TAILIEUCHUNG - Theory and applications of ofdm and cdma wideband wireless communications phần 10

Tham khảo tài liệu 'theory and applications of ofdm and cdma wideband wireless communications phần 10', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CDMA 375 channel. Having received this information the transmission of the dedicated channel is switched off by all cells of the active set except for the strongest one. Obviously this feature can only be active if no closed-loop transmission diversity requiring the FBI is used. While a soft handover can be managed using the multiple fingers of the MS RAKE receiver additional means are required for a hard handover between different frequency carriers. To perform measurements either an additional measurement receiver is needed or the so-called slotted or compressed mode has to be applied. In this mode data transmission is compressed to shorter intervals to gain some time for measurements on carrier frequencies different from the present one. Compression can be achieved by a reduction of the data rate by higher layers transmitting the data at twice the original rate using half the spreading factor and increasing the puncturing. By these methods several idle slots per frame can be produced. Time Division CDMA A part of the spectrum allocated to IMT-2000 by the ITU consists of unpaired frequency bands and is therefore not suited for operation within the FDD mode. For this reason also a TDD mode for UTRA has been specified. The TDD mode has been derived from a system proposal called TD-CDMA that combines time division and code division multiple access. The original idea behind this proposal submitted to the ETSI was to reduce the number of intracell interferers by dividing a frequency carrier into several disjoint time slots and thereby having only a few code channels per time slot. Since there are only a few interfering connections within a cell these can be jointly detected and separated with a moderate calculation complexity. Since the specific joint detection JD algorithm was an essential ingredient of the system proposal it also was called JD-CDMA. Having selected TD-CDMA as a TDD mode for IMT-2000 it has been harmonized to WCDMA for example the chip rate has

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