PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6An Energy-Efficient MAC Protocol for Wireless Sensor Networks (S-MAC) [Ye+ 2002](S-MAC) [Ye+ 2002]Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23MAC Protocols In Sensor NetworksMAC allows multiple users to share a common channel. MAC allows multiple users to share a common channel. Conflict-free protocolsConflict-free protocols ensure successful transmission. Channel can be ensure successful transmission. Channel can be allocated to users statically or dynamically.allocated to users statically or dynamically.Only static conflict-free protocols are used in cellular mobile communicationsOnly static conflict-free protocols are used in cellular mobile communications- - Frequency Division Multiple Access (FDMA): provides a fraction of the (FDMA): provides a fraction of the frequency range to each user for all the timefrequency range to each user for all the time- - Time Division Multiple Access (TDMA)(TDMA) : : The entire frequency band is The entire frequency band is allocated to a single user for a fraction of timeallocated to a single user for a fraction of time- - Code Division Multiple Access (CDMA) : provides every user a portion of (CDMA) : provides every user a portion of bandwidth for a fraction of timebandwidth for a fraction of timeContention based protocolsContention based protocols must prescribe ways to resolve conflicts must prescribe ways to resolve conflicts- Static Conflict Resolution: Carrier Sense Multiple Access (CSMA) - Static Conflict Resolution: Carrier Sense Multiple Access (CSMA) - Dynamic Conflict Resolution: the Ethernet, which keeps track of various - Dynamic Conflict Resolution: the Ethernet, which keeps track of various system parameters, ordering the users accordinglysystem parameters, ordering the users accordinglyMultiple Access Control (MAC) ProtocolsChannels are assigned to the user for the duration of a call. No other user Channels are assigned to the user for the duration of a call. No other user can access the channel during that time. When call terminates, the same can access the channel during that time. When call terminates, the same channel can be re-assigned to another userchannel can be re-assigned to another userFDMA is used in nearly all first generation mobile communication FDMA is used in nearly all first generation mobile communication systems, like AMPS (30 KHz channels)systems, like AMPS (30 KHz channels)Number of channels required to support a user population depends on Number of channels required to support a user population depends on the average number of calls generated, average duration of a call and the the average number of calls generated, average duration of a call and the required qualityrequired quality of service (e.g. percentage of blocked calls) of service (e.g. percentage of blocked calls)Channel 1Channel 1Channel 2Channel 2Channel 3Channel 3Channel 4Channel 4BandwidthBandwidthTimeTimeFrequency Division Multiple Access (FDMA)The whole channel is assigned to each user, but the users are The whole channel is assigned to each user, but the users are multiplexed in time during communication. Each communicating user multiplexed in time during communication. Each communicating user is assigned a particular time slot, during which it communicates using is assigned a particular time slot, during which it communicates using the entire frequency spectrumthe entire frequency spectrumThe data rate of the channel is the sum of the data rates of all the The data rate of the channel is the sum of the data rates of all the multiplexed transmissionsmultiplexed transmissionsThere is always channel interference between transmission in two There is always channel interference between transmission in two adjacent slots because transmissions tend to overlap in time. This adjacent slots because transmissions tend to overlap in time. This interference limits the number of users that can share the channelinterference limits the number of users that can share the channelTimeTimeChannel 1Channel 1BandwidthBandwidthChannel 2Channel 2Channel 3Channel 3Channel 4Channel 4Channel 1Channel 1Channel 2Channel 2Channel 3Channel 3Time Division Multiple Access (TDMA)CDMA, a type of a CDMA, a type of a spread-spectrumspread-spectrum technique, allows multiple users to technique, allows multiple users to share the same channel by multiplexing their transmissions in code space. share the same channel by multiplexing their transmissions in code space. Different signals from different users are encoded by different codes Different signals from different users are encoded by different codes (keys) and coexist both in time and frequency domains(keys) and coexist both in time and frequency domainsA code is represented by a wideband pseudo noise (PN) signalA code is represented by a wideband pseudo noise (PN) signalWhen decoding a transmitted signal at the receiver, because of low cross-When decoding a transmitted signal at the receiver, because of low cross-correlation of different codes, other transmissions appear as noise. This correlation of different codes, other transmissions appear as noise. This property enables the multiplexing of a number of transmissions on the property enables the multiplexing of a number of transmissions on the same channel with minimal interferencesame channel with minimal interferenceThe maximum allowable interference (from other transmissions) limits the The maximum allowable interference (from other transmissions) limits the number of simultaneous transmissions on the same channelnumber of simultaneous transmissions on the same channelAll channels share bandwidthAll channels share bandwidthBandwidthBandwidthTimeTimeCode Division Multiple Access (CDMA)Spreading of the signal bandwidth can be performed usingSpreading of the signal bandwidth can be performed using- - Direct SequenceDirect Sequence (DS): the narrow band signal representing digital data (DS): the narrow band signal representing digital data is multiplied by a wideband pseudo noise (PN) signal representing the is multiplied by a wideband pseudo noise (PN) signal representing the code. Multiplication in the time domain translates to convolution in the code. Multiplication in the time domain translates to convolution in the spectral domain. Thus the resulting signal is widebandspectral