Analysis of Asynchronous Long-Code Multicarrier CDMA Systems With Correlated Fading

Abstract

Abstract-The effects of inter-carrier interference (ICI) and aperiodic random spreading sequences on the performance of asynchronous multicarrier code-division multiple-access (CDMA) systems with correlated fading between sub-carriers are investigated in this research. To conduct theoretical analysis for the maximal ratio combining (MRC) receiver, random parameters including asynchronous delays, correlated Rayleigh fading, and spreading sequences are averaged to find the unconditional covariance matrix of the interference-plus-noise vector. We demonstrate that the ICI in the system proposed by Kondo and Milstein (1996) can be mitigated by assigning a common random spreading sequence over all sub-carriers for each user, rather than using a set of distinct spreading sequences, where code sequences are assumed perfectly time-synchronized. Moreover, the analytic expression for the bit error probability (BEP) can be obtained with the Gaussian approximation. Simulation results are used to demonstrate the accuracy of our analysis. Various design tradeoffs including the number of sub-carriers, fading correlations, ICI and multipath effect are presented in simulation. We conclude that, when properly choosing a sufficiently large number of sub-carriers, the benefit of mitigating multipath interference and exploiting potential hidden frequency diversity shall prevail the impairment brought by increased ICI.Index Terms-Asynchronous transmission, code division multiple access (CDMA), correlated fading, inter-carrier interference (ICI), multicarrier CDMA, random signature sequence.

Interference‐resistant cooperative wireless networks based on complementary codes

“…The synchronous MC‐CDMA is also included as the benchmark. Since these systems perform different degrees of spreading over the frequency and time domains, we set the same composite spreading ratio 28, defined as the product of the number of subcarriers and the length of a signature sequence, for all systems. Figure 4 shows the comparison results when the composite spreading equals 512 and the number of users is 8.…”

A Joint Power Control and Interference Avoidance Code Assignment Strategy for Downlink MC-DS-CDMA with 2D Spreading

“…In the recent years, MC-DS-CDMA has shown its potential to be the transmission technology for the next generation broadband wireless access [1], [2]. Among the MC-DS-CDMA family, the MC-DS-CDMA with 2D spreading provides more flexibility in system design [3].…”

“…Secondly, the power control mechanism is used to maintain a predefined SINR target. Note that with the first step to avoid extra MAI, the power control mechanism in the second step can use less transmission power 1 The contact author's email: cwchang@ee.ncku.edu.tw. 2 This work was jointly supported by the National Science Council, Taiwan, under the contracts 95-2218-E-006-041 and 96-2221-E-006-020.…”