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With recent advances in in-band full duplex techniques, full duplex capable relays have been shown feasible in many recent works. Instead of generating data itself to transmit, a full duplex relay can forward the received signal while receiving it. It also has the opportunity to properly modify the signal before forwarding it, which has been explored to enable constructive and destructive full duplex relaying recently. With these designs, the signal through the full duplex relay could constructively or destructively add up with the signal from the direct link at the receiver side. As a result, the received signal power may be boosted or greatly reduced, compared with direct forwarding. In this paper, we do detailed analysis on whether such constructive and destructive full duplex relays are possible. We find that for OFDM signals, such relays can not be achieved if the additional latency of the relayed path is more than one sample time than the direct link. Our analysis and results challenge the assumptions on the relay latency requirements of previous works to realize such systems. [ABSTRACT FROM AUTHOR]

Channel information plays an important role in modern wireless communication systems. Systems that use different frequency bands for uplink and downlink communication often need feedback between devices to exchange band specific channel information. The current state-of-the-art approach proposes a way to predict the channel in the downlink based on that of the observed uplink by identifying variables underlying the uplink channel. In this paper we present a solution that greatly reduces the complexity of this task, and is even applicable for single antenna devices. Our approach uses a neural network trained on a standard channel model to generate coarse estimates for the variables underlying the channel. We then use a simple and efficient single antenna optimization framework to get more accurate variable estimates, which can be used for downlink channel prediction. We implement our approach on software defined radios and compare it to the state-of-the-art through experiments and simulations. Results show that our approach reduces the time complexity by at least an order of magnitude (10x), while maintaining similar prediction quality. [ABSTRACT FROM AUTHOR]

Full duplex techniques can potentially double the channel capacity and achieve lower delays by empowering two radios to simultaneously transmit in the same frequency band. However, full duplex is only available between two adjacent nodes within the communication range. In this paper, we present BiPass to break this limitation. With the help of full duplex capable relays, we enable simultaneous bidirectional in-band cut-through transmissions between two far apart nodes, so they can do full duplex communications as if they were within each other's transmission range. To design such a system, we analyze interference patterns and propose a loop-back interference cancellation strategy. We identify the power amplification problem at relay nodes and develop an algorithm to solve it. We also develop a routing algorithm, an opportunistic forwarding scheme, and a real-time feedback strategy to leverage this system in ad-hoc networks. To evaluate the real world performance of BiPass, we build a prototype and conduct experiments using software defined radios. We show that BiPass can achieve 1.6x median throughput gain over state-of-the-art one-way cut-through systems, and 4.09x gain over the decode-and-forward scheme. Our simulations further reveal that even when the data traffic is not bidirectional, BiPass has 1.36x throughput gain and 47% delay reduction over one-way cut-through systems in large networks. [ABSTRACT FROM AUTHOR]

To meet the growing demand for wireless data, it is time to move away from the age-old paradigm of prohibiting interfering nodes from transmissions. Instead, through proactive management of interference among multiple colliding packets, we can design high throughput wireless systems. This is well explored in the Information Theory community and there are also a few implementational efforts that have been recently reported. The existing solutions are non-trivial to use in real systems as they require either tight time/frequency synchronization or exchange of data between transmitters prior to the transmissions. These requirements are hard to meet in practice especially for uplink transmissions. This paper proposes BASIC, a lightweight multi-user uplink transmission strategy that does not require tight synchronization or exchange of samples among nodes, which makes it an attractive alternative compared to its counterparts. BASIC exploits receiver diversity by controlling the data rates of the clients. A novel greedy algorithm is proposed for data rate selection. We implement BASIC on a software-defined radio platform. Our experiments on a real testbed show that BASIC outperforms TDMA by 48% in terms of overall throughput. Our trace-driven simulations show up to 4.8x gain in throughput with similar ow fairness. [ABSTRACT FROM AUTHOR]

This paper describes the design and implementation of Air-Express, a system that enables in-band wireless cut-through transmission. Unlike wired cut-through, wireless cut-through can reduce latency and improve throughput performance of the network at the same time. In AirExpress, all the forwarders along the cut-through path forward the signal they received immediately without decoding. The hierarchical structure of AirExpress enables its interference cancellation ability to handle all kinds of interference among the radios. Novel MAC and routing algorithms based on cut-through transmission are also proposed to support the realization of AirExpress in multi-hop mesh networks. AirExpress is implemented on an NI-based SDR platform. Through experiments in the 2.4GHz ISM band, we show a throughput gain of up to 3.4 times with a 4-hop AirExpress system. Trace driven evaluation of AirExpress on the NS3 platform shows an average throughput gain of 2.85 for Air- Express over optimal TDMA. [ABSTRACT FROM AUTHOR]

Today's Enterprise Wireless LANs are comprised of densely deployed access points. This paper proposes BBN, an interference nulling scheme that leverages the high density of access points to enable multiple mobile devices to transmit simultaneously to multiple access points (APs), all within a single collision domain. BBN also leverages the capability of the APs to communicate with each other on the wired backbone to migrate most of the decoding complexity to the APs, while keeping the design at the mobile clients simple. Finally, we leverage the static nature of the access points to make BBN more practical in networks where the mobility of clients inhibit the use of traditional interference alignment schemes. We implement a prototype of BBN on USRP testbed showing its feasibility. The experiment results show that BBN provides a throughput gain of 1:48x over omniscient TDMA. Results from our trace-driven simulations show that BBN obtains a throughput of up to 5.6x over omniscient TDMA. [ABSTRACT FROM AUTHOR]

Existing secret key extraction techniques use quantization to map wireless channel amplitudes to secret bits. This paper shows that such techniques are highly prone to environment and local noise effects: They have very high mismatch rates between the two nodes that measure the channel between them. This paper advocates using the shape of the channel instead of the size (or amplitude) of the channel. It shows that this new paradigm shift is significantly robust against environmental and local noises. We refer to this shape-based technique as Puzzle. Implementation in a software-defined radio (SDR) platform demonstrates that Puzzle has a 63% reduction in bit mismatch rate than the state-of-art frequency domain approach (CSI-2bit). Experiments also show that unlike the state-of-the-art received signal strength (RSS)-based methods like ASBG, Puzzle is robust against an attack in which an eavesdropper can predict the secret bits using planned movements. [ABSTRACT FROM AUTHOR]

This paper explores if wireless cut-through is possible. Unlike wired cut-through, wireless cut-through, if realized, can reduce latency and improve throughput by upto 3x. This paper shows that one way to implement cut-through is for every node to forward the previously decoded packet while receiving the current packet. This strategy is called decode-and-forward (D&F). Another way is to have every node forward without decoding. This strategy is called amplify-and-forward (A&F). This paper shows that both D&F and A&F have many shortcomings. It proposes a new way to realize cut-through that reduces latency and increases throughput over traditional routing. This paper implements the first cut-through routing modules. Through multiple emulations of existing operational networks, it shows that cut-through switching can improve sum network throughput by up to 2.2x compared to traditional routing. [ABSTRACT FROM AUTHOR]

In this paper, we propose Symphony, a packet recovery architecture that encourages collisions among transmitters, and utilizes the unused capacity in the backbone to transmit recovered data packets and coordinate the efficient recovery of collided packets. Symphony improves the wireless throughput while incurring a low overhead on the typically under-utilized wired backbone. In Symphony, upon receiving the collided transmissions, the APs carefully suppress a subset of the transmissions. Realizing this idea in practice entails several challenges including identification of clients that have data to transmit and ensuring that the algorithm works despite imperfect time-synchronization and non-zero latency among APs. We present Symphony that addresses these challenges and show how it leverages Successive Interference Cancellation (SIC) to further increase the network throughput. Experiments performed on an USRP testbed shows that on an average, Symphony provides 43% and 187% higher throughput over Omniscient TDMA and IEEE 802.11, respectively. ns-3 based simulation results show that on an average, Symphony provides a throughput of up to 1.63x compared to omniscient TDMA and 5.6x compared to IEEE 802.11. [ABSTRACT FROM AUTHOR]

This paper presents a full duplex radio design using signal inversion and adaptive cancellation. Signal inversion uses a simple design based on a balanced/unbalanced (Balun) transformer. This new design, unlike prior work, supports wideband and high power systems. In theory, this new design has no limitation on bandwidth or power. In practice, using a channel sounder, we find that the signal inversion technique alone can cancel at least 45dB across a 40MHz bandwidth. Further, combining signal inversion cancellation with cancellation in the digital domain can reduce self-interference by up to 73dB for a 10MHz OFDM signal. This paper also presents a full duplex medium access control (MAC) design and evaluates it using a testbed of 5 prototype full duplex nodes. Full duplex reduces packet losses due to hidden terminals by up to 88%. Full duplex also mitigates unfair channel allocation in AP-based networks, increasing fairness from 0.85 to 0.98 while improving downlink throughput by 110% and uplink throughput by 15%. These experimental results show that a redesign of the wireless network stack to exploit full duplex capability can result in significant improvements in network performance. [ABSTRACT FROM AUTHOR]

This paper presents a full duplex radio design using signal inversion and adaptive cancellation. Signal inversion uses a simple design based on a balanced/unbalanced (Balun) transformer. This new design, unlike prior work, supports wideband and high power systems. In theory, this new design has no limitation on bandwidth or power. In practice, using a channel sounder, we find that the signal inversion technique alone can cancel at least 45dB across a 40MHz bandwidth. Further, combining signal inversion cancellation with cancellation in the digital domain can reduce self-interference by up to 73dB for a 10MHz OFDM signal. This paper also presents a full duplex medium access control (MAC) design and evaluates it using a testbed of 5 prototype full duplex nodes. Full duplex reduces packet losses due to hidden terminals by up to 88%. Full duplex also mitigates unfair channel allocation in AP-based networks, increasing fairness from 0.85 to 0.98 while improving downlink throughput by 110% and uplink throughput by 15%. These experimental results show that a redesign of the wireless network stack to exploit full duplex capability can result in significant improvements in network performance. [ABSTRACT FROM AUTHOR]

This paper explores metrics that capture to what degree packet reception on different links is correlated. Specifically, it explores metrics that shed light on when and why opportunistic routing and network coding protocols perform well (or badly). It presents a new metric, κ that, unlike existing widely used metrics, has no bias based on the packet reception ratios of links. This lack of bias makes κ a better predictor of performance of opportunistic routing and network coding protocols. Comparing Deluge and Rateless Deluge, Deluge's network coding counterpart, we find that κ can predict which of the two is best suited for a given environment. For example, irrespective of the packet reception ratios of the links, if the average κ of the link pairs is very high (close to 1.0), then using a protocol that does not code works better than using a network coding protocol. Measuring κ on several 802.15.4 and 802.11 testbeds, we find that it varies significantly across network topologies and link layers. κ can be a metric for quantifying what kind of a network is present and help decide which protocols to use for that network. [ABSTRACT FROM AUTHOR]

This paper discusses the design of a single channel full-duplex wireless transceiver. The design uses a combination of RF and baseband techniques to achieve full-duplexing with minimal effect on link reliability. Experiments on real nodes show the full-duplex prototype achieves median performance that is within 8% of an ideal full-duplexing system. This paper presents Antenna Cancellation, a novel technique for self-interference cancellation. In conjunction with existing RF interference cancellation and digital baseband interference cancellation, antenna cancellation achieves the amount of self-interference cancellation required for full-duplex operation. The paper also discusses potential MAC and network gains with full-duplexing. It suggests ways in which a full-duplex system can solve some important problems with existing wireless systems including hidden terminals, loss of throughput due to congestion, and large end-to-end delays. [ABSTRACT FROM AUTHOR]

This paper explores metrics that capture to what degree packet reception on different links is correlated. Specifically, it explores metrics that shed light on when and why opportunistic routing and network coding protocols perform well (or badly). It presents a new metric, ? that, unlike existing widely used metrics, has no bias based on the packet reception ratios of links. This lack of bias makes ? a better predictor of performance of opportunistic routing and network coding protocols. Comparing Deluge and Rateless Deluge, Deluge's network coding counterpart, we find that ? can predict which of the two is best suited for a given environment. For example, irrespective of the packet reception ratios of the links, if the average ? of the link pairs is very high (close to 1.0), then using a protocol that does not code works better than using a network coding protocol. Measuring ? on several 802.15.4 and 802.11 testbeds, we find that it varies significantly across network topologies and link layers. ? can be a metric for quantifying what kind of a network is present and help decide which protocols to use for that network. [ABSTRACT FROM AUTHOR]