cdma technology optimization
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
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
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
Diversity Reception: Multiple Antennas at Base Station Each Antenna is Affected by Multipath Differently Due to Their Different Location Allows Selection of the Signal Least Affected by Multipath Fading If Diversity Antennas are Good, Why Not Use Base Stations as a Diversity Network? – Soft Handoff The concept of diversity reception has been well known … 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
IP Networks use Routers to do the switching based on IP addresses, Layer 3 routing protocols like BGP or OSPF an Ethernet networks use 48 bit MAC addresses Spanning Tree is used to route because users, base stations, routers, etc will all need IP addresses (It is an IP-based system) There are Public (Internet routable) … Read more
CDMA takes advantage of quiet times during speech to raise capacity. A variable rate vocoder is used; for the original vocoder the channel is a 9,600 bps when the user is talking. When the user pauses, or is listening, the data rate drops to only 1,200 bps (CDMA Variable Rate Speech Coder). Data rates of … Read more
Closed loop power control is used to allow the power from the mobile unit to deviate from the nominal as set by open loop control. This is done with a form of delta modulator. The base station monitors the power received from each mobile station in reverse link and commands the mobile to either raise … Read more
The Open Loop Power Control require in cdma due to following reason. Assumes Loss is Similar on Forward paths and Reverse Paths Receive Power + Transmit Power = -73 All Powers in dBm Example: For a Received Power of -85 dBm Transmit Power = (-73) – (- 85) Transmit Power = +12 dBm Provides an … Read more