MXPA97003293A - Switching symbols of accessometric channels to class division - Google Patents

Abstract

A digital switch included within a satellite, processes of the uplink beams and the traffic channels included in a symbol level, rather than a bit level, is described. In this system, the switch behaves as a repeater on a per user basis and as a switch on the beam level. The individual user signals (i.e., channels) are separated from the uplink beam and recombined in the appropriate downlink beam.

Description

COMMUTATION OF SYMBOLS OF MULTIPLE ACCESS CHANNELS TO DIVISION IN KEY Field of the Invention This invention relates to the multipoint, input-to-output switching of the signals and, in particular, to the switching of broad spectrum signals. (i.e., CDMA). Specifically, the invention concerns the switching of signals CDMA (Multiple Access to Key Division) at the symbol level to allow efficient use of space and limited load switching systems, such as a switch contained in a satellite. It definitely concerns the switching that occurs in a CDMA synchronous transmission system.

Background of the Invention Satellites have traditionally been used as transponders or "sky-repeaters" for signal beams, in which all channels in the beam share a common destination. This arrangement has been referred to as an "elbow pipe" system, which requires that any signal that is commuted be located on the ground. This limits the total utility of the satellite to deal with a plurality of productive channels, whose switching processing must be located on the ground. With a switch on the ground, two double-hop transmissions REF: 24057 (ie, satellite-to-earth-to-satellite) must be exchanged, to couple together the users connected to the satellite, resulting in a large undesirable delay in the signal. A "sky-switch" satellite allows both end users to be directly coupled together (e.g., via the satellite dishes). With the switching located within the satellite, the signal delay is reduced to half that of the elbow tube system using ground-based switching. This greatly improves the satellite's ability to handle voice calls with acceptable quality. A commutation that has a desirable space and load characteristics is essential to the "sky-commutation" concept; otherwise, a rather massive satellite switching architecture is required. This switching should include the ability to connect directly to the end users in a traffic channel. Because the traffic channels are bundled, particularly in CDMA systems, the traffic channels must be extracted from the uplink beams and constituted into downlink beams, in which all the downlink channels with a common destiny are combined in bundles that have the same destiny. Signal switching, of the digitized modulated signals, is typically performed at the sampled waveform level, which requires extensive processing circuits to support the switching load. Even with advances in VSLI technology, which increases circuit density and supports significant productivity, switching to the sampled waveform level requires a certain processing capacity of the satellite; Load and power restrictions adjust that limit to their capacity on any reasonably sized satellite. For example, a constant delay must be maintained for all bit streams. It is desirable, from an economic and size / load point of view, for a satellite signal processor to provide the advantages of elbow-tube and "sky-switch" systems and still avoid disadvantages associated with each one.

Brief Description of the Invention A digital switching system having an important capacity, without the size, weight and power requirement, is provided, as defined in claim 1. In a particular illustrative embodiment, a digital switch, included within a satellite, processes the uplink beams and the traffic channels included at a symbol level, instead of at a sampled waveform level. In this system, the switch behaves as a repeater on a per user basis and as a switch on the beam level. The signals of individual users (i.e., channels) are separated from the uplink beam and recombined in the appropriate downlink beam. Samples are taken from the arrival waveform. These samples are processed on a per user basis to extract the symbol information. The symbol information then passes to a swing process to channel it to the appropriate output beam. The processor that works based on the output then combines the symbols of the user and reconstructs a sampled waveform to be transmitted in the downlink.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of a multi-point-to-point communication system using a satellite to couple uplink and downlink CDMA beams, where the channels coupled from the link beams ascending towards the downlink beams have a common destination with their assigned channels. Figure 2 is a schematic view of a processing circuit of the uplink beam; and Figure 3 is a schematic view of a downlink beam processing.

Detailed Description of the Invention An illustrative point-to-point communication system, which couples a transmitting user station to a receiving user station, is schematically shown in Figure 1. While individual transmitting and receiving stations, 101 and 102, are illustrated illustratively , the stations can be transmission points and reception points of a telephone system. These stations are fixed spatially / geographically, in contrast to mobiles. In addition, the stations can be bi-directional transceivers. Only one uni-direction is shown, for simplicity. Station 101-1 includes a dish antenna 103, from the satellite, which directs signals from the RF CDMA beam to a satellite, 105. Station 102-1 receives signals from the RF CDMA beam of satellite 105, via its antenna of plate, 104, of the companion satellite. Each beam signal includes a plurality of bands, as shown. The satellite receives signals from the RF CDMA beam of other transmitting stations 101-N and transmits signals from the RF CDMA beam to a plurality of receiver stations 102-N.

- - The beam signals each include a plurality of bands including the aerial guidance, access and paging channels, and a plurality of voice and data traffic channels. Synchronization is provided through the pilot channel and connections to the satellite are initiated through the access channel. The paging channel is used by the satellite to initiate a connection to the receiving, receiving station. The air interface between the ground station and the satellite includes a synchronous CDMA beam, which is referenced from a fixed point. The adjacent beams are separated between them by the application of separation codes (e.g., Gold codes) and the individual channels with the beam are assigned and separated by a unique code from a group of orthogonal vectors. Synchronization is important in this application as a means to limit multiple access interference, which limits traffic capacity significantly, by synchronizing all beams with a common reference point, the uplink beam can be demodulated down to the symbol level, and then allow the original bit signal to be regenerated before the downlink switched transmission. The downlink beam is directed towards a suitable target beam and coded for downlink transmission. The primary processes performed by the satellite on the uplink arrival CDMA beam are the synchronization of the beam with some reference point and beam demodulation. In order to limit the size and the load, timing and synchronization are not carried out on each user channel but it is more dependent on a timing and synchronization repository, shared between the different beams, to periodically analyze the users of the link. ascending and provide timing information to the main processor. The demodulation of the uplink beam starts with a downward conversion, up to IF, in which each channel is applied to a mixer 201, excited by a local IF oscillator 202, as shown in Figure 2. The mixed signal it is applied, via a bandpass filter 203, to an analog-to-digital converter 205, where the signal is digitized at a 4X sampling rate to produce a flow of digital samples, with an 8-bit resolution. The 8-bit digital domain symbol signal is applied to an ISI 209 filter, cosine raised to the root, which minimizes intersymbol interference in the signal flow. The signal is then applied to a quadrature demodulator, comprising the one-bit multipliers / mixers, 211 and 213, and the one-bit cosine and sinus excitation generators, 212 and 214, respectively. This demodulation process separates - the in-phase (I) and quadrature-phase (Q) components of the signal. Because the 4X oversampling is the one used in the illustrative example, only one bit is needed to represent the sine and cosine waveforms. The multipliers 211 and 213 are followed by the integrators 217 and 218, respectively, and are used to convert the flow of 4X oversampled input samples into a symbol stream IX. This symbol flow now represents the sum of all the users in the current beam, all the users that intervene in adjacent beams and the noise in the channel. In order to extract the beam users from the beam codes GN, provided by the beam code generators 221 and 223, they are applied to the stream of I and Q symbols, bit by bit, by their application to the multipliers 222. and 224, respectively. By applying this beam code G "to the symbol flow, the interference due to users in adjacent beams is" blanked ". The output of the beam code processing step is applied to a manifold 226 which applies the multiplier output signals 222, 224 to the retrieval units of the traffic channel. The retrieval units of the traffic channel each extract a flow of symbols on a band basis for a particular user. The process involves separating the signal - from complex, arrival sample, with the user's psrticular code and detecting the phase of the resulting baseband signal. Each recovery unit of the traffic channel includes a multiplier / mixer 235-N, excited by an orthogonal code of the user Wi, generated by the generator 236-N, to apply the particular orthogonal code of the users, bit by bit, to the flow of complex arrival sample. The output samples are accumulated by adders 237-N and transferred at the end of the code. The complex output samples, which arrive at the baseband symbol ratio, are applied to the phase decoders, 240-L, which convert the flow of complex samples into a decoded baseband symbol. These symbols are passed to a switch to direct them to the destination beam. The first component of the switch is the TDM concentrator, 242, which is connected to the TDM separator, 302, of Figure 3. The processing of the downlink beam, as shown in Figure 3, accepts the individual streams of symbols of the baseband and converts them to a properly modulated channel, in the appropriate target beam. The output signal of the TDM separator is applied to the symbol encoders, 303-L, which map the symbols onto a complex modulation plane. The complex symbol is repeated at the speed of the chip by the repeaters of symbols xl28, 305-N, so that the orthogonal distribution codes, W. and W, of the individual users can be applied, from the code generators 307- N, to multipliers 309-N. The results of the distribution with the related I and Q codes are added separately, in the adders 310 and 311, in flows of combined I and Q samples. A beam code, G, is supplied by generators 314 and 315 to the sample flows I and Q, through multipliers 312 and 313, and then applied to the symbol repeaters, x4, 317 and 318, for provide space for the oversampling head, for the filtering by means of inter-symbol interference filters, 321 and 323. These filters are of the same cosine variety raised to the root as in the uplink circuit of the Figure 2; with a filter, 321, for the in-phase samples and a filter, 323, for the quadrature samples of the phase. The in-phase samples are multiplied by a signal, supplied by the generator of the Sine function, of a bit, 325, in the multiplier 326. The quadrature samples are multiplied by a cosine signal, of a bit, of the generator of the Sine function, 327, in the multiplier 328. These two signals are combined in the adder 331 and are applied to a transmitter, for its transmission on the output line 333, via the adder 332. It is noted that, in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it refers. Having described the invention as above, the content of the following is claimed as property.

Claims (11)

1. A satellite-based switching system for coupling user channels in an uplink CDMA beam with a downlink CDMA beam, wherein the system comprises: means for receiving, from a transmitting land station, the CDMA uplink beam and separate the individual channels from the uplink beam; means for extracting symbols from the uplink channels, wherein the satellite-based switching system is characterized in that it comprises: means for switching the uplink channels at a symbol level; - means for combining the symbol levels of the uplink channels in downlink CDMA beams; means for transmitting the downlink CDMA beams to a receiving land station.

2. In addition, it comprises: means for switching, including means for sampling a symbol representation, processing the samples by switching and reconstituting the symbol after the switching process .

3. In addition, it comprises: - means for modulating a channel by manipulation by phase shift to obtain symbols of bit combinations.

4. A switching system for coupling user channels, in a modulated arrival beam, with a modulated output beam, wherein each beam includes a plurality of user channels comprising: - means for sampling the arrival beam, where the system switch is characterized in that it contains: - means for processing the samples on a per-user basis, to extract the information from the symbols; - means for switching the information of the symbols, to direct it to a suitable output beam; - means for combining the symbols of the user; - means for reconstructing a waveform sampled from the user's combined symbols for the output transmission as a beam.

5. A method for coupling user channels, from the modulated arrival beams to the modulated output beams, where the method is characterized in that it comprises the steps of: - sampling the arrival beam; - process the samples on a per-user basis, to extract the symbol information. - switching the symbol information to direct it to an appropriate output beam; - combine the user's symbols; - reconstruct a waveform sampled from the combined user symbols for the output transmission as a beam.

6. A method of switching the user channels in the sky, from a modulated uplink arrival beam to a downlink output modulated beam, wherein the method is characterized in that: - symbols are generated representing information in each channel of the user; symbols of each uplink user channel are switched with a downlink beam having a common destination with a predetermined destination of the user channel.

7. A method for switching user channels in the sky, according to claim 6, characterized in that it comprises the steps of: - additionally sampling the incoming, uplink modulated beam, and processing the samples on a per-user basis to extract information of symbols

8. The method of switching the user channels in the sky, according to claim 6, characterized in that it comprises the steps of: - reconstructing a waveform sampled from the symbols switched for transmission in the downlink beam.

9. The method of switching the user channels in the sky, according to claim 6, characterized in that it comprises the steps of: generating symbols that represent combinations of bits by manipulation by phase shift.

10. A sky switching system for switching the uplink user channels, extracted from the uplink beams, in the downlink beams having a destination, with a predetermined destination of the uplink aggregate user channels, forming the downlink beams, wherein the switching system is characterized in that it contains: means for sampling the uplink beams; - means for processing the samples on a per-user basis, to generate symbol information representing each user's channel; - means for switching the symbol information, for adding uplink user channels with a predetermined common destination, in downlink beams having a common destination with the predetermined destinations of the user channels it contains.

11. A switching system in the sky, according to claim 10, characterized in that it comprises: means for separating the individual channels from the uplink beams; and - the means for switching, which further include means for processing by switching with samples of a symbol level and means for reconstituting the symbols after switching.