A SYSTEM AND METHOD OF POINT-TO-MULTIPOINT WIRELESS COMMUNICATION USING A POINT-TO-POINT COMMUNICATION
STRUCTURE
FIELD OF THE INVENTION
The present invention relates to the asynchronous transfer mode (ATM) technology, and more particularly a ATM transmission method and structure for performing point-to-multipoint wireless communication.
DESCRIPTION OF RELATED ART
Asynchronous transfer mode is a method of information transmission in which data (e.g. voice, video, data, or any other information) is fragmented into fixed sized data bits (referred to as cells) and transmitted over a communication network. The ATM cells are typically a set data size (e.g. 53 bytes). In general, the cell is divided into two parts the header and the payload. The header contains control, routing, and other information to implement the transmission. The payload contains the information being transmitted.
One type of physical transmission structure for performing a point-to-point ATM communication includes a base station for controlling the transmission transactions and one or more switching networks to route the ATM signals between the base station and each end user. In this type of system, the local switching network (i.e. last network prior to the end user) includes line cards that perform various user specific functions such as provide busy and dial tones to the user, call waiting features, etc. Each line card is hardwired to a single end user.
A transmission in this type of structure is accomplished by establishing a line of communication between the end user and the base station. For this purpose, the end user has an associated call reference ID number. When a communication occurs that is initiated by the end user, the end user identifies itself with its call
reference ID number and is assigned a dedicated line card. During the communication, only that end user may pass calls through that line card. Due to this type of prior art structure in which each end user is communicating with a single line card, more than one end user can identify itself with the same reference ID number. This is made possible by the system keeping track of which reference ID number came from which line card port for each communication.
Thus far, the above ATM structure has not been considered a viable system for an ATM point-to-mutltipoint wireless transmission (i.e. a single line card used to transmit to multiple wireless users) due to confusions that can arise when multiple end users that are communicating with a single ATM switch port identify themselves with a common call reference ID. In this case, what can occur is that end users having a common reference identification number may either receive transmissions or control signals which, among other problems, can result in erroneous terminations of the calls meant for another end user.
SUMMARY OF THE INVENTION
The present invention generally speaking is a system and method for performing point-to-multipoint wireless communications over a point-to-point communication structure including a transparent wireless interface between multiple end users and a local ATM switch. In one embodiment, the communication structure of the present invention includes a main control station, an ATM switch, multiple wireless end user units, and the wireless transparent interface coupled between a single hardwire port of the ATM switch and the multiple wireless end user units. The control station provides the overall control of all transmissions and receptions of various types of communication signals in the communication system and is adapted for the transmission and reception of ATM signals. The ATM switch functions to route portions of ATM signals received from the main control station through the dedicated hardware I/O ports depending on each port's associated port designator.
In one embodiment, the I/O port is a line card in an ATM switch. The transparent interface in accordance with the present invention, translates control signal channel designators and reference ID designators of ATM signals being transmitted between the multiple wireless end users and the single port of an ATM switch such that the ATM switch perceives that it is communicating with a single end user unit and such that each end user perceives that it is communicating directly with the single port of the ATM switch wherein no calling conflicts arise due to multiple end users communicating with a single ATM port.
The wireless interface in one embodiment includes a first translation portion for translating ATM signals received from the main control station by translating the common network control channel designator to a user-specific control channel designator and by translating an interface assigned reference ID designator to a user-assigned reference ID designator and a second translation port for translating ATM signals from the end users by translating user-assigned reference ID designators to interface assigned reference identification designators. The wireless interface further includes at each end user unit a means of only accepting ATM signals having the user-assigned reference identification designators and the end user-specific control channel designator. This ensures that a given end user receives only ATM control signals intended for its reception. The wireless interface further includes a third translation unit at each of the end user units for translating ATM signals having user-specific control channel designators to the common network control channel designator and providing them to the end user.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A shows a prior art transmission structure used for point-to-point
ATM communications.
Figure IB shows a typical ATM cell.
Figure 2 shows one embodiment of a transmission structure for performing point-to-multipoint wireless communications including a transparent wireless
interface.
Figure 3A shows the steps performed by the transparent wireless interface of the present invention for transmitting an ATM signal from a single port connection of the ATM switch to multiple end users. Figure 3B shows the steps performed by the transparent wireless interface of the present invention for transmitting an ATM signal from each of the multiple end users to the single port connection of the ATM switch.
Figure 4A shows a block diagram of one embodiment of the base station portion of the wireless interface. Figure 4B shows a block diagram of one embodiment of the end user station portion of the wireless interface.
Figure 5A shows the steps performed when an external user on the communication network according to the present invention initiates a call with one of the multiple end users. Figure 5B shows the steps performed when one of the end users initiates a call with an external user on the communication network according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 A shows a prior art point-to-point communication structure which is used for transmitting ATM signals and other types of communication signals to end users. An ATM signal generally comprises a header which contains control, routing, and other information to implement the transmission and the payload contains the information being transmitted.
The central control station 10 controls all transactions within the structure to ensure that no conflicts arise between the communications within the system. In this type of prior art communication system, the central control system 10 typically cannot directly interface with ATM signals and hence requires a central ATM interface switch 11 to put received signals into a format understandable by control
station 10 and then to convert signals from control station 10 into ATM format for ATM transmissions to the remainder of the system.
Communications of ATM signals in this type of system are controlled using a common control signaling channel. The control signaling channel is identified in the header of an ATM cell and, when received within the system, indicates specific control information associated with a given communication in the structure. For instance, in a given communication structure, the common control signaling channel may be designated as channel 05. Whenever an ATM signal having a channel 05 header is received, it is understood in the system that it contains control information. Also encoded within the header of the ATM cells are reference ID numbers. These numbers identify which end user is to receive the data in the cell of the ATM signal being transmitted. For instance, in the above system, if an end user desires to initiate a communication, it identifies itself with a reference ID number. Thus, any cell having this reference ID number will be transmitted to the end user having the same reference ID number.
In this type of communication structure, the local ATM switch 12 includes line cards - one per end user 14- which perform various end user control functions such as providing a busy signal or dial tone to the end user. Figure 1 A illustrates the end user line card connection 13 wherein each end user is coupled to a single hardwire line card port connection (note: the line card is not shown in Figure 1 A, only the connection). The local ATM switch receives a stream of ATM cells, (i.e. the ATM signal) from the central office and routes cells through the line card to its corresponding end user depending on the header information within each cell. This prior art system is described as a point-to-point communication system since communication occurs between the central office 10 and a single end user 14 through a dedicated hardwire communication route.
As an overview, the system is a communication structure for performing a point-to-multipoint wireless communication. Specifically, the communication structure performs communications between the central control station and multiple
end users through a single dedicated hardwire communication route by controlling transmissions with a transparent wireless interface. The wireless interface remaps reference identification numbers and control channels signal designators in the header of the ATM cells being transmitted between the single line card port of a local ATM switch and multiple end users such that each end user unit perceives that it is communicating with a single dedicated line card and the ATM switch perceives it is communicating with a single end user. Consequently, a pre-existing point-to- point ATM communication structure can easily be adapted to perform point-to- multipoint wireless communications by simply adding the transparent wireless interface between the local ATM switch and the multiple wireless end users.
Figure 2 shows the point-to-multipoint communication structure including a central control office 16. central ATM interface switch 17, local ATM switch 18, a transparent wireless interface 19, and multiple end users 20. As shown in Figure 2, a single hardwire connection 21 is made between the single line card port of the local ATM switch 18 and wireless interface 19. Wireless interface 19 transmits a wireless communication 22 to the multiple end users 20. The central control office, central ATM interface switch, local ATM switch and end user units function in the same manner as they would in a point-to-point system as described in conjunction with Figure 1 A. Wireless interface 19 functions to re-map information being transmitted between the end users and the single ATM switch port connection 21. In the case when ATM cells are being transmitted from the end user to the single ATM switch port it is necessary to ensure that each end user has a unique reference identification number. However, according to the current prior art system structure it is possible that two of the end users can identify themselves with the same number. In the prior art system this was not a problem because each end user was connected with a single ATM switch port and the prior art system kept track of both the port and end user number to route communications. However, when coupling multiple end users to a single port a situation can occur such that more than two end users will be
communicating through the same port using the same ID reference number and could potentially receive each others communications.
Hence to avoid this problem, the wireless interface 19 reassigns reference ID numbers within the ATM cells received from the end users so that each end user is uniquely identified within the remainder of the communication structure. In this way, the ATM switch port connection 21 perceives that each end user has identified themselves with a unique number. Wireless interface 19 reassigns reference identification numbers by keeping track of which reference numbers have been used and remaps end user reference identification numbers to a new unique number when an end user identifies itself with a number that has already been designated. As an example, if a first end user 20A identifies itself as ID#5 and a second end user 20B also identifies itself by the same ID number, each of these users can erroneously receive the others communications. In this case, the wireless interface 19 functions to reassign end user 20-B's identification number to a new unique number and reassigns this reference identification number in all ATM cells received from end user 20B to the new unique number for the duration of the communication.
In the opposite communication direction, i.e. from the ATM switch port to the end user, interface 19 remaps reference ID numbers received in ATM cells from the remainder of the network back to the reference ID number that the user originally assigned or designated and now expects. In this way, the end user receives cells with the originally designated reference ID number and perceives that it is the only end user coupled to the single port using its originally designated reference ID number.
In addition, interface 19 reassigns common network control channel designators in the ATM protocol signaling channel being transmitted from the ATM switch to the end user. In the prior art system, protocol signaling channels provide control to structures within the communication system to allow the communication to occur. Among other things, the protocol signaling channel sends control information which can initiate and terminate communications between end users
and which provides routing information. In the prior art system, a common network channel is recognized within the network as the protocol signaling channel. For example channel 05 is commonly used as the protocol signaling channel recognized throughout the network. When an end user receives information on the protocol signaling channel with its reference ID number it acknowledges and uses the control information. In a communication system in which multiple end users can have the same reference ID number however, protocol signaling channels can be routed to the wrong end user resulting in erroneous disconnections.
The above described system solves the confusion of erroneous protocol signaling channels in a point-to-multipoint wireless communication system by assigning each end user a unique protocol signaling channel other than the common network channel. When wireless interface 19 receives a protocol signaling cell from the ATM switch on the common network protocol signaling channel for a given end user, wireless interface 19 reassigns the common network protocol channel to an end user specific protocol channel for the given end user. All ATM cells are broadcast to all of the end users via the wireless connection 22 between the end users 20 and interface 19. However, each end user includes a means for only accepting their own user specific protocol signaling channels. As a result, end users only receive their own protocol signals and ATM cells having their original user assigned reference number. The wireless interface 19 additionally includes at each end user unit a means for converting the end user specific protocol channel designator to the common network channel designator. Once converted, the end user unit is provided with the protocol signal. As a result, the end user unit receives, as expected, protocol signals on the common network channel. Consequently, the end user is unaware of the previous remapping and filtering of protocol control signals.
In accordance with the above described interface 19, a method of transparently interfacing between a single port of an ATM switch and multiple wireless end users includes the steps as shown in Figures 3 A and 3B wherein Figure
3 A shows the steps performed by the wireless interface 19 when transmitting an ATM signal from the single port of the ATM switch to the multiple end users and Figure 3B shows the steps performed by the wireless interface 19 when transmitting an ATM signal from each of the multiple end users to the single port of the ATM switch. It should be noted that the dashed line in each of Figures 3 A and 3B divide the steps so as to show parallel steps being performed by multiple end users.
As shown in Figure 3A. the ATM signal received from the ATM single port connection 21 have interface assigned reference ID numbers remapped to their original user assigned reference ID numbers (step 1, block 23) and common network protocol channel designators are remapped to an end user specific protocol channel designator (step 2, block 24). All of the translated ATM cells are then broadcast to the multiple end users (step 3, block 25). At each end user, any ATM cell having the end user reference ID number is accepted and any received ATM cells designated by the user specific protocol channel designator is accepted (steps 4, blocks 26 and 27). The user specific channel designator is converted back to the common network protocol channel and provided to the end user (step 5, block 28). Any other protocol channels are ignored.
Figure 3B illustrates the general steps for communicating between the multiple end user 20 to the single port connection 21 of an ATM switch 18. Each end user generates a stream of ATM cells which include protocol cells having the common network designators and ATM data cells having the user specific reference ID numbers. All of the streams of ATM cells received from the multiple end users are converted into a single ATM data stream (step 1 , block 29) ATM cells having the common network designator are broadcast back to interface 19 and are passed directly to the single port connection 21 since these protocol signals are in a form already recognizable to the remainder of the network. The ATM data cells including a header having the user specific identification reference number are evaluated (step 2, block 30) to determine whether the user specific reference ID number is the same as any other reference ID number currently being used by the
other multiple end users. If it is. reference ID numbers are remapped and a new unique reference ID number is assigned to identify the end user. This translation is performed on ATM cells transmitted from that end user for the duration of the communication. If the reference ID number associated with the ATM cell has not 5 been used, no translation is necessary and all ATM cells from this end user do not need to be translated. Finally the translated ATM signal is provided to port connection 21 of the local ATM switch.
Figures 4A and 4B illustrate a block diagram of one embodiment of the wireless interface 19 . Figure 4A illustrates elements in the embodiment which
10 relate to the base station of interface 19 and Figure 4B illustrates the elements of this embodiment which relate to the end user station of interface 19.
Figure 4A shows a first translator 34 for translating (under the control of the system controller 46A) reference ID designators and protocol channel designators in ATM cells received from port connection 21. Translated ATM cells from translator
15 34 are then modulated by Mod 35 and transmitted by Tran 36 from antenna 37 the base station to all of the end users. The input antenna 38 of the base station receives with Rcvr 39 all ATM cells transmitted from the end users. These ATM cells are applied to parallel paths which function to convert modulated ATM signals received from the end users into parallel ATM data streams, each stream representing a 0 separate channel of ATM cells from a given end user. Each of the parallel paths includes a tuner 40 which filters out a channel corresponding to a given end user, wherein each tuner is tuned to a different channel carrier frequency corresponding to each end user. A Demod 41 demodulates the channels to obtain the ATM signals that had been modulated onto the carrier frequency. An optional forward error 5 correciton unit (FE 42) functions to insert error correction information into the signal to be transmitted to facilitate error detection so as to reduce the signal-to noise ratio of the signal after transmission. The resulting ATM cells from each path are multiplexed together to form a single digital ATM data stream. In one embodiment, cells are time division multiplexed (TDM) together. However it
should be understood that other types of multiplexing techniques are available. The ATM signal is then applied to the second translator 44 which functions to translate any duplicate reference ID numbers to a new unique number. The resulting single digital ATM data stream comprises ATM cells wherein each end user is identified by a unique reference ID designator. An optional reformatting may be performed by block 45 wherein the ATM data stream is put into a standardized packet transmission format.
In general the system controller 46A has the following duties:
• setup and control the segmentation and reassemble chips (NICStAR). • remember address registration information set by end user stations
• allocate return channel and frequency for end user stations
• allocate special signaling VPINCI that will be unique for each end user station
• tell the end user station its return channel, frequency and special signaling VPINCI
• map signaling messages coming from network to special signaling VPINCI
• trap and discard any signaling messages for the global reference (0)
• inform end user station of all VPI VCI's that it should receive • inform end user station of all VPI/VCI's that it should remap to normal signaling
• map call reference ID to unique value in signaling messages from end user
• map signaling messages from end user to special signaling VPI/VCI • watch for invalid call reference ID's and VPLNCI's; send error
• any other valid cell simply gets sent to the transmitter
It should be noted that not all of these duties are required in order to implement the above described system and method but instead this list is a
guideline for the manner in which system controller 46A functions.
The end user station shown in Figure 4B illustrates the portion of the transparent wireless interface 19 of the present invention residing at each end user unit. Hence, the number of end user stations used in the system corresponds to the number of end users performing wireless communications with the wireless interface 19 of the present invention. The end user station includes an antenna 47 and Rcvr 48 for receiving the broadcast modulated ATM signal from the base station of the interface 19. The modulated ATM signal received by antenna 47 represents the ATM signal received from single port connection 21 after translation by the base station of the wireless interface 19 of the present invention. Next the received signal is demodulated by the Demod unit (block 49) and then error correction encoding information is removed by the forward error correction unit (FE 50) to put into the form of a single stream of ATM cells representative of the signal received by antenna 47. This stream of ATM cells is then provided to a select/remap unit (block 51).
The select/remap unit 51 performs two functions. First, it selects only those ATM cells designating the end user specific protocol channel as defined by the system controller 46 A of the base station. Specifically, as described above, prior to transmitting any ATM cells which designate the common network protocol channel the base station translates these designators into user specific protocol control channel designators. System controller 46 A indicates to system controller 46B what its end user's protocol channel is. System controller 46B then controls select/remap unit 51 so that it only receives protocol signals on that channel. Hence, each of the end user stations receives a stream of ATM cells which include various user specific protocol channel designators, however, the select/remap unit 51 within a given end user station only acknowledges those ATM cells designating the corresponding user specific protocol control channel and disregards any other ATM cells designating any other protocol channels.
Second, select remap unit 51 translates the end user specific protocol
channel designator back to the original common network protocol channel designator so as to put the ATM cell in a form recognizable to the end user unit. For instance, current cell phone design is one in which all elements within the communication system expected protocol control signals to be provided on the common network channel. Hence, once the ATM cell designating the user specific protocol channel is accepted via the select portion of the select/remap unit 51 it is necessary to translate the user specific protocol channel designator to the common network channel designator so that the phone will recognize that this is a protocol signal. Once this is accomplished, the ATM cell is in condition to be passed to the end user unit 53. A final reformatting is performed by block 52 to put into a standardized ATM cell format.
The end user station path for transmitting signals from the end user unit 53 includes FE 54, Mod 55, Tuner 56, Tran 57, and antenna 58. These elements basically convert the digital ATM signal generated by end user unit 53 into an RF signal to be transmitted wirelessly to the base station. Each end user transmits their ATM signal on a different carrier frequency unique to each end user station. Mod 55, modulates the digital ATM signal onto a carrier signal and Tuner 56 adjusts the carrier frequency to the unique end user station carrier frequency. The carrier frequency (or channel) is allocated and tracked by the base station system controller 46A so as to ensure that each end user has a unique channel to transmit signals to the base station. Tran 57 amplifies and further processes the modulated signal to put into condition for transmission from antenna 58. Note that system control 46B controls Tuner 56 so that the end user carrier frequency is unique from the remainder of the end users. It should be noted Figure 4B shows a system controller 46B providing control to select/remap 51 of the end user station. Controller 46B receives and transmits control information with controller 46A in the base station. For instance when the base station designates a unique protocol channel designator, it informs control block 46B that end processor is to receive its protocol signal on that
channel. System control 46B then controls select/remap unit 51 so that it accepts ATM protocol cells only having the unique protocol channel designator associated with the given end user. The control module 46A and the control module 46B send control messages back and forth over a special signal channel using ATM cells. The end user station of interface 19 may, in one embodiment, be implemented as a transmitter tower. The end user station of interface 19 may be implemented to include an antenna/receiver portion residing in a location ( e.g., the roof) to provide clear reception and transmission of signals. The end user station also includes a customer premise equipment portion for accepting and using the transmitted signals once received and for providing new signals for transmission. Examples of customer premise equipment include a telephone, a computer, or an internet connection and each of these are adapted to receive the various types of signals transmitted through the wireless structure which include 1) direct digital data, 2) conventional telephone signals, 3) internet signals, and 4) video data. Figure 5 A shows the steps performed when an external user in the communication network according to the present invention initiates a call with one of the multiple end users. Initially, the base station receives a SETUP message from the network. This message includes encoded information that indicates that 1) a communication is being initiated by an external user, 2) the external user's address, 3) the end user's address, and 4) other information concerning the communication (step 1 , block 59). The base station (i.e. system control 46A) also either assigns or looks-up (if already assigned) the call reference ID number that corresponds to the address registration data provided in the SETUP message and finds the VPINCI to be used for the connection between the external user and the end user (step 2, block 60). Next the base station (i.e. system controller 46A) either assigns or looks-up (if already assigned) the end users protocol channel and this information is transmitted to the end user station so that it will now accept protocol signals on this channel only (step 3, block 61). Once the protocol channel is established the end user can now receive protocol signaling messages on its private
protocol signal channel and remap it to the normal (i.e. common network) protocol signaling channel (step 4, block 62). Any ATM cells received on the VPINCI are simply transmitted on to the end user. It should be understood that eventually, the above described connection will be torn down and the call reference value retired 5 and the end user told to stop receiving the associated VPINCI.
Figure 5B shows the steps performed when one of the end users initiates a call with an external user on the communication network according to the present invention. Initially, the end user designates a call reference ID and transmits a SETUP message to the base station on the common network signaling channel (e.g.
10 05) indicating the end user designated call reference ID number (step 1 , block 70). Next the base station receives the SETUP message and remaps the call reference ID number to a unique value and then sends the SETUP message to the network, (step 2, block 71). The next protocol signaling message that the base station receives on the remapped call reference ID number contains the VPINCI to be used for the
15 connection. The VPINCI information is saved by the base station and communicated to the end user station (step 3, block 72). The protocol signaling message has it's corresponding call reference ID number mapped back to the one expected by the end user and it's protocol signaling channel designator mapped to the end user private signaling channel (step 4, block 73). The end user selector (i.e.
20 select/remap unit 51 ) is set to receive signaling messages on the end user private signaling channel (step 5, block 74) after which the SETUP message is then transmitted to the end user on its private signaling channel (step 6, block 75). The end user station receives the signaling message on it's private channel and remaps it to the common network channel (e.g. 05) and sends it to the end user (step 7, block
25 76). Any further signaling messages have the appropriate remapping done and is transferred on to either the end user or external user (step 8, block 77). Any ATM cells received on the VPINCI designated in step 3 are simply transmitted on to the end user (step 9, block 78). It should be understood that eventually, the above described connection will be torn down and the call reference value retired and the
end user told to stop receiving the associated VPI/VCI.
In the preceding description, numerous specific details are set forth, such as specific frequencies and signaling protocol formats in order to provide a thorough understanding of the present invention. It should be apparent, however, to one skilled in the art that these specific details need not be employed to practice the present invention. In other instances, well-known communication structures have not been described in detail in order to avoid unnecessarily obscuring the present invention.
Moreover, although the elements of the present invention have been described in conjunction with certain embodiments, it is appreciated that the invention can be implemented in a variety of other ways. Consequently, it is to be understood that the particular embodiments shown and described by way of illustration are in no way intended to be considered limiting. Reference to the details of these embodiments is not intended to limit the scope of the claims which themselves recite only those features regarded as essential to the invention.