الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 136 |  |  |
| | | from | 136 | | |
Abstract
Recently, the mobile communication systems have been exploded. CDMA is just introduced as a multiple access interface scheme. Ideal performance of a CDMA system requires orthogonal spreading codes among different users. There are two types of codes in use. The first is the orthogonal code set, such as Walsh-Hadamard codes, which is used to maintain synchronization and the second is the scrambling code set, such as Gold codes or Kasami codes. This code set is used to make other-user’ signals appear as random disturbances. This disturbance is called multiple access interference (MAI). As a result of MAI and thermal noise, the system’ users are interfered. Hence, each user may increase its transmission power to achieve his required SIR. However, this may leads to increase the MAI to other users, which in turn leads to increase the users power until some or all of them reach their saturation power levels. Therefore, power control is a necessary requirement for wireless systems based on CDMA. This is due to the fact that power control leads to minimize the total transmitted power, enhance the battery life, decrease the MAI, and increase the capacity. Therefore, power control was the objective of the work reported here. The results obtained from the study in this thesis may be summarized in the following conclusion remarks: 1. For the power distribution problem, a matrix inequality for the power vector of N users in a cell in terms of traffic demands is established. The traffic demands must not exceed unity for a solution to the above mentioned power vector to exist. It is also found that, the closer the traffic demands per cell to unity, the higher the required transmission powers. 2. The analysis and performance for different types of power control algorithms have been conducted to recommend the one which provide better performance. It is found that the algorithm based on the minimum total transmitted power minimizes the MAI whereas the algorithm based on maximum total rate maximizes the system throughput. 3. To enhance the performance of the power control even further, an adaptive power control algorithm is introduced. In this algorithm a parameter K is used to control the speed of convergence of the power adaptation function so that transmitted power reach the level required to attain the minimum Eb/No required. 4. In the last part of the work reported here, the performance of two transmission modes was concluded. In the first mode, the class 2 users (delay tolerant class) could transmit signals at any time while in the second mode, the class 2 users are scheduled. Therefore, at any time, a limited number of users transmit signals while the others are connected to the base station to maintain synchronization. The two modes are applied according to the following two cases: Case 1, there was no constraints on the peak transmitted power. It is concluded for this case that: • The average power in either transmission mode for each user in both user classes is the same. • In the second mode, the peak power required for class 2 users is less than that required in the first mode. • The throughput achieved by the second mode is greater than that achieved by the first mode. Case 2, here there was a constraint on the peak transmitted power. It is concluded for this case that: • The average power required for both classes of users is less in the second mode than in the first mode. • The peak power required in class 2 is identical in both transmission modes. Hence the throughput gain is simply a consequence of the transmission mode. •The throughput achieved by the second mode is greater than that achieved by the first mode.