In this paper, we present the design, implementation, and evaluation of the novel downlink Multi-User MIMO sounding protocol called MUTE. Our protocol decouples the sounding set selection used to collect Channel State Information (CSI), from the transmission set selection in order to minimize or even eliminate the overhead associated with sounding, while maximizing user selection performance. To this end, MUTE exploits channel statistics to all the different users to predict whether a particular user's channel will remain sufficiently stable, thereby allowing the access point to preclude channel sounding before a MU-MIMO transmission. We show that in indoor WLANs, MUTE can reduce sounding overhead by close to 73% under certain conditions while minimizing rate performance losses due to inaccurate channel estimation.

In this paper, we design, implement, and evaluate 802.11ec (Encoded Control), an 802.11-based protocol without control messages: Instead, 802.11ec employs correlatable symbol sequences that, together with the timing the codes are transmitted, encode all control information and change the fundamental design properties of the MAC. The use of correlatable symbol sequences provides two key advantages: 1) efficiency, as it permits a near order of magnitude reduction of the control time; 2) robustness, because codes are short and easily detectable even at low signal-to-interference-plus-noise ratio (SINR) and even while a neighbor is transmitting data. We implement 802.11ec on a field programmable gate array (FPGA)-based software defined radio. We perform a large number of experiments and show that, compared to 802.11 (with and without RTS/CTS), 802.11ec achieves a vast efficiency gain in conveying control information and resolves key throughput and fairness problems in the presence of hidden terminals, asymmetric topologies, and general multihop topologies.

In this paper, we design, implement and evaluate 802.11ec (Encoded Control), an 802.11-based protocol without control messages: instead, 802.11ec employs correlatable symbol sequences, which together with the timing the codes are transmitted, encode all control information and change the fundamental design properties of the MAC. The use of correlatable symbol sequences provides two key advantages: (i) efficiency, as it permits a near order of magnitude reduction of the control time; (ii) robustness, because codes are short and easily detectable even at low SINR and even while a neighbor is transmitting data. We implement 802.11ec on an FPGA-based software defined radio. We perform a large number of experiments and show that, compared to 802.11 (with and without RTS/CTS), 802.11ec achieves a vast efficiency gain in conveying control information and resolves key throughput and fairness problems in the presence of hidden terminals, asymmetric topologies, and general multi-hop topologies.

In 802.11 managed wireless networks, the manager can address underserved links by rate-limiting the conflicting nodes. In order to determine to what extent each conflicting node is responsible for the poor performance, the manager needs to understand the coordination among conflicting nodes' transmissions. In this paper, we present a management framework called Management, Inference, and Diagnostics using Activity Share (MIDAS). We introduce the concept of Activity Share, which characterizes the coordination among any set of network nodes in terms of the time they spend transmitting simultaneously. Unfortunately, the Activity Share cannot be locally measured by the nodes. Thus, MIDAS comprises an inference tool that, based on a combined physical, protocol, and statistical approach, infers the Activity Share by using a small set of passively collected, time-aggregate local channel measurements reported by the nodes. MIDAS uses the estimated Activity Share as the input of a simple model that predicts how limiting the transmission rate of any conflicting node would benefit the throughput of the underserved link. The model is based on the current network conditions, thus representing the first throughput model using online measurements. We implemented our tool on real hardware and deployed it on an indoor testbed. Our extensive validation combines testbed experiments and simulations. The results show that MIDAS infers the Activity Share with a mean relative error as low as 4% in testbed experiments.

The increase in WiFi physical layer transmission speeds from 1~Mbps to 1 Gbps has reduced transmission times for a 1500 byte packet from 12 ms to 12 us. However, WiFi MAC overheads such as channel access and acks have not seen similar reductions and cumulatively contribute about 150 us on average per packet. Thus, the efficiency of WiFi has deteriorated from over 80% at 1 Mbps to under 10% at 1 Gbps.

In 802.11 managed wireless networks, the manager can address under-served links by rate-limiting the conflicting nodes. In order to determine to what extent each conflicting node is responsible for the poor performance, the manager needs to understand the coordination among conflicting nodes' transmissions. In this paper, we present a management framework called MIDAS (Management, Inference, and Diagnostics using Activity Share). We introduce the concept of Activity Share which characterizes the coordination among any set of network nodes in terms of the time they spend transmitting simultaneously. Unfortunately, the Activity Share cannot be locally measured by the nodes. Thus, MIDAS comprises an inference tool which, based on a combined physical, protocol, and statistical approach, infers the Activity Share by using a small set of passively collected, time-aggregate local channel measurements reported by the nodes. MIDAS uses the estimated Activity Share as the input of a simple model that predicts how limiting the transmission rate of any conflicting node would benefit the throughput of the under-served link. The model is based on the current network conditions, thus representing the first throughput model using online measurements. We implemented our tool on real hardware and deployed it on an indoor testbed. Our extensive validation combines testbed experiments and simulations. The results show that MIDAS infers the Activity Share with an average normalized relative error below 12% in all testbed experiments.

Recent research activities have recognized the relevant role of k-hop clustering in Mobile Ad Hoc NETworks (MANET). k-hop clustering determination and maintenance is especially crucial to achieve scalability in large MANET scenarios, where a high number of mobile terminals dynamically build collaboration communities in ad hoc mod. Some first solutions have recently appeared in order to exploit k-hop clustering to effectively build an optimal backbone (crucial to achieve scalability) connecting all determined clusterheads in fixed ad hoc networks. However, few papers in the literature have addressed the innovative issue of evaluating how node mobility quantitatively affects the degradation of clustering quality as time passes by. To the best of our knowledge, the most relevant contribution is (Bettstetter and Krausser, 2001), where the stability of DMAC single-hop clustering is evaluated via ideal coarse-grained discrete-step simulations, by neglecting low-layer communication issues. Our paper significantly extends that contribution, (i) by focusing on k-hop clustering; (ii) by proposing a simple updating protocol to maintain clustering quality notwithstanding node mobility; (iii) by introducing a novel intuitive metric to evaluate the effects of mobility on clustering consistency; and (iv) by reporting a relevantly wider set of more realistic simulations based on ns2.

Several recent research activities have started to recognize the relevant role of k-hop clustering in Mobile Ad hoc NETworks (MANET) to effectively support many relevant tasks, e.g., packet routing and information dissemination at the network and application layer, respectively, k-hop clustering determination and maintenance is especially crucial to achieve good scalability in dense MANET scenarios, i.e., geographical areas with relatively high and almost constant density of mobile devices communicating in ad-hoc mode (such as in airport terminals, shopping malls, and university campuses), which are becoming of growing industrial relevance. The paper specifically addresses a primary aspect not yet widely investigated in the literature about k-hop clustering: how to exploit the k-hop clustering process also to effectively build an optimal backbone connecting all clusterheads identified by the process. We propose an original k-hop backbone formation protocol that, under the dense MANET assumption, outperforms other solutions in the literature especially in terms of imposed overhead, by exploiting highly localized intra-cluster interactions and by avoiding any kind of multi-hop broadcasts.

Underwater environment represents a challenging and promising application scenario for sensor networks. Due to hard constraints imposed by acoustic communications and to high power consumption of acoustic modems, in underwater sensor networks (USN) energy saving becomes even more critical than in traditional sensor networks. In this paper the authors propose delay-tolerant data dolphin (DDD), an approach to apply delay-tolerant networking in the resource-constrained underwater environment. DDD exploits the mobility of a small number of capable collector nodes (namely dolphins) to harvest information sensed by low power sensor devices, while saving sensor battery power. DDD avoids energy-expensive multi-hop relaying by requiring sensors to perform only one-hop transmissions when a dolphin is within their transmission range. The paper presents simulation results to evaluate the effectiveness of randomly moving dolphins for data collection.

In this paper we study multi-hop ad hoc routing in a Underwater Sensor Network (UWSN), a novel network paradigm for ad hoc underwater investigation with a large number of low cost underwater sensors. In UWSN, sensors are mobile with water current and dispersion, and use a wireless acoustic channel for communications. However, the large propagation latency and very low bandwidth of an acoustic channel could cause widespread collisions. Moreover, the mobility of sensors requires route management and causes additional traffic, thus worsening the situation. In this paper, we propose Under-Water Diffusion (UWD), a multi-hop ad hoc routing and in-network processing protocol. Since any on-demand flood or proactive exchange is considered harmful in underwater, UWD uses no proactive routing message exchange and negligible amount of ondemand floods in the environment with homogeneous GPSfree nodes and random node mobility. We validate UWD through both the mathematical analysis and simulations.

There is an emerging market interest in service provisioning over dense mobile ad-hoc networks (MANETs), i.e., limited spatial regions, such as shopping malls, airports, and university campuses, where a high number of mobile wireless peers can autonomously cooperate without exploiting statically deployed network infrastructures. We claim that it is possible to exploit the high node population of dense MANETs to simplify the replication of common interest resources, in order to increase availability notwithstanding unpredictable node exits from dense regions. To this purpose, we have developed the REDMAN middleware that supports the lightweight and dense MANET-specific management, dissemination and retrieval of replicas of data/service components. In particular, the paper focuses on the presentation of different solutions for replica retrieval and for dissemination of replica placement information. We have compared and quantitatively evaluated the presented solutions by considering their ability to retrieve available replicas and their communication overhead. The original SID solution has demonstrated to outperform the others in dense MANETs and has been integrated in the REDMAN prototype.

The increasing diffusion of wireless-enabled portable devices is pushing towards service provisioning over dense mobile ad-hoc networks (MANETs), i.e., in limited spatial regions, such as shopping malls, railway stations and airports, where a high number of mobile wireless peers autonomously cooperate, without the need for statically deployed network infrastructures. Dense MANET deployment scenarios can take advantage of high node population to replicate common-interest resources to increase their availability, by overcoming the unpredictable node exit from the dense region. The paper proposes a lightweight middleware, called REDMAN (replication in dense MANETs), to manage, retrieve and disseminate replicas of data/service components made available by cooperating nodes in a dense MANET. In particular, the paper focuses on the REDMAN original solutions to determine the nodes belonging to dense MANETs without exploiting any positioning system and also to elect dynamically a suitable replica manager node in charge of enforcing the desired resource replication degree in a lazy consistent way. Experimental results show that REDMAN solutions are lightweight and effective in dense MANET scenarios with almost constant node density and even high node mobility.