GB2335831A

GB2335831A - Transmission of signalling information in a radio communications system

Info

Publication number: GB2335831A
Application number: GB9905816A
Authority: GB
Inventors: Michael Faerber; Meik Kottkamp; Stefan Oestreich
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1998-03-13
Filing date: 1999-03-12
Publication date: 1999-09-29
Anticipated expiration: 2019-03-12
Also published as: DE19811002A1; GB2335831B; GB9905816D0

Abstract

A radio communications system provides a user data channel for the transmission of user data symbols provided with redundancy by a channel coding in at least one data block according to a known transmission protocol. The user data symbols are replaced by signalling information and are transmitted together with the remaining user data symbols in the user data block according to the transmission protocol.

Description

2335831 METHOD AND BASE STATION FOR THE TRANSMISSION OF INFORMATION IN A

RADIO COMMUNICATIONS SYSTEM.

The invention relates to a method and a base station for the transmission of information in a radio communications system, in particular of a mobile radio system.

In second generation mobile radio systems, for is example GSM (Global System for Mobile Communication), as is known from J. Biala, 11Mobilfunk und intelligente Netzell, Vieweg Publishers, 1995, in particular from pages 57 to 92, signalling information, for example for the power regulation of the radio station, is transmitted as trafficchannel-accompanying outer band signallings by way of the air interface. Two signalling channels are used for this purpose. On the one hand there is the SACCH (Slow Associated Control Channel), which is part of a 26 block multiframe and in which, in upward and downward direction, among other things system information and SMS-related (Short Message Service) information is transmitted. The content of the SACCH within a multiframe is allocated in each case to a certain time slot. Because several time slots are required for a few signallings, in the design of a function controlled by the signalling information a long delay can therefore result. Several seconds elapse in order to regulate, for example, the transmitting power of a radio station over the entire range (26 dB) A power regulation of this kind is too slow for an application in hierarchical cell structures, especially in the small cells, for example micro cells and pico cells.

Furthermore, there is the rapid signalling channel FACCH (Fast Associated Control Channel) However, this should generally only be used in cases of emergency because, by means of a "Frame Stealing", i.e. the purposeful use of a complete time frame for the is transmission of signalling information, a high user data loss for the communications connections normally to be transmitted in the time slots occurs. The use of this signalling channel is therefore likewise not suitable for a continuous control of an adaptive multirate coder/decoder AMR (Adaptive Multirate) In the GSM mobile radio system, voice coders are used which reduce the supplyside 64 kbit/s data rate of PCM30 channels to, for example, a data rate of 13 kbit/s (net data rate). In a downstream channel coder, subsequently by means of an error correction method, additional redundancy is added to the voice signal,-so that the gross data rate is increased, for example, to 22.8 kbit/s. This example relates to a full- rate coder, with half-rate coders also being used as a further development, which only use half the data rate for the voice transmission. Such a compression of the voice signals is necessary because the available radio engineering resources are scarce and as large a number of users as possible is to be supplied by the mobile radio system.

The portion of the error protection at the gross data rate (= net data rate of the user data + error protection) with the voice coders used is generally high and is overdimensioned with good channel conditions. For this reason, the use of an adaptive multirate coder/decoder (AMR Adaptive Multi Rate) is suggested, with the]ortion of the error protection being continually varied in dependence upon the transmission conditions on the radio interface. By means of a reduction of the error protection the data rate of the voice coding can be increased and therefore the voice quality improved or the gross data rate can be reduced and therefore additional transmission capacity for further users can be created.

The invention seeks to realize a method and a base station which enables a reduction of the delay in the transmission of signalling information.

According to a first aspect of the invention, there is provided a method for the transmission of information by way of an air interface of a radio communications system, which makes available a user data channel for the transmission of user data symbols in at least one user data block according to a known transmission protocol, wherein at least one user data symbol provided with redundancy by a channel coding is replaced by signalling information and is transmitted together with the remaining user data symbols in the user data block according to the transmission protocol.

According to a second aspect of the invention, there is provided a base station for the transmission of information about an air interface of a radio communications system, which has a control device for the replacement of.user data symbols provided with redundancy by a channel coding by signalling information; a transmitting/receiving device for transmitting and receiving, in a user data channel according to a known transmission protocol, the signalling information in at least one user data block together with the remaining user data symbols; and an evaluating device for evaluating the signalling information.

Advantageous developments of the invention are set out in the sub-claims.

In this respect, a radio communications system makes available a user data channel for the transmission of user data symbols, provided with redundancy by a channel coding, in at least one user data block according to a known transmission protocol. Characteristically, user data symbols are replaced by signalling information and are transmitted together with the remaining user data symbols in the user data block according to the transmission protocol.

The method in accordance with the invention makes possible a more rapid transmission of signalling information by way of the radio interface of a radio communications system. In this respect, the transmission takes place according to the known transmission protocol, whereby, advantageously, no special adaptation of the known transmission protocol to this new method has to be carried out. Advantageously, furthermore, by means of this development an unrestricted downward compatibility with respect to radio stations which do not support this method is guaranteed.

In a first development of the invention, the transmission of the signalling information together with the user data symbols by a base station is announced to a radio station by means of system information which is transmitted in a signalling channel and contains information about functions which are globally supported by the radio communications system.

Ey means of this development it is announced to a radio station that the base station is carrying out the transmission of the signalling information together with the user data symbols. In this way, the radio station supporting the method in accordance with the invention is in a position to evaluate as signalling information the signalling information transmitted within the user data block and to undertake an appropriate control.

In a second development of the invention, a base station carries out the transmission of the signalling information together with the user data symbols in a connection-individual manner to a radio station, if the latter announced a support to the base station with the aid of class information which contains information about characteristics of the radio station.

In contrast with this development is a third development of the invention, where a base station carries out the transmission of the signalling information together with the user data symbols to all radio stations in the radio supply range of the base station.

In this respect, the second development has the advantage that a support of the method according to claim 1 is communicated to the base station by means of extended class information, for example in the event of a request of a radio station to establish a connection, whereby it is requested to transmit the signalling information together with the user data symbols. A radio station which does not support the method in accordance with the invention will not experience any change compared with the hitherto-existing signalling.

on the other hand, the third development has the advantage of a simpler implementation of the method in accordance with the invention in the base stations and radio stations. However, proceeding from an only insignificant impairment of the transmission quality for the radio stations which do not support this method, the method signifies a great improvement of the transmission quality on the basis of the faster transmission of the signalling information for the radio stations which support the method.

In another development of the invention, the user data symbols w hich, for the transmission on the air interface, are only protected by a small additional channel coding or are not protected are replaced by the signalling information.

user data symbols which only experience a small or no additional channel coding belong to classes of user data symbols which are not essential for the transmission quality. A radio station which does not is support the inventive method, despite the replacement of user data symbols with only a small channel coding by signalling information, is entirely or at least partially in a position to correct this signalling information, interpreted by it as user data symbols, which information generates errors depending on a conformity or a difference. In the selection of the user data symbols with no additional channel coding, likewise errors arise on the receiving-side if the signalling information does not happen to correspond with the original user data symbols. However, such errors cause only a limited reduction of the transmission quality. Radio stations which support the inventive method can evaluate the signalling information and can undertake an appropriate control. Concerning the transmission quality, the quality gain as a result of the faster signalling is dominant compared with the few faults as a result of the user data loss.

According to another development of the invention, the number of items df signal!-ing information in comparison with the number of user data symbols in the user data block is-kept low. If, for example with a GSM mobile radio system, in accordance with the invention four user data symbols of a user data block are replaced by signalling information, this corresponds to only 3.5% of the total number of user data symbols of a user data block. A reduction of -the transmission quality is therefore to be regarded as negligible.

Two further developments of the invention relate to a control carried out by a radio station and/or by a base station with the aid of the signalling information. Here, on the one hand, a control of a transmitting power, and, on the other hand, a control of an adaptive multirate coder/decoder is carried out.

1 A rapid signalling for the rapid transmittingpower control has an advantageous application in hierarchical cell structures. In this respect, handovers take place between macro cells and micro cells, with the connections in the respective cells requiring different output powers of a radio station. A radio station in a micro cell transmits with as little power as possible in order to generate as little interference as possible in the reuse cell. If a handover takes place from the micro cell into a macro cell, a rapid increase of the transmitting power is necessary in order to transmit the connection across the correspondingly larger distance to the base station of the macro cell with adequate quality. If the regulation of the transmitting power proceeds too slowly, an impairment of the quality of the connection results until the regulating process is concluded, with there being danger of a loss of connection. By means of the possibility of a rapid regulation, the transmitting power could be controlled so dynamically that the reliability of the regulating mechanisms makes possible a reduction of the interference reserves in hierarchical systems. Advantageously, this makes possible a capacity increase in the radio communications system without requiring additional frequency spectrum.

The control of an adaptive multirate coder/decoder by means of the transmission of signalling information in accordance with the invention has the advantage that, depending on the transmission conditions on the radio interface, an adequate error protection with good voice quality is always guaranteed. However, because the transmission conditions can change rapidly, particularly with movement of the radio station, with a signalling according to the prior art the result can be a very rapid worsening of the voice quality or even the loss of the communications connection. On the other hand, by way of the transmission of the signalling information in accordance with the invention, a rapid readjustment of the error protection can be carried out.

In a last development of the invention, measuring results of measurements of a radio station of characteristics of the user data channel are transmitted to a base station in the signalling information and measuring results of measurements of a base station are transmitted to a radio station in the signalling information. This development has the advantage that in the base station a more accurate estimation of the transmission conditions on the air interface can be undertaken, and on this basis a faster control, for example of the transmitting power and/or the adaptive multirate coder/decoder, can be carried out. Furthermore, so far as the measuring results of the radio station also contain the characteristics of user data channels of further base stations, a faster control of a transfer of the communications connection to another base station can be carried out.

For a better understanding of the present invention, and to show how it may be brought into effect, reference will now be made, by way of example, to the accompanying drawings, in which:Figure 1 shows a block diagram of a radio Figure 2 communications system, in particular a mobile radio system. shows a diagrammatic representation of the frame structure of the radio interface and the assembly of a radio block.

Figure 3 shows a diagrammatic representation of a distribution of the user data symbols on time frames.

Figure 4 shows diagrammatic representations of the is different classes in a user data block.

Figure 5 shows a flow chart of an establishment of a connection with a radio station.

Figure 6 shows a flow chart of an establishment of a connection with a base station.

The radio communications system shown in Figure 1 and designed, by way of example, as a mobile radio system, corresponds in its structure to a known GSM mobile radio system which consists of a plurality of mobile switchingpoints MSC which are linked to each other and produce the access to a fixed system PSTN. Furthermore, these mobile switching points MSC are connected to in each case at least one base station control BSC. Each base station control BSC makes possible, in turn, a connection with at least one base station BS. This base station BS is a radio station which can establish communications connections with radio stations MS by way of a radio interface. The functionality of this structure is used by the method in accordance with the invention. A use of the method in accordance with the invention, for example in an access network, is likewise possible.

Figure 1 shows, by way of example, a connection for the transmission of user data symbols in user data blocks in a user data channel between a mobile radio station MS and the base station BS. The base station BS is connected to an aerial device AE which consists, for example, of three individual radiators. Each of the individual radiators radiates in a directed manner into a sector of the radio cell which is supplied by the base station BS. However, alternatively, a larger number of individual radiators (in accordance with adaptive aerials) can also be used, so that a spatial user separation according to an SDMA method (Space Division Multiple Access) can also be used.

The frame structure of the radio interface can be is seen in Figure 2. According to a TDMA component, a division of a wide- band frequency range, for example the bandwidth B = 1.2 MHz, into several time slots ts, for example 8 time slots tsO to ts7, is provided. Each time slot ts within the frequency range B forms a frequency channel fk. Within a wide-band frequency range B the successive time slots ts are arranged according to a frame structure. In this way, eight time slots tsO to ts7 are combined to form one frame.

With a use of a TDD transmission method, a section of the time slots tsl to ts7 is used in upward direction and a section of the times slots tso to ts7 is used in downward direction, whereby the transmission in the u:)ward direction takes place, for example, before the transmission in the downward direction. A changeover instant SP lies there between. A frequency channel fk for the upward direction corresponds in this case to the frequency channel fk for the downward direction. The further frequency channels fk. are structured in the same way.

Within the freauency channels fk which are provided for the user data transmission, information of several connections is transmitted in radio blocks. These radio blocks for the user data transmission consist of sections with data d, in which in each case sections with training sequences tseql to tseqn, known on the receiving-side, are embedded. The data d is distributed in a connection-individual manner with a fine structure, a distribution code c (CDMA, code), so that on the receiving side, for example n connections can be separated by this CDMA component.

The distribution of individual symbols of the data d with Q chips has the effect that within the symbol duration tsym Q subsections of the duration tchip are transmitted. In this respect, the Q chips form the individual CDMA code c. Furthermore, within the time slot ts a protection time gp for the compensation of different signal running times of the connections of successive time slots ts is provided.

In Figure 3, by way of example, the error is protection coding of a voice signal in accordance with the prior art according to the GSM mobile radio system is shown. A full rate coder/decoder (FR - Full Rate) is taken as the basis for the description of the channel coding of the source code, whereby, however, the principle of the coding can be applied in exactly the same way to a half-rate coder/decoder (HR - Half Rate) or to an adaptive multirate coder/decoder (AMR Adaptive Multirate). Proceeding from an output data rate of the series-connected voice coder of 13 kbit/s, 260 bit all 20 ms are applied to the channel coder input. Redundant information calculated from the source code in the channel coder is added to this source code. In this respect, the channel coding of the source code takes place in different ways in order to make possible a recovery of the user data symbols in the event of possible disturbances during the transmission on the air intertace which signity an impairment of the transmission quality depending on the significance of the coded user data symbols. The output signal of the channel coder has a data rate of 22.8 kbit/s for the full-rate coderr/decoder which is assumed as example.

In the channel coding 182 of the 260 bits source code are convolut ioncoded at the rate 1/2 (class Ib) of which, in turn, 50 bits are additionally protected by a detection code, where 3 redundant bits are added, which, for their part, are likewise protected by the convolution coding (class Ia) 4 bits are additionally added to the resulting 185 bits and a double convolution is carried out, so that a total of 378 bits result. The remaining 78 bits of the 260 source-coded bits remain uncoded (class II). The length of the source-coded and channel-coded voice signal therefore results to form a user data block ndb which is a total of 456 bits long. This user data block ndb --'-s distributed on to 8 half bursts with in each case 57 bits of a time slot tsi in the time frames tfl to tf4. The user data symbols ndsym coded according to class Ia contain the essential part of the voice signal to be protected. If an error occurs in these 50 bits, the receiving user will hear a loud interference noise instead of a 20 ms long voice block. Figure 4a) shows, by way of example, the distribution of the channelcoded user data symbols ndsym, specified according to classes Ia, Ib and II, in a user data block ndb with 456 bits before the distribution on to eight half bursts according to the prior art of the GSM mobile radio system. According to Figure 4b), for example 16 bits of the channel-coded user data symbols ndsym of class II are replaced by the signalling information sinf, this corresponding to two bits per half burst after the distribution of the -user data-block ndb on to the eight half bursts. For the receiving radio stations MS, this loss of four user data bits per burst means, in the worst case, i.e. with no random conformity between the signalling information items sinf-and the original coded user data symbols ndsym, a loss of only 3.5% of the total information per burst. Radio stations MS which support the method in accordance with the invention can evaluate the signalling information sinf and, by means of the latter, can carry out a control of one or more functions which will be explained in more detail in the further description.

According to the same principle, as shown in Figure 4c), 16 bits of the channel-coded user data symbols ndsym of class Ib can be replaced by the 1 signalling information sinf. By means of the convolution coding carried out in the channel coder, the content of the user data symbols ndsym replaced by the signalling information sinf can be recovered again. A bit error is produced for the receiving radio stations MS which do not support the method in accordance with the invention only if the convolution decoder is no longer in a position to correct the bit error. However, this usually only occurs if the preceding and subsequent user data current is already faulty, i.e. if the entire connection has already suffered over a certain period under poor transmission conditions. In this respect, it is to be stressed again that the protocol for the transmission on the air interface remains unchanged compared with the prior art.

The components AW, ST and SEE used for the method in accordance with the invention and drawn in Figure 1 are in each case realized both in the base station BS and in the radio station MS. The realization c.' all components also in the radio station MS is, in this respect, not imperative, because even reactions of radio station MS to the signalling information sinf are conceivable by the base station BS. The transmission of signalling information sinf according to the invention also leads to the desired success with a onesided realization in the base station ES.

According to Figure 1, in the base station BS the output signals of the channel coder (not drawn) are guided in the form of a user data block ndb, known from Figure 4a), with user data symbols ndsym protected by redundancy, to a transmitting/receiving device SEE. A control device ST connected to the transmitting/receiving device SEE replaces in a purposeful manner, according to the principle shown in Figure 4b) or c), parts of the channel-coded user data symbols ndsym with signalling information sinf. Thereupon, in the user data block ndb which is changed in this way, the signalling information sinf is transmitted together with the remaining user data symbols ndsym across the air interface to the radio station MS. In this respect, for the transmission a transmission protocol known from the prior art is used for the transmission, which transmission protocol does not undergo any further change.

In the radio station MS the received signalling information sinf is evaluated by an evaluating device AW and supplied to a control device ST. The evaluated signalling information sinf can then be used by the control device ST in the receiving radio station MS in order for the control device ST to undertake a control of the transmitting power of the transmitting/receiving device SEE and/or a control of a channel coder developed as adaptive multirate coder/decoder. This adaptive multirate coder/decoder makes it possible for the protection to useful bit ratio in the channel coding to be adapted optimally to the transmission characteristics on the air interface, so that, for example with good transmission conditions, the portion of the user data symbols ndsym is increased and thereby the voice quality is increased. On the other hand, with poorer transmission conditions the user data symbols ndsym are provided with a greater redundancy, in order to still guarantee an adequate transmission quality. Due to the fact that the radio station MS is in motion, the transmission conditions change very quickly, whereby a rapid regulation of the adaptive multirate coder/decoder becomes necessary. The method in accordance with the invention with the transmission of signalling information sinf together with the user data symbols ndsym makes a rapid regulation possible by way of the relatively high bit rate of the signalling -is- is information sinf.

Figures 5 and 6 show flow charts for the method in accordance with the invention, with Figure 5 showing an establishment of a connection from the base station BS to the radio station MS and- Figure 6 showing an establishment of a connection from the radio station MS to the base station BS. According to Figure 5, the base station BS transmits on a signalling channel BCCH, as is known from the prior art, system information sys, which in the base station BS is impressed by the control device ST on to the signalling channel BCCH and is transmitted by the transmitting/receiving device SEE. The transmission of the system information sys can take place permanently with the signalling according to the prior art and is not directly dependent on an establishment of a connection. By means of the system information sys it is communicated to the radio station MS that the base station BS is the transmission of the signalling information -sinf together with the user data symbols ndsym, so that the radio station MS can interpret the transmitted signalling information sinf as such.

In the establishment of a connection on the part of the base station BS, the radio station MS transmits class information cm to the base station BS, in which -there are statements about the transmitting power and the supported services. According to the invention, in this class information cm the support of the method in accordance with the invention is additionally also stated. With the aid of this statement it is made possible for the base station BS to carry out the transmission of the signalling information sinf together with the user data symbols ndsym only to the radio station MS which announces a support by way of the class information cm. By way of this confirmation a situation is avoided where radio stations MS which do carrying out is not support the method and which do not contain any corresponding statement in the class information em are subject to an additional degradation of the transmission quality, whereas radio stations MS supporting the method can use the rapid signalling.

If the class information em is not used for the described purpose of announcing the support by the radio station MS, the base station BS carries out the transmission of the signalling information sinf together with the user data symbols ndsym in a user data block ndb to all radio stations MS which are located in the radio supply range of the base station BS. In the process, a substantial impairment of the transmission quality does not occur, in accordance with the above explanations for the non-supporting radio stations MS. Subsequent to these signallings and further standard signallings for the establishment of a connection, which are not drawn in the flow chart, the transmission of the user data symbols ndsym with the signalling information sinf in the user data blocks ndb takes p-lace in the user data channel TCH associated with the connection.

Figure 6 shows a simplified flow chart for an establishment of a connection proceeding from the radio station MS. As already described withrespect to Figure 5, the base station BS transmits system information sys in the signalling channel BCCH, which the radio station MS permanently listens to if it is located in the radio supply range of the base station BS. The radio station MS now carries out an attempt to establish a connection (Random Access) and, in the process, simultaneously transmits the class information em with the announcement of the support of the method, whereby the base station BS can recognize that the radio station MS supports the transmission of the signalling information sinf together with the user data is symbols ndsym. The base station BS assigns to the radio station MS a user data channel TCH (Access Grant) and carries out further known signallings according to the prior art (not drawn). Subsequent to the establishment of the connection, the transmission of the user data symbols ndsym with the linked signalling information sinf in the user data blocks ndb begins in the assigned user data channel TCH. On the part of the radio station MS, in the signalling information sinf, for example measuring results of measurements of the characteristics of the allocated user data channel TCH can be transmitted to the base station BS, whereupon this carries out, for example, a control of the transmitting power and/or of an adaptive multirate coder/decoder, as described above.

Generally, the transmission of the signalling information sinf can also take place in dependence upon certain events, for example if there is a change of the receiving power or of the level of the occurring interferences by a certain amount. Furthermore, a transmission of the signalling information can also be carried out depending on a change of the reception quality which is judged, for example, by the bit error rate. In this respect, a respective threshold can be defined for the individual parameters, upon the exceeding of which the emission of the signall-ing information sinf is undertaken.

is

Claims

1. A method for the transmission of information by way of an air interface of a radio communications system, which makes available a user data channel for the transmission of user data symbols in at least one user data block according to a known transmission protocol, wherein at least one user data symbol provided with redundancy by a channel coding is replaced by signalling information and is transmitted together with the remaining user data symbols in the user data block according to the transmission protocol.

2. The method according to claim 1,where the transmission of the signalling information together with the user data symbols by way of a base station is announced to a radio station by way of system information, transmitted in a signalling channel, about functions supported globally by the radio communications system.

3. The method according to claim 1 or 2, where a base station carries out the transmission of the signalling information together with the user data symbols to a radio station in a connection-individual manner, if the radio station announced a support to the base station with the aid of class information about characteristics of the radio station.

4. The method according to one of claims 1 or 2, where a base station carries out the transmission of the signalling information together with the user data symbols t o all radio stations in the radio supply range of the base station.

5. The method according to one of the preceding claims, where user data symbols which, for the transmission on the air interface, are only protected by a small additional channel coding or are not additionally protected are replaced by the signalling information.

is

6. The method according to one of the preceding claims, where the number of signalling information items is kept small in comparison with the number of user data symbols in the user data block.

7. The method according to one of the preceding claims, where a radio station and/or a base station carries out a control of a transmitting power with the aid of the signalling information.

8. The method according to one of the preceding claims, where a radio station and/or a base station carries out a control of an adaptive multirate coder/decoder with the aid of the signalling information.

9. The method according to one of the preceding claims, where in the signalling information measuring results of measurements of a radio station of characteristics of the user data channel are transmitted to a base station or measuring results of measurements of a base station are transmitted to a radio station.

10. A base station for the transmission of information about an air interface of a radio communications system, which has a control device for the replacement of user data symbols provided with redundancy by a channel coding by signalling information; a transmitting/receiving device for transmitting and receiving, in a user data channel according to a known transmission protocol, the signalling information in at least one user data block together with the remaining user data symbols; and an evaluating device for evaluating the signalling information.

11. The base station according to claim 10, where the control device impresses system information about functions supported globally by the radio communications system on to a signalling channel, which information is transmitted by the transmitting/ receiving device, and, with the aid of the one radio station, the transmission of the signalling information together with the user data symbols is announced.

12. The base station according to claim 10 or 11, where the transmitting/receiving device carries out the transmission of the signalling information together with the user data symbols in a connection-individual manner, if a radio station announced a support with the aid of class information.

13. The base station according to claim 10 or 11, where the transmitting/receiving device carries out the transmission of the signalling information together with the user data symbols to all radio stations in the radio supply range of the base station.

14. The base station according to one of claims to 13, where the control device replaces with signalling information those user data symbols which, for the transmission on the air interface, are only protected by a small additional channel cod-ing or are not additionally protected.

15. The base station according to one of claims to 14, where the evaluating device evaluates the signalling information transmitted by a radio station, and the control device carries out a control of an adaptive multi-rate coder/decoder.

16. The base station according to one of claims to 15, where the evaluating device evaluates the signalling information transmitted by a radio station, and the control device carries out a control of a transmitting power of the transmitting/receiving device.

17. A method for the transmission of information by a radio communications system substantially as herein described, with reference to the accompanying drawings.

1

18. A base station of a radio communications system, substantially as herein described, with reference to the accompanying drawings.