Molecular networks have the potential to enable bio-implants and biological nano-machines to communicate inside the human body. Molecular networks send and receive data between nodes by releasing molecules into the bloodstream. In this work, we explore how we can scale molecular networks from a single transmitter single receiver paradigm to multiple transmitters that can concurrently send data to a receiver. We identify unique challenges in enabling multiple access in molecular networks that prevent us from using standard multiple access protocols. These challenges include the lack of synchronization and feedback, the non-negativity of molecular signals, the extremely long tail of the molecular channel leading to high ISI (Inter-Symbol-Interference), and the limited types of molecules that can be used for communication. We present MoMA (Molecular Multiple Access), a protocol that enables a molecular network with multiple transmitters. We introduce packet detection, channel estimation, and encoding/decoding schemes that leverage the unique properties of molecular networks to address the above challenges. We evaluate MoMA on a synthetic experimental testbed and demonstrate that it can scale up to four transmitters while significantly outperforming the state-of-the-art.

In order to meet the capacity needs of LoRa networks, Adaptive Data Rate (ADR) has been proposed and implemented in LoRaWANs. The network server running ADR determines the optimum data-rate and hence spreading factor setting for each LoRa device in a network. This in turn requires the gateway to be capable of receiving all possible spreading factors. Existing gateways achieve this by using multiple RF front ends, increasing their overall cost and complexity. In this work, we propose a Discrete Wavelet Transform based spreading factor detection algorithm that is agnostic to transmitter settings. This computationally light-weight algorithm can be implemented on any off-the-shelf SDR, bringing down the cost and ease of LoRaWAN gateway implementations. Using experimental, real-world datasets, we show that the proposed algorithm can detect the spreading factor of over 99.5% of the received packets at SNRs down to -10dB.

Wireless communication over long distances has become the bottleneck for battery-powered, large-scale deployments. Low-power protocols like Zigbee and Bluetooth Low Energy have limited communication range, whereas long-range communication strategies like cellular and satellite networks are power-hungry. Technologies that use narrow-band communication like LoRa, SigFox, and NB-IoT have low spectral efficiency, leading to scalability issues. The goal of this work is to develop a communication framework that is energy efficient, long-range, and scalable. We propose, design, and prototype WiChronos, a communication paradigm that encodes information in the time interval between two narrowband symbols to drastically reduce the energy consumption in a wide area network with large number of senders. We leverage the low data-rate and relaxed latency requirements of such applications to achieve the desired features identified above. We design and implement chirp spread spectrum transmitter and receiver using off-the-shelf components to send the narrowband symbols. Based on our prototype, WiChronos achieves an impressive 60% improvement in battery life compared to state-of-the-art LPWAN technologies in transmission of payloads less than 10 bytes at experimentally verified distances of over 4 km. We also show that more than 1,000 WiChronos senders can co-exist with less than 5% collision probability under low traffic conditions.

LoRa has seen widespread adoption as a long range IoT technology. As the number of LoRa deployments grow, packet collisions undermine its overall network throughput. In this paper, we propose a novel interference cancellation technique -- Concurrent Interference Cancellation (CIC), that enables concurrent decoding of multiple collided LoRa packets. CIC fundamentally differs from existing approaches as it demodulates symbols by canceling out all other interfering symbols. It achieves this cancellation by carefully selecting a set of sub-symbols -- pieces of the original symbol such that no interfering symbol is common across all sub-symbols in this set. Thus, after demodulating each sub-symbol, an intersection across their spectra cancels out all the interfering symbols. Through LoRa deployments using COTS devices, we demonstrate that CIC can increase the network capacity of standard LoRa by up to 10x and up to 4x over the state-of-the-art research. While beneficial across all scenarios, CIC has even more significant benefits under low SNR conditions that are common to LoRa deployments, in which prior approaches appear to perform quite poorly.

Wireless communication over long distances has become the bottleneck for battery-powered, large-scale deployments. Currently used low-power protocols such as Zigbee and Bluetooth Low Energy have limited communication range, whereas long-range communication strategies used in cellular and satellite networks are heavy on energy consumption. Methods that use narrow-band communication such as LoRa, SigFox, and NB-IoT have low spectral efficiency, leading to scalability issues. The goal of this work is to develop a communication framework that can satisfy the following requirements: (1) Increased battery life, (2) Longer communication range, (3) Scalability in a wireless network. In this work, we propose, design, and prototype WiChronos, a communication paradigm that encodes information in the time interval between two narrowband symbols in order to drastically reduce the energy consumption in a wide area network with a large number of senders. We leverage the low data-rate and relaxed latency requirements of such applications to achieve the desired features identified above. Based on our prototype using off-the-shelf components, WiChronos achieves an impressive 60% improvement in battery life compared to state-of-the-art LPWAN technologies at distances of over 800 meters. We also show that more than 1000 WiChronos senders can co-exist with less than 5% probability of collisions under low traffic conditions.

Power efficient wireless communication has become a bottleneck for long range and large scale deployments. We propose and prototype WiChronos, an energy efficient modulation technique for long range wireless communication in a large scale network. Using off-the-shelf (OTS) components, we demonstrate that WiChronos achieves an impressive 60% improvement in battery life compared to state-of-the-art LPWAN technologies at distances over 800 meters. We also show that more than 1000 WiChronos senders co-exist with less than 5% probability of collisions in low traffic conditions.

The ubiquitous adoption of WiFi implicitly introduces large diversity in types of application requirements and topological characteristics. Consequently, considerable attention is being devoted to making WiFi networks controllable without compromising their scalability. Within this broad paradigm, we propose Rhythm, a MAC protocol that achieves scheduled WiFi efficiently and that is subject to the following constraints: (i) It does not need fine-grained time synchronization, (ii) it adds no "active listening" time, (iii) it does not need to gather the queue status from clients, and (iv) it requires no additional hardware. It also has the following properties: (i) low overhead, (ii) work conservation, (iii) robustness to partial connectivity, and (iv) backward compatibility.

In this work we consider nano-scale communication using bacterial populations as transceivers. We demonstrate using a microfluidic test-bed and a population of genetically engineered Escherichia coli bacteria serving as the communication receiver that a simple modulation like on-off keying (OOK) is indeed achievable, but suffers from very poor data-rates. We explore an alternative communication strategy called time elapse communication (TEC) that uses the time period between signals to encode information. We identify the severe limitations of TEC under practical non-zero error conditions in the target environment, and propose an advanced communication strategy called smart time elapse communication (TEC-SMART) that achieves over a 10× improvement in data-rate over OOK.

Bacterial populations housed in microfluidic environments can serve as transceivers for molecular communication, but the data-rates are extremely low (e.g., 10-5bits per second.). In this work, genetically engineered Escherichia coli bacteria were maintained in a microfluidic device where their response to a chemical stimulus was examined over time. The bacteria serve as a communication receiver where a simple modulation such as on-off keying (OOK) is achievable, although it suffers from very poor data-rates. We explore an alternative communication strategy called time-elapse communication (TEC) that uses the time period between signals to encode information. We identify the limitations of TEC under practical non-zero error conditions and propose an advanced communication strategy called smart time-elapse communication (TEC-SMART) that achieves over a 10x improvement in data-rate over OOK. We derive the capacity of TEC and provide a theoretical maximum data-rate that can be achieved.