MXPA98006801A - Methods and systems of access of cdma of multiple carrier sustract - Google Patents

Abstract

The present invention relates to apparatuses and methods for practicing CDMA techniques of subtractive multiple carriers. A channel is divided into a plurality of contiguous subchannels, wherein in each subchannel a dispersion amount is reduced in accordance with the number of subchannels. The channel can be divided into a plurality of time slots and a fraction of the total number of conversions that share the channel can be assigned to each time slot. A radio communications device, which uses said method, may employ one time slot for transmission and another time slot for reception.

Description

METHODS AND SYSTEMS OF CDMA ACCESS OF MULTIPLE SUBSTRACTIVE CARRIER BACKGROUND The present invention relates generally to the field d? mobile radio systems, such as cellular systems, that employ Code Division Multiple Access (CDMA) and subtraction or cancellation of use interference to elevate the - | _g multi-user capability. The systems d? spectrum d? conventional dispersions, including CDMA systems, have a limit on the number of simultaneous conversations per cell per unit bandwidth determined by auto -j_5 interference. Improved CDMA systems that use interference cancellation or subtraction have been developed to overcome this capacity limit, however, the signal processing effort that must be spent on that receiver increases with at least 2? Cube of the bandwidth. The cellular standard band width of E.U.A. EIA / TIA IS-95 describes a CDMA system that has instantaneous bandwidths in the order of 1 Mhz that can support various conversations in the same bandwidth and location. The IS-95 standard also describes a CDMA system that uses continuous transmission and reception and requires an expensive diplexion filter to couple the transmitter and receiver to the same antenna. In contrast, the European standard, GSM, defines a Time Division Multiple Access (TDMA) system through which the time slotted transmission is used to accommodate eight users on the same 200 KHz channel, and each uses a slot of transmission time that is deviated from the reception time slot to avoid needing a diplexing filter. Instead of the expensive dip filter used in complicated IS-95 systems, these TDMA systems employ a much cheaper and lower transmission / reception (T / R) switch. The Patent of E.U.A. No. 5,151,919 entitled "Subtractive CDMA demodulation" (to Paul W. Dent, issued September 29, 1992), the disclosure of which is incorporated herein by reference, discloses, among other things, a technique to overcome the limit. of auto interference to the CDMA capability by demodulating overlapping CDMA signals iteratively in order to decrease the measured signal strength so that the stronger signals are demodulated and subtracted from the received composite signal before dealing with the demodulation of weaker signals. The Patent of E.U.A. No. 5,218,619 entitled "Reortogonalization" (to Paul W. Dent, issued June 18, 1993), the disclosure of which is incorporated herein by reference, is a continuation in part of the U.S. Patent. 5,151,919 and describes for example, additional subtractions at a later stage in the process of signals already identified and subtracted a first time on a previous occasion in order to reduce residual subtraction errors. The exemplary implementations described in the above incorporated patents use digital signal processing to untangle a signal by using its known strain code, transforming the signal to the spectral domain, and then assembling the spectral component associated with that signal. After assembly, the remaining non-zero components represent the transformation of the other signals that have been disassembled with the first signal code. The rest is then transformed back to the waveform domain and the disassembly code is applied again to restore the signals to their original domain with one of them now subtracted. In the patent of E.U.A. No. 5,218,619, it is described that subtraction of imperfect signal caused by errors in the amount of signal subtracted due to the interference of the other overlapping, weaker signals can be eliminated by subtracting a signal already subtracted again in an appropriate amount, after having subtracted some of the other signs. This process of new subtraction, commonly referred to as reorthogonalization, can be performed by digital signal processors. However, this technique has the characteristic that the amount of processing increases with at least the cube of the spectrum bandwidth, making this technique costly for broadband signals depending on the costs of process processing performance available. The application of. Patent of E.U.A. Serial No. 08 / 570,431 entitled "Broadband Reortogonalization" and filed on December 11, 1995 (to Paul W. Dent), describes, among other things, a technique to reduce the processing necessary to implement the interference subtraction in Broadband CDMA systems using some steps of analog signal processing. "However, analog signal processing is not the most cost-effective technology for implementing small, low-cost mobile phones. of Series 08 / 608,811 entitled "CDMA / Subtractive TDMA" (to Paul W. Dent) discloses an interference subtractive CDMA system in which a narrow band CDMA signal is compressed in time towards a time slot which increases its width of band for transmission.When receiving, the signal received in the time slot is captured in buffer.The captured signal can then be taken out of the memory in the régime n narrow-band original so that "narrow-band interference of subtractive CDMA algorithms of acceptable complexity can be used to process the captured signals. or Both of the above-mentioned patent applications are also incorporated by reference herein. The joint demodulators for simultaneously demodulating or decoding various overlapping CDMA signals are also known. These are sometimes ] _ describe as multi-user detectors. See for example (Sergio Ver'dhu, Trans IEEE on Communications, Vol. COM-34 No. 9, September 1986). Joint demodulators tend to increase in complexity with at least the square of the number of 2nd users, and then using the Optimal Maximum Probability Sequence Calculation algorithm, the increment is exponential. In this way, joint demodulation does not now provide an acceptable solution to the limit of self-interference capacity of CDMA systems. SUMMARY The difficulties described above are solved when the multiple carrier subtractive CDMA techniques are practiced in accordance with the present invention. An exemplary system in accordance with the present invention divides the broadband channel into N subchannels in each of whose subchannels the amount of dispersion has been reduced by the factor N over that which would have been used * in the broadband channel. The signal processing complexity for processing of each sub-channel using an interference cancellation algorithm reduces faster than N, for example by N cubed, and the total processing complexity to process the entire bandwidth comprising all N's. subchannels is reduced in this way by N squared. The wider bandwidth receivers can be employed in systems embodying the invention without an undesirable increase in complexity while still providing an advantage of flexible data transmission rates, known as bandwidth on demand, for example, the channel of Broad band can be divided into M time slots and a fraction 1 / M of the total number of conversions that share the bandwidth can be distributed to each time slot. A manual telephone, or radio communications device, which uses this exemplary method can then use a time slot for transmission and a different time slot for reception in order to share components such as the antenna in a more cost efficient manner. The particularity of on-demand bandwidth can then be provided by distributing multiple time slots to a particular user if it is needed to achieve higher data rates, such as the 144 kb / s ISDN rate. In particular,; according to an exemplary method embodying the invention, wherein the information is communicated between a first station and a plurality of second stations, each of the plurality of second stations is distributed a frequency band containing a first number of subchannels , at least one time slot in a repeating time division multiple access frame period, and an access code. The information is modulated for transmission by the first station to one of the plurality of second stations to a radio signal using a distributed time slot, subchannels and an access code. The modulated signals of the first station are transmitted > simultaneously to the second stations that use the same distributed time slot and have at least some of the first numbers of subchannels in common. The transmissions are received in one of the plurality of second stations in the distributed time slot and the information intended for the second station is decoded with the help of the distributed access code. An exemplary apparatus in accordance with the present invention involves a receiver system for receiving signals in a designated time slot using a plurality of radio subchannel frequencies in a designated frequency channel and a designated access code. Said system includes an antenna element for receiving radio signals; a receiving element coupled to the antenna element to filter and amplify signals received in the designated frequency channel and convert them into a representative stream of numerical samples; the frequency decimation elements for processing the numerical sample stream to produce separate sample streams, each separate sample stream being representative of the signal in an associated sub-channel; a sub-channel processing element for processing signals in each of the sub-channels using the designated access code in order to separate a desired signal from unwanted signals having other access codes and to produce output information symbols carried by the signal desired.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing, and other objects, features and advantages of the invention of the Applicant will become apparent upon reading of this description in conjunction with the drawings, in which: Figure 1 illustrates a multi-carrier time slot TDMA format in accordance with an exemy embodiment of the invention; Figure 2 illustrates a subframe structure in accordance with an exemy embodiment of the invention; and Figure 3 illustrates a mobile terminal circuit block diagram in accordance with an exemy embodiment of the invention.

DETAILED DESCRIPTION A broadband CDMA system, in accordance with the present invention, is constructed by dividing a distributed channel bandwidth (e.g., 800 KHz) by a number N of subchannels (eg, eight subchannels). , each having a bandwidth of 100 KHz) and an M number (eg, eight) of time slots. The limiting case of M = l corresponds to continuous transmission in N subchannels and is also encompassed by the present invention. The total channel bandwidth can be shared by L users by distributing a fraction of the time slots and a fraction of the subchannels to carry traffic for each user. For example, L / M users can be distributed with the same time slot in all N subchannels. Although the distribution of time slots and subchannels can be done in a variety of ways, this description focuses on the exemy case where all the subchannels are used by each user in a single time slot, that is, each user has the same data regime. This selection is made for brevity and simplicity of the description without restricting the scope of the invention. However, the present invention also includes all cases of providing variable data regimes when employed with interference reduction, interference subtraction or joint demodulation algorithms to improve capacity. Figure 1 shows an exemy signal comprised of eight frequency channels of 100 Khz within a total receiving bandwidth of 800 Khz and divided into eight timeslots of a repeating TDMA frame period. A first user (USER 1) slot 1 is distributed to all eight carriers to receive signals from a base station. A second user (USER 2) distributes slot 2 on all eight carriers. Other users could be assigned, for example two slots in all eight carriers to receive twice the data rate or a slot in half the carriers to receive half the data rate. USER 1 processes eight signals of 100 Khz of broad received during 1/8 of time. The amount of processing needed by USER 1 is therefore equivalent to that needed to continuously process a 100 KHz carrier. This is 512 times less than the processing of an 800 kHz carrier continuously 64 times less than the processing of a 800 kHz carrier for 1/8 of the time, given a cubic relationship between processing power and bandwidth. Each slot can contain a number of overlapping CDMA signals. In this way, the USER 1 can be considered to be the "USER GROUP 1" while the USER 2 denotes the "USER GROUP 2". Each group of overlapping users may contain, for example, up to 10 individual users of which five on average have signals transmitted to them while the other five traffic signals are temporarily silent due to the other party being the active talker. One of the active signals in each sub-channel and the slot may be a Broadcasting Control Channel (BCCH) permanently transmitted which is used to alert inactive mobiles to a call from the network and to broadcast diverse total information, eg, network and information station ID and information in surrounding base stations. Some exemy parameters for a system of CDMA subtractive interference according to the present invention are shown in the Table and below.

Table 1 EXAMPLE VALUE PARAMETER Pill rate by sub135.4166 KB / s (13 MHz / 96) 100 kHz channel QPSK pad modulation Deviated Number of pads per ra64 nura Rear pads 3-3 Maintenance time -in8.125 periods of slot pick slot slot number 78.125 slot per slot number of slots per TDMA board Pasture period number 625 tilla per frame Information encoding (64.6) user Walsh encoding per slot; orthogonal An exemplary superframe structure composed of 4 x 26 TDMA frames is shown in Figure 2. This exemplary superframe structure assigns numbers 1-9 of the TDMA frame to traffic. Table 13 is not used to transmit traffic in this exemplary format and is an INACTIVE box that the receiver can use for other purposes such as exploring other base station frequencies to determine whether it is desirable to listen to a different control channel. The next 12 frames are also used for traffic and frame 26 is used to transmit a Slow Associated Control Channel Information slot (SACCH). The SACCH is used to convey less urgent information that is repeated relatively less frequently than other information, eg, that of diffusion in the BCCH. The above format is applied to each subchannel in this exemplary mode. The format can be synchronized or staggered between the subchannels. The exemplary superframe repeat period of 104 TDMA frames expands 480 mS. A complete SACCH message is therefore transmitted every 480 mS. The above slot parameters and superframe formats are derived from the GSM digital cellular TDMA system with a view to simplifying the construction of mobile phones that can operate in both GSM systems and systems operating in accordance with the present invention. The formats described above, and below, are exemplary only and are not intended to limit the scope of the invention. Instead, it will be provided to further describe exemplary format organizations in accordance with systems embodying the present invention. On a row of the superframe structure that lasts 120 mS, 24 traffic slots are received per subchannel each containing an access code, such as a Walsh encoded information symbol (64.4). In this way, after the Walsh decoding of the 64-bit codeword, six information bits are obtained, providing 6 x 24 bits per subchannel per 120 mS. The gross information regime in this manner is 2.3 KB / S per subchannel, or 9.7 KB / S when all eight subchannels are used. The raw information rate of 9.6 KB / S or 192, symbols of 6 bits by 120 mS can be protected from error using, for example Reed-Solomon codes to correct symbol errors or erasures, For example, the 192 symbols can be divided into four groups for coding in the following ways; 63.53 RS-coded providing 53 decoded 6-bit symbols 63.53"" providing 53 decoded 6-bit symbols 63.53"" providing 53 6-bit decoded symbols 3 x 6-bit 1/3 bit providing 6 decoded bits or 2 bits block RS TOTAL 192 coded symbols providing 160 symbols those encoded by 120 mS or 53 x 6 + 2 bits by 40 mS The 320 bits. decoded by 40 mS provide a net decoded information rate of 8 KB / S, and can be used, for example, to transmit digitally coded speech in accordance with the ITU 8 KB / S speech coder standard, ITU coder transforms speech of PCM composed of normal 64 KB / S u-law or linear PCM speech at eight kilograms per second towards the reduced data rate of 8 KB / s. The encoder operates in blocks of 10 S of speech samples, taking 80 speech samples at a time and compressing them to 80-bit blocks. Four successive blocks of 80 bits form the 320 bits transmitted each time an e 63.53 RS coding is transmitted with two bits that are transmitted by the 1/3 rate code. The above coding is merely exemplary of ods for encoding source and speech error control for transmission in accordance with the present invention and is not intended to restrict or limit the types of systems in which the present invention may be applied. For example, transformations can be performed using Walsh-Hadamard transformers. By transmitting an 80 bit ITU coded block that uses all eight subcarriers and one slot in two consecutive frames, little transmission delay is introduced. However, in accordance with an exemplary embodiment, it may be preferable to intersperse the transmission of speech blocks over longer periods to provide fading protection. This may be preferable, for example, because the error correction coding operates more effectively when the error probability is not correlated between successive symbols or symbols within a coded block. This correlation is reduced by spacing the 63 coded RS symbols of a coded block (in the previous example) over eight or more frames. In eight frames, 64, 6-bit symbols are decoded from the eight subcarriers. Of these, 63 are supplied to the RS decoder while the remaining symbol is applied to the 1/3 rate decoder. The 1/3 rate decoder, for example, can be configured as six convolutional decoders in the 1/3 regime bit direction operating on each bit of the symbol. The same decoder can be shared in time six times due to the very low information rate of individual bits. The symbols; SACCH and traffic can be interspersed through 25 frames, excluding the INACTIVE frame. A different INACTIVE box, in which the receiver does not receive traffic or SACCH, is desirable so that the receiver has the freedom to perform various functions, eg, change which 800 kHz block of eight 100 kHz channels is received during that picture. It is also desirable, even if not necessary, to restrict SACCH transmissions to the same frame (v, gr., Frame 26 in the repetitive structure of Figure 2) so that, during periods of voice inactivity, the other 25 frames of traffic they do not need to be transmitted, without disturbing the transmission and reception of the SACCH frame. If SACCHs are transmitted even when there is temporarily no traffic for a mobile, the number of SACCHs transmitted may be double the number of traffic frames transmitted in each slot. In this way, it may be desirable to stagger the frame used for SACCH from one overlapping signal to another so that not all SACCHs are transmitted in the same frame. Also, the INACTIVE frames can be staggered so that an overlapping signal is silent in successive frames, instead of being all silent in the same frame, eg, frame 13 in the example of Figure 2. The staggering of frames INACTIVE and SACCH matches the co-channel interference in different frames. The staging pattern can be coordinated with the transmissions of coca fields in cells or surrounding sectors,. particularly the strongest of them, in order to extend the interference that averages over more than one cell or sector in the same place. It is also possible to stagger the transmissions SACCH of a single channel so that an SACCH uses, for example, a carrier of eight on eight successive frames. however, in each time slot, each subcarrier would be likely to contain an overlapping SACCH transmission for; a different mobile, and this is probably not as convenient for the mobile receiver to handle as when the SACCH in a slot belongs to the same mobile in all eight carriers. Those skilled in the art will note that the particular type of SACCH scaling can be varied to accommodate the needs of a particular system. A mobile terminal containing an exemplary apparatus in accordance with the present invention is shown in Figure 3; An antenna 10 is shared in time between transmission and reception functions by the 11 T / R switch that is operated at appropriate times by a control and timing unit 25 alternately to connect the receiver 13 or the transmitter 12 to the antenna 10. The The receiver includes, for example, downconversion functionality provided by any appropriate circuit that converts a received signal into a complex baseband, after which the signal is made digital to form a stream of complex numbers for processing. For example, the downconversion may be performed by a quadrature downconverter including reception band selection filter 14, low noise RF amplifier 15, quadrature mixes 16a and 16b and quadrature local oscillator 17 to produce so-called signals 1 and Q which are filtered by low weight through the filters 18a and 18b. In the exemplary case of reception of a bandwidth of 800 KHz, the filters 18a, 18b pass signals having a frequency scale of 0 to 400 KHz, with an even number of carriers such as eight, if the half are in the high side of the local oscillator 17 and half on the low frequency side, the AC, or frequency of zero, as a component of the mixers 16a and 16b corresponds to the half between two subchannels, and can be discarded. In this way, the problem of DC deviation associated with direct conversion receivers can be avoided. The signals 1 and Q of the mixers 16a and 16b are made digital using a double or complex channel A / D converter 19. Many other ways of producing a stream of complex numbers representative of a composite received signal are known and can be used as an alternative to that described above. For example, the polar-based technique described in the US Patent. No. 5,048,059 to Dent (issued September 10, 1991) may be used, the patent of which is hereby incorporated by reference in its entirety. The digitally made I, Q currents representative of the sum of the subchannels are processed by a frequency decimation processor 20 to separate the individual subchannels, e.g., eight in this example. The streams 1, Q can first be captured in memory (not shown) on the reception time slot so that processing subsequently by the processors 20 and 21, respectively, do not need to operate in real time. Alternatively, if the frequency decimation processor 20 operates in real time, the individual subchannel output signals can be memorized instead of the decoding processor 21 not having to operate in real time. The decoding processor 21 operates on the subchannel signals from the decimation processor 20 to decode symbols of the designated subchannels. The decoding processor 21 may, for each channel, implement, for example, an iterative, subtractive CDMA decoding operation as described in the U.S. Patent. No. 5,151,919 and U.S. Patent. to. No. 5,218,6129 both of which are incorporated herein by reference in the foregoing. These operations decode signals according to the signal strength in order from the strongest to the weakest, and subtract the strongest signals, decoded before decoding the weakest signals. For example, in some systems the first signal (i.e. the strongest) to decode and subtract by the decoding processor 21 may be a pilot signal modulated with a fixed access code. In other systems, the first and strongest signal to be decoded may be a broadcast control channel (BCCH) carrying various total messages, eg, call or call alert messages addressed to individual receivers. Additionally, in the systems cHaving both a pilot signal and a BCCH, the pilot signal can be decoded first followed by the BCCH. Alternatively, the decoding processor 21 can implement a joint decoding technique in which various overlapping signals are simultaneously decoded. Known techniques of joint demodulation include, for example, decorrelation techniques that perform matrix multiplication operations to eliminate the effect of each signal mutually on the others. Another technique is a partial decorrelation algorithm in which the effect d? the weakest signals on the strongest are reduced by de-correlation, the strongest is quantized to a decoded symbol, the decoded symbol is subtracted from the rest leaving the second strongest signal, and then the process repeats to decode the second strongest signal and so on. Yet another technique that can be used is the Viterbi maximum sequence probability sequence calculation algorithm in which a symbol for each overlapping signal becomes hypothetical and all possible hypotheses are tested. The hypothesis that best precedes the signal received in a subchannel is then retained to provide a jointly decoded symbol for each of the overlapping signals. The output symbols of the decoding processor 21 intended for the mobile terminal (of FIG. 3) in question can be further processed by an error correction encoder 22 which may, for example, include Reed-Solomon disabling. as discussed above. The decoding of Reed-Solomon is particularly appropriate when the symbols decoded by the first stage processor 21 are multi-bit symbols. A Reed-Solomon decoder can bridge a number of erroneous symbols that the decoding processor 21 is likely to output due to noise or co-channel interference, but it can bridge twice "erased" symbols when the processor 21 Decoding provides an indication of erasure reliability or symbol along with each symbol. Symbols corrected in error of the encoder 22 comprise either digitally made speech, in which case they are fed to a speech encoder / decoder 23, or signaling messages such as those found in the associated slow control channel (SACCH), which is they feed a control processor 25. The control processor also coordinates inputs and outputs of the user through the board and display 30, LEDs 32 and bell 34. In an exemplary embodiment, the speech coder / decoder 23 also encodes speech for transmission. . The encoded speech can be encoded in error correction and converted into the transmission signal format in the transmission signal generating unit 24, and then modulated and converted to the final frequency for transmission in the transmitter 12. The control processor 25 controls the transmission and reception phases including switching of the T / R switch 11 to connect the antenna 10 to the transmitter 12 and capacitate the transmitter 12 during the transmission slots. The waveform transmitted by the mobile unit in accordance with this invention it is not necessarily the same as that received. For example, the Patent Application of E.U.A. Serial No. 08 / 179,954 entitled "Hybrid Access Methods" (to Paul W. Dent, filed January 11, 1994), incorporated herein by reference, describes reasons why mobile communications are asymmetric in the links ascending and descending, and describes how different types of uplink channels (i.e., FDMA) can be advantageously associated with downlink channels using a different access method (e.g., CDMA or TDMA). In accordance with the present invention, the multi-channel CDMA / TDMA downlink method can be associated with an uplink access method having a TDMA element, so as to preserve the characteristic of the mobile unit of not needing to transmit and receive at the same time, allowing the 11 T / R switch to be used to share the antenna 10. The transmitter, for example, could be implemented as a CDMA / 800 kHz TDMA that has eight time slots without decimating multiple carriers, a subtractive CDMA system of 400 kHz in which transmission occurs during four of the eight downlink slots, or a subtractive CDMA system of 200 kHz in the that the transmission occurs during all seven downlink slots for which the receiver is not receiving. The capacity of uplink and downlink must be the same, but it is not so important to minimize the processing effort in the base station where energy, size and cost are not as important as in a portable mobile phone, operated by battery. The systems according to the present invention relate mainly to mobile communications in the base-to-mobile direction (downlink), but can also be used in the mobile-to-base (uplink) direction. However, transmitter efficiency exchanges, as well as factors mentioned in patents and incorporated patent applications, may suggest constant envelope modulation during mobile transmission bursts. A method incorporating the invention used for downlink is not limited to being associated with a particular uplink method and the invention when used as in the uplink is not limited to use with a particular downlink method. The invention has been described with reference to modal modalities. However, it will be appreciated by those skilled in the art that it is possible to modalize the invention in specific forms other than those of the exemplary embodiments described above. Therefore, the modalities described herein are merely illustrative and should not be considered restrictive in any way. The scope of the invention is provided by the appended claims, rather than by the foregoing description, and all variations and equivalents that fall within the scope of the claims are intended to be encompassed herein.

Claims (18)

CLAIMS:

1. - A method for communication information between a first station and a plurality of second stations, the method comprising: assigning to each of the plurality of second stations a frequency band containing a first number of subchannels, at least one time slot in a repetitive time division multiple access frame period, and an access code; modulating information for transmission by the first station to one of the plurality of second stations towards a radio signal using the allocated time slot, subchannels and access code; simultaneously transmitting the modulated signals of the first station to the second stations using the same assigned time slot and having at least some of the first number of subchannels in common; and receiving the transmissions in one of the second stations in the at least one assigned time slot and decoding the intended information for the second station using the assigned access code.

2. A receiver system for receiving signals in a designated time slot using a plurality of radio sub-channel frequencies in a designated frequency channel, and a designated access code, the receiving system comprising: an antenna element for receive radio signals;; a receiving element coupled to the antenna element for filtering and amplifying the radio signals received in the designated frequency channel and converting the received radio signals into a stream of numerical samples; a frequency decimation element for processing the stream of numerical samples to produce separate sample streams, each separate sample stream being representative of a signal in an associated sub-channel; and a sub-channel processing element for processing signals in each of the sub-channels using the designated access code to separate a desired signal from unwanted signals having other access codes and producing output information symbols carried by the desired signal.

3. The receiving system according to claim 2, wherein the sub-channel processing element includes an interference reduction element for processing an unwanted signal using its designated access code to reduce an interference effect when the signal is processed. desired signal that uses the access code of the desired signal.

4. The receiving system according to claim 3, wherein the interference reduction element includes an element for processing signals in order of descending signal strength.

5. The system according to claim 4, wherein the first strongest signal processed is a pilot signal modulated with a fixed access code.

6. The system according to claim 4, wherein the first strongest signal processed is a broadcast control channel signal carrying call alert messages directed to individual receivers.

7. The system according to claim 5, wherein the second strongest signal is the broadcast control signal carrying call alert messages addressed to individual receivers.

8. The system according to claim 3, wherein the interference reduction element includes: a signal transformation element that uses an access code of a first signal to perform a transformation of received signals to a domain of transformation; a nullification element for adjusting a component in the transformation domain that corresponds to the first signal to zero; and an inverted transformation element to use the access code and proceed to decode a second signal using its access code.

9. The system according to claim 8, wherein the transformation element performs a Walsh-Hadamard transformation.

10. The system according to claim 8, in which the transformation domain is the frequency domain.

11. The system according to claim 10, wherein the transformation domain component set to zero by the nullification element is a DC component or frequency of zero.

12. The system according to claim 3, wherein the interference reduction element is a joint demodulation element that decodes at least two signals simultaneously using its access codes designated in combination.

13. A method according to claim 1, including the step of: assigning time slots for transmission from one of the plurality ofsecond stations to the first station that are deviated in time from the at least one time slot that is assigned for reception by one of the plurality of second stations.

14. The method according to claim 1, wherein the step of assigning further comprises the step of: selecting a number of the subchannels and time slots assigned to one of the second stations or in a transmission mode of desired information to provide bandwidth capacity on demand.

15. A method for communicating information between at least one of a plurality of base stations and at least one of a plurality of mobile stations, the method comprising the steps of: assigning, to each of at least one of the plurality of stations, mobile, a frequency band that contains a number of subchannel frequencies; modulating information for transmission by the at least one base station to the at least one mobile station to a radio signal that includes the subchannel frequencies; transmitting the radio signal modulated in information to the at least one mobile station; receiving the transmission of the at least one mobile station together with signals transmitted to other mobile stations that overlap at least partially on some of the sub-channels; and processing each sub-channel of the received signal using interference reduction processing to reduce the interference in each sub-channel separately.

16. The method according to claim 15, wherein the interference reduction processing step further comprises demodulating at least two overlapping signals together.

17. The method according to claim 15, wherein the interference reduction processing step further comprises demodulating an interference signal in a sub-channel and then subtracting the demodulated interference signal before proceeding to demodulate a desired signal in the subchannel.

18. The method according to claim 15, wherein the step of assigning further comprises the step of: allocating frequency bands to mobile stations that are either overlapping, partially overlapping and non-overlapping. 19, - A receiver for receiving radio transmissions in which the information is modulated in multiple frequency subchannels within a frequency channel comprising: a local oscillator element for generating a local oscillator signal having a frequency that is between frequencies associated with two of the multiple frequency subchannels; a quadrature downconversion element for converting a received signal into quadrature baseband signals 1 and Q using the local oscillator signal; and a CD bypass removal element for processing signals 1 and Q to eliminate unwanted CD deviations therefrom. 20. A method for communicating information between a first station and a plurality of second stations, the method comprising: dividing an assigned channel bandwidth into a plurality of subchannels, each subchannel having a plurality of time slots; grouping the plurality of time slots in each subchannel to a repetitive frame structure; assign to each of the plurality of second stations at least. one of the plurality of time slots in at least one of the plurality of subchannels and an access code; assigning, for each of the plurality of second stations, a frame in the repeating frame structure of each subchannel to transmit total information from the first station; and transmit the total information in the assigned tables. 21, - The method according to claim 20, wherein the total information is SACCH information. 22. The method according to claim 20, wherein the table assigned to one of the plurality of second stations is different from the assigned table for another of the plurality of second stations. 23. The method according to claim 20, wherein the frames assigned to each of the plurality of second stations are staggered within the repetitive frame structure. 24. The method according to claim 20, wherein the frame assigned to one of the plurality of second stations is different for each sub-channel assigned to one of the plurality of second stations. 25. The method according to claim 20, wherein the table assigned to one of The plurality of second stations is the same for each sub-channel assigned to one of the plurality of second stations. 26. A method for communicating information between a first station and a plurality of second stations, the method comprising: dividing an assigned channel bandwidth into a plurality of subchannels, each subchannel having a plurality of time slots; grouping the plurality of time slots in each subchannel to a repetitive frame structure; assigning to each of the plurality of second stations at least one of the plurality of time slots in at least one of the plurality of subchannels and an access code; assign, for each of the plurality of second stations, a frame in the repetitive frame structure of each sub-channel in which the first station does not transmit to the second station; and transmitting the signals to the second stations in the respective assigned at least one time slot other than those associated with the associated frame. 27. The method of claim 26, wherein the assigned frame is the same frame within the repetitive frame structure for each of the plurality of second stations. 28. The method of claim 26, wherein the assigned table for at least one of the plurality of second stations is different from the assigned table for another of the plurality of second stations. 29.- The method d? claim 26, wherein the frames assigned to the plurality of second stations are staggered within the structure of repetitive frames.