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mac_gsm.ppt mac_gsm.ppt Presentation Transcript

  • Example Wireless Networks Y. Richard Yang 09/27/2006
  • Admin.  Please think about projects  Homework 2 to be posted tonight  I will send out an email reminder 2
  • Recap: GSM Radio Subsystem (PHY/MAC)  Spectrum (in USA) is divided into regions (e.g., Cellular Market Area); each region has two licenses (A and B)  A license holder (a GSM operator) uses SDMA, TDMA and FDMA to divide its allocated frequency  divides allocated spectrum into different physical channels; each physical channel has a frequency band of 200 kHz  assigns physical channels to cells  partitions the time of each physical channel into frames; each frame has a duration of 4.615 ms  divides each frame into 8 time slots (also called a burst) • each slot is a logical channel • user data is transmitted through a logical channel 3
  • GSM - TDMA/FDMA 935-960 MHz 124 channels (200 kHz) downlink 890-915 MHz 124 channels (200 kHz) uplink higher GSM frame structures time GSM TDMA frame 1 2 3 4 5 6 7 8 4.615 ms GSM time-slot (normal burst) guard guard space tail user data S Training S user data tail space 3 bits 57 bits 1 26 bits 1 57 bits 3 546.5 µs 577 µs S: indicates data or control; tail = 000 4
  • GSM Coding and Modulation: Speech Viterbi’s Use GMSK, a algorithm variant derived from OQPSK (270k sym/sec); but 1 bit/symbol An option of slow hopping per slot See A brief Overview of the GSM Radio Interface by Thierry Turletti http://citeseer.ist.psu.edu/515017.html 5
  • GSM Coding and Modulation: Speech  Source speech coding:  one sample (260 bits) per 20 ms Audio sample (20ms) 6
  • GSM Channel Encoding  Encode the important segments (Types Ia Ib) of each audio sample using convolutional coding A good tutorial: http://home.netcom.com/~chip.f/viterbi/tutorial.html 7
  • GSM Speech: Convolutional Encoding A Flip-Flop stores one bit for one unit of time y1 x: 101100… y2 Questions: - what is the relationship between the sequences y1 (y2) and x? - how do you decode? 8
  • Interleaving  Spread a single audio sample (20 ms) into 8 bursts 9
  • Many Types of Logical Channels  Control channels  Example: call setup from an  broadcast control channel MS (BCCH) MS BTS • from base station, announces cell identifier, synchronization, hopping sequence RACH (request signaling channel)  common control channels (CCCH) • random access channel AGCH (assign signaling channel) (RACH): MSs for initial access, slotted Aloha SDCCH (request call setup) • access grant channel (AGCH): BTS informs an MS its allocation • paging channel (PCH): base SDCCH message exchange transceiver station (BTS) pages a mobile host (MS) SDCCH (assign TCH)  dedicated control channels • standalone dedicated control channel (SDCCH): signaling and short message between MS and an MS Communication  Traffic channels (TCH) Interesting pointer: http://web.media.mit.edu/~ladyada/techproj/freshair/doc/stahlberg%20cell%20jamming.pdf 10
  • GSM Data Services  An MS can reserve a (logical) traffic channel (slot) to send data  data rate standardized at 9.6 kbps  Improving GSM transmission rate  High Speed Circuit Switched Data (HSCSD) • allocate multiple traffic channels • problem: data traffic is bursty; reserving multiple slots is not efficient  General Packet Radio Service (GPRS) • allocate multiple slots from the same frame • only request slots when needed  Enhanced Data Rates for GSM Evolution (EDGE) • extending GPRS from GMSK (1 bit/symbol) to 8-PSK (3 bits/symbol) http://www.ericsson.com/technology/whitepapers/edge_wp_technical.pdf 11
  • GPRS PRACH: Pkt. Random Access Channel; PAGCH: Pkt. Access Grant Channel; PTCH: Pkt. Traffic Channel USF: Up Link Status Flag 12
  • GPRS Coding: One Slot Infobits Parity Output Punct Data Coding Pre-cod. Tail Code without bits conv. ured rate scheme USF bits rate USF BC encoder bits kbit/s CS-1 3 181 40 4 456 0 1/2 9.05 CS-2 6 268 16 4 588 132 ~2/3 13.4 CS-3 6 312 16 4 676 220 ~3/4 15.6 CS-4 12 428 16 - 456 - 1 21.4 g(1)(D) = 1 + D3 + D4 g(2)(D) = 1 + D + D3 + D4 , 1000 ms / 240 ms/frame * 48frame * 114 bytes/frame * 181/456 = 9.05kbps 13
  • GSM: Summary  Physical layer  how does GSM handle deep fading?  how about interference?  how about delay spread?  MAC layer  what are the dimensions used in multiplexing?  physical and logical channel sizes?  MAC? 14
  • Rate Requirements of 3G  Bit rate:  rural outdoor 144 kbps (500 km/h)  suburban outdoor 384 kbps (120 km/h)  indoor 2 Mbps (10 km/h)  Variable bit rate capability 15
  • W-CDMA  One of the IMT-2000 standards  Mainly in Europe, US is CDMA2000 1X-EV-DO  Objective: extension of GSM to achieve high speed data services  Total spectrum:  1920-1980 MHz uplink  2110-2170 MHz downlink  Using CDMA for data channel  per channel size: 5 MHz; Rake receiver  fixed chipping rate at 3.840 Mchip/s  frame length: 10 ms (38400 chips per frame)  no. of slots (bursts) per frame: 15 (2560 chips per slot/burst)  modulation: BPSK up link; QPSK down link 16
  • Orthognal Variable Spreading Factor (OSVF)  Flexible code (spreading factor) allocation  up link SF: 4 – 256 1,1,1,1,1,1,1,1  down link SF: 4 - 512 1,1,1,1 ... 1,1,1,1,-1,-1,-1,-1 1,1 1,1,-1,-1,1,1,-1,-1 1,1,-1,-1 ... X,X 1,1,-1,-1,-1,-1,1,1 X 1 1,-1,1,-1,1,-1,1,-1 X,-X 1,-1,1,-1 ... 1,-1,1,-1,-1,1,-1,1 SF=n SF=2n 1,-1 1,-1,-1,1,1,-1,-1,1 1,-1,-1,1 ... 1,-1,-1,1,-1,1,1,-1 SF=1 SF=2 SF=4 SF=8 17
  • W-CDMA Down Link Capacity 18
  • Outline  Admin. and recap  Example networks  GSM/GPRS/W-CDMA  IEEE 802.11 19
  • 802.11: Infrastructure 802.11 LAN  Station (STA) 802.x LAN  terminal with access mechanisms to the wireless medium and radio contact to the access point STA1 BSS1  Access Point Access Portal  station integrated into the wireless Point LAN and the distribution system  Basic Service Set (BSS) Distribution System  group of stations using the same AP Access ESS  Portal Point  bridge to other (wired) networks BSS2  Distribution System  interconnection network to form one logical network (EES: Extended Service Set) based STA2 STA3 on several BSS 802.11 LAN 20
  • IEEE 802.11 Family Protocol Release Freq. Rate Rate Range Data (typical) (max) (indoor) Legacy 1997 2.4 GHz 1 Mbps 2Mbps ? 802.11a 1999 5 GHz 25 Mbps 54 ~30 m Mbps 802.11b 1999 2.4 GHz 6.5 Mbps 11 ~30 m Mbps 802.11g 2003 2.4 GHz 25 Mbps 54 ~30 m Mbps 802.11n 2008 2.4/5 200 Mbps 540 ~50 m GHz Mbps 21
  • IEEE 802.11 Physical Layer  Family of IEEE 802.11 standards:  unlicensed frequency spectrum: 900Mhz, 2.4Ghz, 5.1Ghz, 5.7Ghz 300 MHz 5.15-5.35 GHz 5.725-5.825 GHz and 802.11b/g 802.11a 22
  • 802.11a Physical Channels 36 40 44 48 52 56 60 64 channel# 5150 5180 5200 5220 5240 5260 5280 5300 5320 5350 [MHz] center frequency = 5000 + 5*channel number [MHz] 149 153 157 161 channel# 5725 5745 5765 5785 5805 5825 [MHz] 23
  • 802.11a Modulation  Use OFDM to divide each physical channel (20 MHz) into 52 subcarriers (20M/64=312.5 KHz each)  48 data, 4 pilot  Adaptive modulation  BPSK: 6, 9 Mbps  QPSK: 12, 18 Mbps  16-QAM: 24, 36 Mbps  64-QAM: 48, 54 Mbps 24
  • Backup Slides
  • GPRS User Data Rates in kbps 2 3 4 5 6 7 8 Coding 1 slot slots slots slots slots slots slots slots scheme CS-1 9.05 18.2 27.15 36.2 45.25 54.3 63.35 72.4 CS-2 13.4 26.8 40.2 53.6 67 80.4 93.8 107.2 CS-3 15.6 31.2 46.8 62.4 78 93.6 109.2 124.8 CS-4 21.4 42.8 64.2 85.6 107 128.4 149.8 171.2 26
  • MS (mobile station) BSC (base station controller) GSM Elements BTS (base transceiver station) MSC (mobile switching center) GMSC (gateway MSC) HLR (home location register) VLR (visiting location register Network & Switching HLR GMSC Subsystem fixed network and Operation Subsystem VLR MSC MSC VLR MS BSC BSC MS BTS Radio MS Subsystem MS MS BTS MS BTS BTS BTS 27