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




       ...
Recap: GSM Radio Subsystem (PHY/MAC)

 Spectrum (in USA) is divided into regions (e.g.,
  Cellular Market Area); each reg...
GSM - TDMA/FDMA
                                                     935-960 MHz
                                         ...
GSM Coding and Modulation: Speech




    Viterbi’s                                                     Use GMSK, a
    al...
GSM Coding and Modulation: Speech

 Source speech coding:
       one sample (260 bits) per 20 ms

Audio sample (20ms)


...
GSM Channel Encoding
   Encode the important segments (Types Ia
     Ib) of each audio sample using convolutional
     co...
GSM Speech: Convolutional Encoding

    A Flip-Flop stores one bit for
    one unit of time
                              ...
Interleaving
 Spread a single audio sample (20 ms) into 8
  bursts




                                                9
Many Types of Logical Channels
   Control channels                                    Example: call setup from an
      ...
GSM Data Services
 An MS can reserve a (logical) traffic channel (slot)
  to send data
      data rate standardized at 9...
GPRS




PRACH: Pkt. Random Access Channel; PAGCH: Pkt. Access Grant Channel; PTCH: Pkt. Traffic Channel
USF: Up Link Stat...
GPRS Coding: One Slot
                            Infobits Parity      Output            Punct             Data
  Coding  ...
GSM: Summary
 Physical layer
    how does GSM handle deep fading?
    how about interference?
    how about delay spre...
Rate Requirements of 3G
 Bit rate:
   rural outdoor 144 kbps (500 km/h)
   suburban outdoor 384 kbps (120 km/h)
   ind...
W-CDMA
 One of the IMT-2000 standards
   Mainly in Europe, US is CDMA2000 1X-EV-DO

 Objective: extension of GSM to ach...
Orthognal Variable Spreading
Factor (OSVF)
 Flexible code (spreading factor) allocation
   up link SF: 4 – 256          ...
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)
                                  ...
IEEE 802.11 Family

 Protocol Release    Freq.      Rate       Rate        Range
           Data               (typical)  ...
IEEE 802.11 Physical Layer
 Family of IEEE 802.11 standards:
      unlicensed frequency spectrum: 900Mhz, 2.4Ghz, 5.1Ghz...
802.11a Physical Channels
             36     40    44    48      52      56   60      64       channel#




5150         ...
802.11a Modulation
 Use OFDM to divide each physical channel
 (20 MHz) into 52 subcarriers
 (20M/64=312.5 KHz each)
    ...
Backup Slides
GPRS User Data Rates in kbps


              2       3       4       5       6       7       8
Coding 1 slot
             ...
MS (mobile station)
                                                          BSC (base station controller)

     GSM Elem...
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mac_gsm.ppt

  1. 1. Example Wireless Networks Y. Richard Yang 09/27/2006
  2. 2. Admin.  Please think about projects  Homework 2 to be posted tonight  I will send out an email reminder 2
  3. 3. 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
  4. 4. 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
  5. 5. 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
  6. 6. GSM Coding and Modulation: Speech  Source speech coding:  one sample (260 bits) per 20 ms Audio sample (20ms) 6
  7. 7. 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
  8. 8. 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
  9. 9. Interleaving  Spread a single audio sample (20 ms) into 8 bursts 9
  10. 10. 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
  11. 11. 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
  12. 12. GPRS PRACH: Pkt. Random Access Channel; PAGCH: Pkt. Access Grant Channel; PTCH: Pkt. Traffic Channel USF: Up Link Status Flag 12
  13. 13. 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
  14. 14. 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
  15. 15. 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
  16. 16. 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
  17. 17. 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
  18. 18. W-CDMA Down Link Capacity 18
  19. 19. Outline  Admin. and recap  Example networks  GSM/GPRS/W-CDMA  IEEE 802.11 19
  20. 20. 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
  21. 21. 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
  22. 22. 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
  23. 23. 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
  24. 24. 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
  25. 25. Backup Slides
  26. 26. 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
  27. 27. 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

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