CDMA, Qualcomm, [Hong Kong, Korea, LA] THE MARKET TEST! Message Board

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Technology Stocks : CDMA, Qualcomm, [Hong Kong, Korea, LA] THE MARKET TEST!

QCOM 163.32

+2.3%

Nov 21 9:30 AM EST

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To: Maurice Winn who wrote (200)	6/22/1996 3:38:00 PM
From: Ingenious	of 1819

Maurice, soft capacity is central to CDMA Conventional wireless systems have a one to one correspondence between a signal frequency and a user. Thus, 64 channels on a base station are allocated in a first come first serve manner until they are all gone. The next caller to come onto to the base station loses and is given a busy signal. This is hard capacity. It is very easy to determine the capacity on these systems (such as TDMA, GSM, analog etc). Most digital and analog systems have a hard capacity because they assign one channel to each user or pair of users. Having hard capacity makes planning base station locations easy. The frequency bandwidht is chopped up and spread over a number of base stations to maximize the guard bands between frequcncies allocated to various users. If the frequencies are properly allocated, the physical seperation between users keeps them from stepping on other users. CDMA uses a different approach. CDMA transmits all user information over one wide frequency band and codes (eg code division) the information using a unique number for each phone. On a typical system all users transmit to the base stations (forward link?) on one frequency. Each phone is allocated the complete bandwidth to communicate with. The phones receive a signal containing coded information from all users on the single frequency and extract their phone call from the stream of digital information using the Viterbi decoder. The decoder is complex and uses the same unique number to extract only the information transmitted to that particular user. Essentially, as the number of users on this frequency increases, the decoder has a more difficult time extracting the information. Hence soft capacity. There is no real limit as to the number of users who can transmit over the same frequency except after awhile it will make EVERYONEs phone call sound more and more like white noise. If the system does not limit the number of users getting onto the system, then the quality of decoding degradates and the signal will become full of more "noise". The bandwidth remains the same but the quality of the signal degnerates incrementally for everyone. It is a very interesting way of doing things. If you read the QCOM marketing hype, they analogize the phone to a group of people in from all over the world in one room at a party. At the beggining of the party several people are talking loudly in their own language (Japanese, English, Polish etc). Even though you can hear all the other voices you understand your conterpart because you are filtering/decoding the other peoples language from your own conversation. HOwever, as more people get into the room the sounds start to mix and you can not even understand your party. The filtering eventually fails UNLESs everyone starts talking quieter and quieter (ie power control). Thus, QCOM solves the problem of noise by controlling power to users. IT is a very complex process that causes the system to dynamically adjust power to limit noise problems. The whole system is quite elegant if they can pull it off. However, I think they will face problems because there are other systems who can transmit at or near the frequencies CDMA is on. If others are tranmitting at the same time (ie QCOM cant stop others from using the airwaves) then the CDMA system tries to limit the noise by lowering their transmissoin signal powers. However, they can not stop others from transmitting at higher power frequencies; they can only limit their own system. Thus, unless the airwaves are perfectly free from other interference the CDMA system is at the mercy of environmental noise and other frequencies. This may have been the problem (current problem) in LA and other metropolis areas where the air is full of signal. Enough for now.. good luck

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