Multiplex communications – Wide area network – Packet switching
Patent
1994-10-19
1996-09-17
Marcelo, Melvin
Multiplex communications
Wide area network
Packet switching
375267, 375347, 455 8, 455137, 4552781, H04B 708
Patent
active
055576036
DESCRIPTION:
BRIEF SUMMARY
SUMMARY OF THE INVENTION
This invention relates to apparatus and a method for provision of diversity in reception for a communications system such as the GSM cellular radio system.
SUMMARY OF THE PRIOR ART
It is a problem in radio systems such as the GSM cellular radio system operating at frequencies of the order 900 MHz that a signal propagates from a transmitting unit to a receiving unit over a number of paths and, at the receiving unit, it exhibits multi-path fading.
It is observed that if two or more receive antennas are provided, separated in distance, supplying signals to separate received channels, then the fading of the various channels is more or less independent, i.e. it is unlikely that all channels will fade together. Techniques known as diversity combining make use of several received signals to improve the realised signal to noise ratio and hence improve the bit error rate. For example a typical dual diversity (2 channel) system might offer an improvement in signal to noise ratio (SNR) of 10 dB.
Providing diversity is not without substantial cost. It is not possible merely to combine the main and diversity signals because they can interfere additively and destructively with equal probability. It is necessary to duplicate the receive circuitry including the receive amplifier and demodulator.
It would be desirable to provide diversity without the additional cost of duplicated circuitry.
SUMMARY OF THE INVENTION
According to the present invention there is provided radio communications apparatus for receiving a plurality of calls comprising: a plurality of receivers tunable to a plurality of frequencies, first and second antennas, switching means for switching the plurality of receivers to selected ones of the first and second antennas and control means coupled to the plurality of receivers for tuning the receivers to receive calls, the control means comprising: means for identifying a received call of low quality received through the first of the antennas and through a first of the plurality of receivers, means for identifying a spare receiver that is not required for receipt of a call, means for causing the switching means to switch the spare receiver to receive the call through the second antenna, means for tuning the spare receiver to the frequency of the call of low quality and means for diversity combining the calls through the first receiver and the spare receiver.
In this way, the control means utilize spare channel capacity to dynamically allocate receiver units to the diversity antenna and in this way there is provided a second source for the call identified as being of low quality.
The invention takes advantage of the realisation that, in a given cell of a cellular radio system, only a proportion of the calls passing through a base station are of such low quality as to substantially benefit from diversity combining. The invention also recognizes that at a given time the receive units are rarely at 100% capacity, so that there is often spare channel capacity which can be utilized for diversity purposes.
The invention provides the ability to add one or more extra receive units which can be dynamically shared for diversity purposes, rather than duplicating every receive unit.
In a time division multiplex system, a spare receive unit is identified for each time slot (it may be a different unit in each time slot). As a preferred feature of the invention, the control means spread the on-going calls in time among different time slots so that there is, as far as possible, spare channel capacity in each time slot. This spare channel capacity can then be used for diversity.
As a further feature of the invention, the receive antenna may be sectorized and the diversity antenna may be an adjacent sector of the receive antenna. This feature recognizes that the lobes of adjacent sectors of a sectorized antenna usually overlap to a degree, so that it is frequently the case that the signal from a mobile unit can be received at two radially separated sectors of a sectorized antenna. This feature
REFERENCES:
patent: 5097484 (1992-03-01), Akaiwa
ICC '82 Conference Record, vol. 1(3), Jun. 1982, NY, USA pp. 2B.5.1-2B.5.5., ASAI, et al., Design and Performance of a 200MB/s Synchronised Switchover Equipment.
Mototola Technical Developments, vol. 10, Mar. 1990, Schaumburg, Illinois, pp. 62-63, Tayloe, Space Deversity Hopper for Digital Data Transmission.
Barlett Ian
Bishop Peter W. D.
Marcelo Melvin
Motorola Inc.
Sitko Anthony G.
Toler Jeffrey G.
LandOfFree
Radio communications apparatus with diversity does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Radio communications apparatus with diversity, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Radio communications apparatus with diversity will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-419506