Operators of UMTS/FDD cellular communications systems will require efficient network planning to distribute the valuable available resources or frequencies. To do so, the ability to identify node-Bs in the field is necessary. A classical trace mobile does not have sufficient sensitivity or signal separation capacity to identify low interfering signals. Space-time processing based on smart antenna techniques is used to suppress co-channel interference caused by other base stations and significantly improve sensitivity. Identification of the interfering node-Bs first includes the synchronization with all the surrounding base stations and then the demodulation and the interpretation of the Primary Common Control Physical Channel (P-CCPCH) providing valuable information such as the Cell Identity (CI), the Mobile Country Code (MCC) or the Mobile Network Code (MNC).
Since UMTS-FDD mode provides synchronization channels containing a known primary synchronization, we can use a detection approach to obtain synchronization. The aim of such a method is to compute a decision statistic for every possible time instant, which can be processed in further stages to decide whether or not a synchronisation sequence is present. The initial objective of ANTIUM was to detect BTS having a P-CPICH Ec/I0 as low as -25dB, since it was shown that such BTS could have an impact on the mobile performance when they are fully loaded. If we consider P-CPICH Ec/I0 between -20dB and -15dB, a mono-channel processing allows detecting only about 61% of the BTS detected with a 5-channel one. This percentage drops to 17% if we consider P-CPICH Ec/I0 between -25dB and -20dB. Therefore a multi-channel processing improves significantly the detection performance and is required to reach the ANTIUM objectives. A 3 or a 4-channel ANTIUM equipment seems to be a good trade-off between performance / cost / complexity, since it allows to detect respectively 64% and 78% of the BTS detected with 5 channels in the range [-25dB; -20dB].
For identification, several multi-sensor demodulation algorithms were developed. As the spreading factors and the spreading codes allocated to the channels transmitted by the detected node-Bs are unknown, it is impossible to use joint detection algorithms in order to detect the symbols transmitted by the P-CCPCH. We therefore study a family of sub-optimal receivers, which only require the knowledge of the spreading code allocated to the P-CCPCH. Roughly speaking, each of them consists in estimating the chip sequence by a spatio-temporal filter. This filter can be interpreted as a multi-channel equalizer because, ideally, it allows both to compensate the effect of the propagation and to cancel signals due to interfering node-Bs. The studied algorithms are the following ones: 2D Rake, Spatial Wiener Filter, Spatial Wiener Filter with Filtered Reference, Spatial Rake with Spatial Whitening, Space-Time Wiener Filter. The Spatial Rake with Spatial Whitening (SRSW) presents the best trade-off in terms of complexity / performance. With a 5-channel processing, the SRSW allows to demodulate the BCH information with a good CRC rate better than 90% when the P-CCPCH Eb/I0 is greater than -1dB (which corresponds to a P-CPICH Ec/I0 greater than -20dB if the P-CCPCH level is 2dB below the P-CPICH one). In comparison, the loss of performance by using a 1-channel processing is equal to 11dB.
Moreover, the UMTS-FDD standard foresees the use of transmit diversity on different downlink physical channel types. Therefore, all the developed algorithms were extended to the Space-Time Transmit Diversity mode that is used on the P-CCPCH. In a first stage, the algorithms have been developed and tested in simulation using a C environment. The results have been published in several conference papers and a doctoral dissertation. Then they have been implemented on a demonstrator and validated on the field on real UMTS/FDD networks. The performance describe above comes from these field trial measurements. The algorithmic study is detailed in D3011b and the validation on the field in D5011.