IL108447A - Time-sequence radio communication system - Google Patents

Description

T I ME -SEQUENCE RADIO COMMUNICATION SYSTEM ΐητ imp 'a *7y τη imtnn1? rmyn GEOTEK INDUSTRIES, C: I85H P-5357 (693) APPLICATION FOR UNITED STATES LETTERS PATENT SPECIFICATION TO ALL WHOM ΓΓ MAY CONCERN: Be it known that George Calhoun and Oliver Hilsenrath have invented certain improvements in a TIME-SEQUENCE RADIO COMMUNICATION SYSTEM of which the following description in connection with the accompanying drawings is a specification, like reference characters in the drawings indicating like parts in the several figures.

TIME-SEQUENCE RADIO COMMUNICATION SYSTEM Background of the Invention This invention relates generally to radio communication systems, and, more particularly, relates to methods and apparatus for implementing time sequencing techniques which utilize the time domain as a resource for the creation of trunked circuits or communication channels available to a pool of contending users.

In conventional radio communication systems which utilize the time domain to create radiotelephone channels, a single carrier frequency is multiplexed into two or more communication channels. For example, one particular carrier frequency can support time frames which can be divided into time-slots. Each slot is associated with a specific communication channel. For example, in a 4-slot system, the first slot is assigned to communication channel A, the second time slot to communication channel B, the third slot to communication channel C, and the fourth slot to communication channel D. The sequence A-B-C-D constitutes the frame, and the sequence is repeated without alteration in every succeeding time frame ad infinitum. If a given user is assigned to communication channel B, that user will transmit in the second slot of every time frame for the duration of the call or connection.

For such systems, the channel rate, that is the rate of transmission of digital information over the channel, must be faster than the user rate, the rate of digital information generated by an individual user, by a factor at least equal to the number of slots per frame. For example, if the user rate is 8 kilobits of data per second, and there are four time slots allowing four users to share the carrier frequency, the channel rate must be at least 32 kilobits per second to allow a continuous circuit-like connection for each user. The data from any individual user is buffered or stored continuously with an input rate of 8 kilobits per second, and then transmitted in that user's assigned time-slot in a burst or noncontinuous transmission at a rate of at least 32 kilobits per second.

This type of architecture suffers from an important disadvantage. Specifically, it does not provide any immunity or protection against co-channel interference. Two users in the same sector or cell, or even in adjacent sectors or cells, cannot use the same time slot on the same RF frequency without substantial mutual interference. Because the frequency and slot assignments are fixed for the duration of the connection, two co-channel users in the same or adjacent cells or sectors will continuously jam each other. This means that standard systems must employ a frequency partitioning and reuse pattern, in which, typically, only l/7th of the available frequencies can be used in any cell, resulting in a reduction in total system capacity.

Accordingly, it is an object of the present invention to provide improved radio communication methods and apparatus. In particular, it is an object to provide improved use of the time domain in a radio communication system.

It is a further object to provide a radio communication system where co-channel interference is managed to allow the reuse of available radio resources in adjacent cells and sectors.

Summary of the Invention The foregoing objects are attained by the invention, which in one aspect provides a radio communication system in which a carrier frequency supports a series of time frames which are divided into a sequence of T time slots to provide communication channels. At least some of said communication channels are defined by a sequence of different ones of said T time slots in the series of time frames. In other words, a given communication channel or circuit, instead of always occupying the same slot in every frame, can occupy any slot in the frame according to the sequence for that channel. The system includes apparatus and methods for defining sequences of time slots for the channels.

Another aspect of the invention provides a radio communication system in which the same carrier frequency is reused in adjacent or nearby communication sites. The sites may be either sectors of a sectorized system or cells of a cellular system. The system includes apparatus and methods for defining a first set of orthogonal radio communication channels associated with a first of the communication sites in which no two of the channels in the first set employ the same one of the T time slots in any time frame and apparatus for defining a second set of orthogonal radio communication channels associated with a second of the adjacent commumcation sites in which no two of the channels in the second set employ the same one of the T time slots in any time frame.

In a further aspect of this invention the system also includes apparatus and methods for defining a third set of the orthogonal radio communication channels associated with a third of the adjacent commumcation sites in which no two of the channels in the third set employ the same one of the T time slots in any time frame.

In accordance with a still further aspect of this invention one or more sets of the orthogonal channels are further defined to be rninimally cross-correlated so that no one of the channels in such set or sets of the channels employ the same one of the T time slots in any time frame as more than a predetermined number of the channels in another of the sets of the orthogonal communication channels. In a preferred embodiment the predetermined number is one.

The invention will next be described in connection with certain illustrated embodiments, however, it should be clear to those skilled in the art that various modifications, additions and subtractions can be made without departing from the spirit or scope of the claims.

Brief Description of the Drawings For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description and the accompanying drawings, in which: FIG. 1 is a diagram depicting a radio commumcation system: FIG. 2 depicts the construction of communication channels from sequences of time slots in accordance with the invention; FIG. 3 is a schematic diagram depicting a first plurality of communication sites operating in accordance with the communication system of the invention; FIG. 4 is a schematic diagram depicting operation of another embodiment of the invention, and showing a second plurality of communication sites suited for cellular systems; FIG. 5 depicts the construction of communication channels for adjacent sectors or cells from sequences of time slots in accordance with the invention: and FIG. 6 depicts a decimation transform in accordance with the invention.

Description of Illustrated Embodiments An Overview FIG. 1 is a diagram depicting a radio communication system. The system has a base station 10 and subscribers 20, 30 and 40. The subscribers communicate with each other and third parties through the base station. In addition, the subscribers can communicate directly between themselves. The subscribers and the base station each have a signal source 60 for providing a carrier frequency which supports time frames. The system may be operated as a multiple access system FIG. 2 depicts a series of five time frames supported by a carrier frequency. The five frames may constitute either a superframe or a portion thereof. A superframe is a number of contiguous frames which contain the entire slot selection sequence of a repeating pattern. The time frames are divided into five time slots (S1-S5) each. A plurality of 15 slot selection sequences for utilizing the carrier frequency for 15 separate radio communication channels C1-C15 is shown. The 15 channels could be used in three adjacent radio communication sites with channels 1-5 being assigned to the first site, 6-10 to the second and 11-15 to the third.

Channels C1-C5 are defined by a sequence of time slots wherein each channel utilizes the same one of the T time slots in each frame. Thus in every frame channel CI uses slot SI, channel C2 uses slot S2, channel C3 uses slot S3, channel C4 uses slot S4 and channel C5 uses slot S5.

Channels C6-C15, in contrast, are defined by a series of different ones of said T time slots. For example, looking at channel C6, it can be seen that it utilizes slot S4 in the first frame, slot S3 in the second frame, slot S2 in the third frame, slot SI in the fourth frame and slot S5 in the fifth frame. Looking at channel C15, as another example, it can be seen that it utilizes slot S5 in frame 1, slot S3 in the second frame, slot SI in the third frame, slot S4 in the fourth frame and slot S2 in the fifth frame. Similarly it can be seen that each of channels C7-C14 do not use the same slot in every time frame.

It can be seen that each of the three sets of channels, i.e., C1-C5, C6-C10 and C11-C15, are orthogonal sets. In other words, no two channels in any set employ the same time slot at the same time. Overall, channels C1-C15 are distinct from one another.

, In other words, none of the channels of one set consistently uses the same time slots in the same time frame as any of the other channels. Thus no channel in one set can continuously share a slot with a channel in another set Assume, for example, that ϊ channel CI is constantly being used. In the first time frame, channel CI would share a slot with users of channels C and C12. In the second time frame, channel CI would share with users channels C8 and Cll. Similarly, in the third through fifth frames, channel CI would share slots respectively with the following pairs of channels C 7 and CIS, C6 and C1.4, and,C10 and C13. Thus instead of always sharing slots with any one or two channels in the other sets, channel CI shares slots with all of channels C6-C15 in the five time frames shown.

The above illustrated property may be put to good use in sectorized or cellular systems as depicted in FIGS. 3 and 4, respectively. FIG. 3 shows a geographic service coverage area scheme. The geographic area of coverage 100 is divided into a plurality of communication sites 102, 104, 106, 108 which are each served by a central base communication station 110 having a sectorized antenna 112. Of course, as in most real systems there is not perfect geographic isolation between the various sectors. One sector of the sectorized antenna 112 defines each of the sites 102, 104, 106, and 108.

If users of the system are at opposite ends of adjacent the sectors, they will not interfere with each other at all even if they are using the same frequency and time slot at the same time, Le., sharing the same time slot. The distance between the users and perhaps topography will prevent the two users from interfering with one another. Similarly, if the system is properly defined, two users in the middle of two adjacent sectors will not interfere with each other. If the distance between the users in adjacent cells or sectors is sufficient, they can share the same time slot without interfering with each other. If, however, two users in adjacent sectors are near each other along the border between the sectors, then, if the users have identical slot selection sequencing, they will continually share slots and will continually interfere with each other thereby preventing either from communicating. If, however, the radio communication channels are defined in accordance with the present invention, two such users cannot continually interfere with one another since a given user will share the same time slot with a different user from another cell or sector in each successive frame of a superframe. Accordingly, if the users are distributed throughout the cells or sectors, users will occasionally but not continually, lose data from interference since not all instances of slot sharing will cause interference and a loss of data.

The sequences illustrated average interference among all of the system's users. This randomizes the interference. As long as the sequence of time slots which defines each channel is substantially distinct from the others, then there will be some interference averaging. The degree of the interference averaging will depend upon sequence of slots which define each channel and their relationship to one another.

Error correction coding can recreate information lost from interference based upon data which is successfully transmitted. Such coding is most effective when the interference is randomized so that it appears as uniform as possible. Thus the interference averaging provided by the present system randomizes the interference in the system so that it can be dealt with effectively by error correction coding techniques. The present technique can also be used in conjunction with other interference randomizing agents such as interleaving processes.

Alternatively, in a system which does not utilize error correction coding, or in one in which the error correction coding can not fully correct the interference being generated by the system, the interference averaging provided by the present invention allows the quality of each channel to gracefully degrade so that no one channel is completely interfered with In a system as set forth above, the base station and mobile users must follow identical slot selection sequences. They can do this according to a predetermined sequence. Alternatively they can select slots in accordance with numbers generated by identical pseudorandom number generators. Other methods of synchronizing the base station and mobile users will be readily apparent to those skilled in the art.

The sequences of time slots defining each channel in FIG. 2 are merely illustrative of the type of sequences which can be used in an interference averaging systems in accordance with the present invention. An important characteristic .of these sequences of time slots is that they are distinct from one another. In other words, no two channels consistently use the same frequency and time slot from frame to frame. In addition, at least some of the sequences utilize different ones of said T time slots.

In a preferred embodiment of the* invention, shown in connection with FIG. 3. A single carrier frequency, supporting a series of frames which are divided into T time slots, is used in each of the adjacent communication sites to provide greater than T minimally cross-correlated radio communication channels. This result is attained by defining a first set of orthogonal channels associated with the first of the communication site 102 such that no two of the channels in the first set employ the same one of the T time slots at the same time. Apparatus and methods for defining the first set of communication channels is discussed in greater detail hereinafter in connection with FIGS. 5 and 6.

A second set of orthogonal radio communication channels associated with the second of the adjacent communication sites 104 is defined such that no two of the channels in the second set of channels use the same one of the T time slots in a given time frame at the same time. Apparatus and methods for defining the second set of channels is discussed in greater detail hereinafter.

Further, a third set of the orthogonal radio communication channels associated with the third of the adjacent communication sites 106 is defined such that no two of the channels in the third set employ the same one of the T time slots at the same time. Apparatus and methods for defining the third set of communication channels is discussed in greater detail hereinafter.

Thus, each of the three sets of channels is self orthogonal. In the preferred embodiment of the invention, at least one set of the orthogonal radio communication channels is defined so that it is minimally cross-correlated with one or more of the other orthogonal sets.

As used herein, the term "minimally cross-correlated" means that no one of the channels in such sets of the minimally cross-correlated communication channels employ the same one of the T time slots in any given time frame as more than a predetermined number of the channels in another of the sets of the rm'mmally cross correlated radio communicauon channels. In a preferred embodiment, the predetermined number is one. This property is discussed in greater detail hereinafter in connection with FIG. 5.

FIG. 4 is a schematic diagram depicting operation of another embodiment of the invention having a plurality of communication sites suited for cellular systems. In the illustrated cellular configuration, the geographic area of coverage 200 is divided into four communication cells 202, 204, 206, 208 which are each served by a central base communication station and corresponding antenna 212, 214, 216, 218. As in the system discussed in connection with FIG. 3, perfect geographic isolation does not exist between the various cells. In particular, areas of overlap exist between the communication cells 202, 204, 206, 208. In conventional cellular systems, interference in these areas of overlap has posed significant difficulties. In connection with the invention, however, interference in the regions of overlap is minimized in the manner described above with regard to FIG. 3. More specifically, the system provides sets of self orthogonal radio communication channels, wherein such sets are characterized by minimal cross correlation between channels of different sets. When implemented in a cellular configuration, as illustrated in FIG. 4, the interference averaging system described herein yields a one cell frequency reuse pattern. These aspects are discussed in greater detail hereinafter.

Finally, a cell may be divided into more than one communication site, as depicted in FIG. 3, which can be an important source for capacity increase. For example, by dividing each omni-cell into four communication sites, as indicated in FIG. 3, significant additional channel capacity can be attained.

FIG. 5 depicts the construction of orthogonal sets of minimally cross-correlated radio communication channels from sequences of time slots. In particular, the minimally cross correlated radio communication channels for use in nearby or adjacent communication sites, such as sectors or cells, are defined in accordance with the technique illustrated in FIG. 5.

FIG. 5 is a chart relating each channel C1-C15 for three adjacent or nearby sites of a radio communication system. Channels C1-C5 are assigned to a first site while, while channels C6-C1O and C11-C15 are assigned to the second and third sites respectively. Each channel is assigned a unique series of time slot selection sequences.

Each set of five channels for each of the sites is orthogonal. In other words, no channels for a given set can use the same time slot in the same frame as any other channel in the set. Orthogonal channels can be defined by identical patterns of slot selection sequences which are shifted framewise with respect to each other. Thus each set of sequences for channels C1-C5 follow identical patterns but are each shifted from each other, frame wise, such that the sequences are mutually orthogonal. Thus even though these sequences follow identical patterns, because they are shifted frame wise relative to each other, they are also distinct and orthogonal with respect to one another.

As illustrated in FIG. 5, multiple radio communication channels, using the same carrier frequency subdivided into frames of T time slots each, are attained by allocating the time slots to each communication channel in a preseleaed sequence. If, the five frames shown constitute an entire sequence which repeats itself in each succeeding set of five frames, then those five frames constitute a superframe. Each channel is defined by a series of different ones of said T time slots.

The slot selection sequences are selected such that channels in each site are assigned mutually orthogonal sequences, Le., intrasite correlation of the slot selection sequences is zero. In addition, the slot selection sequences are minimally cross-correlated. In other words, no channel from any of the sets of orthogonal channels, can empty the same one of the T timeslots as more than a predetermined number of channels in another of the minimally cross-correlated sets. In a preferred embodiment of the invention, the predetermined number is one.

With proper selection of system parameters, radio communication system described herein offers unique advantages. The user capacity is enhanced by the intrinsic interference averaging afforded by the system. Moreover, due to the orthogonal operation described herein, interference from co-users of a user's site is eliminated. When implemented in a cellular configuration, as illustrated in FIG. 4, the system described herein also yields a one site frequency reuse pattern.

From an implementation standpoint, the radio communication system described herein can be readily implemented with existing technologies.

Another aspect of this invention is that the second and third sets of the minimally cross-correlated radio communication channels are decimated transformations of the first set of minimally cross correlated radio communication channels.

FIG. 6 depicts a decimation transform utilized in one practice of the invention. In accordance with the transform depicted in FIG. 6, each of the minimally cross correlated radio communication channels in the first set is defined by a unique sequence of the time slots and the decimating transformation is performed on each of the channels in the first set by selecting time slots from each channel of the first set in their sequential order skipping a first decimation number of time slots in the sequence, and repeating this process on the remaining time slots in the sequence of each channel in their remaining order, until all of the time slots in each channel are used to define a second set of minimally cross correlated radio communication channels.

A second decimating transformation is performed on each of the minimally cross correlated channels in the first set by selecting time slots from in the first set in their sequential order skipping a second decimation number of time slots in the sequence, and repeating this process on the remaining time slots in the sequence of each channel in their remaining order, until all of the time slots in each channel are used to define a third set of minimally cross correlated radio communication channels.

In accordance with the invention, the first and second decimation numbers 108,447/2 are different and each is less than the minimum factor of T, where the minimum factor of a number is the smallest number, greater than one, that can be divided into the number with a remainder of zero.

For example, suppose that Channel 1 of a first set of orthogonal radio communication channels associated with a first communication site is defined by the following time slot selection sequence: SI S2 S3 S4 S5 SI S2 S3 S4 S5 SI S2 S3 S4 S5 ... (Set 1, Ch. 1) Decimation is executed on Channel 1 of the first set by selecting time slots from the above listed time slot selection sequence in sequential order slapping a first number of time slots in the sequence. This number is referred to herein as the "decimation number" or "decimation factor." For purposes of this example, suppose a decimation factor .of 3.

Decimating the above sequence with a decimation factor of 3 yields the following time slot selection sequence: S5 SI S2 S3 S4 S5 SI S2 S3 S4 S5 SI S2 S3 S4... (Set 2, Ch.6) In accordance with the invention, this sequence is used to define Channel 6, which is the first channel of a second set of channels. The second set of channels is, of course, associated with a second communication site.

Time slot selection sequences for remaining channels C7-C10 of Set 2 are constructed similarly, by decimating the sequences for each of the channels of Set 1 by the same decimation factor of 3.

Then, to generate the time slot selection sequence defining Channel Cll, the first channel of the third set of channels, the third set being associated with the third communication site, the Set 1, Channel 1 sequence is decimated by a different decimation number, selecting time slots from the Set 1, Channel CI sequence in their sequential order skipping the second decimation number of time slots in the sequence. In particular, the following sequence can be dedmated, for example, by the deamation factor of 2, such that the decimation of the sequence SI S? S3 S4 S5 SI S2 S3 S4 S5 SI S2 S3 S4 S5_ (Set 1. Ch. 1) yields S4 S5 SI S2 S3 S4 S5 SI S2 S3 S4 S5 SI S2 S3... (Set 3, Ch. l l) This process is repeated on the remaining time slots in the sequence of each channel in their remaining order until all of the time slots in each channel are used to define a third set of minimally cross-correlated radio communication channels.

It will be appreciated that the above-described operations provide sets of sequences having minimum cross -correlation, and support communication sites .or sectors in which no two of channels in a given site employ the same one of the allocated time slots in a given time frame. The resulting system is thus characterized by orthogonal operation v thin a given site or sector, and minimum sector-to-sector cross-correlation.

This system has the property that the number of available adjacent communication sites is one less than the minimum factor of the number of time slots per time frame. The minimum factor of a number is the smallest number, greater than one, that can be divided into the number with a remainder of zero. Thus, if the number of time slots per frame is three, then the minimum factor is three, and the maximum number of adjacent minimally cross correlated cornmunicau'on sites is two. If the number of time slots per frame is four, then the minimum factor is two, and only one site can be serviced.

Similarly, if the number of time slots per frame is 10, then only one site can be serviced. If the number of time slots per frame is seven, then six sites can be serviced. Accordingly, the maximum number of sites can be serviced by a system of this invention, using a time frame subdivided into T time slots, if T is a prime number, is T-1. Thus, in a preferred embodiment of this invention, the number T of time slots per frame is a prime number.

The capacity of the system described herein is determined by the average interference over the entire time frame. In a multiple-site embodiment of the invention, interference can occur in the form of collisions, i.e., simultaneous use of the same time slot, by users in the same communication site, or by users in a different communication site. System performance depends upon the probability of collisions, and the power of the colliding interferer.

It will thus be seen that the invention efficiently attains the objects set forth above, among those made apparent from the preceding description.

It will be understood that changes may be made in the above construction and in the foregoing sequences of operation without departing from the scope of the invention. For example, while the present invention is particularly suited for radiotelephone "multiple access" communication systems, it will be readily apparent that it can be utilized in non-multiple access radio commumcation systems as welL It is accordingly intended that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative rather than in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention as described herein, and all statements of the scope of the invention which, as a matter of language, might be said to fall there between.

Having described the invention, what is claimed as new and secured by Letters Patent is:

Claims (26)

1. In a radio communication system employing a carrier frequency which supports a series of time frames divided into T time slots, said carrier frequency being reused in a plurality of adjacent communication sites of said communication system to provide greater than T radio commumcation channels in said system, said system including: means for defining a first set of radio communication channels associated with a first of said plurality of adjacent communication sites in which no two of said channels in said first set of said radio commumcation channels employ the same one of said T time slots in any given time frame; and means for defining a second set of said radio communication channels associated with a second of said plurality of adjacent communication sites in which no two of said channels in said second set of radio commumcation channels employ the same one of said T time slots in any given time frame.

2. The communication system as defined in claim 1 wherein: each of said commumcation channels is defined by a sequence of different ones of said T time slots in a series of said time frames.

3. The communication system as defined in Claim 1 further comprising: means for defining a third set of radio communication channels associated with a third of said plurality of adjacent communication sites in which no two of said channels in said third set of said minimally cross correlated communication channels employ the same one of said T time slots in any given time frame.

4. The communication system as defined in Claims 1 in which: said second set of radio communication channels is further defined so that no one of said channels in said second set of channels employ the same one of said T time slots in any given time frame as more than a predetermined number of said channels in said first set of radio communication channels.

5. The communication system as defined in Claim 3 in which: said third set of radio communication channels is further defined so that no one of said channels in said third set of said channels employ the same one of said T time slots in any given time frame as more than a predetermined number of said channels in said first set of radio communication channels and also does not employ the same one of said T time slots in any given time frame as more than said predetermined number of channels in said second set of said minimally cross- correlated radio communication channels.

6. The radio communication system as defined in Claim 4 in which the predetermined number is one.

7. The radio communication system as defined in Claim 5 in which the predetermined number is one.

8. The communication system as defined in any of the preceding claims in which said second set of said radio communication channels is further defined as a first decimated transformation of each of said radio communication channels in said first set

9. The communication system as defined in Claim 5 in which: in which said second set of said radio communication channels is further defined as a first decimated transformation of each of said radio communication channels in said first set; and said third set of said radio communication channels is further defined as a second decimated transformation of each of said radio communication channels in said first set.

10. The communication system as defined in Claim 8 in which: each of said radio communication channels in said first set is defined by a unique sequence of said T time slots and said first decimating transformation relates said first set of radio communication channels to said second set of radio communication channels as though time slots from each of said radio communication channels in said first set were selected in their sequential order skipping a first decimation number of said T time slots in said sequence and repeating this process on the remaining of said T time slots in said sequence of each of said channels in their remaining order until all of the said T time slots in each of said channels are used to define said second set of radio communication channels; and said first decimation number is less than the minimum factor of T.

11. The communication system as defined in Claim 9 in which: each of said radio communication channels in said first set is defined by a unique sequence of said T time slots and said first decimating transformation relates said first set of radio communication channels to said second set of radio communication channels as though time slots from each of said radio communication channels in said first set were selected in their sequential order skipping a first decimation number of said T time slots in said sequence and repeating this process on the remaining of said T time slots in said sequence of each of said channels in their remaining order until all of the said T time slots in each of said channels are used to define said second set of radio communication channels and said first decimation number is less than the rriinimum factor of T; and each of said radio communication channels in said third set is defined by a unique sequence of said T time slots and said second decimating transformation relates said first set of radio communication channels to said third set of radio communication channels as though time slots from each of said radio communication channels in said first set were selected from each time frame of said minimally cross correlated radio communication channels in said first set in their sequential order skipping a second decimation number of said T time slots in said sequence and repeating this process on the remaining of said T time slots in said sequence of each of said channels in their remaining order until all of the said T time slots in each of said channels are used to define said third set of radio communication channels, wherein said second decimation number is less han the minimum factor of T and wherein said second decimation number is different than said first decimation number.

12. In a method of providing a radio communication system employing a carrier frequency which supports a series of time frames which are divided into T time slots, said carrier frequency being used in a plurality of adjacent communication sites to provide communication channels in said system, said method including: defining a plurality of adjacent communication sites associated with said communication system; selecting ones of said T time slots in a first predetermined order to define a first set of radio communication channels associated with a first of said plurality of adjacent communication sites so that no two of said channels in said first set of radio communication channels use the same one of said T time slots at the same time; and selecting ones of said T time slots in a second predetermined order to define a second set of radio communication channels associated with a second of said plurality of adjacent communication sites so that no two of said channels in said second set of radio communication channels use the same one of said T time slots at the same time.

13. In the method of providing a radio communication system as defined in Claim 12, said method also including: selecting ones of said T time slots in a third predetermined order to define a third set of radio communication channels associated with a third of said plurality of adjacent communication sites so that no two of said channels in said third set of radio communication channels use the same one of said T time slots at the same time.

14. In the method of providing a radio communication system as defined in Claim 12, said method also including: said second set of channels being further defined so that no one of said channels in said second set of radio communication channels employ the same one of said T time slots at the same time as more than a predetermined number of said channels in said first set of radio communication channels.

15. In the method of providing a radio communication system as defined in Claim 14 wherein said predetermined number is one.

16. In the method of providing a radio communication system as defined in Claims 12, 13, 14, or 15, said method also including: said second set of radio communication channels being further defined as a first decimated transformation of each of said radio communication channels in said first set.

17. In the method of providing a radio communication system as defined in Claim 12, said method also including: said second set of radio communication channels being further defined as a first decimated transformation of each of said radio communication channels in said first set in which each of said radio communication channels in said first set is defined by a unique sequence of said T time slots and said first decimating transformation relates said first set of radio communication channels to said second set of radio communication channels as though time slots from each of said radio communication channels in said first set were selected in their sequential order skipping a first decimation number of time slots in said sequence and repeating this process on the remaining of said T time slots in said sequence of each channel in their remaining order until all of the T time slots in each channel are used to define said second set of radio communication channels.

18. In the method of providing a radio communication system as defined in Claim 13, said method also including: said second set of radio communication channels being further defined as a first decimated transformation of each of said radio commumcation channels in said first set in which each of said radio commumcation channels in said first set being defined by a unique sequence of said T time slots and said first decimating transformation relating said first set of radio communication channels to said second set of radio communication channels as though time slots from each of said radio commumcation channels in said first set were selected in their sequential order skipping a first decimation number of time slots in said sequence and repeating this process on the remaining of said T time slots in said sequence of each channel in their remaining order until all of the T time slots in each channel of the first set are used to define said second set of radio communication channels; and said third set of radio communication channels being further defined as a second decimated transformation of each of said radio communication channels in said first set in which each of said radio communication channels in said first set is defined by a unique sequence of said T time slots and said second decimating transformation relating said first set of radio communication channels to said third set of radio commumcation channels as though time slots from each of said radio communication channels in said first set were selected in their sequential order skipping a second decimation number of time slots in said sequence and repeating this process on the remaining of said T time slots in said sequence of each channel in their remaining order until all of the T time slots in each channel of the first set are used to define said third set of radio communication channels wherein said first and second decimation numbers are different and each is less than the minimum factor of N.

19. In a radio communication system employing a carrier frequency which supports a series of time frames with each of said time frames being divided into T time slots to provide channels of a radio communication system, said system including: a plurality of adjacent communication sites associated with said communication system; and a central base communication station which uses said T time slots for defining on said carrier frequency a first set of radio communication channels associated with a first of said plurality of adjacent communication sites in which no two of said channels in said first set of radio communication channels employ the same one of said T time slots at the same time; and which also uses said T time slots for defining on said carrier frequency a second set of radio communication channels associated with a second of said plurality of adjacent communication sites in which no two of said channels in said second set of radio communication channels employ the same one of said T time slots at the same time.

20. In the radio communication system as defined in Claim 19, said second set of channels being further defined so that no one of said channels in said second set of radio communication channels employ the same one of said T time slots at the same time as more than a predetermined number of said channels in said first set of radio communication channels. e

21. In the radio communication system as defined in Claim 20, said predetermined number being one.

22. In the radio communication system as defined in claim 19, 20, or 21, said second set of radio communication channels being further defined as a first decimated transformation of each of said radio communication channels in said first set

23. In the radio communication system as defined in claim 19 in which said second set of radio communication channels is further defined as a first decimated transformation of each of said radio communication channels in said first set: each of said radio communication channels in said first set being defined by a unique sequence of said T time slots and said first decimating transformation relating said first set of radio communication channels to said second set of radio communication channels as though time slots from each of said radio communication channels in said first set were selected in their sequential order skipping a first decimation number of time slots in said sequence and repeating this process on the remaining of said T time slots in said sequence of each channel in their remaining order until all of the T time slots in each channel are used to define said second set of radio communication channels.

24. In a communication system employing a carrier frequency which supports a series of time frames with each of said time frames being divided into a plurality of time slots, said system including: a central base station which communicates with remote users on said carrier frequency over a plurality of channels defined by said time slots, at least one of said channels being defined by different ones of said time slots.

25. In a communication system according to claim 24, at least one of said channels being defined as the same time slot in every frame.

26. In a method of providing a radio communication system employing a carrier frequency to support a series of time frames which are divided into time slots, said method including: defining a plurality of radio communication channels on said carrier frequency as a sequence of said time slots in said series of time frames, some of said channels being defined as different ones of said time slots. SAN FORD T C OLB C : 1 85 1 4