Reverse link is weak in CDMA because of use of PN Long codes compared to Walsh codes in the forward link. Since, walsh codes are perfectly orthogonal in nature there is less interference in the forward link. PN long codes on the other hand are non-orthogonal in nature. However, we cant use walsh codes for the reverse link as it may seem from the above as the best possible solution. This is because walsh codes are very small in number (64/128/512 max), and hence are not sufficient for identification of large number of users in the reverse link for which the PN long codes are employed.