Overview
This project focuses future detection, acquisition and tracking algorithms for the FDD mode of UMTS. These sort of algorithms are crucial for system performance, which is limited by the air interface of UMTS. Therefore, it is necessary to drive algorithm development in this area to meet future performance requirements.
So far, the single element antenna case at the base transceiver station (BTS) has been analyzed. During the current phase of the project BTS using multiple-element antennas are considered.
When using these multi-element antennas, the BTS can either use spatial separation of the users within its cell by forming a directional pattern (SDMA) or it can make use of diversity, where disadvantageous fading conditions at one antenna may be averaged out by better conditions at the other antenna element.
The question, which one of these effects can be utilized, strongly depends on the specific channel scenario or the physical realization of the antenna (element spacing etc.).
In addition to these effects, the system experiences an array gain. This gain comes from averaging the different noise processes at the output of each element of the antenna. This also improves system performance.
A consequence of these facts is, that in order to reduce the overall interference level, the mobile may reduce its transmit power and this again complicates the tasks of detection, acquisition and tracking in the two dimensional UMTS receiver.
Issues analyzed throughout the project:
- detection and acquisition algorithms (timing)
- synthesis of detection and acquisition units of the receiver
based on detection algorithms - initial- and post acquisition concepts derived
- receiver structure
- Rake receiver structure for channel scenarios
formed by clusters (incl. channel estimation) - loss expected regarding ideal case
- outperforms standard approach when clusters are present
- post-acquisition takes over tracking task
- case study: Initial Frequency Offset Estimation
Interesting future issues:
The use of multiple element antenna systems enables the exploitation
of spatial structure in addition to temporal structure. In WCDMA this helps
to reduce inter-user interference and hence results in increased capacity.
- Challenging Problems
- in addition to temporal spreading the signal components
are also spread in the spatial domain, which leads to - single paths of very low power
- increase in dimension of search domain during
acquisition tasks
