Abstract:
A method for transmitting signals, consisting of receiving a plurality of signals generated in an isolated region, the signals encoding respective individual payloads and payload envelopes. At least two of the signals operate under different protocols. The method includes deriving information from the signals on respective connections of the signals, and aggregating the payloads into one or more aggregated payloads. The method further includes transmitting the one or more aggregated payloads and the information via a satellite link to a receiver outside the region, the one or more aggregated payloads and the information amounting to less data than an aggregated amount of data in the individual payloads and payload envelopes. The method also includes reconstituting the plurality of signals at the receiver using the one or more aggregated payloads and the information.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to signal transmission, and specifically to transmission of multiple types of signals between an isolated region and a station outside the region. 
     BACKGROUND OF THE INVENTION 
     In passenger aircraft, there is typically a large number of different types of wireless signals originating from, and being directed to, the passengers and/or crew. Some of these signals are internal to the aircraft, but typically most are between the aircraft and an entity external to the aircraft. The signals may be classified as voice communications, or as data communications. 
     Both types of communication are typically transmitted as packets using various protocols such as the Internet Protocol (IP), the User Datagram Protocol (UDP), the Transmission Control Protocol (TCP), and/or the Real-Time Transport Protocol (RTP). These protocols are respectively described in Request For Comments (RFC) documents RFC 791, RFC 768, RFC 793, and RFC 1889, which may be found at www.faqs.org/rfcs/, and which are incorporated herein by reference. Voice communications are also transmitted using specific cellular telephone protocols, such as a Code Division Multiple Access (CDMA) protocol, a global system for mobile (GSM) protocol, and/or various orthogonal frequency division multiplexing (OFDM) protocols. 
     The communications external to the aircraft are typically transmitted via links which are limited in bandwidth, and the bandwidth limitation causes problems, such as dropped data connections, long voice call setup times, and reduced voice quality. While some solutions to the problems caused have been found, for example, the application of a differentiated services architecture, the solutions are at best partial fixes for the problems. 
     Thus, an improved method for transmitting traffic from an isolated system such as an aircraft cabin would be advantageous. 
     SUMMARY OF THE INVENTION 
     In embodiments of the invention, a multiplicity of heterogeneous wireless communication networks operate in an isolated region, such as an aircraft cabin, are described. The isolated region communicates with an external station, typically a ground station node, by a satellite link which enables each of the heterogeneous networks to communicate with a corresponding network coupled to the external station. 
     The wireless communications of the isolated region networks are transmitted as packets, each of the packets comprising a payload enclosed in an envelope. For each network, the payload and the envelop characteristics of each transmitted packet are prescribe by one or more predefined protocols under which the network operates. An infrastructure in the isolated region receives packets of on-going connections; the infrastructure extracts the payloads from the packets, assembles the payloads into an ordered aggregated packet, and transmits the ordered packet to the external station. In some embodiments the ordered packet may be compressed. 
     At initiation of connections, the infrastructure stores respective information regarding the connections. The infrastructure also assigns a unique identifier, such as an order number, to each connection, according to which payloads of each connection are assembled in the aggregated packet. The infrastructure transmits the information and the order numbers, optionally in a compressed form, to the external station. The infrastructure may also apply a differentiated service parameter, such as a quality of service (QoS), to each connection. 
     On receipt of the aggregated packet, the external station divides the packet into the payloads. The external station uses the information and order number received from the infrastructure to reconstitute the original packets from their payloads, which the external station then transmits to their final destination in the corresponding networks. By separating payloads from their envelopes, and transmitting the payloads as an ordered aggregated packet, significant savings in bandwidth are realized. 
     By processes substantially similar to those described above, the external station also receives inbound packets destined for the isolated region from the networks coupled to the external station, and generates reduced size inbound aggregated packets. These reduced size packets are conveyed via the satellite link to the isolated region infrastructure, which converts them to their original form inbound packets. The isolated region infrastructure then conveys the original form inbound packets to their correct destinations in the isolated region. 
     Thus, both outbound and inbound packets are transmitted in a reduced size form via the satellite link, so that the transmission bandwidth with the isolated region is correspondingly increased. 
     There is therefore provided, according to an embodiment of the invention, a method for transmitting signals, including:
         receiving a plurality of signals generated in an isolated region, the signals encoding respective individual payloads and payload envelopes, at least two of the signals operating under different protocols;   deriving information from the signals on respective connections of the signals;   aggregating the payloads into one or more aggregated payloads;   transmitting the one or more aggregated payloads and the information via a satellite link to a receiver outside the region, the one or more aggregated payloads and the information totaling less data than an aggregated amount of data in the individual payloads and payload envelopes; and   reconstituting the plurality of signals at the receiver using the one or more aggregated payloads and the information.       

     Typically, the isolated region may include a moving region. 
     Deriving the information from the signals may include deriving the information from the payload envelopes, and aggregating the payloads may include incorporating a portion of the respective payload envelope into the payload. 
     In an embodiment, deriving the information includes storing the information in a session table at the isolated region, and transmitting the information includes storing the session table at the receiver. 
     In an alternative embodiment, aggregating the payloads includes assembling the payloads in a specific order into the one or more aggregated payloads, transmitting the information includes transmitting the specific order to the receiver, and the specific order references the respective connections. 
     In another embodiment, receiving the plurality of signals includes receiving and applying a quality of service (QoS) parameter for at least one of the signals, and the method also includes applying at least one of respective priorities and respective bandwidths to the at least two signals, in response to the QoS parameter. 
     In another disclosed embodiment, the payloads have fixed lengths; alternatively, the payloads have variable lengths, and aggregating the payloads includes incorporating values of the length into the aggregated payload. 
     Typically, the different protocols are chosen from industry-standard protocols. 
     There is further provided, according to an embodiment of the invention, apparatus for transmitting signals, consisting of:
         a remote backhaul infrastructure (RBI) which is adapted to:   receive a plurality of signals generated in an isolated region, the signals encoding respective individual payloads and payload envelopes, at least two of the signals operating under different protocols,   derive information from the signals on respective connections of the signals,   aggregate the payloads into one or more aggregated payloads, and   transmit the one or more aggregated payloads and the information via a satellite link, the one or more aggregated payloads and the information consisting of less data than an aggregated amount of data in the individual payloads and payload envelopes; and   a receiver outside the region which is adapted to receive the one or more aggregated payloads and the information and to reconstitute the plurality of signals therefrom.       

     The invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings, a brief description of which is given below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a communication system, according to an embodiment of the invention; 
         FIG. 2  illustrates a relation between packets transmitted in the system of  FIG. 1 , and an aggregated packet generated by the system, according to an embodiment of the invention; 
         FIG. 3  is a flowchart showing steps of a process performed on initiation or teardown of a connection, according to an embodiment of the invention; 
         FIG. 4  is a flowchart showing steps of a process performed during an on-going connection conducted via a satellite, according to an embodiment of the invention; and 
         FIG. 5  is a flowchart showing steps of a process performed on receipt of a specific aggregation packet, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Reference is now made to  FIG. 1 , which is a schematic illustration of a communication system  10 , according to an embodiment of the invention. System  10  comprises one or more isolated regions  12 , which are typically mobile regions such as aircraft cabins, although it will be appreciated that each region  12  may be any other isolated region wherein electromagnetic radiation generated within the region does not radiate significantly beyond the boundaries of the region. Such regions include, but are not limited to, ships, islands, and isolated habitations. Except where otherwise stated, by way of example region  12  is hereinbelow assumed to be an aircraft cabin. 
     Two or more heterogeneous wireless communication systems, i.e., electromagnetic signaling systems that operate under different protocols, are implemented within cabin  12 . Typically the protocols are industry-standard protocols. Herein, it is assumed that the following four systems are operative in the cabin: a code division multiple access (CDMA) cellular telephone system  14 , which has one or more CDMA mobile stations  16  communicating via a local CDMA base-station transceiver system (BTS)  18 ; a global system for mobile (GSM) cellular telephone system  20 , which has one or more GSM mobile stations  22  communicating via a local GSM BTS  24 ; a wireless local area network (WLAN) data communication network  26  which has one or more computing systems  28  having communications controlled by a local controller  30 ; and a session initiated protocol LAN (SIPLAN)  32  which has one or more computing systems  36  having communications controlled by a local controller  34 . It is contemplated that many other transmission schemes and/or protocols could be used, as OFDM protocols, various 802.xx protocols (such as 802.11, 802.16, 802.20, 802.15 . . . ). SIPLAN  32  may operate as either a wired or as a wireless network. 
     Hereinbelow, stations  16  and  22 , and systems  28  and  36  are also referred to collectively as remote stations  17 . BTS  18 , BTS  24 , controller  30 , and controller  34  are also referred to hereinbelow collectively as remote controllers  19 . 
     In addition to controlling their respective local communications, all remote controllers  19  are coupled, typically by wireline, to a remote backhaul infrastructure (RBI)  40 . RBI  40  acts as a conduit for communications between the wireless/wired communication systems within cabin  12  and corresponding systems outside the cabin, such as ground-based systems. These communications are herein termed external communications. In order to act as a conduit, RBI  40  uses respective protocol-specific adapters, the functions of which are described in more detail below. Thus, in the example described herein, RBI  40  has a CDMA adapter  41 A, a GSM adapter  41 B, a WLAN adapter  41 C and a SIPLAN adapter  41 D; the adapters are also referred to generically as adapters  41 E. 
     In order to provide the necessary linkage for the external communications, a satellite  46 , typically a transponder, acts as a signal relay for a satellite link  49  between RBI  40  and ground station node  48 . Ground station node  48  comprises a central backhaul infrastructure (CBI)  50 , which is coupled via a network  58  such as the Internet to corresponding networks/communication systems, and which also acts as a conduit for communications with cabin  12 . CBI  50  is generally similar to RBI, and includes protocol-specific adapters generally similar in function to adapters  41 E. Thus, CBI  50  has a CDMA adapter  51 A, a GSM adapter  51 B, a WLAN adapter  51 C and a SIPLAN adapter  51 D; these adapters are also referred to generically as adapters  51 E. Consequently, CDMA system  14 , GSM system  20 , WLAN network  26 , and SIPLAN  32  are able to communicate respectively with a CDMA system  60 , a GSM system  62 , a WLAN network  64 , and a SIPLAN  66 . Stations operating within CDMA system  60 , GSM system  62 , WLAN network  64 , and SIPLAN  66  are generically termed ground stations  61 . 
     Typically, satellite  46  also acts as a relay between other isolated region RBIs, generally similar to cabin  12 , and ground station node  48 . In some embodiments of the invention, a multiplicity of satellites act as satellite  46 . Thus, while the description herein, by way of example, refers to one region  12  communicating via one satellite  46 , it will be understood that the scope of the invention includes more than one isolated region and/or more than one satellite. 
     RBI  40  comprises a processing unit (PU)  44 , which operates the remote infrastructure using a memory  45  incorporating a remote integration framework (RIFR) module  42 . Module  42  comprises a session table  47 , a session order list  29 , an aggregation module  39 , a buffer  37 , and adapters  41 E. 
     CBI  50  comprises a PU  52 , which operates the central infrastructure using a memory  56  which incorporates a central integration framework (CIFR) module  54 . Module  54  in turn comprises a session table  53 , a session order list  57 , an aggregation module  59 , a buffer  55 , and adapters  51 E. 
     Tables  47  and  53  are substantially identical single column tables which contain information on communication sessions in progress between RBI  40  and CBI  50 . Lists  29  and  57  are substantially identical lists having the order in which session payloads are placed in aggregated packets generated by modules  39  and  59 . Aggregation module  59  and adapters  51 E perform similar functions to module  39  and adapters  41 E respectively. The functions of tables  47 ,  53 , lists  29 ,  59 , modules  39 ,  59 , buffers  37 ,  55 , and adapters  41 E,  51 E, are described in more detail below. 
     Embodiments of the invention reduce the bandwidth limitation problems described in the Background of the Invention by optimizing and compressing the external communications in an outbound direction from cabin  12 , as well as in an inbound direction to the cabin. Thus RBI  40  optimizes and compresses heterogeneous wireless signals received from cabin  12  to form compacted outbound signals. RBI  40  then transmits the compacted signals to CBI  50 , which reconstitutes the signals to their original form and conveys the reconstituted outbound signals to their appropriate systems/networks. CBI  50  and RBI  40  perform substantially the same operations on inbound heterogeneous wireless signals that are received at ground station node  48  and that are directed to cabin  12 . The process of generating the outbound and inbound compacted signals is described below with respect to  FIGS. 2 ,  3 ,  4  and  5 . 
       FIG. 2  illustrates a relation between packets  70  transmitted to RBI  40  from controllers  19 , and aggregated packets  90  generated by RBI  40 , according to an embodiment of the invention. The processes by which aggregated packets  90  are generated from packets  70  are described below in reference to  FIGS. 3 and 4 . Traffic to and from remote stations  17  is assumed to be in the form of packets, each packet  70  comprising a payload  74  and an envelope  80  typically formed from a header  76  and a trailer  78 . Envelope  80  of each packet comprises information necessary for successful delivery of the packet to its destination. The contents and structure of each envelope  80  depend on the type of traffic from a specific remote station  17 , for example whether the traffic is classified as part of an ongoing voice or data connection, and/or as part of a reliable or an unreliable connection. The contents and structure of each envelope  80  are also a function of the one or more protocols under which remote station  17  is operating. By way of example, packets to and from remote stations  17  are assumed to be transmitted using an Internet Protocol (IP), but it will be appreciated that any other suitable protocol may be used for packet transmission. It will also be appreciated that packets may use other protocols, such as those exemplified in the Background of the Invention, as well as the Internet Protocol, the protocols used contributing data to each envelope  80 . 
     Packets  70  may be grouped into a number of different classifications, for example, station registration packets, connection setup packets, on-going connection packets, and teardown connection packets, as well as other classifications that will be apparent to those skilled in the art. Depending on their classification, each envelope  80  of packets transmitted to and from each remote station  17  typically comprises data that is repeated. For example, in an ongoing RTP/UDP/IP connection, repeating data in each envelope of the ongoing connection comprises, inter alia, a source address and port, and a destination port and address. Depending on the classification of the packet, the repeating data may comprise a relatively large fraction of the total envelope. 
     Embodiments of the invention use the presence of repeated data in the envelopes of the packets, together with the fact that the information within the packets is to be transferred between two known infrastructures, i.e., RBI  40  and CBI  50 , to reduce the amount of data transmitted between the infrastructures over satellite link  49 . The repeated data is stored as session entries  72  of session table  47 . 
     Each session entry  72  of session table  47  gives information regarding a specific connection upon which a subgroup of packets  70  are transmitted. By way of example, table  47  is illustrated as having four information entries labeled session data  1 ,  2 ,  3 , and  4 . Each entry  72  may also include a differentiated service data parameter  73 , such as a quality of service (QoS), a type of service (ToS) value, and/or a traffic shaping value, that is assigned to the connection of the entry. The differentiated service data parameter may typically be generated by an operator of system  10 . For example, the differentiated service parameter may provide a higher priority and/or larger bandwidth to a remote station  17  situated in a first class region of cabin  12 , compared to one situated in an economy class region. Typically, connections such as voice or video connections that require real-time transmission are assigned a higher priority than connections which may be successfully operated in non-real-time. Alternatively, the differentiated service data parameter may be applied within system  10  by any other convenient method known in the art. 
     As illustrated in  FIG. 2 , RBI  40  receives packets  70 , and transfers the packets to their appropriate adapter  41 E. For packets that are part of an on-going connection, each adapter  41 E transfers payload  74  of the packet to aggregation module  39 . Module  39  acts as a buffer for the payloads and also generates aggregated packets  90  that are transmitted from RBI  40 . 
     Each aggregated packet  90  comprises an aggregated payload  92  and an envelope  94 ; module  39  is assumed, by way of example, to generate aggregated packets  90  to be compatible with the Internet Protocol, so that envelopes  94  are constructed accordingly. However, any other convenient protocol which is able to convey aggregated payload  92  from RBI  40  to CBI  50  via satellite link  49  may be used. Module  39  assembles aggregated payload  92  in the form of ordered payloads  74 , the ordering of payloads  74  being derived from a unique order number which processor  44  establishes during call setup, and which the processor stores in session order list  29 . Module  39  refers to list  29  to decide the order in which payloads  74  are placed in aggregated payload  92 . In  FIG. 2 , by way of example processor  44  is assumed to have assigned the order numbers  12 ,  3 ,  20 , and  14  respectively to session  1  data, session  2  data, session  3  data, and session  4  data, as shown in list  29 . Payload  92  is shown as using the order numbers derived from list  29 . 
     Typically, each payload  74  has a fixed length which is established using a management channel (described further below) between RBI  40  and CBI  50 . Alternatively or additionally, at least some of payloads  74  inserted into aggregated payload  92  may have a variable length. In the latter case, the length of the payload is typically passed with the payload as one of a number of predefined lengths. In some embodiments of the invention, aggregated payload  92  may be compressed, typically using a compression algorithm such as a Lempel-Ziv-Welch (LZW) algorithm. Alternatively or additionally, other forms of compression to individual payloads and/or the aggregated payload may be applied, such as checking for a level and/or duration of silences in voice data being sent, and compressing the data corresponding to such silences. After formation of each aggregated packet  90 , module  39  passes the assembled packet to RBI  40  for transmission to satellite  46  via link  49 . 
     In addition to transmitting aggregated packets  90 , link  49  also comprises a management channel  63  over which data may be passed between RBI  40  and CBI  50 . The data may also be passed in a compressed form. Functions of channel  63  are described in more detail below. 
       FIG. 3  is a flowchart showing steps of a process  150  performed by RBI  40  on initiation or teardown of a connection, according to an embodiment of the invention. The steps described herein apply to a connection via satellite  46  that is initiated or torn down due to transmissions from within cabin  12 . Those skilled in the art will be able to apply the steps described herein, mutatis mutandis, to a connection via satellite  46  that is initiated or torn down due to transmissions from systems  61 . 
     In a first step  152 , remote controllers  19  transmit outgoing packets  70  received from their respective remote stations  17  to RBI  40 . RIFR module  42  receives packets  70 , stores them temporarily in its incoming buffer  37 , and then passes the packets to the appropriate adapters  41 E. 
     In a classification step  154 , each adapter  41 E inspects the packet envelope and determines that the packet is related to initiation or teardown of a connection. The adapter passes the content of the envelope to processor  44 . 
     In an updating step  156 , processor  44  updates session table  47  according to the envelope contents received. Thus, if the envelope contents correspond to initiation of a connection, processor  44  stores the information for the connection, derived from the envelope contents, in session table  47 . The information stored typically includes addresses of specific remote stations  17  and ground stations  61  between which the connection is to be initiated. Alternatively, if the envelope contents correspond to teardown of a connection, processor  44  removes the information for the connection from session table  47 . 
     Also in step  156 , processor  44  updates session order list  29 . Thus if table  47  has had a connection added, processor  44  adds an order number for the connection to list  29 . If table  47  has had a connection torn down, list processor  44  removes the order number of the connection from list  29 . 
     In a coordination step  158 , RBI  40  transmits the updated data for session table  47  and list  29  to CBI  50 , using management channel  63  between the RBI and the CBI, and as illustrated by arrow  65  ( FIG. 2 ). Typically, the management channel uses a reliable connection such as a TCP/IP transmission, and may use any convenient protocol, including non-standard protocols, for transferring the communications. 
     In a final step  160 , processor  52  uses the updated data to update session table  53  and list  57  of CBI  50 , so that session tables  47  and  53 , and lists  29  and  57 , are substantially identical. Process  150  then concludes. 
       FIG. 4  is a flowchart showing steps of a process  170  performed by RBI  40  during an on-going connection conducted via satellite  46 , according to an embodiment of the invention. The steps described herein are those performed within cabin  12  for outbound packets  70  on the on-going connection, and correspond to the process illustrated in  FIG. 2 . Those skilled in the art will be able to apply the steps described herein, mutatis mutandis, to steps performed within CBI  50  for inbound packets during an on-going connection conducted via satellite  46 . 
     First step  172  and classification step  174  are generally similar to steps  152  and  154  of process  150 , except that in step  174  each adapter  41 E classifies the packet as part of an on-going connection. 
     In a step  176 , the adapter selects payload  74  ( FIG. 2 ) from the packet  70  it has received, and passes the payload to aggregation module  39 . The payload selected and passed typically depends on the type of connection. Thus, for an unreliable connection such as that used by a UDP packet, the payload comprises all data except the envelope of the packet. For a reliable connection, such as that used by a TCP/IP packet, the payload also includes data selected from the envelope, such as a number of the packet, that may be necessary for correct continuation of the connection. 
     In a step  178 , aggregation module  39  checks with session table  47  to determine on which connection the payload is to be delivered, and from order list  29  the module determines the order in which the payload is to be placed in aggregation packet  90  sent from the module. The aggregation module then places the payload into the aggregation packet in the order it has determined, forming aggregated payload  92 . 
     In a final step  180 , when a specific aggregation packet  90  has been filled, or after a preset time, whichever occurs first, the aggregation module passes the aggregation packet  90  to processor  44 , which transmits the packet via satellite  46  to CBI  50 . Process  170  then ends. 
       FIG. 5  is a flowchart showing steps of a process  190  performed by CBI  50  on receipt of a specific aggregation packet  90 , according to an embodiment of the invention. Those skilled in the art will be able to apply the steps described herein, mutatis mutandis, to steps performed by RBI  40  on receipt of an aggregation packet. 
     In a first step  192 , CBI  50  receives aggregation packet  90 , stores it in its buffer  55 , and divides the aggregation packet into its payloads. The division is performed using knowledge of the lengths of the payloads, which typically have the preset fixed length described above. In the cases where the payload length is not fixed, the length is passed with the payload and is included in aggregation packet  90 , as is also described above. In these cases, CBI  50  uses the values of the length to correctly divide aggregation packet  90  into its payloads. 
     In a second step  194 , processor  52  refers to order list  57  and session table  53 . From the list and the table, processor  52  determines to which adapter  51 E each payload is to be sent, and forwards the payloads accordingly. (As stated above, session tables  47  and  53 , and lists  29  and  57 , are substantially identical). 
     In a final step  196 , each adapter uses the session information in table  53  to reconstitute the complete packet of the payload. The adapter then forwards the complete packet, via its respective network, to the appropriate ground station  61 . Process  190  then concludes. 
     The descriptions above with reference to  FIGS. 2 ,  3 ,  4  and  5  have described the process of transfer of outbound packets from region  12  to ground station node  48 , and from the ground station node to the final destination of the packets. It will be appreciated that in the transfer of the outbound packets, the amount of data transmitted via link  49  is significantly less than the amount of data in the outbound packets themselves, since the packets are compressed into aggregated packets and information transmitted via management channel  63 . The reduction in data transmitted leads to a corresponding increase in bandwidth. 
     Generally similar processes to those described above are followed for inbound packets from networks  60 ,  62 ,  64 , and  66  to region  12 , and those skilled in the art will be able to adapt the processes described herein, mutatis mutandis, to apply to inbound packets. 
     It will be appreciated that the embodiments described above are cited by way of example, and that the invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.