WO2011057674A1

WO2011057674A1 - Cell selection in a digital broadcast network

Info

Publication number: WO2011057674A1
Application number: PCT/EP2009/065169
Authority: WO
Inventors: Jani Petteri VÄRE; Miika Sakari Tupala
Original assignee: Nokia Corporation
Priority date: 2009-11-13
Filing date: 2009-11-13
Publication date: 2011-05-19

Abstract

A communication system may include a single frequency network or cell having multiple transmitting apparatuses, configured to transmit a data stream to receiving devices within respective coverage areas. The data stream may include a series of frames having preambles that indicate whether the transmitting apparatus from which it is transmitted is located in a border region towards the edge of its cell. A receiving apparatus that experiences deterioration in the signal received from a transmitter can use the indication in the preamble to determine whether to start preparations for a handover to a transmitting apparatus in a neighbouring single frequency network. In this manner, the receiving apparatus can distinguish between a potential handover situation and a temporary deterioration in the received signal from other factors, such as interference and unnecessary handover preparations may be avoided.

Description

CELL SELECTION IN A DIGITAL BROADCAST NETWORK

Description

This specification relates to a technique for transmitting data in a communication system.

A communication network may be composed of cells having multiple transmitters. For example, broadcast or multicast networks may include cells having multiple transmitters within one Single Frequency Network (SFN) area, that is, where the transmitters transmit a common signal at the same frequency. A receiving device may switch reception between transmitters in order to receive an uninterrupted service.

If the receiving device reaches a boundary between a present cell and another cell, for instance, if the strength of a signal received from a present transmitting apparatus drops below a predetermined threshold, a handover procedure may be performed to allow the receiving device to continue receiving a service via an alternative transmitting apparatus in the other cell. The receiving apparatus may perform a number of operations in order to determine whether a handover is to be initiated. For example, the receiving device may scan for signals from one or more alternative transmitting apparatuses and compare the strength of signals received from the present and alternative transmitting apparatuses. If it is determined that the signal from an alternative transmitting apparatus is preferred, the receiving device will continue receiving the service from the alternative transmitting apparatus.

According to a first aspect, an apparatus according to an embodiment of the invention comprises a receiver configured to receive at least one data stream from a first transmitting apparatus in a first cell of a communication network and a processing arrangement configured to determine, from the at least one data stream, location information of the first transmitting apparatus, to determine, based at least in part on the location information, whether a handover to a second transmitting apparatus in a second cell of the communication network is to be performed and to respond to a determination that a handover to the second transmitting apparatus is to be performed by triggering the handover.

The presence of information in the at least one data stream from which location information of the first transmitting apparatus can be determined allows the receiving apparatus to distinguish between signal deterioration caused by

approaching a cell boundary and temporary signal deterioration caused by factors such as interference. The indication data may then be used by the receiving apparatus to determine whether to perform operations in preparation for a possible handover.

The processing arrangement may be configured to determine from the location information whether the first transmitting apparatus is located at an edge of the first cell.

The processing arrangement is configured to determine the location information based on information in a preamble of at least one frame in the at least one data stream, for example, by extracting the information from the preamble of such a frame.

The processing arrangement may be configured to repeat periodically the

determination of location information and the determination of whether a handover is to be performed. This aspect also provides a method according to an embodiment of the invention, comprising receiving at least one data stream from a first transmitting apparatus in a first cell of a communication network, determining, from the at least one data stream, location information of the first transmitting apparatus, determining, based at least in part on the location information, whether a handover to a second transmitting apparatus in a second cell of the communication network is to be performed and, in response to a determination that a handover to the second transmitting apparatus is to be performed, triggering the handover. The communication network may be a digital video broadcast network and, furthermore, the location information may be extracted from PI channel signalling in a preamble of at least one frame in the at least one data stream. This aspect also provides a computer program according to an embodiment of the invention, comprising computer readable instructions that, when executed by a processing arrangement of an apparatus, cause the apparatus to perform the method and/ or a computer readable medium according to an embodiment of the invention, on which is stored such a computer program.

According to a second aspect, a system according to an embodiment of the invention comprises a first transmitting apparatus configured to transmit at least one data stream in a first cell of a communication network and a receiving apparatus comprising a receiver configured to receive at least one data stream from the first transmitting apparatus in a first cell and a processing arrangement configured to determine, from the at least one data stream, location information of the

transmitting apparatus, to determine, based at least in part on the location information, whether a handover to a second transmitting apparatus in a second cell of the communication network is to be performed and to respond to a

determination that a handover to the second transmitting apparatus is to be performed by triggering the handover.

The system may include a stream generator apparatus configured to include in the data stream information indicating whether the first transmitting apparatus is located at an edge of the first cell.

The location information may be determinable based on information in a preamble of at least one frame of the at least one data stream.

In some embodiments, the communication network may be a digital video broadcast network.

The first and second cells may be single frequency networks. According to a third aspect, another embodiment be in the form of an apparatus comprising a stream generator configured to output a data stream comprising a series of frames and to include in at least one of the frames information regarding a location of a transmitting apparatus in a cell in a communication system from which the data stream is to be transmitted.

The apparatus may be configured so that the information indicates whether the first transmitting apparatus is located at an edge of the cell of the communication system.

The data stream may be a digital video broadcast stream. In this case, the information may be included in a preamble of the one or more frames as PI channel signalling. Furthermore, the apparatus may be configured so that the preamble of the one or more frames includes P2 symbols, the PI channel signalling includes an indication of the number of P2 symbols in the at least one preamble and the indication is a number that, when multiplied by a predetermined constant, provides the number of P2 symbols. The predetermined constant may be the size of a Fast Fourier Transform (FFT) function associated with the one or more frames, for example, the size of a FFT function used in the modulation of one or more symbols in the frame.

This aspect also provides one or more of a method according to another

embodiment, comprising generating a data stream comprising a series of frames and including in the frames information regarding a location of a transmitting apparatus in a cell in a communication system from which the data stream is to be transmitted, a computer program that, when executed by a processing arrangement of an apparatus, causes the apparatus to perform the method and a computer readable medium on which is stored such a computer program.

Example embodiments of the invention will now be described, with reference to the accompanying drawings, of which: Figure 1 depicts a communications network according to an exemplary embodiment of the invention;

Figure 2 depicts portions of three cells of the communications network of Figure 1 ;

Figure 3 depicts an example of a transmitting apparatus of a cell of Figure 2;

Figure 4 depicts an example of a data stream that may be generated by the transmitting apparatus of Figure 3;

Figure 5 depicts an example of another data stream that may be generated by the transmitting apparatus of Figure 3;

Figure 6 is a flowchart depicting an example of a method of transmitting data that may be performed by the transmitting apparatus of Figure 3;

Figure 7 depicts an example of a receiving apparatus arranged to receive data from the transmitting apparatus of Figure 3; and

Figure 8 is a flowchart depicting an example of a method of receiving data that may be performed by the receiving apparatus of Figure 7.

Figures 1 and 2 depict a communications network 1, according to an exemplary embodiment of the invention, comprising cells 2a, 2b, 2c. In this example, the cells 2a, 2b, 2c are Single Frequency Network (SFN) areas and including multiple transmitting apparatuses 3a-3r, 4a-4r, 5a-5c. In other words, the transmitting apparatuses 3a-3r within a first cell 2a transmit a particular signal in a

simultaneously at a first frequency Fl, so that receiving apparatuses 6a, 6b, 6c within the first cell 2a may receive the signal from any of the transmitting apparatuses 3a-3r within their cell 2a without retuning. Meanwhile, the transmitting apparatuses 4a-4r in a second cell 2b may transmit the signal at a second frequency F2. Therefore, in this example, a receiving apparatus 6a at position C is moving from the first cell 2a to the second cell 2b. The receiving apparatus 6a receives the signal at frequency Fl from a transmitting apparatus 3m in the first cell 2a before undergoing a handover to continue receiving the signal at second frequency F2 from a transmitting apparatus 4d in the second cell 2b. Similarly, a receiving apparatus 6c moving from the first cell 2a to a third cell 2c may be handed over to a transmitting apparatus 5a of the third cell 2c that transmits the signal at a third frequency F3. The transmitting apparatuses 3a-3r, 4a-4r, 5a-5c include, or receive at least a data stream from, a stream generator apparatus. Figure 3 depicts an exemplary stream generator apparatus 7m includes an input 8 capable of receiving data 9 from a content source, not shown, and at least one output 10 through which one or more data streams 11 may be forwarded for transmission by one or more transmitting apparatuses 3a-3r, 4a-4r, 5a-5c via a second network, not shown, such as a local network or an external network such as the Internet. This particular example will be described with reference to one data stream 11. A processor 12, such as a microprocessor, controls processing of the data 8 and the generation and onward transmission of the data stream 11. While the example shown in Figure 3 includes a processing arrangement that includes only one processor 12, in other embodiments, the stream generator apparatus 7m may include a processing arrangement having more than one processor.

A frame builder module 13 is provided, which performs scheduling and data mapping functions, mapping data physical layer pipes (PLPs) to a physical layer frame. The frame builder module 13 also generates Layer 1 (LI) pre/post signalling, in the form of P2 symbols, to be described later, for inclusion in a preamble of a frame conveying the data 9.

A modulator 14 is configured to modulate the data 9 and P2 symbols received from the frame builder module 13 and to generate further preamble information, in the form of PI symbols to be described later. The modulator 14 is configured to output the data stream 11 in the form of a series of frames. Each frame may include a preamble, which in this example comprises the PI and P2 symbols, and a data portion in which the data 9 is conveyed. In this particular example, the modulator 14 is configured to generate Orthogonal Frequency Division

Multiplexing (OFDM) symbols.

A memory facility 15 is provided for storing software executed by the processor 12 and for use in processing. The incoming data 9 may be stored in a cache 16 or, if required, in an external buffer, not shown. The various components of the stream generator apparatus 7m may be connected to a data bus 17 for communication there between.

The stream generator apparatus 7m is configured to include in the data stream 11 information that indicates whether the transmitting apparatus 3a that transmits the data stream 11 is located at the edge, or border, of its cell 2a. In other words, if no other transmitting apparatus 3b-3r, 4a-4r, 5a-5c separates the transmitting apparatus 3a from a border between its cell 2a and another cell 2b, the data stream 11 transmitted by that transmitting apparatus 3a will include information indicating that the transmitting apparatus 3a is located at the edge of the first cell 2a.

In this particular example, the network 1 is a Digital Video Broadcast (DVB) network and the transmitting apparatuses 3a-3r, 4a-4r, 5a, 5b broadcast respective data streams that include a series of frames. Figure 4 depicts an example series of frames 18, 18' configured in accordance with a DVB standard. In this example each frame 18, 18' includes a preamble 19, 19' and a data portion 20, 20'. The data portion 20, 20' includes data which may correspond to a number of services, while the PI and P2 symbols 19a, 19b in the preamble 19, 19' may provide information such as the locations of the different services inside the data portion 20, 20' of the frame 18, 18'.

In this example, the PI symbols 19a, 19b and P2 symbols 19c carry layer one (LI) signalling. The PI symbols may carry information regarding the timing, frequency offset and the size of a Fast Fourier Transform (FFT) function associated with the frames 19, 19' in the data stream 11, such as a FFT used in the modulation of one or more symbols, such as data symbols and/or pilot symbols, in the frames 19, 19'. The PI symbols may also be used by a receiving apparatus 6a, when performing an initial band scan, to detect the signal from the transmitting apparatus 3a carrying the data stream 11. Meanwhile, the P2 symbols may convey information for use by a receiving apparatus 6a when performing fine frequency and timing synchronization and/ or initial channel estimation. Alternatively, or additionally, P2 symbols may carry further signalling information and may also be used to carry data. As shown in Table 1 below, a first one of the PI symbols 30a includes a SI field, which may include information regarding the format of the preamble 19 and a S2 field indicating FFT size and whether the preambles 19, 19' of the frames 18, 18' are of mixed type. The preamble format may depend on the type of the communication network 1, for instance, whether it is configured in accordance with the Digital Video Broadcast Second Generation Terrestrial (DVB-T2) standard or a standard with certain similarities, such as the proposed Digital Video Broadcast Next Generation Handheld (DVB-NGH) standard. The preamble format may also depend on the multi-antenna scheme used in the cell 2a, such as Single-Input- Single-Output (SISO), Multiple-Input-Single-Output (MISO) or Multiple-Input- Multiple-Output (MISO). Certain schemes may relate to an arrangement of m transmitting apparatuses and n antennas in the receiving apparatus. Where such an arrangement is one of a plurality of possible configurations, this is indicated by "m x n" in the definitions in Table 1.

Table 1

Field Meaning Value Definition

SI P2_TYPE, indicating 000, T2_SISO,

preamble format 001, T2_MISO,

010, NGH_SISO,

011, NGH_MISO,

100, NGH_MIMO_2x2,

101, NGH_MIMO_4x2,

110, Reserved,

111. Reserved.

S2 FFT-SIZE, when the OOOx to l l lx. Ik, 2k, 4k, 8k, 16k or

value of SI is any of 32k.

000 to 101

MIXED_BIT, xxxO, Not mixed,

indicating whether xxx 1. Mixed.

preambles 30, 30' are

of mixed type In the example, some of the field values in Table 1 are reserved values, which may be used to provide further definitions/ extensions if required.

In this example, the preamble 19 includes another PI symbol 19b, having a SI field that indicates number of P2 symbols 19c in the preamble 19 and a S2 field that includes guard interval information and cell edge information as shown in Table 2. The number of P2 symbols 19c may be indicated explicitly. However, in this example, the number of P2 symbols 19c is conveyed in the form of a number that can be multiplied by an integer that is dependent on FFT_SIZE, in order to obtain the number of P2 symbols 19c. Meanwhile, the cell edge information is a single bit, taking the value 0 or 1 depending on whether the transmitting apparatus 3a is located at a cell edge.

Table 2

Field Meaning Value Definition

SI P2_LENGTH, from 000 - 111 1-8

which the number of

P2 symbols may be

calculated

S2 GUARD_INTERVAL, OOOx, 1 /32,

indicating guard OOlx, 1 /16,

interval fraction OlOx, 1 /8,

Ol lx, 1 /4,

lOOx, 1 /128,

lOlx, 19/128,

11 Ox, 19/256,

l l lx. Reserved.

CELL_EDGE/ xxxO, NO_CELL_EDGE,

NO_CELL_EDGE, Transmitting apparatus indicating cell edge is not at cell edge, information. xxxl.

CELL_EDGE,

Transmitting apparatus is at cell edge. Figure 5 depicts an example data stream 11 ' according to another embodiment of the invention, which comprises a series of frames 21, 21 ' that are configured in accordance with a second standard that is different to the standard to which the network 1 conforms. The frames 21, 21 ' include further signalling specific to the second standard.

As in the previous example, the frames 21, 21 ' include a preamble 22, 22', with PI and P2 symbols 22a, 22b, 22c and a data portion 23, 23'. In this particular example, the frames are configured in accordance with the currently proposed Digital Video Broadcast Next Generation Handheld (DVB-NGH) standard and signalling specific to that standard is transmitted in a field 23a in the data portion 23, separate from the PI and P2 symbols 22a, 22b, 22c of the preamble 22.

The number of symbols in the field 23a may be indicated by PI symbols 22a or 22b in the preamble. For instance, the number of P2 symbols 22c may be derivable from the FFT size, which is conveyed in the S2 field of a first PI symbol 22a.

Therefore, in some embodiments of the invention, the second PI symbol 22b need not include the number of P2 symbols P2_LENGTH, since this information may be redundant. In this case, the S2 field of the second PI symbol 22b may instead indicate the number of symbols relating to the second standard,

NGH_L1_LENGTH, in the field 23a. If required, the parameter

NGH_L1_LENGTH may convey the number of symbols relating to the second standard explicitly or in the form of a number to be multiplied by a constant dependent on the FFT size in order to obtain the number of symbols in field 23a.

The provision of a separate signalling field 23a for symbols specific the second standard can, in effect, increase the number of symbols 22a, 22b, 23a used to convey preamble information in the frames 21, 21 ', when compared with the example frames 18, 18' of Figure 4, without sacrificing compatibility with other DVB systems. For example, the frames 21, 21 ' may be compatible with a DVB-T2 system, while including signalling, in field 23a, relating to a second standard such as DVB-NGH. An example procedure for generating a data stream 11 that may be performed by the stream generator apparatus 7m will now be described, with reference to Figure 6. Beginning at step s6.0, data 9 is received via the input 8 (step s6.1) and is mapped to a data portion 20 of a physical layer frame 18 (step s6.2) by the frame builder module 13. The frame builder module 13 then generates the P2 symbols 19c (step s6.3). The data portion 20 and P2 symbols 19c are then modulated (step s6.4). The PI symbols 19a, 19b are then generated (step s6.5), with one symbol 19b including the cell edge information. The PI symbols are inserted into a frame 18 (step s6.6) with the modulated P2 symbols 19c and data portion 20. If the frames 21 has the format shown in Figure 5, DVB-NGH specific signalling may be included in an additional, dedicated, field 23a. The resulting frame 18, 21 is then forwarded for transmission by a transmitting apparatus 3m in data stream 11, 11 ' (step s6.7), completing the procedure (step s6.8).

An example of a receiving apparatus 6a is shown in Figure 7. The receiving apparatus 6a supports at least one antenna 24 and a receiver 25, operable to receive the data stream 11, 11 ' from the network 1. While only one antenna 24 is shown in Figure 7, in other embodiments, the receiving apparatus 6a may comprise or be configured to be connected to several antennas.

A demodulator 26 is configured to process and extract the data 9 relating to a particular content item or service from the received data stream 11, under the control of a processor 27. The demodulator 26 is configured to decode the PI symbols 19a, 19b, 22a, 22b of a received frame 18, 21 and to use the preamble information obtained from those PI symbols to decode the corresponding P2 symbols 19c, 22c and obtain the Ll-pre/post signalling. The information obtained from the P2 symbols 19c, 22c may then be used to decode and process the data portion 20, 23 to obtain the data 9.

While only one processor 27 is shown in Figure 6, in other embodiments, the receiving apparatus 6a may be provided with a multi processor arrangement.

A memory facility 28 is provided for storing software executed by the processor 27 and for use during processing respectively.

A user interface may be provided. In this example, the receiving apparatus 6a includes a user interface having a keypad 29, through which a user may input commands, together with a display 30 and a speaker 31 that may present

information and received multimedia content under the control of the processor 27. In another embodiment, the receiving apparatus 6a may include a user interface comprising a touch-screen display or a touch-sensitive area.

In this particular example, the receiving apparatus 6a is powered by a battery 32. Charging circuitry, not shown, may be included to facilitate recharging of the battery 32.

The receiving apparatus 6a may include features relating to other functionality. For example, the receiving apparatus 6a may be a mobile telephone handset, a smartphone or similar device, in which case other conventional features of mobile telephone handsets, such as a microphone, a second antenna and a transceiver configured to transmit and receive voice data over a telephone network may be included. The receiving apparatus 6a may be a mobile terminal including other features depending on its required functionality. Such other features are omitted from Figure 7 for the sake of clarity.

As noted above, in this particular example the cells 2a, 2b, 2c are SFNs and a receiving apparatus 6a can receive the data stream 11 from the transmitting apparatuses 3a-3r within a particular cell 2a without retuning. For example, if the receiving apparatus 6a follows a path 33 between points A, B & C, as shown in Figure 1, the receiving apparatus 6a may receive the data stream 11 from

transmitting apparatuses 3g, 3k, 31 and 3m without interruption. However, at position C, the receiving apparatus crosses into cell 2b and must be handed over to a transmitting apparatus 4d in order to continue receiving the service. The receiving apparatus 6a may then continue to position D, where it receives the data stream 11 from transmitting apparatus 4e, without retuning.

As the receiving apparatus 6a moves away from the transmitting apparatus 3a-3r from which it currently receives the data stream 11, the signal should deteriorate and a handover may be required in order for a service to continue being received. The receiving apparatus 6a may be configured to determine when such a handover is required and to prepare for it automatically. For example, one of, or a combination of any of, the receiver 25, demodulator 26 and processor 27 may be configured to monitor the strength and/ or quality of the received signal. However, temporary signal deterioration may be caused by factors other than the distance between the receiving apparatus 6a and a current transmitting apparatus 3a-3r. For example, a signal received by the receiving apparatus at position A may be affected by temporary interference, such as multipath interference, or be otherwise temporarily obstructed, causing a temporary deterioration in the signal when no handover is required. The inclusion of cell edge information CELL_EDGE/ NO_CELL EDGE in the preamble 19, 22 of the frames 18, 21 provides an additional check regarding the potential need for a handover and may, therefore, avoid handover preparations being carried out unnecessarily.

An example handover monitoring procedure performed by the receiving apparatus 6a when receiving a service from a data stream 11 will now be described with reference to Figure 8. Starting at step s8.0, the receiving apparatus 6a receives a data stream 11 (step s8.1) that, in this example, comprises at least one frame 18 and determines whether a check for cell edge information is required (step s8.2). For example, instead of checking the cell edge information in each received frame 18, 18', the decoder 26 and/ or the processor 27 may be configured to check for cell edge information periodically, after a predetermined time interval has elapsed or after a

predetermined number of frames 18, 18' have been received since a previous check was performed. If a cell edge check is not required (step s8.2), steps s8.1 and s8.2 are repeated for one or more further frames, until it is determined at step s8.2 that a cell edge check is to be performed. If a cell edge check is required (step s8.2), the PI symbols 19a, 19b are decoded (step s8.3) and the processor 27 determines whether the current transmitting apparatus 3a-3r is at a cell edge the value of the cell edge information field is determined (step s7.4). If the cell edge information corresponds to

"NO_CELL_EDGE" (step s7.4), for example, if the receiving apparatus 6a is at position A or B in cell 2a, the procedure returns to step s8.1 and the receiving apparatus 6a continues to receive frames from a transmitting apparatus 3a-3r within the current cell 2a.

If the cell edge information corresponds to "CELL_EDGE" (step s8.4), for example, if the receiving apparatus 6a is at position B in cell 2a, handover monitoring is performed (steps s8.5, s8.6, s8.7, s8.8). For instance, one or more of the receiver 25, decoder 26 and processor 27 may monitor the strength and/or quality of the signal received from the current transmitting apparatus 3i in order to determine whether a handover is required (step s8.6).

If a handover is not required (step s8.6), the receiving apparatus 6a continues receiving the data stream 11 (step s8.7) from the current transmitting apparatus and performing cell edge checks (step s8.8, s8.3, s8.4) and handover monitoring (step s8.5, s8.6), until it is determined at step s8.6 that a handover is required or until it is determined at step s8.4 that the receiving apparatus 6a is no longer receiving the data stream from a transmitting apparatus at the edge of the current cell 2a. For example, if a receiving apparatus 6a at position B returned to position A, handover monitoring could be stopped as the receiving apparatus 6a moves from a coverage area of transmitting apparatus 3i into the coverage area of transmitting apparatus 31, based on the cell edge information obtained from the PI symbol 19b.

If it is determined that a handover is required (step s8.6), the receiving apparatus 6a prepares for a handover (step s8.9). For example, the receiving apparatus 6a may scan for signals from nearby transmitting apparatuses 3i, 3m, 3p, 4a, 4d, comparing the strength and/ or quality of signals from those transmitting apparatuses and selecting a new transmitting apparatus 4a accordingly. The receiving apparatus 6a may then tune to the frequency at which the new transmitting apparatus 4a transmits its data stream 11, 11 ', synchronise with the new transmitting apparatus 4a and continue to receive the service via a data stream transmitted by the new transmitting apparatus 4a (step s8.10).

In the embodiments described above, unnecessary handover preparations, such as scanning for signals from alternative transmitting apparatuses and/or obtaining signal quality measurements may be avoided. This potentially reduces unnecessary use of processing resources and/or waste of battery power in a receiving apparatus 6a, 6b, 6c. The above described embodiments are intended as examples only. For instance, while the location information in the preambles 19, 19', 22, 22' of the frames 18, 18', 21, 21 ' described above include a field having a value CELL_EDGE or

NO_CELL_EDGE that indicates whether a transmitting apparatus 3a-3r, 4a-4r, 5a- 5c is located at the edge of a cell 2a, 2b, 2c, other embodiments of the invention may be devised in which the format of the frames in a data stream indicate the location of the transmitting apparatus. For example, in some embodiments, transmitting apparatuses located at a cell edge, such as transmitting apparatuses 3a, 3b, 3e, 3i, 3m and so on in cell 2a of Figure 1, may be arranged to transmit a data stream having frames that include an indication that the transmitting apparatus is at a cell edge while transmitting apparatuses that are not at a cell edge, such as transmitting apparatuses 3d, 3g, 3h, 3k, 31, 3o in Figure 1, may be arranged to transmit a data stream having frames that do not include such an indicator.

Alternatively, the transmitting apparatuses 3d, 3g, 3h, 3k, 31, 3o that are not at the cell edge may transmit a data stream having frames with an indicator that the transmitting apparatus is not at a cell edge while the transmitting apparatuses 3a, 3b, 3e, 3i, 3m and so on located at cell edges transmit frames that do not include an indication. In such arrangements, the location information is conveyed by the presence or absence of the indicator. In other words, the format of the frames transmitted by the transmitting apparatuses 3a-3r may convey the location information.

In the above examples, the location information is included in the preambles 19, 19', 22, 22' of frames 18, 18', 21, 21 ' of a data stream 11, 11 '. However, in another example, the location information might be provided elsewhere in the frame, for example, following a data portion 20, 20', 22, 22'.

In each of the examples discussed above, the location information is included in each frame 18, 18', 21, 21 ' of a data stream 11, 11 '. However, in yet another other example, a data stream may be configured with such location information included in some, but not all, of the frames in a data stream.

While the example in Figure 5 was described in relation to a data stream 11 ' configured in accordance with the currently proposed DVB-NGH standard for compatibility with a DVB-T2 system, the provision of an additional field 23a for standard specific signalling may be used in data streams configured according to other standards and/ or for compatibility with other types of network. While the network 1 shown in Figure 1 is a DVB network that broadcasts the data stream 11, the above described method can be utilised in other types of

communication network having multiple transmitting apparatuses are used to transmit data within a cell, single frequency network or coverage area. Examples of such networks include digital broadcast networks, for example, a DVB network, an Integrated Services Digital Broadcasting (ISDB) network or a China Multimedia Broadcasting (CMMB) network, cellular communication networks such as mobile telephone networks and so on.

In the above examples, the data stream 11 is broadcast by the transmitting apparatuses 3a-3r, 4a-4r, 5a-5c. In some embodiments of the invention, the data stream 11 may be broadcast, multicast or even unicast, depending on the application. As noted above, the embodiments have been described with reference to one data stream 11. However, the stream generator apparatus 7m may be configured to generate more than one data stream 11. Meanwhile, one or more of the transmitting apparatuses 3a-3r, 4a-4r, 5a-5c may transmit multiple data streams 11. Also, one or more of the receiving apparatus 6a, 6b, 6c may be configured to receive such multiple data streams 11.

Claims

1. An apparatus comprising:

a receiver configured to receive at least one data stream from a first transmitting apparatus in a first cell of a communication network; and

a processing arrangement configured to determine, from the at least one data stream, location information of the first transmitting apparatus, to determine, based at least in part on the location information, whether a handover to a second transmitting apparatus in a second cell of the communication network is to be performed and to respond to a determination that a handover to the second transmitting apparatus is to be performed by triggering the handover.

2. An apparatus according to claim 1, wherein the processing arrangement is configured to determine from the location information whether the first

transmitting apparatus is located at an edge of the first cell.

3. An apparatus according to claim 1 or 2, wherein the processing arrangement is configured to determine the location information based on information in a preamble of at least one frame in the at least one data stream.

4. An apparatus according to claim 3, wherein the processing arrangement is configured to extract the location information from the preamble of at least one frame in the at least one data stream.

5. An apparatus according to any of the preceding claims, wherein the communication network is a digital video broadcast network.

6. An apparatus according to any preceding claim, wherein the processing arrangement is configured to repeat periodically the determination of location information and the determination of whether a handover is to be performed.

7. A method comprising:

receiving at least one data stream from a first transmitting apparatus in a first cell of a communication network;

determining, from the at least one data stream, location information of the first transmitting apparatus;

determining, based at least in part on the location information, whether a handover to a second transmitting apparatus in a second cell of the communication network is to be performed; and

in response to a determination that a handover to the second transmitting apparatus is to be performed, triggering the handover.

8. A method according to claim 7, wherein the determining of the location information comprises determining whether the first transmitting apparatus is located at an edge of the first cell.

9. A method according to claim 7 or 8, wherein the determination of the location information is based on information in a preamble of at least one frame in the at least one data stream.

10. A method according to claim 7, 8 or 9, wherein the communication network is a digital video broadcast network and the location information is extracted from PI channel signalling.

11. A method according to any of claims 7 to 10, comprising periodically repeating the determination of location information and the determination of whether a handover is to be performed.

12. A computer program comprising computer readable instructions that, when executed by a processing arrangement of an apparatus, cause the apparatus to:

receive at least one data stream from a first transmitting apparatus in a first cell of a communication network;

determine, from the at least one data stream, location information of the transmitting apparatus; determine, based at least in part on the location information, whether a handover to a second transmitting apparatus in a second cell of the communication network is to be performed; and

in response to a determination that a handover to the second transmitting apparatus is to be performed, trigger the handover.

13. A computer readable medium on which is stored a computer program according to claim 12.

14. A system comprising:

a first transmitting apparatus configured to transmit at least one data stream in a first cell of a communication network; and

a receiving apparatus comprising a receiver configured to receive at least one data stream from the first transmitting apparatus in a first cell and a processing arrangement configured to determine, from the at least one data stream, location information of the transmitting apparatus, to determine, based at least in part on the location information, whether a handover to a second transmitting apparatus in a second cell of the communication network is to be performed and to respond to a determination that a handover to the second transmitting apparatus is to be performed by triggering the handover.

15. A system according to claim 14, comprising a stream generator apparatus configured to include in the data stream information indicating whether the first transmitting apparatus is located at an edge of the first cell.

16. A system according to claim 14 or 15, wherein the location information can be determined based on information in a preamble of at least one frame in the at least one data stream.

17. A system according to claim 14, 15 or 16, wherein the communication network is a digital video broadcast network.

18. A system according to any of claims 14 to 17, wherein the first and second cells are single frequency networks.

19. An apparatus comprising:

a stream generator configured to output a data stream comprising a series of frames and to include in one or more of the frames information regarding a location in a cell of a communication system of a transmitting apparatus from which the data stream is to be transmitted.

20. An apparatus according to claim 19, wherein the information included in the frame indicates whether the transmitting apparatus is located at an edge of the cell of the communication system.

21. An apparatus according to claim 19 or 20, wherein the data stream is a digital video broadcast stream.

22. An apparatus according to claim 19, 20 or 21, wherein the information is included in a preamble of the one or more frames.

23. An apparatus according to claim 22, wherein the information included in the preamble of the one or more frames is included as PI channel signalling.

24. An apparatus according to claim 23, wherein the preamble of the one or more of the frames includes one or more P2 symbols, the PI channel signalling includes an indication of the number of P2 symbols in the preamble and the indication is a number that, when multiplied by a predetermined constant, provides the number of P2 symbols.

25. An apparatus according to claim 24, wherein the predetermined constant is the size of a Fast Fourier Transform function associated with the one or more frames.

26. A method comprising:

generating a data stream comprising a series of frames; and

including in the data stream at least one frame comprising information regarding a location of a transmitting apparatus in a cell in a communication system from which the data stream is to be transmitted.

27. A method according to claim 26, wherein the information included in the at least one frame indicates whether the transmitting apparatus is located at an edge of the cell of the communication system.

28. A method according to claim 26 or 27, wherein the data stream is a digital video broadcast stream and the information is included in a preamble of the at least one preamble as PI channel signalling.

29. A computer program comprising computer readable instructions that, when executed by a processing arrangement of an apparatus, causes the apparatus to: generate a data stream comprising a series of frames; and

include in at least one of the frames information regarding a location of a transmitting apparatus in a cell in a communication system from which the data stream is to be transmitted.

30. A computer readable medium on which is stored a computer program according to claim 29.

31. An apparatus comprising:

receiving means for receiving at least one data stream from a first transmitting apparatus in a first cell of a communication network; and

processing means for determining, from the at least one data stream, location information of the first transmitting apparatus, determining, based at least in part on the location information, whether a handover to a second transmitting apparatus in a second cell of the communication network is to be performed and, in response to a determination that a handover to the second transmitting apparatus is to be performed, triggering the handover.

32. An apparatus comprising:

means for outputting a data stream comprising a series of frames; and means for including in one or more of the frames information regarding a location of a transmitting apparatus in a cell in a communication system from which the data stream is to be transmitted.