This paper presents a comprehensive study of the impact of Group Velocity 
Dispersion (GVD) on the performance of two-dimensional wavelength hopping/time 
spreading optical code division multiple access (2-D WH/TS OCDMA) systems. A 
realistic model of Gaussian pulse shape is assumed and heterodyne detection 
receiver is used so that the receiver's sensitivity can be improved. Many noise 
and interference, including multiple access interference (MAI), optical beating 
interference (OBI), and receiver's noise are included in the analysis. 
Analytical results show that, under the impact of GVD, the number of supportable 
users is significantly decreased and the maximum transmission length (i.e. the 
length at which BER $\leq 10^{-9}$ can be maintained) is remarkably shortened in 
the case of normal single mode fiber (ITU-T G.652) is used. The main factor that 
limits the system performance is time skewing. In addition we show how the 
impact of GVD is relieved by dispersion-shifted fiber (ITU-T G.653). For 
example, a system with 32 $\times$ 1 Gbit/s users can achieve a maximum 
transmission length of 100 km when transmitted optical power per bit is -5 dBm