信息与通信工程专业英语.ppt

Wireless Communication 2 Jin Wang Subject Outline nIntroduction to Cellular Mobile Communications nRadio Propagation : Large Scale Effects qPath loss prediction models qShadowing nRadio Propagation : Small Scale Effects qMulti-path models : Rayleigh, Rician qDoppler effect, power spectra and signal correlation qCoherence time and bandwidth, flat and selective fading channel nModulation Techniques qConstant envelope and phase modulation qQPSK, /4 QPSK, FSK, GMSK 3 Subject Outline nEqualization, Diversity and Coding Techniques qLinear and non-linear equalization qSelection, equal-gain and maximal ratio combining qInterleaving and convolution coding nMultiple Access Techniques qFDMA, TDMA, CDMA, SDMA qPacket radio and random access nCellular System Concepts qFrequency reuse qChannel assignment and control qCellular traffic qCellular coverage qSystem expansion techniques 4 Subject Outline nCDMA Cellular Systems qPower Control and Interference qMulti-user Detection qCapacity and Enhancement n More Advanced Topics (if time allows) qOrthogonal Frequency Division Mulitplexing (OFDM) qMulti-carrier CDMA System nSpeech Coding Fundamentals of quantization, PCM, Vocoder nBrief Overview of System Standards GSM, IS-95, IMT2000 5 References nTheodore S. Rappaport, Wireless Communications: Principles digital features such as DSSS and FHSS are generally only available on the higher frequencies. nThe recently allocated 1.9 GHz band is used by the popular DECT phone standard from Europe 14 Mobile 15 Base Station 16 Introduction nThe target for mobile communications is to provide communications for anyone, from anywhere, at any time. nA demanding task. Technological challenges include: qTimevarying, hostile communication channel. q Location and tracking complexities due to mobility. q Efficient use of scarce resources such as frequency spectrum cellular structure. The amount of interference generated is critical. q Power restrictions due to health issues. 17 Introduction nThe exponential growth of mobile subscribers worldwide is due to the decreasing service charges and diminishing hardware costs. The continuous development of the enabling technologies is the key. 18 Introduction RF technologies (such as improved frequency stability in electronics) 19 Introduction qIC design (size) qBattery technology (weight and size) qHigher order modulation is made possible due to the use of more sophisticated advanced digital signal processing techniques. qSpeech coding techniques reduces the required bandwidth per channel. 20 Cellular system Example : qConsider a system allocated total bandwidth of 12.5MHz and each voice channel requires a 10kHz slot. We can only support 12.5MHz/10kHz or 1250 simultaneous conversations. qSupposing the penetration rate in Singapore is 10%, for a population of 3M+, this is equivalent to 300k users. What happen if 1% of the users making call at the same time? Channels need to be in someway reused or shared? 21 Cellular system What can we do? qFrequency bands are reused at different locations. With this, higher user capacity in the same frequency spectrum can be achieved. qTechnical challenge: interference issue, location tracking, etc., needs to be overcome. 22 Cellular system 23 Cellular system nEach cell has a base station (BS), providing the radio interface to the mobile station (MS). nA sophisticated switching technique called a handover enables a call to proceed uninterrupted across cell boundaries. nAll the BSs are connected to a mobile switching center (MSC) which is responsible for connection users to the public switched telephone network (PSTN). nControl channels transmit and receive data messages that carry call initiation and service requests, and are monitored by mobiles when they do not have a call in progress. 5% of total available channels. 24 Cellular system nCommunication between the BS and the mobiles is defined by a standard common air interface that specifies 4 different physical channels qForward (Downlink) voice/data channel : BS to MS qReverse (Uplink) voice/data channel : MS to BS qForward (Downlink) control channel : BS to MS qRevers