Conclusiones sobre las distancias biológicas intra e intermuestrales:

Another direction in manipulating the behavior of the wireless interface is through the usage of routing information. The main idea behind this is to enable wireless hosts to determine their position within the network. At the same time, routing topology is used to study potential interferences among wireless hosts. This information can be wisely used to achieve efficient utilization of bandwidth resources through allowing simultaneous communication between non-interfering hosts.

which mobile host should occupy a time slot. Fig.2.9 illustrates how PEDAMACS learns the topology from the network layer, and schedules the sleep time slots for nodes to construct an energy efficient route. The first phase of this protocol is to construct a routing tree at the access point by broadcasting topology learning packets. Knowing the network topology, the access point determines when a host will be able to use a particular slot, and the schedule will be broadcast to other hosts.

Figure 2.9: PEDAMACS: Joint Routing and MAC Layer Sleep Scheduling.

Other solutions allow mobile hosts to gain information about their position in order to perform self-scheduling. TDMA-based protocol presented in [71] assumes a small number of wireless hosts rooted at the sink. Topology awareness could be acquired and the interference patterns among neighboring hosts could be known and controlled. In this scheme, time is divided into epochs, and each host has K slots in an epoch for the purpose of retransmission. A packet is retransmitted for K times at most if not successfully acknowledged by the receiver, thus the delay is controlled and does no exceed the duration of an epoch. Energy efficiency is achieved by assigning different duty cycles for each host according to their position in the predetermined data gather- ing tree. Routing information is required by each host to construct the data gathering tree.

D-MAC [72] includes a mechanism that builds a data gathering tree which de- scribes the depth of a host within a set of multi-hop paths. An offset is specified as U, and any hosts that resides at the depth of N in the tree will wake up U time units ahead of the destination, which is the top host of the tree. In this case, every host is assigned

its own time slot, and the next hop of a path will be able to wake up after the previous hop’s host wakes up and sends out the packets. This protocol efficiently saves energy by letting only the hosts on the path wake up, and it also helps reduce packet delay by letting hosts waking up sequentially. However, collisions may still occur when differ- ent branches of the same host try to send packets at the same time although a back off scheme is included in this protocol.

In the scheme proposed in [73], each host wakes up when it is time for it to sense the environment and when it expects packets from neighbouring hosts, which means it has to route the packets to the next host. To be specific, if there is a route starting from host A to host C via host B, host A samples and transmits a packet, both of which processes take 5ms, then host B has to wake up 10ms later when host A starts to transmit.

Wu et al. [74] proposed to organize a tree of sensor hosts, which allows data aggregation to be performed along the tree structure in a more energy efficient man- ner than normal tree structure. Furthermore, from the viewpoint of the MAC layer, sensors consume different energy in different states and during state transitions. This mechanism ensures every host has to wake up only two times in one scheduling period for receiving data from the children and sending data to the parent in order to reduce the frequency of state transition which causes energy waste. This enhanced wake-up scheduling mechanism with the energy efficient data aggregation tree achieves better energy efficiency.

Some joint protocols utilize information from network layer within MAC proto- cols, while others are intelligent routing protocols which adjust routes dynamically according to host schedules in order to avoid sleeping hosts along the path and de- crease end-to-end delay.

Bernardos et al. [75] introduces a TDMA communication scheme allowing neigh- bor hosts to cooperatively find required communication time slots and avoid redundant

message exchange. In this manner, mobile hosts will schedule their wake up time ac- cording to predetermined timetables and transmit packets to the neighbours only if both parties are awake prolonging the sleep time. Based on hosts wake up schedules, this routing solution carefully selects the precise path from the source to the destina- tion that includes as many hops as possible in one time frame, so mobile hosts do not have to wait too long before each of them forwards the packets to the next hop in order to achieve shorter delay.