原创,无线网络信道接入方法最全总结,干扰管理技术总结

1、Ad Hoc and Sensor Networks Roger Wattenhofer 6/1Ad Hoc and Sensor Networks Roger Wattenhofer 无线网络信道接入方法紫泉1897QQ 562687381Ad Hoc and Sensor Networks Roger Wattenhofer 6/2Ad Hoc and Sensor Networks Roger Wattenhofer 无线信道接入方法分类基于非竞争基于竞争(固定接入)(随机接入)TDMAFDMACDMASDMAALOHACSMA/CA干扰避免(认为干扰 是有害的)干扰利用(认为干扰 是有

2、益的)干扰对齐 (IA, interference alignment)干扰消除 (IC, interference cancellation)迫零编码，物理层网络编码相继干扰消除允许并发传输Eg: 903.Eg: Wifi, 蓝牙, Zigbee.Eg:蜂窝网Eg:联通CDMAEg: OFDMA (LTE, WiMax)世界最早的无线电计算机网络Ad Hoc and Sensor Networks Roger Wattenhofer 6/3Ad Hoc and Sensor Networks Roger Wattenhofer 信道接入方法：无线网络研究的核心无线通信 (wireless c

3、ommunication) ： 提高信道容量无线网络 (wireless networking) ：协调众多节点对共享信道的接入，即“瓜分”信道本质上是一个资源分配问题。信道资源的稀缺性和用户数的剧烈增长对如何分好“蛋糕”提出了更高的要求主要限制：干扰 (interference) . 干扰：(可能是) 无线信道与有线信道最本质的区别ABCDAd Hoc and Sensor Networks Roger Wattenhofer 6/4Ad Hoc and Sensor Networks Roger Wattenhofer MotivationCan we apply media access

4、 methods from fixed networks? No !Problems in wireless networks broadcast nature of wireless channel 干扰 (interference) signal strength decreases quickly with distance senders apply CS (载波侦听) and CD (冲突检测), but the collisions happen at receivers Energy efficiency: having the radio turned on costs alm

5、ost as much energy as transmitting, so to seriously save energy one needs to turn the radio off! Ad Hoc and Sensor Networks Roger Wattenhofer 6/5Ad Hoc and Sensor Networks Roger Wattenhofer Motivation Hidden Terminal ProblemA sends to B, C cannot receive A C wants to send to B, C senses a “free” med

6、ium (CS fails)collision at B, A cannot receive the collision (CD fails)A is “hidden” for CBACAd Hoc and Sensor Networks Roger Wattenhofer 6/6Ad Hoc and Sensor Networks Roger Wattenhofer Motivation Exposed Terminal ProblemB sends to A, C wants to send to DC has to wait, CS signals a medium in usesinc

7、e A is outside the radio range of C waiting is not necessaryC is “exposed” to BBACDAd Hoc and Sensor Networks Roger Wattenhofer 6/7Ad Hoc and Sensor Networks Roger Wattenhofer Motivation - Near and Far TerminalsTerminals A and B send, C receives the signal of terminal B hides As signal C cannot rece

8、ive AThis is also a severe problem for CDMA networksprecise power control requiredABCAd Hoc and Sensor Networks Roger Wattenhofer 6/8Ad Hoc and Sensor Networks Roger Wattenhofer 无线信道接入方法分类基于非竞争基于竞争(固定接入)(随机接入)TDMAFDMACDMASDMAALOHACSMA/CA干扰避免(认为干扰 是有害的)干扰利用(认为干扰 是有益的)干扰对齐 (IA, interference alignment)

9、干扰消除 (IC, interference cancellation)迫零编码，物理层网络编码相继干扰消除允许并发传输Eg: 903.Eg: Wifi, 蓝牙, Zigbee.Eg:蜂窝网Eg:联通CDMAEg: OFDMA (LTE, WiMax)世界最早的无线电计算机网络Ad Hoc and Sensor Networks Roger Wattenhofer 6/9Ad Hoc and Sensor Networks Roger Wattenhofer Frequency Division Multiplex (FDM)Separation of the whole spectrum i

10、nto smaller frequency bandsA channel gets a certain band of the spectrum for the whole time+ no dynamic coordination necessary+ works also for analog signals waste of bandwidth if traffic is distributed unevenly inflexiblek2k3k4k5k6k1ftcAd Hoc and Sensor Networks Roger Wattenhofer 6/10Ad Hoc and Sen

11、sor Networks Roger Wattenhofer FDD/FDMA - general scheme, example GSM 900Mhzft1241124120 MHz200 kHz890.2 MHz935.2 MHz915 MHz960 MHzAd Hoc and Sensor Networks Roger Wattenhofer 6/11Ad Hoc and Sensor Networks Roger Wattenhofer ftck2k3k4k5k6k1Time Division Multiplex (TDM)A channel gets the whole spectr

12、um for a certain amount of time+ only one carrier in the medium at any time+ throughput high even for many users precise synchronization necessaryAd Hoc and Sensor Networks Roger Wattenhofer 6/12Ad Hoc and Sensor Networks Roger Wattenhofer TDD/TDMA - general scheme, example DECT1 2 31112 1 2 31112td

13、ownlinkuplink417 sAd Hoc and Sensor Networks Roger Wattenhofer 6/13Ad Hoc and Sensor Networks Roger Wattenhofer fTime and Frequency Division MultiplexCombination of both methodsA channel gets a certain frequency band for some time+ protection against frequency selective interference + protection aga

14、inst tapping+ adaptive precise coordination required Example: GSM tck2k3k4k5k6k1Ad Hoc and Sensor Networks Roger Wattenhofer 6/14Ad Hoc and Sensor Networks Roger Wattenhofer Code Division Multiplex (CDM)Each channel has a unique codeAll channels use the same spectrum at the same time+ bandwidth effi

15、cient+ no coordination or synchronization+ hard to tap+ almost impossible to jam lower user data rates more complex signal regenerationExample: UMTS Spread spectrumk2k3k4k5k6k1ftcAd Hoc and Sensor Networks Roger Wattenhofer 6/15Ad Hoc and Sensor Networks Roger Wattenhofer Code Division Multiple Acce

16、ss (CDMA)Example: Direct Sequence Spread Spectrum (DSSS) Each station is assigned an m-bit code (or chip sequence)Typically m = 64, 128, . (in our examples m = 4, 8, )To send 1 bit, station sends chip sequenceTo send 0 bit, station sends complement of chip sequenceExample: 1 MHz band with 100 statio

17、nsFDMA each station a 10 kHz band assume that you can send 1 bit/Hz: 10 kbpsCDMA each station uses the whole 1 MHz band less than 100 chips per channel: more than 10 kbpsAd Hoc and Sensor Networks Roger Wattenhofer 6/16Ad Hoc and Sensor Networks Roger Wattenhofer CDMA BasicsEach station has unique -

18、bit chipping code or complement Bipolar notation: binary 0 is represented by 1 (or short: )Two chips , are orthogonal iff 0 is the inner (scalar) product: smSSS TS TS TS 11Note: 1,1Note: 00miiiTSTmS SS SS TS TAd Hoc and Sensor Networks Roger Wattenhofer 6/17Ad Hoc and Sensor Networks Roger Wattenhof

19、er SDMA: 空分复用Ad Hoc and Sensor Networks Roger Wattenhofer 6/18Ad Hoc and Sensor Networks Roger Wattenhofer 空分复用：定向天线 (Directional Antenna)全向天线全向天线 Omni-directional Antenna在水平方向图上表现为360都均匀辐射，也就是平常所说的无方向性。一般情况下波瓣宽度越小，增益越大。全向天线在通信系统中一般应用距离近，覆盖范围大，价格便宜。定向天线定向天线 Directional Antenna在水平方向图上表现为一定角度范围辐射，也就是平

20、常所说的有方向性。同全向天线一样，波瓣宽度越小，增益越大。定向天线在通信系统中一般应用于通信距离远，覆盖范围小，目标密度大，频率利用率高的环境。Directional Antenna: allowing a sender to direct his transmissions in the direction of the intended receiver clearly reduces the level of contention with other nodes, thereby allowing for more simultaneous transmissions.Ad Hoc a

21、nd Sensor Networks Roger Wattenhofer 6/19Ad Hoc and Sensor Networks Roger Wattenhofer Cocktail party as analogy for multiplexingSpace multiplex: Communicate in different roomsFrequency multiplex: Use soprano, alto, tenor, or bass voices to define the communication channelsTime multiplex: Let other s

22、peaker finishCode multiplex: Use different languages and hone in on your language. The “farther apart” the languages the better you can filter the “noise”: German/Japanese better than German/Dutch.Can we have orthogonal languages? Comparison SDMA/TDMA/FDMA/CDMAJ.SchillerALOHA世界上最早的无线电计算机通信网。它是1968年美

23、国夏威夷大学的一项研究计划的名字。70年代初研制成功一种使用无线广播技术的分组交换计算机网络，也是最早最基本的无线数据通信协议。纯纯ALOHA协议协议的工作原理和特点的工作原理和特点工作原理：站点只要产生帧，就立即发送到信道上；规定时间内若收到应答，表示发送成功，否则重发。重发策略：等待一段随机的时间，然后重发；如再次冲突，则再等待一段随机的时间，直到重发成功为止优点：简单易行缺点：极容易冲突时隙ALOHA协议的工作原理和特点基本思想：把信道时间分成离散的时间槽，槽长为一个帧所需的发送时间。每个站点只能在时槽开始时才允许发送。其他过程与纯ALOHA协议相同。代价：需要全网同步；可设置一个特殊站点，由该站点发送时钟信号CSM