Method and apparatus for reducing effects of multiple access interference in a radio receiver in a code division multiple access communication system

A radio receiver for receiving a plurality of radio channels in a CDMA spread spectrum radio communication system comprising:

• a receiving antenna;
• receiving circuitry for converting an RF signal received by the antenna into an IF signal;
• circuitry for applying despreading codes to the IF signal to recover signals for each of the plurality of radio channels;
• decision circuitry for evaluating the signals of each channel and identifying signals with a high probability of correctness and signals with a low degree of correctness;
• memory storage for storing the signals of each channel;
• coding circuitry for applying spreading codes to the signals having a high probability of correctness;
• summing circuitry responsive to the coding circuitry for generating an IF broadband signal including all the encoded signals of the coding circuitry;
• subtracter circuitry connected to receive a first input from the receiving circuitry and a second input from the summing circuitry and operative for generating an IF broadband difference signal representing a difference between the first and second input
• means for applying the despreading codes of the channels having a low probability of correctness to the IF broadband difference signal to recover the signal channels;
• means for coupling the recovered signal channels to the memory storage;
• and
• output circuitry for outputing the stored signals from the memory storage.

A digital radio receiver for receiving a plurality of radio channels in a CDMA spread spectrum radio communication system, comprising:

• receiving circuitry for converting an RF signal into an IF signal;
• decoding circuitry for applying despreading codes to the IF signal to recover information signals for each of the plurality of radio channels;
• wherein the improvement comprises:
• decision circuitry having three level hard decision logic for evaluating the signals of each channel by comparing the signals to a threshold and converting signals having a high probability of correctness to a logic level and converting signals with a low probability of correctness to an erasure level;
• memory storage for storing output signals of each channel as supplied by the decision circuitry;
• pseudo transmission circuitry for applying spreading codes to the signal output of the decision circuitry having a high probability of correctness to produce broadband signals;
• and including
• summing circuitry for summing the broadband signals;
• means for deriving a difference signal representing the difference between the broadband signal and the signal output of the receiving circuitry;
• means for applying the despreading codes of the signals having a low probability of correctness to the broadband signal derived from the difference signal to recover the original signal transmitted;
• and
• means for coupling the recovered signals to the memory storage to overwrite erasure signals contained therein;
• and
• output circuitry for outputing the stored signals from the memory storage.

A method of reducing the influence of multiple access interference in a direct sequence spread spectrum radio receiver,

• comprising the steps of:
• recovering narrow band signals from a transmitted broadband spread spectrum signal by applying spreading codes as originally applied to transmitted narrowband signals and storing these recovered signals in a memory circuit;
• selecting the recovered signals stored in the memory circuit having an expectation of correctness as determined by comparing the detected signals with a logic threshold;
• spreading the selected signals having an expectation of correctness into a second broadband spread spectrum signal;
• delaying the transmitted broadband spread spectrum signal and summing the delayed signal with the second broadband spread spectrum signal to generate a difference signal representing a difference between them;
• and
• recovering new narrow band information signals from the difference signal and replacing stored signals in the memory with an expectation of incorrectness with the new narrow band information signals.