Transcription

ECE 5325/6325: Wireless Communication SystemsLecture Notes, Fall 2011Prof. Neal PatwariUniversity of UtahDepartment of Electrical and Computer Engineeringc 2011

ECE 5325/6325 Fall 20112Contents1 Cellular Systems Intro1.1 Generation Zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.2 Cellular . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.3 Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Frequency Reuse2.1 Transmit Power Limits . . . . . . . . . . .2.2 Cellular Geometry . . . . . . . . . . . . .2.2.1 Channel Assignment within Group2.3 Large-scale Path Loss . . . . . . . . . . .2.4 Co-Channel Interference . . . . . . . . . .2.4.1 Downtilt . . . . . . . . . . . . . . .2.5 Handoff . . . . . . . . . . . . . . . . . . .2.6 Review from Lecture 2 . . . . . . . . . . .2.7 Adjacent Channel Interference . . . . . .6677.999101112131415153 Trunking3.1 Blocked calls cleared . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.2 Blocked calls delayed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .161717184 Increasing Capacity and4.1 Sectoring . . . . . . .4.1.1 Determining i04.1.2 Example . . . .4.2 Microcells . . . . . . .4.3 Repeaters . . . . . . .4.4 Discussion . . . . . . .181820202021215 Free Space Propagation5.1 Received Power Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.2 Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.3 Power Flux Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22222323Coverage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 Large Scale Path Loss Models246.1 Log Distance Path Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246.2 Multiple Breakpoint Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Reflection and Transmission268 Two-Ray (Ground Reflection) Model288.1 Direct Path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298.2 Reflected Path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298.3 Total Two-Ray E-Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

ECE 5325/6325 Fall 201139 Indoor and Site-specific Large Scale Path Loss Models309.1 Attenuation Factor Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309.2 Ray-tracing models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3110 Link Budgeting3210.1 Link Budget Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3210.2 Thermal noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3310.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3411 Diffraction3512 Rough Surface Scattering3613 Multipath Fading13.1 Multipath . . . . . . . . . .13.2 Temporal . . . . . . . . . .13.3 Channel Impulse Response .13.4 Received Power . . . . . . .13.5 Time Dispersion Parameters13.6 Review from Lecture 9 . . .37383939404141.14 Fade Distribution4114.1 Rayleigh Fading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4214.2 Ricean fading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4315 Doppler Fading4315.1 One Component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4515.2 Many Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4615.3 System Design Implications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4616 Digital Communications: Overview16.1 Orthogonal Waveforms . . . . . . . . . .16.2 Linear Combinations . . . . . . . . . . .16.3 Using M Different Linear Combinations16.4 Reception . . . . . . . . . . . . . . . . .16.5 How to Choose a Modulation . . . . . .16.6 Intersymbol Interference and Bandwidth17 Modulation17.1 PAM . . . . . . . . . . . . . .17.2 M-ary QAM and PSK . . . .17.3 FSK . . . . . . . . . . . . . .17.4 MSK . . . . . . . . . . . . . .17.5 Receiver Complexity Options18 Fidelity.47474949495051.52525353545454

ECE 5325/6325 Fall 2011419 Link Budgets with Digital Modulation5519.1 Shannon-Hartley Channel Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5619.2 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5719.3 Q-Function and Inverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5820 Implementation Costs20.1 Power Amplifiers and Constant Envelope20.1.1 Offset QPSK . . . . . . . . . . . .20.1.2 Other Modulations . . . . . . . . .20.2 Synchronization . . . . . . . . . . . . . . .20.2.1 Energy Detection of FSK . . . . .20.2.2 Differential PSK . . . . . . . . . .6060616263636421 Multi-carrier Modulation21.1 OFDM . . . . . . . . . . . . . . . . . . . .21.1.1 Orthogonal Waveforms . . . . . . .21.1.2 Fourier Transform Implementation21.1.3 Cyclic Prefix . . . . . . . . . . . .21.1.4 Problems with OFDM . . . . . . .21.1.5 Examples . . . . . . . . . . . . . .6566666768686822 Forward Error Correction Coding6922.1 Block vs. Convolutional Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6922.2 Block Code Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7022.3 Performance and Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7123 Error Detection via CRC7223.1 Generation of the CRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7223.2 Performance and Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7324 Spread Spectrum24.1 FH-SS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24.2 DS-SS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24.3 PN code generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7373747625 Medium Access Control7926 Packet Radio8026.1 Aloha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8026.2 Slotted Aloha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8027 CSMA-CA27.1 Carrier Sensing . . . . . .27.2 Hidden Terminal Problem27.3 802.11 DCF . . . . . . . .27.4 In-Class DCF Demo . . .27.5 RTS/CTS . . . . . . . . .818181818384

ECE 5325/6325 Fall 201128 Diversity28.1 Methods for Channel Diversity . .28.1.1 Space Diversity . . . . . . .28.1.2 Polarization Diversity . . .28.1.3 Frequency Diversity . . . .28.1.4 Multipath diversity . . . . .28.1.5 Time Diversity . . . . . . .28.2 Diversity Combining . . . . . . . .28.2.1 Selection Combining . . . .28.2.2 Scanning Combining . . . .28.2.3 Equal Gain Combining . . .28.2.4 Maximal Ratio Combining .5.84858585858686878789898929 Shannon-Hartley Bandwidth Efficiency9030 MIMO30.1 Revisit Maximal Ratio Combining30.2 Alamouti code . . . . . . . . . . .30.3 MIMO Channel Representation . .30.4 Capacity of MIMO Systems . . . .9292939495.

ECE 5325/6325 Fall 20116Lecture 1Today: (1) Syllabus, (2) Cellular Systems Intro1Cellular Systems Intro1.1Generation ZeroThe study of the history of cellular systems can help us understand the need for the system designconcepts we have today.One of the major developments in WWII was the miniaturization of FM radio components toa backpack or handheld device (the walkie-talkie), a half-duplex (either transmit or receive, notboth) push-to-talk communication device. After returning from war, veterans had the expectationthat 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 telephoneexchanges. 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 wascreated for purpose of connection with the mobile telephones [26]. The MTS and later the improvedmobile telephone system (IMTS), introduced in 1964, were not particularly spectrally efficient. They were allocated a total bandwidth of about 2 MHz. Frequency modulation (FM) wasused. For multiple user access, the system operated frequency division multiple access(FDMA), in which each channel was allocated a non-overlapping frequency band within the2 MHz. The PTSN is full duplex (transmit and receive simultaneously) in IMTS, so it required twochannels for each call, one uplink (to the base station) and one downlink (to the mobilereceiver). 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 coveragewas 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 bandwidthwas cut to 60 kHz in 1950 and again to 30 kHz in 1965. Thus there were 2 MHz / 2 / 120kHz 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 wererequired to be listening to the control channel. When the switching operator wanted to connect toany mobile user, they would announce the call on the control channel. If the user responded, theywould tell the user which voice channel to turn to. Any other curious user could listen as well. Amobile user could also use the control channel to request a call to be connected. The system wascongested, 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]. Theonly way to increase the capacity was to allocate more bandwidth, but satisfying the need wouldhave required more bandwidth than was available.

ECE 5325/6325 Fall 20117The downsides to MTS took a significant amount of technological development to address, andthe business case was not clear (AT&T developed the technologies over 35 years, but then largelyignored it during the 1980s when it was deployed [11]).1.2CellularThe cellular concept is to partition a geographical area into “cells”, each covering a small fractionof a city. Each cell is allocated a “channel group”, i.e., a subset of the total list of channels. Asecond cell, distant from a first cell using a particular channel group, can reuse the same channelgroup. This is called “frequency reuse”. This is depicted in Figure 3.1 in Rappaport. This assumesthat at a long distance, the signals transmitted in the first cell are too low by the time they reachthe second cell to significantly interfere with the use of those channels in the second cell.There are dramatic technical implications of the cellular concept. First, rather than one basestation, you need dozens or hundreds, deployed across a city. You need automatic and robustmobility management (handoff) to allow users to cross cell lines and continue a phone call. Both ofthese are actually enabled by semiconductor technology advancement, which made the base stationsand the automated wired PSTN cheaper [26].Frequency reuse and handoff are topics for upcoming lectures.1.3Key TermsCommunication between two parties (a “link”), in general, can be one of the following: Simplex : Data/Voice is transferred in only one direction (e.g., paging). Not even an acknowledgement of receipt is returned. Half Duplex : Data/Voice is transferred in one direction at a time. One can’t talk and listenat the same time. One channel is required. Full Duplex : Data/Voice can be transferred in both directions between two parties at thesame time. This requires two channels.In a cellular system, there is full duplex communication, between a base station and a mobile.The two directions are called either uplink (from mobile to base station) or dow