Motorola AN2254/D free download

File name AN2254.pdf

Application Note AN2254/D Rev. 0, 4/2002 Scrambling Code Generation for WCDMA on the StarCore SC140 Core by Imran Ahmed CONTENTS 1 Pseudo-Random ... Sequences ... 1 1.1 Randomness Properties 1 1.2 Generating Pseudo-Random Sequences ... 2 2 Scrambling Codes for WCDMA ... 2 2.1 Generating Long Complex Scrambling Codes... 3 2.2 Scrambling an I-Q/Code Multiplexed Signal ... 5 3 Software Implementation on the StarCore SC140 Core ... 6 3.1 Allocating Memory Space ... 6 3.2 Generating Binary PN Code and Forming Complex Scrambling Sequences ... 7 3.3 Forming the Complex Scrambling Sequences.. 9 3.4 Complex Scrambling of an IQ/Code Multiplexed Signal ... 13 4 Results ... 16 5 References ... 18 In a Wideband Code Division Multiple Access (WCDMA) environment, each user is assigned a unique complex scrambling sequence to encode its information-bearing signal. The receiver has the scrambling code of the user, unscrambles the received signal, and recovers the original data [1]. This application note presents a method for complex pseudo-random sequence (PN code) generation and complex scrambling of an I/Q code multiplexed signal on a StarCore® SC140 digital signal processor (DSP). The PN codes in this application note are generated for a WCDMA Universal Mobile Telecommunications Systems (UMTS) uplink (signal from handset to base station) according to the third-generation partnership project (3GPP) specifications. This application note provides practical information to help users understand PN code generation and complex scrambling, which are required in the WCDMA standards. Typically, these operations are performed on Architecture-Specific Integrated Circuits (ASICs), but here we explore the use of the Motorola StarCore SC140 digital signal processing (DSP) core to accomplish the same task. 1 Pseudo-Random Sequences Pseudo-random sequences or PN codes are sequences of 1s and 0s generated by an algorithm so that the resulting numbers look statistically independent and uniformly distributed. A random signal differs from a pseudo-random signal in that a random signal cannot be predicted. A pseudo-random signal is not random at all; it is a deterministic, periodic signal that is known to both the transmitter and the receiver. Even though the signal is deterministic, it appears to have the statistical properties of sampled white noise. To an unauthorized listener, it appears to be a truly random signal. 1.1 Randomness Properties CDMA systems achieve their multiple access capability using large sets of sequences with three basic properties that are applied to a periodic binary sequence as a test for the appearance of randomness [2]: · Balance Property. In each period of the sequence, the number of binary 1s must differ from the number of bi