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0 TRANSMITTING DATA TO A DUAL-MODE COMMUNICATION UNIT Field of the Invention This invention relates to radio broadcast systems and cellular radio communication systems. This invention also relates to a dual-mode communication unit or terminal which can operate on both such systems.
Background of the Invention In the field of this invention it is known that broadcast systems such as digital video broadcast (DVB) and digital audio broadcast (DAB) are able to deliver data to a communication unit such as a remote terminal. In order to deliver that data some redundancy in the form of forward error correction (FEC) is applied to the data stream. The FEC has to be sufficiently strong that the remote terminal has an excellent chance of receiving the data plus redundancy and recovering the original data without bit errors. Generally speaking the redundancy applied in the form of the FEC is in almost all circumstances wasteful of bandwidth as the FEC is overdimensioned for all but the most extreme remote terminal receiver scenarios. Broadcast systems have no return path and consequently there is no scope for reducing the FEC redundancy and substituting an (automatic repeat request) ARQ form of redundancy on an as needed basis.
FEC and ARQ schemes are well known in the art and are both exploited in 2-way radio systems, such as cellular systems.
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" iii However, a disadvantage of the current broadcast system is that because of the absence of ARQ, the FEC must be overdimensioned for the majority of remote terminal receiver scenarios. This is wasteful of bandwidth and therefore wasteful of scarce spectrum resources. This wastefulness prevents other content from being delivered.
It would therefore be desirable to provide ARQ for broadcast data such that the abovementioned disadvantages may be alleviated.
Statement of Invention In accordance with a first aspect of the present invention there is provided a method of transmitting data to a dual-mode communication unit, as claimed in claim 1.
In accordance with a second aspect of the present invention there is provided a radio broadcast method of transmitting data to a dual-mode communication unit, as claimed in claim 17.
In accordance with a third aspect of the present invention there is provided a method of operating a cellular radio communication system, as claimed in claim 30.
In accordance with a fourth aspect of the present invention there is provided a method of operating a cellular radio communication system, as claimed in claim 33.
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'v In accordance with a fifth aspect of the present invention there is provided a method of receiving data in a dual-mode communication unit, as claimed in claim 34.
In accordance with a sixth aspect of the present invention there is provided apparatus for a dual-mode communication unit, as claimed in claim 44.
In accordance with a seventh aspect of the present invention there is provided a dual-mode communication unit, as claimed in claim 54.
In accordance with an eighth aspect of the present invention there is provided a radio broadcast system, as claimed in claim 55.
In accordance with a ninth aspect of the present invention there is provided a cellular communication system, as claimed in claim 56.
In accordance with a tenth aspect of the present invention there is provided a storage medium storing processorimplementable instructions, as claimed in claim 57.
Further aspects of the present invention are as claimed in the dependent claims.
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Brief Description of the Drawings Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 shows a block diagram illustrating application ofFEC to data; FIG. 2 shows a block diagram illustrating a combined broadcast/cellular system; FIG. 3 shows a block diagram illustrating coupled broadcast and cellular systems; and FIG. 4 is a flowchart showing the process steps performed by a communication unit in an embodiment of the present invention.
Description of Preferred Embodiments In FIG. 1, the application of forward error correction to a block of raw data (100) is shown. When the FEC algorithm is applied (110) to the block of raw data (100), the output is a block of FEC encoded data (120). There are many FEC schemes, both block based and stream based. These are well known to the art and this invention applies equally regardless of the FEC algorithm chosen. The main characteristic of applying the FEC is that the output contains more bits than the input. This is
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D represented by the notation F (n) > n, in FIG. 1 where n is the block size in number of bits of the block of raw data (100).
In FIG. 2 is shown a combined Broadcast/Cellular system (200) comprising a hybrid core network (205) which serves and is coupled to both a broadcast access network (210) and a cellular access network (220). These access networks are well known in the art and typically comprise base stations, antenna masks, amplifier means, processing means and information distribution means (all not shown). The broadcast access network (220) and the parts of the hybrid core network (200) responsible for broadcast together constitute a radio broadcast system. The broadcast access network (210) provides a broadcast radio interface (240). The cellular access network (210) and the parts of the hybrid core network (200) responsible for cellular operation together constitute a cellular radio communication system. The cellular access network (220) provides a cellular radio interface (230). In this embodiment the cellular communication system is a Universal Mobile Telephone Standard (UMTS) system, although the invention may be applied to any suitable cellular system.
One or more communication units or remote terminals (250, in this embodiment a mobile telephone, is able to access both the broadcast radio interface (240) and the cellular radio interface (230).
In FIG. 3 is shown an alternative arrangement of a combination system (300) comprising a broadcast system coupled to a cellular system. In this instance there is a separate cellular core network (305) coupled to a separate broadcast core network (310) by means of a link (320), which in this example is a direct access landline. The cellular core network (305)
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I is coupled to the cellular access network (220), and together these constitute a cellular radio communication system. The broadcast core network (310) is coupled to the broadcast access network (210), and together these constitute a radio broadcast system. The remaining elements of FIG. 3 are as described in FIG. 2.
In this embodiment the broadcast system transmits blocks of data by broadcasting over the broadcast radio interface 240.
The broadcast system additionally feeds the blocks of data to the cellular communication system, in the example of FIG. 2 by means of internal transfer of data in the hybrid core network (200), and in the example of FIG. 3 by means of feeding the data by means of the link (320).
The process steps performed by the remote terminal (250) are shown in FIG. 4. In this example the FEC is a block-based FEC and the ARQ is a stop and wait style ARQ. Both are well known in the art. It will be evident to those skilled in the art that alternative FEC and ARQ schemes may be used instead. The remote terminal (250) receives (step 410) a block of encoded data (120) via the broadcast radio interface (240). The remote terminal then applies the FEC decoding algorithm (step 420) to derive an estimate of the original block of raw data (100).
The remote terminal then applies an error detection algorithm (step 430) to determine if the estimate derived from step 420 is an accurate representation of the original raw data (100).
This is therefore an example of an FEC schemes that provides error detection capabilities. Alternatively a specific Cyclic Redundancy Check (CRC) may be performed on a checksum value which is included in the original block of raw data (100).
CRCs and checksums are well known in the art and do not need
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toll to be further described herein. If the remote terminal does not detect errors (step 440) the data is accepted. If there is no more data to be received (step 450) the process ends. If there is more data to be received (step 450) the remote terminal receives (step 410) the next block of encoded data.
If, however, at step 440 the remote terminal detected an error in the estimate of the block of raw data, the remote terminal requests (step 470) correction data, in the correction data in this embodiment being retransmission of the erroneously received block of data. This request is transmitted using the cellular radio interface (230) to the cellular communication system. The cellular communication system then re-transmits the requested block of data to the remote terminal (250) via the cellular radio interface (230). Meanwhile, the remote terminal waits for and then receives (step 480) this ARQ retransmission. In a different embodiment, the ARQ retransmission may instead be delivered using the broadcast radio interface (240). Once the ARQ retransmission has been received the remote terminal continues with the decoding process (step 420) and following functions in conventional fashion.
It will be evident that, by repeatedly implementing the method described with reference to FIG. 4, the delivery of a stream of data via the broadcast radio interface need not be interrupted and that the same data may be received via the broadcast radio interface (240) by a huge number of independent remote terminals conforming to this invention, with the respective ARQ requests of the individual remote terminals being supported via the cellular system.
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In the above embodiments, the remote terminal (250) may distinguish between, and either operate both, or control switching between, a radio broadcast receipt mode and a cellular radio receipt mode, and vice-versa, by any appropriate known method. One preferred way is to provide two receive chains operating in parallel, one operating on the broadcast interface and the other on the cellular interface.
In a preferred embodiment, in the remote terminal (250) the stream of broadcast blocks of data is passed through a buffer before being released to whatever the application the data is for. This buffer holds sufficient information to allow the ARQ to operate prior to the data being released to the application in the remote terminal (250). The delay caused by doing this is usually no longer in the time domain than would have been the case had the ARQ protocol been effected over the radio broadcast system.
In this embodiment the data being transmitted to the remote terminal 250 is software for downloading to the terminal 250 i. e. the mobile telephone constituting the terminal 250 in this embodiment is a software-defined radio. However, the invention is applicable to any data required to be transmitted to a remote terminal or other communication unit, including for example DVB and/or DAB content.
As a further advantage, the operator of the broadcast system may vary the FEC applied according to the rate of ARQ requests arriving via the cellular system. A high level of ARQ requests would indicate that there is insufficient FEC redundancy being applied. The amount of FEC redundancy may be set at a level which minimises the overall cost of delivering the data taking
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I a into account the cost of the FEC redundancy on the broadcast system and the cost of the ARQ load on the cellular system.
In the above embodiments, the correction data requested by and sent to the remote terminal (250) comprised are-transmitted copy of the erroneously received block of data. In other embodiments, the correction data may instead comprise additional redundancy sufficient for the communication unit to calculate missing data in combination with the originally received data.
In the above embodiments, the communication unit (i. e. the remote terminal 250) was a mobile telephone with broadcast receipt functionality. In other embodiments, the communication unit may be another form of equipment, such as a personal organiser or primarily a DVB and/or DAB player with additional mobile telephony functionality. Indeed, the unit may even be, say, a DVB and/or DAB player whose only mobile telephony functionality is the ability to send the above described correction requests and receive the above described correction data.
Apparatus for implementing the above described arrangements and performing the above described processes is provided by adapting conventional apparatus and/or providing additional modules to the remote terminal (250), the broadcast system and the cellular communication system as appropriate. In the case of the broadcast system and the cellular communication system, additional apparatus may be provided at any one or any combination (e. g. in distributed form) of the elements shown in FIGS. 2 and 3, or in other elements in other network arrangements. The apparatus may be in the form of hardware,
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. 11 firmware, or software, or a combination of these. The apparatus may comprise one or more processors, for implementing instructions and using data stored in a storage medium such as a computer disk or PROM.
It will be understood that the use of mobile cellular system to provide ARQ for broadcast data described above tends to provide the following advantages: * Ability to deliver more content over the broadcast radio interface.
* Improved efficiency of the broadcast interface.
* Improved exploitation of strengths and advantages of a custom designed broadcast system and strengths and advantages of a custom designed cellular system.