Reduced gain spread spectrum communication system and method

Details Reduced gain spread spectrum communication system and method Reduced gain spread spectrum communication system and method

1997-09-26

2001-08-07

Chin, Stephen (Department: 2634)

Pulse or digital communications

Spread spectrum

C375S140000, C375S146000, C370S335000, C370S342000

Reexamination Certificate

active

06272166

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates to the field of multi-user communication systems, and more particularly to a reduced gain spread spectrum communication system and method.
BACKGROUND OF THE INVENTION
The popularity of wireless communication systems, such as cellular telephones, has lead to the need for different techniques to allow multiple users to communicate simultaneously. Some existing wireless communication systems support different users transmitting both voice and data.
A code division multiple access (CDMA) system assigns specific codes to users, thus allowing a base station to separate out individual communications based on the code. A time division multiple access (TDMA) system assigns specific time slots for communication to ensure that user communications do not interfere with each other. These systems suffer from several drawbacks including the complexity required for both the transmitting device and the base station, the inability for all users to transmit at once, and a reduced system capacity based on the number of available codes or time slots.
Some systems that attempt to solve some of these drawbacks use the Aloha protocol. One version of the Aloha system allows multiple users to transmit simultaneously but there is no spreading of the signal. This system suffers from reduced capacity for an available transmission bandwidth. Another version of the Aloha system spreads the signal throughout the available transmission bandwidth. This systems offers increased capacity but may not be suitable for real-time communication, such as voice, that depends on a guaranteed transmission rate.
SUMMARY OF THE INVENTION
In accordance with the present invention, a reduced gain spread spectrum communication system and method are provided which substantially eliminate or reduce disadvantages and problems associated with prior multi-user wireless communication systems.
In accordance with one embodiment of the present invention, an apparatus for wireless communication includes a spreader having an input and an output. The spreader receives a digitized voice signal and spreads the digitized voice signal using a voice spreading sequence length less than an available spreading gain to generate a voice spread signal. A transmitter transmits the voice spread signal. The spreader can also receive a data signal and spread the data signal using a data spreading sequence length greater than the voice spreading sequence length to generate a data spread signal.
Technical advantages of the present invention include a multi-user wireless communication system that allows more than one user to transmit the same code, thus reducing system complexity. Additionally, since this is an asynchronous system, the present invention allows users to transmit simultaneously. Also, by choosing a voice spreading sequence length less than the total available spreading gain, the transmission time decreases sufficiently to allow for retransmission in the event packets from different users interfere or collide with each other. Therefore, the present invention allows for the real-time transmission of voice in a multi-user environment.


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