Adaptive tuning of radio channel

Conditions of radio communication over the links connecting subscribers to a base station vary considerably in mobile communication systems. Mismatching takes place due to varying distances, different speeds that give rise to the Doppler’s frequency shifts and due to many different characteristics of the paths (various frequency-selective fading, suppression levels, diffractions, refractions, re-reflections etc.). A radio-channel adaptive tuning for each existing connection is used in mobile communication systems to overcome these difficulties. The first significant limitation is the distance between the subscriber and the base station location. In 2G and 3G systems, a distance of 30 km is a limit. In the McWiLL system, the adaptive control methods based on using the RANGE signal make it possible to reach a limit of 34 km. The second important peculiarity that makes the McWiLL system special among other well-known mobile and cellular systems is the use of an adaptive tracking of subscribers by the beams of the base-station antenna patterns with the simultaneous suppression, within this pattern, of powerful interfering signals from point sources (other subscribers) at the reception and the suppression of the emission of the channel under consideration in the direction of the signals transmitted  towards the same point sources (other subscribers). This effect is reached by implementing the DOA algorithm that ensures, in the TDD mode, the full coincidence of patterns at the reception and at the transmission. The McWiLL system implements an adaptive control of the size of training sequences in active communication channels. These sequences according to the classification used in cellular communications represent RS (reference) signals and are used for communication-channel frequency –response and phase-response equalization so that frequency-selective fading can be cancelled. For mobile subscribers, the specific percentage of training sequences in the resource block was increased by a factor of 2 in comparison to fixed subscribers. In the conditions of varying S/N ratio, the McWiLL system implements the control over Loading Factor index allowing the change of information transmission rate by a factor of 8 (from 1 to 1/8) which is noticeably more than the change implemented in the known systems of 2G – 4G generations. Also supported is the use of QPSK, PSK-8, QAM-16 and QAM-64 modulations. The PKS-8 modulation is not used as rule and this, to a certain extent, limits the means of adaptive tuning. It is well known the OFDM signals used in the systems of 4G generation and later generations are relatively unstable with respect to Doppler’s frequency shifts. Moreover, non-uniform Doppler’s spectrum shifts may appear during the operation in the areas of overlapping coverages.  The McWiLL system employs an algorithm that corrects multi-Doppler’s distortions and achieves thereby the possibility to increase the permissible speeds of subscriber movement by a factor of  2…2, 5. Besides, the McWiLL system provides monitoring of the interference situation by observing it in the special SOW spectrum-time windows and carries out the ensuing re-configuration as necessary. The power-tuning and delay control are carried out exactly in the way is done in the known cellular communication systems.