MXPA98008738A - Ds-cdma systems and methods in compressed mode with increase in cod speed - Google Patents

Abstract

The present invention relates to discontinuous transmission in the CDMA communication techniques is obtained using selective encoded output of perforation of a convolutional encoder. By temporarily increasing the coding speed during a frame, the information only fills a part of the information of a frame in a compressed mode, leaving a vacant part of the frame, in which it performs other functions, such as the evaluation of other frequencies for use in transfer between frequencies

Description

SYSTEMS AND METHODS DS-CDMA IN COMPRESSED MODE WITH INCREASE IN CODE SPEED BACKGROUND The present invention relates to the use of Multiple Access communications techniques by Code Division.

(CDMA) in the cell phone radio communication systems, and more specifically, to a method and system related to the transfer of connections between frequencies using Direct Access Division (DS-CDMA) Multiple Streaming transmissions (DS-CDMA) non-continuous.

The DS-CDMA is a type of broad-spectrum communication. Broad-spectrum communications have existed since the days of the Second World War. The first applications were mainly oriented to the militia. However, there has been a growing interest in the use of broad spectrum systems in commercial applications. Some examples include digital cellular radio, land mobile radio, satellite systems and indoor and outdoor personal communication networks, collectively referred to herein as cellular systems. At present, access to the channel in cellular systems is achieved using the methods of Multiple Access by Division of Frequency (FDMA) and Multiple Access by Time Division (TDMA). In the FDMA, a communication channel is a single radio frequency band in which a power of signal transmission is concentrated. Interference with adjacent channels is limited by the use of bandpass filters that pass substantial signal energy only within the specified frequency band. In this way, with each channel being assigned a different frequency band, the capacity of the system is limited by the number of frequency bands available as well as by the limitations imposed by the frequency rejection. In DTMA systems that do not employ frequency hopping, a channel consists of a time slot in a periodic stream of time slots over the same frequency band. Each period of time slots is known as a frame. A certain signal energy is confined to one of these time slots. Interference in adjacent channels is limited by the use of a time gate or other synchronization element that passes the received signal energy at the appropriate time. In this way, the problem of interference from different relative signal intensity levels is reduced. With FDMA or TDMA systems (or mixed FDMA / TDMA systems), one goal is to ensure that two potentially interfering signals do not occupy the same frequency at the same time. In contrast, Code Division Multiple Access (CDMA) is an access technique that uses broad-spectrum modulation to allow signals to overlap in time and frequency. There are a number of potential advantages associated with CDMA communication techniques. The capacity limits of CDMA-based cellular systems are projected to be larger than those of existing analogue technology as a result of the properties of broadband CDMA systems, such as improved interference diversity and electronic voice switching. In a direct sequence (DS) CDMA system the symbol flow to be transmitted (ie, a symbol flow that has passed through channel coding, etc.) is printed with a much higher speed data stream known as a sequence of signatures. Typically, signature sequence data (commonly referred to as "chips") are binary or quaternary, providing a chip flow that is generated at a rate commonly known as "chip rate." One way to generate this sequence of signatures is with a pseudo-noise (PN) process that seems random, but can be reiterated by an authorized receiver. The flow of symbols and the flow of the signature sequence can be combined by multiplying the two flows together. This combination of the flow of the sequence of signatures with the flow of symbols is known as the dispersion of the signal of the flow of symbols. A unique scatter code is assigned to each symbol or channel flow. The relationship between chip velocity and symbol velocity is known as the dispersion relation. A plurality of scattering signals modulate a radio frequency carrier, for example, by manipulation by quadrature phase shift (QPSK), and are jointly received as a composite signal in a receiver. Each of the scattering signals is superimposed on the other scattering signals, as well as on the signals related to noise, both in frequency and time. If the receiver is authorized, then the composite signal is correlated with one of the unique codes, and the corresponding signal can be isolated and decoded. For future cellular systems, the use of hierarchical cellular structures will be valuable in yet another growing capacity of the system. In hierarchical cell structures, smaller cells or micro cells exist within a larger cell or macro cell. For example, the base stations of the micro cell can be placed at a level of a lamp post along urban streets to handle the increasing level of traffic in congested areas. Each micro cell can cover several blocks of a street or a tunnel, for example, while a macro cell can cover a radius of 3-5 km. Even in CDMA systems, the different cell types (macro and micro) will operate at frequencies different to increase the capacity of the global system. See, H. Eriksson et al., "Multiple Access Options for Cellular Based Personal Comm.," Proc. 43rd Vehic. Tech. Soc, Conf., Secaucus, 1993. Reliable transfer procedures must be supported between different cell types, and thus between different frequencies so that mobile stations moving between cells have continuous support of their connections . There are several conventional techniques to determine the new frequency and cell that should be selected among plural transfer candidates. For example, the mobile station can assist in determining the best transfer candidate (and the new associated base station) to which communications will be transferred. This process, commonly referred to as mobile-assisted transfer (MAHO), includes the mobile station periodically or by demand (making measurements at each of the various candidate frequencies to help determine a best transfer candidate based on some predetermined selection criteria (for example, RSSI received with more intensity, the best BER, etc.) In TDMA systems, for example, the mobile station can be directed to explore a list of candidate frequencies during the slot (s) of idle time, so that the system will determine a reliable transfer candidate if the quality of the signal on its current link degrades below a predetermined quality threshold.In conventional TDMA systems, however, the mobile station is continuously busy In fact, CDMA mobile stations usually receive on a continuous basis and transmit at the link addresses. and ascending and downlink. Unlike TDMA, there are no idle time slots available to switch to other carrier frequencies, which creates a problem when considering how to determine whether the transfer to a given base station at a given frequency is adequate at a specific time. Since the mobile station can not provide any of the measurements between frequencies for a transfer evaluation algorithm operating in the network or the mobile station, the transfer decision will be made without full knowledge of the interference situation experienced by the station. mobile, and therefore, can be unreliable. One possible solution to this problem is • the provision of an additional receiver in the mobile unit that can be used to take measurements on the candidate frequencies. Another possibility is to use a broadband receiver that is capable of simultaneously receiving and demodulating various carrier frequencies. However, these solutions add complexity and cost to the mobile unit. In the prior patent application of Willars et al., This problem is solved by introducing discontinuous transmission in the CDMA communication techniques. for example, a compressed transmission mode is provided using a lower dispersion ratio (ie, decreasing the number of chips per symbol (so that with a fixed chip rate the scattering information only fills a part of a frame. This leaves part of each frame mentioned here as an empty part, during which the receiver can perform other functions, such as the evaluation of the candidate cells on other frequencies for transfer purposes.This solution is easily applicable to the systems CDMA where non-orthogonal code words are used to disperse the sequence of information data In these types of systems, commonly known as "large code" systems, a sequence of signatures is much longer than a symbol (often thousands of millions of long symbols.) Since these codes are non-orthogonal to begin with, the temporal change of the relationship Dispersion of one or more channels to provide transmissions in compressed mode does not create additional interference between codes. The solution proposed in the preceding application becomes problematic, however, for DS-TDMA systems where orthogonal code words are used for dispersion data streams. In code systems known as "short", a series of short codes (for example, including 128 codes of 128 chips in length) are chosen so that all codes are orthogonal to each other over a range of symbols, ie , about the length of the code. Consequently, the number of chips per symbol, that is, the dispersion ratio, can not be changed in one or several channels. Accordingly, it would be desirable to provide a DS-CDMA system in which the transmission and reception is discontinuous but does not depend on a reduction in the dispersion ratio to provide inactive time for the receiver to measure at different frequencies.

Compendium The introduction of discontinuous transmission in the CDMA communication techniques is achieved by, for example, the selective use of perforated or distructive encoded output of a convolutional encoder. By temporarily increasing the coding rate during a frame, the encoded information only fills a part of information of a frame in a compressed mode, leaving an empty part of the frame in which other functions are performed, such as the evaluation of other frequencies for use in transference between frequencies. A mode control device may, for example, switch a coded signal flow output from a convolutional coder between a first signal processing branch associated with a normal transmission mode and a second signal processing branch associated with a mode of compressed transmission, the last of which includes a code drilling unit.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other features, objects and advantages of the present invention will be apparent from the detailed description which is set forth below when read in conjunction with the drawings, in which: Figure 1 is a schematic illustration of a cellular radio communications system; Figure 2A is a schematic illustration of a downlink traffic information processor according to the present invention; Figure 2B is a schematic illustration of a short code modulator according to an embodiment of the present invention; Figure 2C is a schematic illustration of a base station transmitter in accordance with an exemplary embodiment of the present invention; Figures 3A and 3B are examples of a transmission in normal mode and a transmission in a compressed mode, respectively, for four frames; and Figure 4 is a block diagram of the alternative signal processing branches for providing normal mode and compressed mode transmissions.

DETAILED DESCRIPTION In the following description, for purposes of explanation and not limitation, specific details are set forth, such as specific circuits, circuit components, techniques, etc., to provide an understanding of the invention. For example, different details are provided in relation to the exemplary modulation and transmission techniques. However, it will be apparent to those skilled in the art that the present invention can be practiced in other embodiments that depart from these specific details. In other cases, detailed descriptions of well-known methods, devices and circuits are omitted so as not to make the description of the present invention less clear with unnecessary details. An exemplary cellular radio communication system 100 is illustrated in FIG. 1. As shown in FIG. 1, a geographic region served by the system is subdivided into a number, n, of smaller radio coverage regions known as cells. -n, each cell having associated thereto a respective radio base station 170a-n. Each radio base station 170a-n has associated therewith a plurality of transmit and receive radio antennas 130a-n. Note that the use of hexagonal shaped cells llOa-n is employed as a graphically convenient way to illustrate the areas of radio coverage associated with a specific base station 170a-ñ. In fact, llOa-n cells may be irregularly shaped, superimposed, and not necessarily contiguous. Each cell llOa-n may also be subdivided into sectors according to known methods. Distributed within the cells 11A-n is a plurality, m, of mobile stations 120a-m. In practical systems the number, m of base stations is much greater than the number, n, of cells. The base stations 170a-n comprises inter alia a plurality of base station transmitters and base station receivers (not shown) that provide two-way radio communication with mobile stations 120a-m located within their respective calls. As illustrated in figure 1, the base stations 170a-n are coupled to the mobile telephony switching office (MTSO) 150 which provides inter alia a connection to the public switched telephone network (PSTN) 160 and from there to the communication devices 180a-c . The cell phone concept is known to those skilled in the art and, therefore, will not be described in more detail herein. In accordance with the present invention, the radio communications between the base stations and the mobile stations are performed using direct sequence code division multiple access (DS-CDMA). In the following, the term "downlink," or "forward" channel, refers to the radio transmission of information-carrying signals from base stations 170a-n to mobile stations 120a-m. In the same way, the term uplink, or return channel, refers to the radio transmission of information carrier signals from the mobile stations 120a-m to the base stations 170a-n. Currently, radio communication systems are being used for a growing array of applications. Traditional voice communications now coexist with radio image transmission, and a combination of other media and high-speed data applications. These applications require a radio channel capable of transporting a variable combination of information signals with low, medium and high bit rate with low transmission delay. To make efficient the use of the radio spectrum, only this bandwidth that is necessary for a specific application must be assigned. This is known as "bandwidth on demand". Accordingly, the following exemplary systems describe a multiple speed DS-CDMA system.

Downlink Figure 2A illustrates a schematic block diagram of a downlink traffic information processor 200. A downlink traffic information processor 200 is part of the transmitter of the base station. Each downlink connection requires the resources of at least one downlink traffic information processor 200. A base station having the dimension to supply a number K of simultaneous downlink connections must have at least an equal number K of processors of downlink traffic information 200. Referring to FIG. 2A, the variable speed downlink traffic information data 205 such as, for example, voice or image information originating from an information source (FIG. not shown) are received by the buffer or frame selection buffer 220 in the form of a variable rate digital bit stream. The source of information may be, for example, an ordinary telephone 180a, a computer 180b, a video camera 180c or any other suitable source of information that is linked through the PSTN 160 to the MTSO 150, or to the MTSO 150 directly. , and from there it is coupled to the base stations 170a-n according to the known methods. The bit rate (i.e., the number of kilo bits per second (kbps)) of the variable rate bit stream received by the frame selection buffer 220 depends on the type or amount of information that is to be transmitted to the stations mobile phones 120a-m. The bit rate can be defined by a Basic Bit Rate and multiples thereof, that is,: Equal Bit Rate (basic bit rate) * k; k = 0,1,2, ... N. where (Basic Bit Rate) * N is the maximum bit rate. In an exemplary embodiment having a basic bit rate of 32 kbps and a time slot of the information frame of 10 ms, each information frame contains 320 bits. For bit rates higher than 32 kbps, more than one information frame per 10 ms time interval is produced. As an example, suppose the bit rate is 128 kbps. Then, four information frames, each with 320 bits, are produced for each 20 ms time interval. In general, the number M of the information frames is the same as the number k of multiples of the basic bit rate. Again in relation to Figure 2A, each information frame is coupled with one of a plurality of modulators known as short code 210a-m for further processing. The number M of short code modulators 210a-m is equal to the number N of possible multiples of the basic bit rate. According to the first exemplary embodiment of the present invention, when the bit rate of received information data is the basic bit rate (e.g., 32 kbps) only one information frame occurs for each 10 ms time slot. , which is coupled with the short code modulator 210a. When the received variable rate bit stream is twice the basic bitrate (i.e., 64 kbps) two information frames are produced for each 10 ms time slot: an information frame is coupled with the code modulator short 210a and the other information frame is coupled with short code modulator 210b. In the same way, the higher received variable rate bitstream produces a greater number of information frames per predetermined time interval. Each information frame resulting from the high bit rate information data is coupled separately to a separate short code modulator resulting in a plurality of those known as parallel short code channels. Arranging the information data bit streams in a sequence of information frames allows the information data to be processed conveniently in the short code modulators 210a-m. Now in relation to figure 2B, at 210 a schematic illustration of the short code demodulators 210a-m is shown. Prior to encoding the channel in the convolutional encoder 230, the first overhead or supplementary bits (Xi) consisting of for example, a portion of the cyclic redundancy check (CRC) bits are added to the information frame in the time multiplexer 220. The frame containing the information bits and the first bits of the head is coupled to the convolutional encoder 230 and is subjected to the channel coding using, for example, a convolutional encoder of a third rate that adds redundancy to the plot. The coded frame is then coupled to a bit interleaver 240 where the coded frame is submitted to block interleaving block by block. After interleaving, the second header bits X2 are added to the coded frame and interleaved in the time multiplexer 250. The downlink power control bits are also added to the coded / interleaved frame in the time multiplexer 260 The downlink power control bits instruct the mobile station to increase or decrease its transmit power level. After the insertion of the power control bits, each frame is coupled to the modulator for quadrature phase shift manipulation (QPSK) 270. Those skilled in the art will appreciate that modulations other than QPSK modulation can also be used. . The QPSK 280 modulator maps the input bits, or symbols, into a sequence of complex symbols. The output of the QPSK modulator is a complex sequence of symbols represented by, for example, Cartesian coordinates in the normal form I + jQ. The dispersion of the output of the QPSK modulator is done using so-called short codes. Other combinations of coding, interleaving and modulation are also possible.

Short Codes Again in relation to Figure 1, each radio base station 170a-n transmits a single downlink signal to allow mobile terminals 120a-m to separate transmitted signals into adjacent cells or adjacent sectors (ie, signals between cells) from the downlink signals received in the cell where the mobile terminal is located. In addition, the signals transmitted to the individual mobile terminals in a particular cell are orthogonal to each other to separate signals from multiple mobile stations 120a-m operating in the same cell (i.e., signals between cells). In accordance with the present invention, downlink transmissions for multiple users in the same cell, or the same sector, are separated by dispersing the modulated signal with different orthogonal short codes. The parallel short code channels representing a high bitrate signal are separated from each other in the same way as the downstream traffic signals for the mobile terminals operating in the same cell are separated, namely by assigning different short codes SM (real) for each parallel CDMA channel. In one embodiment, short orthogonal codes are orthogonal Gold codes of real value with a length of a symbol interval. For example, with a total bit rate of 120 kbps (60 kbps in each quadrature branch) and a chip rate of 7.68 Mcps, the code length is 128 chips. Orthogonal gold codes are usually gold codes of length 2m-l, where a 0 (or one) is added to the end of all code words that produce 2m orthogonal code words, each of 2m length. The gold codes are known to those skilled in the art. Again in relation to Figure 2A, the output of each short code modulator 210a-M is coupled to the adder 215 where the individually dispersed signals of each information frame are formed into a single composite signal.

Long Codes Now relative to Figure 2C, the composite signals of each downlink traffic information processor 200A-K are coupled to the transmitter of the base station 150. The signals of each downlink traffic information processor they are added in block 290. In order to separate the downlink signals transmitted from different base stations, each base station 170a-n is assigned with unique long code, in one embodiment of the present invention, the long code may be of complex value : for example, an ordinary gold code of length 2 -l chips. After randomizing or disturbing (in blocks 300 and 302) the composite signal with the long code generated by the long code generator 285, the signal is filtered (blocks 304, 306). They become (blocks 308, 310) are added (block 312, amplified and transmitted according to known techniques.

Discontinuous transmission Normally in CDMA systems, the information is transmitted in a frame structure with fixed length, for example, 5-20 ms. The transmission that is to be transmitted within a frame is encoded and dispersed together. This information is scattered over each frame, resulting in continuous transmission throughout the frame at a constant power level, as shown for example in Figure 3A. This type of continuous, full-frame transmission is referred to herein as "transmission in normal mode". As already described, the present invention introduces discontinuous transmission in CDMA systems for, for example, evaluation of reliable transfer candidates. In accordance with the present invention this is achieved by temporarily increasing the speed of the channel encoder by deleting bits from the encoded bit stream (i.e., drilling the code). This results in coded information that is compressed in a portion of a frame, leaving an empty, residual interval in which no power is transmitted, as shown in Figure 3B. This is known herein as "compressed mode transmission". An illustrative example will further serve to 'explain' how the empty intervals can be created in accordance with the present invention.

Perforated convolutional coding techniques in digital communication systems are, per se, known as shown by the teachings of the following documents, each of which is incorporated herein by reference: U.S. Patent No. 5,029,331, published on July 2, 1991, by Heichler et al .; U.S. Patent No. 4,908,877, published March 13, 1990, by Gates; U.S. Patent No. 4,462,101, published July 24, 1984, by Yasuda et al .; Punctured Convolutional Codes of rate (n-l) / n and Simplified Maximum Likelihood Decoding, by J. Bibb Cain, George C. Clark, Jr., and John M Geist, in IEEE Transactions on Information Theory, vol. IT-25, No.l, Jan. 1979, pp. 97-100; and High Rate Punctured Convolutional Code for Soft Decision Viterbi Decoding, by Yutaka Yasuda, Kanshiro Kashiki, and Yasuo Hirata, in IEEE Transactions on Communications, vol. COM-32, No.3, March 1984, pp.315-319. In general, communication systems using perforated convolutional encoding include an encoder for encoding a digital input to be transmitted from a transmitter, and a decoder for decoding the encoded input received at the receiver. The encoder includes a convolutional encoder circuit that receives the digital input and sends a convolutional encoded output. The digital input is coded by the convolutional coding circuit so that, for each K-bits inserted in the convolutional coding circuit, n corresponding bits are output, where n > K. The introduced k-bits and the corresponding n-bits that come out are known as k-tupios and n-tuples, respectively. A convolutional coding rate for the convolutional coding circuit is defined as the ratio of the number of k bits entered to the number of n-bits output, and can be expressed as k / n. for example, the coding rate is 1/2 when there are two corresponding output bits for each bit entered in the convolutional encoder circuit. To increase the encoder code rate, the convolutional encoded output is passed through a perforation circuit that includes a transmission mask and memory pattern of the erase pattern to transmit only the selected bits of the coded convolutional output. The perforation circuit sends a perforated output having a perforated code rate of z / q. A "perforated code rate of z / q means that for every z input bits entered in the convolutional encoder circuit q bits leave the perforation circuit." The desired puncture code rate is achieved by passing a convolutional encoded output through the circuit. transmitting mask and puncturing convolutional output coded block by block Each block to be drilled is formed from a plurality of n-tuples and is known as a drill block, The number of n-tuples used to form each block The drilling rate is currently determined by recognizing that to provide a perforated code rate of z / q, where z =? k, for each convolutional encoded output of rate k / n, at least? n convolutionally encoded tuples should be grouped and punched as a drill block to achieve the desired punched code rate, therefore, the bit length of each drilling block is equal to ? convolutionally encoded tupios multiplied by the number of bits in each n-tupio. The bit length of the drill block can be expressed as L =? N. The drilling blocks are drilled according to an erase pattern having a length equal to that of the drilling block. The bits of the erase pattern have a correspondence with the bits in each of the perforation blocks. Accordingly, the erase pattern is chosen with a length that can be expressed as L =? N. The chosen erasure pattern has the minimum bit length necessary to achieve the desired perforated code rate of z / q for a convolutional coding rate of k / n. The erase pattern used by * the drilling circuit is a block of length L of ones and zeros, where each represents a transmission bit and each zero represents a non-transmission bit. (The transmission bits and the non-transmission bits are also known as non-deletion bits and deletion bits, respectively.) The ratio of ones to zeros in the erase pattern of length L is chosen to achieve the desired puncture code rate. . The relative number of zeros in the erase pattern is what determines the perforated code rate. For example, a 2/3 perforated rate is achieved for a 1/2 rate convolutional coding circuit using a deletion pattern of length 4 (ie L = zn = 2 x 2 = 4). The erase pattern of length 4 is chosen to have 3 transmission bits and one non-transmission bit, i.e., a perforation rate of 1/4, so that the new perforation rate of 2/4 is obtained. There is a plurality of different erasing patterns that have the same ratio of ones to zeros and that have the same bit length but have arrays or patterns of unique ones and zeros. The arrangement or pattern of ones and zeros in a deletion pattern affects the distance properties of the perforated code. To minimize the bit error rate of the communication system, the erase pattern having the desired bit length and the ratio of ones to zeros, is usually chosen in an attempt to optimize the distance properties of the code Perforated.

To select an optimal erase pattern once the ratio and length of ones to zeroes is determined, it is possible to consult a perforation table of the potential erasure patterns in which the distance properties for each pattern have been calculated. erased. The selection of an optimal erasing pattern for a determined length and ratio of ones to zeros of the erasure pattern is well known as indicated by the documents incorporated in the foregoing. The optimal erase pattern selected from a drill table is used by the drilling circuit during block-by-block drilling of the coded convolutional output. In accordance with the present invention, drilling is performed selectively to create empty intervals when necessary, for example, to perform measurements between frequencies. Referring to Figure 4, consider an uncoded data stream having M-bits / frame entering the convolutional channel encoder 400. The encoder 400 may, for example, correspond to the convolutional encoder 230 in Figure 2B. Assume that the encoder has an encoding rate of Rc and the data flow is provided in the frames that have length Tf. This means that the output M of the channel encoder 400 will be N = M / Rc. When the frequency measurements are carried out, the mode control device 402 operates the switch 404 to move from the upper processing branch of FIG. 4 (associated with the transmission in normal mode) to the signal processing branch. lower (associated with compressed mode transmission). In the lower signal processing branch, the coded bitstream is drilled in block 406 with a drilling rate Rp, ie, each l / RPavo bits is eliminated. The number of bits per frame in this way is reduced to N '= N * l-1 / Rp. These N 'bits / frame are then provided to the frame generator 408 (eg, interleaver 240 in FIG. 2B) resulting in a frame having a length Tf being sent to the modulator (e.g., modulator 270 in the FIG. 2B). For a bit rate of a given channel, the data of a frame can now be transmitted in a time interval of length Tf '= Tf * N' / N. The remaining time interval of length T? = Tf - TF 'can be used for measurements between frequencies.

Use of idle time Having created the idle time for a mobile station receiver, this idle time can be arranged for different advantageous uses. First, the receiver can use this time to explore other frequencies. The evaluation of carrier frequencies other than those to which a mobile station is currently assigned is performed using the compressed transmission mode in the downlink or uplink in a regular, predetermined manner. The mobile station performs measurements (e.g., the carrier signal strength, the pilot channel signal strength or the bit error rate) at other carrier frequencies during the idle part of the frame in compressed mode since during this time it does not require listening to the base station to which it is currently linked. After switching to another frequency, the evaluation of this frequency can be carried out in any suitable way, for example, such as that described in U.S. Patent No. 5,175,867 of ej ke et al. The measurements are retransmitted to the network (through the base station or base stations currently linked) providing the information used for the mobile-assisted transfer (MAHO). The compressed mode is used intermittently at a rate determined by the mobile station or the network in this exemplary mode, however, it may be preferable for the network to control the use of compressed mode transmission for the downlink. The mobile station or the network can determine the frequency of use of the compressed mode based on different factors, such as the propagation conditions of the radio, the speed of the mobile station and other interference factors, the relative call density, and the proximity of the limits of the cell where the transfer is most likely to be required. This information, together with the details of the measurement and the transfer algorithm used in the system, can be used by the mode control device 402 to synchronize the movement of the switch 404. The execution of a call transfer can also be handled in compressed mode in an exemplary embodiment of the present invention. Two different transfer processes can be instrumented using the idle time provided by the compressed mode, specifically the continuous transfer or soft transfer, for the purposes of the continuous transfer, the receiver of the mobile station can use the idle time to receive time slots from the new base station and use the known synchronization techniques to synchronize the new base station before the transfer occurs, thereby accelerating the transfer process by establishing communication with the new base station before leaving its connection with the previous base station .

For the smooth transfer, after deciding on the transfer to a new base station (or base stations) the transmission on another carrier frequency, the compressed mode is entered. Communication with the above base station (s) is maintained while a new link is established during the empty part of the frame. By maintaining the previous link (s) after the new link is synchronized, communication with all base stations can be used simultaneously (establishing macro diversity on two or more carrier frequencies) making the scheme a make-before method. "to break". This scheme for smooth transfer between frequencies can be used for uplink and downlink. The transfer is completed leaving the previous link (s) and returning to the transmission in normal mode. The busy cycle of the information part of a frame for the duration of the frame is controlled from frame to frame. For measurements at other frequencies, the utilization factor can remain relatively high (for example 0.8) since only a short period of time is necessary for the measurement. For the execution of macrodiversity between two frequencies, the same information is sent in both. Therefore, the occupation example should be approximately 0.5. The compressed mode is used only intermittently and the normal mode (utilization factor = 1) is used the rest of the time. To control the quality of the transmission, the power of the transmission used during the part of the frame information is a function of the utilization factor, in an exemplary embodiment of the present invention. For example, the transmission power P can be determined as: P = Utilization factor where Pi = power used for transmission in normal mode. This increased power is necessary to maintain the quality of the transmission in the detector if the utilization factor is reduced. During the rest of the frame, that is, the empty part, the power or energy goes out. The variation in the total power transmitted from a base station can be smoothed by staggering (dispersing over time) the deployment of the compressed mode over a number of users in a certain time interval. Since the measurement of the strength of the signal on another carrier sequence probably requires only one reaction of a frame, the utilization factor can be high, thereby reducing the variation in energy transmission.

The use of normal mode and compressed mode frames of the present invention provides the ability to exploit the advantages of slot transmission / reception in hierarchical cell structures while using the DS-CDMA but without reducing the dispersion ratio. This makes it possible to measure other carrier frequencies, thereby providing reliable transfer decisions. In addition, the execution of the transfer between carrier frequencies can be done continuously by establishing a new link before releasing the old one. This can be done without the need for two receivers. The above description of the preferred embodiments is provided to enable any person skilled in the art to make and use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the principles described herein may be applied without departing from the scope and spirit of the present invention. In this way, the present invention is not limited to the described modalities, but can be adapted to the broader scope consistent with the following claims.

Claims (25)

1. CLAIMS 1. A method of multiple access by division of code in cellular communications, where the information is transmitted in frames that have a specific time duration, the method consists of the steps of: coding a flow of symbols in a channel associated with a frame that it will be transmitted to produce a stream of encoded symbols; selectively increasing a channel coding rate of the stream of coded symbols to generate a frame in compressed mode, wherein the frame in compressed mode includes a first part having a duration of time less than the specific time duration and containing a signal of complete encoded information, and a second part; printing the stream of coded symbols to be transmitted over a sequence of signatures to produce a scattered information signal; and transmitting the scattered, coded information signal, as a normal frame or as a compressed frame based on a result of the selective increment step. The method of claim 1, wherein the coding step of the channel further consists of the step of convolutionally coding the flow of symbols. 3. The method of claim 1, wherein the step of selectively increasing further comprises the step of: selectively drilling the coded symbol stream. 4. The method according to claim 1, further comprising the step of increasing a level of transmission energy that is used during the first part of a frame in compressed mode as a function of a utilization factor, defined as a ratio of the duration of the time of the first part to the specific time duration of the frame in compressed mode. 5. The method according to claim 1, wherein no energy is transmitted during the second part. The method according to claim 1, wherein the compressed mode is used in a radio link without coordination with the use of compressed mode in other radio links. 7. The method according to claim 4, further comprising the step of smoothing variations in the total transmitted energy by dispersing the time usage of the frames in compressed mode over a number of users in a given period of time. The method according to claim 1, wherein a frequency of use of the compressed mode is based on or a combination of one or more of the following factors: the speed of the mobile station, the interference load, relative density of the calls and proximity to the limits of the cell. 9. The method according to claim 1, wherein the compressed mode is used in a downlink. The method according to claim 1, wherein the compressed mode is used in a downlink and an uplink. The method according to claim 1, wherein the compressed mode is used in an uplink. 12. The method according to claim 9, further comprising the step of performing measurements, on a mobile station, on carrier frequencies during the second part of a frame in compressed downlink mode. 13. The method according to claim 10, further comprising the step of making measurements, in a mobile station, on carrier frequencies during the second part of a frame in downlink compressed mode. 14. The method according to claim 10 further comprises the step of using the compressed mode when synchronizing at a new carrier frequency and establishing a new radio link during the second part of a frame in compressed mode. 15. The method according to claim 14, further comprising the step of maintaining communication on both a currently used radio link and a new radio link, using the second part of a frame in compressed mode for communication on the new radio link. 16. The method according to claim 15, further comprising the step of releasing the radio link currently used and returning to a frame transmission in normal mode on the new radio link, wherein the frame in normal mode consists of only coded information for the entire duration of the specific time. 17. The method according to claim 13, further comprising the steps of using the compressed mode when communication is synchronized at a new carrier frequency and establishing a new radio link during the second part of a frame in compressed mode. 18. The method according to claim 17 further comprises the step of maintaining communication on both a currently used radio link and a new radio link using the second part of a frame in compressed mode for communication on the new link of radio. 19. The method according to claim 18 further comprises the steps of releasing the radio link currently used and returning to frame transmission in normal mode on the new radio link, where the normal mode frame consists of only information coded for the entire duration of the specific time. 20. The method according to claim 12, further comprising the steps of performing transfer evaluation using measurements of a carrier frequency different in frequency from a carrier frequency with which a current link is established. 21. The method according to claim 13 further comprises the steps of performing transfer evaluation using measurements of a carrier frequency different in frequency from a carrier frequency with which a current link is established. 22. The method according to claim 21 further comprises the steps of using the compressed mode when the communication on a new carrier frequency is synchronized and establishing a new link, based on the transfer evaluation, during the second part of a frame in compressed mode. 23. The method according to claim 22, further comprising the steps of maintaining communication both in the radio link currently used and in the new radio link, using the second part of a frame in compressed mode for communication over the new radio link. 24. The method according to claim 23, further comprising the steps of releasing the radio link currently used and returning to a frame transmission in normal mode, wherein the frame in normal mode consists of only encoded information for the duration specific time 25. The method according to claim 10, further comprising the step of using the compressed mode when streaming is executed by: performing communications on a current radio link during the first part, synchronizing communication on a new carrier frequency during the second part, establish a new radio link during the second part, leave the current link when the communication on the new radio link has been established, and make communications on the new radio link using a transmission in normal mode, in where the frame in normal mode consists of only encoded information during the entire specific duration of time. 26 * The method according to claim 13 further comprises the step of using the compressed mode when executing continuous transfer by: Performing communications on a current radio link during the first part, synchronizing communications on a new carrier frequency during the Second part, Establish a new radio link during the second part, Leave the current link when the communication on the new radio link has been established, and Perform communications on the new radio link using a transmission in normal mode, where a frame in normal mode consists of only encoded information for the entire duration of the specific time. 28. An apparatus for transmitting information in a code division multiple access system that transmits information in frames of specific time duration, the apparatus consists of: means for encoding and selecting data frames in a normal mode, wherein a frame in normal mode includes encoded information during the entire specific time duration, or, a compressed mode, wherein the compressed frame includes a first part of less than the specific time duration, the first part containing a complete encoded information signal, and a second part, the means of coding and selection of frames includes an input and an output; means for controlling the compressed mode and normal mode that is used in the means of frame coding and selection; and the means for transmitting the encoded information signal that leaves the frame coding and selection means. 29. The apparatus according to claim 28, wherein the means for encoding and selecting data frames includes a first branch of signal processing associated with the normal mode, and a second branch of signal processing associated with the compressed mode, and wherein the means for controlling the mode includes a switch by means of which the mode controller means can selectively switch a signal flow to the first or second branch. 30. The apparatus according to claim 28, wherein the mode control means selects a mode according to a measurement / transfer algorithm. 31. The apparatus according to claim 28, wherein the apparatus is part of a mobile station. 32. The apparatus according to claim 28, further comprises means for decoding channels with fixed dispersion ratios. 33. The apparatus according to claim 28 wherein the apparatus is part of a base station. 34. The apparatus according to claim 30, wherein part of the algorithm is implemented in a mobile station and part of the algorithm is implemented in a base station. 35. The apparatus according to claim 28, wherein one apparatus is located in a mobile station and another apparatus is located in a base station. 36. The apparatus according to claim 28, wherein the energy supplied to the means for transmitting during a first part of a frame is controlled by the mode control means. 37. The apparatus according to claim 29, wherein the second branch includes a code drilling unit. 38. The apparatus according to claim 30, wherein a utilization factor of the compressed mode frame of the receiving means is controlled by the mode control means. 39. A CDMA transmitter consisting of: a node for receiving a bit stream of uncoded data; a channel encoder for encoding the data bit stream; a first branch of signal processing for receiving the bit stream of encoded data and generating a normal frame for transmission; a second branch of signal processing for receiving the coded data bitstream, removing some of the coded bits and generating a compressed frame for transmission; an operable switch for selecting the first or second branches of signal processing; and downstream processing circuits to receive the compressed or normal frame and transmit the same. 40. The CDMA transmitter of claim 39, wherein the channel encoder is a convolutional encoder.