Sharif Digital Repository

In this paper, we explore some of the fundamentals of synchronous Code Division Multiple Access (CDMA) as applied to wireless and optical communication systems under very general settings (of any size) for the user symbols and the signature matrix entries. The channel is modeled by real/complex additive noise of arbitrary distribution. Two problems are addressed. The first problem concerns whether uniquely detectable overloaded matrices exist in the absence of additive noise under these general settings, and if so, whether there are any practical optimum detection algorithms. The second one is about the bounds for the sum channel capacity when user data and signature matrices employ any real... 

Overloaded code division multiple access being the only means of the capacity extension for conventional code division multiple access accommodates more number of signatures than the spreading gain. Recently, ternary Signature Matrices with Orthogonal Subsets (SMOS) has been proposed, where the capacity maximization is 200%. The proposed multi-user detector using matched filter exploits the twin tree hierarchy of correlation among the subsets to guarantee the errorless recovery. In this paper, we feature the non-ternary version of SMOS (i.e., 2k-ary SMOS) of same capacity, where the binary alphabets in all the k constituent (orthogonal) subsets are unique. Unlike ternary, the tree hierarchy... 

In this paper, we analyze the effect of applying leaky bucket as a well known traffic shaper on data users in a variable spreading gain CDMA (VSG-CDMA) uplink wireless cellular network. To this end, we model the effect of leaky bucket mechanism on a typical data user, with a closed product form queueing network. Each node in this queueing network corresponds to a specific processing gain or equivalently transmission rate and power. By solving such a queueing network we obtain the steady state probability with which a typical data user will exist at each node. By aggregating the effects of all data users we compute the mean and variance of interference and obtain the throughput and average...