MXPA00010711A - Cellular radiotelephone systems and methods that broadcast a common control channel over multiple radio frequencies - Google Patents

Abstract

Cellular radiotelephone systems and methods communicate with cellular radiotelephones via multiple base stations. Radiotelephone traffic channels are used by the base stations for radiotelephone communications with the telephones. A common control channel is transmitted by the base stations, to control radiotelephone communications with the radiotelephones over the radiotelephone traffic channels. The common control channel is transmitted by a first one of the base stations over a first radio frequency and is transmitted by a second one of the base stations over a second radio frequency that is different from the first radio frequency. By providing a common control channel, excess control channel capacity can be reduced, thereby conserving control channel radio spectrum. Moreover, by transmitting the common control channel using multiple radio frequencies, the radio frequencies can be selected to reduce and preferably eliminate interference.

Description

"CELLULAR RADIOTELEPHONE SYSTEMS AND METHODS SPREADING A COMMON CONTROL CHANNEL THROUGH RADIO FREQUENCY MULTIPLE " FIELD OF THE INVENTION This invention relates to systems and methods of communications, and in particular to systems and methods of radiotelephone communications.

BACKGROUND OF THE INVENTION Cellular radiotelephone systems are commonly employed to provide voice and data communications to a plurality of subscribers. For example, analog cellular radiotelephone systems, such as those designated AMPS, ETACS, NMT-450, and NMT-900, have been successfully deployed throughout the world. More recently, digital cellular radiotelephone systems such as those designated IS-54B in North America and the pan-European GSM system have been introduced. These systems, and others, are described, for example, in the book called Cellular Radio Systems by Balston et al., Published by Artech House, Nor ood, MA., 1993.

Figure 1 illustrates a conventional terrestrial cell phone communication system 100. The cellular radiotelephone communication system 100 includes one or more radiotelephones 102 communicating with a plurality of cells 104, each of which is served by this station. base (BS) 106a-106n. The base stations 106a-106n communicate with a mobile telephone switching office (MTSO) 108. Although shown in Figure 1, only six cells, a typical cellular network may comprise hundreds of cells, may include more than one MTSO and can service thousands of radiotelephones. The cells 104 generally serve as nodes in the communication system 100 from which links are established between the radiotelephones 102 and the MTSO 108 through the base stations 106a-106n that service the cells 104. Each cell will be assigned to the same one or more dedicated control channels HO-11On, and one or more traffic channels 112a-112n. The radiotelephone traffic channels are used by the base stations for radiotelephone communications (such as voice and / or data communications) with the radiotelephones. The control channels are used by the base stations to control the radiotelephone communications with the radiotelephones through the radiotelephone traffic channels. In this way, for example, the control channel can be used to broadcast system information to the radiotelephones and also to send and receive access messages to and from the individual radiotelephones. The base stations 106a-lQ6n are connected to the MTSO by a plurality of bidirectional links 114a-114n, which may be wired or wireless links. Through the cellular network 100, a duplex radio communication link can be made between the two radiotelephones 102 or between a radiotelephone 102 and a user of the landline phone. The base stations 106a-106n handle radio communication between the radiotelephones in the associated cell 104 and the MTSO 108. In this capacity, the base stations 106a-106n function primarily as a relay station for data and voice signals. . As shown in Figure 1, the dedicated control channels HOa-llOn are generally broadcast using a different radio frequency F] _- Fn per cell. The traffic channels 112a-112n are allocated among a plurality of radio frequencies to reduce and preferably eliminate the interference using conventional frequency assignment techniques that are well known to those skilled in the art. As also shown in Figure 1, several cells can be combined into larger groups 120, called radiolocation areas in the IS-136 cellular radiotelephone normal or GSM location areas. The grouped radiolocation areas can reduce the radiolocation and registration charges in the system. Radiolocations to radiotelephones can only be transmitted to the radiolocation area 120 where the radiotelephone is placed. Registration only needs to be made when a radiotelephone moves between the radiolocation areas. Unfortunately, a cellular radiotelephone system 100 as described in Figure 1 may have excess control channel capacity in each cell. More specifically, each control channel may have the capacity to control many more radiotelephones than those generally found within the cell. Correspondingly, a valuable radio spectrum can be wasted. This wasted control channel radio aspect can be reduced by distributing a common control channel through many base stations, forming a larger logical cell including many smaller cells around each base station. The common control channel is multicast on the same frequency at each base station. Correspondingly, as shown in Figure 2, the cellular radiotelephone system 2Q0 includes the radiotelephones 1Q2, the cells 104, the MTSO 108, the traffic channels 112a-112n and the links 114a-114n, as already described in connection with with Figure 1, however, in contrast to Figure 1, each base station 206a-206n diffuses the same control channel 210 on the same frequency F? _. In this way, a common control channel is transmitted by the base stations to control the radiotelephone communications with the radiotelephones through the radiotelephone traffic channels. By using a common control channel at a common frequency Fi, excess capacity in the control channel can be reduced. U.S. Patent Number 5,535.15 issued to Hieatt, III, discloses a method and apparatus in a radiocommunication system that provides mouldable control channels simultaneously for a coverage area, and message channels transmitted in coverage areas within the area of coverage on a time division multiplex base. A first modulation technique generates each of the message channels at a first average output power essentially less than the maximum output power of a transmitter. A second modulation technique generates each of the control channels a second average output power approximately equal to the maximum output power of the transmitter, thereby increasing the coverage distance usable from the transmitter for the control channel compared to the message channel. The control channels are assigned to the coverage areas in a stepped geographical pattern in such a way that the reception of the control channels is maintained essentially through the coverage area. Unfortunately, it may be difficult to find a frequency F? _ That can be used by the common control channel of all base stations without interference. Interference can occur in conventional cellular radiotelephone systems, as described in relation to Figures 1 and 2. In addition, interference can be exacerbated in Wireless Office Systems (WOS) that are installed in a building to provide cellular radiotelephone communication between the cellular radiotelephones that are placed in the building. When a wireless office system is installed in a building, there may be excess capacity in the control channel. For example, a wireless office system can be designated for installation in offices with up to 450 users. However, the control channel can have a capacity of up to 1000 users. In this way, a common control channel can be preferred to reduce excess capacity. However, it can be difficult to identify a radio frequency that can be used by all WOS base stations to transmit the common control channel.

COMPENDIUM OF THE INVENTION It is therefore an object of the present invention to provide improved cellular radiotelephone systems and methods. Another object of the present invention is to provide cellular radiotelephone systems and methods that can reduce the excessive capacity in the control channel that is transmitted by the base stations. Still another object of the present invention to provide systems and methods that can reduce cellular radiotelephone overcapacity control channel without incurring excessive interference channel control. These and other objects are provided, in accordance with the present invention, by transmitting a common control channel in a cellular radiotelephone system from a first of the base stations through a first radiofrequency and from a second of the base stations to through a second radiofrequency that is different from the first radiofrequency. Providing a common control channel, it can reduce channel capacity excessive control and preferably can be removed, thus conserving radio spectrum control channel. In addition, by transmitting the common control channel using multiple radio frequencies, the radio frequencies can be selected to reduce and preferably eliminate the interference. More specifically, the systems and methods of cellular radiotelephone according to the invention communicate with a plurality of cellular radiotelephones over a plurality of base stations. A plurality of radiotelephone traffic channels are used by the base stations for radiotelephone communications with the radiotelephones. A common control channel is transmitted by the base stations to control the radiotelephone communications to the radiotelephones over the radiotelephone traffic channels. According to the invention, the common control channel is transmitted by a first of the base stations through a first radio frequency and is transmitted by a second of the base stations through a second radio frequency which is different from the first one. radiofrequency The cellular radiotelephone system preferably also comprises a manipulator central control channel (CCH) transmitting synchronously the common control channel to the plurality of base stations. In a preferred embodiment of the present invention, the plurality of base stations are the base stations of Wireless Office Systems (OS) that are placed in a building to provide cellular radiotelephone communication between cellular radiotelephones that are placed in the building . The common control channel is transmitted by the base stations in the building to control the radiotelephone communications with the radiotelephones in the building through the traffic channels of the radiotelephone. The common control channel is transmitted through the first of the base stations in the building through a first radiofrequency that is transmitted by a second of the base stations in the building through a radio frequency security that is different from the first radiofrequency A first group of base stations can transmit the common control channel through the first frequency, and a second group of base stations can transmit the common control channel through the second frequency. In a wireless office system as described above, the first group of base stations can be placed in a first portion of a building, and the second group of base stations can be placed in a second portion of the building. Correspondingly, a radio frequency for groups of base stations in a building can be selected to reduce and preferably eliminate interference with the cellular system to the exterior of the building, while at the same time a common control channel is broadcast through all of them. These base stations, to reduce the excess capacity of control channel. A cellular radiotelephone system according to the present invention can be initiated to allow simultaneous reduction of excess control channel capacity and reduction of interference with external cellular control channels. In particular, a determination is made first whether the common control channel can be transmitted from all base stations through a first radio frequency without interference. If the common control can not be transmitted from all the base stations through the first radio frequency without interference, then at least one of the base stations can not transmit the common control channel through the first radio frequency without interference, it is identified of course.

A second radio frequency that is different from the first radio frequency is assigned for transmission by at least one of the base stations identified in this way. Once started, the common control channel is transmitted from all base stations except for at least one of the base stations identified in this way through a first radio frequency. The common control channel from at least one of the base stations identified in this way is transmitted through a second radio frequency which is different from the first radio frequency. The steps of determining, identifying and assigning can be carried out repeatedly for the second radiofrequency and the successive radio frequencies until all the stations can transmit the common control signal without interference. The initialization according to the invention can be particularly useful in an in-office office system where the base stations are placed in a building and may be subject to interference from other wireless office systems in the building, or from a system of cellular radiotelephone outside the building. This interference can be difficult to predict in advance. Therefore, excess capacity of the control channel can be reduced without the need for interference sanctions.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a functional diagram of a conventional cell phone communication system. Figure 2 is a functional diagram of a conventional cellular radiotelephone system using a common control channel. Figure 3 is a functional diagram of the first embodiments of the cellular radiotelephone communication systems and methods in accordance with the present invention. Figure 4 is a functional diagram of the second modalities of the cellular radiotelephone communication systems and methods in accordance with the present invention. Figure 5 illustrates the initialization of cellular radiotelephone systems in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The present invention will now be described more fully below with reference to the accompanying drawings, in which the preferred embodiments of the invention are shown. This invention, however, may be encompassed in many different forms and should not be construed as limited to the embodiments set forth herein; instead, these embodiments are provided so that this disclosure is complete and complete, and fully transmits the scope of the invention to those skilled in the art. Equal numbers refer to the same elements through it. Referring now to Figure 3, the cellular radiotelephone systems and methods in accordance with the present invention will now be described. As shown in Figure 3, a cellular radiotelephone system 300 includes a plurality of radiotelephones 302 in a plurality of cells 304. A plurality of base stations 306a-306n use a plurality of radiotelephone traffic channels 312a-312n for communications of radiotelephone with the radiotelephones 302. As shown also in Figure 3, a common control channel is transmitted synchronously from a control channel handler in the MTSO 308 to the base stations by the base stations to the radiotelephones to control the radiotelephone communications, with the radiotelephones through the radiotelephone traffic channels. The common control channel is transmitted by a first of the base stations through a first radio frequency and is transmitted by a second of the base stations through a second radio frequency which is different from the first radio frequency. More specifically, as shown in Figure 3, the base stations 306a, 306b and 306e broadcast the common control channel 310a through a first radio frequency F] _. The remaining base stations 306b, 306c and 306n broadcast the common control channel 310b through a second radio frequency F. Correspondingly, even though all the base stations 306a-3Q6n broadcast the same common control channel, the base stations are grouped into a first group of base stations (306a, 306d and 306e in Figure 3) that transmit the channel of common control through a first radiofrequency Fi, and a second group of base stations (306b, 306c and 306n) that transmit the common control signal using a second radiofrequency F2- Since the common control channel is broadcast by all stations 306a-306n, instead of having a separate control channel for each base station 306a-306n, the excess channel capacity of the channel can be reduced and preferably eliminated. control. However, since two radio frequencies F? _ And F are used to transmit the common control channel, the interference can be reduced by appropriately allocating the frequencies to the appropriate base station. In this way, even when interference can be created with other cellular systems if all base stations are assigned to the Fi frequency or if all the base stations are assigned to the F2 frequency for their common control channel, it can be reduced and preference is to eliminate interference by dividing the common control channel into two or more radio frequencies. The cellular radiotelephone system 300 is preferably a microcell or picocell system. In these systems, the distance between the base stations using the same frequency to diffuse the common control channel may be short. Correspondingly, the difference in propagation delay can be maintained at less than the minimum propagation delay compensation capability of the mobile radiotelephone, for example, by using multipath compensation. When larger distances are involved, other compensation projects may be used.

Referring now to Figure 4, a second embodiment of cellular radiotelephone systems and methods according to the invention will now be described. More specifically, Figure 4 illustrates cellular radiotelephone systems and methods that are adapted for use in a building in a Wireless Office System (WOS), which is also referred to as the Digital Wireless Office System (DWOS). In a WOS, a plurality of cellular base stations are installed, which are referred to herein as "radio heads" (RH) 406a-406n on a floor 450 of a building to provide a plurality of cells 404. Although Figure 4 illustrates a floor view of a single floor 450 in a building, it will be understood that the WOS may extend across multiple floors or through only part of a floor of a building. On a floor 450, a plurality of radio heads 406a-406n are connected to a Cellular Radio Interchange (CRE) 408, which provides the functions of a Mobile Phone Switching Office (MTSO) and which may also provide other functions. Even though the CRE 408 is indicated as being on the same floor 450, it can be installed remotely. The CRE 408 may include a central control channel handler. The CRE 408 is linked to the radius heads 406a-406n by a plurality of radiofrequency links or wire 414a-414n. A plurality of radiotelephones 402 is also placed on the floor 450 and communicates with the radio heads 406a-406n using a plurality of radiotelephone traffic channels 412a-412n. Still referring to Figure 4, the building in which the cellular radiotelephone system 400 is installed can be subjected to interference by a cellular radiotelephone system that is outside the building. More specifically, as shown in Figure 4, a cell 420 from an external cellular radiotelephone system may include a control channel in the radio frequency F] _ and a cell 430 from an external cellular radio telephone system may include a channel radio frequency control F2 - In accordance with the invention, the common control channel is transmitted in more than one radio frequency to reduce and preferably eliminate interference, in this way, the common control channel is transmitted synchronously by all the radio heads 406a-406n.However, the common control channel 410a from the base stations 406a-406c use radio frequency F? _, so that the walls of the building between the cell 420 and the radio heads 406a-406c and / or the distance from cell 420 can attenuate the radiofrequency Fj_ sufficiently to reduce or preferably eliminate interference with these radio heads. Similarly, the radio heads 406d-406n transmit the control channel 401b using the radiofrequency F2, so that interference with the cell 430 can be reduced and preferably minimized due to attenuation by distance and / or the walls of the building. Correspondingly, a common control channel is used by all the radio heads, in order to reduce the excess capacity in the control channels. At least two radio frequencies are used to spread the common control channel in order to thereby reduce and preferably minimize the interference. More specifically, in a WOS of up to 450 users, one control channel can be sufficient for the entire WOS. The common control channel is broadcast by the radio heads to provide coverage in all the system. The intelligence of the control channel may be located in the CRE 408. The downlink information of the control channel from the base stations to the mobile radiotelephones 402 is multicast from the CRE 408 through all the base stations 406a-406n, through the common control channel. In this way, all radiotelephones within the building can decode all the information in the downlink. The uplink information of the control channel from the radiotelephones is detected by the radio heads 406a-406n. The information is transferred to the baseband and sent to the CRE 408. It will be understood that the radio head closest to the mobile radiotelephone will usually receive the strongest radio signal, while the more distant radio heads may receive a signal weaker or not receive a radio signal from the mobile radiotelephone. Since the intelligent part of the preference control channel is placed in the CRE, the uplink information can be sent from all the radio heads to the CRE. The CRE then uses a diversity detector to select the radio head with the best signal received from the mobile radiotelephone. In this way, the WOS can communicate with the mobile stations in the digital control channel without having to be aware of which radio head is closest to the mobile radiotelephone. The result of the diversity detector can also be stored and used by the WOS to select which radio head to assign to a mobile radiotelephone, if the traffic channel is to be installed. Since the WOS uses the same frequency band as the outer cellular system, it can be difficult for the WOS to find unused frequencies and assign the best frequency to the control channel. This can be especially difficult in very tall buildings with the site line to many outside base stations and the interference of other wireless office systems in a building that rises very high. According to the invention, the different control frequencies can be assigned to the different sides of the floor. In other words, some of the radio heads can be returned to another frequency. This return does not need to change the architecture of the WOS except in regard to the frequency tuning of at least one of the radio heads. The frequency tuning can be carried out manually or by sending a tuning message to the appropriate radio head (s). The CRE can still use the same multicast project in the downlink and the same diversity detector in the uplink. Correspondingly, all the data of the control channel in the downlink and uplink directions can be the same. In addition, the radiotelephones themselves do not need to be modified. In order to establish the small portions of the Digital Coded Channel Control Channel (CDL) Locator appropriately in the digital traffic channels, small portions of CDL bits can be stored by each radio head to reflect the correct control channel frequency for that radio head. Referring to Figure 5, operations to initialize a cellular radiotelephone system in accordance with the present invention will now be described. As shown in Block 510, a determination is made as to whether the common control channel can be transmitted from all base stations through a first radio frequency without interference. If this is the case, when the configuration of Figure 2 can be used where a common control channel is transmitted by all base stations using a single radio frequency. The common control channel is transmitted in Block 516. Alternatively, if all base stations can not transmit the common control channel using a single radio frequency in Block 510, then in Block 512 base stations that can not transmit in a single radiofrequency without interference, they are identified of course. A second radio frequency is assigned to the base stations identified in Block 514. Then, in Block 516, each of the base stations transmits the common control channel using the assigned frequency.

It will be understood by those skilled in the art that the operations of Block 510 can be carried out repeatedly using all available radiofrequencies in order to determine whether any single radio frequency can be used by all base stations to transmit the common control channel. In addition, it will be understood that the operations of Block 510, 512 and 514 can be carried out repeatedly if two radio frequencies can not be used by all the base stations to transmit the common control channel. In this way, three or more radio frequencies can be used in order to allow the common control channel to be transmitted through all the base stations without interference. Correspondingly, a common control channel can be used by the multiple base stations, in order to thereby reduce and preferably eliminate excess control channel capacity. Two or more radio frequencies can be used to synchronously transmit the common control channel and thereby reduce and preferably eliminate the interference. In this manner, efficient high-performance cellular radiotelephone systems and methods can be provided. In the drawings and in the specification, typical preferred embodiments of the invention have been disclosed and, even when specific terms are employed, they are used in a generic and descriptive sense not for limitation purposes, the scope of the invention having been noted. in the following claims.

Claims (15)

CLAIMS:

1. A cellular radiotelephone system (300) communicating with a plurality of cellular radiotelephones (302), comprises: a plurality of base stations (306); a plurality of radiotelephone traffic channels (312) that are used by the base stations for radiotelephone communications with the radiotelephones; and a common control channel (310) which is transmitted by the base stations to the control radiotelephone communications with the radiotelephones through the radiotelephone traffic channels, characterized by: the common control channel being transmitted by the first of the base stations (306a) through a first radiofrequency (F] _), and being transmitted by a second of the base stations through a second radio frequency (F2), which is different from the first radio frequency.

2. A cellular radiotelephone system according to claim 1, further comprising a central control channel handler (308) that synchronously transmits the common control channel to the plurality of base stations.

3. A cellular radiotelephone system according to claim 1 wherein the plurality of base stations are base stations of the Wireless Office System (WOS) (406) that are placed in a building (450) to provide cellular radiotelephone communication between the cellular radiotelephones (402) that are placed in the building; wherein the common control channel (410) is transmitted by the base stations in the building to control the radiotelephone communications with the radiotelephones in the building through the radiotelephone traffic channels (412); and wherein the common control channel is transmitted by the first of one of the base stations (406a) in the building through the first radio frequency (F_), and is transmitted by the second of the base stations (406d) in the building through a second radio frequency (F2) that is different from the first radiofrequency.

A cellular radiotelephone system according to claim 1: wherein the common control channel is transmitted by a first group of the base stations (306a, 306d, 306e) through the first radio frequency; and wherein the common control channel is transmitted by a second group of the base stations (306b, 306c, 306n) through the second radio frequency.

A cellular radiotelephone system according to claim 4, wherein the first group of base stations is placed in a first portion of a building and wherein the second group of base stations is placed in a second portion of a building.

6. A method for controlling a cellular radiotelephone system (300) including a plurality of radiotelephone traffic channels (312) that are used by a plurality of base stations (306) for radiotelephone communications with a plurality of radiotelephones ( 302), using a common control channel (310) that is transmitted by the base stations to the control radiotelephone communications with the radiotelephones through the radiotelephone traffic channels, the method is characterized by: transmitting the channel of common control (312a) from the first of the base stations (306a) through a first radio frequency (Ft_); and transmitting the common control channel (312b) from a second of the base stations (306b) through a second radio frequency (F2) that is different from the first radio frequency.

7. A method according to claim 6, further comprising the step of synchronously transmitting the common control channel to the plurality of base stations.

8. A method according to claim 6: wherein the plurality of base stations are base stations (406) of the Wireless Office System (WOS) that are placed in a building (450) to provide cellular radiotelephone communication between the cellular radiotelephones (402) that are placed in the building, and where the common control channel (410) is transmitted by the base stations in the building to control the radiotelephone communications with the radiotelephones in the building through the radiotelephone traffic channels (412); wherein the step of transmitting the common control channel from a first of the base stations through the first radio frequency comprises the step of transmitting the common control channel (410a) from the first of the base stations (406a) to the building through first radiofrequency (F) _); and wherein the step of transmitting the common control channel from a second of the base stations through a second radio frequency comprises the step of transmitting the common control channel (410d) from the second of the base stations (406d) in the building through the second radiofrequency (F2) that is different from the first radiofrequency.

9. A method according to claim 6, wherein the step of transmitting the common control channel from a first of the base stations through a first radio frequency comprises the step of transmitting the common control channel from a first group. of base stations (306a, 306d, 306e) through the first radio frequency; and wherein the step of transmitting the common control channel from a second of the base stations comprises the step of transmitting the common control channel from the second group of base stations (306b, 306c, 306n) through the second one. frequency.

A method according to claim 9, wherein the first group of base stations is placed in a first portion of a building and wherein the second group of base stations is placed in a second portion of a building.

11. A method according to claim 6, wherein the transmission steps are preceded by the steps of: determining (510) whether the common control channel can be transmitted from the plurality of base stations through the first radio frequency without interference; if the common control channel can not be transmitted from the plurality of base stations through the first radio frequency without interference, identify (512) at least one of the base stations that can not transmit the common control channel through the first radiofrequency without interference; and assigning (514) the second radio frequency that is different from the first radio frequency for transmission of the common control channel by at least one of the base stations identified in this manner.

A method according to claim 11: wherein the step of transmitting the common control channel from the first of the base stations comprises the step of transmitting (516) the common control channel from the plurality of base stations except at least one of the base stations identified in this way through the first radio frequency; and wherein the step of transmitting the common control channel from a second of the base stations comprises the step of transmitting (516) the common control channel from at least one of the base stations identified in this way through the second radiofrequency that is different from the first radiofrequency.

A method according to claim 11, wherein the steps of determining, identifying and assigning are carried out repeatedly for the second radiofrequency and the successive radio frequencies until all the base stations can transmit the common control signal without interference .

14. A method according to claim 11, further comprising the step of synchronously transmitting the common control channel to the plurality of base stations.

15. A method according to claim 12: wherein the plurality of base stations are the base stations of the Wireless Office System (WOS) that are placed in a building to provide cellular radiotelephone communication between cellular radio telephones that are placed in the building, and wherein the common control channel is transmitted by the base stations in the building to control the radiotelephone communications with the radiotelephones in the building through the radiotelephone traffic channels; wherein the step of transmitting the common control channel from the plurality of base stations except at least one of the base stations identified in this way through the first radio frequency comprises the step of transmitting the common control channel from the plurality of base stations in the building through the first radio frequency except at least one of the base stations identified in this way; and wherein the step of transmitting the common control channel from at least one of the base stations identified in this way through the second radio frequency which is different from the first radio frequency, comprises the step of transmitting the common control channel from at least one of the base stations identified in this way in the building through the second radio frequency which is different from the first radio frequency.