Performance analysis of type-I and type-II hybrid ARQ protocols using concatenated codes in a DS-CDMA Rayleigh fading channel

To achieve reliable data transmission in a power-controlled, direct-sequence code division multiple access cellular system, we investigate two error-control schemes based on the concatenation of Reed-Solomon and convolutional codes. The first scheme is a type-I hybrid selective repeat ARQ protocol (CC/HARQ) where the error detection capability of the RS outer code is used to trigger retransmission requests. The second scheme is a type-II hybrid selective repeat ARQ protocol where the error correction capability is adapted to the varying channel conditions, The performance criteria are the protocol error probability, the throughput and delay efficiencies over a Rayleigh fading DS-CDMA channel with a Gaussian approximation for the multiple access interference. While type-I CC/HARQ yields superior throughput when the number of active users is small, the results show that type-II CC/HARQ provides reliable data transfer to the largest number of users, even in the presence of imperfect power control.