WO1999026358A1

WO1999026358A1 - Architecture for integrated wll/vsat system

Info

Publication number: WO1999026358A1
Application number: PCT/US1998/024270
Authority: WO
Inventors: Dilip S. Gokhale
Original assignee: Comsat Corp
Current assignee: Comsat Corp
Priority date: 1997-11-14
Filing date: 1998-11-13
Publication date: 1999-05-27
Anticipated expiration: 2000-05-14
Also published as: WO1999026358A9

Abstract

The handling of voice and data calls originating from digital Wireless Local Loop (WLL) subscribers and destined for either local or long distance subscribers is improved by integrating WLL and Very Small Aperture Terminal (VSAT) satellite technology. The integrated system uses identical vocoder, rate adapter (38), and data/fax inter-working units (40) in both systems, together with the associated controls (30) to enable/disable these units during call establishment to ensure a higher quality of service than can be obtained otherwise.

Description

Architecture for Integrated WLL/VSAT system

Background

The present invention is directed to a technique for the integration of digital Wireless Local Loop (WLL) and Very Small Aperture Terminal (VSAT) satellite technology that enhances the quality of service offered to end users. VSAT satellite technology has enabled the cost effective provisioning of long-distance telecommunication services to remote areas around the world. Similarly, WLL technology is being used in several locations around the world to offer cost effective alternatives to wire-line solutions, especially when the subscribers are dispersed over a large geographic area. Service providers are also combining WLL and VSAT technologies in order to cost effectively provide "local" and "long-distance" telephony services.

Currently, the integration of the two technologies is accomplished by interconnecting the two systems via the use of a standard signaling protocol such as R2, SS#5, or SS#7. In this approach, the VSAT appears as a transparent alternative to a terrestrial PSTN trunk as far as the WLL system (which also includes the local exchange function) is concerned. This is generally shown in fig. 6, where calls from a WLL subscriber will be routed from a WLL Base Transciever Station (BTS) 114 through a Transcoder and rate adapter (TRAU) 138 to a WLL switch 116a containing a Switch Controller, WLL Interface, PSTN Interface, Cross-Connect, and Fax/Data Inter-working Unit. The call then passes through a VSAT switch 116b which includes a switch controller, PSTN Interface, VSAT Interface, Cross Connect and Fax/Data Inter- working Unit. Finally, the call passes through a TRAU 138b and a VSAT modem into the satellite link. Other functions such as O&M are not shown in the figure for the sake of clarity. This approach has the benefit of allowing the two technologies to be selected independently of each other as long as both of them support the common inter-operable signaling interface. However a major disadvantage associated with this approach is the fact that service quality is degraded for the following reasons. Increasingly, both VSAT and WLL systems are based on digital technology, and use low data rate encoding (e.g., 8 Kbit s) for voice services to make efficient utilization of the bandwidth resources. Tandem vocoders (e.g., vocoders 138a and 138b in series, one within the WLL system, the other within the VSAT system) can seriously degrade voice quality. Also, typically the low rate compression techniques used by the two vocoders are different which further worsens the voice quality.

A low rate vocoder incurs buffering delays associated with voice compression at the transmit end, and with decompression at the receive end. Since the two vocoders (one in the WLL system, the other in the VSAT system) operate independently, each incur these delays and hence contribute to a larger overall delay with respect to the end-to-end voice path.

The use of low data rate transport (e.g., 8 Kbit/s, 16 Kbit/s) within the VSAT or WLL network also requires the use of facsimile and data inter-working (F-IWF, D-IWF) units for the support of voice band facsimile and data (e.g., V.32), respectively. As is the case with the voice service, the transport of voice band data or facsimile also incurs additional delays and quality degradation given the tandem D- IWF/F-IWF units that are required.

Summary of the Invention

It is therefore an object of the present invention to improve the integration of digital Wireless Local Loop (WLL) and Very Small Aperture Terminal (VSAT) satellite technology that enhances the quality of service offered to the end users.

It is a further object of the invention to improve the handling of voice and data calls originating from WLL subscribers and destined for either local or long distance subscribers. These and other objects of the invention are accomplished by an integrated system which uses identical vocoder, rate adapter, and data/fax inter-working units in both systems, together with the associated controls to enable/disable these units during call establishment to ensure a higher quality of service than can be obtained otherwise, e.g., voice quality, reduction in BER, and reduction in end-to-end delays.

Brief Description of the Drawing

The invention will be more clearly understood from the following description in conjunction with the accompanying drawing, in which:

Fig. 1 illustrates an integrated WLL/VSAT network architecture in accordance with the present invention;

Fig. 2 is a functional diagram of the arrangement of the integrated WLL/VSAT switch 16 of Fig. 1; Figs. 3a-3b illustrate the handling of local calls by the integrated WLL VSAT switch in accordance with the present invention;

Figs. 4a-4b illustrate the handling of long distance voice calls by the integrated WLL/VSAT switch in accordance with the present invention;

Fig. 5 illustrates the handling of long distance fax/data calls by the integrated WLL/VSAT switch in accordance with the present invention; and

Fig. 6 is a diagram of a conventional arrangement for handling calls from a WLL base stations destined for a subscriber through a satellite link..

Detailed Description of the Invention

Figure 1 depicts an integrated WLL/VSAT network architecture according to the present invention. The primary nodes within the network are the integrated

WLL/VSAT nodes 10 and the VSAT PSTN gateway nodes 12. Other associated entities such as the Network Control Center are not shown in the figure for the sake of clarity. The integrated WLL/VSAT node 10 consists of a WLL Base Transceiver Station (BTS) 14, an integrated WLL/VSAT switch 16, and a satellite VSAT modem subsystem 18. It should be noted that these entities are functional representations only and can be combined in physical implementations. The VS AT/PSTN gateway 12 provides an interface from the satellite network to the terrestrial Public Switched Telephone Network (PSTN) 20 as well as any required echo cancellation equipment. Note that several such gateways 12 may be provided to allow for least cost routing. The architecture shown in Fig. 1 is applicable to VSAT networks with different multiple access technologies such as FDMA, TDMA, and CDMA as well as networks that support either "star" or "mesh" topologies. Similarly, the architecture is applicable to WLL networks that conform to technologies such as GSM & IS 54 (TDMA), and IS-95 (CDMA), as well as proprietary digital networks. The only restriction is that the VSAT must use vocoder and fax/data interworking schemes that are identical to those used in the WLL network.

Figure 2 shows a high level depiction of the Integrated WLL/VSAT Switch 16 (IWVS). As the figure indicates, the major components involved and relevant to this invention are Switch Controller 30, WLL Interface 32, VSAT Interface 34, Cross-Connect 36, Transcoder and rate adapter (TRAU) 38, and Fax/Data Interworking Unit 40. Other functions such as O&M are not shown in the figure for the sake of clarity. It should be noted that the figure provides a functional representation, and it is possible that some of the components may be implemented on separate physical entities. The Switch controller 30 is responsible for the centralized control of all signaling from the WLL and the VSAT, and for the control of the hardware resources (e.g., TRAU, Cross Connect) within the Switch 16. The WLL interface 32 is typically expected to conform to DS-1 or E-l specifications, with system specific signaling and O&M communications with the BTS 14, and signaling communications (e.g., to setup/tear-down calls) with the WLL subscribers. The VSAT interface 34 is also expected to conform to digital DS-1 or E-l specifications, and implement system specific signaling and O&M communications to the Network Control Center, e.g., for call setup/tear-down, and in-band signaling with the remote node, e.g., during the call. The cross connect 36 provides for the interconnection of the time slot resources on the external WLL/VSAT interface as well as to other switch resources such as the TRAU 38 and the F-IWF/D-IWF 40. It should be noted that the cross-connect 36 is required to support sub-rate (e.g., 16 Kbit/s) switching.

As noted earlier, an implementation could combine the WLL-BTS and/or the VSAT modem function into the WLL/VSAT switch 16.

The Switch Controller 30 is responsible for interpreting the signaling exchange with the WLL subscriber 50 (via the BTS) and for determining whether an incoming call is local (i.e., switched to another WLL subscriber at the site) or long distance (either to a PSTN subscriber or to a WLL subscriber at another site). As shown in Figure 3a, for local calls, the IWVS switches the call through the TRAU function and then back out through the WLL interface to WLL BTS, and thence to the second subscriber.

If a data/fax call is detected, the F-IWF/D-IWF is introduced in the traffic path instead of the transcoder 38. It should be noted that it may also be possible to bypass the TRAU 38 and F-IWF/D-IWF functions for a local call depending upon the WLL system that is being used, as is illustrated in Fig. 3b.

Figs. 4a and 4b show the path associated with a "long distance" voice call that is placed by the WLL subscriber in communication with the WLL BTS 14. In this scenario, the IWVS 16 at the subscriber site does not introduce the TRAU function 38 in the traffic path. At the remote end, where the call is destined to a

PSTN subscriber via the PSTN gateway station 20 (Fig. 4a), the TRAU 120 provides for the voice compression/decompression functions. If the remote station is another WLL/VSAT node, then depending upon the WLL technology, the same technique may be applied as described above with reference to Fig. 3b, as is illustrated in Fig. 4b.

Finally, Figure 5 shows the path associated with a "long distance" voice band facsimile or data call. In this scenario, the F-IWF or D-IWF function, along with the rate adapter function within the TRAU 138, is introduced in the traffic path only at the PSTN gateway node 12.

Claims

What is claimed is:

1. An interconnection system for connecting calls from a first subscriber in first communications system to one of a plurality of second subscribers, said system comprising: a first interface between said interconnection system and said first communications system; a second interface between said interconnection system and a second communications system; a transcoder and rate adaptation unit (TRAU); and a connection element for selectively connecting calls from said first subscriber through said TRAU or bypassing said TRAU depending on the destination of said call.

2. An interconnection system according to claim 1, wherein said first communications system comprises a wireless local loop (WLL) system and wherein at least one of said second subscribers is in a second communications system connectable to said first communications system via a satellite link, said interconnection system bypassing said TRAU and connecting said calls to said second interface for calls destined to said second subscriber.

3. An interconnection system according to claim 1, wherein said first communications system comprises a wireless local loop (WLL) system and wherein at least one of said second subscribers is in a second communications system connectable to said first communications system via a satellite link, said interconnection system further including a second TRAU between said satellite link and said second communications system, said interconnection system bypassing said first TRAU and connecting said calls to said second interface for calls destined to said second subscriber.

4. An interconnection system according to claim 3, wherein said interconnection system switches said call through said second TRAU unit when a call destined for said second subscriber bypasses said first TRAU.

5. A system for connecting calls from a first subscriber in a first communications system through a satellite channel to a second subscriber in a second communications system, said system comprising: a first interface for receiving calls from said first subscriber; a second interface for passing calls to said satellite channel; a first transcoder and rate adaptation unit (TRAU) between said first subscriber and said satellite channel; a second transcoder and rate adaptation unit between said satellite channel and said second subscriber; a connection element for connecting said call through only one of said TRAU's .

6. An interconnection system according to claim 1, further comprising a facsimile/data interworking function, said connection element selectively connecting calls from said first subscriber through said facsimile/data interworking function or bypassing said facsimile/data interworking function depending on the destination of said call.

7. An interconnection system for connecting facsimile data calls from a first subscriber in first communications system to one of a plurality of second subscribers, said system comprising: a first interface between said interconnection system and said first communications system; a second interface between said interconnection system and a second communications system; a facsimile/data interworking unit; and a connection element for selectively connecting calls from said first subscriber through said facsimile/data interworking unit or bypassing said facsimile/data interworking unit depending on the destination of said call.

8. An interconnection system according to claim 7, wherein said first communications system comprises a wireless local loop (WLL) system and wherein at least one of said second subscribers is in a second communications system connectable to said first communications system via a satellite link, said interconnection system bypassing said facsimile/data interworking unit and connecting said calls to said second interface for calls destined to said second subscriber.

9. An interconnection system according to claim 7, wherein said first communications system comprises a wireless local loop (WLL) system and wherein at least one of said second subscribers is in a second communications system connectable to said first communications system via a satellite link, said interconnection system further including a second facsimile/data interworking unit between said satellite link and said second communications system, said interconnection system bypassing said first facsimile/data interworking unit and connecting said calls to said second interface for calls destined to said second subscriber.

10. An interconnection system according to claim 9, wherein said interconnection system switches said call through said facsimile/data interworking unit when a call destined for said second subscriber bypasses said first facsimile/data interworking unit.

11. A system for connecting facsimile or data calls from a first subscriber in a first communications system through a satellite channel to a second subscriber in a second communications system, said system comprising: a first interface for receiving calls from said first subscriber; a second interface for passing calls to said satellite channel; a first facsimile/data interworking unit between said first subscriber and said satellite channel; a second facsimile/data interworking unit between said satellite channel and said second subscriber; a connection element for connecting said call through only one of said facsimile/data interworking units.