Rake Receiver Instead of trying to overpower or correct multipath problems, CDMA takes advantage of the multipath to improve reception quality in fading conditions. CDMA does this by using multiple correlating receivers and assigning them to the strongest signals. This is possible because the CDMA mobile is synchronized to the serving base station. The mobile’s … Read more
Vocoders Human voice is made up of a combination of voiced and unvoiced sounds Vocoders exploit these properties of speech production mechanism Vocoders do not respond to music, non-human sounds and tones from voice band modems PCM vs VOCODERS CDMA VOCODERS 8 kbps variable rate coder Rate 1 Rate 1/2 Rate 1/4 Rate 1/8 Cdma … Read more
Why Power Control Essential in CDMA ? Power control is essential for the smooth operation of a cdma system. Because all users share the same rf band through the use of pn codes Each user looks like random noise to other users. The power of each individual user therefore, must be carefully controlled so that no … Read more
There are Four channel in Forward direction in cdma. PILOT CHANNEL (1) SYNC CHANNEL (1) FORWARD TRAFFIC + PAGING CHANNELS (62) PAGING CHANNELS ( MAXIMUM 7) PILOT CHANNEL PILOT SIGNALS ARE TRANSMITTED BY EACH CELL SITE TO ASSIST MOBILE RADIO IN ACQUIRING AND TRACKING THE CELL SITE DOWNLINK SIGNAL PILOT CHANNEL IS ASSIGNED CODE CHANNEL … Read more
When we talk, we pause between syllables and words. CDMA takes advantage of these pauses in speech activity. Analog to digital conversion The voice signal is converted to a digital signal using PCM. Variable rate vocoder The vocoder (Voice Coder) is used to compress the digital signal from the Codec (Code/Decode). The vocoder, used in … Read more
The Global Positioning System (GPS) is a radio-navigation system that employs RF transmitters in 24 satellites. The satellite configuration when completed will guarantee that a GPS receiver located anywhere on earth can receive RF signals from at least four satellites 24 hours a day (with unobstructed visibility). For commercial use, each satellite transmits unique bi-phase … Read more
Downtilting is the method of effectively adjusting the vertical radiation pattern of the antenna to increase the amount of power radiated downwards. Downtilting can be used to increase the amount of coverage close to the site where “nulls” (holes) may exist due to the effective height of the antenna. Downtilting can also be used to … Read more
Voltage Standing Wave Ratio Voltage Standing Wave Ratio (VSWR) is another parameter used to describe an antenna performance. It deals with the impedance match of the antenna feed point to the feed or transmission line. The antenna input impedance establishes a load on the transmission line as well as on the radio link transmitter and … Read more
Antenna beamwidth is measured in degrees between the half power points (3 dB) of the major lobe of the antenna, Beamwidth can be expressed in terms of azimuth (horizontal or H-plane) and elevation (vertical or E-plane). The predominant type of antenna configuration within urban areas at PCS frequencies will be three sectored. This implies that … Read more
CDMA forward channel carrier power varies greatly depending on how many traffic channels are in use, the characteristics of the users voices, the Forward Power Control settings as requested by each subscriber unit in use, and the power allocated for overhead functions (Pilot, Page and Sync). An approximation of the CDMA forward channel carrier power … Read more