MXPA97008913A - Multiple access communication system frequency condivision and double-earth code - Google Patents

Abstract

The present invention relates to an orthogonal code division multiple access radio communication system (BPSK) having at least one base station and a plurality of subscriber / user terminals, for communicating data, transmitting means including: MPSK modulators connected to receive the data, biphasic modulator means (BPSK) connected to the MPSK modulator, a generator of a set of RW functions having means to select a set of given RW functions, each RW function has a predetermined RW cutting speed , a carrier frequency synthesizer, connected to the MPSK modulator that generates selected carrier frequencies, which are separated by the cut-off speed RW, a PN code generator to provide a selected PN code signal, means to sum a set of signals of RW functions given with the PN code signal and provide a scatter function signal In the biphasic modulating means, the two-phase modular means produce a composite signal that leaves the modulating means MPSK and the signal of the dispersion function, the selected set of functions RW is a member of fixed binary sequences, which are orthogonal on a period of symbols, and means for converting the composite signal of the biphasic modulator to an emission frequency band for transmission

Description

MULTIPLE ACCESS COMMUNICATION SYSTEM WITH FREQUENCY DIVISION AND DOUBLEM ORTEGONAL CODE.

BACKGROUND OF THE I NVENTION: Broadcast spectrum communication is being used in a large number of commercial applications and is proliferating at a fairly large speed. Orthogonal code division multiple access (OCDMA) has been proposed (from U.S. Patent No. 5,375, "Wireless Direct Sequenced Broadcast Spectrum Digital Cell Phone System", and U.S. Patent Application No. 08 / 257,324, presented on June 7, 1994, incorporated herein by reference), as an effective technique to improve capacity, that is, the bandwidth efficiency of the more conventional quasi-orthogonal CDMA. In CDMA systems of conventional direct sequence (DS) broadcast spectrum, individual users transmit to the same frequency using different pseudo-noise (PN) codes. The PN codes are quasi-orthogonal, that is, they have relatively low but not zero cross-correlation values between them. In an OCDMA system, each user is assigned a code that is orthogonal to all other user codes (this is the orthogonal code has a cross-correlation value of zero between them). In addition, the orthogonal code period is chosen so that the code repeats a whole number of times (usually one time) in time data symbol. The epoch code is synchronized with the transitions symbol so that no data transition occurs within the code. The number of users is limited by the number of orthogonal functions available, which for binary codes is equal, at most, the length of the code. An example is the RADAMACEER-WALSH function set for which there are 2N orthogonal functions of length 2N where N is a positive integer. Note that the relation of "elimination of errors" is equal to the maximum number of orthogonal users times the relation of the symbol. This implies that a higher ratio of elimination of imperfections is required at a high data rate. The OCDMA systems are designed in such a way that all signals are received in synchronous time and frequency. Then all the orthogonal users remain between them and, in an ideal world, any user can be recovered without multiple access noise from another user. This is more practical in a star configuration network where a multiplicity of users transmits to and receives from a single station. This configuration is often used in satellite networks. There are, of course, a number of practical considerations and real world effects that cause the functioning of the OCDMA to degrade and not become the ideal. For example, multicamino returns that have been delayed by a significant portion of a chip are no longer truly orthogonal and cause access to noise. This is a problem for high data relation systems, since the "CHIPPING" relationship is correspondingly high, and the diffused multipath delay becomes significantly increased. A technique for combating this effect is disclosed in MAGILL, US Patent Application No. 08 / 352,313, filed on December 8, 1994 entitled "MULTI ACCESS COMMUNICATION SYSTEM BY ORTOGONAL CODE DIVISION HAVING MULTIPORTING MODULATION", also incorporated herein by reference. . In this application, it is disclosed that multiple OCDMA signals are transmitted on orthogonally spaced carriers (this is spaced to a "CHIPPING" relationship) and the data from a single user is multiplexed on the multiple carriers. In this way, the "CHIPPING" relationship is reduced by the number of carriers.

OBJECTIVES OF THE INVENTION: The invention described below is an extension of the multi-carrier OCDMA invention disclosed in the American patent application No., in which it employs multiple OCDMA signals transmitted at orthogonally spaced frequencies. In this case, however, a single user transmits in only a single orthogonal function in a single frequency.

That is, the system can accommodate a total number of users equal to the product of the number of orthogonal functions and the number of carriers. Another way of looking at this is that the system uses as much time as the orthogonal properties of waveform frequency, giving rise to the name of "CDMA doubly orthogonal (DOCDMA)". For a given number of users, the CHIPPI NG ratio is reduced by the number of carriers compared to the strict OCDMA. This has several benefits including: 0 Easier to acquire due to the low "CHIPPI NG" ratio. 0 Multipath delayed broadcasting causes less access to noise due to the longer chip period. O A more uniform power spectral density. O Higher bandwidth efficiency. O A lower dissipation of the received power due to the lower clock ratio. The attributes mentioned above make OCDMA multi-carrier very attractive for satellite networks with a multiplicity of mobile users, such as those that support personal communications.

DESCRIBE OF THE I NVENTION: Consistent with the invention, a communication system based on multiple access orthogonal code division (OCDMA) terrestrial or satellite is provided having at least one base station and a plurality of terminals of remote subscribers, the OCDMA sensitivity to access noise due to time base error and multipath delayed broadcast is reduced by reducing the size of the set of orthogonal signals in a single carrier (and then the number of subscribers that can be assigned to this frequency) and employing additional carriers often orthogonally spaced for additional subscriber capacity. This produces a multiple frequency division access and double orthogonal code communication system.

DESCRIPTION OF THE DRAWINGS: The above and other objectives, advantages and characteristics of the invention will be more apparent when considered with the following specifications and accompanied by the following drawings: Figure 1 A is a block diagram of a base OCDMA communication system satellite incorporating the invention, Figure 1 B is a block diagram of a ground based OCDMA communication system incorporating the invention, Figure 2 is a block diagram of a transmitter for a double orthogonal code multiple access system (DOCDMA ) incorporating the invention, Figure 3 illustrates the composite spectrum for OCDMA signals, and Figure 4 is a functional block diagram for a DOCDMA receiver incorporating the invention.

DESCRIPTION OF THE INVENTION: As mentioned above, this invention is an extension of the OCDMA multicarrier scheme of the American patent application with serial number, in which it uses multiple OCDMA signals transmitted at orthogonally spaced frequencies. In the present invention, however, a single user transmits in only one simple orthogonal function at a single frequency. One embodiment of the transmitter is shown in Figure 2. The input data of source ten are transiently stored and formatted eleven and then modulated on a carrier using MPS K modulation, where M is greater than or equal to 2. One could typically use M = 4, ie QPSK modulation. The coding and inter-leveling of forward error correction (FEC) can also be used, depending on the application. The signal is then modulated BPS K with a binary sequence which is the Mod-2 sum 16 of a PM sequence from a generator 14 PM and a member of a set of binary sequences that are orthogonal over a symbol period. The RADAMACHER-WALSH (RW) 15 functions, for which 2N orthogonal functions of length 2N exist where N is a positive integer, can be assumed here for illustrative purposes. An RW function selects signals from controller C that selects the desired member of the game or the set of RW sequences for Mod-2 by summing with the selected PN code. The same PN code is used by each of the members of a single cell or orthogonal game. The PN clock ratio from time logic circuit 17 which is operated by clock 18 is usually selected to be the same as the RW chip ratioHowever, this is not necessary. A synchronization signal system for timing the logic circuit 17 and a frequency selection signal for synthesizing conventional carriers 19. The waveform of the DPSK modulator signal is cover jacket 20, the power amplifier 21 and antenna broadcag 22. As mentioned above, each user is assigned with a code which is orthogonal to the user code of all others (this is the orthogonal code has a cross-correlation value of zero with any other). In addition, the period of the orthogonal code is chosen so that the code repeats a whole number of times (usually once) in a data symbol time. The epoch code is synchronized with the transition symbol in such a way that no data transition occurs within the code. Note that the relation "CHIPPING" as such is equal to the maximum number of orthogonal users times the symbol relationship.

The frequency of the modulated carrier is selected from one of N frequencies that are orthogonal over a chip interval RW, that is, the frequencies of the carriers are spaced by the CHIPPING RW relationship.

The composite signal is converted to a higher frequency for a frequency band suitable for transmission. The individual transmissions are synchronized to reach the base station in synchronism of time and frequency. The resulting reception spectrum is as shown in Figure 3 for the case where the CHIPPING relationship is 166.4 kHz and 5 orthogonal carriers are employed. A block diagram of the DOCDMA receiver is shown in the figure 4. The signals received in antenna signals 23 are converted at a downward frequency 24 to the Q baseband and converted from analog to digital 25I, 25Q and for processing. Tracking curls are used to estimate the frequency of the received carrier and the code phase. The phase of the tracking loop code includes phase of discriminating code 30, filter 31, controller oscillator of number 32, which controls the generator PN 34 and generator RW 35 that generate the respective PN and RW functions. The receiver controller CR provides a selected RW signal to the RW generator 35 to select a particular RW function. The functions PN and RW are combined 36 and applied to the mixer 37. The carrier of the tracking loop incorporates a carrier frequency discriminator 38, and a filter 39. The frequency of the selected carrier of the reception controller is selected 40, the frequency of the carrier via the controller number 41 oscillator. The quadratic signals (COS, SEN) of the NCO 41 are applied to the complex multiplier 28 to close the "tracking" loop of the carrier. The KPSK modulation 42 is carried out in the usual way using both differentially coherent detection or coherent detection to provide the data to a utilization device 43. While the preferred embodiment of the invention has been shown and illustrated, it will be appreciated that other The embodiments are readily apparent to those skilled in the art and are restricted by the claims appended hereto.

Claims (4)

1. CLAIMS 1. Multiple access radio communication system by orthogonal code division having at least one base station and a plurality of remote terminals of subscribers and modulator, a source of code sets of orthogonal functions, means to reduce the size of the set of orthogonal signals in a single carrier and means to employ additional carriers with orthogonal frequency spacing for additional subscriber capacity to reduce the sensitivity of the OCDMA to noise access due to time base error and multipath delay diffusion.
2. 2. The radio communication system defined in claim 1 wherein said at least one base station is terrestrially located.
3. 3. The radio communication system defined in claim 1, including a communication satellite and wherein said at least one base station communicates with said remote subscriber terminals via said communication satellite.
4. 4. An orthogonal code division multiple access radio communication system having at least one base station and a plurality of subscriber subscriber terminals, for communicating data, a transmission means including: MPKS modulator means connected to receive said data, a modulator means biphase (BPSK) connected to said MPSK modulator, a carrier frequency synthesizer connected to said MPKS modulator generating selected carrier frequencies that are spaced by the "chipping" ratio RW, a generator set of RW function having means to select a conju nt of given RW functions, a PN code generator for providing a selected PN code signal, means for summing a series of selected given RW function signals, with said PN code signal, said selected RW function series being a member of a series of binary sequences which are orthogonal over a symbol period, and means for converting the composite signal of said biphase modulator to a broadcast frequency band for transmission. The system defined in claim 4 including receiving means for receiving and demodulating said composite signal to recover said data. The system defined in claim 5, wherein said receiver means includes: second generator means PN to provide a second PN code signal, second function function generating means RW to provide a second series of function signals RW, means for adding said second PN code and series of RW function signals to provide a decoded and despread signal, a code phase tracking loop having an NCO controlling said second PN generator means and said second function generating means RW, mixing means for receiving said composite signal and said despread and decoded signal to produce a despread and decoded output signal, and a frequency carrier tracking loop having an NCO and a half to select a specific carrier frequency. In an orthogonal code division multiple access radio communication system (OCDMA) having at least one base station and a plurality of remote subscriber terminals, the improvement comprising the method of reducing the sensitivity of the OCDMA to the access of noise due to the error time base and multipath delay dispersion comprising (1) reducing the size of the series of orthogonal signals in a single carrier, and (2) providing additional carriers with orthogonal frequency spacing for additional capacity of subscribers.