MXPA98001460A - Method for multip multiple tone division access communications - Google Patents

Abstract

A method for multiple users to have access to a common channel in which encoded application bits are generated and transmitted for a plurality of applications for a plurality of users. A plurality of tones are assigned to the coded application bits for each application. The application bits encoded for each application are encoded in multi-tone symbols in a transmitter using the plurality of tones assigned to the encoded application bits. The multi-tone symbols for each application are synchronized to be transmitted over a common channel. At the receiver, the multi-tone symbols for each application are received from the common channel and the tone is decoded with the application bits for each application using the plurality of tones assigned to the encoded application bits. The encoded application bits are then decoded for each application

Description

METHOD WILL PROMOTE MULTIPLE TONE DIVISION MULTIPLE ACCESS COMMUNICATIONS FIELD OF THE INVENTION The present invention relates to the field of telecommunications. More particularly, the invention relates to a method for multiple user telecommunications.

BACKGROUND OF THE INVENTION Currently, there are three main non-random access techniques for multiple user communications: FDMA, TDMA and CDMA. In multi-media transmissions, that is, applications that have different data rates, none of these three multiple access techniques is effective in terms of performance efficiency, implementation of physical components, or signal quality. For example, to accommodate a bit rate data type, an FDMA method allocates several frequency subbands that are separated by frequency protection bands and are performed by different carriers, resulting in spectral efficiency and REF: 25466 of the physical components. Similarly, a TDMA method uses several time slots that are separated by time protection bands and require exact synchronization at both the transmitter and the receiver. TDMA leads to loss of performance and interference between symbols, caused by channel distortion, multipath dispersion and loss of synchronization. Finally, a CDMA method breaks the high-speed bit stream into several lower-rate bit streams to achieve a sufficiently large processing gain. Each low speed flow requires dispersion and agglutination processing. The performance to several low speed flows is also necessary if the dynamic allocation of any data type for a CDMA channel must be achieved. In addition, CDMA inclined receiver operation degrades considerably in the presence of intersymbol interference. What is needed is a multiple access technique for multi-user communications that is resistant to inter-symbol interference that occurs in high-speed transmission, that accommodates data rates from multiple users, while retaining a component implementation. simple physicists.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a multiple access technique for multi-user communications that is resistant to inter-symbol interference that occurs in high-speed transmission, accommodates data rates of multiple users, and retains a simple physical component implementation. In this regard, the present invention provides a new multiple access method for multi-user communications that allows the transmission of data rates from multiple users over a common channel and has a complexity of implementation comparable to that of systems providing high-speed data rates. data for a single user. Inter-symbol interference that arises from damage to the channel, such as channel distortion and multipath propagation, as well as baseband filtering between the transmitter and receiver, are avoided without using the channel equalization. For wireless applications that have space diversity reception, selective frequency fading is also overcome. The present invention avoids interference between users for both point-to-point and point-to-point communications, and at the same time greatly relieves the requirement for synchronization accuracy in a receiver when compared to other multiple access techniques such as CDMA and TDMA. The advantages of the present invention are provided by a method for multiple users to have access to a common channel. The requested application bits are generated with a plurality of applications for a plurality of users. A plurality of tones, which are preferably a subset of available tones, are assigned to the coded application bits for each application. The application bits encoded for each application are encoded in multi-tone symbols in a transmitter using the plurality of tones assigned to the encoded application bits. The multi-tone symbols for each application are tuned to be transmitted over a common channel. In a receiver, the multi-tone symbol for each application is received from the common channel and the decoded tone in the application bits encoded for each application using the plurality of tones assigned to the encoded application bits. The encoded application bits are then decoded for each application.BRIEF DESCRIPTION OF THE DRAWINGS The present invention is illustrated by way of example and not limitation in the accompanying figures in which similar numerical references indicate similar elements and in which: Figure 1 shows a block diagram of the basic functional elements for a transmitter and a receiver for a downlink (from a point to multiple points) according to the present invention; Figure 2 shows a block diagram of the basic functional elements of a modem (modulator / demodulator) Multi-tone DPSK based on FFT configured as a transmitter according to the present invention; Figure 3 shows a block diagram of the basic functional elements of a multi-tone FPS-based DPSK modem configured as a receiver according to the present invention; and Figure 4 shows a block diagram of the basic functional elements for a transmitter and a receiver for an uplink (from multiple points to a point) according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a multiple access method for multi-user communications. The method of the present invention, known as Multiple-Tone Division Multiple Access (MDMA), is effective for transmitting multiple data types of different speeds, resists inter-symbol inter-reference and maximizes channel performance. For single or multiple data rate transmissions, the method of the present invention does not increase the complexity of the physical components of the system, nor decrease the performance of the channel compared to the FDMA, TDMA, and CDMA methods. MDMA is resistant to inter-symbol interference without using channel equalization, as required by the FDMA, TDMA and CDMA methods. In addition, to realize interference-free communications between users for multi-point links to a point, such as an uplink in a satellite or cellular system, the present invention does not impose a strict transmitter and receiver synchronization accuracy, such as This is the case of the TDMA and CDMA methods. The present invention uses multi-tone modulation and assigns different application data to different tones. The multi-tone modulation technique not only serves as a modulation scheme, but also provides a multiple access mechanism. In particular, the bits encoded for various applications that originate from, or are intended for, a plurality of users are plotted on different sets of tones that are assigned to the respective applications at the time the calls are initiated. The bits are encoded in symbols (tones) for a discrete, multi-tone modulation, and the inverted demodulation process is performed to recover the received tones and the information bits. Unassigned symbols are set to zero. For a downlink transmission (from a point to multiple points), a user receiver selects the assigned tones for the intended applications by the user's receiver after the demodulation of discrete multiple tones so that only the information bits are decoded that belong to that user. For uplink transmission (from multiple points to multiple points), the transmission is synchronized between all the associated users of a particular receiver. The demodulated symbols are aligned with associated applications and users so that the decoded bits can be identified appropriately for future processing. The synchronization accuracy can be greatly relaxed by properly designing the multi-tone modem. Figure 1 shows a block diagram of the basic functional elements for a transmitter 1, receiver 2 for a downlink (one point to multiple points) MDMA. The multiple data streams c (l) through c (a) represent different applications and different users assigned to the different subsets of tones in 10. A subset of tones can comprise the entire set of available tones, and are established during the process of growing a call. With this tone pre-assignment, the encoding of the encoded data bits of the channel into multiple-tone symbols proceeds at 11. Symbols that are not associated with any application become zero. The encoded data for the multiple data streams were then processed by the block 12, which represents the modulation and transmission of the multiple data streams by the transmitter 1, and the reception and demodulation of the data streams in the receiver 2. Figures 2 and 3 show functional details of a FFT-based multi-tone modem (modulator / demodulator) system DPSK that is suitable for block 12. After multi-tone demodulation in receiver 2, the recovered symbols are selected by symbol and channel coding, and if and only if, the symbols are associated with applications in the receiver 2. The symbols are appropriately identified with an application and decoded. Figure 2 shows a block diagram of the basic functional elements in a FFT-based multi-tone DPSK modem according to the invention which is configured as a transmitter for a single block of bits.

In Figure 2,. a sequence of encoded information bits (from trellis) 20 is fed to an MPSK tracer 21. The tracer MPSK 21 traces groups of data bits over MPSK constellation points. In particular, the coded information bits are segmented into blocks of M bits. (In this case, the number of constellation points (M) and the number of bits (M) per block coincidentally uses the same symbol M. For the purposes of the present invention, the number of constellation points M may be different from the number of M bits per block). Each block of M bits is then analyzed grammatically in N groups, where the kth group is assigned m (k) bits, and M = m (0) + m (l) + ... + m (N-l). Each group is plotted separately in a different phase? F? (K), where k = 0, 1, ..., N-l, according to the chosen PSK constellation. A differential phase encoder 22 operates on two consecutive blocks in a well-known manner to generate an absolute phase f? (K). The absolute phase f? (K) is then used by a symbol encoder (tone) 23 to generate a complex symbol Xt (k), or a discrete tone, on the plane of complex signals. A complex symbol X? (K) equal to X? (k) exp [jfi (k)]. The amplitude of Xi (k) is chosen to maximize the total capacity of the channel or to achieve the desired signal-to-noise ratios across the tones.

Next, N complex symbols within each block pass through a serial to parallel (S / P) converter 24 and apply to the input of a Discrete Fourier Modulated Discrete Fourier Modulator (IDFT) 25. The N Complex symbols within each block are inverted discrete Fourier transformed into N (complex) samples in the time domain via an FFT. The N parallel samples in each block are converted to a series sequence by a parallel to serial (P / S) converter 26, which also adds a cyclic prefix and suffix to each block and also converts the elongated complex sample sequence in two sequences of real data separating each complex sample into a real part and an imaginary part (R / I). The length of. cyclic suffix is one or two samples, while the length of the cyclic prefix is the length of the cyclic suffix plus the response of the unit sample of the total digital channel including the transmission and reception filters as well as the means of transport between the filters. transmission and reception. The one or two samples added for both prefix and suffix allows a greater synchronization deviation in the synchronization and sampling in the receiver, although the other samples attached to the prefix allow a free interference between blocks, and in this way a free interference between symbols, over a time dispersive channel. The two real sequences are then passed through two identical low-pass filters 27a and 27b for digital-to-analog (D / A) conversion. In this way two baseband signals are generated, and subsequently two quadrature carriers are demodulated in the mixers 28a and 28b. After quadrature multiplexing, the appropriate power amplification and bandpass filtering at 29, successive (elongated) blocks are transmitted. The modem of Figure 2 processes blocks of multiple bits that have each been associated with sets of different tones in a similar fashion. Figure 3 shows a block diagram of the basic functional elements of a FFT-based multi-tone DPSK modem configured as a receiver according to the present invention. A received RF signal 30 is filtered by bandpass, amplified by power and divided into two components at 31 for non-coherent quadrature demodulation (i.e., frequency upconversion) in mixers 32a and 32b and filters low step 33a and 33b. The resulting quadrature baseband components were sampled in parallel by analog to digital (A / D) converters 34a and 34b. The output of the A / D converters 34a and 34b are fed to an S / P and R / I converter., where the two real sampling sequences are converted to a complex sampling sequence by treating each pair of real samples as the real part and the imaginary part (R / I) of a complex sample. Samples at the two ends of the elongated block that are associated with the added prefix and suffix are discarded here, and the resulting N complex samples within each block are additionally recognized in a parallel format by means of a serial converter a in parallel (S / P). The N parallel complex numbers within each block are then transformed by the Fourier method in a discrete way via an FFT by the discrete multiple tone demodulator 36 to produce N complex symbols. The N complex symbols are the transmitted tones weighted by the exponential of the phase difference of the locally generated carrier received and the frequency response of the total channel in the corresponding tones, and further corrupted by noise. The N complex symbols pass through a serial to parallel (P / S) converter 37, which has a serial output that is sent to a block delay device 38 and a differential phase comparator 39. The output of the block delay device 38 is the input delayed by a block. The differential phases between the corresponding symbols of two consecutive blocks are evaluated by the differential phase comparator 39 in a well-known manner without having to determine the phase of the received carrier or the frequency response of the channel. The values of the extracted differential phase are again plotted to encoded bits by means of an MPSK plotter 40 for subsequent decoding of the channel (not shown). Alternatively, the MPSK plotter and the channel decoder, such as a Viterbi decoder, can be combined to decode flexible decisions. Figure 4 shows a block diagram of the basic functional elements for a transmitter 3 and a receiver 4 for an MDMA uplink (from multiple points to a point). The architecture of an uplink is similar to that of the downlink (Figure 1). In particular, each application that has access to the uplink is assigned a different set of multi-tone symbols so that the messages generated by each application are distinguishable from the messages generated by other applications. Unused symbols are re-zeroed. All transmissions are blocks synchronized with respect to the receiver to avoid interference between users when more than one user 15 has access to the channel. Synchronization errors of one or even two sample intervals will not cause substantial transmission errors for the present invention where one or two cyclic samples are added to the prefix and suffix of the sequences of modulated multi-tone samples for each block before the transmission, as mentioned above. All the symbols recovered in the receiver after the demodulation of multiple tones are identified with the applications - and respective users, followed by the decoding of the symbol and channel. Although the present invention has been described in connection with the illustrated embodiments, it should be appreciated and understood that modifications can be made without departing from the true spirit and scope of the invention.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (8)

1. A method for communicating multiple users using a common communications channel, characterized in that it comprises the steps of: generating coded application bits for a plurality of applications; assigning a plurality of tones to each of the application bits coded for each application; encoding the application bits coded for each application in multi-tone symbols in a transmitter using the plurality of tones assigned to the respective coded application bits; and transmitting the multiple tone symbols for each application on a common channel using a discrete multiple tone modem.

2. The method in accordance with the claim 1, characterized in that the plurality of tones assigned to the coded bits of an application is a subset of available tones.

3. The method in accordance with the claim 2, characterized in that the step of generating coded application bits is performed by a plurality of users; and the step of transmitting the multi-tone symbols over the common channel includes the step of synchronizing the transmissions between the plurality of users with respect to a destination receiver.

4. The method according to claim 3, characterized in that the common channel is a multi-point uplink channel to a point.

5. The method in accordance with the claim 1, characterized in that it further comprises the step of: receiving the multiple tone symbols for each common channel application using the discrete multiple tone modem; decoding the multiple tone symbols for each application in the application bits encoded for each application in a receiver using the plurality of tones assigned to the encoded application bits; and decoding the encoded application bits for each application.

6. The method according to claim 5, characterized in that the step of generating decoded application bits is performed by a plurality of users.

. A method for multiple users to receive communications using a common communication channel, characterized in that it comprises the steps of: receiving multiple tone symbols for each of the plurality of applications of a common channel using a discrete multiple tone modem in a receiver, the multi-tone symbols for each application are a plurality of encoded application bits, encoded using a plurality of tones assigned to each respective plurality of application bits; decoding the multiple tone symbols for each application in the application bits coded for each application in the receiver using the plurality of tones assigned to the encoded application bits; and decoding the encoded application bits for each application.

8. The method according to claim 7, characterized in that the step of generating decoded application bits is performed by a plurality of users.