信息與通信工程專業(yè)英語(yǔ).ppt

1、Wireless Communication,2,Jin Wang,Subject Outline,Introduction to Cellular Mobile Communications Radio Propagation : Large Scale Effects Path loss prediction models Shadowing Radio Propagation : Small Scale Effects Multi-path models : Rayleigh, Rician Doppler effect, power spectra and signal correla

2、tion Coherence time and bandwidth, flat and selective fading channel Modulation Techniques Constant envelope and phase modulation QPSK, /4 QPSK, FSK, GMSK,3,Subject Outline,Equalization, Diversity and Coding Techniques Linear and non-linear equalization Selection, equal-gain and maximal ratio combin

3、ing Interleaving and convolution coding Multiple Access Techniques FDMA, TDMA, CDMA, SDMA Packet radio and random access Cellular System Concepts Frequency reuse Channel assignment and control Cellular traffic Cellular coverage System expansion techniques,4,Subject Outline,CDMA Cellular Systems Powe

4、r Control and Interference Multi-user Detection Capacity and Enhancement More Advanced Topics (if time allows) Orthogonal Frequency Division Mulitplexing (OFDM) Multi-carrier CDMA System Speech Coding Fundamentals of quantization, PCM, Vocoder Brief Overview of System Standards GSM, IS-95, IMT2000,5

5、,References,Theodore S. Rappaport, Wireless Communications: Principles digital features such as DSSS and FHSS are generally only available on the higher frequencies. The recently allocated 1.9 GHz band is used by the popular DECT phone standard from Europe,14,Mobile,15,Base Station,16,Introduction,T

6、he target for mobile communications is to provide communications for anyone, from anywhere, at any time. A demanding task. Technological challenges include: Timevarying, hostile communication channel. Location and tracking complexities due to mobility. Efficient use of scarce resources such as frequ

7、ency spectrum cellular structure. The amount of interference generated is critical. Power restrictions due to health issues,17,Introduction,The exponential growth of mobile subscribers worldwide is due to the decreasing service charges and diminishing hardware costs. The continuous development of th

8、e enabling technologies is the key,18,Introduction,RF technologies (such as improved frequency stability in electronics,19,Introduction,IC design (size) Battery technology (weight and size) Higher order modulation is made possible due to the use of more sophisticated advanced digital signal processi

9、ng techniques. Speech coding techniques reduces the required bandwidth per channel,20,Cellular system,Example : Consider 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. Supposing the pen

10、etration 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? Frequency bands are reused at different locations. With this,

11、higher user capacity in the same frequency spectrum can be achieved. Technical challenge: interference issue, location tracking, etc., needs to be overcome,22,Cellular system,23,Cellular system,Each cell has a base station (BS), providing the radio interface to the mobile station (MS). A sophisticat

12、ed switching technique called a handover enables a call to proceed uninterrupted across cell boundaries. All the BSs are connected to a mobile switching center (MSC) which is responsible for connection users to the public switched telephone network (PSTN). Control channels transmit and receive data

13、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,Communication between the BS and the mobiles is defined by a standard common air interface that specifies 4 different physical channels Forward (Downlink) voice/data channel : BS to MS Reverse (Uplink) voice/data channel : MS to BS Forward (Downlink) control channel : BS to MS Reverse