WO2002080583A2

WO2002080583A2 - Communication system, communication unit and method of communicating information

Info

Publication number: WO2002080583A2
Application number: PCT/EP2002/002761
Authority: WO
Inventors: William Neil Robinson; Edgar Fernandes; Richard Burbridge
Original assignee: Motorola Inc
Priority date: 2001-03-30
Filing date: 2002-03-11
Publication date: 2002-10-10
Also published as: GB2373972A; WO2002080583A3; HK1048041A1; GB0108007D0; AU2002253124A1

Abstract

A communication system (100), comprising a first communication unit (112) communicating (118) with a second communication unit (122), said first communication unit (112) transmitting to said second communication unit a preamble (516) prior to a message, wherein the preamble is a concatenation of signals, said second communication unit receives and decodes the preamble (516) and compares the received concatenated signals with know pre-determined concatenated signals to determine whether an error has occurred in said preamble (516) or said first message.This enables a system employing the FAUSCH concept to carry more information than a simple request for a channel. For example, it could include the data rate of the required channel. It also allows an extra degree of flexibility when designing the protocols. It allows forward error correction to be applied to the channel. Hence, the receiver can detect and correct some transmission errors.

Description

COMMUNICATION SYSTEM, COMMUNICATION UNIT AND METHOD OF COMMUNICATING INFORMATION

Field of the Invention

This invention relates to an enhancement to an access mechanism for a communication system. The invention is applicable to, but not limited to, a random access mechanism for a Universal Terrestrial Radio Access (UTRA) Wideband-CDMA system, as used in the Universal Mobile Telecommunication Standard (UMTS) .

Background of the Invention

Wireless communication systems, for example cellular telephony or private mobile radio communication systems, typically provide for radio telecommunication links to be arranged between a plurality of base transceiver stations (BTSs) and a plurality of subscriber units, often termed mobile stations (MSs) .

Wireless communication systems are distinguished over fixed communication systems, such as the public switched telephone network (PSTN) , principally in that mobile stations move between BTS (and/or different service providers) and, in doing so, encounter varying radio propagation environments. Methods for communicating information simultaneously exist where communication resources in a communication network are shared by a number of users . Such methods are termed multiple access techniques. A number of multiple access techniques exist, whereby a finite communication resource is divided into any number of physical parameters, such as:

(i) frequency division multiple access (FDMA) whereby the total number of frequencies used in the communication system are shared,

(ii) time division multiple access (TDMA) whereby each communication resource, say a frequency used in the communication system, is shared amongst users by dividing the resource into a number of distinct time periods (time-slots, frames, etc.), and

(iii) code division multiple access (CDMA) whereby communication on the system uses all of the respective frequencies, in all of the time periods, and the resource is shared by allocating each communication link a particular code, to differentiate desired signals from undesired signals .

Within such multiple access techniques, different duplex (two-way communication) paths are arranged. Such paths can be arranged in a frequency division duplex (FDD) configuration, whereby a frequency is dedicated for up- link communication and a second frequency is dedicated for down-link communication. Alternatively, the paths can be arranged in a time division duplex (TDD) configuration, whereby a first time period is dedicated for up-link communication and a second time period is dedicated for down-link communication.

In a wireless communication system, each BTS has associated with it a particular geographical coverage area (or cell) . The coverage area is defined by a particular geographical range where the BTS can maintain acceptable communications with MSs operating within its serving cell. Often these cells combine to produce an extensive coverage area.

The communication link from the BTS to a MS is referred to as the down-link (DL) . Conversely, the communication link from a MS to the BTS is referred to as the up-link (UL) .

Present day communication systems, both wireless and wire-line, have a requirement to transfer data between communications units. Data, in this context, includes speech communication. Such data transfer needs to be effectively and efficiently provided for, in order to optimise use of limited communication resources.

In the field of this invention, it is known that in the planned Universal Mobile Telecommunications Standard (UMTS) each cell site (a local collection of BTS) , and correspondingly each base station controller (BSC) co- ordinating communications for a number of such BTS, will have limited hardware, software and firmware resources. These limitations must be taken into account when performing admission control of a new radio link and also potentially when performing scheduling of air interface transport blocks. The general term used for a cell site in the UMTS arena is a Node B, with a BSC known as a Radio Network Control (RNC) .

In the field of this invention the working assumption within UTRA is that a random access transmission consists of a 1-msec preamble part and a 10-msec message part.

The preamble consists of a sequence of sixteen symbols, chosen from a set of sixteen such sequences, and spread by a cell specific spreading code with a spreading factor of sixteen. Effectively, the preamble contains four bits of information.

The message part consists of data modulated on the Q- component with a spreading factor of 256, 128, 64, or 32, and a control part modulated on the I -component with a spreading factor of 256. The control part includes rate- information (number and size of data blocks) that identifies the spreading factor used for the data. The four-bits of information contained within the preamble identify the ^' spreading code used for the control part and together with the two rate-information bits, the spreading code used for the data part . The message part is then scrambled by a cell specific scrambling code.

The initial proposal for MSs accessing a UMTS system was based on the well-known random access technique. The problems associated with such a random access technique are shown in FIG . 1.

FIG. 1 shows a timing diagram 10 highlighting two MSs 20, 30 attempting to access a communication resource from a Node B (or BTS) 40. FIG. 1 shows the random access transmission sequences from the two MS 20,30 and an indication of the random access sequences that are received at the Node B 40, over a time period 15. If, as is shown, the two MSs 20, 30 transmit 22, 32 at the same time and, for example in a CDMA system with the same spreading code, then a collision occurs. In this case, both messages will likely be lost, as they are received concurrently by Node B 40, in received sequence 42.

In this situation, both MSs 20, 30 wait for a random period of time and re-transmit their respective random access requests 24, 34. Again, as can be seen, the Node B 40 fails to adequately receive 44 either random access request based on a collision over part of each access message. Such random access attempts are continued until the first MS 20 transmits a random access sequence 26 that is adequately received 46 by Node B 40, without there being a collision. Clearly, only a few re- transmissions are needed before the random access delay starts to become significant, typically a delay of greater than 100msec' s is deemed undesirable.

It is worth noting that in FIG. 1, the start of one sequence may overlap the end of a previous sequence. In such a case in a CDMA system, it is still possible for a Node B to distinguish the two sequences as belonging to two different users even in the situation that the users are using the same spreading code. For this to be true the delay between the start of one sequence and the start of the next sequence must be significantly greater than the combination delay spread and propagation delay uncertainly (i.e. they must be far enough apart so that the Node B can be sure it is seeing two transmissions and not seeing two paths from the same transmission) . Hence, in Fig 1, received sequence 42 would definitely be a collision, whereas received sequence 44 could be adequately received, and received sequence 45 would probably be a collision.

A second random access technique has been proposed that reduces the random access delay, as shown in FIG. 2. This is termed the Fast Uplink Signalling Channel (FAUSCH) . The FAUSCH proposal was motivated by the recognition that:

(i) The random access channel (RACH) has an inherent risk of collision; and

(ii) when only a small message is to be conveyed, the corresponding overhead associated with the use of the RACH is significant.

FIG. 2 shows a timing diagram 50 highlighting any number of MSs (four MS transmissions shown here for clarity purposes only) attempting to access a communication resource from a Node B (or BTS) . The random access transmission sequences from the four MSs 60, 70, 80, 90 are shown over a time period 52.

To avoid any collisions, MSs wishing to make use of the communication system's FAUSCH are allocated a dedicated access slot 54-58. In such a manner, a first MS 60 transmits an access request 62 in its dedicated time period 54 and is guaranteed, if the signal propagation conditions are favourable, of reaching the Node B.

The current proposal is for an uplink resource to be requested on the RACH channel , then granted on the forward access channel (FACH) , and the packet transmission would then begin using a dedicated channel (DCH) . The procedure would be similar if a DCH is reactivated after a break in transmission. An alternative would be to request the uplink resource using the FAUSCH transmission. The signal-to-noise level (including overheads) measured at a receiver, termed Eb/No, is found to be lower using FAUSCH in this way than using a random access channel (RACH) in FIG. 1. This is the case whether the RACH channel is used to set up a DCH or whether the user data is sent as part of RACH packet .

The FAUSCH channel shown in FIG. 2 therefore offers a collision-free signalling channel with low data overhead. The most beneficial use of the FAUSCH approach is when a MS has much more data to send and therefore wants to request the network to allocate a dedicated channel (DCH) as recourse. In this case, the use of FAUSCH can provide significant advantages in terms of signal-to-noise (Eb/No) , leading to a higher system capacity. The fact that FAUSCH is substantially collision-free gives improved reliability and reduced transmission delay, particularly in high system-loading situations.

The Eb/No improvement is most significant where a large number of packets are to be sent, but where the average bit-rate and transmission duty cycle are low enough that continuous use of a DCH would be inefficient. With such duty cycle the efficient way to handle the date is frequent switching to and from a DCH. Therefore employing the FAUSCH principle is beneficial as it provides an efficient means to signal a request to switch to a DCH.

The code sequence proposed using the FAUSCH principle is identical to that used for the RACH preamble. In particular, a 256 chip Gold code is used to spread a sixteen-bit signature, as per the RACH preamble. A MS would be allocated a fast access slot with a specific timing offset in the 10msec frame, relative to the downlink synchronization channel (SCH) .

Although the time slots 54-58 are distinct, the transmissions from different terminals would typically overlap at the receiver in the network. However, in a CDMA system, the receiver can identify which mobiles have signalled by detecting separate peaks in the output of a correlator or filter (matched to the spread signature) . The minimum useable separation between fast access slots will depend to some extent on the deployment scenario. The limiting factors are delay spread and round trip propagation time. This means that in large cells the spacing between fast access slots should be increased. This is accommodated for by specifying a minimum spacing (16 chips) . In small cells all the fast access slots may be allocated. In larger cells every N'th slot could be used.

The same receiver hardware can be used for RACH and FAUSCH, and minimal additional complexity is required to support both. If more RACH and/or FAUSCH capacity is needed, then additional codes could be used to provide additional PRACH channels. These could be allocated to RACH and/or FAUSCH as appropriate for the prevailing traffic conditions.

With this mechanism, the mobile only needs to transmit single (for example 1-bit) chip sequences of defined length (for example 256-chip or 4096 chip sequences) that is specific to a Node B. The mobile is allocated a time offset (an ^''access slot') within the frame in which it is permitted to transmit this sequence. A Node B can detect this chip sequence with a very simple matched filter and the timing of the peak from the matched filter identifies the MS. As each MS is allocated its own unique time offset there is no contention between mobiles and so retransmissions are less likely and the random access delay is shorter. The signalling message sent by the FAUSCH mechanism is determined in advance. It may be, for example, a request for a dedicated uplink channel.

However, the FAUSCH proposal has the disadvantages that the amount of information that it can convey is limited. When a Node B (or BTS) receives a sequence it can infer some information but it cannot actually make a binary l' or binary ^Λ0' decision from the sequence effectively, if the sequence carries less than one bit of information.

There are two ways in which the technique can be extended to send more information. First, more than one time offset can be allocated to a single mobile. Secondly, the mobile could be permitted to transmit more than one sequence. For example, if the mobile can transmit one of two sequences then a single bit of information can be conveyed. This can be extended to four sequences to convey two bits, and so on.

The inventors of the present invention have recognised the limitations in the FAUSCH mechanism, in that the time offset needs to be allocated by the network. As such, the FAUSCH channel cannot be used for initial access to the network. An example use of the FAUSCH channel is to request a channel, once registered, on which to transmit a data packet .

Details of this FAUSCH proposal can be found in temporary document 227/98 presented to ETSI/SMG2 Physical Layer expert group by Philips. Thus there exists a need to provide a communication system, communication unit and method of communicating information, for example making a random access request, wherein the abovementioned disadvantages may be alleviated.

Statement of Invention

In accordance with a first aspect of the present invention there is provided a communication system, as claimed in claim 1.

In accordance with a second aspect of the present invention there is provided a communication unit, as claimed in claim 14.

In accordance with a third aspect of the present invention there is provided a method of performing a random access request, as claimed in claim 15.

In accordance with a fourth aspect of the present invention there is provided a communication unit, as claimed in claim 19.

In accordance with a fifth aspect of the present invention there is provided a storage medium storing processor-implementable instructions for controlling a processor to carry out any of the aforementioned method steps, as claimed in claim 20.

Brief Description of the Drawings

FIG. 1 shows a timing diagram showing a prior art random access mechanism.

FIG. 2 shows a timing diagram showing the FAUSCH proposal that avoids the collisions associated with the prior art random access mechanism of FIG. 1.

Exemplary embodiments of the present invention will now be described, with reference to the accompanying drawings, in which:

FIG. 3 shows a block diagram of a cellular radio communications system adapted to support the various inventive concepts of a preferred embodiment of the present invention.

FIG. 4 shows a block diagram of a cellular radio communications system adapted to support the various inventive concepts in accordance with a preferred embodiment of the present invention.

FIG. 5 shows a sequence of preambles used to convey information and provide a FEC capability, in accordance with the preferred embodiment of the present invention. FIG. 6 shows a flowchart of a method of random access request of a MS , in accordance with the preferred embodiment of the present invention.

FIG. 7 shows a flowchart of a method of receiving and processing a random access request at a Node B, in accordance with the preferred embodiment of the present invention.

Description of Preferred Embodiments

In summary, the novel and inventive features over the prior art include combining forward error correction with the transmission of multiple sequences. Two preferred examples of seamlessly introducing a FEC function into such multiple sequence include:

(1) A single preamble, with one of say, sixteen possible sequences, conveys four bits of information. A peak from a code-matched filter indicates the particular sequence that was transmitted.

(2) Three preambles are transmitted each with sixteen possible sequences.

In particular, the preferred embodiment of the invention is described as an extension to the FAUSCH concept to allow a system employing the FAUSCH principle to transmit more information. Some examples of information that it would be useful to send via the new sequence of preambles include :

(i) The spreading factor or data rate of the channel being requested.

(ii) The size of the data packet to be transmitted or the number of data packets queued awaiting transmission. The radio resource controller within the network can then efficiently allocate resources for this packet.

(iii) The priority level of the data that is awaiting transmission if the MS has several streams of data associated to different services and each service has been assigned a different priority level .

Referring now to FIG. 3, a cellular-based telephone communication system 100 is shown in outline, in accordance with a preferred embodiment of the invention. The cellular-based telephone communication system 100 is compliant with, and contains network elements capable of operating over, a UMTS and/or a GPRS air-interface. In particular, the invention relates to the Third Generation Partnership Project (3GPP) specification for wide-band code-division multiple access (WCDMA) standard relating to the UTRAN radio Interface (described in the 3G TS 25.xxx series of specifications).

A plurality of mobile stations (MSs) 112, 114, 116 communicate over radio links 118, 119, 120 with a plurality of base transceiver stations, referred to under UMTS terminology as Node-Bs, 122, 124, 126, 128, 130, 132. The system comprises many other MSs and base transceiver stations, which for clarity purposes are not shown.

The wireless communication system, sometimes referred to as a Network Operator' s Network Domain, is connected to an external network 134, for example the Internet. The Network Operator's Network Domain includes:

(i) a core network, namely at least one Gateway GPRS Support Node (GGSN) 144 and or at least one Serving GPRS Support Nodes (SGSN) ,- and (ii) an access network, namely:

(ai) a GPRS (or UMTS) Radio network controller (RNC) 136-140; or

(aii) Base Site Controller (BSC) in a GSM system and/or (bi) a GPRS (or UMTS) Node B 122-132; or

(bii) a Base Transceiver Station (BTS) in a GSM system.

The GGSN/SSGN 144 is responsible for GPRS (or UMTS) interfacing with a Public Switched Data Network (PSDN) such as the Internet 134 or a Public Switched Telephone Network (PSTN) 134. A SGSN 144 performs a routing and tunnelling function for traffic within say, a GPRS core network, whilst a GGSN 144 links to external packet networks, in this case ones accessing the GPRS mode of the system The Node-Bs 122-132 are connected to external networks, through base station controllers, referred to under UMTS terminology as Radio Network Controller stations (RNC) , including the RNCs 136, 138, 140 and mobile switching centres (MSCs) , such as MSC 142 (the others are, for clarity purposes, not shown) and SGSN 144 (the others are, for clarity purposes, not shown) .

Each Node-B 122-132 contains one or more transceiver units and communicates with the rest of the cell-based system infrastructure via an I_u interface, as defined in the UMTS specification.

Each RNC 136-140 may control one or more Node-Bs 122-132. Each MSC 142 provides a gateway to the external network 134. The Operations and Management Centre (OMC) 146 is operably connected to RNCs 136-40 and Node-Bs 122-132 (shown only with respect to Node-B 126 for clarity) . The OMC 146 administers and manages sections of the cellular telephone communication system 100, as is understood by those skilled in the art.

In the preferred embodiment of the invention, at least one MS 112-116 and at least one Node-B 122-132 and/or, a RNC 136-140 and/or MSC 142 and/or SGSN/GGSN 144 have been adapted, to offer, and provide for, transmission, reception, processing and responding to such processing of message preambles generated in accordance with the approach detailed below. More particularly, in this embodiment the above elements have been adapted to implement the present invention in both transmitting and receiving modes of operation, such that in this embodiment the invention may be applied to both down-link and up-link transmissions.

More generally, the adaptation may be implemented in the respective communication units in any suitable manner. For example, new apparatus may be added to a conventional communication unit, or alternatively existing parts of a conventional communication unit may be adapted, for example by reprogramming one or more processors therein. As such the required adaptation may be implemented in the form of processor-implementable instructions stored on a storage medium, such as a floppy disk, hard disk, PROM, RAM or any combination of these or other storage multimedia.

It is also within the contemplation of the invention that such adaptation of transmission characteristics may alternatively be controlled, implemented in full or implemented in part by adapting any other suitable part of the communication system 100. For example, the OMC 146 (or equivalent parts in other types of systems) may be adapted to provide some or all of the implementation provided in this embodiment.

Further, in the case of other network infrastructures, implementation of the processing operations may be performed at any appropriate node such as any other appropriate type of base station, base station controller, etc.

Alternatively the aforementioned steps may be carried out by various components distributed at different locations or entities within any suitable network or system.

FIG. 4 shows a block diagram of a MS employing some of the inventive concepts of the present invention (for simplicity only MS 112 will be described in detail) . The MS 112 contains an antenna 202 coupled to a duplex filter or circulator 204 that provides isolation between the receive chain 240 and transmit chain 250 within the MS 112.

The receiver chain 240, as known in the art, may include scanning and/or switchable receiver front-end circuitry 206 (effectively providing reception, filtering and intermediate or base-band frequency conversion) . The scanning front-end circuit is serially coupled to a signal processing function 208.

An output from the signal processing function may be provided to suitable output devices such as a display screen 210, and other output devices, not shown, such as a display.

The receiver chain 240 also includes received signal strength indicator (RSSI) circuitry 212, which in turn is coupled to a controller 214 that operates to maintain overall control of the different functions and modules of the MS 112. The controller 214 is also coupled to the scanning receiver front-end circuitry 206 and the signal processing function 208 (generally realised by at least one digital signal processor (DSP) ) .

The controller 214 includes a memory 216 that stores operating regimes, such as decoding/encoding functions and the like. The controller also contains error detection function 215, for detecting errors in the received data stream. A timer 218 is typically coupled to the controller 214 to control the timing of operations (transmission or reception of time-dependent signals) within the MS 112.

As regards the transmit chain 250, this essentially includes an input device 220 such as a keyboard. The input devices are each coupled in series through transmitter/modulation circuitry 222 and a power amplifier 224 to the antenna 202. The transmitter/ modulation circuitry 222 and the power amplifier 224 are operationally responsive to the controller.

In accordance with a preferred embodiment of the invention, the MS transmits a new preamble sequence in order to obtain access to the respective communication system. Instead of transmitting the single chip sequence as proposed in the FAUSCH concept, the MS transmits a preamble sequence. Concatenating two or more of these preambles can be used to send further information. s is known in the art, substantially the same elements and functionality in the MS can be found in the Node B, albeit with the Node B having slightly more functional capabilities in order to cope, for example, with transmissions from, and to, a large number of MS. Hence, the receiver chain 240, processor 208 and controller 214 in the Node B have also been adapted to receive the new preamble sequence, process the received signal to interpret the particular message contained in the preamble sequence .

Furthermore, a feature of the present invention is that only a subset of possible preamble sequences are used. Consequently, the Node B may be able to determine whether the received preamble and/or a subsequent message will contain any errors. Such a determination follows from receiving a preamble sequence that does or does not comply with the pre-assigned preamble sequences.

The various components within the MS 112 are realised in this embodiment in integrated component form. Of course, in other embodiments, they may be realized in discrete form, or a mixture of integrated components and discrete components, or indeed any other suitable form. Further, in this embodiment the controller 214 including memory 216 is implemented as a programmable processor, but in other embodiments can comprise dedicated circuitry or any other suitable form.

It is noted that corresponding features to those described above with respect to MS 112 are also found in existing communication units. However, MS 112 differs over a conventional MS 112 by virtue that the controller 214, including memory 216, and where appropriate, the signal processing function 208 and the receiver and transmitter chains 240, 250, is adapted to generate, process, transmit and/or receive preamble data in the manner which is described in more detail below.

The different options for the preambles may be introduced to the MS 112, Node B (or any other appropriate apparatus) in the form of processor-implementable instructions and/or data.

It is within the contemplation of the invention that the controller 214 described in the above embodiments can be embodied in any suitable form of software, firmware or hardware. The controller 214 may be controlled by processor-implementable instructions and/or data, for carrying out the methods and processes described, which are stored in a storage medium or memory, for example the memory 216. The memory can be a circuit component or module, e.g. a RAM or PROM, or a removable storage medium such as a disk, or other suitable medium.

As mentioned earlier, when a preamble sequence is generated from a concatenation of preamble signals then a form of forward error correction (FEC) may be applied. The FEC technique is best described by means of an example, as shown in FIG. 5. Two examples of using the preamble mechanism according to the preferred embodiment of the invention are provided:

(1) A single preamble, with one of sixteen possible sequences 502-510, can convey four bits of information (2 to the power of 4) . A peak from a code-matched filter 514 indicates the sequence that was transmitted.

(2) Three preambles, for example, are transmitted each with 16 possible sequences, providing up to 16^A3 alternative preamble sequences.

Let us consider the first case where sixteen preambles 502-510 are used. Each of these potential preambles may be distinguished from any others that are used. As mentioned, a decision on whether a preamble exists, or not, may be made by determining whether a sequence peak, once passed through a code match filter 514, has exceeded a threshold level 512, as shown with preamble 516.

Let us further consider the second case where three concatenated preamble periods 520, 530, 540 are used. In principle, each preamble, used in any one period, could be one of the sixteen preamble sequences 502-510. However, in accordance with a preferred embodiment of the invention, a restriction is imposed so that only certain combinations of sequences are permissible.

The arrows show permissible and non-permissible combination of sequences. For preamble 2, noise or interference 522 caused a peak from the filter matched to code sequence 1 504. However, this sequence of 516 to 522 to 516 would not be a permissible combination of sequences and so an error is detected.

Furthermore, the Node B can also determine the most likely sequence to have been transmitted and thereby possibly correct the error. To do this the Node B needs to look at the sizes of the peaks from the matched filters, rather than considering if the peak crossed a decision threshold. If Node B determines a sequence of 516 to 506 to 516, and knows that the predetermined preamble for 506 equates to noise, the node B can make an assessment on the most likely correct sequence. In this case, the smaller peak 518 from the filter matched to code sequence 2 enables the Node B to determine that

0/2/0 is the most likely combination of sequences to have been transmitted.

It is within the contemplation of the invention that such a signal transmission sequence, in particular in the use of preambles, is not limited to CDMA systems or the use of matched filter (s) to detect a coded sequence. Indeed, such concepts can be applied to any system where "signals" rather than bits are transmitted.

Furthermore, it is within the contemplation of the invention that the preamble is not necessarily followed by a message, and as such can be a self-contained message or request. In addition, it is within the contemplation of the invention that if a preamble is used, any number of bits, not necessarily limited to 4-bits, can be used to define say, the spreading code to be used to decode a subsequent message.

Referring now to FIG. 6, a flowchart 600 shows a method for a MS to make an access request of a MS, in accordance with the preferred embodiment of the present invention. First, the MS registers with its serving communication unit, as shown in step 602. The MS then continues to check, as in step 604, whether it needs to access the communication system. Such a check is performed by comparing the data content being processed in the transmitter portion of the unit's processor to a threshold.

Once it is determined that the MS wants to access the communication system, and the threshold in step 604 is exceeded, the MS determines the number of blocks of information that is to be sent, in step 606. This information is coded into a sequence of preambles, as shown in step 608.

Furthermore, the amount of data to be transmitted may be sufficient to require a number of concatenated preamble signals. Particular time-slots are then allocated to the MS to send the coded sequence of preambles, as shown in step 610. Such a coded sequence (s) of preambles is then received by the Node B, as shown in FIG. 7. Referring now to FIG. 7 a flowchart 700 is shown of a method of receiving and processing an access request at a Node B, in accordance with the preferred embodiment of the present invention. The Node B receives the coded sequence of preambles .sent from the MS, as shown in step 702. The receiver is preferably implemented as a matched filter or series of matched filters.

The coded sequence of preambles is then decoded, as shown in step 704. If the Node B determines that an access request has been received, resource is requested from the system by sending a resource request to a RNC. If there is no available resource, the RNC informs the Node B, which in turn informs the MS, as shown in step 706. If sufficient resource is available, such resource is allocated, as shown in step 708. Such resource may include a dedicated channel .

In such a manner, a MS makes an access request using a novel sequence of preambles, which can be decoded by the resource allocation function, such as a Node B/RNC. The sequence of pre-determined preambles is arranged such that all potential preamble sequences are not used, thereby inherently providing an opportunity to perform error correction within the preamble mechanism.

It will be understood that the communication system, communication unit and method of communicating information described above provides at least the following advantages: (i) excessive signalling in a communication system is avoided by using a coded preamble to take the place of, for example a request for capacity and then, in response, a capacity created signalling message, particularly for small packet lengths;

(ii) it enables a communication system, for example one employing the FAUSCH system access concept , to carry more information than a simple request for a channel. For example, it could include the data rate of the required channel . This allows an extra degree of flexibility when designing the protocols; and

(iii) it allows forward error correction to be applied to the channel, based on minimal information allocated to preambles. Hence, the receiver can detect and correct some transmission errors . This is important as radio resources are being allocated as a result of these transmissions.

Thus a communication system, a communication unit and a method of communicating information, for example making a random access request have been provided wherein the abovementioned disadvantages associated with prior art arrangements have been substantially alleviated.

Claims

1. A communication system, comprising a first communication unit communicating with a second communication unit, said first communication unit transmitting to said second communication unit a preamble prior to a first message, wherein the preamble is a concatenation of signals selected from a plurality of predetermined concatenation of signals and said second communication unit receives and decodes the preamble and compares the received concatenated signals with at least one pre-determined concatenated signal to determine whether an error has occurred in said preamble or said first message.

2. The communication system according to claim 1, wherein the preamble selected by the first communication unit provides in itself a second message.

3. The communication system according to claim 2, wherein the second message content is a random access request .

4. The communication system according to any of the preceding claims, wherein said second communication unit performs error correction on the preamble based on the comparison of said decoded concatenated signals to at least one of the plurality of pre-determined concatenation of signals.

5. The communication system according to any of the preceding claims, wherein said preamble instructs said second communication unit how to decode the first message .

6. The communication system according to any of the preceding claims, wherein said preamble is sent in a number of time-slots allocated for use by the first communication unit, for example using a Fausσh pre- determined time-slot arrangement.

7. The communication system according to any of the preceding claims, wherein said communication system is a code division multiple access communication system.

8. The communication system according to claim 7 , wherein said preamble contains an indication of the spreading codes to be used to decode the message.

9. The communication system according to claim 8, wherein the spreading codes indicated in the preamble are decoded at the second communication unit by using a plurality of matched filters.

10. The communication system according to claim 9, wherein the spreading codes are determined by assessing a size of a peak output from at least one of said plurality of matched filters.

11. The communication system according to claim 10, wherein the size of a peak output from at least one of said plurality of matched filters is compared to a predetermined threshold to see if a particular signal from the concatenated signals has been sent.

12. The communication system according to any of the preceding claims, wherein said preamble or a sequence of preambles is used to send at least one of the following to the second communication unit: spreading factor, data rate of the channel being requested, size of the data packet to be transmitted, priority of data to be transmitted.

13. The communication system according to any of the preceding claims, wherein the preamble and/or first message includes a portion of a communication system registration process or an establishment of a service on the communication system.

14. A communication unit adapted to operate in the communication system of any of the preceding claims.

15. A method of communicating in a communication system between a first and second communication unit, the method comprising the steps of: at said first communication unit: concatenating a number of signals into a preamble; transmitting said preamble prior to a first message from said first communication unit to said second communication unit ; and at said second communication unit: receiving and decoding the preamble; and comparing the received concatenated signals with known pre-determined concatenated signals to determine whether an error has occurred in said preamble or said first message.

16. The method of communicating in a communication system according to claim 15, wherein the step of concatenating signals to form the preamble provides in itself a second message based on a particular concatenation of signals.

17. The method of communicating in a communication system according to claim 16, the method further comprising the step of : determining, by the second communication unit, that a random access request has been sent by the first communication unit based on the decoded second message.

18. The method of communicating in a communication system according to claim 16 or claim 17, the method further comprising the step of performing error correction on the preamble based on the comparison of the received concatenated signals to the known plurality of pre-determined concatenated signals.

19. The method of communicating in a communication system according to any of claims 16 to 18, wherein the step of concatenating includes the step of selecting a concatenated sequence of signals from a plurality of predetermined concatenation of a sequences.

20. A communication unit adapted to perform any of the method steps of preceding claims 15 to 19.

21. A storage medium storing processor-implementable instructions for controlling a processor to carry out the method any of claims 15 to 19.

22. A communication system substantially as hereinbefore described with reference to and/or as illustrated by FIG. 3 of the accompanying drawings.

23. A communication unit substantially as hereinbefore described with reference to and/or as illustrated by FIG. 4 of the accompanying drawings.

24. A method of communicating substantially as hereinbefore described with reference to and/or as illustrated by FIG. 6 or 7 of the accompanying drawings.