Pulse or digital communications – Testing – Data rate
Reexamination Certificate
1997-11-07
2001-05-01
Chin, Stephen (Department: 2634)
Pulse or digital communications
Testing
Data rate
C375S132000, C375S140000
Reexamination Certificate
active
06226320
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to multirate coding and detection in a multiple access mobile communication system in which a transmitter selects the data transfer rate, and forwards information on the selected data transfer rate to a receiver which adapts reception to the selected rate.
BACKGROUND OF THE INVENTION
In present-day digital mobile communication systems, user information, i.e. speech and data, are transferred over the radio interface in digital form. In some cases, it is possible to select out of many transfer rates the one which is best suited to a speech coding rate used and to data transfer requirements of the user. The transfer rate is typically chosen at the beginning of a call and maintained unchanged for the duration of the call. In mobile communication systems to come, more flexibility is required at the radio interface for embodying various kinds of services. One of the consequences of this requirement for flexibility is a rapidly varying transfer rate during a call. In a digital mobile communication system, for example, in which user information is packed into transmission frames (10 ms of duration, for example), each frame may have a transfer rate independent of the previous or the subsequent transfer frame. However, a problem emerges in how to transfer information on the current transfer rate as quickly as possibly from the transmitter to the receiver in order for the receiver to be able to adapt its operation to the transfer rate being used. In addition, in interference limited mobile communication systems such as spread spectrum radio systems, it is advantageous to employ a fast closed loop power control. By means of power control, a base stations seeks to adjust the transmit power of mobile stations so that all the signals transmitted by the mobile stations are received by the base station at the same nominal power level. In other words, by means of power control, the aim is to average the energy of a symbol transmitted over the radio path, and therefore the transmit power is also proportional to rate. Due to this, when employing closed loop power control, the receiver needs to know the current transfer rate without delay.
A known solution is to employ on the radio path a separate signalling channel through which information on the transfer rate is conveyed from the transmitter to the receiver. The closed loop power control can be carried out with such a signalling channel. Separate signalling, however, causes delay in the practical implementation. The message indicating transfer rate is protected against interference and interleaved in the transmitter. The most efficient interleaving lasts for the length of the transfer frame. Prior to knowing the transfer rate and completing the user signal processing, deinterleving and error correction are carried out in the receiver. As a consequence the received user signal has to be buffered until these reception operations are completed. A further consequence is that activating the closed loop power control is delayed. If the receiver of a spread spectrum system utilizes interference cancellation (IC) or multiuser detection (MUD), the delay caused by detecting the transfer rate employed also concerns the interfering signals (other users). In an asynchronous spread spectrum mobile communication system, the propagation delay, with the above assumptions, will be twice the interleaving depth+signal processing delay.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a system and an apparatus by means of which a receiver of a mobile communication system is able to detect, with a reasonable delay and an economical receiver construction, the transfer rate employed by a transmitter at any one time.
This is achieved with a method comprising the steps of selecting, at the transmitting end, the data transfer rate to be used on the radio path for transferring user information; forwarding information on the current transfer rate to the receiving end; adapting reception to the transfer rate employed. The method of the invention is characterized by allocating different signal waveforms to different transfer rates; selecting, at the transmitting end, the signal waveform to be used on the radio path according to the selected transfer rate; detecting, at the receiving end, the signal waveform used on the radio path; selecting, at the receiving end, a transfer rate corresponding with the detected signal waveform.
The invention also relates to an equipment for multirate coding in a transmitter of a multiple access mobile communication system, which transmitter sends user information to the radio path with a varying transfer rate. The equipment of the invention is characterized in that the transmitter is arranged to allocate different signal waveforms to different transfer rates, and the equipment is arranged to convey a data transfer rate information to the receiving end by using a signal waveform allocated to the transfer rate on the radio path.
In addition, the invention relates to an equipment for detecting a varying transfer rate in a receiver of a multiple access mobile communication system, the receiver receiving user information from the radio path with a varying transfer rate. The equipment of the invention is characterized in that the receiver is arranged to allocate different signal waveforms to different transfer rates, and that the equipment comprises a detector which detects the transfer rate used at the transmitting end on the basis of the received signal waveform.
According to the invention the varying transfer rate is coded at the transmitting end by using a signal waveform which is selected according to the transfer rate employed at any one time. At the reception end, the waveform of the received signal is recognized, and, consequently, the transfer rate employed by the transmitter will be recognized. For example, in a mobile communication system utilizing frequency hopping (FH) or time hopping (TH), the hopping pattern may be selected in the transmitter according to the transfer rate. In a multi-carrier HFDMA system the carrier waves used, or combinations thereof, may be selected according to the transfer rate. In a CDMA system, the spreading code may be selected according to the transfer rate. In addition, these methods can be combined.
In other words, methods similar to those being used to distinguish different users from one another are employed for the recognition of the transfer rates of different users. It is characteristic for the aforementioned multiple access methods that there is a higher number of proper spreading waveforms available than the number of simultaneous users allowed by the interference limitations of the mobile communication system. Due to the above, the mobile communication system has extra “channels” available by means of which the “multiple access” can be extended to cover transfer rate as well. However, it must be noted that the multiple access methods and waveforms employed for recognizing the users in a mobile communication system from one another may be based on a different method than the transfer rate coding according to the present invention in the same system.
One of such methods differing from the multiple access methods is to shape the user information with Rademacher waveforms or similar waveforms that have adequate cross correlation characteristics. This is an economical method as far as the implementation of a receiver, particularly in a CDMA mobile communication system, is concerned.
As the different transfer rates are identified according to the invention by means of different signal waveforms, the signal waveforms and, consequently, the transfer rate can be detected in the receiver after reception of only a few symbols (speech or data). The detection of a user signal can thus be started in the receiver after a relatively short delay without having to wait, e.g., for the end of the frame and deinterleaving. As a result, it is possible to activate closed loop power control and multiple access interference cancellati
Hakkinen Hannu
Pehkonen Kari
Rikkinen Kari
Chin Stephen
Fan Chieh M.
Nokia Telecommunications Oy
Pillsbury & Winthrop LLP
LandOfFree
Method and equipment for multirate coding and detection in a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and equipment for multirate coding and detection in a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and equipment for multirate coding and detection in a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2553481