CDMA underlay network with cognitive interference‐minimizing code assignment and semi‐blind interference suppression

Abstract

In this paper, we propose a code‐division multiple‐access (CDMA) secondary network to operate cognitively as an underlay for a primary network. A novel interference‐minimizing code assignment (IMCA) for secondary users is proposed such that the interference from existing primary and secondary users is minimized. This is accomplished by minimizing the mean square cross‐correlations between the candidate codes and the received signal. Since the codes of the primary CDMA network are unknown to the secondary network the scheme operates blindly and the problem is formulated as a constrained optimization of a Boolean quadratic form. The solution is obtained exhaustively and we demonstrate significant performance gains compared to random code assignment (RCA). We then slightly relax the constraint on the user code space and obtain a near‐optimal solution with complexity that is linear in the spreading factor. For the secondary network, we propose a slightly modified minimum‐output energy receiver that operates semi‐blindly as a first stage followed by parallel interference cancellation. For this receiver structure, we derive improved log‐likelihood ratios for the single‐user decoders based on partial knowledge of the user codes and channel coefficients. Significant error probability performance improvements of 2 dB or more are obtained due to IMCA in the coded case. Copyright © 2008 John Wiley & Sons, Ltd.

Multicarrier Spread Spectrum Modulation Schemes and Efficient FFT Algorithms for Cognitive Radio Systems

“…In [33,34], the authors have proposed an interference-minimizing code assignment strategy for the secondary users in the CDMA underlay cognitive radio networks. The interference caused from the existing primary and secondary users is minimized by minimizing the mean square cross-correlations between the candidate codes and the received signal.…”

Spread-spectrum cognitive networking: Distributed channelization and routing

“…Power control under an "interference temperature" constraint (total secondary user disturbance power over primary band) was considered [18] in cognitive code-division systems, but no code-channel (signature) optimization was carried out for the secondary users. In contrast, in [19] a secondary code assignment scheme was presented to obtain the binary secondary signature by hard-limiting the code sequence that exhibits the minimum mean-square crosscorrelation with the primary received signal. Secondary code set of multiple secondary users was also constructed in an iterative way.…”

Cognitive Code-Division Channelization with Admission Control

“…In all the above literature of cognitive code-division networks, no optimization was carried out with respect to code channels (signatures) of secondary users. In contrast, code design for secondary code-division links was considered in [12][13][14], where SUs coexist with a wideband primary code-division multiple access (CDMA) system. In [12], a single secondary code-divison link is designed such that it achieves the maximum SINR subject to primary SINR requirements [12].…”

“…In [12], a single secondary code-divison link is designed such that it achieves the maximum SINR subject to primary SINR requirements [12]. The extension to the design of multiple secondary code-division links is studied in [13,14]. In practice, there exist many scenarios where the primary (legacy) users communicate with modulated narrowband signals.…”