1 / 19

Basics of Wireless Networks – Ch. 2 (pp 6-14)

Basics of Wireless Networks – Ch. 2 (pp 6-14). ENTC 455: Wireless Transmission Systems Ana Goulart Assistant Professor Texas A&M University. Existing Wireless Technologies (p.6. Mobile Networks Originator and/or Recipient are in motion Fixed Wireless Networks

oria
Download Presentation

Basics of Wireless Networks – Ch. 2 (pp 6-14)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Basics of Wireless Networks – Ch. 2 (pp 6-14) ENTC 455: Wireless Transmission Systems Ana Goulart Assistant Professor Texas A&M University

  2. Existing Wireless Technologies (p.6 • Mobile Networks • Originator and/or • Recipient are in motion • Fixed Wireless Networks Known as RLL – radio in the loop FRA – fixed radio access WLL – wireless local loop Subscribers are stationary Fixed cellular systems Proprietary fixed radio access Affects communication: channel behavior, system performance

  3. Examples of WLL • Emerging economies • Remote places with no infrastructure • Rural communities • To connect subscribers to the Public Switched Network • Or to connect subscribers to the Internet (e.g., voice-over-IP)

  4. Analog Cellular Systems – First Generation • AMPS • Analog FM radio system • Frequency re-use • 800 MHz range, 25KHz carrier spacing • Hexagonal cells • To increase capacity => instead of omnidirectional antennas, use 3 sets of directional antennas • Re-use factor: K = 7 x 3 = 21

  5. Cellular Digital Packet Data (CDPD) (with AMPS) • Packet services on an existing cellular telephone network • 30 KHz channel spacing • Assign some channels for data only • Bit rates up to 19.2 kbps

  6. FDMA • Based on frequency division multiplexing (FDM) • Digitally encoded speech signal modulate the carrier (digital FDMA) • Single chanell <=> user • First generation cellular (AMPS)

  7. FDMA ch1 ch2 ch3 ch4 … frequency time

  8. TDMA • 800 MHz and 1.9 GHz markets • TDMA-136 (1988) • 30 KHz carrier spacing in a 3-slot TDMA solution: 3 users access a single radio channel (frequency) without interference, each user has a unique time-slot • Current TDMA systems => 6 slots/channel, each user two slots (TDD) • 3 to 1 gain over AMPS • Examples of TDMA systems: Japan Digital Cellular (JDC), North American Digital Cellular (NADC), Global System for Mobile Communications (GSM)

  9. TDMA ch1 ch2 ch3 ch4 … frequency time

  10. GSM – Second Generation • 1991 – Europe • Leading second generation standard (2G) • 900 MHz band, also 1800 MHz (DCS 1800 in UK) • 8-slot TDMA system • 200 KHz carrier spacing • Packet services – GPRS (General Packet Radio Service)

  11. GPRS • Data rates around 170 kbps (using all 8 time slots at the same time) • Connectivity to IP • Overlaying a packet-based air interface on the existing circuit-switched GSM network

  12. GPRS SGSN Internet GGSN IP Base Station MSC PSTN

  13. Comparing Wireless Packet With Circuit Switched Data Circuit switching data Packet switching (GPRS, CDPD) • Call setup • Channel is allocated even if no data is sent • Example: HSCSD = High Speed Circuit Switched Data • No call setup (always on) • Radio resources are used only when users have data to send • Not a dedicated channel to a mobile user • Packets may take different paths, may be lost and corrupted • Retransmission, and data integrity schemes add delays

  14. CDMA • Spread-spectrum technology • At the transmitter: every digital packet is encoded with a key • At the receiver: receiver responds only to that key • Key = Walsh codes • Diverse reception – frequency, spatial, time, and path diversity • 1993: CDMA IS-95 standard or cdmaOne (2G) • Channels are 1,250 KHz

  15. CDMA • Different approach to frequency re-use (theoretical value is 1) • Simplified system planning through the use of the same frequency in every sector of every cell • Subscriber’s power control is very important to control interference • Capacity increases of 8 to 10 times than an AMPS systems, and 4 to 5 times than of a GSM system

  16. CDMA code ch3 key3 ch2 ch5 key2 … ch1 ch 4 key1 frequency wide band (1.25 Mhz) time

  17. CDMA • 2G: IS-95 (narrrowband CDMA) • 3G: new flavors of CDMA

More Related