Correcting the Bias of Subtractive Interference Cancellation in CDMA: Advanced Mean Field Theory

In this paper we introduce an advanced mean field method to correct the inherent bias of conventional subtractive interference cancellation in Code Division Multiple Access (CDMA). In simulations, we get a performance quite close to that of the individual optimal exponential complexity detector and significant improvements over current state-of-the-art subtractive interference cancellation in all setups tested, for example in one case doubling the number of user at a bit error rate of. To obtain such a good performance for finite size systems, where the performance is normally degraded by the presence of suboptimal fix-point solutions, it is crucial to use the method in conjunction with mean field annealing, i.e. solving the fixed point equations at decreasing temperatures (noise levels). In the limit of infinite large system size, the new subtractive interference cancellation scheme is expected to be identical to the individual optimal detector. The computational complexity is cubic in the number of users whereas conventional (naive mean field) subtractive interference cancellation is quadratic. We also present a quadratic complexity approximation to our new method that also gives performance improvements, but in addition requires knowledge of the spreading code statistics. The proposed methodology is quite general and is expected to be applicable to other digital communication problems

Cultures of Agility – Agile Software Development in Practice

Agile Software Development (ASD) has gained much attention as an approach that provides values and principles for dealing with turbulent environments and change as they are now common for many systems development projects. Literature stresses the importance of organizational culture for agile development, but only little empirical research about their relationship has been conducted. On this background we carried out a cultural analysis in 3 organizations which perform systems and software development according to agile principles. We found that agile development thrives in different organizational cultures as long as the 4 core values are present to a significant extent. This is possible because agile methods bear to compromise even with central elements of the agile approach; this is the essence of agility