes in the network more than non-context-aware OFs. In addition CAOF enhances the delivery ratio when compared with RPL non-context -aware OFs.
We propose and evaluate the performance of an integrated quality-of-service (QoS) aware radio res... more We propose and evaluate the performance of an integrated quality-of-service (QoS) aware radio resource management (RRM) framework for LTE uplink access. Unlike related work, our integrated RRM framework jointly takes into account 1) the class of service requirements of the different connections, 2) the constraints on the contiguity in resource block allocation due to the single-carrier frequency division multiple access (SC-FDMA) mechanism adopted for the LTE uplink, and 3) the selection of the appropriate modulation and coding scheme with full integration with the LTE uplink closed-loop fractional power control for proper power allocation. The proposed RRM framework uses closed loop power control and interference limit per cell to provide an autonomous inter-cell interference coordination scheme that is applied locally without the need of exchanging interference related information between neighboring cells. Simulation results show the ability of the proposed framework to meet the QoS of a highly loaded system with four classes of service. The interference-aware scheme also manages to limit interference and provides fair resource sharing between cell-edge and cell-center users.
Proceedings - International Conference on Computer Communications and Networks, ICCCN, 2008
Previous work has shown that CSMA-based protocols such as the IEEE 802.11 can yield flow starvati... more Previous work has shown that CSMA-based protocols such as the IEEE 802.11 can yield flow starvation in multihop wireless networks. While prior protocol designs alleviated such starvation by utilizing MIMO, they require global synchronization to temporally align transmissions and require perpacket distribution of the complete channel state information. In this paper, we experimentally show that MIMO networks based on pre-802.11n medium access, the state-of-the-art for asynchronous MIMO CSMA, worsen starvation as compared to SISO networks. Consequently, we design an asynchronous MIMO MAC protocol that counters starvation. We show that randomized and non-greedy antenna allocation coupled with local residual capacity estimation results in previously-starving nodes capturing a fair share of system resources while simultaneously exploiting throughput gains available to multi-antenna systems.
In this paper, we demonstrate that multiple concurrent asynchronous and uncoordinated Single-Inpu... more In this paper, we demonstrate that multiple concurrent asynchronous and uncoordinated Single-Input Multiple-Output (SIMO) transmissions can successfully take place even though the respective receivers do not explicitly null out interfering signals. Thus motivated, we propose simple modifications to the widely deployed IEEE 802.11 MAC to enable multiple nonspatially-isolated SIMO sender-receiver pairs to share the medium. Namely, we propose to increase the physical carrier sensing threshold, disable virtual carrier sensing, and enable message in message packet detection. We use experiments to show that while increasing the peak transmission rate, spatial multiplexing schemes such as those employed by the IEEE 802.11n are highly non-robust to asynchronous and uncoordinated interferers. In contrast, we show that the proposed multi-flow SIMO MAC scheme alleviates the severe unfairness resulting from uncoordinated transmissions in 802.11 multi-hop networks.
Opportunistic Spectrum Access (OSA) is foreseen as the future of wireless communications. OSA rel... more Opportunistic Spectrum Access (OSA) is foreseen as the future of wireless communications. OSA relies on the cognitive radio transceiver that tracks the spectral opportunities over a wide spectrum range (multiple GHz). The cognitive radio should be able to analyze the huge amount of acquired spectral information, decide the best course of action, and reconfigure its transceiver parameters accordingly in a very short time due to the highly dynamic nature of the radio environment. This poses stringent requirements on the hardware and processing power of the transceiver. Despite the recent advances in the radio transceiver technologies, existing radios do not allow for exploiting OSA to its full potential. Furthermore, the absence of a centralized entity that controls the spectrum access decisions in distributed ad-hoc networks makes implementing OSA more challenging. In this article, we experimentally demonstrate the ability of implementing distributed OSA schemes given the practical limitations of existing low-cost transceiver technologies. Furthermore, we evaluate the performance of different OSA approaches.
Existing distributed opportunistic spectrum management schemes do not consider the inability of t... more Existing distributed opportunistic spectrum management schemes do not consider the inability of today's cognitive transceivers to measure interference at primary receivers. Consequently, optimizing the constrained cognitive radio network performance based only on local interference measurements at cognitive senders does not lead to truly optimal performance due to hidden and exposed primary senders. In this paper, we present the rate-adaptive probabilistic medium access protocol (RAP-MAC) for opportunistic spectrum management. In contrast to existing techniques, our approach addresses the unavoidable inaccuracy in spectrum sensing via a probabilistic spectrum access strategy. Furthermore, RAP-MAC allows multiple cognitive flows to fairly share the available bandwidth without explicit coordination by adopting a non-greedy transmission approach that prevents a single cognitive transmitter from monopolizing an available spectral opportunity. We analytically formulate the cognitive user performance optimization problem as a mixed integer non-linear programming to derive the optimal parameter values. Packet-level simulations show that RAP-MAC achieves between 65% to 119.5% higher goodput with significantly better fairness characteristics compared to existing greedy approaches that overlook the spectrum sensing limitations.
International Conference on Electrical, Electronic and Computer Engineering, 2004. ICEEC '04., 2004
A programmable/reconfigurable baseband chain with filter and amplifier sections that can be share... more A programmable/reconfigurable baseband chain with filter and amplifier sections that can be shared by two different wireless standards, GSM and DECT, is presented in this paper. This results in a simplified, low power and cost-effective design solution. Filters and amplifiers of the baseband chain were implemented using a fully balanced differential difference amplifier (FBDDA). A new approach is used to implement an analog to digital converter using the FBDDA in order to enhance the design regularity. The noise and linearity performance of individual stages was investigated, and simulations of the overall system showed that it complies with both standards under consideration. Using a suitable algorithm implemented by the digital signal processor (DSP) of the receiver, the chain could be configured to operate efficiently in different environments.
Femtocells randomly deployed in a given macrocell coverage area share the wireless spectrum avail... more Femtocells randomly deployed in a given macrocell coverage area share the wireless spectrum available to the macrocell. The unplanned and ad hoc nature of the femtocell deployment in the macrocell environment renders centralized frequency planning inapplicable. Furthermore, the femtocells are unable to apriori know neither the channel assignment of their neighbours nor the impact of their transmissions on nearby macrocell users due to the lack of explicit coordination. In this paper, we present the distributed Autonomous Opportunistic Channel Access (AOCA) framework that allows the femtocells to share the available spectrum with the overlaying macrocell without any kind of coordination neither between the macrocell and femtocells nor amongst the femtocells. Furthermore, it provides statistical guarantees on the performance of the macrocell users. We formulate the AOCA constrained spectrum access problem as non-linear program to find its optimized parameters' settings. Simulation results show that AOCA achieves multiple folds improvement in the average femtocell network rate due to its probabilistic and non-greedy access that enables multiple neighbouring femtocells to simultaneously use a given channel.
The Cognitive Radio (CR) technology is envisioned as a primary solution to the spectrum scarcity ... more The Cognitive Radio (CR) technology is envisioned as a primary solution to the spectrum scarcity problem in future wireless communication networks. Cognitive radio networking allows the exploitation of unutilized spectrum in an opportunistic manner, and thereby, improves the efficiency of the spectrum utilization. Cognitive radio Networks (CRNs) provide wireless connectivity via heterogeneous wireless architectures and dynamic spectrum access techniques. The enabling technologies and the benefits of CR and CRNs have received significant research and industry interest. However, the energy efficiency of such technologies has received far less interest. In this paper, we shed the light on the move towards energy-efficient CRN that fits the global vision of green communication networks.
IPv6 Neighbor Discovery (ND) based on RFC 4861 is not designed for non-transitive wireless links.... more IPv6 Neighbor Discovery (ND) based on RFC 4861 is not designed for non-transitive wireless links. Its heavy use of multicast transmission makes it inefficient and sometimes impractical for IPv6 over Low power Wireless Personal Area Networks (6LoWPAN). Recently, further optimizations have been proposed by Internet Engineering Task Force (IETF) to make ND more suitable for 6LoWPAN. In this paper, we provide an implementation of the most prominent features of the new optimized ND protocol based on RFC 6775 over the Contiki operating system (OS). First, we evaluate the performance of the basic non-optimized IPv6 ND protocol, and analyze its originally implemented functions to set up a good foundation for our implementation and to maintain compatibility. Then, we implement the new optimized Router Solicitation (RS) and Router Advertisement (RA) messaging scheme that reduces the effect of multicasting and unfavorable periodic RA messages. Our results show that the optimized RFC 6775 ND protocol reduces the number of the exchange radio messages in the network by 60-80%. Such optimization alleviates network congestion and saves more power. Index Terms-neighbor discovery; Contiki OS; performance evaluation; RFC 6775. I. * This work is part of the ITEA2 Web of Objects Project funded in Egypt by the Egyptian Ministry of Communication and Information Technology.
The Routing Protocol for Low power and Lossy Networks (RPL) has recently been considered as the s... more The Routing Protocol for Low power and Lossy Networks (RPL) has recently been considered as the standard routing protocol for wireless sensor networks (WSN). RPL builds routes between nodes based on specific metrics that reflect arbitrary optimization objectives through the RPL Objective Functions (OFs). In this paper, we propose a Context-Aware Objective Function (CAOF) that takes into account the limited resources of the sensor nodes and their temporal changes. The proposed CAOF optimizes the power exploitation as a critical resource by taking the battery level into consideration in the routing decision. Simulation results show that our CAOF increases the network lifetime by up to 44% compared to noncontext-aware OFs of RPL. Furthermore, CAOF ensures more fairness in the exploitation of batteries of the different nodes in the network more than non-context-aware OFs. In addition CAOF enhances the delivery ratio when compared with RPL non-context -aware OFs.
We propose and evaluate the performance of an integrated quality-of-service (QoS) aware radio res... more We propose and evaluate the performance of an integrated quality-of-service (QoS) aware radio resource management (RRM) framework for LTE uplink access. Unlike related work, our integrated RRM framework jointly takes into account 1) the class of service requirements of the different connections, 2) the constraints on the contiguity in resource block allocation due to the single-carrier frequency division multiple access (SC-FDMA) mechanism adopted for the LTE uplink, and 3) the selection of the appropriate modulation and coding scheme with full integration with the LTE uplink closed-loop fractional power control for proper power allocation. The proposed RRM framework uses closed loop power control and interference limit per cell to provide an autonomous inter-cell interference coordination scheme that is applied locally without the need of exchanging interference related information between neighboring cells. Simulation results show the ability of the proposed framework to meet the QoS of a highly loaded system with four classes of service. The interference-aware scheme also manages to limit interference and provides fair resource sharing between cell-edge and cell-center users.
Proceedings - International Conference on Computer Communications and Networks, ICCCN, 2008
Previous work has shown that CSMA-based protocols such as the IEEE 802.11 can yield flow starvati... more Previous work has shown that CSMA-based protocols such as the IEEE 802.11 can yield flow starvation in multihop wireless networks. While prior protocol designs alleviated such starvation by utilizing MIMO, they require global synchronization to temporally align transmissions and require perpacket distribution of the complete channel state information. In this paper, we experimentally show that MIMO networks based on pre-802.11n medium access, the state-of-the-art for asynchronous MIMO CSMA, worsen starvation as compared to SISO networks. Consequently, we design an asynchronous MIMO MAC protocol that counters starvation. We show that randomized and non-greedy antenna allocation coupled with local residual capacity estimation results in previously-starving nodes capturing a fair share of system resources while simultaneously exploiting throughput gains available to multi-antenna systems.
In this paper, we demonstrate that multiple concurrent asynchronous and uncoordinated Single-Inpu... more In this paper, we demonstrate that multiple concurrent asynchronous and uncoordinated Single-Input Multiple-Output (SIMO) transmissions can successfully take place even though the respective receivers do not explicitly null out interfering signals. Thus motivated, we propose simple modifications to the widely deployed IEEE 802.11 MAC to enable multiple nonspatially-isolated SIMO sender-receiver pairs to share the medium. Namely, we propose to increase the physical carrier sensing threshold, disable virtual carrier sensing, and enable message in message packet detection. We use experiments to show that while increasing the peak transmission rate, spatial multiplexing schemes such as those employed by the IEEE 802.11n are highly non-robust to asynchronous and uncoordinated interferers. In contrast, we show that the proposed multi-flow SIMO MAC scheme alleviates the severe unfairness resulting from uncoordinated transmissions in 802.11 multi-hop networks.
Opportunistic Spectrum Access (OSA) is foreseen as the future of wireless communications. OSA rel... more Opportunistic Spectrum Access (OSA) is foreseen as the future of wireless communications. OSA relies on the cognitive radio transceiver that tracks the spectral opportunities over a wide spectrum range (multiple GHz). The cognitive radio should be able to analyze the huge amount of acquired spectral information, decide the best course of action, and reconfigure its transceiver parameters accordingly in a very short time due to the highly dynamic nature of the radio environment. This poses stringent requirements on the hardware and processing power of the transceiver. Despite the recent advances in the radio transceiver technologies, existing radios do not allow for exploiting OSA to its full potential. Furthermore, the absence of a centralized entity that controls the spectrum access decisions in distributed ad-hoc networks makes implementing OSA more challenging. In this article, we experimentally demonstrate the ability of implementing distributed OSA schemes given the practical limitations of existing low-cost transceiver technologies. Furthermore, we evaluate the performance of different OSA approaches.
Existing distributed opportunistic spectrum management schemes do not consider the inability of t... more Existing distributed opportunistic spectrum management schemes do not consider the inability of today's cognitive transceivers to measure interference at primary receivers. Consequently, optimizing the constrained cognitive radio network performance based only on local interference measurements at cognitive senders does not lead to truly optimal performance due to hidden and exposed primary senders. In this paper, we present the rate-adaptive probabilistic medium access protocol (RAP-MAC) for opportunistic spectrum management. In contrast to existing techniques, our approach addresses the unavoidable inaccuracy in spectrum sensing via a probabilistic spectrum access strategy. Furthermore, RAP-MAC allows multiple cognitive flows to fairly share the available bandwidth without explicit coordination by adopting a non-greedy transmission approach that prevents a single cognitive transmitter from monopolizing an available spectral opportunity. We analytically formulate the cognitive user performance optimization problem as a mixed integer non-linear programming to derive the optimal parameter values. Packet-level simulations show that RAP-MAC achieves between 65% to 119.5% higher goodput with significantly better fairness characteristics compared to existing greedy approaches that overlook the spectrum sensing limitations.
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