d). This means that one chip is 0.26 us. Now these spreading codes contain two more codes: scrambling code and channelisation code. Actually: Spreading code = scrambling code X channelisation code. Scrambling Codes Scrambling codes are used on top of the spreading codes, thus not changing the bandwidth of the signal but only making it different for the purpose of separation. These codes are used to separate the users and cells (and/or base station) in the uplink and downlink directions respectively. In the downlink direction, it is possible to generate about 262 148 (218 scrambling codes. However, not all these codes can be used. The scrambling codes are divided into 512 groups and each of these groups has one primary and 15 secondary scrambling codes. Based on these principles, it is possible to have 8191 codes. In the uplink direction, there are 224 scrambling codes. These uplink codes are subdivided into long and short codes. Channelisation Codes Channelisation codes are used in the downlink direction to separate users and channels within the same cell. In the uplink direction they are used to separate data and control channels from same user equipment. These codes are based on a technique known as OVSF (orthogonal variable spreading factor). The OVSF technique maintains the orthogonality between the different spreading codes while allowing the spreading factor to be changed. These codes increase the transmission bandwidth. 7.3.3 Rate Matching This is a process by which the number of bits that are to be transmitted is matched to the num- ber of bits that are available on a single frame. If the number of bits transmitted is lower than the maximum, then the transmission may get interrupted. Thus processes such as repetition and puncturing are used to make the two numbers (transmitted and maximum) equal. In the uplink direction, repetition is the preferred way of rate matching. In the downlink direction, puncturing is the preferred method. UL rate matching is a dynamic process that varies with the processing of e