CZ222199A3 - Method of processing data items and communication controller, reception controller, central terminal, subscriber terminal, wireless communication system - Google Patents

Abstract

Receiver and causes data items to be processed intended for transmission over a wireless link connecting the central one a terminal (10) and a wireless terminal (20) telecommunications system (1), while transmitting data items associated with a number of wireless connections one frequency channel. This transfer controller includes orthogonal code generator to provide orthogonal the code from the set of nortogonial codes used to create the heterogeneous channels within a single frequency channel; a first encoder for combining a data item for transmitting to each frequency channel with said orthogonal code from an orthogonal code generator wherein the orthogonal code defines an orthogonal channel over which the data item is transmitted, and the data items' associated with different wireless connections can be transmitted simultaneously in different orthogonal channels one frequency channel; overlay generator for Provide overlay »code from the first set of overlay codes which are orthogonal to each other; and a second encoder arranged to apply code overlay from the generator code overlay to the specified data item, using the Receiver Controller and causing data items to be processed, intended for transmission over a wireless link connecting the central one a terminal (10) and a wireless terminal (20) telecommunications system (1), while transmitting data items associated with a number of wireless connections one frequency channel. This transfer controller includes orthogonal code generator to provide orthogonal the code from the set of nortogonial codes used to create the heterogeneous channels within a single frequency channel; a first encoder for combining a data item for transmitting to each frequency channel with said orthogonal code from an orthogonal code generator wherein the orthogonal code defines an orthogonal channel over which the data item is transmitted, and the data items' associated with different wireless connections can be transmitted simultaneously in different orthogonal channels one frequency channel; overlay generator for Provide overlay »code from the first set of overlay codes which are orthogonal to each other; and a second encoder arranged to apply code overlay from the generator code overlay to the specified data item, using the Receiver Controller and causing data items to be processed, intended for transmission over a wireless link connecting the central one a terminal (10) and a wireless terminal (20) telecommunications system (1), while transmitting data items associated with a number of wireless connections one frequency channel. This transfer controller includes orthogonal code generator to provide orthogonal the code from the set of nortogonial codes used to create the heterogeneous channels within a single frequency channel; a first encoder for combining a data item for transmitting to each frequency channel with said orthogonal code from an orthogonal code generator wherein the orthogonal code defines an orthogonal channel over which the data item is transmitted, and the data items' associated with different wireless connections can be transmitted simultaneously in different orthogonal channels one frequency channel; overlay generator for Provide overlay »code from the first set of overlay codes which are orthogonal to each other; and a second encoder arranged to apply code overlay from the generator code overlay to the specified data item, using the Receiver Controller and causing data items to be processed, intended for transmission over a wireless link connecting the central one a terminal (10) and a wireless terminal (20) telecommunications system (1), while transmitting data items associated with a number of wireless connections one frequency channel. This transfer controller includes orthogonal code generator to provide orthogonal the code from the set of nortogonial codes used to create the heterogeneous channels within a single frequency channel; a first encoder for combining a data item for transmitting to each frequency channel with said orthogonal code from an orthogonal code generator wherein the orthogonal code defines an orthogonal channel over which the data item is transmitted, and the data items' associated with different wireless connections can be transmitted simultaneously in different orthogonal channels one frequency channel; overlay generator for Provide overlay »code from the first set of overlay codes which are orthogonal to each other; and a second encoder arranged to apply code overlay from the generator code overlay to the specified data item, using the Receiver Controller and causing data items to be processed, intended for transmission over a wireless link connecting the central one a terminal (10) and a wireless terminal (20) telecommunications system (1), while transmitting data items associated with a number of wireless connections one frequency channel. This transfer controller includes orthogonal code generator to provide orthogonal the code from the set of nortogonial codes used to create the heterogeneous channels within a single frequency channel; a first encoder for combining a data item for transmitting to each frequency channel with said orthogonal code from an orthogonal code generator wherein the orthogonal code defines an orthogonal channel over which the data item is transmitted, and the data items' associated with different wireless connections can be transmitted simultaneously in different orthogonal channels one frequency channel; overlay generator for Provide overlay »code from the first set of overlay codes which are orthogonal to each other; and a second encoder arranged to apply code overlay from the generator code overlay on the specified data item, with 'nato data belonging to different wireless links it can be transmitted simultaneously within the same »orthogonal channel

Description

Technical field

The present invention relates generally to wireless telecommunications systems, and in particular this invention relates to techniques for processing data transmitted and received over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system.

BACKGROUND OF THE INVENTION

Previously, a wireless telecommunications system has been devised in which a geographic area is divided into cells, each cell having one or more central terminals (CTs) for communicating over wireless links with a plurality of subscriber terminals (STs) in the cell. These wireless links are realized through predetermined frequency channels, the frequency channel usually consisting of one frequency for uplink signals from the ST to the central terminal and another frequency for the downlink signals from the ST to the ST.

Due to bandwidth constraints, it is not practical for each individual subscriber terminal to have its own assigned frequency channel for communication with the central terminal. Thus, certain techniques must be used to allow the transmission of data items related to different communications over the same frequency channel without interfering with each other. In today's wireless telecommunications systems, this condition can be achieved through the use of a multi-sided code division approach (" CDMA). One embodiment of CDMA is that data items intended for transmission on a particular frequency channel can be applied with a set of orthogonal codes and data items relating to different communications are combined with different orthogonal codes from that set. A suitable set of orthogonal codes is the set of 16 16-bit Rademacher-Walsh (RW) codes. Orthogonal codes have the property that when in perfect alignment, all codes have zero cross-correlation, allowing to decode a signal to which one orthogonal code has been applied, while eliminating interference from signals to which other orthogonal codes have been applied.

Signals to which an orthogonal code has already been applied can be considered to be transmitted over the corresponding orthogonal channel in a particular frequency channel. Therefore, when a set of 16 orthogonal RW codes is used, 16 orthogonal channels can be created in one frequency channel, and thus up to sixteen separate communication signals (corresponding to sixteen separate wireless links) can be transmitted simultaneously over one frequency channel when they are on each communication signal applied different orthogonal RW codes.

WO-A-95/03652 discloses a technique for assigning a set of sequences of variable length orthogonal PN codes between user channels operating at different data rates in an extended spectrum communication system.

It is known to provide a plurality of modem grates within one central terminal and to use a different frequency channel for each modem grate. Therefore, if the central terminal has four modem grids and a frequency set of 16 RW codes is used for each frequency channel, the central terminal could be able to support wireless links of up to 60 subscriber terminals simultaneously.

However, as more subscribers connect to a wireless telecommunications network, it becomes desirable that each central terminal support more and more subscriber terminals. However, there is only a limited number of frequency channels that can be assigned to a wireless telecommunications system, and it is desirable that neighboring cells use different frequency channels to reduce interference, so the above requirements cannot be met simply by adding modem grids to each central terminal.

SUMMARY OF THE INVENTION

Accordingly, according to the present invention, a transmission controller is provided for processing data items to be transmitted over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, wherein one frequency channel is used to transmit data items corresponding to a plurality of wireless links. an orthogonal code generator for providing an orthogonal code from a set of 'm' orthogonal codes used to form 'm' orthogonal channels within a single frequency channel; a first encoder for combining a data item to be transmitted on a single frequency channel with said orthogonal code from an orthogonal code generator, the orthogonal code determines the orthogonal channel over which the data item is transmitted, and wherein the data items belonging to different wireless links

Ί I can be transmitted simultaneously in different orthogonal channels of the same frequency channel; an overlay code generator for providing the overlay code from the first set of 'n' overlay codes that are orthogonal to each other;

and a second encoder arranged to apply an overlay code from the overlay code generator to said data item, wherein 'n' of data items belonging to different wireless links may be transmitted simultaneously within the same orthogonal channel.

In a second aspect, the present invention provides a receive controller for processing data items received over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, wherein a single frequency channel is used to transmit data items corresponding to a plurality of wireless links. an orthogonal code generator for providing an orthogonal code from a set of 'm' orthogonal codes used to form 'm' orthogonal channels within one frequency channel; a first decoder for applying an orthogonal code θ provided by the orthogonal code generator to a signal received on one frequency channel to isolate data items transmitted within a corresponding orthogonal channel; an overlay code generator to provide an overlay code from the first set of £

'n' overlay codes that are orthogonal to each other, the set of 'n' overlay codes allowing 'n' data items belonging to different wireless links to be transmitted simultaneously within the same orthogonal channel; and a second decoder for applying the overlay code from the θ overlay generator to the orthogonal tilt data items. · A channel to isolate a particular data item transmitted using this overlay code.

By using overlay codes alongside a known set of orthogonal codes, it is possible for the selected orthogonal

channels to be further subdivided to form additional orthogonal channels. For example, if there are initially sixteen orthogonal channels and a set of four overlay codes is defined, with each orthogonal channel being overlayed, up to 64 orthogonal channels may be defined. By applying appropriate orthogonal codes and overlay codes, up to 64 separate communication signals could be transmitted simultaneously on one frequency channel, although at a quarter of the rate at which the communication signals could be transmitted if the overlay codes were not used.

Such an approach has the advantage of maintaining compatibility with current hardware and software equipment that uses a set of orthogonal codes but which does not support the use of overlay codes. By designating certain orthogonal channels as channels for which the overlay codes are not used, current equipment can communicate through these channels without any changes required on that equipment.

In preferred embodiments of the present invention, the overlay code generator is arranged to store one or more sets of overlay codes having different numbers of overlay codes than the first set of overlay codes. This allows the orthogonal channels to be subdivided differently depending on

3q to a selected set of overlay codes. For example, if the orthogonal channel is operating at 160 kbps and for splitting this

4 1 «!

I * I 4 t t t 4 4 ‘4 4 * 4

4 4 t * 44 * 4

A set of four overlay codes is used in the orthogonal channel, then four orthogonal channels at 40 kbps can be created from one original orthogonal channel. Alternatively, if a set of two overlay codes is used, then two original 80 kbps orthogonal channels can be created from one original orthogonal channel. This flexibility is useful because, for some communications, such as faxing, 40 kbps may not be acceptable and therefore a set of four overlay codes would not be appropriate.

The orthogonal code generator and overlay code generator may generate orthogonal codes and " overlap " codes using predetermined algorithms. Alternatively, however, the orthogonal code generator may be formed as a memory arranged to store a saoy orthogonal code, and the overlay code generator 15 may be formed as a memory arranged to store a set of overlay codes. Appropriate orthogonal codes and overlay codes could then be read into encoders and decoders as desired.

In preferred embodiments of the present invention, the orthogonal code set comprises a Rademacher-Walsh (RW) code set, preferably the set comprises a matrix of 16 x 16 RW codes. In addition, the set of overlay codes is preferably derived from RW codes, wherein each set of 'n' overlay codes preferably comprises a matrix of η χ n RW codes.

The transmission controller of the present invention may be formed within a central terminal of a wireless telecommunications system. In preferred embodiments of the invention, the first of the orthogonal channels is reserved for transmission

The 3q wireless reservation signals and the transmission controller are formed in the central terminal to enable the wireless link reservation.

............

applying overlay codes to data items to be transmitted within said first orthogonal channel from the central terminal to one of said subscriber terminals. Similarly, the second orthogonal channel is preferably reserved for transmitting call control related signals, and the transmission controller at the central terminal also allows overlay codes to be applied to data items to be transmitted within said second orthogonal channel from the central terminal to one of said subscriber terminals.

However, a number of said orthogonal channels are referred to as traffic channels for transmitting data items related to communication content, and in preferred embodiments of the invention, a TDM encoder configured to apply time multiplexing techniques (TDM) to data items to be transmitted is provided within the central terminal. via a traffic channel from said central terminal to said subscriber terminal to allow a plurality of data items belonging to different wireless links to be transmitted within one orthogonal traffic channel during a predetermined frame period.

This use of the hybrid CDMA / TDM approach for downlink traffic channels preserves the advantages of the CDMA approach, i.e., the reduction of interference in the reduction of traffic, while reducing the dynamic range of the receiver.

In addition, or as an alternative to having a central terminal having a transmission controller, the central terminal may also include a reception controller according to the present invention.

In addition, the central terminal preferably includes channel assignment means to determine which of the orthogonal channels will be subjected to overlay codes, and to transmit this information to a plurality of subscribers. terminals inside the telecommunications system. This is useful because, for example, certain orthogonal channels may be designated as reserved for communication with subscriber terminals that do not contain the features needed to support the overlay codes and which therefore require an orthogonal channel with a maximum rate of 160 kbps.

In preferred embodiments of the present invention, the channel assignment means also determines, for orthogonal channels subject to overlay codes, which set of overlay codes will be applied to each orthogonal channel. This provides a considerable degree of flexibility in how channels are used, since some channels may be split, while others may not, and those channels that are split may be split differently to obtain different numbers of channels at different speeds.

As was the case with the central terminal, the subscriber terminal of the wireless telecommunications system may include a transmission controller and / or a reception controller according to the present invention. Compared to the central terminal, however, it is advantageous for the ST to use overlay codes for all types of channels, whether they are traffic channels or others. On these uplink traffic channels, a pure CDMA approach, using overlay codes, eliminates the need for time synchronization of central terminals to reference TDM frames, and limits peak power requirements that process requests in the high frequency transmission chain of the subscriber terminals.

In a third aspect, the present invention provides a wireless telecommunications system comprising a central terminal and a plurality of subscriber terminals, wherein the central terminal comprises a transmission controller according to the present invention, and at least one of the subscriber terminals comprises a reception controller according to the present invention. Alternatively or additionally, within this wireless telecommunications system, at least one of the subscriber terminals may include a transmission controller according to the present invention, and the central terminal may include a reception controller according to the present invention.

In a fourth aspect, the present invention provides a method of processing data items intended for transmission over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, wherein a single frequency channel is used to transmit data items corresponding to a plurality of wireless links. providing an orthogonal code from a set of 'm' orthogonal codes used to form 'm' orthogonal channels within a single frequency channel; combining a data item to be transmitted on one frequency channel with said orthogonal code, wherein the orthogonal code determines the orthogonal channel over which the data item is transmitted, and wherein data items belonging to different wireless links may be transmitted simultaneously in different orthogonal channels of said single frequency channel; providing an overlay code from a first set of 'n' overlay codes that are orthogonal to each other; and applying an overlay code to said data item, wherein 'n' of data items belonging to different wireless links may be transmitted simultaneously within the same orthogonal channel.

* »A a a a

In a fifth aspect, the present invention provides a method of processing data items received over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, wherein one frequency channel is used to transmit data items corresponding to a plurality of wireless links. a code from a set of 'm' orthogonal codes used to create 'm' orthogonal channels within one frequency channel;

applying an orthogonal code to a signal received on one frequency channel to isolate data items transmitted within a corresponding orthogonal channel; providing an overlay code from a first set of 'n' overlay codes that are orthogonal to each other, the set of 'n' overlay codes allowing 'n' data items belonging to different wireless links to be transmitted simultaneously within the same orthogonal channel; and applying an overlay code to the orthogonal channel data items to isolate a particular data item transmitted using the overlay code.

he

By using overlay codes in addition to the known set of orthogonal codes, it is possible for selected orthogonal channels to be further subdivided to form additional orthogonal channels, thereby allowing support for multiple wireless links on a single frequency channel.

In the following, an embodiment of the present invention will be described, by way of example only, with reference to the accompanying drawings, in which like reference numerals are used for like features.

• 0 • * I I I I I I • • • • • • • • • • • • ** ** ** **

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a schematic overview of an example of a wireless telecommunications system incorporating an example of the present invention;

Giant. 2 is a schematic illustration of an example of a subscriber terminal of the telecommunications system of FIG. 1;

Giant. 3 is a schematic illustration of an example of a central terminal of the telecommunications system of FIG. 1;

Fig. 3A shows a schematic illustration of the modem grid of the central terminal of the telecommunications system of Fig. 1;

Fig. 4 is an illustration of an example frequency map for the telecommunications system of Fig. 1;

Fig. 5A is a schematic diagram illustrating an optional arrangement for cells of the telecommunications system of Fig. 11;

Fig. 8B is a schematic diagram illustrating an optional arrangement for cells of the telecommunications system of Fig. 11;

Fig. 6 is a schematic diagram illustrating aspects of a code division multilateral access system for the telecommunications system of Fig. 1;

7A and 7B are schematic diagrams illustrating the phases of signal transmission processing for the telecommunications system of FIG.

1;

Fig. 8A and Fig. 8B are schematic diagrams illustrating signal reception processing phases for the telecommunications system of Fig. 1;

Fig. 9A and Fig. 9B are schematic diagrams illustrating downlink and uplink communication procedures when the system is fully loaded;

10 illustrates a CDMA channel hierarchy according to preferred embodiments of the present invention;

Fig. 11 is a schematic diagram illustrating downlink and uplink communication paths for a wireless telecommunications system;

Fig. 12 is a schematic diagram illustrating the generation of a downlink signal transmitted by the central terminal;

Fig. 13A and Fig. 13B illustrate frame structures of information transmitted via descending and uplink paths;

14A and 14B illustrate the structure of the added downlink and uplink path frame;

Fig. 15A and Fig. 15B illustrate typical downlink and uplink channel structures that could arise in a loaded system according to preferred embodiments of the present invention;

• tφφφ φ

Φ Φ Φ Φ · 4 «

Φ Φ Φ «

Φ · ΦΦ «Φ φφ • φ * • φφ« · Φ

ΦΦ

Figure 16 illustrates how, in preferred embodiments of the present invention, available traffic channels are classified;

Figure 17 illustrates the elements used by the central terminal 5 to reduce interference;

Fig. 18 illustrates optional antenna arrangements that may be used in a wireless telecommunications system according to a preferred embodiment of the present invention; and

19A and 19B show a graphical illustration of a method by which channel switching is facilitated in preferred embodiments of the present invention.

Ί

DETAILED DESCRIPTION OF THE INVENTION

Giant. 1 is a schematic overview of an example of a wireless telecommunications system 1. The telecommunications system comprises one or more service areas 12, 14 and 16, each of which is served by a respective central terminal (CT) 10, which establishes a radio (high frequency) connection to the STs. ) 20 within the corresponding area. The area covered by the central terminal 10 may vary. For example, in a rural area with a low density of subscribers, the service area 12 could cover an area with a radius of 15 to 20 km. Service area 14 in an urban environment with high density of subscriber terminals 20 could only cover an area with a radius of the order of 100 m. In suburban areas with medium density of subscriber terminals 20, service area 16 could cover an area with a radius of about 1 km. But it should be quite clear, that

The II area covered by a particular central terminal 10 may be selected to meet the local requirements of expected or actual subscriber density, local geographic conditions, and the like, and is not limited to the examples illustrated in Fig. 1. its surface due to antenna design requirements, geographic conditions, buildings and the like that will affect the distribution of the transmitted signals.

The central terminals 10 for the corresponding service areas 12, 14, 16 may be connected to each other via links 13, 15, 12 / which connect them, for example, to a public switched telephone network (PSTN) 18. These links may include conventional telecommunications technology using copper conductors, optical fibers, satellites, microwaves and the like.

The wireless telecommunications system of Figure 1 is based on establishing fixed microwave links between subscriber terminals 20 at fixed locations within a service area (e.g., 12, 14, 16) and a central terminal 10 for that service area. Each subscriber terminal 20 may be provided with a permanent landline access to its central terminal 10, but in preferred embodiments, access is established on a request basis such that the number of subscribers that can be supported by the system exceeds the number of available wireless links. The manner in which the request-based approach is implemented will be discussed in more detail in the description below.

Giant. 2 illustrates an example configuration for a subscriber terminal 20 for the telecommunications system of FIG. 1. FIG. 2 includes a schematic representation of a customer building;

• · · 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 »» » ·

The customer radio unit (CRU) 24 is mounted on the customer building 22. The customer radio unit 24 comprises a flat plate antenna 23 or the like. The customer radio unit 24 is mounted at such a location on the customer building 22, or on a pole or the like, and in an orientation such that the flat plate antenna 23 within the customer radio unit 24 points in the direction 26 to the central terminal 10 for the service area. the customer radio unit 24 is located.

The customer radio unit 24 is connected via an outlet line 28 to a PSU 30 inside the customer building 22. This power source unit 30 is connected to a local power supply to provide power to the customer radio unit 24 and the network unit 32,

terminal (NTU). The customer radio unit 24 is also connected via a power supply unit 30 to a network terminal unit 32 which is further connected to telecommunications equipment in a customer building 22, for example, one or more telephones 34, facsimile devices 36 and computers 38.

The telecommunications equipment is represented as being within one customer building. Of course, this may not always be the case, as the subscriber terminal 20 preferably supports either a single or dual line, so that two subscriber lines may be supported by one subscriber terminal 20.

5

The subscriber terminal 20 may also be arranged to support analog and digital telecommunications, for example analog communication at 16, 32 or 64 kbps or digital communication according to the ISDN BRA standard.

Giant. 3 is a schematic illustration of an example of a central terminal of the telecommunications system of FIG. 1. A common frame. The equipment 40 includes a plurality of equipment grids 42, 44, 46, including a radio frequency combiner and power amplifier (RFC) grate 42, a power supply (PS) grate 44, and a plurality (in the illustrated example, four) of the modem grids 46 (MS). The high frequency combiner grate 42 allows the modem grids 46 to operate in parallel. If 'n' modem gratings 46 are formed, then the high frequency combiner grate 42 merges and amplifies the power of the 'n' transmitted signals, each transmitted signal being from a corresponding one of the 'n' modem gratings 46, and amplifies and splits the received signals 'n' honestly, so that the separate signals can be transmitted to the respective modem grates 44. The power supply grid 44 provides connection to the local power supply and protection for the various components in the common equipment frame 40. The bi-directional connection is between the high frequency combiner grate 42 and the main terminal 52 antenna of the central terminal, such as the omnidirectional antenna mounted on the column 50 of the central terminal.

This example of the central terminal 10 is connected via a point-to-point microwave link to a location where an interface to the public switched telephone network 18, shown schematically in Figure 1, is established. As mentioned above, other types of connections (for example, copper conductors or optical fibers) they can also be used to connect the central terminal 10 to the public switched telephone network 18

5 of this example, modem grids 46 are connected via line 47 to microwave terminal 48 (MT). Microwave lines 49 extend from this microwave terminal 48 to a point-to-point microwave antenna 54 mounted on a pole 50 for basic connection to the public switched telephone network 18.

* • • ♦ ♦ ♦ ·

A personal computer, workstation, or the like may be used as a local control unit 56 (SC) to support the central terminal 10. This local control unit 56 may be connected to each modem grate 46 of the central terminal 10 via, for example, RS232 interface connections 55. The local control unit 56 may then provide support functions such as fault, alarm and status location and configuration of the central terminal 10. The local control unit 56 could operate in a network to support a number of central terminals.

As an alternative to RS232 interface links 55 that lead to local control unit 56, data links, such as X.25 interface links 57 (shown in FIG. 2), could be established from board 228 to junction 60 of base control system 58 (EM) instead. dashed lines in Fig. 3). The base control system 58 may support a plurality of distributed central terminals 10 connected via corresponding links to the switch node 60. The base control system 58 allows a potentially large number (e.g. up to 1000 or even more than 1000) of the central terminals 10 to be integrated into the control network. The base control system 58 is arranged in conjunction with the executive workstation 62 and may include a plurality of computer terminals 64 for network engineers and management personnel.

Giant. 3A illustrates various portions of modem rack 46. The transceiver RF unit 66 (RFU, for example, implemented on a card in a modem rack) generates modulated RF signals at medium power levels and regenerates and amplifies baseband RF signals for subscriber terminals. This radio frequency unit 66 is coupled to an analog card 68 (ΑΝ) that performs AD / DA conversions, baseband filtering, and vector sums of 15 transmitted signals from modem cards 70 ( MC). This analog unit 68 is associated with a plurality (typically 1 to 8) of modem cards 70. The modem cards 70 perform baseband signal processing for transmitted and received signals to / from subscriber terminals 20, which may include convolutional coding with 1/2 at a speed of 16 and extension with code division multi-access codes (CDMA) on the transmitted signals, and recovery of synchronization, narrowing and error correction on the received signals. However, in order to incorporate redundancy so that the modem can be replaced in the subscriber line when an error occurs, generally only 15 modems on one modem rack 16 are used. The sixteenth modem is then used as a backup that can be involved in the Activity when one of the two fails 15 modems, modem cards 70.

they are connected to a slave unit 74 which terminates the connection to the host public switched telephone network 18 (e.g. via one of lines 47) and processes signaling of telephone information to the subscriber terminals via one of 15 out of 16 modems.

5

Wireless telecommunications between the central terminal and the subscriber terminals 20 could be implemented at different frequencies. Giant. 4 illustrates one possible example of frequencies that could be used. In the present example, the wireless telecommunications system 30 is intended to operate in the 1.5 to 2.5 GHz band. More precisely, it is intended that • * · · * * * * This presented example worked in the band defined in ITU-R (CCIR) Recommendation F.701 (2025 to 2110 MHz, 2200 to 2290 MHz). Giant. 4 illustrates the frequencies used for uplink from subscriber terminals 20 to central terminal 10 and downlink from central terminal 10 to subscriber terminals 20. It is evident that 12 uplink and 12 downlink radio (radio frequency) signals are generated centrally around a frequency of approximately 2155 MHz. channels of 3.5 MHz each. The space between the receive and transmit channels exceeds the required minimum separation of 70 MHz.

In the present example, each modem rack supports 1 frequency channel (i.e., one uplink frequency plus the corresponding downlink frequency). Currently, in a wireless telecommunications system, as described above, CDMA encoding is used to support up to 15 subscriber lines on a single frequency channel (i.e., one subscriber line on each modem). Thus, if the central terminal has four modem grids, it can support 60 (15 x 4) subscriber lines (i.e. 60 subscriber terminals can be connected to one central terminal). However, it is becoming increasingly desirable that more than 60 subscriber terminals are supported from one central terminal, and, in preferred embodiments of the present invention, improvements are made in the CDMA encoding technique to increase the number of subscriber lines that can be supported by the central terminal. Both CDMA encoding and improvements made to this CDMA encoding according to preferred embodiments of the present invention will be discussed in more detail in the description below.

* · • «t 9 9 9 999

Typically, radio (high frequency) traffic from a particular central terminal 10 will extend to an area covered by a neighboring central terminal 10. To prevent, or at least reduce interference (interference) problems caused by adjacent areas, only any given central terminal 10 will be used. a limited number of available frequencies.

Giant. 5A illustrates one cellular (cellular) type arrangement for frequencies to reduce interference θ problems between adjacent central terminals 10. In the arrangement illustrated in FIG. 5A, the hatch lines for cells 76 show a frequency set (FS) for these cells. Selecting three frequency sets (for example, where FS1 = F1, F4, F7, F10;

FS2 = F2, F5, F8, F11; FS3 = F3, F6, F9, F12) and by arranging so that the immediately adjacent cells do not use the same frequency set (see, for example, the arrangement shown in Fig. 5A), it is possible to create a fixed array of omni-directional cells in which interference can be reduced between adjacent cells. The transmission power of each central θ terminal 10 is preferably set such that transmission does not reach the nearest cell that uses the same frequency set. Thus, according to the arrangement illustrated in FIG. 5A, each central terminal 10 may use four frequency pairs (for uplink and downlink respectively) within its cell, each modem grating in the central terminal 10 being associated with a corresponding high frequency channel (frequency pair).

Giant. 5B illustrates a cellular (cellular) type arrangement that uses split cells into sectors to reduce interference problems between adjacent central terminals.

10. As in Fig. 5A illustrates a different type of hatch lines in Fig. 5B illustrates different frequency sets. As in Fig. 5A, Fig. 5B represents three frequency sets (for example where FS1 = F1, F4, F7, Fl0; FS2 = F2, F5, F8, F11; FS3 = F3, F6, F9, F12). However, in Fig. 5B, the cells are divided into sectors by using a sector split central terminal 13 (SCT) that includes three central terminals 10, one for each sector S1, 52 and S3, with the transmission for each of the three central terminals 10 is directed to a suitable sector from sectors S1, S2 and S3. This allows the number of subscribers per cell to be increased three times, while still providing permanent fixed access for each subscriber terminal 20.

Arrangements such as those shown in FIG.

5A and 5B may help to reduce interference, but to ensure that cells operating at the same frequency do not inadvertently decode all other data, a seven cell repetition pattern is used so that for a cell operating at that frequency all six adjacent cells working on a unique pseudo-random noise code (PN) is assigned to this same frequency. The use of PN codes will be discussed in more detail below. The use of different PN codes prevents neighboring cells operating on the same frequency from inadvertently decoding all other data.

²⁵

As mentioned above, CDMA techniques can be used in a fixed allocation arrangement (i.e., an arrangement in which each subscriber terminal is assigned to a particular modem on a modem rack) to allow each channel frequency to support 15 subscriber lines. Giant. 6 provides a schematic overview of CDMA encoding and decoding.

· · · · • • • • * * * * * * «*«

In order to encode a CDMA signal, baseband signals, e.g., user signals for each respective subscriber line, are coded in blocks 80 to 80N to a baseband signal with 160 kits / s, each symbol representing 2 data bits (see, for example, the signal represented in block 81). This signal is then augmented by a factor of 16 using the expansion function 82-82N to produce signals with an actual video rate of 2.56 Msymbl / s at 3.5 MHz. The extension function includes applying a PN code (which is specified for the central terminal base) to the signal, as well as applying a Rademacher-Walsh (RW) code that ensures that the signals for the corresponding subscriber terminals are orthogonal to each other. Once this extension function has been applied, the next step signals for the respective subscriber links are merged in block 84 and converted to a high (radio) frequency (RF) to produce many user channel signals (see, for example, block 85) for transmission from a broadcast antenna. 86.

During transmission, the transmitted signal will be exposed to interference sources 88, including external interference 89 and interference from other channels 90. Accordingly, at a time when a CDMA signal is received in a receiving antenna 91., multiple user channel signals may be distorted as represented in Block 93.

To decode signals for a given subscriber link from a received multiple user channel, the correlator 94 to 94N uses the same RW and PN codes that were used to encode each subscriber link to obtain a signal (e.g., as represented in block 95) for the respective received signals. 96 to 96N baseband. It can be seen that (even the received signals will contain some residual noise. However, unwanted noise can be removed using low-pass and signal processing.

The key to CDMA is the application of RW codes, which is a mathematical series of sequences that have an orthonormality function. In other words, if any RW code is multiplied by any other RW code, the result is always zero. The set of RW codes that can be used is illustrated in Table 1 below.

Table 1

RWO 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 RW1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 RW2 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 RW3 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 RW4 1 1 1 1 “1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 RW5 1 -1 1 -1 -1 1 -1 1 1 -1 1 -1 -1 1 -1 1 RW6 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 1 1 RW7 1 -1 -1 1 -1 1 1 -1 1 -1 -1 1 -1 1 1 -1 RW8 1 1 1 1 1 1 1 1 -1 -1 -1 -1 -1 -1 -1 RW9 1 -1 1 -1 1 -1 1 -1 -1 1 -1 1 -1 1 -1 1 RW10 1 1 -1 -1 1 1 -1 -1 -1 -1 1 1 -1 -1 1 1 RW11 1 -1 -1 1 1 -1 -1 1 -1 1 1 -1 -1 1 1 -1 RW12 1 1 1 1 -1 -1 -1 -1 -1 -1 -1 -1 1 1 1 1 RW13 1 -1 1 -1 -1 1 -1 1 -1 1 -1 1 1 -1 1 -1 RW14 1 1 -1 -1 -1 -1 1 1 -1 -1 1 1 1 1 -1 -1 RW15 1 -1 -1 1 -1 1 1 -1 -1 1 1 -1 1 -1 -1 1

* 0 0 0

0,000 • 0 0

00 · 0 · 0 · ·

00 * 0 0 0 • 00 000 Β 0 • 0 00

The above set of RW codes are orthogonal codes that allow multiple user signals to be transmitted and received at the same frequency at the same time. Once the bit stream is orthogonally isolated using RW codes, the signals for the respective subscriber links do not interfere with each other. Because the RW codes are orthogonal, they have zero cross-correlation when all codes are perfectly aligned, which allows to decode the signal while clearing interference from users working on other RW codes.

In preferred embodiments of the present invention, it is desirable to provide a central terminal with the ability to support more than 15 subscriber links (lines) on each channel frequency, the above set of 16 RW codes being improved to achieve this. However, in order to maintain compatibility with earlier products using these 16 RW codes, it was desirable that any enhancement retain the same set of 16 RW codes.

The way in which these improvements have been realized provides flexibility in the method of configuring the frequency channels, thereby creating certain configurations allowing the support of more subscriber lines but with a lower overall bit rate. In preferred embodiments of the invention, a channel may be selected to operate at the following overall bit rates:

160 kbps maximal speed (FI) 80 kbps half speed (H1, H2) 40 kbps quarter speed (Q1, Q2, Q3, Q4) 10 kbps low speed (LI, L2, L3, L4) for

. 30 ascending reservation '4' f 'r »f r. I

In preferred embodiments of the present invention, the manner in which these channel associations are implemented differs for the downlink (central terminal to the subscriber terminal) and the uplink (subscriber terminal to the central terminal) communication paths. This is because it has been found that there are different operational requirements for downlink and uplink communication paths. On the downlink, all the signals come from one source, namely the central terminal, and thus these signals will be synchronized. However, on the uplink path, the signals will be based on a plurality of independent subscriber stations and hence will not be synchronized.

In view of these conditions, in preferred embodiments of the invention, the uplink operation is performed at maximum speed (160 kbps) using a basic set of RW codes discussed in detail above, but half and quarter speeds are achieved by using overlay codes, which include high-speed symbol patterns encoded by RW codes that are transmitted for each medium-speed data symbol. Two 2-bit overlay codes are created for half-speed operation, while four-bit overlay codes are created for quarter-speed operation. In generating the signal for transmission, one of the overlay codes, where appropriate, is applied to the signal next to the appropriate RW code. When this signal is received, in the CDMA demodulator, the incoming signal is multiplied by PN, RW and channel overlay code. The correlator integration period is set to match the length of the overlay code.

* · ··· ··· • ·

Overlay codes are used extensively to provide uplink variable speed traffic channels. Overlay codes will also be used to realize downlink control channels, and these control channels will be discussed in more detail below. However, as mentioned in the previous description, another approach is used to provide flexible channel aggregation on downlink traffic channel paths. The downlink traffic channels will operate in high speed mode, i.e. 160 kbps, with lower data rates of 80 and 40 kbps being supported by the time multiplex (TDM) available bandwidth.

In preferred embodiments of the present invention, the TDM slot numbering will follow the CCITT standard

G.732 with bits transmitted in the beat 1, bit 2, ..., bit 8 sequence.

- - The byte organization is specified per channel as either the highest valid bit (MSB) first, the lowest valid bit (LSB) first, or N / A.

Creating a hybrid CDMA / TDM approach for downlink

2Q traffic channels retain the advantages of CDMA access, that is, interference is limited when traffic is limited. In addition, the use of TDM ensures that the CDMA signal is limited to a constellation of 256 Quadrature Amplitude Modulation (QAM), which reduces the dynamic range of receiver requirements. QAM constellations are familiar to those skilled in the art.

On uplink channels, a pure CDMA approach using overlay codes eliminates the need for time synchronization of subscriber terminals to the TDM frame control.

This has the advantage that TDM delays and security time between TDM frames are eliminated. Another advantage is the reduced peak power that handles RF requests

4 4 4 4 444 4 4 4 4

44 • 4 4

4 4 • 444 • 4 4

44 • 4 4 • 4 444 •

444

4 to a transmission terminal of a subscriber terminal that would otherwise be required for group TDM data transmission. High dynamic range requirements are also reduced for the central terminal receiver.

The manner in which the transmitted and received signals are processed according to preferred embodiments of the present invention will be described with reference to Figs. 7 and 8. 7A is a schematic diagram illustrating the phases of the signal transmission according to the arrangement in the subscriber terminal 20 in the telecommunications system of FIG. 1. In FIG. 7A, the analog signal from the phone 100 is routed via an interface such as a two-wire interface 102 to a hybrid audio processing circuit 104; then through the encoder-decoder 106 to generate a digital signal into which an additional channel including control information is inserted in block 108. If the subscriber terminal supports a number of telephones or other telecommunications equipment, then elements 102, 104 and 106 may be repeated for each piece of telecommunications equipment.

^{20 May}

At the output of the additional insertion circuit 108, the signal will have a bit rate of either 160, 80 or 40 kbit / s, depending on which channel has been selected for signal transmission.

The resulting signal is then processed by convolutional encoder 110 to produce two signals at the same bit rate as the input signal (together these signals will have a transmission rate of 160, 80 or 40 kS / s (kbaud / s)). 11, wherein, if a reduced bit rate channel has been selected, an appropriate overlay code is applied to the signals by means of a signal overlay. ·. ·· ·· ·· ·· ·· ·.

the overlay code generator 113. At the output of this diffuser 11, the signals will have a transmission rate of 160 kS / s regardless of the bit rate of the input signal, because the overlay code has increased this transmission rate by the required amount.

The signals output from the diffuser 111 are routed to the diffuser 116 where Rademacher-Walsh codes and PN codes are applied to these signals via a PN code generator 112 or a PN code generator 114, respectively. The resulting signals, now at a rate of 2.56 mc / s (2.56 mega images per second, where the image is the smallest data element in the extended (scattered) sequence), are routed through a digital-to-analogue converter 118. This digital-to-analog converter 118 shapes digital samples into an analog wave and provides power baseband control. The signals are then routed to the low pass filter 120 to be further modulated in the modulator 122. The modulated signal from the modulator 122 is mixed with a voltage generated signal controlled by an oscillator 126 that operates in response to the synthesizer 124. The mixer output 128 is then amplified in a low noise amplifier 130 before it is routed through the bandpass filter 132. The output of the bandpass filter 132 is further amplified in another low noise amplifier 134 before being passed to the power control circuits 136. The output of these power control circuits 136 is further amplified in the power amplifier 138 before it is routed through another bandpass filter 140 and transmitted from a transmit antenna 142.

Giant. 7B is a schematic diagram illustrating the phases of signal transmission processing according to the arrangement in the central terminal 10 in the telecommunications system of FIG. 1. As shown in FIG. 1. Obviously, the central terminal is configured to perform a signal processing similar to that of the subscriber terminal 20 illustrated in FIG. 7A. , but does not include elements 100, 102, 104 and 106 associated with telecommunications equipment. Further, the central terminal includes a TDM encoder 105 for performing a time multiplex, if desired. The central terminal will have a network interface through which incoming calls for the subscriber terminal will be received. When such an incoming call is received, the central terminal contacts the subscriber terminal to which the call is intended and prepares a suitable channel through which this incoming call can be made with the subscriber terminal (in preferred embodiments of the invention, this operation is performed using the call control channel , which will be discussed in more detail below). The channel created for the call will determine the time period to be used for the call data routed from the central terminal to the subscriber terminal, and the TDM encoder 105 will be provided with this information.

Therefore, when incoming call data is routed from

With the network interface to the TDM encoder 105 over the line 103, the TDM encoder will apply the appropriate TDM encoding to this data so that it can be inserted into a suitable period of time. From this point on, the signal processing is the same as the equivalent processing performed at the subscriber terminal as described with reference to FIG. 7A, where the overlay code generator produces one overlay of '1' so that the signal output from the diffuser 111 is the same as a signal input to this diffuser 111.

As mentioned earlier, in preferred embodiments of the invention, overlay codes are used rather than TDM for

················ · 9 · · · * · ·

999 9

9 «9 • · · ···

The realization of downlink control channels and data related to such channels are fed from the request assignment device (which will be discussed in more detail below) through line 107 through switch 109 to bypass insertion circuit 108, thereby bypassing The TDM encoder 105. The signal processing is then the same as the equivalent processing performed at the subscriber terminal, where the overlay code generator provides suitable overlay codes to the divider 111. The overlay code generator will be controlled to produce the desired overlay code, and in preferred embodiments of the present invention control from a DA device (which will be discussed in more detail below).

Giant. 8A is a schematic diagram illustrating the phases of signal reception processing according to the arrangement in the subscriber terminal 20 in the telecommunications system of FIG. 1. In FIG. 8A, the signals received through the receive antenna 150 are routed through the bandpass filter 152 before being amplified in the low noise amplifier 154. from this low-noise amplifier 154 is then passed through another bandpass filter 156 before being further amplified by another low-noise amplifier 158. The output of the low-noise amplifier 158 is then routed to a mixer 164 where it is mixed with a signal generated by a voltage controlled oscillator

5

162, which operates in response to the synthesizer 160. The output of the mixer 164 is then passed through the I / Q demodulator 166 and the low pass filter 168 before being fed to the analog to digital converter 170. The digital output of this A / D converter 170 at 2.56 mC / s (mega images per second) is then fed to correlator 178 to which

The same Rademacher-Walsh codes and PN codes are applied via the RW code generator 172 (which corresponds to the RW code generator 112) and the PN code generator 174 (which corresponds to the PN code generator 114) respectively. as they were used during the broadcast. The output of the 160 kS / s correlator 178 (kilo of symbols (baud) / s) is then fed to the correlator 179 where any overlay code used in the transmission phase for signal coding is applied to the signal via the overlay code generator 181. The elements 170, 172, 174, 178, 179 and 181 form a CDMA demodulator. The output of this CDMA demodulator (at the location of correlator 179) then has a rate of either 160, 80, or 40 kS / s depending on the overlay code applied by correlator 179.

The output from the correlator 179 is then fed to the decoder

180 Viterbi. The output from this Viterbi decoder 180 is then routed to a withdrawal circuit 182 to extract additional channel information. As for the speech data, the output from this extract circuit 182 is routed through the TDM decoder 183 to extract the speech data from a specific period of time that has been inputted by the TDM encoder 150 of the central terminal. Then, the speech data is routed through the encoder-decoder 184 and the hybrid circuit 188 to an interface, such as a two-wire interface 190, in which the resulting analog signals are routed to the telephone 192. As mentioned above in connection with the transmission processing stages in the subscriber terminal , elements 184, 188, 190 may be repeated for each piece of telecommunications equipment 192 in the subscriber terminal.

If the data output generated by the withdrawal circuit 182 is data on the downlink control channels, instead of routing the data to the telecommunications equipment, this data is routed via the switch 187 to the call control logic 185 where the data will be interpreted by the subscriber terminal.

At the subscriber terminal 20, the automatic control acquisition phase is integrated into the IF phase (interface phase). The control signal is derived from the digital portion of the CDMA receiver using the signal output to estimate the signal quality.

Giant. 8B illustrates the signal reception processing phases according to the arrangement in the central terminal 10 in the telecommunications system of FIG. 1. As will be seen from this figure, the signal processing phases between the receiving antenna 150 and the extracting circuit 182 are the same as the processing phases in the subscriber terminal discussed. above with reference to Fig. 8A. However, in the case of the central terminal, the speech data output from the removal circuit 182 is routed via line 189 to the network interface within the central terminal, while the control channel data is routed via the switch 191 to the DA processing device 380. The DA device 38Q is discussed in more detail below.

The channel overlay codes and schedules are chosen to ensure the orthogonality of the signals - that is, in a properly synchronized system, the contribution of all channels, except the channel being demodulated, gives a sum of zero during the correlator integration period. In addition, the uplink power is controlled to maintain a constant energy per bit. The exception to this procedure is low speed operation at which the signal will be transmitted at the same power as the quarter speed signal. Table 2 below illustrates · · · · φ »

• Overlay codes used for operations at maximum, half and quarter speeds. • • • • • • • • • •

Table 2

clean allocation power ST overlay integrative reservation speed (kbps) channels Tx. due to Fl-U (dB) code period correlator (ps) overlap 160 -Fl-U 0 1 6.25 IF 80 -Hl-U -3 1 1 12.5 IF 80 -H2-U -3 1 -1 12.5 L3 40 -Ql-U -6 1111 25 IF 40 -Q2-U -6 1-11-1 25 L2 40 -Q3-U -6 11-1-1 25 L3 40 -Q4-U -6 1-1-11 25 L4

In preferred embodiments of the invention, a 20 kbps reservation mode is provided that uses chained overlays to create a reservation delay; this procedure is illustrated in Table 3 below:

Table 3

reservation overlap Equivalent pattern with high speed Ll-U 1111111111111111 L2-U 11-1-111-1-111-1-111-1-1 L3-U 1-11-11-11-11-11-11-11-1 L4-U 1-1-111-1-111-1-111-1-11

- · ·· «» 4 * * · 4 4 * 4 4 444 * • 44 · · · · 44 «4 · • · ♦ 4 • 44 4 *

Giant. 9A and 9B are diagrams illustrating the uplink and downlink transmission procedures when the system is fully loaded, and illustrate the difference between using the overlay codes as illustrated in Fig. 9A and using the TDM as illustrated in Fig. 9B. When using overlay codes, the RW code is split in the area of the RW space to allow operation of up to four sub-channels at the same time. In contrast, using the TDM, the RW code is split in a time domain to allow up to four signals to be transmitted using one RW code, but at different times during a 125 ps frame. As illustrated in Figs. 9A and 9B, in the preferred embodiments of the present invention, the last two RW codes, RW14 and RW15, are not used for data traffic because they are reserved for call control and reservation functions; which will be discussed in more detail below.

The CDMA channel hierarchy is illustrated in Figure 10. Using this hierarchy, the following CDMA channel assignments are possible:

. 25

F1 Hi + H2 HI + Q3 + Q4 H2 + Q1 + Q2 Q1 + Q2 + Q3 + Q4

After discussing how CDMA codes are improved to allow flexible channel allocation, and bit rates may be reduced to allow processing of multiple subscriber lines per channel frequency, it will be read with reference to 11 and 12, a general overview of how descending and uplink paths are realized.

Giant. 11 is a block diagram of the downlink and uplink communication paths between the central terminal 10 and the subscriber terminal 20. The downlink communication path is implemented from the transmitter 200 at the central terminal 10 to the receiver 202 at the subscriber terminal 20. 20 to the receiver 206 in the central terminal 10. Once the downlink and uplink communication paths have been established in the wireless telecommunications system 1, telephone communication via the downlink signal 212 may be made between the user 208, 210 of the subscriber terminal 20 and the user serviced via the central terminal 10. The uplink signal 214. The downlink signal 212 is transmitted via the transmitter 200 of the central terminal 10 and is received through the receiver 202 of the subscriber terminal 20. The uplink signal 214 is transmitted via the transmitter. e 204 and subscriber terminal 20 is received by receiver 206 CT 10th

The receiver 206 and the transmitter 200 inside the central terminal 10 are synchronized with each other in terms of time and phase, and aligned for information limits. In order to realize the downlink path, the receiver 202 in the subscriber terminal 20 should be synchronized with the transmitter 200 in the central terminal 10. The synchronization is performed by performing the reservation mode function and the tracking mode function on the downlink signal 212. First, the transmitter • I I I I I I I I I I I I I I I I I

200 of the central terminal 10 transmits a downlink signal 212. FIG. 12 shows the contents of the downlink signal 212. The frame information signal 218 is combined with the overlay code 217, if appropriate, and the resulting signal 219 is then combined with the code sequence signal 216 for the central terminal 10 to produce the downlink signal 212. This code sequence signal 216 it is derived from a combination of a pseudo-random noise code signal 220 and a Rademacher-Walsh code signal 222.

The downlink signal 212 is received at the receiver 202 of the subscriber terminal 20. The receiver 202 compares its phase and code sequence with the phase and code sequence within the signal.

216 of the downlink code sequence 212. The central terminal is considered to have a master code sequence, and the subscriber terminal 20 is considered to have a code sequence acquired. Receiver 202 incrementally sets the phase of its dependent code sequence to detect match and superior code sequence and brings receiver 202 of subscriber terminal 20 into phase with transmitter 200 of central terminal 10. The dependent code sequence of receiver 202 is not initially synchronized with the master code sequence of transmitter 200 and central terminal. 10 due to the path delay between the central terminal 10 and the subscriber terminal 20. This path delay is due to the geographical separation between the subscriber 25 terminal 20 and the central terminal 10 and other environmental and technical factors that affect wireless transmission.

After acquiring and initiating tracking on the central terminal 10 superiors code sequence signal 216 code ^{30 _} 'sequence within downlink signal 212, receiver 202 enters a frame alignment mode in to form the downlink communication path. The receiver 202 analyzes the frame information within the frame information signal 218 of the downlink signal 212 to identify the frame position start for that downlink signal 212. Since the receiver 202 does not know at what point in the downlink data stream 212 it has received information, so as to be able to process the information received from the transmitter 200 of the central terminal 10. Once the receiver 202 has already identified one other start of the frame position, a downlink communication path has been established from the transmitter 200 of the central terminal 10 to the receiver 202 of the subscriber terminal 20.

The structure of the high-frequency (radio) frames of information transmitted over the downlink and uplink communication paths will now be discussed with reference to Figs.

14. In Figures 13 and 14, the following terms are used:

.......

Bn subscriber payload, 1 x 32 to 2 x 64 kbps

Dn signaling channel, 2 to 16 kbps

OH radio (high frequency) additional channel

- 16 kbps operating mode

- 10 kbps reservation / standby mode

13A and 13B both show a 125 ps subframe format that is repeated throughout

2Q of a radio frame, the frame typically lasting 4 milliseconds (ms). Giant. 13A illustrates a high frequency frame structure that is used in preferred embodiments of the present invention for the downlink path. The subframe (i) in Fig. 13A shows the high-frequency frame structure used for the low speed, i.e. 10 kbps, in the reservation mode (Ln-D), during which only the additional channel is transmitted. The subframe (ii) in Fig. 13A illustrates the structure of the high frequency frame used for the call control channel operating in a quarter-rate (Qn-D) mode, i.e. 40 kbps, while the subframe (iii) in Fig. 13. 13A illustrates a high-frequency frame structure used for traffic channels in maximum speed mode (F1-D), i.e., 160 kbps.

Similarly, the subframe (i) in Fig. 13B illustrates the structure of the high frequency frame used for the uplink when operating at low speed in the reservation and call control (Ln-U) mode. The subframes (ii) to (iv) show the high-frequency frame structure used for the traffic channels when operating in quarter speed (Qn-U) mode, half speed (Hn-U) mode, and at, maximum mode, respectively. speed (Fl-U).

An additional (overhead) channel will now be described in some detail in conjunction with Figs. 14A and 14B, which illustrate the structure of the additional frame used for various data rates. The additional channel may include a plurality of fields - frame alignment word (FAW), code synchronization signal (CS), power control signal (PC), channel control and maintenance signal (OMC), mixed OMC / D-channel signal (HDLC), identification channel byte (ch.ID) and certain unused fields.

* · ♦ 9 9 9 9 9 9 9 9 9 · 9 * *

The frame alignment word identifies the beginning of the frame position for its corresponding frame of information. The code synchronization signal provides information for controlling the synchronization of the transmitter 204 at the subscriber terminal 20 and the receiver 206 at the central terminal 10. The power control signal provides information for controlling the transmit power of the transmitter 204 at the subscriber terminal 20. The channel control and maintenance signal provides status information relating to downlink and uplink communication paths, and a path from the central terminal 10 to the subscriber terminal, to which a communication protocol that operates on a modem rack between a rack controller and modem cards is also propagated. The OMC / D signal is a combination of the OMC signal and the signaling signal (D), while the ch.ID signal is used to uniquely identify the RW channel, the ch.ID signal being used by the subscriber terminal to ensure that the correct channel has been reserved.

In preferred embodiments of the present invention, the ST will receive downlink traffic channel data at 160 kbps. Depending on the byte channel rate, the subscriber channel will be assigned the appropriate sharing of the high-frequency additional (overhead) signal. The following TDM mapping is created:

’· *’ Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi «,

Table 4

Speed (kbps) Allocation channels Nositelský channel CS PC OMC speed added 160 -Fl-D-Tl / 1 Bl, B2, B3, B4 CS1, CS3 PCI, PC3 OMCl, OMC 3 4 ms 80 -F1-D-T2 / 1 B1, B2 CS1, CS3 PCI, PC3 OMC1, OMC3 4 ms 80 -F1-D-T2 / 2 B3, B4 CS2, CS4 PC2, PC4 OMC2, OMC 4 4 ms 40 -F1-D-T4 / 1 Bl CS1 PCI OMCl 8 ms 40 -F1-D-T4 / 2 B2 CS2 PC2 OMC2 8 ms 40 -F1-D-T4 / 3 B3 CS3 PC3 OMC 3 8 ms 40 -F1-D-T4 / 4 B4 CS4 PC4 OMC 4 8 ms

In the above table, the scheme used to identify the channel is as follows. Speed code 'Fl' indicates

2Q maximum speed, i.e. 160 kbps, 'D' indicates that the channel is a downlink channel, and 'Tn' indicates that the channel is time-multiplexed between subscriber terminals, where 'n' indicates the total number of TDM slots, and indicates the selected operating time period.

All subscriber terminals operating on the traffic channel will receive 160 kbps D-channel information; the D-channel protocol includes an address field to specify which subscriber terminal is to process the contents in the message.

· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·

- * * · · · · · ft · · · ♦ · ft ft ft ftft

The channel structure has been illustrated in the foregoing description in connection with FIGS. 9A and 9B. In preferred embodiments of the present invention, the channel structure is flexible, but includes:

at least one line reservation channel (LAC) at least one call control channel (CCC) usually one priority traffic channel (PTC) up to 13 traffic channels (TC)

The manner in which the channel assignment is created ensures that prior fixed assignment arrangements using a set of 16 RW codes as discussed above are still supported as well as on-demand access services available using the system according to the preferred embodiment of the present invention. . Giant. 15A and 15B illustrate typical downlink and uplink channel structures that could occur in a loaded system according to preferred embodiments of the present invention. As illustrated in Fig. 15A, downlink paths may have certain 160 kbps signals and may utilize the entire RW channel. An example of such signals could be those that are transmitted over fixed-link links to products that do not support CDMA enhancements provided by the systems according to the preferred embodiments of the present invention, as illustrated for RW1 and RW2 in Fig. 15A. Alternatively, the user may be authorized to use the entire RW channel, for example, when sending a fax as illustrated by RW12 in FIG. ISA.

As illustrated by RW5 to RW11, a TDM may be used on downlink traffic channels to allow more than one central terminal to subscriber terminal communication on the same RW channel during each frame. In addition, as illustrated for RW3 and RW4, in preferred embodiments of the present invention, certain channels may be blocked to reduce interference from other adjacent cells, as discussed in more detail below.

A similar channel assignment can be achieved for uplink paths, but as illustrated in Fig. 15B overlay codes are used instead of TDM to allow it to run during each frame (as shown in Fig. 158 for RW5 to RW11) more than one subscriber terminal communication to the central terminal on the same RW channel. It should be understood that in both Figures 15A and 15B, the RW14 and RW15 channels are reserved as a call control channel and a line reservation channel, respectively, and that overlay codes are used on these channels regardless whether the path is descending or ascending. These two channels will be discussed in more detail below.

Reservation / access to the network will be via the line reservation channel (LAC). Subsequent to power up, the ST will automatically attempt a downlink LAC reservation on a predetermined 'home' radio channel.

The downlink LAC (e.g., RW15 in preferred embodiments of the present invention) will operate at a rate of 10 kbps and at full power per user. The descending reservation will be present for all subscriber terminals.

Each CT Modem Shelf will maintain a database containing the serial numbers of all participating ♦ · ²⁵ · * * · ΦΦ • φ φ φ φ • · · φ φφφ φ φ φ φ φ · · · φ ♦ ♦ ··· ·· terminals , which could possibly be supported by this central terminal. The status of each ST will be recorded with upper level states as follows:

unencumbered standby call in progress

Transition states will also be defined. The ST is considered unloaded when the ST is rebuilt, the central terminal has lost control communication with the ST, or the ST has been turned off from the power supply. Via the LAC channel, the central terminal transmits the individual serial numbers of the subscriber terminals and thus provides an offer for uplink reservation via the LAC channel. An unloaded uplink reservation will be made on the low speed line reservation channel. The central terminal will offer an unloaded (cold) start over the control channel to certain subscriber terminals.

Assuming an uplink channel is available, a suitable reservation overlap will be selected and the reservation will be initialized.

Switching to the 'fast' downlink RW channel can be supported at speeds other than Ln-D. 'Fast' in this context means that coherent demodulation is maintained and only convolutional decoding and frame synchronization processes need to be repeated.

· · · * * * * * * * · * ·

When booking, the management information will be changed. A short subscriber_terminal identifier (between 12 and 16 bits) will be authorized and assigned to the ST, which will be used for subsequent addressing. The uplink of the subscriber terminal will operate long enough for the uplink to be parameterized via the subscriber terminal in terms of code phase and transmission power. These parameters will be used by the ST for subsequent bookings on a busy (warm) start and will also be maintained by the central terminal to allow the central terminal to force the unloaded ST to a warm start. Upon successful completion of network access, the ST will be put in a standby state and instructed to terminate uplink communication and forward a call control channel (CCC) (RW14 in preferred embodiments of the invention).

The time required to reach the network can be monitored, and, if desired, the following techniques can be used to reduce this time to access the network:

(i) assigning priorities so that users with high GOS (service quality) are offered network access first.

(ii) converting traffic channels to LAC channels.

(iii) In the event of the central terminal being restarted, the STs are invited to attempt an ascending warm start. This could reduce the network entry time with a factor of 4. This mechanism would have to be • <

• 4 ’· 4 * and 4 * 4 4 I« and 14 «

1-4 f · * I «4« 14 «

41

Even secured against possible change of the uplink hot start parameters - that is, it should only be enabled while ensuring that no high-frequency parameter of the central terminal 5 has been changed. The central terminal would have to transmit the ID and would have to allow the subscriber terminal to check that the uplink hot start parameters were valid for that central terminal.

(iv) In the case of a reboot of the ST, the central terminal will maintain copies of the WT Start parameters so that the unloaded ST can receive these WT Start parameters at 15 reservation request and then be instructed to perform the Warm Start.

After entering the network, all subscriber terminals follow the CCC channel. This channel transmits control and call control information over a ²⁰ kbps 32 kbps HDLC channel. To maintain control communication, the central terminal invites each subscriber terminal in sequence. Each prompt includes a broadcast prompt for an addressed uplink CCC subscriber terminal, followed by a change in control information (authorization, subscriber terminal alert signal update 25, hot start parameters, downlink RF power data, and the like).

The control prompt may fail for one of the following reasons:

• 9 444 4 4 4 4 • 4 4 · 4 · 4

44 44 44 44 44 44

4

44 (i) the ST is or is disconnected from the power supply. The EM (Emergency) Alert can be set if this occurs and the database for this ST should be marked as unloaded. The network entry process will follow.

(ii) the ST is in the process of making or attempting to make a call. The call cycle may be temporarily interrupted and control communication may be performed on a suitable traffic channel.

When a control call fails, it should be followed by a number of quicker calls until either the ST responds or is marked unloaded. The CCC channel is requested to transmit all copies of the LAC channel reservation prompts so that the ST can be forced to reserve the uplink LAC channel.

Upstream traffic channel reservation procedure

The basic reservation process by the ST is:

(i) switching downlink circuits to kbps and selecting appropriate RWs and traffic channel overlays. The downlink traffic channel reservation 25 is limited to achieving frame alignment.

(ii) the downlink PC / CS channel will be decoded to form a busy / standby flag. If

The PC / CS channel indicates busy, then it means another subscriber terminal is currently using this

9 9 »

99 «99 * 9 * 99 · 10 ·»

the traffic channel and the ST will cancel the reservation process.

(iii) switching uplink circuits to kbps and selecting appropriate RWs and overlays for the traffic channel. Allowing the ST terminal transmitter to transmit at the rated power level at a maximum rate minus 18 dB. While

The PC / CS channel indicates the standby state, the ST will continue to uplink the fast code search, increasing incrementally the power level by +2 dB at the end of each search. The uplink should be reserved at full rated power minus 6 dB. The uplink reservation 15 is canceled when the maximum transmission level is reached and the PC / CS channel continues to indicate standby.

(iv) The PC / CS channel indicates busy. At this time, the ST can have a real traffic channel ²⁰ booked, or can instead watch that the PC / CS channel has entered a busy state because another ST has already reserved that traffic channel. The ST is sent an authentication request and transmits its response 25 identifikátor_úč ^and t ⁿ ického_ terminal. The central terminal grants uplink access by returning this subscriber_terminal identifier. The ST terminates the reservation process if the returned 30 ST_ID is not in the STB.

is detected (i.e., is not the subscriber_teraiinal identifier that was sent).

This authorization process decides between two subscriber terminals applying for uplink access, and also keeps the subscriber terminals not to reserve traffic channels that have already been reserved for downlink access.

Incoming call

A number of traffic channels will be reserved for incoming calls, with the processing of an incoming call as follows:

(i) Checking the central terminal database - if the ST is in the ongoing_ call state, the call is rejected.

(ii) checking that the uplink traffic channel of the desired bandwidth is available. If Bandwidth is available, then the traffic channel is reserved.

(iii) the incoming call setup message is transmitted over the CCC channel to inform the addressed subscriber terminal of the incoming call 25 and the specification of the traffic channel on which to receive the call. If the traffic channel is not available, but the central terminal forms part of the service area, then the incoming call setup message is sent with 30 empty (no) traffic channel, otherwise it is • 4M The call was rejected. The service areas will be discussed in more detail below. The incoming call setup message is repeated for a certain number of times.

(iv) the subscriber terminal is attempting to uplink. The subscriber terminal monitors the downlink and still attempts to uplink until the central terminal sends a message to the subscriber terminal to return the subscriber terminal to the CCC channel. The ST also triggers a timer to return to the CCC channel in the event of an incoming call failure to complete it.

(v) after successful uplink reservation, the central terminal 15 authorizes the subscriber terminal.

(vi) the speed switching is from a central terminal modem. A command to switch the downlink to the desired one is sent via the PC / CS channel

2q bandwidth. The ST will return this command to switch the speed over the uplink PC / CS channel. The connection is now at the desired bandwidth.

Outgoing call

Outgoing calls are supported by allowing random access to uplink traffic channel slots. The outgoing call is processed as follows:

(i) the central terminal issues a 'free list' of available traffic channels and priority '9 • 9 • 999'

9 9 • 9 9 9 9

999 * 9

9 9 »· 99 99 · · 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 This list is made available periodically (in preferred embodiments of the invention every 500 ms) and is used to denote uplink access segments.

(ii) the subscriber terminal detects a login status. The subscriber terminal starts the call setup timer.

(iii) the ST is waiting for the following free list to be received via the CCC channel. If this free list is empty, the outgoing call is blocked. The ST will generate a busy tone.

(iv) if the free list contains available channels, the ST randomly selects a channel from that free list. The algorithm that the subscriber channel uses to select the channel will need to be specified in the free list.

For example, the ST may be required to always select from the minimum bandwidth channel area so that the upper bandwidth channels remain available to users with GOS (high quality service). Alternatively, for minimal blocking, the ST can be allowed to select any channel regardless of bandwidth. In preferred embodiments of the invention, the subscriber terminals will not select lower bandwidth channels and convert the rate.

«Β

9 · ··· 25 · * · • 25 25 25 »» »» »» »»

(V) the subscriber terminal attempts to uplink on the specified traffic channel, this process has already been described in the description above.

If this reservation is successful, the outgoing call is processed. Otherwise, the ST returns to the CCC channel and waits for the next available free list. In order to prevent multiple STs from retrying the same traffic channel reservation and thus blocking each other, an appropriate protocol can be used to determine how each ST will proceed after receiving the free list.

(vi) the ST may not be able to reserve the traffic channel at the time the call setup timer has expired. In such cases, the ST can interrupt uplink access attempts and generate a busy tone.

Priority outgoing call

It is found that the random access protocol used to set up routine outgoing calls could lead to barring. In preferred embodiments of the invention, access will be granted to a mostly unlocked priority traffic channel. Priority calling is complicated because the ST must:

(i) capture and decode dialed digits.

• 4 4 4 4 4 4 4 4 4 4 4 4 444 444 44 44 44

(Ii) regenerate digits when a locked state occurs.

(iii) Enable transparent network access in an unlocked state.

(iv) categorize all outgoing calls as priority or normal, so that normal calls are canceled at the expense of priority calls.

The priority call procedure is in preferred q embodiments of the invention as follows:

(i) the central terminal shall publish a directory of numbers (DN) for emergency services numbers via the CCC channel.

(ii) the ST will attempt uplink access according to a conventional algorithm.

If this uplink approach is successful, then the subscriber can make a normal call. All dialed digits are checked against the Emergency DN list so that all calls can be categorized into common or priority in the central terminal.

(iii) if the busy tone is returned, the subscriber may dial the emergency number in the subscriber terminal. If the ST detects an emergency DN sequence, it attempts uplink access via the priority traffic channel (PCT).

(iv) upon reservation of the priority traffic channel, the ST terminal transmits the sequence selected in W * * ############### ··· · PSTN (Public Switched Telephone Network) numbers.

(iv) the central terminal converts the priority traffic channel to a traffic channel and reassigns another 5 traffic channel to become a priority traffic channel, canceling the current call in progress if necessary.

Reduce interference (select channel list size)

Compared to the widespread expansion of cells, optimal capacity is achieved by minimizing radio (high frequency) traffic while maintaining acceptable service quality. The lowest possible radio frequency operation results in improved 'carrier to interference' ratios (C / I ratios) for users within the respective cell and for users of the common channel in adjacent cells. The C / I ratio is a measure (usually expressed in dB) of how far above the interference the transmitted signal must be to be effectively decoded.

In preferred embodiments of the present invention, the central terminal is equipped with the ability to deal with C / I traffic, thereby allowing network planning to be performed more flexibly.

This feature can be realized through a CDMA-based system, as in preferred embodiments of the present invention, with the advantage of what CDMA offers over TDMA and FDMA systems.

In preferred embodiments, the central terminal will control the number of traffic channels to minimize access noise. Traffic channels will be classified as:

(i) busy - carrying traffic;

(Ii) Inbound Inbound (Access_In) - reserved for inbound access;

(iii) accessible, outgoing (Access__Out) - reserved for outgoing access - such traffic channels appear on a free list;

(iv) priority - reserved for priority outgoing access - such traffic channels appear on a free list;

(v) free - available for any purpose; and (vi) blocked - unavailable due to interference reduction.

This classification scheme is illustrated in Figure 16. The central terminal will allocate traffic on the following basis:

(i) the central terminal shall monitor incoming and outgoing call setup times and convert accessible traffic channels from free traffic channels to achieve the required quality of service.

(ii) when the call is set up, the accessible traffic channel is converted to a busy traffic channel. If a free traffic channel is available, it is converted to a new accessible traffic channel.

If there are no free traffic channels, then the accessible traffic channel is empty until the call ends.

(iii) when the call ends, the busy traffic channel is converted to a free traffic channel. If the previous call setup resulted in an "empty" traffic channel, then the available traffic channel is empty, then it is empty. the busy channel is converted back to an accessible traffic channel.

(iv) if a priority traffic channel is used, then a new priority traffic channel is created by transferring a free, accessible or busy (normal call) traffic channel.

(v) the central terminal shall monitor the number of volatile errors on the downlink and uplink occupied traffic channels in an attempt to estimate the quality of the connection. If the central terminal detects less than the average number of volatile errors and at the same time long call setup times are recorded, the blocked traffic channel can be converted to a free traffic channel. In contrast, if the central terminal encounters a higher than average number of volatile errors, the free or accessible traffic channel may be converted to a blocked traffic channel.

Giant. 17 illustrates how the central terminal performs the interference reduction function described above. When incoming call data arrives at the central terminal modem 320, encoder 325 encodes this data for transmission over wireless link 30Q to subscriber terminal 20. At subscriber terminal 20, the decoder 326 decodes this data and forwards the decoded user data via line 328 to subscriber telecommunications equipment. As the decoder 326 decodes the data, it is able to produce an estimate of the 330 bit error rate (BER) associated with the φφφ BER φ φ φ φ BER φ φ BER Signal transmission over the wireless link 300, which may be forwarded to the multiplexer 332 for combining with other signals, such as signals from call control function 336 or user data on line 338 before being routed to the encoder

334. Here, this BER estimate 330 is coded and transmitted on the channel

OMC via wireless link 310 to decoder 340 inside the central terminal modem 320. Once decoded by the decoder 340, this signal passes to the multiplexer 345, in which the BER estimate from the subscriber terminal is detected and transmitted via line 355 to the channel list dynamic determination function 360.

Further, as in the subscriber terminal 20, the decoder 340 within the central terminal modem 320 is able to make an estimate.

350 bit error rate (BER) associated with signal transmission 15 over wireless link 310. This BER estimate 350 is also transmitted via line 355 to the channel list dynamic determination function 360. This dynamic channel list size determination function 360 is formed on the modem terminal 302 of the central terminal and receives BER estimates from each of the modems on that grid indicated by the lines entering from below the dynamic channel list size determination function 360.

In addition to BER estimates, service quality data (GOS) is obtained from two sources. First, in each subscriber terminal 25, the call control function 336 will record how easily it is possible to create traffic channels for transmitted and received data, and from this can make an estimate of the GOS to the multiplexer 332 to be encoded by the encoder 334 for subsequent transmission over wireless central terminal.

Here, this GOS estimate is decoded by the decoder 340, passed through Η ft <1 ι multiplexer 345, and then this GOS estimate is routed via line 355 to the channel list dynamic determination function 360.

Additionally, the incoming call information, other than 5 call information from the subscriber terminal 20 associated with the central terminal, is provided to the central terminal via a focused network interface 390 to the DA device 380. This DA device includes a call control function similar to the call control function 336 in each of the subscriber terminals 20, for each of the modems on the modem rack. Thus, in a similar way to call control function 336 in subscriber terminals 20, call control functions in DA device 380 are also capable of making GOS estimates for incoming calls, and these GOS estimates are passed over line 395 to dynamic channel list size 360 function 360. .

At setup, the control system 370 within the base control system will be coupled to the central terminal and provide the channel list dynamic determination function 360 within the modem rack with data identifying the desired BER, the desired GOS, and the channel list size limit (i.e., the number of channels that can be used). data traffic). The dynamic channel list size determination function 36Q then compares this data from the control system 370 with information about the current BER, the current GOS, and the current channel list size ²⁵ it receives. An appropriate algorithm can be developed to determine whether the size of the channel list is appropriate based on this information. For example, if the current bit error exceeds the requested BER provided by the control system 370, then the channel list dynamic determination function 360 may be arranged to send a request for ft ft ft ft ft ft ft ft ft ft ft · · Ftft ftft ftft ftftft «·· ftftft ft · ft * ftft. 25 determining the size of the channel list to the DA (request assignment) of the device 380.

This DA device 380 (for granting requests) supplies modem release signals via lines 400 to each of the modems on the modem terminal grid. If the dynamic channel list size determination function 360 requested the DA device 380 to perform a channel list size determination, then the DA device 38Q may deactivate one or more of the modems, causing interference and thus the current BER to be reduced. In addition to being used to reduce interference, the DA device 380 in preferred embodiments of the invention is also responsible for providing instructions to encoders 325 to set overlay codes, or to determine how many TDM slots are to be used for signals to be transmitted to subscriber terminals 20. .

Dynamic channel list size determination function 360 may store in memory 365 received BER and GOS information and periodically transmit this data to control system 370 for analysis. In addition, if the system is unable to reach the desired BER or GOS with the allocated channel list size, this dynamic channel list size determination function 360 may be arranged to issue an alarm to control system 370. Receiving this alarm signal will notify personnel using control system 370 that manual intervention may be required to resolve the situation, for example, by providing more central terminal hardware to support STs.

The CDMA approach used in the preferred embodiments of the present invention exhibits the property that removing any of the orthogonal channels (deactivating the modem) will improve the interference immunity of the other channels. Thus, a suitable approach for the request assignment device 380, upon receipt of the channel list size determination request from the dynamic channel list size determination function 360, is to deactivate the modem through which the least traffic passes.

RF (high frequency) channel switching

In preferred embodiments of the present invention, it has been found that if the subscriber terminal is allowed to operate from more than one central terminal / radio channel modem rack, the following advantages can be obtained:

(i) Error Tolerance - Should a fault occur in the modem terminal sub-system error of the central terminal, the subscriber terminal may switch to an alternative service frequency.

(ii) call barring - a service denied to the subscriber terminal from one central terminal grid can select to switch to an alternative service frequency.

(iii) traffic load balancing - the base control system can choose to move the STs between the central terminal grids based on call barring statistics.

(iv) Frequency selection - in the presence of selective channel fading (slow multiple path), the ST can operate at a frequency frequency. ** 99 99 99 channel offering the highest signal strength and the lowest number of volatile errors.

High-frequency channel switching is only possible where there are two or more co-assigned central terminal grids that serve the same geographical area on different high-frequency channels within the same high-frequency band. An extension that meets this criterion can be arranged as a 'service area'.

Possible scenarios of such an extension are illustrated in Figure 18. 18 (i) illustrates an arrangement in which omni-directional antennas are used to cover a whole cell with four frequency channels, for example F1, F4, F7, F10. Giant. 18 (ii) shows an arrangement in which sector antennas are used to cover six separate sectors within a cell, each sector being covered by two frequency channels.

Giant. 18 (iii) illustrates an alternative arrangement in which three sector antennas are used to divide a cell into three sectors, each sector being covered by a separate frequency channel, and an omnidirectional antenna is used to provide an 'umbrella' coverage for the whole cell. utilizes a frequency channel different from the three frequency channels used by sector antennas.

In order for the system to operate efficiently, the STs must be able to switch channels quickly, and fast channel switching requires the central terminal grids to be synchronized at the following levels:

(i) CDMA PN code. This maintains the uplink code phase over the high frequency channels during a warm start; and

I i

(Ii) the radio frequency carrier frequency. This completely eliminates the need for coarse frequency lookup on the downlink radio frequency switch.

During installation, each subscriber terminal will be programmed with a high frequency channel code and a PN code, which codes specify the initial home channel of the subscriber terminal.

The manner in which channel switching is facilitated in preferred embodiments of the invention will be described with reference to Figs. 19A and 19B. The service area control unit 400 is preferably designed to act as an interface between the control panel connected to the service area control unit 400 via path 405, and a plurality of central terminals 10 connected to the service area control unit 400 via paths 410. Central terminals 10 connected to the service area control unit 400 forms a 'service area' of the central terminals which can be used by the subscriber terminal 20 to process the communication.

In preferred embodiments of the invention, the service area control unit 400 is used to provide appropriate information to each central terminal 10 about other central terminals within the service area. Each central terminal may then transmit a 'service area' message, including a list of radio frequency frequencies and central terminal identifiers that make up the service area, for use by the subscriber terminals in subsequent radio frequency switching functions. The subscriber terminal then stores this information for future reference when establishing a connection with one of the central terminals. It is preferred that 9 lil 199

Each central terminal transmits a service area message because the subscriber terminal can watch any of the central terminals at the time of transmission of the message.

Each central terminal database will contain an input for each subscriber terminal located within the service area. Each database entry describes how the central terminal monitors its relationship with the ST and can be labeled as:

(i) primary service provider - the central terminal is the home channel of the ST. All control communication with the subscriber terminal takes place via its home central terminal.

(ii) the backup service provider - the central terminal shall provide the service to the subscriber terminal.

(iii) available for back-up service - the central terminal shall provide the service to the ST, if requested.

It should be understood that the subscriber terminal does not need to switch to a completely different central terminal, but may instead switch to another central terminal grid (and hence to another radio frequency channel) within the same central terminal. However, in preferred embodiments of the present invention, the ST will usually switch to a different central terminal because certain errors occurring on one central terminal grid may also affect other grids within the same central terminal, so that for error tolerance (which will be

999 »» in w> »• · · 9 9 9 9 9 9 9 9

9 # 9 9 9 9 »99 99 999

9 9 9 9 9 · 9 9 ··· 99 99 99 99 99 described in more detail below) it is preferred that the ST can be switched to a separate central terminal.

The database consistency on the grids of the central terminal is preferably supported by the service area control unit 400. The database consistency must be maintained in real time, so that the subscriber terminal entering the network is given instantly full access in the service area (the service area message is transmitted to all subscriber terminals, thus the new subscriber terminal will expect access throughout the service area).

Inbound access via redundant central terminals requires the provision of a function to transmit duplicate incoming call setup messages to all central terminals that make up the service area. Preferably, this function is provided by a service area control unit 400 that routes incoming call setup messages to each central terminal operating in the service area. All central terminals will allocate Acces_In (access incoming) traffic channels and will transmit an incoming call setup message through the call control channel (CCC). Upon successful uplink access, one central terminal will respond to the service area controller with a received call message, with the other central terminals possibly responding with call setup failure messages. Outbound access via a backup central terminal is similar to conventional outbound access.

Another operation that can be performed by the service area control unit is to assist the base control system 58 in reconfiguring the equipment in case of failure. For example, if one central terminal is taken out of service ‘I«

I 4 *

I 4 «I 4 14«

11 4 4 «

As a result of the failure, a different central terminal may be connected and the service area control unit may provide this new central terminal with information about other central terminals in the service area.

Giant. 19B illustrates those subscriber terminal elements that are used to realize radio frequency switching. The radio subsystem 420, which includes the signal processing phases during transmission and reception, will forward any received data to the call control channel (CCC) via line 425 to the message decoder 430. If the decoder 430 detects that the data on the call control channel constitutes a service area message, then this message is forwarded via line 435 to the controller

440 selects channels where information from the service area message is stored in memory 445.

Similarly, if the message decoder 430 identifies data as a 'free list' identifying available traffic channels at a particular radio frequency, then this data is passed to the call control function 336 and the channel selection controller 440 via path 450. The call control function 336 stores the free list in memory 445 for subsequent use by this call control function 336 and the channel selection controller 440.

If the message decoder 430 detects that the data constitutes an incoming call setup message, then this information is passed via line 455 to the call control function 336 and the channel selection controller 440 for further processing. The incoming call setup message will typically specify the traffic channel on the current frequency channel that should be used to access the incoming call, and the channel selection controller 440 will

3Q attempt to establish a connection on this traffic channel. In such cases, the channel selection controller 440 will instruct * 9 9 9 9 9 9 9 9 9

99 99 99

999 999

9

99 the radio subsystem 420 over line 465 to use the current frequency channel to establish the desired connection. If, on the other hand, the traffic channel specified in the call setup message is 'empty' (none), then the channel selection controller 440 has the ability to change the radio frequency using information stored in memory 445 about other central terminals in the service area.

To allow the channel selection controller 440 to receive the link state information, the link operating state signal may be transmitted via line 470 from the radio subsystem 420. This signal will provide an indication of the quality of the radio link, and may be a simple indication of ΌΚ 'or' error ', or alternatively may include special information such as BER values for the connection. This information can be used by the channel selection controller 440 to determine whether or not a particular frequency channel should be used.

To allow the call control function 336 to specify a particular access-out channel for outgoing calls, a line 460 is established between this call control function 336 and the channel selection controller 440. The call control function 336 can select an access outgoing channel from a free list in the memory 445 and can instruct the channel selection controller 440 over the line 460 to try to reserve this channel.

The following examples show how the structure described above can be used to perform channel switching in certain circumstances.

»* * · * * * * * * * * * * * * * * * * * * * * * * * * * ·· ·· ·· ··

Radio frequency switching for error tolerance

If a single RF channel suffers from a complete downlink loss, the following process proceeds in preferred embodiments 5 of the invention:

(i) the ST attempts to re-book the downlink for a certain period of time, say 20 seconds.

(ii) if the reservation fails, the subscriber terminal channel selection controller 440 will select the next available channel from the service area information in the memory 445 and attempt the downlink reservation. This process will be repeated until the downlink signal is reserved.

(iii) Once a backup high-frequency channel is assigned, the ST will 'wait' on the call control channel (CCC) and can then be granted operational access.

(iv) if the central terminal failure persists, then the base control system 58 may use the service area control unit 400 to reconfigure the service area so that the functioning grids of the central terminals become the primary service providers for the subscriber terminal list without home channels.

An error that does not result in complete loss of the downlink signal will not result in switching the RF channels as a whole. Rather, the error may be due to 9 9 9 9 9 9 9 9 9 9 99 9 9 9 999

999999 9 9 9 • · 99 99 99 99 99 result in excessive or complete call barring as discussed below.

Switching high-frequency channels for call barring

If incoming access traffic channels are blocked, then in preferred embodiments of the invention the following process is used:

(i) the call setup message sent through the call control channel will specify the traffic channel on which the call is to be accessed.

(ii) if incoming access is blocked, the central terminal will specify an empty (no) traffic channel. The subscriber terminal channel selection controller 440 will in such cases switch to the next high frequency channel from the service area information in the memory 445 and monitor the call control channel.

(iii) if the ST receives a call setup message with a valid traffic channel, then the call is processed as usual.

(iv) when the call terminates, the downlink subscriber terminal preferably switches back to the home central terminal.

When outgoing access traffic channels are blocked, in the preferred embodiments of the present invention the following process is used:

· 9 · 9 · 9 · 9 · · · «« «« · «·« «·« «« · « «« ·· * «(i) the ST is recording the login signal. The free list in memory 445 is checked and, if a traffic channel is available, call control function 336 forwards channel request to line 460 to channel selection controller 440 and attempts a normal uplink access.

(ii) if the loose list shows that there are no available on the current frequency channel

Access_Out channels, then the channel selection controller 440 will be used to switch the ST to the next RF channel in the service area, then the ST will wait for the next free list.

(iii) when the ST finds a free list with an available Access_Out channel, then uplink access is attempted and the call is processed as usual.

(iv) when the call is terminated, the downlink connection of the subscriber terminal preferably switches back to the home central terminal.

Switching of high-frequency channels for balancing the traffic load

Balancing the traffic load, in preferred embodiments of the present invention, is provided by a static configuration over the base control system 58. The call barring statistics 30 and call set-up time can be transmitted

- · · 44 44 4 4 4 4 4

4,444 4,444 4,444 4

4 4 4 4 4 4 444 444 444

444445 4 4 4

44 44 44 · 4 44 to this basic control system 58. where to decide to move the ST terminal to the RF channel.

The operator can go to another

High frequency channel switching for frequency selection

Frequency selection is, in preferred embodiments of the present invention, provided by static alignment over the base control system 58. Radio link statistics may be transmitted to the base control system 58, where the operator may decide to move the ST to another RF channel.

Although a particular embodiment of the invention has been described in the above description, it should be understood that the invention is not limited thereto and that many modifications and additions to this exemplary embodiment may be made within the scope of the invention. For example, without departing from the scope of the present invention, various combinations of features of the appended dependent claims may be made with those of the appended independent claims.

Claims (32)

PATENT CLAIMS A transmission controller for processing data items to be transmitted over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, wherein a single frequency channel is used to transmit data items corresponding to a plurality of wireless links, comprising: an orthogonal code generator for providing an orthogonal code from a set of 'm' orthogonal codes used to form 'm' orthogonal channels within one frequency channel; a first encoder for combining a data item to be transmitted on a single frequency channel with said orthogonal code from an orthogonal code generator, wherein the orthogonal code determines the orthogonal channel over which the data item is transmitted, and wherein data items belonging to different wireless links may be transmitted simultaneously in different orthogonal channels of said one frequency channel; an overlay code generator for providing an overlay code from a first set of 'n' overlay codes that are orthogonal to each other; and a second encoder arranged to apply an overlay code from the overlay code generator to said data item, wherein 'n' of the data items belonging to the different 25 wireless links may be transmitted simultaneously within the same orthogonal channel. The transmission controller of claim 1, wherein the overlay code generator is configured to 30 provision of overlay codes from one or more sets of overlays · zajištění * * * * zajištění zajištění zajištění zajištění zajištění zajištění zajištění zajištění zajištění zajištění zajištění zajištění zajištění zajištění zajištění zajištění zajištění Codes that have different numbers of overlay codes than the first set of overlay codes. 3. The transmission controller of claim 1, wherein the orthogonal code generator is a memory 5 configured to store a set of orthogonal codes. 4. The transmission controller of claim 1, wherein the overlay code generator is a memory arranged to store a set of overlay codes. The transmission controller of claim 1, wherein the orthogonal code set comprises a Rademacher-Walsh (RW) code set. 6. The gear transmission according to claim 5, wherein t _1C in that the set of overlay codes are derived from RW codes, each set of 'n' overlay codes comprising a matrix η χ n RW codes. 7. A central terminal of a wireless telecommunications system comprising: 20 a transmission controller having: an orthogonal code generator for providing an orthogonal code from a set of 'm' orthogonal codes used to form 'm' orthogonal channels within one frequency channel; 25 is a first encoder for combining a data item to be transmitted on a single frequency channel with said orthogonal code from an orthogonal code generator, wherein the orthogonal code determines the orthogonal channel over which the data item is transmitted, and wherein the data items belonging to different 30 wireless links can be transmitted simultaneously in different 9 * 9 * 9 * • 9 * 9 * 9 * 9 orthogonal channels of said one frequency channel; an overlay code generator for providing the overlay code from the first set of 'n' overlay codes that are orthogonal to each other; and a second encoder arranged to apply an overlay code from the overlay code generator to said data item, wherein n of data items belonging to different wireless links may be transmitted simultaneously within the same orthogonal channel, wherein the overlay code generator is arranged to provide overlay codes from one or more sets of overlay codes having different numbers of overlay codes than said first set of overlay codes, wherein the orthogonal code generator is memory arranged to store the set of orthogonal codes, wherein the overlay code generator is memory arranged to store the set of overlay codes, the orthogonal code set comprising the set Rademacher-Walsh (RW) codes, and wherein the set of overlay codes is derived from RW codes, wherein each set of 'n' overlay codes comprises a matrix of η χ n RW codes. 8. The central terminal of claim 7, wherein the first of the orthogonal channels is reserved for transmitting wireless link reservation signals, and the transmission controller is provided in the central terminal to allow application of the overlay codes to the data items to be determined. for transmitting within said first orthogonal channel of —i λ J CUUXXkJXX ^ 1 1 TT u. in cuci y uxi / l zA-, 4- VS ϊ Z * »1λ 1-1 U. o J. 1 ± U JX J UU i terminals. 9. The central terminal of claim 8, wherein the second orthogonal channel is reserved for transmitting call control related signals and a controller. 30 • 4 4 4 4 4 ·· 4 4 4 4 4 4 4 «44 * ♦ 4 4 4 4 4 4 4 444 4 4 4 4 4 4 4 4 44 4 4 The transmission in the central terminal is designed to allow overlay codes to be applied to data items intended to be transmitted within said second orthogonal channel from the central terminal to one of said subscriber stations. 5 terminals. 10. The central terminal of claim 7, further comprising means for assigning channels to determine which of the orthogonal channels will be overlapped and to transmit this information to a plurality of subscriber terminals within the wireless telecommunications system. 11. The central terminal of claim 7, wherein a plurality of said orthogonal channels are designated as traffic channels for transmitting data items related to the content of the communication, the central terminal further comprising: A TDM encoder configured to apply time multiplexing techniques (TDMs) to data items to be transmitted via a traffic channel from said central terminal to said subscriber terminal to allow a plurality of data items belonging to different wireless links to be transmitted within one orthogonal traffic channel during predetermined frame periods. 12. A receive controller for processing data items received over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, wherein one frequency channel is used to transmit data items corresponding to the plurality of wireless links, comprising: «· Použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých použitých 4 4 4 • 4 4 44 a 4 orthogonal code generator for providing an orthogonal code from a set of 'm' orthogonal codes to form 'm' orthogonal channels within one frequency channel; 5 shows a first decoder for applying an orthogonal code provided by an orthogonal code generator to a signal received on one frequency channel to isolate data items transmitted within a corresponding orthogonal channel; 10, an overlay code generator for providing an overlay code from a first set of 'n' overlay codes that are orthogonal to each other, the set of 'n' overlay codes allowing 'n' data items belonging to different wireless links to be transmitted simultaneously inside 15 of the same orthogonal channel; and a second decoder for applying an overlay code from the overlay code generator to the orthogonal channel data items to isolate a particular data item transmitted using the overlay code. 13. The receive controller of claim 12, wherein the overlay code generator is configured to provide overlay codes from one or more sets of overlay codes having different numbers of overlay codes than said first set of overlay codes. 14. The receive controller of claim 12, wherein the orthogonal code generator is a memory arranged to store a set of orthogonal codes. • 0 • 000 • 0 0 • 0 0 · 0 0 0 0 * 0,000 0 0 0 0 00 00 0 0 0 0 0 0 · 0 • 00 000 0 0 00 00 15. The receive controller of claim 12, wherein the overlay code generator is a memory arranged to store a set of overlay codes. 16. The reception controller of claim 12, wherein the orthogonal code set comprises a Rademacher-Walsh (RW) code set. 17. The receive controller of claim 12, wherein the set of overlay codes is derived from RW codes, wherein each set of 'n' overlay codes comprises a matrix of η χ n RW codes. 18. A central terminal of a wireless telecommunications system, comprising: a receive controller having: an orthogonal code generator for providing an orthogonal code from a set of 'm' orthogonal codes used to form 'm' orthogonal channels within one frequency channel; a first decoder for applying an orthogonal code provided by the orthogonal code generator to a signal received on one frequency channel to isolate data items transmitted within a corresponding orthogonal channel; An overlay code generator to provide an overlay code from a first set of 'n' overlay codes that are orthogonal to each other, the set of 'n' overlay codes allowing 'n' data items belonging to different wireless links to be transmitted simultaneously within the same orthogonal channel ; and a second decoder to apply the overlay code from the overlay code to the overlay code. An overlay code generator to orthogonal channel data items to isolate a particular data item transmitted using the overlay code. 19. The central terminal of claim 18, further comprising means for assigning channels to determine which of the orthogonal channels will be overlayed and to transmit this information to a plurality of subscriber terminals within the wireless telecommunications system. 20. The central terminal of claim 18, wherein the channel assignment means also determines for orthogonal channels subjected to overlay codes which set of overlay codes will be 15 applied to each orthogonal channel. 21. A wireless telecommunications system subscriber terminal comprising: a transmission controller having: orthogonal code generator for security 9 η of an orthogonal code from a set of 'm' orthogonal codes used to form 'm' orthogonal channels within one frequency channel; a first encoder for combining a data item to be transmitted on one frequency channel with said orthogonal 28,,,,, by a code from an orthogonal code generator, wherein the orthogonal code determines the orthogonal channel over which the data item is transmitted, and wherein data items belonging to different wireless links may be transmitted simultaneously in different orthogonal channels of said one frequency channel; Overlay Generator to Provide Overlay • 4 »* 4 *» 14 4 II 'ι code from the first set of' n 'overlay codes that are orthogonal to each other; and a second encoder arranged to apply the overlay code from the overlay code generator to said data item, 5 wherein 'n' data items belonging to different wireless links can be transmitted simultaneously within the same orthogonal channel, wherein the overlay code generator is arranged to provide overlay codes from one or more sets of overlay codes having different numbers 10 overlay codes than said first set of overlay codes, wherein the orthogonal code generator is a memory arranged to store the set of orthogonal codes, the set of orthogonal codes comprising a set of Rademacher-Walsh (RW) codes, and wherein the set of overlay codes is derived from RW codes; each set 15 'n' overlay codes include a matrix of η χ n RW codes; wherein the transmission controller allows the application of the overlay codes to the data items transmitted from the subscriber terminals to the central terminal. 22. A wireless telecommunications system subscriber terminal comprising: a receive controller having: an orthogonal code generator for providing an orthogonal code from a set of 'm' orthogonal codes used to form 'm' orthogonal channels within one frequency channel; a first decoder for applying an orthogonal code provided by the orthogonal code generator to a signal received on one frequency channel to isolate data items transmitted within a corresponding orthogonal channel; Ftft overlay code generator to provide an overlay code from the first set of 'n' overlays that are orthogonal to each other, this set of 'n' overlays allowing 'n' data items belonging to different 5 wireless links to be transmitted simultaneously within the same orthogonal channel; and a second decoder for applying an overlay code from the overlay code generator to the orthogonal channel data items to isolate a particular data item transmitted using 10 of the overlay code, wherein the overlay code generator is configured to provide overlay codes from one or more sets of overlay codes having different numbers of overlay codes than said first set of overlay codes, wherein the orthogonal code generator is a memory arranged to store 15 of the set of orthogonal codes, wherein the overlay code generator is a memory arranged to store a set of overlay codes, the set of orthogonal codes comprising a set of Rademacher-Walsh (RW) codes, and wherein the set of overlay codes is derived from RW codes, of codes 20 includes a matrix of η x n RW codes. 23. A wireless telecommunications system comprising a central terminal and a plurality of subscriber terminals, wherein the central terminal comprises: a transmission controller having: an orthogonal code generator for providing an orthogonal code from a set of 'm' orthogonal codes used to form 'm' orthogonal channels within one frequency channel; the first encoder for combining a data item, designed for a data item designed for a data item. Transmission on one frequency channel with said orthogonal code from an orthogonal code generator, wherein the orthogonal code determines the orthogonal channel over which the data item is transmitted, and wherein data items belonging to different wireless links may be transmitted simultaneously in different orthogonal channels said one frequency channel; an overlay code generator for providing the overlay code from the first set of 'n' overlay codes that are orthogonal to each other; and a second encoder arranged to apply an overlay code from the overlay code generator to said data item, wherein 'n' of data items belonging to different wireless links may be transmitted simultaneously within the same orthogonal channel; and at least one of the subscriber terminals comprises: a reception controller having: an orthogonal code generator for providing an orthogonal code from a set of 'm' orthogonal codes used to form 'm' orthogonal channels within one frequency channel; a first decoder for applying an orthogonal code provided by the orthogonal code generator to a signal received on one frequency channel to isolate data items transmitted within a corresponding orthogonal channel; An overlay code generator to provide an overlay code from a first set of 'n' overlay codes that are orthogonal to each other, the set of 'n' overlay codes allowing 'n' data items belonging to different wireless links to be transmitted simultaneously inside ·· ♦ . 30 r. f. r t.l f.i of the same orthogonal channel; and a second decoder for applying an overlay code from the overlay code generator to the orthogonal channel data items to isolate a particular data item transmitted using the overlay code. 24. A wireless telecommunications system comprising a central terminal and a plurality of subscriber terminals, wherein at least one of the subscriber terminals comprises: a transmission controller having: an orthogonal code generator for providing an orthogonal code from a set of 'm' orthogonal codes used to form 'm' orthogonal channels within one frequency channel; a first encoder for combining a data item to be transmitted on a single frequency channel with said orthogonal code from an orthogonal code generator, wherein the orthogonal code determines the orthogonal channel over which the data item is transmitted, and wherein data items belonging to different wireless links may be transmitted simultaneously in different orthogonal channels of said one frequency channel; an overlay code generator for providing the overlay code from the first set of 'n' overlay codes that are orthogonal to each other; and a second encoder arranged to apply the overlay code of The CACii ^ ldbčč u uččč u u CA CA CA CA CA CA CA CA CA CA CAkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk.... .K.. na u υ cu n n u u and k-M v u ycrur; wherein 'n' of data items belonging to different wireless links can be transmitted simultaneously within the same orthogonal channel; and the central terminal includes: • 9 9 ♦ * · 9 99 9999 * 99 99 99 99 99 99 income controller having: orthogonal code generator to provide an orthogonal code from a set of 'm' orthogonal codes used to create 'm' orthogonal channels within one 5 of the frequency channel; a first decoder for applying an orthogonal code provided by an orthogonal code generator to a signal received on a single frequency channel to isolate data items transmitted within a corresponding 10 orthogonal channel; an overlay code generator to provide an overlay code from a first set of 'n' overlay codes that are orthogonal to each other, the set of 'n' overlay codes allowing 'n' data items belonging to different 15 wireless links to be transmitted simultaneously within the same orthogonal channel; and a second decoder for applying an overlay code from the overlay code generator to the orthogonal channel data items to isolate a particular data item transmitted using 20 of this overlay code. 25. A method of processing data items intended for transmission over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, wherein a single frequency channel is used to transmit data items corresponding to a plurality of wireless 25 links, comprising the steps of: provision of orthogonal code from set 'm ^? orthogonal codes used to form 'm' orthogonal channels within one frequency channel; combining a data item to be transmitted on one · 9 ·· 99> 9 9999 • 9 9 9 ·> 9 999 · 999 999 9 9 9 · «· · A frequency channel, with said orthogonal code, wherein the orthogonal code determines the orthogonal channel over which the data item is transmitted, and wherein the data items belonging to the different wireless links can be transmitted 5 simultaneously in different orthogonal channels of said one frequency channel; providing an overlay code from a first set of 'n' overlay codes that are orthogonal to each other; and applying an overlay code to said data item, wherein n 'data items belonging to different wireless links can be transmitted simultaneously within the same orthogonal channel. 26. The method of claim 25, further comprising the step of: 15, providing one or more sets of overlay codes having different numbers of overlay codes than said first set of overlay codes. 27. The method of claim 25, further comprising the steps of: determining which of the orthogonal channels will be overlaid; and transmitting this information to a plurality of subscriber terminals in the wireless telecommunications system. o 5 28. The method of claim 27, further comprising the step of: determining for orthogonal channels subjected to overlay codes, which set of overlay codes will be applied to each orthogonal channel. Flflflfl flflflfl flflflfl flflfl flflfl flflflfl flfl flfl flfl flfl A method of processing data items received over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, wherein for transmitting data items corresponding to a plurality of wireless 5 connections are provided with one frequency channel, comprising the steps of: providing an orthogonal code from a set of 'm' orthogonal codes used to create 'm' orthogonal channels within one frequency channel; 10 applying an orthogonal code to a signal received on one frequency channel to isolate data items transmitted within a corresponding orthogonal channel; providing an overlay code from a first set of 'n' overlay codes that are orthogonal to each other, 15 the set of 'n' overlay codes allows 'n' data items belonging to different wireless links to be transmitted simultaneously within the same orthogonal channel; and applying the overlay code to the orthogonal channel data items to isolate the particular data item 20 transmitted using this overlay code. 30. The method of claim 29, further comprising the step of: providing one or more sets of overlay codes having different numbers of overlay codes than said first set of overlay codes. 31. The method of claim 29, further comprising the steps of: determining which of the orthogonal channels will be subjected 30 overlay codes; a • φ φ · • • φ φ φ φ φ φ φ φ φ φ φ φ φ φ Přenosu · φφ transmission of this information to a plurality of subscriber terminals in a wireless telecommunications system. 32. The method of claim 31, further comprising the step of: determining for orthogonal channels subjected to overlay codes, which set of overlay codes will be applied to each orthogonal channel.