Title

Transmissions in wireless systems

This disclosure relates to transmissions in wireless systems, and more particularly transmissions in single frequency networks, for example of broadcast and/or multicast services.

A communication system can be seen as a facility that enables communications between two or more nodes such as fixed or mobile communication devices, access points such as base stations, servers and so on. A communication system and compatible communicating entities typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the standards, specifications and related protocols can define the manner how communications between communication devices and the access points shall be arranged, how various aspects of the communications shall be implemented and how the equipment shall be configured.

Signals can be carried on wired or wireless carriers. Examples of wireless systems include public land mobile networks (PLMN) such as cellular networks, satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). Wireless systems can be divided into coverage areas referred to as cells, and hence the wireless systems are often referred to as cellular systems. A base station can provide one or more cells, there being various different types of base stations and cells. A user can access the communication system by means of an appropriate communication device or terminal. A communication device is provided with an appropriate signal receiving and transmitting arrangement for enabling communications with other parties. Typically a communication device is used for enabling receiving and transmission of communications such as speech and data. The communication device may access a carrier provided by a base station, and transmit and/or receive communications on the carrier. An example of cellular communication systems is an architecture standardized by the 3rd Generation Partnership Project (3GPP). A development in this field is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. In LTE systems base stations are commonly referred to as enhanced NodeBs (eNodeB; eNB).

A group of eNodeBs can be synchronised to transmit simultaneously the same data on a single frequency resource to communication devices in the service area thereof. This can be provided by means of providing multicast broadcast multimedia service (MBMS) on a single frequency network (SFN) comprising a multiple of synchronised cells and associated controllers.

In certain scenarios scalability of the system would be desired as the number of receiver group members in an area may be unlimited, and/or can vary. In accordance with a proposal it should be possible to decide dependent upon the number of users in a group whether to distribute future media/data via an existing established point to point service, and/or a multicast broadcast multimedia service (MBMS) broadcast service.

Multicast broadcast single frequency network (MBSFN) transmission requires synchronized transmission by the participating eNBs of the same, bit-identical content on the same time-frequency resources. Participating eNBs should not transmit anything differently from neighbouring eNBs as this would cause interference. For example, if for a given scheduling period of an established MBMS bearer an eNB does not receive any SYNC-protocol packet data units (PDUs), it cannot simply infer that there was no data at all and transmit a multicast channel (MCH) scheduling information (MSI) medium access control (MAC) control element indicating that to communicating devices, because the eNB cannot know if there actually was some data but it was lost in transit. Transmitting the MSI indicating "no data" would risk interfering with neighbouring eNBs transmitting an MSI with different content.

Accordingly, it is defined in the LTE standard that in SFN transmission for a packet loss case the transmission of radio blocks potentially impacted by the lost packet should be muted. It is further defined that if two or more consecutive SYNC synchronization distribution units (SDUs) within a SYNC bearer are not received by the eNB, or if no SYNC PDUs of Type 0 or 3 are received for some synchronization sequence, the eNB may mute the exact subframes impacted by lost SYNC PDUs using information provided by the SYNC protocol. If eNB does not mute only those exact subframes, the eNB stops transmitting the associated MCH from the subframe corresponding to the consecutive losses until the end of the corresponding MCH scheduling period (MSP) and it does not transmit in the subframe corresponding to the MSI of that MSP. If there is no data frame in a synchronization sequence, scheduling information shall still be transmitted by the eNB. This means that even for an established MBMS bearer with no data to transmit at a given moment, the Broadcast Multicast Service Center (BM-SC) needs to keep sending SYNC PDUs of type 0 or 3 for every MCH scheduling period, to enable any eNB where the bearer is established to confidently indicate "no data" to the communication device receiving the bearer. If the BM-SC sends nothing when there is no data, eNBs would need to refrain from transmitting any MSI as a precaution. This in turn can result increased battery consumption for the communication devices in the area as these would know no better than to receive several if not all MCH subframes in every MCH scheduling period in which this happens, to make sure they did not just fail to receive the MSI successfully and miss any service data because of that.

Another restriction caused by MBSFN synchronization among eNBs relates to packet dropping when data offered by one or more services for MBMS tramsmission exceeds reserved radio resources. In case the SYNC protocol delivers more data for an MCH than the air interface can transport in the scheduling period, the procedure currently used by the eNBs requires dropping of packets as follows. If the eNB needs to drop a packet because it has too much data for a MCH scheduling period, it selects the last bearer according to the order in the MCCH list with a SYNC SDU available for dropping. For the selected bearer, the available SYNC SDU with the highest Packet Number among the SYNC SDUs with the latest Timestamp is dropped. A SYNC SDU is considered available for dropping when the eNB knows its size and it has not been dropped by the eNB.

If an MBSFN area only spans on a single eNB or a single cell within an eNB, a problem may occur when the eNB receives nothing for an MBMS bearer (be it due to packet loss in transit, or because nothing is sent). In such situation refraining from indicating "no data" also to the communication device in the cell can be an unnecessary precaution.

It is noted that the above discussed issues are not limited to any particular communication environment and station apparatus but may occur in any appropriate system. Embodiments of the invention aim to address one or several of the above issues.

In accordance with an embodiment there is provided a method comprising receiving an indication whether synchronisation between controllers of base stations in a single frequency network area is required and controlling transmission of data based on the indication.

In accordance with an embodiment there is provided a method comprising causing communication to at least one controller of one or more base stations in a single frequency network area an indication whether synchronisation between controllers of base stations in the single frequency network area is required.

In accordance with an embodiment there is provided an apparatus for a base station, the apparatus comprising at least one processor, and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to receive an indication whether synchronisation between controllers of base stations in a single frequency network area is required, and to control transmission of data based on the indication.

In accordance with an embodiment there is provided an apparatus for a network entity, the apparatus comprising at least one processor, and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause communication to at least one controller of one or more base stations in a single frequency network area an indication whether synchronisation between controllers of base stations in the single frequency network area is required.

In accordance with a more specific aspect the indication is from an multi- cell/multicast coordination entity (MCE), a broadcast multicast service center (BM-SC), or an operation and maintenance (O&M) system.

The indication may be determined according to the number of users in a certain area. The indication can be determined to be that synchronisation between the controllers is not required when the number of users of a group in the area is determined to be below a threshold.

When the indication is that synchronisation is not required and accurate information of the amount of data intended to be transmitted in unknown, a controller of one or more base stations may cause transmission of scheduling information. A first sequence of a first type of data unit can be received such that at least one first type of data unit is received correctly and at least one first type of data unit is not received correctly during a period, the first sequence being for transmission of a second sequence of a second type of data unit and transmission of the second sequence being controlled according to the indication. When synchronisation is not required, the second sequence of a second type of data unit includes data from the correctly received first type of data units that were received during the period. When synchronisation is required, the second sequence of a second type of data unit excludes data from the correctly received first type of data units. The second sequence of a second type of data unit may comprise a rearrangement of the data from the first sequence, the re-arrangement comprising at least one of segmentation and concatenation.

The transmission may comprise broadcasting or multicasting.

Switching between a synchronised mode and a non-synchronised mode may be provided.

Data for at least one service may be received such that there is at least one period during which data is received and at least one period during which no data is received. When synchronisation is not required, a first sequence of a first type of data unit may be communicated to at least one base station controller, wherein the first sequence of a first type of data unit excludes dummy synchronisation units that correspond to the period during which no data is received. When synchronisation is required, a first sequence of a first type of data unit may be communicated to at least one base station wherein the first sequence of a first type of data unit includes dummy synchronisation units that correspond to the period during which no data is received. According to a specific aspect it can be determined that that a first sequence of a first type of data unit contains more data than can be transmitted in a second sequence of a second type of data unit, and in response thereto data units can be dropped from the first sequence differently from a predefined order of dropping data units.

A computer program comprising program code means adapted to perform the herein described methods may also be provided. In accordance with further embodiments apparatus and/or computer program product that can be embodied on a computer readable medium for providing at least one of the above methods is provided. A network node such as a base station controller apparatus or a controller entity associated with broadcasting or multicasting in an area or otherwise controlling operation in an area can be configured to operate in accordance with at least some of the embodiments. A communication system embodying the apparatus and principles of the invention may also be provided.

It should be appreciated that any feature of any aspect may be combined with any other feature of any other aspect.

Embodiments will now be described in further detail, by way of example only, with reference to the following examples and accompanying drawings, in which:

Figure 1 shows a schematic diagram of a cellular system where certain embodiments can be implemented;

Figure 2 shows a schematic diagram of a control apparatus according to some embodiments;

Figure 3 shows a flowchart according to certain embodiments; and

Figure 4 shows an example of communication of data between various entities.

In the following certain exemplifying embodiments are explained with reference to a wireless or mobile communication system serving mobile communication devices. Before explaining in detail the exemplifying embodiments, certain general principles of a wireless communication system, access systems thereof, and mobile communication devices are briefly explained with reference to Figures 1 and 2 to assist in understanding the technology underlying the described examples.

A non-limiting example of the recent developments in communication system architectures is the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) that is being standardized by the 3rd Generation Partnership Project

(3GPP). The LTE employs a mobile architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN). Base stations of such systems are known as evolved or enhanced Node Bs (eNBs) and may provide E-UTRAN features such as user plane Radio Link Control/Medium Access Control/Physical layer protocol (RLC/MAC/PHY) and control plane Radio Resource Control (RRC) protocol terminations towards communication devices. Other examples of radio access system include those provided by base stations of systems that are based on technologies such as wireless local area network (WLAN) and/or WiMax (Worldwide Interoperability for Microwave Access). Communication devices or terminals 21 can be provided wireless access via base stations or similar wireless transmitter and/or receiver nodes providing radio service areas or cells. In figure 1 different neighbouring cells 10, 12, 14 and 16 are shown being provided by base stations 1 1 , 13, 15 and 17, respectively. It is noted that the cell borders are shown only schematically for illustration purposes in Figure 1 . A base station site can provide one or more cells or sectors. A sector may provide a cell or a subarea of a cell. Thus it shall be appreciated that the number, size and shape of the cells may vary considerably from those shown in Figure 1 .

Base stations and hence communications in cells are typically controlled by at least one appropriate controller apparatus so as to enable operation thereof and management of mobile communication devices in communication with the base stations. The control apparatus can be interconnected with other control entities. The control apparatus can typically be provided with memory capacity and at least one data processor. The control apparatus and functions may be distributed between a plurality of control units. In some embodiments, each base station can comprise a control apparatus. In alternative embodiments, two or more base stations may share a control apparatus. For example, in LTE a given eNB typically controls several cells.

Different types of possible cells include those known as macro cells, pico cells and femto cells. For example, transmission/reception points or base stations can comprise wide area network nodes such as a macro eNode B (eNB) which may, for example, provide coverage for an entire cell or similar radio service area. Base station can also be provided by small or local radio service area network nodes, for example Home eNBs (HeNB), pico eNodeBs (pico-eNB), or femto nodes. Some applications utilise radio remote heads (RRH; denoted by 15 in the example) that are connected to for example an eNB (denoted by 1 1 in the example).

Base stations and associated controllers may communicate via each other via fixed line connection and/or air interface. The logical connection between the base station nodes can be provided for example by an X2 interface. In Figure 1 this interface is shown by the dashed line denoted by 20. Base station controllers can be arranged to provide a synchronised single frequency network (SFN). As explained earlier, a SFN can be used e.g. to provide multicast broadcast multimedia service (MBMS). For example, in LTE the MBMS is currently based on multicast broadcast single frequency network (MBSFN) broadcast where adjacent cells are tightly synchronized to broadcast identical content on the same time-frequency resources. An MBSFN area can span several cells where they are under control of the same eNB. The MBSFN operations can be controlled by entities such as multi-cell/multicast coordination entity (MCE) 22 over M2 control interfaces established to several eNBs. Figure 1 shows also a Broadcast Multicast Service Center (BM-SC) 24 and an operation and maintenance (O&M) system node 26. Other entities may also be involved in the multicast/broadcast operations.

The communication devices or terminals 21 may comprise any suitable device capable of at least receiving wireless communication of data. For example, the terminals can be handheld data processing devices equipped with radio receiver, data processing and user interface apparatus. Communication devices of users can be referred to as user equipment (UE).

Figure 2 shows an example of a control apparatus for a node, for example to be integrated with, coupled to and/or otherwise for controlling any of the base stations. The control apparatus 30 can be arranged to provide control on communications in the service area of a base station site. The control apparatus 30 can be configured to provide control functions in association with scheduling of single frequency transmission and/or synchronisation with other controllers in accordance with certain embodiments described below. For this purpose the control apparatus comprises at least one memory 31 , at least one data processing unit 32, 33 and an input/output interface 34. Via the interface the control apparatus can be coupled to at least one receiver and at least one transmitter of the base station. The control apparatus can be configured to execute an appropriate software code to provide the control functions. It shall be appreciated that similar components can be provided in a control apparatus provided elsewhere in the system for controlling transmissions in a single frequency network, for example in any of entities 22, 24 and 26 of Figure 1 .

As shown in Figure 1 , cells can overlap and thus can interfere with each other. Interference control can be provided to manage interference caused by stations of other cells. Currently, MBSFN transmission in the area requires synchronized transmission by the participating eNBs to avoid interference. This requires an eNB to not transmit anything when no packets are received. This subsequently requires the user equipment (UE) to continuously be in receiving mode, in order to receive information about when data might be scheduled.

Messages and procedures are described below for enabling dynamic use of single cell MBSFN areas or MBSFN areas restricted to a single eNB. This can be provided to address the energy consumption of UEs that would otherwise need to be continuously in the receive mode and also situations where packets are not correctly received by an eNB for transmission, i.e. are faulty or are not received at all.

It has been proposed that SFN area can be provided by an area controlled by a single eNB, or even by a single cell. This can be the case e.g. in mission-critical group communications (e.g. communications by police, fire brigade, and other rescue / emergency services).

In accordance with an embodiment an indication is communicated from a multi- cell/multicast coordination entity (MCE) to at least one eNB for indicating that content synchronization of the SFN with other eNBs is not required. Thus an SFN can be restricted to a single eNB, or even a single cell therein. This subsequently permits the eNB to inform the UE or UEs in its area when there is "no data" and also to provide accurate multicast channel (MCH) scheduling information, even when the eNB has uncertainty of whether it received everything it was supposed to receive. Operation in a control apparatus of an access area provided by one or more cells is illustrated by the flowchart of Figure 3 where step 40 relates to operation in a network entity and steps 42 and 44 relate to operation in controller apparatus of one or more base stations. The control apparatus receives at 42 an indication whether synchronisation to control apparatuses of neighbouring cells is required. The indication can be explicit indication generation and sending of which is caused by e.g. an O&M, BM-SC or MCE entity according to step 40.

The control apparatus can then control transmission in its area at 44 based on the indication. The transmission in the one or more cells of the single frequency network area can take place with or without enforcement of synchronisation with other control apparatuses operating in a similar role, and the control apparatus can treat data received for transmission differently depending on the indication.

Thus e.g. in a Multicast Broadcast Multimedia Service (MBMS) arrangement an indication can be provided in view of need of content synchronization with other base station controllers. In accordance with one scenario an indication is provided that content synchronization with other base station controllers need not be enforced for at least one

Multicast Broadcast Single Frequency Network (MBSFN) area. In another scenario, such as in case of possible reconfigurations or enlargement of the SFN area, an indication can be signalled that content synchronization with other base station controllers needs to be enforced. The indication can be received by an eNB which then takes the indication into account in deciding what and how to transmit as a part of an MBSFN area.

An eNB may receive the indication e.g. over the M2AP protocol from an MCE, or by means of O&M system. The transmission can be provided based on packet data units (PDUs) received and/or PDUs not received. If PDUs are not received at all or are not received correctly it is possible that there is no knowledge at the intended receiver of the PDUs how much data to be transmitted in a given scheduling period for at least one service it was supposed to receive. If there is an indication that the synchronization need not be enforced, scheduling information related to said service and/or all data that was correctly received for said service transmitting is transmitted in the MBSFN area in that scheduling period.

An eNB can perform the different scheduling on condition that PDUs are not received and the amount of data to be transmitted by the eNB in a given scheduling period is unknown in the eNB for at least one service that it is supposed to receive. Also, it can be determined, when no synchronisation is needed, that a first sequence of a first type of data unit contains more data than can be transmitted in a second sequence of a second type of data unit. In response thereto data units can be dropped from the first sequence differently from a predefined order of dropping data units. For example, when it has been indicated that cell synchronization need not be enforced, and when more data (summed over more than one service) to be transmitted is received in a given scheduling period than can be accommodated by radio resources jointly reserved for said services, received packets can be dropped selectively from transmission in that scheduling period without following an order of dropping that would need to be used if the synchronisation was active. Thus, unlike is the case currently, packets other than the last packets of the last service in a scheduling order may be selected to be dropped from transmission in that scheduling period. For example, an eNB can perform the selective packet dropping on condition that PDUs are received and the eNB receives too much data for the MCH scheduling period. For example, if there is more data than the sum of the guaranteed bit rate (GBR) of the services (i.e. the reserved resources) for that period, packets can be dropped from the service(s) exceeding the guaranteed bit rates instead of always dropping the service that happens to be configured last in the scheduling order, even if its data amount does not exceed its GBR. An advantage of selecting earlier services for dropping transmitting the last packets of the last service in a scheduling order can be that the guaranteed bit rate (GBR) of the last service in the scheduling order can be satisfied while packets of a service earlier in the scheduling order are dropped because the received data exceeded the GBR of that service.

Also, when it has been indicated that the synchronization need not be enforced, received PDUs can be mapped to transport blocks to be transmitted based on only those PDUs that were correctly received. It is not necessary to transmit all data that was received. For example, too much data may have been received and packet dropping may need to be performed.

Figure 4 illustrates in more detail an embodiment where a first sequence 50 of a first type of data unit based on data received from at least one service is communicated on a user plane connection 51 from BM-SC 24 to eNB 1 1 . The data for the service is shown to be received by the BM-SC 24 from at least one service provider entity 28. It is possible that the service is not active all the time, i.e. there are gaps in receiving data from entity 28. This is illustrated by gap 57 between the service data blocks 56.

It is possible that at the eNB 1 1 at least one first type of data unit is received correctly while at least one first type of data unit is not received successfully during a period. For example, packets may have been lost in internet protocol (IP) transport e.g. due to congestion or are otherwise not correctly received. The unsuccessfully received data units are indicated by the two crossed out data units 59. The three last data units 58 of sequence 50 are correctly received. According to an embodiment, the MCE 22 has received on control plane an explicit indication 52 that synchronization between controllers is not needed and has forwarded this indication 53 on control plane to the eNB 1 1 . The eNB can now, based on the indication that synchronization is not needed schedule received packets based on any other appropriate scheduling policy for transmission of a second sequence 54 of a second type of data unit. For example, radio transmission blocks of sequence 54 can be filled with the correctly received data unit and other data needing transmission in the service area of node 1 1 .

The second sequence 54 of a second type of data unit can comprise a rearrangement of the data from the first sequence in the transport blocks. The re- arrangement can comprise e.g. segmentation and/or concatenation.

Thus, when said synchronisation is not required data from the correctly received first type of data units 58 that were received during the period can be transmitted without a reservation in the transmission for data units 59 that were not correctly received even though node 1 1 belongs to a SFN. In the absence of indication that cell synchronisation is not required, because of such a reservation the second sequence of a second type of data unit may have to exclude data from the correctly received first type of data units that were received during the period. Thus e.g. an MCE can signal an indication that for at least one MBSFN area content synchronization with other base station controllers does not need to be enforced or that the synchronization needs to be enforced. The sending of the indication can be preceded by receiving an indication e.g. from BM-SC that MBSFN areas of limited scope or full scope should be configured, respectively. According to a possibility the operation and maintenance (O&M) system can signal to a Broadcast Multicast Service Center (BM-SC) a message indicating that content synchronization between eNBs is not required. This message subsequently permits the BM-SC to refrain from transmitting synchronization information whenever there is no service data to send. A further potential optimization can be obtained by use of bearer rather than cell / eNB level indications. An MBMS bearer transmitted by the BM-SC can be distributed by IP multicast and this multicast stream can be transmitted e.g. by a single-eNB MBSFN in one part part of E-UTRAN and also a multi-eNB MBSFN in another part of E-UTRAN. Since all eNBs receive the same IP multicast stream an indication of the "no-need" condition shall be signalled to all relevant eNBs in order that the BM-SC can refrain from transmitting the synch information. A per radio bearer indication can be provided to indicate that for at least one MBMS bearer content synchronization between base station controllers need not (or need to) be enforced. This indication can be send to a BM-SC. In response to the indication, the BM-SC can refrain from (or resume) transmitting synchronization information whenever there is no service data to send within a time period. Thus, if the necessary condition holds everywhere for an MBMS bearer, the need-not synchronise case saves the BM-SC and the transport network from the "no data" indications that are currently required. This may help scalability if use of pre-established eNB-specific MBMS bearers is extensive in the network. This indication is most likely seen as received by O&M.

The 'no need to synchronise' case allows an eNB to single-handedly transmit on its MBSFN area no more and no less than the service data that it has actually received, and also to always transmit the MCH Scheduling Information accurately based on how the eNB best determines fit to schedule the data for transmission in every MCH Scheduling Period. This can also be used to optimize the power consumption of the receiving UEs. This is contrary to the current arrangement where, if an eNB detects from SYNC-header counters that it has not received e.g. one PDU with given size (the size is known from the following SYNC headers), then in order not to deviate from the content synch with other eNBs during the rest of the scheduling period, the eNB must leave a hole the size of the not-received PDU in the mapping of PDUs to transport blocks (TBs) and mute the TBs for which it does not have the complete content.

Group communications on single frequency networks can be used for various purposes. A potential use of SFN is for public safety or critical mission broadcasting / multicasting.

The indication can be determined according to the number of users in a certain area by an entity controlling the communications to a group of users. For example, an indication can be generated to indicate that synchronisation is not required when the number of users belonging to a group and associated with an eNB is below a threshold. For example, the indication can depend on user distributions in cells across several eNBs. As this information can be made available to a network entity such as the MCE, it can provide appropriate determination of the need for the synchronisation, and indicate the outcome of this accordingly to the controllers in the access system.

It is noted that whilst embodiments have been described in relation to LTE, similar principles can be applied to any other communication system or indeed to further developments with LTE. Also, instead of carriers provided by base stations at least one of the carriers may be provided by a mobile communication device. For example, this may be the case in application where no fixed equipment provided but a communication system is provided by means of a plurality of mobile equipment, for example in adhoc networks or other mobile stations that can act as a base or relay station. Therefore, although certain embodiments were described above by way of example with reference to certain exemplifying architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

The required data processing apparatus and functions of a base station apparatus, a communication device and any other appropriate apparatus may be provided by means of one or more data processors. The described functions at each end may be provided by separate processors or by an integrated processor. The data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), gate level circuits and processors based on multi core processor architecture, as non- limiting examples. The data processing may be distributed across several data processing modules. A data processor may be provided by means of, for example, at least one chip. Appropriate memory capacity can also be provided in the relevant devices. The memory or memories may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory.

In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of the invention may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD.

The foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of the exemplary embodiment of this invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the spirit and scope of this invention as defined in the appended claims. Indeed there is a further embodiment comprising a combination of one or more of any of the other embodiments previously discussed.