ECE 4331, Fall, 2009OutlineMultiple AccessWireless System Architecture and FunctionsMedium Access ControlWireless Media Access ControlDuplexingSlide 8Duplexing - FDDDuplexing - TDDDuplexing – TDD versus FDDMultiple Access - CoordinatedNarrow- and Wideband SystemsSlide 14Cellular Systems and MACFrequency Division Multiple AccessFeatures of FDMACapacity of FDMA SystemsTime Division Multiple AccessTDMA ConceptTDMA FramesGeneral Frame and Time Slot Structure in TDMA SystemsA TDMA FrameEfficiency of a Frame/TDMA-SystemTDMAContemporary TDMA SystemsFeatures of TDMACapacity of TDMA SystemsSpread Spectrum AccessFrequency Hopping (FHMA)Capacity of CDMA SystemsSlide 32Case Study - BluetoothCase Study: Bluetooth – Piconet and FHSSCase Study: Bluetooth – Scatternet and FHSSCase Study: Bluetooth - Media access in a piconet802.11ChannelChannelization schemeSlide 40Wireless hotpot plannerDesign ProcedureFuture WIFISignal to Noise Ratio at homeFail of Iridium Satellite SystemECE 4331, Fall, 2009Zhu HanDepartment of Electrical and Computer EngineeringClass 26Nov. 19th, 2009OutlineOutlineTerm paper, only journal. For those who did not give me the title on time, I think you would not work for the term project, right?  General Wireless System ArchitectureMedia Access Control–Classes of MAC protocols–Simplex and Duplex ChannelsCoordinated MAC Schemes–FDMA–TDMACapacity of TDMA systems and which factors affect the capacity.–Spread Spectrum Access MethodsFHMACase study: BluetoothCDMAHybrid Spread Spectrum Schemes. Case StudyMultiple AccessMultiple AccessHow can we share a wireless channel: –Results in Wireless Media Access Control ProtocolsHow we can change base stations: Results in Handoff algorithms and protocolsHow can we seamlessly support mobile applications over wireless links: –Results in mobility protocols like Mobile IP, Cellular IP, etc. How can we design efficient transport protocols over wireless links: –Results in solutions like SNOOP, I-TCP, M-TCP, etc. How different wireless networks/systems are designed? –Bluetooth, IEEE 802.11, GSM, etc.Wireless System Architecture and FunctionsWireless System Architecture and FunctionsPhysical RadioTransceiverFrame ControllerLink ControllerWireless Subnet ControllerTCP/IPCarrier frequency, channel bandwidth, carrier detect, Captude detect, channel data rate, modulation,Received signal strength (RSSI), transmit power, Power control, …Framing and frame synchronization, error control, CRC, bit scrambling, widening, ….Medium Access Control, MAC level Scheduling, Link Layer Queueing, Link Layer Reliability – ACKs, NACKs, ….Neighbor Discovery and Registration,Multicasting, Power Saving Modes, AddressTranslation (IP-MAC), Routing, Quality of Services,Subnet Security Wireless Link Layer(Layers 1 and 2 in ISO/OSI Network Reference Model)ApplicationsMedium Access ControlMedium Access ControlWireless spectrum (frequency band) is a very precious and limited resource. –We need to use this resource very efficientlyWe also want our wireless system to have high user capacity–A lot of (multiple) users should be able to use the system at the same time.For these reasons most of the time, multiple users (or stations, computers, devices) need to share the wireless channel that is allocated and used by a system. –The algorithms and protocols that enables this sharing by multiple users and controls/coordinates the access to the wireless channel (medium) from different users are called MEDIUM ACCESS, or MEDIA ACCESS or MULTIPLE ACCESS protocols, techniques, schemes, etc…)Wireless Media Access ControlWireless Media Access ControlRandom Schemes (Less-Coordinated)–Examples: MACA, MACAW, Aloha, 802.11 MAC,… –More suited for wireless networks that are designed to carry data: IEEE 802.11 Wireless LANsCoordinated Schemes–Examples: TDMA, FDMA, CDMA–More suited for wireless networks that are designed to carry voice: GSM, AMPS, IS-95,…Polling based Schemes–Examples: Bluetooth, BlueSky,…–Access is coordinated by a central node–Suitable for Systems that wants low-power, aims to carry voice and data at the same time.DuplexingDuplexingIt is sharing the media between two parties. If the communication between two parties is one way, the it is called simplex communication.If the communication between two parties is two- way, then it is called duplex communication.Simplex communication is achieved by default by using a single wireless channel (frequency band) to transmit from sender to receiver. Duplex communication achieved by: –Time Division (TDD)–Frequency Division (FDD)–Some other method like a random access methodDuplexingDuplexingUsually the two parties that want to communication in a duplex manner (both send and receive) are: –A mobile station –A base stationTwo famous methods for duplexing in cellular systems are: –TDD: Time Division Duplex–FDD: Frequency Division DuplexDuplexing - FDDDuplexing - FDDA duplex channel consists of two simplex channel with different carrier frequencies–Forward band: carries traffic from base to mobile–Reverse band: carries traffic from mobile to baseReverse ChannelForward Channelfrequencyfc,Rfc,,FFrequency separationFrequency separation should be carefully decidedFrequency separation is constantBMFRBase StationMobileStationDuplexing - TDDDuplexing - TDDA single radio channel (carrier frequency) is shared in time in a deterministic manner. –The time is slotted with fixed slot length (sec)–Some slots are used for forward channel (traffic from base to mobile)–Some slots are used for reverse channel (traffic from mobile to base)BMBase StationMobileStationF R R R R 0 1 2 3 4 5 6 7 … ….Reverse ChannelForward ChanneltimeTiTime separationTi+1channelSlot numberF F FDuplexing – TDD versus FDDDuplexing – TDD versus FDDFDD–FDD is used in radio systems that can allocate individual radio frequencies for each user. For example analog systems: AMPS–In FDD channels are allocated by a base station. –A channel for a mobile is allocated dynamically–All channels that a base station will use are allocated usually statically. –More suitable for wide-area cellular networks: GSM, AMPS all use FDDTDD –Can only be used in digital wireless systems (digital modulation). –Requires rigid timing and synchronization–Mostly used in