Self-deployment describes the task of spreading an autonomously moving swarm of mobile robots over a given area. All these robots have to move to locations such that the set of robot locations satisfies a desired property. In this work, we describe a fully distributed deployment algorithm executed locally at each robot. The approach requires only few local information per node: the distances and very coarse angular information to immediate neighbors. It has been developed for use on small robots with very restricted memory, communication, and processing capabilities. In this paper, we specify the algorithm and evaluate it in an empirical study. This includes both simulation studies and real test bed experiments. For the test bed, we consider two different platforms: ground moving robots and aerial robots. The results of our simulations show that our local deployment rules achieve almost globally optimal results. The test bed study supports and substantiates our simulation study and shows as a proof of concept that our algorithm works both with real ground based and aerial based robot swarms.

Present broadcast approaches for wireless multihop networks distribute packets quickly to all nodes (i.e., with low latency) by constructing small broadcast trees, thereby reducing the number of forwarding transmissions. While these trees are sufficient in non-fading environments, we show that they have a low delivery rate under fading. As a solution, we (1) incorporate the Rayleigh fading model directly into tree construction to re-obtain complete distribution with high probability. To still achieve low latency at the same time, we combine transmissions at individual nodes to exploit cooperation diversity. Since in broadcasts, a packet has to be retransmitted by nodes along the tree anyway, we do not have to pay the multiplexing loss which hampers cooperation diversity in the unicast case. Thus, we (2) additionally exploit cooperation diversity during tree construction to gain improved reliability while still keeping the size of the tree low. This enables us to significantly decrease the time for broadcasts while still distributing packets to all nodes under fading with high probability. To justify our heuristic approach, we (3) show that finding minimum latency cooperative broadcasts is NP-complete.

Rate adaptation based on signal-to-noise ratio (SNR) measurements is a common channel adaptation scheme to increase throughput in wireless communication systems. To use rate adaptation efficiently in cooperative wireless networks, an adaptation algorithm must consider multiple channels (source- destination, source-relays, and relays-destination) to select modulation and code rates that maximize throughput. In this paper we analyze the potential gains that combining cooperation with rate adaptation brings in three steps: (1) We derive the theoretical capacity bounds for ideal rate adaptation schemes for typical topologies. (2) We propose an offline heuristic for computing SNR thresholds aimed at reaching the derived bounds. (3) Using this heuristic, we compare rate adaptation for maximal ratio combining (MRC), where links are equally adapted, with soft-bit MRC (SBMRC), where links are individually adapted. We find that adapting the rate per link is superior in terms of throughput.

Interference limits throughput in wireless networks. To protect themselves against interference, many wireless protocols create areas around receivers in which no node is allowed to transmit. If such an exclusion area is small, more transmissions can proceed simultaneously but observe higher interference, creating a tradeoff between network capacity and link capacity.

Cooperative relaying has been shown to provide diversity gains which can significantly improve the packet error rate (PER) in wireless transmissions. In ad hoc wireless routing where packets may travel over a number of hops before reaching the destination, hop-wise cooperative relaying may severely reduce network capacity. This approach was mainly addressed in literature so far. In this paper, we efficiently apply cooperative relaying along a complete path and over multiple hops at the same time. We use information from the routing layer to improve the medium access control (MAC) layer's performance. Simulations and testbed implementation show appealing gains through diversity resulting in up to 66% better PER performance and up to 148% goodput increase compared to conventional approaches.

Opportunistic Relaying (OR) and Selection Decode-and-Forward (SDF) cooperation protocols can both substantially improve the performance of wireless networks but fundamentally differ in utilized redundancy, relays, and channel knowledge. To analyze when SDF or OR improves error and data rate, we (1) derive their general outage probability and capacity for arbitrary relay configurations, (2) systematically benchmark both approaches in two-hop configurations, (3) study how often beneficial configurations occur in large networks, and, finally, condition our capacity results by this occurrence probability. Our results clearly show that OR maximizes the outage capacity at high acceptable error rate while SDF succeeds if a low error rate is required. SDF performs best if even the relays can cooperate among themselves, supported frequently in networks with more than three neighbors. Consequently, cooperating relays, adapting between OR and SDF, and joining these two approaches should be the focus of future protocol design. To this end, our paper provides a theoretical basis, adaptation rules, and design guidelines.

In this paper a cooperative retransmission scheme for 802.11 WLANs is proposed. The mechanism allows stations with good channel to the access point to retransmit packets on behalf of other stations with worse channel. The cooperative partner selection is carried out in a completely opportunistic and distributed way that is compatible with 802.11. Simulations performed in a realistic WLAN scenario with adaptive modulation show that the system provides considerable gains in terms of goodput and packet error rate in comparison with legacy 802.11.

We propose a practical medium access control (MAC) protocol and transceiver design for mobile cooperative WLANs. Our MAC protocol integrates selection decode-and-forward (SDF) cooperative relaying into IEEE 802.11. Unlike previous approaches, its cooperative signaling cycle allows communication if the direct link fails even for small signaling frames. Further SDF functions are efficiently supported by our ready- to-use transceiver design. We implement this design, including our MAC protocol, on a software defined radio (SDR) resulting in a cooperative IEEE 802.11g prototype. Using this prototype, we validate feasibility and performance of our approaches by extensive field measurements in indoor and railroad scenarios with an actual train moving the cooperating terminals.