ECE 5325/6325: Wireless Communication Systems Lecture Notes, Fall 2011 Prof. Neal Patwari University of Utah Department of Electrical and Computer Engineering c 2011 ECE 5325/6325 Fall 2011 2 Contents 1 Cellular Systems Intro 6 1.1 GenerationZero .................................. .... 6 1.2 Cellular ........................................ ... 7 1.3 KeyTerms ........................................ 7 2 Frequency Reuse 9 2.1 TransmitPowerLimits. .. .. .. .. .. .. .. .. ...... 9 2.2 CellularGeometry ................................ ..... 9 2.2.1 ChannelAssignmentwithinGroup . ...... 10 2.3 Large-scalePathLoss ............................. ...... 11 2.4 Co-ChannelInterference . ........ 12 2.4.1 Downtilt...................................... 13 2.5 Handoff .......................................... 14 2.6 ReviewfromLecture2.............................. ..... 15 2.7 AdjacentChannelInterference . ......... 15 3 Trunking 16 3.1 Blockedcallscleared ............................. ....... 17 3.2 Blockedcallsdelayed.. .. .. .. .. .. .. .. ....... 17 3.3 Discussion...................................... 18 4 Increasing Capacity and Coverage 18 4.1 Sectoring ....................................... 18 4.1.1 Determining i0 ................................... 20 4.1.2 Example....................................... 20 4.2 Microcells ...................................... 20 4.3 Repeaters ....................................... 21 4.4 Discussion...................................... 21 5 Free Space Propagation 22 5.1 ReceivedPowerReference . ....... 22 5.2 Antennas ........................................ 23 5.3 PowerFluxDensity ................................ 23 6 Large Scale Path Loss Models 24 6.1 LogDistancePathLoss ............................. ..... 24 6.2 MultipleBreakpointModel . ....... 26 7 Reflection and Transmission 26 8 Two-Ray (Ground Reflection) Model 28 8.1 DirectPath ...................................... 29 8.2 ReflectedPath .................................... 29 8.3 TotalTwo-RayE-Field. .. .. .. .. .. .. .. .. ...... 29 ECE 5325/6325 Fall 2011 3 9 Indoor and Site-specific Large Scale Path Loss Models 30 9.1 Attenuation Factor Models . ....... 30 9.2 Ray-tracingmodels............................... ...... 31 10 Link Budgeting 32 10.1 LinkBudgetProcedure . ...... 32 10.2Thermalnoise................................... ..... 33 10.3Examples ....................................... 34 11 Diffraction 35 12 Rough Surface Scattering 36 13 Multipath Fading 37 13.1Multipath ...................................... 38 13.2Temporal ....................................... 39 13.3 ChannelImpulseResponse. ........ 39 13.4ReceivedPower.................................. ..... 40 13.5 TimeDispersionParameters. ......... 41 13.6 ReviewfromLecture9. .. .. .. .. .. .. .. .. ...... 41 14 Fade Distribution 41 14.1 RayleighFading................................. ...... 42 14.2Riceanfading ................................... ..... 43 15 Doppler Fading 43 15.1OneComponent ................................... 45 15.2 ManyComponents ................................. 46 15.3 SystemDesignImplications . ......... 46 16 Digital Communications: Overview 47 16.1 OrthogonalWaveforms. ....... 47 16.2 LinearCombinations . ....... 49 16.3 Using M DifferentLinearCombinations . 49 16.4Reception ...................................... 49 16.5 HowtoChooseaModulation . ...... 50 16.6 Intersymbol Interference and Bandwidth . ............. 51 17 Modulation 52 17.1PAM............................................ 52 17.2M-aryQAMandPSK ................................. 53 17.3FSK ............................................ 53 17.4MSK............................................ 54 17.5 Receiver Complexity Options . ......... 54 18 Fidelity 54 ECE 5325/6325 Fall 2011 4 19 Link Budgets with Digital Modulation 55 19.1 Shannon-Hartley Channel Capacity . ........... 56 19.2Examples ....................................... 57 19.3 Q-FunctionandInverse . ....... 58 20 Implementation Costs 60 20.1 Power Amplifiers and Constant Envelope . .......... 60 20.1.1 OffsetQPSK .................................... 61 20.1.2 OtherModulations. 62 20.2 Synchronization................................ ....... 63 20.2.1 Energy Detection of FSK . 63 20.2.2 DifferentialPSK ................................ 64 21 Multi-carrier Modulation 65 21.1OFDM........................................... 66 21.1.1 OrthogonalWaveforms. ..... 66 21.1.2 Fourier Transform Implementation . ......... 67 21.1.3 CyclicPrefix .................................. 68 21.1.4 ProblemswithOFDM . .. .. .. .. .. .. .. .. 68 21.1.5 Examples ..................................... 68 22 Forward Error Correction Coding 69 22.1 Blockvs. ConvolutionalCoding. .......... 69 22.2 BlockCodeImplementation . ........ 70 22.3 PerformanceandCosts. ....... 71 23 Error Detection via CRC 72 23.1 GenerationoftheCRC. .. .. .. .. .. .. .. .. ...... 72 23.2 PerformanceandCosts. ....... 73 24 Spread Spectrum 73 24.1FH-SS.......................................... 73 24.2DS-SS .......................................... 74 24.3 PNcodegeneration............................... ...... 76 25 Medium Access Control 79 26 Packet Radio 80 26.1Aloha .......................................... 80 26.2SlottedAloha................................... ..... 80 27 CSMA-CA 81 27.1 CarrierSensing ................................. ...... 81 27.2 HiddenTerminalProblem . ....... 81 27.3802.11DCF...................................... 81 27.4 In-ClassDCFDemo ................................ 83 27.5RTS/CTS........................................ 84 ECE 5325/6325 Fall 2011 5 28 Diversity 84 28.1 MethodsforChannelDiversity . ......... 85 28.1.1 SpaceDiversity............................... 85 28.1.2 Polarization Diversity . ....... 85 28.1.3 FrequencyDiversity . ..... 85 28.1.4 Multipathdiversity. ...... 86 28.1.5 TimeDiversity ................................ 86 28.2 DiversityCombining . ....... 87 28.2.1 SelectionCombining . ..... 87 28.2.2 ScanningCombining . 89 28.2.3 EqualGainCombining. 89 28.2.4 MaximalRatioCombining. ..... 89 29 Shannon-Hartley Bandwidth Efficiency 90 30 MIMO 92 30.1 Revisit Maximal Ratio Combining . ......... 92 30.2Alamouticode ................................... 93 30.3 MIMOChannelRepresentation . ........ 94 30.4 CapacityofMIMOSystems . ...... 95 ECE 5325/6325 Fall 2011 6 Lecture 1 Today: (1) Syllabus, (2) Cellular Systems Intro 1 Cellular Systems Intro 1.1 Generation Zero The study of the history of cellular systems can help us understand the need for the system design concepts we have today. One of the major developments in WWII was the miniaturization of FM radio components to a backpack or handheld device (the walkie-talkie), a half-duplex (either transmit or receive, not both) push-to-talk communication device. After returning from war, veterans had the expectation that wireless communications should be available in their civilian jobs [26]. But the phone system, the Public Switched Telephone Network (PSTN) was: wired, and manually switched at telephone exchanges. In 1952, the Mobile Telephone System (MTS) was designed to serve 25 cities in the US [11] (including one in Salt Lake City [10]). In each city, an additional telephone exchange office was created for purpose of connection with the mobile telephones [26]. The MTS and later the improved mobile telephone system (IMTS), introduced in 1964, were not particularly spectrally efficient. They were allocated a total bandwidth of about 2 MHz. Frequency modulation (FM) was • used. For multiple user access, the system operated frequency division multiple access (FDMA), in which each channel was allocated a non-overlapping frequency band within the 2 MHz. The PTSN is full duplex (transmit and receive simultaneously) in IMTS, so it required two • channels for each call, one uplink (to the base station) and one downlink (to the mobile receiver). Note MTS had been half duplex, i.e., only one party could talk at once. The FCC required them to operate over an entire city (25 mile radius). Since the coverage • was city wide, and coverage did not exist outside of the cities, there was no need for handoff. Initially channels were 120 kHz [7], due to poor out-of-band filtering. The channel bandwidth • was cut to 60 kHz in 1950 and again to 30 kHz in 1965. Thus there were 2 MHz / 2 / 120 kHz or 8 full duplex channels at the start, and up to 32 in 1965, for the entire city. Control was manual, and the control channel was open for anyone to hear. In fact, users were required to be listening to the control channel. When the switching operator wanted to connect to any mobile user, they would announce the call on the control channel. If the user responded, they would tell the user which voice channel to turn to. Any other curious user could listen as well. A mobile user could also use the control channel to request a call to be connected. The system was congested, so there was always activity. The demand was very high, even at the high cost of about $400 per month (in 2009 dollars). There were a few hundred subscribers in a city [11] but up to 20,000 on the waiting list [26]. The only way to increase the capacity was to allocate more bandwidth, but satisfying the need would have required more bandwidth than was available. ECE 5325/6325 Fall 2011 7 The downsides to MTS took a significant amount of technological development to address, and the business case was not clear (AT&T developed the technologies over 35 years, but then largely ignored it during the 1980s when it was deployed [11]). 1.2 Cellular The cellular concept is to partition