Iterative Signal Processing for Blind Code Phase Acquisition of CDMA 1x Signals for Radio Spectrum Monitoring

Abstract

This paper addresses the problem of recovering the code phase of the composite spreading sequence for a CDMA 1x signal transmitted from a handset, without the benefit of a priori information from the system. The spreading code is required for the radio spectrum monitoring system for signal detection and measurements rather than for communications. The structure of the CDMA 1x signal is exploited by processing sequential pairs of received samples to form a single soft sample for each pair. The approach models the combination of the long-code generator and the two short-code generators, along with the pair-wise processing, by a single linear system over GF(2), with the initial states of the long- and short-code generators forming the input vector. Consequently, a vector of the pair-wise soft samples can be treated as a noisy received codeword that is decoded using iterative soft-in decoding techniques. If the decoder yields the correct candidate “codeword,” the original states of the code generators can be computed. This approach does not require direct access to the transmitted spreading sequence but can be applied to the data modulated signal. Simulation results provide performance estimates of the method with noise, Rayleigh fading, and co-channel interference.

Selection of Parity Check Equations For the Iterative Message-Passing Detection of M-Sequences

“…Since t, K and N are fixed parameters, the minimization of I 6 is equivalent to minimizing tr(A 3 ). This can be done by selecting the set of trinomials leading to the smallest value of I 6 , according to (12). The complexity of computing tr A 3 could be reduced.…”

“…The results provided by (12) and (13) have been successfully cross-checked with the software library developed by Halford and Chugg [26]. It used to be downloadable, but this is unfortunately no longer the case.…”

“…Subtracting the number of native cycles of length 6 and 8 from the actual number of native cycles gives a measure of the number of hybrid cycles. I 6 and I 8 are given by (12) and (13). We will now evaluate the number of native cycles.…”

“…Compute I 6 according to (12) if I 6 == N K then compute I 8 according to (13) if (I 8 < min) then save configuration (g 0 (x), · · · , g K−1 (x)) and min ← I 8 end if end if end while…”

“…This solution was originally proposed in cryptography for fast correlation attacks on stream ciphers [7][8] [9]. It has been applied more recently in wireless communications and localization domains [10][11] [12][13] [14] [15]. The task of the decoder is to simultaneously decide whether an m-sequence is received, and if so, to decode its initial state [16].…”