In Network Processing and Data Aggregation in

More documents

Recommendations

Info

Proposes a bottom (physical layer)–up (application layer) approach in thedevelopment of a protocol for a wireless sensor network. Application, MAC and physicallayers have to be tightly integrated with the hardware of the sensor node. For example theenergy penalties of switching states or the consumed power at each state of a transceiver,might determine the policy of the MAC layer scheme or even affect the network layerrouting algorithm. Multiple access schemes (Time Division Multiple Access, FrequencyDivision Multiple Access) are compared and the same is also done for modulationschemes (binary, M-ary modulation). It is found that a hybrid TDMA-FDMA scheme andthe M-ary modulation scheme achieve significant power savings. Another energyexpensive factor is the frequent turning on/off of the transceiver of a node because thecontrol input spends not negligible time on setting the right voltage to the transceiver(start-up energy). All the previous notes show that layer-1 has not to be considered as ablack box when designing an upper level protocol or even an application for a WSN.2.2 Data Link Layer (MAC)2.2.1 Medium Access Control (MAC) functionalityAbove the Physical Layer (Layer-1) resides the Data Link Layer (Layer-2). Havingonly the tools that are provided by the layer 1 in means of services, the link layer isresponsible for the transmission of data packets between two communicating nodes. Thecommunication pattern may be point-to-point or even point-to-multipoint. Nevertheless,this function is not as simple as it sounds. There are several services that the link layermay offer to the upper layers like:• medium access,• packet encapsulation in link-layer frames and data frame detection,• flow control,• error detection/correction,• data stream multiplexing and• reliable communication mode.
Medium access functionality is so important that it constitutes an individual sub-layer,the Medium Access Control sub-layer, widely known as MAC. In order to understand themajor importance of the MAC sub-layer, its primary functions are indicated below :• medium access control before transmitting,• bit-stream fragmentation into frames upon reception,• level-2 frame encapsulation before transmission,• insertion of checksums for error detection,• insertion of the source-destination MAC addresses inside all transmitting framesand• frame filtering by checking the destination MAC address of the packet.For the rest of this section, we will be concerned for the medium access problem.2.2.2 MAC issues for wireless communicationsBefore analyzing the MAC sub-layer issues from the perspective of the WSNs, it isuseful to review the main problems that a general purpose wireless network faces.Wireless (radio, infrared, optical) medium has to be tightly controlled since it has abroadcasting nature. When a host transmits, the nodes inside its transmission range willlisten to it, the nodes inside its detection range will just detect its signal and finally thenodes within its interference range will receive a vague and confusing signal. When twoor more nodes within the same “neighborhood” transmit packets at the same time, thenearby nodes that listen to these transmissions will get a confusing mixed signal andfinally they will discard the received packets. This phenomenon is called collision andresults in the loss of all the transmitted packets. When a collision occurs, the senders haveto retransmit their data.The need for a mechanism that will play the role of the traffic controller is imperative.This mechanism must give everyone the opportunity to talk, prevent the monopolizationof the conversation by a single participant and guarantee that no one can interrupt the
Page 1: Athens University of Economics and
Page 4 and 5: 1 IntroductionRecently, the technol
Page 7 and 8: Thus, in-network processing is one
Page 11 and 12: The following figure (Figure 4) vis
Page 13: 2.1.3 Proposed schemesSeveral syste
Page 17 and 18: encodes the data before transmissio
Page 19 and 20: o CSMA/CA - Is also an extension of
Page 21: made a discussion over the issues t
Page 24 and 25: amount of noise to the channel for
Page 27 and 28: wild animals are monitored inside a
Page 29 and 30: than the whole network (GAF, GEAR).
Page 31 and 32: In the data-centric approach we ass
Page 33 and 34: 3 Data Aggregation in WSNs3.1 Gener
Page 35 and 36: 2. Less packet collisions.Packet co
Page 37 and 38: Exemplary aggregates, on the other
Page 39 and 40: consumes more energy than the initi
Page 41 and 42: Tree. To be more specific, as the q
Page 43 and 44: a) Sensors that heard aggregate req
Page 45 and 46: of communication failures because e
Page 47 and 48: function SE() to translate its loca
Page 49 and 50: Benefits1. It is a completely distr
Page 51 and 52: application can tolerate big estima
Page 53 and 54: REFERENCES[1] W. Ye, J. Heidemann,

In Network Processing and Data Aggregation in

Create successful ePaper yourself

Delete template?

Save as template?