Sistem komunikasi berbasis code division multiple access (CDMA) dewasa ini berkembang sangat pesat. Untuk mendukung teknologi generasi ketiga atau third-generation (3G), CDMA diharapkan mampu memenuhi kebutuhan layanan audio, data, maupun video dengan kapasitas sistem yang besar. Layanan audio, data maupun video yang terdapat dalam suatu sistem CDMA dapat dipandang sebagai sistem multiclass CDMA. Pada kenyataannya, kapasitas CDMA dibatasi oleh interferensi, sehingga untuk meningkatkan kapasitas dilakukan dengan mengurangi interferensi.Salah satu metode untuk mengurangi interferensi adatah sektorisasi dan pengendalian daya. Pada penelitian akan dianalisa pengaruh pengendalian daya tak sempurna (imperfect power control) dan sektorisasi tak sempurna (imperfect sectorization) pada kapasitas user dari sistem CDMA arah reverse-link berdasarkan signal to interference ratio (SIR) dengan menggunakan beamforming pada pengirim mobile station (MS) dan penerima base station (BS). Kapasitas user dipengaruhi oleh jumlah elemen antena beamforming, jumlah sektor, besar sudut overlap akibat sektorisasi tidak sempurna., dan pengendalian daya tidak sempurna.Hasil penelitian menunjukkan bahwa kapasitas sistem multiclass CDMA menurun akibat pengendalian daya dan sektorisasi tak sempurna. Sektorisasi dengan antena beamforming menghasilkan kapasitas sistem multiclass yang lebih besar dibandingkan penggunaan antena beamforming tanpa sektorisasi. Peningkatan total jumlah elemen antena beamforming pada penerima BS dan pengirim CIS tidak selalu menghasilkan kapasitas sistem multiclass yang lebih besar, akan tetapi tergantung dari pendistribusian jumlah elemen antena beamforming pada penerima BS dan pengirim MS. Sektorisasi dengan antena beamforming menghasilkan kapasitas sistem multiclass lebih besar dibandingkan dengan sektorisasi tanpa antena beamforming. Kapasitas sistem multiclass optimum dicapai bila jumlah elemen antena penerima beamforming genap.

---

Communications systems based on code division multiple access (CDMA) are growing fast this day. To support third generation technology (3G), CDMA has been expected to fulfill requirements of audio, data, and video services with higher system capacity. Audio, data and video services in CDMA systems can be viewed as multiclass CDMA system. In practice, capacity of CDMA is limited by interferences, so that any reduction of the interference will directly cause capacity increases.

Methods, such as sectorization and power control could reduce the interference. In this research, the impact of imperfect power control and imperfect sectorization to reverse-link user capacity of CDMA system based on signal to interference ratio (SIR) by using beamforming at mobile station (MS) transmitter and base station (BS) receiver will he analyzed. User capacities are influenced by number of antenna beamforming elements, number of sectors, overlap angle due to imperfect sectorization, and imperfect power control.

Results of this research indicate that capacity of multiclass CDMA system decreases caused by the imperfect power control and imperfect sectorization. The system with sectorization using beamforming has large capacity of multiclass system than the system using beamforming without sectorization, The total addition of antenna beamforming elements at SS receiver and MS transmitter not always has large capacity of multiclass system, however depend on distribution of antenna beamforming elements at BS receiver and MS transmitter. The system with sectorization using beamforming has large capacity of multiclass system than the system with sectorization without beamforming. Optimum capacity of multiclass system achieved, when beamforming has even number of receive antenna elements.