In wireless networks without nodes equipped with multiple antennas, cooperative Multiple Input Multiple Output (MIMO) transmissions may be used to harness diversity gains. In general, diversity gains are larger if more nodes are involved in the transmission. However, a transmission policy that maximizes the diversity gain or throughput need not maximize the stability region, since queues at the nodes may grow while waiting for a sufficient number of nodes to become available. To address this issue, this paper develops a mechanism for maximizing the throughput while reducing the energy consumption and maintaining queue stability. We develop a sufficient condition that ensures the throughput optimality of a stable transmission policy and then use it to design a distributed, dynamic threshold based Medium Access Control (MAC) protocol for cooperative MIMO transmissions. The MAC protocol requires only limited local information for its operation. Simulation results are provided to evaluate the performance of the proposed protocol and compare it against regular point-to-point and existing cooperative MIMO MAC protocols. The results show that the proposed scheme can provide considerable gains in the throughput and energy savings compared to cooperative MIMO based on fixed number of cooperating nodes.

While decentralized medium access control (MAC) protocols are more popular in wireless environments, cluster based sensor networks are particularly amenable to centralized, polling based protocols. In this paper we present an analytic model to evaluate the performance of polling based MAC protocols for wireless networks in terms of the packet delay, buffer overflow rates and energy consumption. We show that polling based protocols can outperform popular decentralized MAC protocols. Simulation results are presented to validate our model and conclusions.

This paper develops a distributed, threshold based MAC protocol for cooperative multi input multi output (MIMO) transmissions in distributed wireless systems. The protocol uses a thresholding scheme that is updated dynamically based on the queue length at the sending node to achieve low power transmissions while ensuring stability of the transmission queues at the nodes. Simulation results are provided to evaluate the performance of the proposed protocol and compare it against regular point to point as well as fixed group size cooperative MIMO MAC protocols.

This paper investigates the performance of IEEE 802.11 in multi-hop scenarios and shows how its aggressive behavior can throttle the spatial reuse and reduce bandwidth efficiency. An adaptive, layer-2, distributed coordination scheme for 802.11 using explicit medium access control (MAC) feedback is then proposed to pace the transmissions on adjacent nodes, thereby assisting the MAC protocol to operate around its saturation state while minimizing resource contention. Simulation results show that the proposed scheme outperforms the original 802.11 MAC.

In this paper we propose a distributed system for facilitating cooperative MIMO transmissions in networks without multiple antenna devices. MIMO diversity is achieved by employing groups of nodes in the vicinity of the source and destination to help with the transmission. The distributed sending nodes are assumed to have different carrier frequency offsets (CFO). Space-time block codes (STBC) and code combining are used to utilize spatial diversity. The estimation of multiple CFO and detector for STBC-coded data under multiple CFO are provided. The BER of the proposed system is shown and discussed. We also consider the energy consumption and compare it with other cooperative designs.

Underwater acoustic sensor networks face unique challenges in the design and development of communication and network protocols, because of the inherently different characteristics of water as a medium for signal propagation. In the mobile sink architecture, a mobile sink that traverses the network to transfer non delay-sensitive data from the sensors directly and avoid multi-hop transmissions. An area partitioning algorithm is proposed in this paper to divide the network in regions to minimize the traveling distance of the sink and the formation of clusters that maximize the throughput. A transmission mechanism based on superposition coding is developed to increase the throughput of downlink control messages to the sensors. Finally, a MAC protocol is developed to facilitate the transmissions.

Cooperative MIMO can achieve higher energy savings and lower delays in distributed systems by allowing nodes to transmit and receive information jointly. In this paper, we develop a new MAC protocol for enabling packet transmissions using cooperative MIMO. The paper also develops analytical models for evaluating the packet error probability, energy consumption and packet delays associated with the proposed MAC protocol. The analysis is validated against simulation results using the NS- 2 simulator. Our results show that the proposed MAC protocol has lower delays and lower energy consumption as compared to regular point to point MAC protocols.

In sensor networks, MAC protocols based on time division multiple access (TDMA) with wakeup and sleep periods have attracted considerable interest because of their low power consumption and collision free operation. In this paper, we develop analytic models to evaluate the performance of such protocols. The model presented in this paper characterizes the queueing delays associated with the MAC layer as well as the energy consumed at MAC layer, by modeling the system as a queue with general service time distribution with both polling and vacations. The analysis is validated by comparison with simulation results using the NS-2 simulator. Our results show that polling based TDMA with sleep and wakeup cycles has lower delays and lower energy consumption as compared to SMAC.

LEACH (low energy adaptive clustering hierarchy) (W. Heinzelman et al., 2000) is one of the popular cluster-based structures, which has been widely proposed in wireless sensor networks. LEACH uses a TDMA based MAC protocol, and in order to maintain a balanced energy consumption, suggests that each node probabilistically become a cluster head. To reduce the energy consumption and to avoid the strict synchronization requirements of TDMA, we first apply a sleep-wakeup based decentralized MAC protocol to LEACH, then we present an analytic framework for obtaining the optimal probability with which a node becomes a cluster head in order to minimize the network's energy consumption. The analysis is first presented for small networks, under the assumption of identical expected distance of all cluster heads from the sink. Then the analysis is extended for large networks to consider the case when the distances of various sections of the network from the sink may be different, since nodes further away have to spend greater energy in order to reach the sink. Our simulation results show that using this optimal probability results in much more efficient energy consumption and compared with the current LEACH, our proposal consumes significantly less power.