Monday, February 18, 2013

Pervasive networks

  • simultaneously connected to several wireless accesstechnologies (Wi-Fi, UMTS for example) and can seamlessly move between them (handover)
  • smart-radio aka cognitive radio technology to efficiently manage spectrum use and transmission power
  • 4G may use OFDM , and also OFDMA.
  • packet switching only (All IP)

lecture 2-18-2013

Bats and Communication Engineering

1. How bats find their way in the dark (Also, dolphins and toothed whales)
2. echolocation similar to radars
3. choice of carrier (low or high pitch)
4. amplitudes, Decibel (Loudness) Comparison Chart
5. pulse (cruise 10 Hz, long range; intercept 200 Hz, short range)
6. antenna (Haeckel Chiroptera.jpg)
7. duplexer (transmit/receive)
8. FM
9. velocity detection
10. interference among groups of bats


OFDMA Technology (slides)

Sunday, February 17, 2013

Spread Spectrum

Spread Spectrum, an in-depth introduction

Technology beyond 3G

From 2G, 2.5G, 3G (IMS, IP Multimedia Subsystem), 3.5G/HSDPA, to 4G

Computer Communications (IT), IP-based, WiFi (Data Comm.), VoIP

Data Services
  • GSM, Circuit Switching, 9.6 (*2), 12.4(*2, HSCSD)
  • GPRS, General Packet Radio Services, Packet Switching, 9.05 kbps/13.4 kbps (*1,2,3,4), speed denoted as *u*d
  • EDGE, 3 times of speed of GPRS by using 8-PSK instead of binary GMSK
  • 3G, 384kbps, up to 2 Mbps, uplink is 128 kbps
  • 3.5G HSDPA (High Speed Downlink Packet Access) 8-10 Mbps (R5), and 20 Mbps (R6) by MIMO, uplink is 384 kbps
  • 4G communication at 100 Mbit/s while moving, and 1 Gbit/s while stationary.

In general, a generation is defined by the result of technology changes over a 10-15 year time frame. Thus, 4G would refer to whatever is deployed in the 2010-2015 period, assuming 3G deployment spans the 2000-2009 period.

cellular technology

1. Start of the cellular technology, the need for new commercial applications of wireless
2. the bottleneck of capacity
3. Examine capacity of FDMA, TDMA, and CDMA (Is TDMA of the same efficiency as FDMA?))
  • TDMA:FDMA 7(theoretically), 3(practically)
  • CDMA:FDMA 40(theoretically), 10 (practically)
4. Why cellular is better than broadcast?
5. Digital wireless with TDMA, CDMA
  • advanced of digital ICs
  • price drop
6. Major issues with CDMA

  • near-far field effect
  • hand-off

  • 7. and their solutions
    • Power control
    • soft handoff
    8. Make use of dead time in telephone conversations, about 65% of the time
    • variable-rate coder

    reference: Chap. 1~Chap. 6, Dave Mock, the Qualcomm Equation, AMACOM, 2005