16. 16-1 CELLULAR TELEPHONY Cellular telephony is designed to provide communications between two moving units, called mobile stations (MSs), or between one mobile unit and one stationary unit, often called a land unit. Frequency-Reuse Principle Transmitting Receiving Roaming First Generation Second Generation Third Generation Topics discussed in this section:
16. Figure 16.8 GSM GSM uses TDMA and FDMA concepts GMSK (Gaussian minimum shift keying): a form of FSK used in European systems
16. Figure 16.9 GSM Multiframe components Lots of overhead!!
16. Figure 16.10 IS-95 CDMA forward (base to mobile) transmission ESN is used to generate 2^42 pseudorandom chips, each having 42 bits. Decimator chooses 1 bit out of the 64, and then is scrambled with digitized voice to create privacy. 19.2 ksps = 19.2 kilosignals per second 19.2 ksps signal converted to 64-chip sequence, giving 1.228 Mcps (mega-chips) ESN: electronic serial number of handset
16. Figure 16.11 IS-95 CDMA reverse (mobile to base) transmission Note: CDMA not used here because no way of syncing all mobile devices together! Frequency reuse is 1, since neighboring channels cannot interfere with CDMA or DSSS transmission. Each 6 symbols are used to index into a 64x64 Walsh matrix; thus each 6-symbol chunk is replaced (not multiplied as it would be with CDMA) with a 64-chip code. A 42-bit unique code is generated by the mobile hand set and combined with the 307.2 kcps signal creating a 1.228 Mcps signal.
16. 2.5 Generation iDEN iDEN (Integrated Dispatch Enhanced Network) <ul><li>Functionally the same as MIRS (Motorola Integrated Radio System) </li></ul><ul><li>A high-capacity digital trunked radio system providing integrated voice and data services to its users </li></ul><ul><li>Used by Nextel Communications </li></ul>
16. 2.5 Generation GPRS GPRS (General Packet Radio Service) <ul><li>The 2.5G version of GSM </li></ul><ul><li>Theoretically allows each user access to 8 GSM data channels at once, boosting data transfer speeds to more than 100 Kbps (30 Kbps in the real world since it only uses 2 GSM channels) </li></ul><ul><li>AT&T Wireless, Cingular, T-Mobile </li></ul>
16. 2.5 Generation 1xRTT 1xRTT (CDMA2000) 1x Radio Transmission Technology <ul><li>The 2.5G backwards compatible replacement for CDMA </li></ul><ul><li>1xRTT will replace CDMA and iDEN </li></ul><ul><li>1x means that it requires only the same amount of spectrum as 2G networks based on CDMA (IS-95) </li></ul><ul><li>Sprint and Verizon </li></ul>
16. 3 rd Generation UMTS UMTS (Universal Mobile Telecommunications System) <ul><li>Also called Wideband CDMA </li></ul><ul><li>The 3G version of GPRS </li></ul><ul><li>UMTS is not backward compatible with GSM, so first UMTS phones will have to be dual-mode </li></ul><ul><li>Based on TDMA, same as D-AMPS and GSM </li></ul>
16. 3 rd Generation 1xEV 1xEV (1x Enhanced Version) <ul><li>The 3G replacement for 1xRTT </li></ul><ul><li>Will come in two flavors </li></ul><ul><ul><li>1xEV-DO for data only </li></ul></ul><ul><ul><li>1xEV-DV for data and voice </li></ul></ul>
16. EDGE EDGE (Enhanced Data rates for Global Evolution) <ul><li>Further upgrade to GSM </li></ul><ul><li>Possible 3G (no – 2.75G) replacement for GPRS </li></ul><ul><li>Uses improved modulation to triple the data rate where reception is clear </li></ul>
16. LTE LTE (3GPP LTE – Long Term Evolution) <ul><li>3G upgrade to UMTS </li></ul><ul><li>3GPP – third generation partnership project </li></ul><ul><li>LTE actually an architecture – contains EPS (evolved packet system), EUTRAN (evolved UTRAN), and EPC (evolved packet core) </li></ul><ul><li>OFDM, QPSK, 16QAM, 64QAM, MIMO </li></ul>
16. 16-2 SATELLITE NETWORKS A satellite network is a combination of nodes, some of which are satellites, that provides communication from one point on the Earth to another. A node in the network can be a satellite, an Earth station, or an end-user terminal or telephone. Orbits Footprint Three Categories of Satellites GEO Satellites MEO Satellites LEO Satellites Topics discussed in this section:
16. What is the period of the Moon, according to Kepler’s law? Example 16.1 Here C is a constant approximately equal to 1/100. The period is in seconds and the distance in kilometers.
16. Example 16.1 (continued) Solution The Moon is located approximately 384,000 km above the Earth. The radius of the Earth is 6378 km. Applying the formula, we get.
16. According to Kepler’s law, what is the period of a satellite that is located at an orbit approximately 35,786 km above the Earth? Example 16.2 Solution Applying the formula, we get
16. This means that a satellite located at 35,786 km has a period of 24 h, which is the same as the rotation period of the Earth. A satellite like this is said to be stationary to the Earth. The orbit, as we will see, is called a geosynchronous orbit. Example 16.2 (continued)
16. Table 16.1 Satellite frequency bands L: GPS S: weather, NASA, Sirius/XM satellite radio C: open satellite communications Ku: popular with remote locations transmitting back to TV studio Ka: communications satellites
16. Figure 16.16 Satellites in geostationary orbit
16. Figure 16.17 Orbits for global positioning system (GPS) satellites